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Time Machines

Recent years have seen a growing consensus in the philosophical community that the grandfather paradox and similar logical puzzles do not preclude the possibility of time travel scenarios that utilize spacetimes containing closed timelike curves. At the same time, physicists, who for half a century acknowledged that the general theory of relativity is compatible with such spacetimes, have intensely studied the question whether the operation of a time machine would be admissible in the context of the same theory and of its quantum cousins. A time machine is a device which brings about closed timelike curves—and thus enables time travel—where none would have existed otherwise. The physics literature contains various no-go theorems for time machines, i.e., theorems which purport to establish that, under physically plausible assumptions, the operation of a time machine is impossible. We conclude that for the time being there exists no conclusive no-go theorem against time machines. The character of the material covered in this article makes it inevitable that its content is of a rather technical nature. We contend, however, that philosophers should nevertheless be interested in this literature for at least two reasons. First, the topic of time machines leads to a number of interesting foundations issues in classical and quantum theories of gravity; and second, philosophers can contribute to the topic by clarifying what it means for a device to count as a time machine, by relating the debate to other concerns such as Penrose’s cosmic censorship conjecture and the fate of determinism in general relativity theory, and by eliminating a number of confusions regarding the status of the paradoxes of time travel. The present article addresses these ambitions in as non-technical a manner as possible, and the reader is referred to the relevant physics literature for details.

• 1. Introduction: time travel vs. time machines

2. What is a (Thornian) time machine? Preliminaries

3. when can a would-be time machine be held responsible for the emergence of ctcs, 4. no-go results for (thornian) time machines in classical general relativity theory, 5. no-go results in quantum gravity, 6. conclusion, other internet resources, related entries, 1. introduction: time travel vs. time machine.

The topic of time machines is the subject of a sizable and growing physics literature, some of which has filtered down to popular and semi-popular presentations. [ 1 ] The issues raised by this topic are largely oblique, if not orthogonal, to those treated in the philosophical literature on time travel. [ 2 ] Most significantly, the so-called paradoxes of time travel do not play a substantial role in the physics literature on time machines. This literature equates the possibility of time travel with the existence of closed timelike curves (CTCs) or worldlines for material particles that are smooth, future-directed timelike curves with self-intersections. [ 3 ] Since time machines designate devices which bring about the existence of CTCs and thus enable time travel, the paradoxes of time travel are irrelevant for attempted “no-go” results for time machines because these results concern what happens before the emergence of CTCs. [ 4 ] This, in our opinion, is fortunate since the paradoxes of time travel are nothing more than a crude way of bringing out the fact that the application of familiar local laws of relativistic physics to a spacetime background which contains CTCs typically requires that consistency constraints on initial data must be met in order for a local solution of the laws to be extendable to a global solution. The nature and status of these constraints is the subject of ongoing discussion. We will not try to advance the discussion of this issue here; [ 5 ] rather, our aim is to acquaint the reader with the issues addressed in the physics literature on time machines and to connect them with issues in the philosophy of space and time and, more generally, with issues in the foundations of physics.

Paradox mongers can be reassured in that if a paradox is lost in shifting the focus from time travel itself to time machines, then a paradox is also gained: if it is possible to operate a time machine device that produces CTCs, then it is possible to alter the structure of spacetime such that determinism fails; but by undercutting determinism, the time machine undercuts the claim that it is responsible for producing CTCs. But just as the grandfather paradox is a crude way of making a point, so this new paradox is a crude way of indicating that it is going to be difficult to specify what it means to be a time machine. This is a task that calls not for paradox mongering but for scientifically informed philosophizing. The present article will provide the initial steps of this task and will indicate what remains to be done. But aside from paradoxes, the main payoff of the topic of time machines is that it provides a quick route to the heart of a number of foundations problems in classical general relativity theory and in attempts to produce a quantum theory of gravity by combining general relativity and quantum mechanics. We will indicate the shape of some of these problems here, but will refer the interested reader elsewhere for technical details.

There are at least two distinct general notions of time machines, which we will call Wellsian and Thornian for short. In The Time Machine , H. G. Wells (1931) described what has become science fiction’s paradigmatic conception of a time machine: the intrepid operator fastens her seat belt, dials the target date—past or future—into the counter, throws a lever, and sits back while time rewinds or fast forwards until the target date is reached. We will not broach the issue of whether or not a Wellsian time machine can be implemented within a relativistic spacetime framework. For, as will soon become clear, the time machines which have recently come into prominence in the physics literature are of an utterly different kind. This second kind of time machine was originally proposed by Kip Thorne and his collaborators (see Morris and Thorne 1988; Morris, Thorne, and Yurtsever 1988). These articles considered the possibility that, without violating the laws of general relativistic physics, an advanced civilization might manipulate concentrations of matter-energy so as to produce CTCs where none would have existed otherwise. In their example, the production of “wormholes” was used to generate the required spacetime structure. But this is only one of the ways in which a time machine might operate, and in what follows any device which affects the spacetime structure in such a way that CTCs result will be dubbed a Thornian time machine . We will only be concerned with this variety of time machine, leaving the Wellsian variety to science fiction writers. This will disappoint the aficionados of science fiction since Thornian time machines do not have the magical ability to transport the would-be time traveler to the past of the events that constitute the operation of the time machine. For those more interested in science than in science fiction, this loss is balanced by the gain in realism and the connection to contemporary research in physics.

In Sections 2 and 3 we investigate the circumstances under which it is plausible to see a Thornian time machine at work. The main difficulty lies in specifying the conditions needed to make sense of the notion that the time machine “produces” or is “responsible for” the appearances of CTCs. We argue that at present there is no satisfactory resolution of this difficulty and, thus, that the topic of time machines in a general relativistic setting is somewhat ill-defined. This fact does not prevent progress from being made on the topic; for if one’s aim is to establish no-go results for time machines it suffices to identify necessary conditions for the operation of a time machine and then to prove, under suitable hypotheses about what is physically possible, that it is not physically possible to satisfy said necessary conditions. In Section 4 we review various no-go results which depend only on classical general relativity theory. Section 5 surveys results that appeal to quantum effects. Conclusions are presented in Section 6.

The setting for the discussion is a general relativistic spacetime \((\mathcal{M},g_{ab})\) where \(\mathcal{M}\) is a differentiable manifold and \(g_{ab}\) is a Lorentz signature metric defined on all of \(\mathcal{M}\). The central issue addressed in the physics literature on time machines is whether in this general setting it is physically possible to operate a Thornian time machine. This issue is to be settled by proving theorems about the solutions to the equations that represent what are taken to be physical laws operating in the general relativistic setting—or at least this is so once the notion of a Thornian time machine has been explicated. Unfortunately, no adequate and generally accepted explication that lends itself to the required mathematical proofs is to be found in the literature. This is neither surprising nor deplorable. Mathematical physicists do not wait until some concept has received its final explication before trying to prove theorems about it; indeed, the process of theorem proving is often an essential part of conceptual clarification. The moral is well illustrated by the history of the concept of a spacetime singularity in general relativity where this concept received its now canonical definition only in the process of proving the Penrose-Hawking-Geroch singularity theorems, which came at the end of a decades long dispute over the issue of whether spacetime singularities are a generic feature of solutions to Einstein’s gravitational field equations. [ 6 ] However, this is not to say that philosophers interested in time machines should simply wait until the dust has settled in the physics literature; indeed, the physics literature could benefit from deployment of the analytical skills that are the stock in trade of philosophy. For example, the paradoxes of time travel and the fate of time machines are not infrequently confused in the physics literature, and as will become evident below, subtler confusions abound as well.

The question of whether a Thornian time machine—a device that produces CTCs—can be seen to be at work only makes sense if the spacetime has at least three features: temporal orientability, a definite time orientation, and a causally innocuous past. In order to make the notion of a CTC meaningful, the spacetime must be temporally orientable (i.e., must admit a consistent time directionality), and one of the two possible time orientations has to be singled out as giving the direction of time. [ 7 ] Non-temporal orientability is not really an obstacle since if a given general relativistic spacetime is not temporally orientable, a spacetime that is everywhere locally the same as the given spacetime and is itself temporally orientable can be obtained by passing to a covering spacetime. [ 8 ] How to justify the singling out of one of the two possible orientations as future pointing requires a solution to the problem of the direction of time, a problem which is still subject to lively debate (see Callender 2001). But for present purposes we simply assume that a temporal orientation has been provided. A CTC is then (by definition) a parameterized closed spacetime curve whose tangent is everywhere a future-pointing timelike vector. A CTC can be thought of as the world line of some possible observer whose life history is linearly ordered in the small but not in the large: the observer has a consistent experience of the “next moment,” and the “next,” etc., but eventually the “next moment” brings her back to whatever event she regards as the starting point.

As for the third condition—a causally innocuous past—the question of the possibility of operating a device that produces CTCs presupposes that there is a time before which no CTCs existed. Thus, Gödel spacetime, so beloved of the time travel literature, is not a candidate for hosting a Thornian time machine since through every point in this spacetime there is a CTC. We make this third condition precise by requiring that the spacetime admits a global time slice \(\Sigma\) (i.e., a spacelike hypersurface without edges); [ 9 ] that \(\Sigma\) is two-sided and partitions \(\mathcal{M}\) into three parts—\(\Sigma\) itself, the part of \(\mathcal{M}\) on the past side of \(\Sigma\) and the part of \(\mathcal{M}\) on the future side of \(\Sigma\)—and that there are no CTCs that lie on the past side of \(\Sigma\). The first two clauses of this requirement together entail that the time slice \(\Sigma\) is a partial Cauchy surface , i.e., \(\Sigma\) is a time slice that is not intersected more than once by any future-directed timelike curve. [ 10 ]

Now suppose that the state on a partial Cauchy surface \(\Sigma_0\) with no CTCs to its past is to be thought of as giving a snapshot of the universe at a moment before the machine is turned on. The subsequent realization of a Thornian time machine scenario requires that the chronology violating region \(V \subseteq \mathcal{M}\), the region of spacetime traced out by CTCs, [ 11 ] is non-null and lies to the future of \(\Sigma_0\). The fact that \(V \ne \varnothing\) does not lead to any consistency constraints on initial data on \(\Sigma_0\) since, by hypothesis, \(\Sigma_0\) is not intersected more than once by any timelike curve, and thus, insofar as the so-called paradoxes of time travel are concerned with such constraints, the paradoxes do not arise with respect to \(\Sigma_0\). But by the same token, the option of traveling back into the past of \(\Sigma_0\) is ruled out by the set up as it has been sketched so far, since otherwise \(\Sigma_0\) would not be a partial Cauchy surface. This just goes to underscore the point made above that the fans of science fiction stories of time machines will not find the present context of discussion broad enough to encompass their vision of how time machines should operate; they may now stop reading this article and return to their novels.

Figure 1. Misner spacetime

As a concrete example of these concepts, consider the \((1 + 1)\)-dimensional Misner spacetime (see Figure 1 ) which exhibits some of the causal features of Taub-NUT spacetime, a vacuum solution to Einstein’s gravitational field equations. It satisfies all three of the conditions discussed above. It is temporally orientable, and a time orientation has been singled out—the shading in the figure indicates the future lobes of the light cones. To the past of the partial Cauchy surface \(\Sigma_0\) lies the Taub region where the causal structure of spacetime is as bland as can be desired. But to the future of \(\Sigma_0\) the light cones begin to “tip over,” and eventually the tipping results in CTCs in the NUT region.

The issue that must be faced now is what further conditions must be imposed in order that the appearance of CTCs to the future of \(\Sigma_0\) can be attributed to the operation of a time machine. Not surprisingly, the answer depends not just on the structure of the spacetime at issue but also on the physical laws that govern the evolution of the spacetime structure. If one adopts the attitude that the label “time machine” is to be reserved for devices that operate within a finite spatial range for a finite stretch of time, then one will want to impose requirements to assure that what happens in a compact region of spacetime lying on or to the future of \(\Sigma_0\) is responsible for the CTCs. Or one could be more liberal and allow the would-be time machine to be spread over an infinite space. We will adopt the more liberal stance since it avoids various complications while still sufficing to elicit key points. Again, one could reserve the label “time machine” for devices that manipulate concentrations of mass-energy in some specified ways. For example, based on Gödel spacetime—where matter is everywhere rotating and a CTC passes through every spacetime point—one might conjecture that setting into sufficiently rapid rotation a finite mass concentration of appropriate shape will eventuate in CTCs. But with the goal in mind of proving negative general results, it is better to proceed in a more abstract fashion. Think of the conditions on the partial Cauchy surface \(\Sigma_0\) as encoding the instructions for the operation of the time machine. The details of the operation of the device—whether it operates in a finite region of spacetime, whether it operates by setting matter into rotation, etc.—can be left to the side. What must be addressed, however, is whether the processes that evolve from the state on \(\Sigma_0\) can be deemed to be responsible for the subsequent appearance of CTCs.

