hypothesis the universe

Cosmic History

The Universe’s History

The origin, evolution, and nature of the universe have fascinated and confounded humankind for centuries. New ideas and major discoveries made during the 20th century transformed cosmology – the term for the way we conceptualize and study the universe – although much remains unknown. Here is the history of the universe according to cosmologists’ current theories.

Cosmic Inflation

Around 13.8 billion years ago, the universe expanded faster than the speed of light for a fraction of a second, a period called cosmic inflation. Scientists aren’t sure what came before inflation or what powered it. It’s possible that energy during this period was just part of the fabric of space-time. Cosmologists think inflation explains many aspects of the universe we observe today, like its flatness, or lack of curvature, on the largest scales. Inflation may have also magnified density differences that naturally occur on space’s smallest, quantum-level scales, which eventually helped form the universe’s large-scale structures.

Big Bang and Nucleosynthesis

When cosmic inflation stopped, the energy driving it transferred to matter and light – the big bang. One second after the big bang, the universe consisted of an extremely hot (18 billion degrees Fahrenheit or 10 billion degrees Celsius) primordial soup of light and particles. In the following minutes, an era called nucleosynthesis, protons and neutrons collided and produced the earliest elements – hydrogen, helium, and traces of lithium and beryllium. After five minutes, most of today’s helium had formed, and the universe had expanded and cooled enough that further element formation stopped. At this point, though, the universe was still too hot for the atomic nuclei of these elements to catch electrons and form complete atoms. The cosmos was opaque because a vast number of electrons created a sort of fog that scattered light.

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Recombination

Around 380,000 years after the big bang, the universe had cooled enough that atomic nuclei could capture electrons, a period astronomers call the epoch of recombination. This had two major effects on the cosmos. First, with most electrons now bound into atoms, there were no longer enough free ones to completely scatter light, and the cosmic fog cleared. The universe became transparent, and for the first time, light could freely travel over great distances. Second, the formation of these first atoms produced its own light. This glow, still detectable today, is called the cosmic microwave background. It is the oldest light we can observe in the universe.

After the cosmic microwave background, the universe again became opaque at shorter wavelengths due to the absorbing effects of all those hydrogen atoms. For the next 200 million years the universe remained dark. There were no stars to shine. The cosmos at this point consisted of a sea of hydrogen atoms, helium, and trace amounts of heavier elements.

First Stars

Gas was not uniformly distributed throughout the universe. Cooler areas of space were lumpier, with denser clouds of gas. As these clumps grew more massive, their gravity attracted additional matter. As they became denser, and more compact, the centers of these clumps became hotter – hot enough eventually that nuclear fusion occurred in their centers. These were the first stars. They were 30 to 300 times more massive than our Sun and millions of times brighter. Over several hundred million years, the first stars collected into the first galaxies.

Reionization

At first, starlight couldn’t travel far because it was scattered by the relatively dense gas surrounding the first stars. Gradually, the ultraviolet light emitted by these stars broke down, or ionized, hydrogen atoms in the gas into their constituent electrons and protons. As this reionization progressed, starlight traveled farther, breaking up more and more hydrogen atoms. By the time the universe was 1 billion years old, stars and galaxies had transformed nearly all this gas, making the universe transparent to light as we see it today.

For many years, scientists thought the universe’s current expansion was slowing down. But in fact, cosmic expansion is speeding up. In 1998, astronomers found that certain supernovae, bright stellar explosions, were fainter than expected. They concluded this could only happen if the supernovae had moved farther away, at a faster rate than predicted.

Scientists suspect a mysterious substance they call dark energy is accelerating expansion. Future research may yield new surprises, but cosmologists suggest it’s likely the universe will continue to expand forever.

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Dark Matter & Dark Energy

The Big Bang

Origins of the Universe 101

How old is the universe, and how did it begin? Throughout history, countless myths and scientific theories have tried to explain the universe's origins. The most widely accepted explanation is the big bang theory. Learn about the explosion that started it all and how the universe grew from the size of an atom to encompass everything in existence today.

Earth Science, Astronomy

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• 25 March 2024

How did the Big Bang get its name? Here’s the real story

• Helge Kragh 0

Helge Kragh is a historian of science at the University of Copenhagen.

You can also search for this author in PubMed   Google Scholar

Today 'Big Bang' is a household phrase, used even by people who have no idea of how the Universe was born some 14 billion years ago. Credit: Henning Dalhoff/SPL

You have full access to this article via your institution.