The most obvious move is to construe “responsible for” in the sense of causal determinism. But in the present setting this move quickly runs into a dead end. For if CTCs exist to the future of \(\Sigma_0\) they are not causally determined by the state on \(\Sigma_0\) since the time travel region \(V\), if it is non-null, lies outside the future domain of dependence \(D^+ (\Sigma_0)\) of \(\Sigma_0\), the portion of spacetime where the field equations of relativistic physics uniquely determine the state of things from the state on \(\Sigma_0\). [ 12 ] The point is illustrated by the toy model of Figure 1 . The surface labeled \(H^+ (\Sigma_0)\) is called the future Cauchy horizon of \(\Sigma_0\). It is the future boundary of \(D^+ (\Sigma_0)\), [ 13 ] and it separates the portion of spacetime where conditions are causally determined by the state on \(\Sigma_0\) from the portion where conditions are not so determined. And, as advertised, the CTCs in the model of Figure 1 lie beyond \(H^+ (\Sigma_0)\).

Figure 2. Deutsch-Politzer spacetime

Thus, if the operation of a Thornian time machine is to be a live possibility, some condition weaker than causal determinism must be used to capture the sense in which the state on \(\Sigma_0\) can be deemed to be responsible for the subsequent development of CTCs. Given the failure of causal determinism, it seems the next best thing to demand that the region \(V\) is “adjacent” to the future domain of dependence \(D^+ (\Sigma_0)\). Here is an initial stab at such an adjacency condition. Consider causal curves which have a future endpoint in the time travel region \(V\) and no past endpoint. Such a curve may never leave \(V\); but if it does, require that it intersects \(\Sigma_0\). But this requirement is too strong because it rules out Thornian time machines altogether. For a curve of the type in question to reach \(\Sigma_0\) it must intersect \(H^+ (\Sigma_0)\), but once it reaches \(H^+ (\Sigma_0)\) it can be continued endlessly into the past without meeting \(\Sigma_0\) because the generators of \(H^+ (\Sigma_0)\) are past endless null geodesics that never meet \(\Sigma_0\). [ 14 ] This difficulty can be overcome by weakening the requirement at issue by rephrasing it in terms of timelike curves rather than causal curves. Now the set of candidate time machine spacetimes satisfying the weakened requirement is non-empty—as illustrated, once again, by the spacetime of Figure 1 . But the weakened requirement is too weak, as illustrated by the \((1 + 1)\)-dimensional version of Deutsch-Politzer spacetime [ 15 ] (see Figure 2 ), which is constructed from two-dimensional Minkowski spacetime by deleting the points \(p_1\)–\(p_4\) and then gluing together the strips as shown. Every past endless timelike curve that emerges from the time travel region \(V\) of Deutsch-Politzer spacetime does meet \(\Sigma_0\). But this spacetime is not a plausible candidate for a time machine spacetime. Up to and including the time \(\Sigma_0\) (which can be placed as close to \(V\) as desired) this spacetime is identical with empty Minkowski spacetime. If the state of the corresponding portion of Minkowski spacetime is not responsible for the development of CTCs—and it certainly is not since there are no CTCs in Minkowski spacetime—how can the state on the portion of Deutsch-Politzer spacetime up to and including the time \(\Sigma_0\) be held responsible for the CTCs that appear in the future?

The deletion of the points \(p_1\)–\(p_4\) means that the Deutsch-Politzer spacetime is singular in the sense that it is geodesically incomplete . [ 16 ] It would be too drastic to require of a time-machine hosting spacetime that it be geodesically complete. And in any case the offending feature of Deutsch-Politzer can be gotten rid of by the following trick. Multiplying the flat Lorentzian metric \(\eta_{ab}\) of Deutsch-Politzer spacetime by a scalar function \(j(x, t) \gt\) produces a new metric \(\eta '_{ab} :=\) j \(\eta_{ab}\) which is conformal to the original metric and, thus, has exactly the same causal features as the original metric. But if the conformal factor \(j\) is chosen to “blow up” as the missing points \(p_1\)–\(p_4\) are approached, the resulting spacetime is geodesically complete—intuitively, the singularities have been pushed off to infinity.

A more subtle way to exclude Deutsch-Politzer spacetime focuses on the generators of \(H^+ (\Sigma_0)\). The stipulations laid down so far for Thornian time machines imply that the generators of \(H^+ (\Sigma_0)\) cannot intersect \(\Sigma_0\). But in addition it can be required that these generators do not “emerge from a singularity” and do not “come from infinity,” and this would suffice to rule out Deutsch-Politzer spacetime and its conformal cousins as legitimate candidates for time machine spacetimes. More precisely, we can impose what Stephen Hawking (1992a,b) calls the requirement that \(H^+ (\Sigma_0)\) be compactly generated ; namely, the past endless null geodesics that generate \(H^+ (\Sigma_0)\) must, if extended far enough into past, fall into and remain in a compact subset of spacetime. Obviously the spacetime of Figure 1 fulfills Hawking’s requirement—since in this case \(H^+ (\Sigma_0)\) is itself compact—but just as obviously the spacetime of Figure 2 (conformally doctored or not) does not.

Imposing the requirement of a compactly generated future Cauchy horizon has not only the negative virtue of excluding some unsuited candidate time machine spacetimes but a positive virtue as well. It is easily proved that if \(H^+ (\Sigma_0)\) is compactly generated then the condition of strong causality is violated on \(H^+ (\Sigma_0)\), which means, intuitively, there are almost closed causal curves near \(H^+ (\Sigma_0)\). [ 17 ] This violation can be taken as an indication that the seeds of CTCs have been planted on \(\Sigma_0\) and that by the time \(H^+ (\Sigma_0)\) is reached they are ready to bloom.

However, we still have no guarantee that if CTCs do bloom to the future of \(\Sigma_0\), then the state on \(\Sigma_0\) is responsible for the blooming. Of course, we have already learned that we cannot have the iron clad guarantee of causal determinism that the state on \(\Sigma_0\) is responsible for the actual blooming in all of its particularity. But we might hope for a guarantee that the state on \(\Sigma_0\) is responsible for the blooming of some CTCs—the actual ones or others. The difference takes a bit of explaining. The failure of causal determinism is aptly pictured by the image of a future “branching” of world histories, with the different branches representing different alternative possible futures of (the domain of dependence of) \(\Sigma_0\) that are compatible with the actual past and the laws of physics. And so it is in the present setting: if \(H^+ (\Sigma_0) \ne \varnothing\), then there will generally be different ways to extend \(D^+ (\Sigma_0)\), all compatible with the laws of general relativistic physics. But if CTCs are present in all of these extensions, even through the details of the CTCs may vary from one extension to another, then the state on \(\Sigma_0\) can rightly be deemed to be responsible for the fact that subsequently CTCs did develop.

A theorem due to Krasnikov (2002, 2003 [Other Internet Resources], 2014a) might seem to demonstrate that no relativistic spacetime can count as embodying a Thornian time machine so understood. Following Krasnikov, let us say that a spacetime condition \(C\) is local just in case, for any open covering \(\{V_{\alpha}\}\) of an arbitrary spacetime \((\mathcal{M}, g_{ab}), C\) holds in \((\mathcal{M}, g_{ab})\) iff it holds in \((V_{\alpha}, g_{ab}|_{V_{\alpha}})\) for all \(\alpha\). Examples of local conditions one might want to impose on physically reasonable spacetimes are Einstein’s gravitational field equations and so-called energy conditions that restrict the form of the stress-energy tensor \(T_{ab}\). An example of the latter that will come into play below is the weak energy condition that says that the energy density is non-negative. [ 18 ] Einstein’s field equations (sans cosmological constant) require that \(T_{ab}\) is proportional to the Einstein tensor which is a functional of the metric and its derivatives. Call a \(C\)-spacetime \((\mathcal{M}', g'_{ab})\) a \(C\)- extension of a \(C\)-spacetime \((\mathcal{M}, g_{ab})\) spacetime if the latter is isometric to an open proper subset of the former; and call \((\mathcal{M}, g_{ab}) C\)- extensible if it admits a \(C\)-extension and \(C\)- maximal otherwise. (Of course, \(C\) might be the empty condition.) Krasnikov’s theorem shows that every \(C\)-spacetime \((\mathcal{M}, g_{ab})\) admits a \(C\)-maximal extension \((\mathcal{M}^{max}, g^{max}_{ab})\) such that all CTCs in \((\mathcal{M}^{max}, g^{max}_{ab})\) are to the chronological past of the image of \(\mathcal{M}\) in \((\mathcal{M}^{max}, g^{max}_{ab})\). So start with some candidate spacetime \((\mathcal{M}, g_{ab})\) for a Thornian time machine, and apply the theorem to \((D^+ (\Sigma_0), g_{ab}|_{D^+ (\Sigma_0)})\). Conclude that no matter what local conditions the candidate spacetime is required to satisfy, \(D^+ (\Sigma_0)\) has extensions that also satisfies said local conditions but does not contain CTCs to the future of \(\Sigma_0\). Thus, the candidate spacetime fails to exhibit the crucial feature identified above necessary for underwriting the contention that the conditions on \(\Sigma_0\) are responsible for the development of CTCs. Hence, it appears as if Krasnikov’s theorem effectively prohibits time machines.

The would-be time machine operator need not capitulate in the face of Krasnikov’s theorem. Recall that the main difficulty in specifying the conditions for the successful operation of Thornian time machines traces to the fact that the standard form of causal determinism does not apply to the production of CTCs. But causal determinism can fail for reasons that have nothing to do with CTCs or other acausal features of relativistic spacetimes, and it seems only fair to ensure that these modes of failure have been removed before proceeding to discuss the prospects for time machines. To zero in on the modes of failure at issue, consider vacuum solutions \((T_{ab} \equiv 0)\) to Einstein’s field equations. Let \((\mathcal{M}, g_{ab})\) and \((\mathcal{M}', g'_{ab})\) be two such solutions, and let \(\Sigma \subset \mathcal{M}\) and \(\Sigma ' \subset \mathcal{M}'\) be spacelike hypersurfaces of their respective spacetimes. Suppose that there is an isometry \(\Psi\) from some neighborhood \(N(\Sigma)\) of \(\Sigma\) onto a neighborhood \(N'(\Sigma ')\) of \(\Sigma '\). Does it follow, as we would want determinism to guarantee, that \(\Psi\) is extendible to an isometry from \(D^+ (\Sigma)\) onto \(D^+ (\Sigma ')\)? To see why the answer is negative, start with any solution \((\mathcal{M}, g_{ab})\) of the vacuum Einstein equations, and cut out a closed set of points lying to the future of \(N(\Sigma)\) and in \(D^+ (\Sigma)\). Denote the surgically altered manifold by \(\mathcal{M}^*\) and the restriction of \(g_{ab}\) to \(\mathcal{M}^*\) by \(g^*_{ab}\). Then \((\mathcal{M}^*, g^*_{ab})\) is also a solution of the vacuum Einstein equations. But obviously the pair of solutions \((\mathcal{M}, g_{ab})\) and \((\mathcal{M}^*, g^*_{ab})\) violates the condition that determinism was supposed to guarantee as \(\Psi\) is not extendible to an isometry from \(D^+ (\Sigma)\) onto \(D^+ (\Sigma^*)\). It might seem that the requirement, contemplated above, that the spacetimes under consideration be maximal, already rules out spacetimes that have “holes” in them. But while maximality does rule out the surgically mutilated spacetime just constructed, it does not guarantee hole freeness in the sense needed to make sure that determinism does not stumble before it gets to the starting gate. That \((\mathcal{M}, g_{ab})\) is hole free in the relevant sense requires that if \(\Sigma \subset \mathcal{M}\) is a spacelike hypersurface, there does not exist a spacetime \((\mathcal{M}', g'_{ab})\) and an isometric embedding \(\Phi\) of \(D^+ (\Sigma)\) into \(\mathcal{M}'\) such that \(\Phi(D^+ (\Sigma))\) is a proper subset of \(D^+ (\Phi(\Sigma))\). A theorem due to Robert Geroch (1977, 87), who is responsible for this definition, asserts that if \(\Sigma \subset \mathcal{M}\) and \(\Sigma ' \subset \mathcal{M}'\) are spacelike hypersurfaces in hole-free spacetimes \((\mathcal{M}, g_{ab})\) and \((\mathcal{M}', g'_{ab})\), respectively, and if there exists an isometry \(\Psi : \mathcal{M} \rightarrow \mathcal{M}'\), then \(\Psi\) is indeed extendible to an isometry between \(D^+ (\Sigma)\) and \(D^+ (\Sigma ')\). Thus, hole freeness precludes an important mode of failure of determinism which we wish to exclude in our discussion of time machines. It can be shown that hole freeness is not entailed by maximality. [ 19 ] And it is just this gap that gives the would-be time machine operator some hope, for the maximal CTC-free extensions produced by Krasnikov’s construction are not always hole free (Manchak 2009b). But Krasnikov (2009) has shown that the Geroch (1977) definition is too strong: Minkowski spacetime fails to satisfy it! For this reason, alternative formulations of the hole-freeness definition have been constructed which are more appropriate (Manchak 2009a, Minguzzi 2012).

Thus, we propose that one clear sense of what it would mean for a Thornian time machine to operate in the setting of general relativity theory is given by the following assertion: the laws of general relativistic physics allow solutions containing a partial Cauchy surface \(\Sigma_0\) such that no CTCs lie to the past of \(\Sigma_0\) but every extension of \(D^+ (\Sigma_0)\) satisfying ________ contains CTCs (where the blank is filled with some “no hole” condition). Correspondingly, a proof of the physical impossibility of time machines would take the form of showing that this assertion is false for the actual laws of physics, consisting, presumably, of Einstein’s field equations plus energy conditions and, perhaps, some additional restrictions as well. And a proof of the emptiness of the associated concept of a Thornian time machine would take the form of showing that the assertion is false independently of the details of the laws of physics, as long as they take the form of local conditions on \(T_{ab}\) and \(g_{ab}\).

Are there "no hole" conditions which show the proposed concept of a time machine is not empty? Let \(J^+(p)\) designate the causal future of \(p\), defined as the set of all points in \(\mathcal{M}\) which can be reached from \(p\) by a future-directed causal curve in \(\mathcal{M}\). The causal past \(J^-(p)\) is defined analogously. Now, we say a spacetime \((\mathcal{M},g_{ab})\) is J closed if, for each \(p\) in \(\mathcal{M}\), the sets \(J^+(p)\) and \(J^-(p)\) are topologically closed. One can verify that J closedness fails in many artificially mutilated examples (e.g. Minkowski spacetime with one point removed from the manifold). For some time, it was thought that a time machine existed under this no-hole condition (Manchak 2011a). But this turns out to be incorrect; indeed a recent result shows that any J closed spacetime \((\mathcal{M},g_{ab})\) of three dimensions or more with chronology violating region \(V \neq \mathcal{M}\) must be strongly causal and therefore fail to have CTCs (Hounnonkpe and Minguzzi 2019). Stepping back, perhaps there are other no-hole conditions which can be used instead to show that the proposed concept of a time machine is not empty. But even if such a project were successful, Manchak (2014a, 2019) has shown that the time machine existence results can be naturally reinterpreted as “hole machine” existence results if one is so inclined. Instead of assuming that spacetime is free of holes and then showing that certain initial conditions are responsible for the production of CTCs, one could just as well start with the assumption of no CTCs and then show that certain initial conditions are responsible for the production of holes. Given the importance of these no hole assumptions to the time machine advocate, much recent work has focused on whether such assumptions are physically reasonable in some sense (Manchak 2011b, 2014b). This is still an open question.

Another open question is whether physically more realistic spacetimes than Misner also permit the operation of time machines and how generic time-machine spacetimes are in particular spacetime theories, such as general relativity. If time-machine spacetimes turn out to be highly non-generic, the fan of time machines can retreat to a weaker concept of Thornian time machine by taking a page from probabilistic accounts of causation, the idea being that a time machine can be seen to be at work if its operation increases the probability of the appearance of CTCs. Since general relativity theory itself is innocent of probabilities, they have to be introduced by hand, either by inserting them into the models of the theory, i.e., by modifying the theory at the level of the object-language, or by defining measures on sets of models, i.e., by modifying the theory at the level of the meta-language. Since the former would change the character of the theory, only the latter will be considered. The project for making sense of the notion that a time machine as a probabilistic cause of the appearance of CTCs would then take the following form. First define a normalized measure on the set of models having a partial Cauchy surface to the past of which there are no CTCs. Then show that the subset of models that have CTCs to the future of the partial Cauchy surface has non-zero measure. Next, identify a range of conditions on or near the partial Cauchy surface that are naturally construed as settings of a device that is a would-be probabilistic cause of CTCs, and show that the subset of models satisfying these conditions has non-zero measure. Finally, show that conditionalizing on the latter subset increases the measure of the former subset. Assuming that this formal exercise can be successfully carried out, there remains the task of justifying these as measures of objective chance. This task is especially daunting in the cosmological setting since neither of the leading interpretations of objective chance seems applicable. The frequency interpretation is strained since the development of CTCs may be a non-repeated phenomenon; and the propensity interpretation is equally strained since, barring just-so stories about the Creator throwing darts at the Cosmic Dart Board, there is no chance mechanism for producing cosmological models.

We conclude that, even apart from general doubts about a probabilistic account of causation, the resort to a probabilistic conception of time machines is a desperate stretch, at least in the context of classical general relativity theory. In a quantum theory of gravity, a probabilistic conception of time machines may be appropriate if the theory itself provides the transition probabilities between the relevant states. But an evaluation of this prospect must wait until the theory of quantum gravity is available.

In order to appreciate the physics literature aimed at proving no-go results for time machines it is helpful to view these efforts as part of the broader project of proving chronology protections theorems , which in turn is part of a still larger project of proving cosmic censorship theorems . To explain, we start with cosmic censorship and work backwards.

Figure 3. A bad choice of initial value surface

For sake of simplicity, concentrate on the initial value problem for vacuum solutions \((T_{ab} \equiv 0)\) to Einstein’s field equations. Start with a three-manifold \(\Sigma\) equipped with quantities which, when \(\Sigma\) is embedded as a spacelike submanifold of spacetime, become initial data for the vacuum field equations. Corresponding to the initial data there exists a unique [ 20 ] maximal development \((\mathcal{M}, g_{ab})\) for which (the image of the embedded) \(\Sigma\) is a Cauchy surface. [ 21 ] This solution, however, may not be maximal simpliciter, i.e., it may be possible to isometrically embed it as a proper part of a larger spacetime, which itself may be a vacuum solution to the field equations; if so \(\Sigma\) will not be a Cauchy surface for the extended spacetime, which fails to be a globally hyperbolic spacetime. [ 22 ] This situation can arise because of a poor choice of initial value hypersurface, as illustrated in Figure 3 by taking \(\Sigma\) to be the indicated spacelike hyperboloid of \((1 + 1)\)-dimensional Minkowski spacetime. But, more interestingly, the situation can arise because the Einstein equations allow various pathologies, collectively referred to as “naked singularities,” to develop from regular initial data. The strong form of Penrose’s celebrated cosmic censorship conjecture proposes that, consistent with Einstein’s field equations, such pathologies do not arise under physically reasonable conditions or else that the conditions leading to the pathologies are highly non-generic within the space of all solutions to the field equations. A small amount of progress has been made on stating and proving precise versions of this conjecture. [ 23 ]

One way in which strong cosmic censorship can be violated is through the emergence of acausal features. Returning to the example of Misner spacetime ( Figure 1 ), the spacetime up to \(H^+ (\Sigma_0)\) is the unique maximal development of the vacuum Einstein equations for which \(\Sigma_0\) is a Cauchy surface. But this development is extendible, and in the extension illustrated in Figure 1 global hyperbolicity of the development is lost because of the presence of CTCs. The chronology protection conjecture then can be construed as a subconjecture of the cosmic censorship conjecture, saying, roughly, that consistent with Einstein field equations, CTCs do not arise under physically reasonable conditions or else that the conditions are highly non-generic within the space of all solutions to the field equations. No-go results for time machines are then special forms of chronology protection theorems that deal with cases where the CTCs are manufactured by time machines. In the other direction, a very general chronology protection theorem will automatically provide a no-go result for time machines, however that notion is understood, and a theorem establishing strong cosmic censorship will automatically impose chronology protection.

The most widely discussed chronology protection theorem/no-go result for time machines in the context of classical general relativity theory is due to Hawking (1992a). Before stating the result, note first that, independently of the Einstein field equations and energy conditions, a partial Cauchy surface \(\Sigma\) must be compact if its future Cauchy horizon \(H^+ (\Sigma)\) is compact (see Hawking 1992a and Chrusciel and Isenberg 1993). However, it is geometrically allowed that \(\Sigma\) is non-compact if \(H^+ (\Sigma)\) is required only to be compactly generated rather than compact. But what Hawking showed is that this geometrical possibility is ruled out by imposing Einstein’s field equations and the weak energy condition. Thus, if \(\Sigma_0\) is a partial Cauchy surface representing the situation just before or just as the would-be Thornian time machine is switched on, and if a necessary condition for seeing a Thornian time machine at work is that \(H^+ (\Sigma_0)\) is compactly generated, then consistently with Einstein’s field equations and the weak energy condition, a Thornian time machine cannot operate in a spatially open universe since \(\Sigma_0\) must be compact.

This no-go result does not touch the situation illustrated in Figure 1 . Taub-NUT spacetime is a vacuum solution to Einstein’s field equations so the weak energy condition is automatically satisfied, and \(H^+ (\Sigma_0)\) is compact and, a fortiori, compactly generated. Hawking’s theorem is not contradicted since \(\Sigma_0\) is compact. By the same token the theorem does not speak to the possibility of operating a Thornian time machine in a spatially closed universe. To help fill the gap, Hawking proved that when \(\Sigma_0\) is compact and \(H^+ (\Sigma_0)\) is compactly generated, the Einstein field equations and the weak energy condition together guarantee that both the convergence and shear of the null geodesic generators of \(H^+ (\Sigma_0)\) must vanish, which he interpreted to imply that no observers can cross over \(H^+ (\Sigma_0)\) to enter the chronology violating region \(V\). But rather than showing that it is physically impossible to operate a Thornian time machine in a closed universe, this result shows only that, given the correctness of Hawking’s interpretation, the observers who operate the time machine cannot take advantage of the CTCs it produces.

There are two sources of doubt about the effectiveness of Hawking’s no-go result even for open universes. The first stems from possible violations of the weak energy condition by stress-energy tensors arising from classical relativistic matter fields (see Vollick 1997 and Visser and Barcelo 2000). [ 24 ] The second stems from the fact that Hawking’s theorem functions as a chronology protection theorem only by way of serving as a potential no-go result for Thornian time machines since the crucial condition that \(H^+ (\Sigma_0)\) is compactly generated is supposedly justified by being a necessary condition for the operation of such machine. But in retrospect, the motivation for this condition seems frayed. As argued in the previous section, if the Einstein field equations and energy conditions entail that all hole free extensions of \(D^+ (\Sigma_0)\) contain CTCs, then it is plausible to see a Thornian time machine at work, quite regardless ofwhether or not \(H^+ (\Sigma_0)\) is compactly generated or not. Of course, it remains to establish the existence of cases where this entailment holds. If it should turn out that there are no such cases, then the prospects of Thornian time machines are dealt a severe blow, but the reasons are independent of Hawking’s theorem. On the other hand, if such cases do exist then our conjecture would be that they exist even when some of the generators of \(H^+ (\Sigma_0)\) come from singularities or infinity and, thus, \(H^+ (\Sigma_0)\) is not compactly generated. [ 25 ]

Three degrees of quantum involvement in gravity can be distinguished. The first degree, referred to as quantum field theory on curved spacetimes, simply takes off the shelf a spacetime provided by general relativity theory and then proceeds to study the behavior of quantum fields on this background spacetime. The Unruh effect, which predicts the thermalization of a free scalar quantum field near the horizon of a black hole, lies within this ambit. The second degree of involvement, referred to as semi-classical quantum gravity, attempts to calculate the backreaction of the quantum fields on spacetime metric by computing the expectation value \(\langle \Psi \mid T_{ab} \mid \Psi \rangle\) of the stress-energy tensor in some appropriate quantum state \(\lvert\Psi\rangle\) and then inserting the value into Einstein’s field equations in place of \(T_{ab}\). [ 26 ] Hawking’s celebrated prediction of black hole radiation belongs to this ambit. [ 27 ] The third degree of involvement attempts to produce a genuine quantum theory of gravity in the sense that the gravitational degrees of freedom are quantized. Currently loop quantum gravity and string theory are the main research programs aimed at this goal. [ 28 ]

The first degree of quantum involvement, if not opening the door to Thornian time machines, at least seemed to remove some obstacles since quantum fields are known to lead to violations of the energy conditions used in the setting of classical general relativity theory to prove chronology protection theorems and no-go results for time machines. However, the second degree of quantum involvement seemed, at least initially, to slam the door shut. The intuitive idea was this. Start with a general relativistic spacetime where CTCs develop to the future of \(H^+ (\Sigma)\) (often referred to as the “chronology horizon”) for some suitable partial Cauchy surface \(\Sigma\). Find that the propagation of a quantum field on this spacetime background is such that \(\langle \Psi \mid T_{ab} \mid\Psi \rangle\) “blows up” as \(H^+ (\Sigma)\) is approached from the past. Conclude that the backreaction on the spacetime metric creates unbounded curvature, which effectively cuts off the future development that would otherwise eventuate in CTCs. These intuitions were partly vindicated by detailed calculations in several models. But eventually a number of exceptions were found in which the backreaction remains arbitrarily small near \(H^+ (\Sigma)\). [ 29 ] This seemed to leave the door ajar for Thornian time machines.