“Words are like harpoons,” UK physicist and astronomer Fred Hoyle told an interviewer in 1995. “Once they go in, they are very hard to pull out.” Hoyle, then 80 years old, was referring to the term Big Bang, which he had coined on 28 March 1949 to describe the origin of the Universe. Today, it is a household phrase, known to and routinely used by people who have no idea of how the Universe was born some 14 billion years ago. Ironically, Hoyle deeply disliked the idea of a Big Bang and remained, until his death in 2001, a staunch critic of mainstream Big Bang cosmology.

Several misconceptions linger concerning the origin and impact of the popular term. One is whether Hoyle introduced the nickname to ridicule or denigrate the small community of cosmologists who thought that the Universe had a violent beginning — a hypothesis that then seemed irrational. Another is that this group adopted ‘Big Bang’ eagerly, and it then migrated to other sciences and to everyday language. In reality, for decades, scientists ignored the catchy phrase, even as it spread in more-popular contexts.

This new map of the Universe suggests dark matter shaped the cosmos

The first cosmological theory of the Big Bang type dates back to 1931, when Belgian physicist and Catholic priest Georges Lemaître proposed a model based on the radioactive explosion of what he called a “primeval atom” at a fixed time in the past. He conceived that this primordial object was highly radioactive and so dense that it comprised all the matter, space and energy of the entire Universe. From the original explosion caused by radioactive decay, stars and galaxies would eventually form, he reasoned. Lemaître spoke metaphorically of his model as a “fireworks theory” of the Universe, the fireworks consisting of the decay products of the initial explosion.

However, Big Bang cosmology in its modern meaning — that the Universe was created in a flash of energy and has expanded and cooled down since — took off only in the late 1940s, with a series of papers by the Soviet–US nuclear physicist George Gamow and his US associates Ralph Alpher and Robert Herman. Gamow hypothesized that the early Universe must have been so hot and dense that it was filled with a primordial soup of radiation and nuclear particles, namely neutrons and protons. Under such conditions, those particles would gradually come together to form atomic nuclei as the temperature cooled. By following the thermonuclear processes that would have taken place in this fiery young Universe, Gamow and his collaborators tried to calculate the present abundance of chemical elements in an influential 1948 paper 1 .

Competing ideas

The same year, a radically different picture of the Universe was announced by Hoyle and Austrian-born cosmologists Hermann Bondi and Thomas Gold. Their steady-state theory assumed that, on a large scale, the Universe had always looked the same and would always do so, for eternity. According to Gamow, the idea of an ‘early Universe’ and an ‘old Universe’ were meaningless in a steady-state cosmology that posited a Universe with no beginning or end.

Over the next two decades, an epic controversy between these two incompatible systems evolved. It is often portrayed as a fight between the Big Bang theory and the steady-state theory, or even personalized as a battle between Gamow and Hoyle. But this is a misrepresentation.

Soviet–US nuclear physicist George Gamow was an early proponent of Big Bang cosmology. Credit: Bettmann/Getty

Both parties, and most other physicists of the time, accepted that the Universe was expanding — as US astronomer Edwin Hubble demonstrated in the late 1920s by observing that most galaxies are rushing away from our own. But the idea that is so familiar today, of the Universe beginning at one point in time, was widely seen as irrational. After all, how could the cause of the original explosion be explained, given that time only came into existence with it? In fact, Gamow’s theory of the early Universe played almost no part in this debate.

Rather, a bigger question at the time was whether the Universe was evolving in accordance with German physicist Albert Einstein’s general theory of relativity, which predicted that it was either expanding or contracting, not steady. Although Einstein’s theory doesn’t require a Big Bang, it does imply that the Universe looked different in the past than it does now. And an ever-expanding Universe does not necessarily entail the beginning of time. An expanding Universe could have blown up from a smaller precursor, Lemaître suggested in 1927.

An apt but innocent phrase

On 28 March 1949, Hoyle — a well-known popularizer of science — gave a radio talk to the BBC Third Programme, in which he contrasted these two views of the Universe. He referred to “the hypothesis that all the matter in the universe was created in one big bang at a particular time in the remote past”. This lecture was indeed the origin of the cosmological term ‘Big Bang’. A transcript of the talk was reproduced in full in the BBC’s The Listener magazine, and Hoyle mentioned it in his 1950 book The Nature of the Universe , which was based on a series of BBC broadcasts he made earlier the same year.

How dwarf galaxies lit up the Universe after the Big Bang

Although Hoyle resolutely dismissed the idea of a sudden origin of the Universe as unacceptable on both scientific and philosophical grounds, he later said that he did not mean it in ridiculing or mocking terms, such as was often stated. None of the few cosmologists in favour of the exploding Universe, such as Lemaître and Gamow, was offended by the term. Hoyle later explained that he needed visual metaphors in his broadcast to get across technical points to the public, and the casual coining of ‘Big Bang’ was one of them. He did not mean it to be derogatory or, for that matter, of any importance.