But fortunes were reversed once again by a result of Kay, Radzikowski, and Wald (1997). The details of their theorem are too technical to review here, but the structure of the argument is easy to grasp. The naïve calculation of \(\langle \Psi \mid T_{ab}\mid\Psi \rangle\) results in infinities which have to be subtracted off to produce a renormalized expectation value \(\langle \Psi \mid T_{ab}\mid\Psi \rangle_R\) with a finite value. The standard renormalization procedure uses a limiting procedure that is mathematically well-defined if, and only if, a certain condition obtains. [ 30 ] The KRW theorem shows that this condition is violated for points on \(H^+ (\Sigma)\) and, thus, that the expectation value of the stress-energy tensor is not well-defined at the chronology horizon.

While the KRW theorem is undoubtedly of fundamental importance for semi-classical quantum gravity, it does not serve as an effective no-go result for Thornian time machines. In the first place, the theorem assumes, in concert with Hawking’s chronology protection theorem, that \(H^+ (\Sigma)\) is compactly generated, and we repeat that it is far from clear that this assumption is necessary for seeing a Thornian time machine in operation. A second, and more fundamental, reservation applies even if a compactly generated \(H^+ (\Sigma)\) is accepted as a necessary condition for time machines. The KRW theorem functions as a no-go result by providing a reductio ad absurdum with a dubious absurdity: roughly, if you try to operate a Thornian time machine, you will end up invalidating semi-classical quantum gravity. But semi-classical quantum gravity was never viewed as anything more than a stepping stone to a genuine quantum theory of gravity, and its breakdown is expected to be manifested when Planck-scale physics comes into play. This worry is underscored by Visser’s (1997, 2003) findings that in chronology violating models trans-Planckian physics can be expected to come into play before \(H^+ (\Sigma)\) is reached.

It thus seems that if some quantum mechanism is to serve as the basis for chronology protection, it must be found in the third degree of quantum involvement in gravity. Both loop quantum gravity and string theory have demonstrated the ability to cure some of the curvature singularities of classical general relativity theory. But as far as we are aware there are no demonstrations that either of these approaches to quantum gravity can get rid of the acausal features exhibited in various solutions to Einstein’s field equations. An alternative approach to formulate a fully-fledged quantum theory of gravity attempts to capture the Planck-scale structure of spacetime by constructing it from causal sets. [ 31 ] Since these sets must be acyclic, i.e., no element in a causal set can causally precede itself, CTCs are ruled out a priori. Actually, a theorem due to Malament (1977) suggests that any Planck-scale approach encoding only the causal structure of a spacetime cannot permit CTCs either in the smooth classical spacetimes or a corresponding phenomenon in their quantum counterparts. [ 32 ]

In sum, the existing no-go results that use the first two degrees of quantum involvement are not very convincing, and the third degree of involvement is not mature enough to allow useful pronouncements. There is, however, a rapidly growing literature on the possibility of time travel in lower-dimensional supersymmetric cousins of string theory. For a review of these recent results and a discussion of the fate of a time-traveller’s ambition in loop quantum gravity, see Smeenk and Wüthrich (2010).

Hawking opined that “[i]t seems there is a chronology protection agency, which prevents the appearance of closed timelike curves and so makes the universe safe for historians” (1992a, 603). He may be right, but to date there are no convincing arguments that such an Agency is housed in either classical general relativity theory or in semi-classical quantum gravity. And it is too early to tell whether this Agency is housed in loop quantum gravity or string theory. But even if it should turn out that Hawking is wrong in that the laws of physics do not support a Chronology Protection Agency, it could still be the case that the laws support an Anti-Time Machine Agency. For it could turn out that while the laws do not prevent the development of CTCs, they also do not make it possible to attribute the appearance of CTCs to the workings of any would-be time machine. We argued that a strong presumption in favor of the latter would be created in classical general relativity theory by the demonstration that for any model satisfying Einstein’s field equations and energy conditions as well as possessing a partial Cauchy surface \(\Sigma_0\) to the future of which there are CTCs, there are hole free extensions of \(D^+ (\Sigma_0)\) satisfying Einstein’s field equations and energy conditions but containing no CTCs to the future of \(\Sigma_0\). There are no doubt alternative approaches to understanding what it means for a device to be “responsible for” the development of CTCs. Exploring these alternatives is one place that philosophers can hope to make a contribution to an ongoing discussion that, to date, has been carried mainly by the physics community. Participating in this discussion means that philosophers have to forsake the activity of logical gymnastics with the paradoxes of time travel for the more arduous but (we believe) rewarding activity of digging into the foundations of physics.

Time machines may never see daylight, and perhaps so for principled reasons that stem from basic physical laws. But even if mathematical theorems in the various theories concerned succeed in establishing the impossibility of time machines, understanding why time machines cannot be constructed will shed light on central problems in the foundations of physics. As we have argued in Section 4, for instance, the hunt for time machines in general relativity theory should be interpreted as a core issue in studying the fortunes of Penrose’s cosmic censorship conjecture. This conjecture arguably constitutes the most important open problem in general relativity theory. Similarly, as discussed in Section 5, mathematical theorems related to various aspects of time machines offer results relevant for the search of a quantum theory of gravity. In sum, studying the possibilities for operating a time machine turns out to be not a scientifically peripheral or frivolous weekend activity but a useful way of probing the foundations of classical and quantum theories of gravity.

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How to cite this entry . Preview the PDF version of this entry at the Friends of the SEP Society . Look up topics and thinkers related to this entry at the Internet Philosophy Ontology Project (InPhO). Enhanced bibliography for this entry at PhilPapers , with links to its database.

• Krasnikov, S., 2003, “ Time Machine (1988-2001) ,” a brief account of the time machine problem; talk given at 11th U.K. Conference on the Foundations of Physics, Oxford, England, 9-13, Sept. 2002.
• Rovelli, C., 2008, “ Loop Quantum Gravity ”, in Living Reviews in Relativity .

determinism: causal | space and time: the hole argument | time: thermodynamic asymmetry in | time travel | time travel: and modern physics

Acknowledgments

We thank Carlo Rovelli for discussions and John Norton for comments on an earlier draft. C.W. acknowledges support by the Swiss National Science Foundation (grant PBSK1-102693).

Copyright © 2020 by John Earman < jearman @ pitt . edu > Christian Wüthrich < christian . wuthrich @ unige . ch > JB Manchak < jmanchak @ uci . edu >

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The Time Machine

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The Time Machine is a science fiction novel by H. G. Wells published in 1895. The book’s protagonist , who is never named and called only the Time Traveller , is a brilliant Victorian inventor who travels 800,000 years into the future. He finds that humans have evolved into two distinct species, called the Eloi and the Morlocks . The Eloi are peace-loving and childlike simpletons who are farmed and eaten by the brutal Morlocks, who live underground. This short novel was Wells’s first, and it made him famous. The work has influenced generations of speculative fiction writers and has twice been made into a motion picture.

Wells also wrote The War of the Worlds , The Invisible Man , The Island of Doctor Moreau , and nearly 50 other books. He was nominated four times for a Nobel Prize in literature. Wells was a prominent figure in the early 20th century, known not only for his novels but also for his modern and scientific approach to major issues of the day and for his support for socialism and pacifism.

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The Time Machine is in the public domain and is widely available on the internet. Readers should be prepared for a small number of anachronistic racial and gender terms in the text. The 2017 Amazon Classics e-book edition forms the basis for this study guide.

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The novel is told in the first person using a frame story about a dinner party. The narrator is a guest at the party, and the Time Traveller is the host. The Time Traveller recounts his adventures in the future to his guests beginning in Chapter 3. His story comprises the bulk of the novel. The novel concludes with a return to the scene of the dinner party, and the final chapter describes the guests’ dismayed reactions to their host’s tale.

The novel opens with a gathering of educated, upper-class men enjoying after-dinner conversation in an elegant home in Richmond, outside London. Their host, an inventor whom the narrator calls only the Time Traveller, is describing his theory that people can travel in time. The guests are intrigued but skeptical.

The Time Traveller shows the guests a clock-sized model of his time machine . He presses a lever on the device and it vanishes, astonishing the guests. Next, the Time Traveller escorts them to his laboratory and shows them the full-sized version of the device. The Traveller insists that none of the evening’s events are tricks and that he fully intends to travel through time when the machine is completed.

The following Thursday, the inventor’s guests assemble again. The host arrives late. His clothes are a mess, and his face is ashen. He claims that he has, since that very morning, experienced eight days of astonishing adventure in his time machine.

He describes climbing into the device and setting the levers to move forward in time. The hours begin to speed by. Day and night replace each other, faster and faster, until they whir by in a blur. Stopping the machine 802,000 years into the future, he discovers a race of diminutive, childlike creatures who are descended from humans. These are the Eloi, who enjoy a diet of fruit, spend their days idly, and are both mentally and physically weak.

The Traveller finds that his time machine has gone missing. A frantic search turns up few clues. He thinks the machine may have been hidden inside a large statue of a white sphinx . Despite his pleas, no one will go near the statue or help him open it.

A female Eloi falls into a stream and, seeing the lack of concern among the Eloi, the Time Traveller jumps in and rescues her. The two become friends. The woman, named Weena , grows devoted to him, and she follows him everywhere.

Early one morning, the Traveller notices white creatures on a distant hillside. These creatures are Morlocks, apelike with large eyes and pale fur. The Traveller learns that the Morlocks live underground, while the Eloi live aboveground. He climbs down one of the wells and finds there, underground, the machinery that keeps the Eloi alive. These machines are tended by the Morlocks. Several Morlocks try to capture him, and he narrowly escapes and returns to the surface.

The Traveller and Weena walk for many miles to a distant building on a hill. The building is an ancient, crumbling museum. Inside there are broken-down exhibits of extinct animals, old machinery, many scientific specimens, and books whose pages have long disintegrated. In the museum, he makes a torch and a weapon for himself out of the bits and pieces of machinery he finds there.

He and Weena trek back toward her home. That night, in the dark forest, they are set upon by Morlocks. The Traveller fends them off, but not before they capture Weena. He lights some camphor that he took from the museum, which further daunts them. The flames ignite a forest fire that forces everyone to retreat to a barren hill, and many Morlocks, stunned and confused, die in the conflagration.

The Traveller survives and returns to the garden with the mysterious white sphinx. The statue’s large pedestal has been opened, and inside sits the time machine. The Traveller enters the pedestal just before it closes. Quickly, he reinstalls the machine’s levers, sending himself far into the future, where he encounters a dying planet Earth: the sun glows huge and dull red, the air is thin, and the animals are monstrous.

Terrified by what he sees, he sets the machine to travel backward to his own time, where he emerges and tells the story to his dinner guests. They refuse to believe him. However, the narrator is curious to learn more, and he returns the next day. He witnesses the Traveller and his machine disappear from the lab—evidently, on another journey through time. The Traveller is never seen again.

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Home » Eras » 19th Century » The Time Machine

The Time Machine

H. g. wells.

(A push on a lever, a blurry dizziness, a clap of thunder… and a veil falls away to reveal the world of our far distant descendants.)

Breaking the rule that you have to proceed constantly forward in time at precisely one second per second is as old as the human imagination, appearing even in ancient stories where a god or a bonk on the head could slip you to another point in history. Surprisingly enough, though, the idea of a device or vessel that can carry one through time in the way that wagons and boats carry us through space is apparently less than a century and a half old. Perhaps the backwards-running clock in an 1881 Edward Page Mitchell story is the first time machine in literature; or else, if you have to be able to climb into the thing for it to count, then Enrique Gaspar’s “ anacronópete ” of his now little-known 1887 novel of that name narrowly beats out H. G. Wells’ 1888 story “The Chronic Argonauts”. Evidently the hyperindustrializing and engine-happy Americans and Western Europeans of the late 19th century, inspired no doubt also by the first stirrings of modern physics, were beginning to let their minds wander as to what a precisely engineered assemblage of gears and rods and bolts might be able to do. The Time Machine is the quintessence of this concept in literature, and is one of the best science fiction stories we have, even given the golden age of that genre that followed.

This is a fun novella to read, full stop. One need not get embroiled in other realms of significance– its symbolism, its physics and anthropology and politics. Nevertheless, some will want to delve into these things, and this particular story rewards us for doing so if we choose. For me the two most intriguing chords  The Time Machine  strikes have to do with future human evolution, and the possibility and nature of time travel.

To touch on the first of these first, Wells, through his science-minded protagonist of course, has a remarkable grasp of evolution, and of adaptation in particular. I mean remarkable for 1895, but also remarkable for writers in general, of novels or anything else, to the present day. Much of this was due certainly to his study of Darwin and other evolutionary writings, in which he was greatly interested. Indeed Wells was a biologist by training, and his first publication was a biology textbook. He frequently infused even his most technological writings with an understanding of natural history, ecology, and evolution, displaying knowledge that is a rarity in the genre even today. His ideas in the  War of the Worlds , for instance, that Martians might die of a rampant infection in a novel environment or that an invasive red weed could sweep across England, make that novel as interesting biologically as it is, shall we say, astrobiologically.  The Time Machine , however, is more surprising. Some of the explanations that he incorporated or implied were proposed prominently in the late 19th century, such as in Darwin’s Descent of Man . Other explanations, however, are thoroughly reasonable today in 21st century evolutionary biology, but we do not generally think of them as having been typical back when he wrote (it would take a more astute historian of biology than myself to know whether the ideas had been raised at all). Wells is well known for his uncanny ability to predict advances in technology (e.g., tanks, planes, nuclear bombs, TV, spaceships, satellites, and biotech); and to this I would not be surprised if we must add the skill of anticipating certain future trends in evolutionary science, or at least wisely selecting from among the vast array of going ideas in his day. Here are perhaps the ten most striking points of  evolutionary realism  in this novel:

• Pervasiveness of adaptation . The differences between the Eloi and the Morlocks, and their differences from us, are considered to have trait-specific functional explanations. This is typical today, and was the hunch of Darwin, but at the  fin de siècle  there was a debate raging between those who attributed evolutionary change to selection vs mutation (and of course the answer was “both”). Wells wisely stayed away from the mechanism of inheritance, which in his day was poorly understood; but he fully embraced adaptation to an extent we would not see as the dominant trend in evolutionary biology for several decades.
• Individual selection . Even Darwin had difficulty separating descriptions of natural selection in terms of group vs. individual advantage. We know now that selection is most powerful at the individual level, and even when it sorts among groups, individual-level language can still handle the situation. All of the adaptations mentioned in  The Time Machine  are discussed in terms of, or at least imply, individual selection. This level of care was hit or miss in popular and even some professional science writings until the 1960s.
• Allopatric divergence and reproductive isolation . Wells realized that physical separation (in this case, some humans above ground and some below) and reproductive isolation (within-caste marriage requirements) would have been necessary for evolutionary divergence to occur. The Time Traveller was explicit about both of these features .
• Rate of speciation . Nobody in Wells’ day would have had the faintest clue how long it would have taken for humans to diverge into the Eloi and Morlocks. We have a better idea today, but our knowledge is still far from definitive. Based on working estimates,  Homo sapiens  probably diverged from our common ancestor with  H.  heidelbergensis  around 400,000 years ago, and from our common ancestor with  H. neanderthalensis  about twice that long ago. So 800,000 years is thoroughly reasonable for speciation to occur in a human lineage, and although the novel doesn’t give us much to go on, the degree of difference between modern humans and Neanderthals could be in the same ballpark as the differences between the Eloi and Morlocks. To be honest, though, the changes in limb length and hair of the Morlocks seem way too rapid for that timescale and moreover are not straightforwardly predictable; and the cognitive and behavioral changes (outlined below) in the Eloi seem too dramatic to be realistic as well.
• Troglodytism . Some of the features of the Morlocks, including loss of pigment, carnivory, and large eyes and poor eyesight in the light, are typical of animals that live underground or in caves. Even more interesting is that, with respect to divergent selection pressures in light vs dark habitats, again Wells is ahead of his time. Assuming a human generation time of about 25 years, the Time Traveller went 32,000 generations into the future. This is within the range over which recent research suggests cave and surface forms of the Mexican tetra  Astyanax mexicanus  have diverged in pigmentation and eyesight.
• Relaxed selection and trait loss . Darwin and (especially) later biologists, influenced by August Weismann, suggested that in evolution, if you don’t use a trait, it will reduce and atrophy through relaxation of selection for functionality combined with natural selection for efficiency. Again the Time Traveller has suggested or implied just this mechanism for the loss of several previously functional traits in the evolution of the Eloi, such as intelligence, stature, omnivory, musculature, creativity, curiosity, cooperation, and perhaps the size of ears and mouths.
• Evolution of sexual dimorphism . The two main reasons why males and females differ in obvious ways beyond their reproductive structures are sexual selection (especially male competition for females, and female or mutual choice of mates), and selection for female fertility and fecundity. These have led in the human ancestry, for instance, to more aggression and larger size in males, as well as musculature, prominent facial bone structure, and deeper voices. In women, selection for childbearing and for signaling fertility to males has led to wide hips, softer facial features, distinctive fat deposition patterns, and permanent breasts. The Time Traveller notes that the sexes look alike in the Eloi, suggesting a dramatic reduction in sexual selection and fertility/fecundity selection. This is precisely what we would expect with the very high survival, absence of conflict, and low reproductive rate (in evolutionary terms, extreme K-selection) that the author describes of the Eloi.
• Paedomorphosis . Humans and domestic animals live in a much safer environment than their ancestors did, and as a result have evolved a lax development that matures at an earlier stage, with the result that we and our domestic animals have evolved to look and act more juvenile for our lineages. The Eloi have essentially become even more extremely self-domesticated, in that they have lived through thousands of generations of coddling and protection from danger. Thus it is predictable that they would evolve to look and act like our children in a wide range of ways, with big eyes, short stature, playful personalities, no facial hair, and low sexuality. Wells is explicit about all of these.
• Ecological dominance and niche construction.  The typical forces Darwin identified as imposing selection on animals were predators, parasites, disease, weather, climate, and starvation; subsequent research has borne that out. Humans, however, have become ecologically dominant, such that we ourselves are our own most significant source of selection. Another phenomenon that has ratcheted up with this is that we modify our habitat to suit ourselves, thus creating the environment that ends up shaping our evolution. These two ideas of ecological dominance and niche construction are explicit features of the evolutionary story of both the Eloi and the Morlocks, but were not widely realized in evolutionary biology until the 1970s and 2000s, respectively.
• Evolution of intelligence & cooperation . The most impressive evolutionary realization of Wells in  The Time Machine  is that our high intelligence, curiosity, and creativity as humans evolved through struggle and conflict as we interacted with each other in social groups. This, more fully explicated, is now termed the “social intelligence hypothesis”, and has emerged as the best explanation of our phenomenal intelligence just since the 1970s, from a rich field of competing theories. Wells also portrayed the Eloi as having lost their ancestral altruistic or cooperative tendency (despite communal living). This too is a corollary of the social intelligence hypothesis, which proposes that cooperation arose in the service of group competition. Thus Wells is turning the social intelligence hypothesis around under relaxed selection, suggesting that without conflict and competition, both intelligence and cooperation would decline. These ideas are extraordinarily sophisticated for his day, and would be eminently suitable for contemporary discussion among evolutionary anthropologists today.

Whether any of these outcomes, especially #7-10, would have been realistic for the future evolution of humans in the environment Wells imagined is another question, of course. In all likelihood, the ancestors of the Eloi would have continued to fight group against group and thus changed much less from their  Homo sapiens  ancestor. Wells’ rosy communist conceptions of human nature influenced him here (although obviously he viewed the endpoint with chagrin!). Most likely, sexual and other social selection and selfish conflict and competition are not going away, which means cooperation and intelligence will not go away… if we persist another 800,000 years that is, of which we should be far from confident.  

SNOP (Sci-fi Nerds Only, Please)—you’ve been warned; seeking realism in the unreal and attending geekily to detail are pervasive henceforth :

I can’t help musing on H. G. Wells’ concept of time travel as it manifests in both the brief dinner discussion and the activity of the time machine itself. I doubt anyone would dispute that we can mark the beginning of serious thought and argument about controlled time travel with this novel. Wells kicked things off in a mighty way. However, the bare snippet of discussion he permits us to overhear among the dinner guests focuses on just one of the many uncertainties and paradoxes that arise with the concept of time travel. To wit, if an object moved into the future but stayed in the same place, wouldn’t you still see it there in all the intervening moments? And if an object moved into the past, wouldn’t you have already seen it there and in fact still see it there unless somebody had moved it (which would surely be remembered)? Actually this raises two interesting questions. One of these regards the status of the memories of everyone who has actually lived through the first version of a past that has now been changed through something moving backwards into it– would those memories update, and how? But we’ll set that aside, as in this story we’re primarily interested in the future. The other question is a pickle Wells puts himself into with his character’s explanation of the possibility of time travel. All physical objects get from point A to point B by going through the space in between (Wells knew nothing of exceptions to this rule as indicated later by quantum mechanics, and besides, those objects are minute and cannot carry humans with them!). Wells has his Time Traveller say that the key to time travel is realizing that the fourth (time) dimension is just like the other three, and not of a radically different sort. If so, then we can infer that movement of an object through time will likewise move through all the intervening time. This conception provides no option for a time leap, but only movement back and forth at various temporal speeds. So in this context, as one of the dinner guests asked of the model, why does the time machine cease to be at the original time point when it goes into the future? If the time machine was in the lab at 3:58, then 3:59, then at 4:00 it increased its velocity along the time dimension into the future, this does not mean that suddenly the object was  not  in the lab at 4:01 or 4:02. It still was there then, but for that object the duration spent at those time points was much shorter than for everyone and everything outside of the machine. This, the Time Traveller says, results in a “diluted presentation”—below the threshold of perception—similar (he says) to the way we cannot perceive a speeding bullet or the spokes of a spinning wheel. This is as far as his explanation goes at the time. I think it is insufficient, and the analogies bad, as one can discover painfully by stepping into the path of a bullet or sticking a finger into the spokes of a spinning wheel. Yes, visual perception of such objects in rapid motion is ineffective, but that doesn’t mean the objects aren’t still occupying all the spatial trajectory without exception. So he hasn’t really explained why the time machine disappears and why, for instance, he could wave his hand through the space the model occupied. He does a somewhat better job later, as he’s about to slow down the thing at the future date:

“I was, so to speak, attenuated–was slipping like a vapour through the interstices of intervening substances! But to come to a stop involved the jamming of myself, molecule by molecule, into whatever lay in my way; meant bringing my atoms into such intimate contact with those of the obstacle that a profound chemical reaction–possibly a far-reaching explosion–would result, and blow myself and my apparatus out of all possible dimensions–into the Unknown. This possibility had occurred to me again and again while I was making the machine; but then I had cheerfully accepted it as an unavoidable risk–one of the risks a man has got to take!” -III.

So the blurring, so to speak, that makes the time machine disappear to our eyes is not just a matter of perception after all, but existence. It allows a time machine and anything in it to move through external objects. On his theory there is a sense in which matter moving through the time dimension at an increased rate is not as solid or compacted as matter moving at the typical rate. So here, in contradiction to the Time Traveller’s earlier argument, we do see a feature of the time dimension that is not true of the three spatial dimensions, and so there is something special about it after all that doesn’t boil down solely to a peculiarity of our constitution as timed entities, forced to move along that trajectory at a constant rate.

Another distinction to the time dimension we could bring up at this point relates to extension and movement. As far as I can tell, Wells conflates or synonymizes these two qualities in the time dimension, stating sometimes that an object of a particular duration is  extended  over that time period (in the way a yardstick extends 36 inches in length); and other times he describes this as  movement  through time, at some velocity. This conflation is easy to do, because apparently in time there is only one thing going on, whereas in space there are two things. A yardstick extends in three dimensions by specific amounts, and can also move in any one or more of those same dimensions; but a yardstick’s extension in  time  would seem to be synonymous with its total movement (duration) in that dimension. If we consider this object’s temporal extension to include any form it takes, including any combination of mass and energy, this value would simply be the duration of the universe. That’s certainly not like the spatial dimensions!

I find the Time Traveller’s idea fascinating, but false, that the only reason that we view the fourth dimension as a different sort than the other three is because of a “natural infirmity of the flesh”. I would turn the tables on him and say that the only reason why time travel seems to us reasonable enough at all such that a book can be written about it—nay, hundreds if not thousands of stories and books– is because of a natural infirmity of the flesh.  We can follow  The Time Machine  without immediate confusion and ridicule upon the Time Traveller’s return to the dinner, only because Wells has arranged the story such that as long as we don’t think too much we won’t be offended in our natural assumption that there is only one timeline– that time is unilineal—and that we can only be in one place at a time.  But the story violates that assumption . If we think about it for a bit, nearly all time travel stories, as cleverly constructed as some are, prevent us from really taking the possibility of time travel seriously if we take our uniqueness as individual selves seriously. And that is regardless of our knowledge of physics. But I’m getting ahead of myself.

Time travel has frequently been a source of paradoxes of interest to physicists and philosophers. They are usually grouped into two categories: consistency problems and causal loops. One example of a consistency problem is going back and killing your grandfather before your parent is born—if you succeed, how can you possibly be alive to have done that? A causal loop is when something in the future affects something in the past, which then affects that thing in the future. The reason we consider these problems is because we assume that there is only one timeline and everyone on it is unique and singular; otherwise, we could just say that killing your grandfather prevented a  different  version of your grandfather from having a  different  version of your parent. In fact that latter way is probably the natural, if subconscious, way we interpret the situation, as ridiculous as it is. “After all,” (we think to ourselves), “I remember my parents—they were indeed alive and did have me. Even if I go back and kill my grandfather, I’m still here, ain’t I?!” Thus, although time travel supposedly involves going back and forth on the same timeline, traversing the same times more than once, we instinctively unravel and stretch it all out in our minds into a single consistent narrative, because that’s what we assume of life.  The Time Machine  carefully avoids breaking this bubble of an assumption.