Hoyle’s ‘Big Bang’ was a new term as far as cosmology was concerned, but it was not in general contexts. The word ‘bang’ often refers to an ordinary explosion, say, of gunpowder, and a big bang might simply mean a very large and noisy explosion, something similar to Lemaître’s fireworks. And indeed, before March 1949, there were examples in the scientific literature of meteorologists and geophysicists using the term in their publications. Whereas they referred to real explosions, Hoyle’s Big Bang was purely metaphorical, in that he did not actually think that the Universe originated in a blast.

The Big Bang was not a big deal

For the next two decades, the catchy term that Hoyle had coined was largely ignored by physicists and astronomers. Lemaître never used ‘Big Bang’ and Gamow used it only once in his numerous publications on cosmology. One might think that at least Hoyle took it seriously and promoted his coinage, but he returned to it only in 1965, after a silence of 16 years. It took until 1957 before ‘Big Bang’ appeared in a research publication 2 , namely in a paper on the formation of elements in stars in Scientific Monthly by the US nuclear physicist William Fowler, a close collaborator of Hoyle and a future Nobel laureate.

How Einstein built on the past to make his breakthroughs

Before 1965, the cosmological Big Bang seems to have been referenced just a few dozen times, mostly in popular-science literature. I have counted 34 sources that mentioned the name and, of these, 23 are of a popular or general nature, 7 are scientific papers and 4 are philosophical studies. The authors include 16 people from the United States, 7 from the United Kingdom, one from Germany and one from Australia. None of the scientific papers appeared in astronomy journals.

Among those that used the term for the origin of the Universe was the US philosopher Norwood Russell Hanson, who in 1963 coined his own word for advocates of what he called the ‘Disneyoid picture’ of the cosmic explosion. He called them ‘big bangers’, a term which still can be found in the popular literature — in which the ultimate big banger is sometimes identified as God.

A popular misnomer

A watershed moment in the history of modern cosmology soon followed. In 1965, US physicists Arno Penzias and Robert Wilson’s report of the discovery of the cosmic microwave background — a faint bath of radio waves coming from all over the sky — was understood as a fossil remnant of radiation from the hot cosmic past. “Signals Imply a ‘Big Bang’ Universe” announced the New York Times on 21 May 1965. The Universe did indeed have a baby phase, as was suggested by Gamow and Lemaître. The cosmological battle had effectively come to an end, with the steady-state theory as the loser and the Big Bang theory emerging as a paradigm in cosmological research. Yet, for a while, physicists and astronomers hesitated to embrace Hoyle’s term.

Work by US physicists Arno Penzias and Robert Wilson vindicated the Big Bang theory. Credit: Bettmann/Getty

It took until March 1966 for the name to turn up in a Nature research article 3 . The Web of Science database lists only 11 scientific papers in the period 1965–69 with the name in their titles, followed by 30 papers in 1970–74 and 42 in 1975–79. Cosmology textbooks published in the early 1970s showed no unity with regard to the nomenclature. Some authors included the term Big Bang, some mentioned it only in passing and others avoided it altogether. They preferred to speak of the ‘standard model’ or the ‘theory of the hot universe’, instead of the undignified and admittedly misleading Big Bang metaphor.

Nonetheless, by the 1980s, the misnomer had become firmly entrenched in the literature and in common speech. The phrase has been adopted in many languages other than English, including French ( théorie du Big Bang ), Italian ( teoria del Big Bang ) and Swedish ( Big Bang teorin ). Germans have constructed their own version, namely Urknall , meaning ‘the original bang’, a word that is close to the Dutch oerknal . Later attempts to replace Hoyle’s term with alternative and more-appropriate names have failed miserably.

The many faces of the metaphor

By the 1990s, ‘Big Bang’ had migrated to commercial, political and artistic uses. During the 1950s and 1960s, the term frequently alluded to the danger of nuclear warfare as it did in UK playwright John Osborne’s play Look Back in Anger, first performed in 1956. The association of nuclear weapons and the explosive origin of the Universe can be found as early as 1948, before Hoyle coined his term. As its popularity increased, ‘Big Bang’ began being used to express a forceful beginning or radical change of almost any kind — such as the Bristol Sessions, a series of recording sessions in 1927, being referred to as the ‘Big Bang’ of modern country music.

In the United Kingdom, the term was widely used for a major transformation of the London Stock Exchange in 1986. “After the Big Bang tomorrow, the City will never be the same again,” wrote Sunday Express Magazine on 26 October that year. That use spread to the United States. In 1987, the linguistic journal American Speech included ‘Big Bang’ in its list of new words and defined ‘big banger’ as “one involved with the Big Bang on the London Stock Exchange”.