After leaving at 4pm and spending 8 days at another time, our Time Traveller decided to re-enter that original day at around 8pm, rather arbitrarily. It was thoroughly his fault he was late, as it would have been just a few taps to the lever and he would have had plenty of time to eat and dress before his guests arrived—even a day or two to heal if he wanted. But at any time earlier than 4pm that day his earlier self would already have been there, which would cause a problem. Arriving back home at a time after he left is therefore convenient for the story writer, as it leaves the protagonist only fully materialized at one place at any given time. However, note that his attenuated self is present twice at all time points between 4pm and the furthest in time he went—that means two of him  at a time  at all time points, one him on the way there and one him on the way back. That means two machines too. When he came back from the death of the sun and whizzed backwards through the year 802,701 without stopping, he was for a brief moment passing through the week during which the time machine was in that sphinx pedestal; the machine passed through the machine for that week. By the way, of course, if he really wanted to take Weena home he could simply have stopped on the backward trip and gotten her. But he’d better stop there before he initially arrived, or else there’d be two of him there and two time machines. Let’s just probe that further. If he did arrive when he was already there, and could manage to convince his other (flabbergasted, to be sure) self to take an immediate jaunt into the future for a bit and then come back, and they decided to return precisely when both of them were already there discussing the matter, then there’d be four of them! With a little planning you could have a whole population of Time Travellers and just as many time machines, as many as you like, never needing any additional materials or anything, all in the same place at the same time and totally stymying the Eloi and kicking major Morlock butt. In fact he could do this back at home too and get so much more done in life, increase his publication rate way beyond the measly 14 it is during this story, send one of himself to family reunions and faculty meetings while another rests at home, carry money back and forth in order to multiply it exponentially, and so on.

The moral of this ramble is that most time travel stories including this (probably the best) one necessarily open the world up to a  proliferation of matter , violating the conservation of mass-energy, including a  proliferation of selves , violating in addition, well, common sense at least. So unless you think that’s all OK, or too abstruse to worry about, or don’t mind an ad hoc solution such as a rule prohibiting occupying the same time twice (some stories do that!), such stories might be frustrating in the same sense and to the same sorts of people as is Rian Johnson’s weaponized hyperspace crash in a certain unmentionable latter-day  Star Wars  movie. Certain sorts of time-travel stories won’t encounter this particular issue, for instance time travel that can only go forward, or invokes conceptions of alternate reality or jumping between timelines, or involves eternal beings that can enter and escape time at will.

All this having been said, I didn’t really care about such problems while reading, and H. G. Wells is ingenious for realizing the paradoxes that he did and hiding most of them from us. Not until the 1920s and later did science fiction aficionados (and philosophers, and cosmologists) really start thinking about temporal paradoxes in earnest, leading to such curiosities as the grandfather, Fermi, and Newcomb paradoxes, and the butterfly effect. But Wells decades earlier had his characters thinking about several of the issues, and laughing at time travel’s “practical incredibleness, the curious possibilities of anachronism and of utter confusion it suggested.”  

Although not parsed this way by the author or any publishers, the book can be seen in three parts: the dinner discussion on time travel; the adventure at year 802701; and the search for the end of the world.

• Dinner discussion on time travel (chs.I-III; see the bottom of TIDBITS OF SIGNIFICANCE for how the chapters are parsed)

The discussion just begins. We have no setting, no cast of characters, and indeed we never get a name for the protagonist. We just learn that the Time Traveller has something unusual on his mind—a “recondite matter”—to share with his dinner guests. [In fact the other, presumably earlier, “Holt” text does begin in a typical way, introducing the main character as a prominent mathematician and so on; but evidently Wells decided he wanted to jump right in.] The Time Traveller begins with an argument for the possibility of time travel, which goes like this: Geometric features like lines and planes and even cubes are abstractions. They only really exist if they extend in the fourth dimension. An object that has no duration has no existence. Time is just a dimension, like the other three. We are tempted to think of time as a different sort of thing from height, length, and width because of our peculiar constitution as beings whose consciousness moves along the time dimension incessantly and at a constant velocity. Moreover, just as we can represent an object by drawing it with depth perspective on a piece of paper, thus demonstrating three-dimensional geometry in only two dimensions, we might be able to have a four-dimensional geometry. In fact he has been working on this for years. The goal is to incorporate time into constructed objects, thus creating “three dimensional representations of [a] Four-Dimensioned being, which is a fixed and unalterable thing.” Hence the possibility, at least in theory, of a time machine. Then, just as gravitation restricts our movement in one dimension but we can override that restriction with balloons, we might be able similarly to use such our 4-D object to violate or alter the restrictions imposed by the forces that push us along the time dimension. Then he excitedly shows his guests precisely such a machine, first in a small model form, which he claims can move equally easily through any dimension. A guest tests it according to the Time Traveller’s instructions, and the object vanishes, off into either the past or the future.  Everyone thinks it’s some sort of trick, a sleight of hand perhaps.

For a second dinner, with an overlapping guest list, the host is late. He arrives discombobulated, grimy, banged up, and exhausted. He excuses himself to clean and change clothes, and the guests are incredulous. They do not believe he had travelled time, but something sure did happen—as an editor said among the humorous comments, “A man couldn’t cover himself with dust by rolling in a paradox, could he?”

When he joins them and has had his fill of food, he insists that he would not argue that evening, nor suffer any interruption, but just wishes to tell his story from beginning to end, and then go to bed. He is tired, and has lived 8 days since 4pm that day. They agree to let him speak, and so the story begins.

The real machine is in the lab; it is apparently spherical, and its mentioned parts include ivory bars, a brass rail, nickel bars, a quartz rod, starting and stopping levers that are removable, and a saddle in the middle of it all. It’s held together with screws, and lubricated with oil.

The Time Traveller tells that he entered the machine and pushed the lever forward. A strange feeling ensued, and he confirmed with an exterior clock that he had just moved through several hours in a span of seconds. Then he went for it. The atmosphere around him got “faint and hazy” and he experienced a “helpless headlong motion”. “An eddying murmur filled my ears, and a strange, dumb confusedness descended on my mind.” An engaging description follows of the view of the world as he accelerated through time. Eventually, “Night followed day like the flapping of a black wing”.

• The adventure at year 802701 (chs.IV-X)

He carefully stops the machine after a while, and finds from the dials that it is the year 802,701. He lands on a lawn, near a large white marble sphinx with wings outstretched, atop a great bronze pedestal. [This forms a landmark, even a centerpiece, of his experiences at that time. The wings form an obvious symbol, but also the sphinx itself suggests a riddle he has to solve in order to move onward. And indeed he spent much of his time there trying to figure out what had happened over the last 800K years, and also how to recover his time machine!]

Immediately upon arrival he meets the Eloi—four foot tall, fragile figures with sandals and short tunics. They are beautiful but frail, given to laughing and playing with flowers. They have “a graceful gentleness, a certain childlike ease”. They are large-eyed, pink-skinned, dull, mild, largely uninterested in the world around them and of short attention, unintelligent, with a simple language. There is no evident difference between males and females. They eat only fruit. The Time Traveller notes, “I never met people more indolent or more easily fatigued.” They dance around, and at some point place a couple of white flowers into his pocket. As he tells this story to his friends “later” at the dinner, he removes them from his pocket and lays them on the table.

They live communally in a large yet dilapidated palace. Indeed the Time Traveller explicitly supposes that this is the ultimate apex of communism as a social doctrine and way of life. With the eventual absence of all conflict and struggle, their life became a paradise. Nobody needed to work, there was no disease, no overpopulation … utopia!  There was no wildness even in nature, as he looked around. No agriculture either—“the whole earth had become a garden… One triumph of a united humanity over Nature had followed another.” Science had evidently progressed, including selective breeding of animals and plants, agriculture, medicine, until nature became thoroughly subservient and solicitous to all the needs of humans. “It was natural on that golden evening that I should jump at the idea of a social paradise.” Then he had a eureka moment—that’s why they’re so dull and soft and unintelligent! Intelligence comes from struggle. “Under the new conditions of perfect comfort and security, that restless energy, that with us is strength, would become weakness… This has ever been the fate of energy in security; it takes to art and to eroticism, and then come languor and decay.” Indeed the civilization of the Eloi appeared to be in decline. There was no industry, no work, no maintenance of buildings. Dancing and singing and playing with flowers were all that was left of the artistic. Eventually, he thought, even that would be gone, and all energy would decline into “a contented inactivity”. He thought he had answered everything—but how wrong he was, at least part wrong anyway.

Then things get complicated, both practically and in terms of his explanatory theory. He loses the time machine. He also notices wells in the ground that appear to be ventilation shafts. He can make sense of none of the technology he sees, although that is hardly surprising with the advancement of the ages. His ignorance becomes fascinating to him—he compares himself to how a Central African would feel if he were brought to London and then back to Africa to explain what he saw to his countrymen. Yet, given the small difference between those two human groups, compare the much larger difference [10x as much to be precise!] between himself and these people he has met! But these people seem so unable to provide for themselves—how can that be explained? How can they be so uncreative and unindustrious, yet not be in need? He notices now also that he can find no cemeteries or crematoria, and no sick or old people.

At one point an individual falls into the water and begins to drown. Nobody tries to rescue her. The Time Traveller jumps in and rescues her, for which she is effusively grateful. She becomes inseparable from him, and they form a “queer friendship”. Her name is Weena. In his words, “she was exactly like a child”. Weena, and all the other Eloi, are deathly afraid of the dark. She will not go near the ventilation wells or stay out late, and desperately wants the Time Traveller to follow the same rules.

Then he sees his first Morlock: a “white, ape-like creature running rather quickly up the hill”. It was “dull white, and had strange large greyish-red eyes; also that there was flaxen hair on its head and down its back”. Eventually he sees one of these loathsome creatures scrambling down a ventilation shaft, “like a human spider”. The shafts lead, he discovers, to another civilization below the earth!

“…gradually, the truth dawned on me: that Man had not remained one species, but had differentiated into two distinct animals: that my graceful children of the Upper-world were not the sole descendants of our generation, but that this bleached, obscene, nocturnal Thing, which had flashed before me, was also heir to all the ages” -V

They are subterranean, they are the workers, enslaved by the Eloi in the past, adapting to darkness with their paleness and sensitive eyes. That is how the Eloi live without industry or ability—the Morlocks provide for them. The Time Traveller continues his theorizing: humans had split into two forms, made possible by a separation between the “Capitalist and the Labourer”, the former living on the surface off of the produce of the latter in underground factories. Long ago, the rich had kept the poor away from everything on the surface, and so the poor stayed underground, and there they worked [Wells had actually been familiar with such underground workhouses as a child]. With marriage rules keeping them separate as well, divergence began to occur. Haves above, have-nots below, renting from those above with the produce of their labor. Evolution continued, each race adapting to its place, the Morlocks no less to theirs than the Eloi to theirs. Hence the Eloi’s “triumph had not been simply a triumph over Nature, but a triumph over Nature and the fellow-man.”

He goes down a shaft and sees that the Morlocks live in darkness and misery amid machinery, and eat meat—including Eloi meat, he comes to realize. He defends himself with matches, and eventually escapes their clutches. He realizes that the reason the Eloi are afraid of the dark is because the Morlocks now emerge at night and hunt them. They still produce for the Eloi, perhaps now out of habit; but in a way they were beginning to get the upper hand: “clearly, the old order was already in part reversed”. [I must say they did not try very hard to stop the man, and do not seem to be very strong in general; nevertheless they were scary enough. Perhaps they have only become as strong as they need to be to hunt the weak Eloi.]

He then explores a bit further from his landing place with Weena, in particular a Palace of Green Porcelain, which he discovers is a museum of human history and natural history, even way back to his time! At some point he hears the patter of Morlock feet, and grabs a metal lever as a weapon and a jar of flammable camphor, and leaves, hoping his new tool can get into the pedestal where, he supposes, the Morlocks have stowed his machine.

He starts a forest fire to scare off the Morlocks when the light begins to fail and he is still far from the sphinx and the palace of the Eloi. He then goes into the wood, outrunning the fire and carrying Weena, as the Morlocks began to emerge and attack. He stops, puts Weena down, and fights! [An excellent fight—it’s amazing how violent action can be exhilarating to the reader when the suspense is long sustained and we have not become inured by too much action. And just as the reader feels it, the Time Traveller as narrator admits to feeling it too, which is delightful.] Eventualy he is saved by the advance of the fire and the Morlock’s fear of it. Weena, however, is lost and presumably dies in the fire or at the hands of the Morlocks. Eventually the beasts get so disoriented in the light of the fire that they mill about aimlessly and are no longer a danger.

He makes his way back to the sphinx in the morning, only to find that the doors to the pedestal are open!  But it is a trap—the Morlocks are waiting for him, and he must fight them off as he struggles to insert the control levers in their proper places and—just in time—is off in time.