Today, searching online for the ‘Big Bang theory’ directs you first not to cosmology, but to a popular US sitcom. Seventy-five years on, the name that Hoyle so casually coined has indeed metamorphosed into a harpoon-like word: very hard to pull out once in.

Nature 627 , 726-728 (2024)

doi: https://doi.org/10.1038/d41586-024-00894-z

Gamow, G. Nature 162 , 680–682 (1948).

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Fowler, W. A. Sci. Mon. 84 , 84–100 (1957).

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Hawking S. W. & Tayler, R. J. Nature 209 , 1278–1279 (1966).

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What Are the Theories of the Universe?

Humans have pondered the beginning of the universe since our species evolved. Generations of people have looked towards the sky as a source of amazement, religion, and wonder. Thankfully, over the last several centuries , scientists from around the world have begun to piece together empirical data to support a variety of hypotheses about how all of life as we know it began. Today, let’s take a closer look at an age-old question: what are the theories of the universe?

The Big Bang Theory

The most robust, well-supported theory as to the origins of the universe is the Big Bang Theory. A Belgian priest, Georges Lemaître , first suggested the idea of big bang theory in the 1920s. Since then, Einstein’s theory of relativity and modern science has lent credibility to this developing theory.

Big Bang Assumptions

Before we can get into specifics, let’s understand a few basic assumptions concerning the Big Bang Theory. Each of the following points is assumed to be true in the universe, and this notion is part of the foundation upon which the Big Bang rests. 

• The universe is constant . This one is first for a reason; it’s important. Our modeling and understanding of the world hinge on the idea that physical properties are the same everywhere. For example, we assume gravity , electricity, magnetism, and light all behave the same way, even in far off places in the galaxy and universe. 
• The universe is homogenous . Secondly, we assume that the universe is roughly the same in all directions. You can think of these like shovelfuls of dirt. Some scoops might have big rocks, some might have worms, and some may have more clay than others. But, in the long term, every 100 shovelfuls will be roughly the same in composition.
• The universe is not centered around us. Physicists refer to this notion as the “ privileged location .” This means that earth is somewhere in the universe, but we really have no idea where it is in relation to the “edge” (more on that later).
• The universe has a beginning. All matter and energy that has ever been and that will ever be were created during the Big Bang. No new material or energy has been created since then.

Basics of the Big Bang

The Big Bang is the leading theory as to the origins of the universe as we know it. It describes the mechanism by which everything we know started as a small singularity that ballooned into the earth, solar system, galaxy, and universe. The easiest way to understand this theory is through a timeline, so let’s dig in.

• 1 second. During the first second, the temperature around the big bang was about 5.5 billion degrees celsius (10 billion Fahrenheit). There would have been nothing to see at this point, though. According to NASA , “the free electrons would have caused light (photons) to scatter the way sunlight scatters from the water droplets in clouds.”
• 3 seconds. The initial explosion contained all the necessary subatomic particles for atoms and molecules: neutrons, protons, and electrons. The first basic elements form at this point: hydrogen, helium, and lithium. 
• 380,000 years. For the first time, light emerges into the universe. This radiation (light) is referred to as the cosmic microwave background. First predicted to exist in 1948 by Ralph Alpher , it is a signature mark of the Big Bang. This background of microwaves can still be observed today, and it used to estimate the age of the universe. 
• 300 million years. We’re jumping forward a bit here. As the initial burst of atoms and gas expands, gravity starts to become a relevant factor. Pockets of different densities of gas give birth to stars and collections of stars start to form galaxies. 
• ~9 billion years. Our sun forms. The universe is roughly 14 billion years old, and our sun is approximately 4.6 billion years old. 

Steady State Universe

The steady state universe hypothesis breaks one of the key Big Bang Theory assumptions. The steady state hypothesis states that matter and energy are being created continuously, steadily. First theorized in the 1920s by Sir James Jeans, the theory imagines a universe without a real beginning or end. 

In the steady state view, the universe has always been expanding and creating matter, and it will continue to do so. Although the theory has been revised and updated throughout the middle of the 20th century, an overwhelming amount of contradictory evidence supports the notion that the steady state hypothesis is largely false . 

Level II Multiverse

The multiverse concept is complicated . And, that may still be an understatement. One of the driving factors leading to the development of this theory is the seemingly perfect nature of physics in our universe. Light, gravity, physics… they all seem to work together perfectly to allow life to exist in our universe. This can be viewed as a major coincidence or an inevitability given a large number of trials. 

The multiverse concept postulates that multiple universes exist, simultaneously, and they each have different physical constants. For example, maybe a universe 2.0 (or 3.0 or 18.0 or 821.0) exists along with ours where light travels at a different speed. Changing this speed changes an exceptionally large number of other universal constants, and thus, everything we know about our universe.

Correct Hypothesis?

So, where does that leave us? What is the “correct” theory for the origin of the universe? By a large margin, the Big Bang is the most well-supported, evidence-based theory. That being said, new technology and new instruments allow us to gather different data every decade, so we will have to see what the future holds!

What other theories of the universe have you heard of? How do you think this all got here?

[Featured image by FelixMittermeier via Pixabay ]

Check us out on  EarthSnap , a free app brought to you by Eric Ralls and Earth.com.

Our expanding universe: Age, history & other facts

The evolution and content of our ballooning universe

The Big Bang

Expanding universe, additional resources, bibliography.

The universe was born with the Big Bang as an unimaginably hot, dense point. When the universe was just 10 -34 of a second or so old — that is, a hundredth of a billionth of a trillionth of a trillionth of a second in age — it experienced an incredible burst of expansion known as inflation, in which space itself expanded faster than the speed of light. During this period, the universe doubled in size at least 90 times, going from subatomic-sized to golf-ball-sized almost instantaneously.

The work that goes into understanding the expanding universe comes from a combination of theoretical physics and direct observations by astronomers. However, in some cases astronomers have not been able to see direct evidence — such as the case of gravitational waves associated with the cosmic microwave background , the leftover radiation from the Big Bang. A preliminary announcement about finding these waves in 2014 was quickly retracted, after astronomers found the signal detected could be explained by dust in the Milky Way .

According to NASA, after inflation the growth of the universe continued, but at a slower rate . As space expanded, the universe cooled and matter formed. One second after the Big Bang, the universe was filled with neutrons, protons, electrons , anti-electrons, photons and neutrinos.

During the first three minutes of the universe, the light elements were born during a process known as Big Bang nucleosynthesis. Temperatures cooled from 100 nonillion (10 32 ) Kelvin to 1 billion (10 9 ) Kelvin, and protons and neutrons collided to make deuterium, an isotope of hydrogen . Most of the deuterium combined to make helium , and trace amounts of lithium were also generated.

For the first 380,000 years or so, the universe was essentially too hot for light to shine, according to France's National Center of Space Research (Centre National d'Etudes Spatiales, or CNES). The heat of creation smashed atoms together with enough force to break them up into a dense plasma, an opaque soup of protons, neutrons and electrons that scattered light like fog.

What is the coldest place in the universe?

Geocentric model: The Earth-centered view of the universe

Do parallel universes exist?

Dark stars: The first stars in the universe

Was there a bang at the end of the universe?

Roughly 380,000 years after the Big Bang, matter cooled enough for atoms to form during the era of recombination, resulting in a transparent, electrically neutral gas, according to NASA . This set loose the initial flash of light created during the Big Bang, which is detectable today as cosmic microwave background radiation . However, after this point, the universe was plunged into darkness, since no stars or any other bright objects had formed yet.

About 400 million years after the Big Bang, the universe began to emerge from the cosmic dark ages during the epoch of reionization. During this time, which lasted more than a half-billion years, clumps of gas collapsed enough to form the first stars and galaxies, whose energetic ultraviolet light ionized and destroyed most of the neutral hydrogen.

Although the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity, about 5 or 6 billion years after the Big Bang, according to NASA , a mysterious force now called dark energy began speeding up the expansion of the universe again, a phenomenon that continues today.

A little after 9 billion years after the Big Bang, our solar system was born.

The Big Bang did not occur as an explosion in the usual way one think about such things, despite one might gather from its name. The universe did not expand into space, as space did not exist before the universe, according to NASA . Instead, it is better to think of the Big Bang as the simultaneous appearance of space everywhere in the universe . The universe has not expanded from any one spot since the Big Bang — rather, space itself has been stretching, and carrying matter with it.

Since the universe by its definition encompasses all of space and time as we know it, NASA says it is beyond the model of the Big Bang to say what the universe is expanding into or what gave rise to the Big Bang. Although there are models that speculate about these questions, none of them have made realistically testable predictions as of yet.

In 2014, scientists from the Harvard-Smithsonian Center for Astrophysics announced that they had found a faint signal in the cosmic microwave background that could be the first direct evidence of gravitational waves, themselves considered a " smoking gun " for the Big Bang. The findings were hotly debated , and astronomers soon retracted their results when they realized dust in the Milky Way could explain their findings. 

How old is the universe?

The universe is currently estimated at roughly 13.8 billion years old , give or take 130 million years. In comparison, the solar system is only about 4.6 billion years old.