• The search for the end of the world, and return (chs.XI-XII)

The Time Traveller, speeding forward in time at a breakneck pace, seeks to find more secrets of the future, especially the fate of the earth, before returning, despite his exhaustion. He had already perceived an increase in the heat of the sun and movements of the stars such that constellations were gone even in 802,701. This leg of the journey reveals other visions, including monstrous crabs, the growth and increasing redness of the sun, a green slime eventually dominating the landscape, and ultimately an “abominable desolation” with white flakes floating down in the sky, and further still, darkness and complete silence.

“So I came back”, comes the almost humorous beginning of the last chapter after that terrifying denouement to world history.

The only verbal reply to this tale, after a pause, is a quip by the newspaper editor, who says merely, “What a pity it is you’re not a writer of stories!”

After the rest of the guests leave, the narrator comes back with the Time Traveller into the house, and asks him again whether he was telling the truth. The Time Traveller does not skip a beat, but says he’ll prove it in a half hour. He goes into the laboratory, vanishes in his machine, and never returns.

Three years have gone by, and the narrator wonders where the Time Traveller went; whether he went backward or forward. He ponders human history and our approaching destiny, as he holds two shriveled flowers—the only evidence of the Time Traveller’s journey.

Tidbits of Significance 

[There are two very different texts of  The Time Machine.  All passages are from the typically reprinted Heinemann, not the Holt, text. Parsing was into 12 chapters and an epilogue; see below the quotations for particulars. All passages in quotation marks are spoken by the Time Traveller character, unless otherwise noted.]

The Time Traveller (for so it will be convenient to speak of him) was expounding a recondite matter to us. -I.

“Clearly,” the Time Traveller proceeded, “any real body must have extension in four directions: it must have Length, Breadth, Thickness, and–Duration. But through a natural infirmity of the flesh, which I will explain to you in a moment, we incline to overlook this fact. There are really four dimensions, three which we call the three planes of Space, and a fourth, Time. There is, however, a tendency to draw an unreal distinction between the former three dimensions and the latter, because it happens that our consciousness moves intermittently in one direction along the latter from the beginning to the end of our lives.” -I.

“[a] Four-Dimensioned being… is a fixed and unalterable thing” -I. [a fascinating idea: once you realize time is a dimension, then any existing entity, including all four of its dimensions, can indeed be conceived as fixed and unalterable, in a medieval or even Platonic way.]

“Time is only a kind of Space” -I.

“Then there is the future,” said the Very Young Man. “Just think! One might invest all one’s money, leave it to accumulate at interest, and hurry on ahead!” “To discover a society,” said I, “erected on a strictly communistic basis.” -I. [In a witty discussion of what one could do if time travel worked; “I” is the narrator.]

“Upon that machine,” said the Time Traveller, holding the lamp aloft, “I intend to explore time. Is that plain? I was never more serious in my life -I.

“As I put on pace, night followed day like the flapping of a black wing. The dim suggestion of the laboratory seemed presently to fall away from me, and I saw the sun hopping swiftly across the sky, leaping it every minute, and every minute marking a day. I supposed the laboratory had been destroyed and I had come into the open air. I had a dim impression of scaffolding, but I was already going too fast to be conscious of any moving things. The slowest snail that ever crawled dashed by too fast for me. The twinkling succession of darkness and light was excessively painful to the eye. Then, in the intermittent darknesses, I saw the moon spinning swiftly through her quarters from new to full, and had a faint glimpse of the circling stars. Presently, as I went on, still gaining velocity, the palpitation of night and day merged into one continuous greyness; the sky took on a wonderful deepness of blue, a splendid luminous color like that of early twilight; the jerking sun became a streak of fire, a brilliant arch, in space; the moon a fainter fluctuating band; and I could see nothing of the stars, save now and then a brighter circle flickering in the blue.” -III.

“Seeing the ease and security in which these people were living, I felt that this close resemblance of the sexes was after all what one would expect; for the strength of a man and the softness of a woman, the institution of the family, and the differentiation of occupations are mere militant necessities of an age of physical force; where population is balanced and abundant, much childbearing becomes an evil rather than a blessing to the State; where violence comes but rarely and off-spring are secure, there is less necessity–indeed there is no necessity–for an efficient family, and the specialization of the sexes with reference to their children’s needs disappears. We see some beginnings of this even in our own time, and in this future age it was complete.” -IV.

“I had happened upon humanity upon the wane.” -IV

“Strength is the outcome of need; security sets a premium on feebleness.” -IV

“…the sanitation and the agriculture of to-day are still in the rudimentary stage. The science of our time has attacked but a little department of the field of human disease, but even so, it spreads its operations very steadily and persistently. Our agriculture and horticulture destroy a weed just here and there and cultivate perhaps a score or so of wholesome plants, leaving the greater number to fight out a balance as they can. We improve our favourite plants and animals–and how few they are–gradually by selective breeding; now a new and better peach, now a seedless grape, now a sweeter and larger flower, now a more convenient breed of cattle. We improve them gradually, because our ideals are vague and tentative, and our knowledge is very limited; because Nature, too, is shy and slow in our clumsy hands. Some day all this will be better organized, and still better. That is the drift of the current in spite of the eddies. The whole world will be intelligent, educated, and co-operating; things will move faster and faster towards the subjugation of Nature. In the end, wisely and carefully we shall readjust the balance of animal and vegetable life to suit our human needs.” -IV

“What, unless biological science is a mass of errors, is the cause of human intelligence and vigour? Hardship and freedom: conditions under which the active, strong, and subtle survive and the weaker go to the wall; conditions that put a premium upon the loyal alliance of capable men, upon self-restraint, patience, and decision. And the institution of the family, and the emotions that arise therein, the fierce jealousy, the tenderness for offspring, parental self-devotion, all found their justification and support in the imminent dangers of the young.  Now  where are these imminent dangers? There is a sentiment arising, and it will grow, against connubial jealousy, against fierce maternity, against passion of all sorts; unnecessary things now, and things that make us uncomfortable, savage survivals, discords in a refined and pleasant life. “I thought of the physical slightness of the people, their lack of intelligence, and those big abundant ruins, and it strengthened my belief in a perfect conquest of Nature. For after the battle comes Quiet. Humanity had been strong, energetic, and intelligent, and had used all its abundant vitality to alter the conditions under which it lived. And now came the reaction of the altered conditions. “Under the new conditions of perfect comfort and security, that restless energy, that with us is strength, would become weakness. Even in our own time certain tendencies and desires, once necessary to survival, are a constant source of failure. Physical courage and the love of battle, for instance, are no great help–may even be hindrances–to a civilized man. And in a state of physical balance and security, power, intellectual as well as physical, would be out of place.” -IV.

“This has ever been the fate of energy in security; it takes to art and to eroticism, and then come languor and decay.” -IV

“We are kept keen on the grindstone of pain and necessity” -IV

“At once, like a lash across the face, came the possibility of losing my own age, of being left helpless in this strange new world. The bare thought of it was an actual physical sensation. I could feel it grip me at the throat and stop my breathing.” -V

“But I was too restless to watch long; I am too Occidental for a long vigil. I could work at a problem for years, but to wait inactive for twenty-four hours—that is another matter.” -V

“Face this world. Learn its ways, watch it, be careful of too hasty guesses at its meaning. In the end you will find clues to it all.” -V [when he had lost his time machine and was frustrated at his inability to get it back]   “There is a tendency to utilize underground space for the less ornamental purposes of civilization… this tendency had increased till Industry had gradually lost its birthright in the sky. I mean that it had gone deeper and deeper into larger and ever larger underground factories, spending a still-increasing amount of its time therein, till, in the end–!” -V (explanation for evolution of the Morlocks).

“Again, the exclusive tendency of richer people–due, no doubt, to the increasing refinement of their education, and the widening gulf between them and the rude violence of the poor–is already leading to the closing, in their interest, of considerable portions of the surface of the land” -V (explanation for the withdrawal of the poor to underground in human history)

“And this same widening gulf–which is due to the length and expense of the higher educational process and the increased facilities for and temptations towards refined habits on the part of the rich–will make that exchange between class and class, that promotion by intermarriage which at present retards the splitting of our species along lines of social stratification, less and less frequent. So, in the end, above ground you must have the Haves, pursuing pleasure and comfort and beauty, and below ground the Have-nots, the Workers getting continually adapted to the conditions of their labour.” -V

“Such of them as were so constituted as to be miserable and rebellious would die; and, in the end, the balance being permanent, the survivors would become as well adapted to the conditions of underground life, and as happy in their way, as the Upper-world people were to theirs.” -V

“…clearly, the old order was already in part reversed. The Nemesis of the delicate ones was creeping on apace. Ages ago, thousands of generations ago, man had thrust his brother man out of the ease and the sunshine. And now that brother was coming back changed! Already the Eloi had begun to learn one old lesson anew. They were becoming reacquainted with Fear.” -VII

“Looking at these stars suddenly dwarfed my own troubles and all the gravities of terrestrial life. I thought of their unfathomable distance, and the slow inevitable drift of their movements out of the unknown past into the unknown future. I thought of the great precessional cycle that the pole of the earth describes. Only forty times had that silent revolution occurred during all the years that I had traversed. And during these few revolutions all the activity, all the traditions, the complex organizations, the nations, languages, literatures, aspirations, even the mere memory of Man as I knew him, had been swept out of existence.” -VII

“I rolled over, and as I did so my hand came against my iron lever. It gave me strength.” -IX

“The strange exultation that so often seems to accompany hard fighting came upon me.” -IX

“I understood now what all the beauty of the Over-world people covered. Very pleasant was their day, as pleasant as the day of the cattle in the field. Like the cattle, they knew of no enemies and provided against no needs. And their end was the same. “I grieved to think how brief the dream of the human intellect had been. It had committed suicide. It had set itself steadfastly towards comfort and ease, a balanced society with security and permanency as its watchword, it had attained its hopes–to come to this at last. Once, life and property must have reached almost absolute safety. The rich had been assured of his wealth and comfort, the toiler assured of his life and work. No doubt in that perfect world there had been no unemployed problem, no social question left unsolved. And a great quiet had followed. “It is a law of nature we overlook, that intellectual versatility is the compensation for change, danger, and trouble. An animal perfectly in harmony with its environment is a perfect mechanism. Nature never appeals to intelligence until habit and instinct are useless. There is no intelligence where there is no change and no need of change. Only those animals partake of intelligence that have to meet a huge variety of needs and dangers.” -X [incredible evolutionary wisdom here. Some of these concepts would not be broadly appreciated by evolutionary anthropologists for another century or more].

“So I travelled, stopping ever and again, in great strides of a thousand years or more, drawn on by the mystery of the earth’s fate, watching with a strange fascination the sun grow larger and duller in the westward sky, and the life of the old earth ebb away.” -XI (as he traveled forward in time)

“The story was so fantastic and incredible, the telling so credible and sober.” -XII

“I, for my own part, cannot think that these latter days of weak experiment, fragmentary theory, and mutual discord are indeed man’s culminating time! I say, for my own part. He, I know–for the question had been discussed among us long before the Time Machine was made–thought but cheerlessly of the Advancement of Mankind, and saw in the growing pile of civilization only a foolish heaping that must inevitably fall back upon and destroy its makers in the end. If that is so, it remains for us to live as though it were not so. But to me the future is still black and blank–is a vast ignorance, lit at a few casual places by the memory of his story.” -Epilogue

“And I have by me, for my comfort, two strange white flowers–shrivelled now, and brown and flat and brittle–to witness that even when mind and strength had gone, gratitude and a mutual tenderness still lived on in the heart of man.” -Epilogue, last sentence.

Editions differ, either naming the chapters (variously) or leaving them unnamed, and some further subdividing certain chapters for a total of 14 or 16. Thus here I present the starting text to each chapter as it is parsed in the version I reference in the quotes above.   

1 – “The Time Traveller…” 2 – “I think that at that time none of us quite believed…” 3 – “I told some of you last Thursday…” 4 – “In another moment we were standing face to face…” 5 – “As I stood there musing…” 6 – “It may seem odd to you…” 7 – “Now, indeed, I seemed in a worse case…” 8 – “I found the Palace of Green Porcelain…” 9 – “We emerged from the palace…” 10 – “About eight or nine in the morning…” 11 – “I have already told you of the sickness…” 12 – “So I came back.” Epilogue – “One cannot choose but wonder.”

READ THIS WHEN…

…you wonder about the future evolution and ultimate fate of humanity

…you find yourself tangling with the paradoxes of time travel

IF YOU LIKE THIS, YOU’D LIKE:

(for the time traveller:)

• Mark Twain,  A Connecticut Yankee in King Arthur’s Court   (1889)
• Ray Bradbury, “A Sound of Thunder”  (1952)
• Isaac Asimov,  The End of Eternity   (1955)
• Madeleine L’Engle,  A Wrinkle In Time   (1962)
• Kurt Vonnegut,  Slaughterhouse-Five   (1969)

(for the fan of Wells’ sci-fi novels)

• H. G. Wells,  The Island of Doctor Moreau  (1896)
• H. G. Wells,  The War of the Worlds  (1897)
• H. G. Wells,  The Invisible Man  (1897)
• H. G. Wells,  The First Men in the Moon  (1901)
• H. G. Wells,  The Sleeper Awakes  (1910)

Hardcover : The Everyman library is always a good bet. This one comes with  The Invisible Man  and  War of the Worlds  as well.

This entry is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license.

Tags: civilization , communism , description , eloi , evolution , future , imagination , morlocks , paradox , physics , science fiction , scifi , socialism , society , speciation , time , time machine , time travel , travel

Re H.G. Wells The Time Machine: It was wise of Wells to picture the future in terms of development of science, not development of human history. By 1895, the work of Darwin had built the great highway to biological understanding. Physics would soon follow a similar flowering. But who at this time could have predicted the collapse of the Russian, Austro-hHngarian, and German empires in 1917-18, the collapse of the British and French empires post-1945, the collapse of the Soviet empire in 1991, the possible collapse of the American empire in xxxx?

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The Time Machine, a novel by H.G. Wells - PowerPoint PPT Presentation

The Time Machine, a novel by H.G. Wells

... or quiver perpetual -lasting for eternity prodigious -impressively great in size, force, or extent; enormous reverted -to return to a former condition, ... – powerpoint ppt presentation.

• What did the Time Traveler conclude about what happened to cause this society to happen when he discovered the subterranean world?
• Why didnt the Time Traveler feel that the girl he rescued from the river would be grateful for his saving her life?
• How did the Time Traveler describe the new creatures he discovered?
• What did the Time Traveler attribute to the existence of the two different descendants of mankind and their differing lifestyles?
• Describe the symbiotic relationship of the Morlock and Eloi.
• What is the significance of the two flowers the Time Traveler showed his guests?
• After the visit to the underground world of the Morlocks, the Time Traveler determines that there is another reason for the development of these two species. What is the reason?
• Why does the Time Traveler unite with the Eloi to improve them instead of the Morlocks?
• In what ways is the world of the Eloi a paradise?
• In what ways is the world of the Morlocks the opposite of a paradise?
• Between the Morlocks and Eloi, which are more like us and why?
• Describe the museum. What is he able to see and what is missing in the description of the artifacts that you would expect to see after some 800,000 years?
• The Morlocks take the time machine and then open the doors so the Time Traveler can get to it. What does this say about the Morlocks?
• These chapters conclude the philosophical discussion of the development of the human race. What is his final decision about what must be done? Does he think there is any hope for the Eloi or Morlock?
• What happens to Weena?
• Describe the changes in the sun and sunset as the Time Traveler goes into the future.
• Describe the evidences of life.
• Why would the Time Traveler go back into the future if it didnt provide him the satisfaction he expected?
• When would he stop in the future? Would he stop periodically along the way, or proceed directly to where he left off when he escaped the Morlocks?
• Wells alludes to a world that reaches a pinnacle of technology and understanding and then regresses to where it began. Provide evidences from the book that supports his theory.

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Home > The Time Machine Ending Explained

• The Time Machine Ending Explained
• UPDATED: September 21, 2023

Table of Contents

H.G. Wells’ classic science fiction novel, The Time Machine, has captivated readers for over a century with its imaginative depiction of time travel. The story follows an unnamed protagonist known as the Time Traveller, who invents a machine that allows him to journey through time. However, the ending of the novel has left many readers puzzled and seeking clarification. In this article, we will delve into the intricacies of The Time Machine’s ending and attempt to shed some light on its meaning.

At the end of the novel, the Time Traveller returns from his final trip to the future and recounts his experiences to a group of friends. He describes how he traveled far into the future and encountered two distinct races: the Eloi and the Morlocks. The Eloi are a peaceful, childlike species that live above ground in idyllic surroundings, while the Morlocks are a subterranean race that prey upon the Eloi.

The Time Traveller’s encounters with these two races lead him to a profound realization about humanity’s future. He comes to understand that over time, society has become divided into two distinct classes: one living a life of leisure and ignorance (the Eloi), while the other toils underground in darkness (the Morlocks). This division is a reflection of the growing disparity between social classes in Wells’ own time.

As the Time Traveller delves deeper into this dystopian future, he discovers that the Morlocks are not just predators but also caretakers for their fragile counterparts, providing them with food and shelter. This revelation challenges his initial assumptions about good and evil, forcing him to question his own biases.

In an attempt to rescue one of his Eloi companions from drowning in a river, the Time Traveller is separated from his time machine and becomes stranded in this distant future. As he struggles to survive among these warring factions, he witnesses the decline and decay of human civilization. The once-great achievements of mankind are reduced to ruins, and the future appears bleak.

Ultimately, the Time Traveller manages to retrieve his time machine and returns to his own time. However, the novel ends on an ambiguous note. He promises to return with evidence of his adventures but never does. The reader is left wondering whether he has chosen not to share his experiences or if he has met an untimely fate.

The open-ended nature of The Time Machine’s ending allows for various interpretations. Some argue that the Time Traveller’s silence suggests a sense of disillusionment with humanity’s future. Others believe that he may have chosen not to share his findings due to their disturbing nature, as they challenge conventional notions of progress and civilization.

The Time Machine serves as a cautionary tale about the dangers of societal division and the potential consequences of unchecked technological advancements. It forces readers to reflect on their own society and consider the implications of their actions.

In conclusion, The Time Machine’s ending leaves much room for interpretation and contemplation. H.G. Wells masterfully crafts a story that raises thought-provoking questions about humanity’s future and the choices we make in the present. Whether one sees it as a pessimistic or hopeful ending, there is no denying the lasting impact this novel has had on science fiction literature and our collective imagination.

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The Time Machine structure

Aug 29, 2014

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Facts about the writer Summary/Analysis of the movie version Summary/Analysis of the chapters from the book version Different aspects between movie and book. The Time Machine structure. The book The Time Machine. Some facts about the Writer H.G.Wells born september 21 st 1866 in Bromley

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Facts about the writer Summary/Analysis of the movie version Summary/Analysis of the chapters from the book version Different aspects between movie and book The Time Machinestructure

The bookThe Time Machine Some facts about the Writer • H.G.Wells • born september 21st 1866 in Bromley • he was an English writer and pioneer of science fiction literatur • works: “The war of the worlds“ and “The Time Machine“ • the movie was released in 1960 and the book in 1895 • the new version of the movie was released in 2002 • Died † August 18th 1946 in london

Summary/Analysis of the film version • directed by Simon Wells, the great-grandson of H.G. Wells • released in 2002 • time machine was built to change the past • travel into the past • seeing for the answer why he can't change the thing that happend in the past • 2030 utopian life • 2037 dystopian life • travel into the future • change the future

Summary/Analysis of the chapters of the book version • first-person narrator • constructtion of a time machine • Part one chapter four: -first travel to the year 802,701 A.D. -connection with the upper-world people, the Eloi -discribing the new world • Part two chapter seven: -differences between Eloi and Morlocks

The book name: Weena differents starts vice versa published in 1859 play in London Different aspects between movie and book The Movie • name: Mara • differents starts • vice versa • The first Movie 1960 a. 2002 • play in New York

Source • The sunset of mankind-H.G.Wells: The Time Machine • The movie “The Time Machine (2002)“ • http://www.youtube.com/watch?v=cSs6eKmTCDY • http://de.wikipedia.org/wiki/H._G._Wells

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Grace and the Time Machine. adapted for Story Theater by Donald Abramson illustrated by Matthew Faulkner. Vocabulary to know:. Aboard Atlas Awkward Capable Chant Mechanical Miracle Reseats Vehicle. Vocabulary to know:. Aboard- on board; in or on a ship, train, bus, airplane, etc.

772 views • 54 slides

Time Machine. Use one word to describe how you felt about your schooling in your middle school years. Are the best practices in a flipped classroom different from those in a successful traditional classroom?. Student’s Taking Ownership of Their Own Learning. Standards-Based Planning.

331 views • 10 slides

Time Machine News

Time Machine News. Presented by: Jonas Habig Sawyer McCloskey. The Battle Field. Setting. The British are coming!. The First Shots. Battle Field Map.

153 views • 9 slides

Grace and the Time Machine. Compiled by: Terry Sams PES. from Starring Grace by Mary Hoffman adapted for Story Theater by Donald Abramson illustrated by Matthew Faulkner. Summary.

1.09k views • 88 slides

Grace and the Time Machine. from Starring Grace by Mary Hoffman adapted for Story Theater by Donald Abramson illustrated by Matthew Faulkner. Summary.

839 views • 57 slides

Roman Time Machine

Roman Time Machine. By Jaxon Emery. Starvation in Rome.

159 views • 4 slides

Time Machine Essay

>>> How to write an essay? Order on the website: HelpWriting.Net <<< The Time Machine Essay, Essay about The Time Machine, Time Machine Thesis, The Time Machine Essay, Time and the Machine

6 views • 10 slides

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AI presentation maker

When lack of inspiration or time constraints are something you’re worried about, it’s a good idea to seek help. Slidesgo comes to the rescue with its latest functionality—the AI presentation maker! With a few clicks, you’ll have wonderful slideshows that suit your own needs . And it’s totally free!

Generate presentations in minutes

We humans make the world move, but we need to sleep, rest and so on. What if there were someone available 24/7 for you? It’s time to get out of your comfort zone and ask the AI presentation maker to give you a hand. The possibilities are endless : you choose the topic, the tone and the style, and the AI will do the rest. Now we’re talking!

Customize your AI-generated presentation online

Alright, your robotic pal has generated a presentation for you. But, for the time being, AIs can’t read minds, so it’s likely that you’ll want to modify the slides. Please do! We didn’t forget about those time constraints you’re facing, so thanks to the editing tools provided by one of our sister projects —shoutouts to Wepik — you can make changes on the fly without resorting to other programs or software. Add text, choose your own colors, rearrange elements, it’s up to you! Oh, and since we are a big family, you’ll be able to access many resources from big names, that is, Freepik and Flaticon . That means having a lot of images and icons at your disposal!

How does it work?

Think of your topic.

First things first, you’ll be talking about something in particular, right? A business meeting, a new medical breakthrough, the weather, your favorite songs, a basketball game, a pink elephant you saw last Sunday—you name it. Just type it out and let the AI know what the topic is.

Choose your preferred style and tone

They say that variety is the spice of life. That’s why we let you choose between different design styles, including doodle, simple, abstract, geometric, and elegant . What about the tone? Several of them: fun, creative, casual, professional, and formal. Each one will give you something unique, so which way of impressing your audience will it be this time? Mix and match!

Make any desired changes

You’ve got freshly generated slides. Oh, you wish they were in a different color? That text box would look better if it were placed on the right side? Run the online editor and use the tools to have the slides exactly your way.

Download the final result for free

Yes, just as envisioned those slides deserve to be on your storage device at once! You can export the presentation in .pdf format and download it for free . Can’t wait to show it to your best friend because you think they will love it? Generate a shareable link!

What is an AI-generated presentation?

It’s exactly “what it says on the cover”. AIs, or artificial intelligences, are in constant evolution, and they are now able to generate presentations in a short time, based on inputs from the user. This technology allows you to get a satisfactory presentation much faster by doing a big chunk of the work.

Can I customize the presentation generated by the AI?

Of course! That’s the point! Slidesgo is all for customization since day one, so you’ll be able to make any changes to presentations generated by the AI. We humans are irreplaceable, after all! Thanks to the online editor, you can do whatever modifications you may need, without having to install any software. Colors, text, images, icons, placement, the final decision concerning all of the elements is up to you.

Can I add my own images?

Absolutely. That’s a basic function, and we made sure to have it available. Would it make sense to have a portfolio template generated by an AI without a single picture of your own work? In any case, we also offer the possibility of asking the AI to generate images for you via prompts. Additionally, you can also check out the integrated gallery of images from Freepik and use them. If making an impression is your goal, you’ll have an easy time!

Is this new functionality free? As in “free of charge”? Do you mean it?

Yes, it is, and we mean it. We even asked our buddies at Wepik, who are the ones hosting this AI presentation maker, and they told us “yup, it’s on the house”.

Are there more presentation designs available?

From time to time, we’ll be adding more designs. The cool thing is that you’ll have at your disposal a lot of content from Freepik and Flaticon when using the AI presentation maker. Oh, and just as a reminder, if you feel like you want to do things yourself and don’t want to rely on an AI, you’re on Slidesgo, the leading website when it comes to presentation templates. We have thousands of them, and counting!.

How can I download my presentation?

The easiest way is to click on “Download” to get your presentation in .pdf format. But there are other options! You can click on “Present” to enter the presenter view and start presenting right away! There’s also the “Share” option, which gives you a shareable link. This way, any friend, relative, colleague—anyone, really—will be able to access your presentation in a moment.

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This is just the beginning! Slidesgo has thousands of customizable templates for Google Slides and PowerPoint. Our designers have created them with much care and love, and the variety of topics, themes and styles is, how to put it, immense! We also have a blog, in which we post articles for those who want to find inspiration or need to learn a bit more about Google Slides or PowerPoint. Do you have kids? We’ve got a section dedicated to printable coloring pages! Have a look around and make the most of our site!