This estimate came from measuring the composition of matter and energy density in the universe. This allowed researchers to compute how fast the universe expanded in the past. With that knowledge, they could turn the clock back and extrapolate when the Big Bang happened . The time between then and now is the age of the universe.

How is it structured?

Scientists think that in the earliest moments of the universe, there was no structure to it to speak of, with matter and energy distributed nearly uniformly throughout. According to NASA , the gravitational pull of small fluctuations in the density of matter back then gave rise to the vast web-like structure of stars and emptiness seen today. Dense regions pulled in more and more matter through gravity, and the more massive they became, the more matter they could pull in through gravity, forming stars , galaxies and larger structures known as clusters, superclusters, filaments and walls , with "great walls" of thousands of galaxies reaching more than a billion light years in length. Less dense regions did not grow, evolving into area of seemingly empty space called voids.

Contents of the universe

Until a few decades ago, astronomers thought that the universe was composed almost entirely of ordinary atoms, or "baryonic matter," according to NASA . However, recently there has been ever more evidence that suggests most of the ingredients making up the universe come in forms that we cannot see.

It turns out that atoms only make up 4.6 percent of the universe. Of the remainder, 23 percent is made up of dark matter , which is likely composed of one or more species of subatomic particles that interact very weakly with ordinary matter, and 72 percent is made of dark energy, which apparently is driving the accelerating expansion of the universe.

When it comes to the atoms we are familiar with, hydrogen makes up about 75 percent, while helium makes up about 25 percent, with heavier elements making up only a tiny fraction of the universe's atoms, according to NASA .

What shape is it?

The shape of the universe and whether or not it is finite or infinite in extent depends on the struggle between the rate of its expansion and the pull of gravity. The strength of the pull in question depends in part on the density of the matter in the universe.

If the density of the universe exceeds a specific critical value, then the universe is " closed " and "positive curved" like the surface of a sphere. This means light beams that are initially parallel will converge slowly, eventually cross and return back to their starting point, if the universe lasts long enough. If so, according to NASA , the universe is not infinite but has no end, just as the area on the surface of a sphere is not infinite but has no beginning or end to speak of. The universe will eventually stop expanding and start collapsing in on itself, the so-called "Big Crunch."

If the density of the universe is less than this critical density, then the geometry of space is " open " and "negatively curved" like the surface of a saddle. If so, the universe has no bounds, and will expand forever .

If the density of the universe exactly equals the critical density, then the geometry of the universe is "flat" with zero curvature like a sheet of paper, according to NASA . If so, the universe has no bounds and will expand forever, but the rate of expansion will gradually approach zero after an infinite amount of time. Recent measurements suggest that the universe is flat with only a 0.4 percent margin of error, according to NASA.

It is possible that the universe has a more complicated shape overall while seeming to possess a different curvature. For instance, the universe could have the shape of a torus, or doughnut .

In the 1920s, astronomer Edwin Hubble discovered the universe was not static . Rather, it was expanding; a find that revealed the universe was apparently born in a Big Bang.

After that, it was long thought the gravity of matter in the universe was certain to slow the expansion of the universe . Then, in 1998, the Hubble Space Telescope 's observations of very distant supernovae revealed that a long time ago, the universe was expanding more slowly than it is today. In other words, the expansion of the universe was not slowing due to gravity, but instead inexplicably was accelerating. The name for the unknown force driving this accelerating expansion is dark energy, and it remains one of the greatest mysteries in science.

Want to explore the universe for yourself? You can roam the Milky Way's stars and galaxies virtually using NASA's Hubble Skymap . Additionally, you can read 10 wild theories about the universe in this article by Live Science.

"The first stars in the Universe". Monthly Notices of the Royal Astronomical Society: Letters, Volume 373, Issue 1 (2006). https://academic.oup.com/mnrasl/article/373/1/L98/989035?login=true

"The molecular universe". Reviews of Modern Physics (2013). https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.85.1021

"Hubble’s Law and the expanding universe". Proceedings of the National Academy of Sciences of the United States of America (2015). https://www.pnas.org/content/112/11/3173.short

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What is the multiverse—and is there any evidence it really exists?

Scientists can only see so far before they run into the edge of the universe. Will we ever know if anything lies beyond?

What lies beyond the edges of the observable universe? Is it possible that our universe is just one of many in a much larger multiverse? Movies can’t get enough of exploring these questions. From Oscar winners like Everything Everywhere All at Once   to superhero blockbusters like Dr. Strange in the Multiverse of Madness , science fiction stories are full of creative interactions between alternate realities. And depending on which cosmologist you ask, the concept of a multiverse is more than pure fantasy or a handy storytelling device.

Humanity’s ideas about alternate realities are ancient and varied—in 1848 Edgar Allan Poe even wrote a prose poem in which he fancied the existence of “a limitless succession of Universes.” But the multiverse concept really took off when modern scientific theories attempting to explain the properties of our universe predicted the existence of other universes   where events take place outside our reality.

“Our understanding of reality is not complete, by far,” says Stanford University physicist Andrei Linde . “Reality exists independently of us.”

If they exist, those universes are separated from ours, unreachable and undetectable by any direct measurement (at least so far). And that makes some experts question whether the search for a multiverse can ever be truly scientific.

Will scientists ever know whether our universe is the only one? We break down the different theories about a possible multiverse—including other universes with their own laws of physics—and whether many versions of you could exist out there.

What is a multiverse?

The multiverse is a term that scientists use to describe the idea that beyond the observable universe, other universes may exist as well. Multiverses are predicted by several scientific theories that describe different possible scenarios—from regions of space in different planes than our universe, to separate bubble universes that are constantly springing into existence.

The one thing all these theories have in common is that they suggest the space and time we can observe is not the only reality.

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Okay … but why do scientists think there could be more than one universe.

“We cannot explain all the features of our universe if there’s only one of them,” says science journalist Tom Siegfried , whose book The Number of the Heavens investigates how conceptions of the multiverse have evolved over millennia.

“Why are the fundamental constants of nature what they are?” Siegfried wonders. “Why is there enough time in our universe to make stars and planets? Why do stars shine the way they do, with just the right amount of energy? All of those things are questions we don’t have answers for in our physical theories.”

Siegfried says two possible explanations exist: First, that we need newer, better theories to explain the properties of our universe. Or, he says, it’s possible that “we’re just one of many universes that are different, and we live in the one that’s nice and comfortable.”

What are some of the more popular multiverse theories?  

Perhaps the most scientifically accepted idea comes from what’s known as inflationary cosmology , which is the idea that in the minuscule moments after the big bang, the universe rapidly and exponentially expanded. Cosmic inflation explains a lot of the observed properties of the universe, such as its structure and the distribution of galaxies.

“This theory at first looked like a piece of science fiction, although a very imaginative one,” says Linde, one of the architects of cosmic inflationary theory. “But it explained so many interesting features of our world that people started taking it seriously.”

One of the theory’s predictions is that inflation could happen over and over again , perhaps infinitely, creating a constellation of bubble universes. Not all of those bubbles will have the same properties as our own—they might be spaces where physics behaves differently. Some of them might be similar to our universe, but they all exist beyond the realm we can directly observe.

What are some other ideas?

Another compelling type of multiverse is called the many-worlds interpretation of quantum mechanics , which is the theory that mathematically describes how matter behaves. Proposed by physicist Hugh Everett in 1957, the many-worlds interpretation predicts the presence of branching timelines, or alternate realities in which our decisions play out differently, sometimes producing wildly different outcomes.

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“Hugh Everett says, Look, there’s actually an infinite number of parallel Earths, and when you do an experiment and you get the probabilities, basically all that proves is that you live on the Earth where that was the outcome of that experiment,” says physicist James Kakalios of the University of Minnesota, who has written about the physics (or not) of superheroes. “But on other Earths, there’s a different outcome.”

According to this interpretation, versions of you could be off living the many different possible lives you could have led if you’d made different decisions. However, the only reality that’s perceptible to you is the one you inhabit.

So where do all of those other Earths exist?

They’re all overlapping in dimensions we can’t access. MIT’s Max Tegmark refers to this type of multiverse as a Level III multiverse , where multiple scenarios are playing out in branching realities.

“In the many-worlds interpretation, you still have an atomic bomb, you just don’t know exactly when it’s going to go off,” Linde says. And maybe in some of those realities, it won’t.

By contrast, the multiple universes predicted by some theories of cosmic inflation are what Tegmark calls a Level II multiverse, where fundamental physics can be different across the different universes. In an inflationary multiverse, Linde says, “you do not even know if, in some parts of the universe, atomic bombs are even possible in principle.”

So if I want to meet myself, how do I get there? Can we travel between multiverses?  

Unfortunately, no. Scientists don’t think it’s possible to travel between universes, at least not yet.

“Unless a whole lot of physics we know that’s pretty solidly established is wrong, you can’t travel to these multiverses,” Siegfried says. “But who knows? A thousand years from now, I’m not saying somebody can’t figure out something that you would never have imagined.”

Is there any direct evidence suggesting multiverses exist?  

Even though certain features of the universe seem to require the existence of a multiverse, nothing has been directly observed that suggests it actually exists. So far, the evidence supporting the idea of a multiverse is purely theoretical, and in some cases, philosophical.

Some experts argue that it may be a grand cosmic coincidence that the big bang forged a perfectly balanced universe that is just right for our existence. Other scientists think it is more likely that any number of physical universes exist, and that we simply inhabit the one that has the right characteristics for our survival .

An infinite number of alternate little pocket universes, or bubbles universes, some of which have different physics or different fundamental constants, is an attractive idea, Kakalios says. “That’s why some people take these ideas kind of seriously, because it helps address certain philosophical issues,” he says.

Scientists argue about whether the multiverse is even an empirically testable theory ; some would say no, given that by definition a multiverse is independent from our own universe and impossible to access. But perhaps we just haven’t figured out the right test.

Will we ever know if our universe is just one of many?

We might not. But multiverses are among the predictions of various theories that can be tested in other ways, and if those theories pass all of their tests, then maybe the multiverse holds up as well. Or perhaps some new discovery will help scientists figure out if there really is something beyond our observable universe.

“The universe is not constrained by what some blobs of protoplasm on a tiny little planet can figure out, or test,” Siegfried says. “We can say, This is not testable, therefore it can’t be real—but that just means we don’t know how to test it. And maybe someday we’ll figure out how to test it, and maybe we won’t. But the universe can do whatever it wants.”

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The Big Freeze: How the universe will die

The cosmos may never end. But if you were immortal, you’d probably wish it would. Our cosmos’ final fate is a long and frigid affair that astronomers call the Big Freeze, or Big Chill.

It’s a fitting description for the day when all heat and energy is evenly spread over incomprehensibly vast distances. At this point, the universe’s final temperature will hover  just  above absolute zero. 

The Big Bang’s accelerating expansion

Some 13.8 billion years ago,  our universe was born in the Big Bang , and it’s been expanding ever since.

Until a few decades ago, it looked like that expansion would eventually end. Astronomers’ measurements suggested there was enough matter in the universe to overcome expansion and reverse the process, triggering a so-called  Big Crunch . In this scenario, the cosmos would collapse back into an infinitely dense singularity like the one it emerged from. Perhaps this process could even spark another Big Bang, the thinking went. 

We’d be gone, but the Big Bang/Big Crunch cycle could infinitely repeat. 

In the years since then, the  discovery of dark energy  has robbed us of a shot at this eternal rebirth. In 1998, two separate teams of astronomers announced that they’d measured special exploding stars in the distant universe, called a  type Ia supernova , which serves as “ standard candles ” for calculating distances. They found that the distant explostions — which should all have the same intrinsic brightness — were dimmer, and therefore farther away, than expected. Some mysterious force was pushing the cosmos apart from within.

This dark energy is now thought to make up some 69 percent of the universe’s mass, while dark matter accounts for another roughly 26 percent. Normal matter — people, planets, stars, and anything else you can see — comprises just about 5 percent of the cosmos. 

The most important impact of dark energy is that the universe’s expansion will never slow down. It will only accelerate. 

Heat death of the universe

Decades of observations have only confirmed researchers’ findings. All signs now point to a long and lonely death that peters out toward infinity. The scientific term for this fate is “heat death.”

But things will be rather desolate long before that happens. 

“Just” a couple trillion years from now, the universe will have expanded so much that no distant galaxies will be visible from our own Milky Way, which will have long since  merged with its neighbors . Eventually, 100 trillion years from now, all star formation will cease, ending the Stelliferous Era that’s be running since not long after our universe first formed.

Much later, in the so-called  Degenerate Era , galaxies will be gone, too. Stellar remnants will fall apart. And all remaining matter will be locked up inside black holes.  

In fact,  black holes  will be the last surviving sentinels of the universe as we know it. In the Black Hole Era, they’ll be the only “normal” matter left. But eventually, even these titans will disappear, too.

Stephen Hawking  predicted that  black holes slowly evaporate  by releasing their particles into the universe. First, the smaller, solar-mass black holes will vanish. And by a googol years into the future (a 1 followed by 100 zeroes), Hawking radiation will have killed off even the  supermassive black holes .  

No normal matter will remain in this final “Dark Era” of the universe, which will last far longer than everything that came before it. And the second law of thermodynamics tells us that in this time frame, all energy will ultimately be evenly distributed. The cosmos will settle at its final resting temperature, just above absolute zero, the coldest temperature possible.  

If this future seems dark and depressing, take comfort in knowing that every earthling will have died long before we have to worry about it. In fact, on this timescale of trillions of years, even the existence of our entire species registers as but a brief ray of sunlight before an infinite winter of darkness.

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Origin Of The Universe: 8 Different Theories

How did the Universe we know come into existence? And how do we explain its origin? These are some of the questions cosmologists and physicists have been trying to unravel for decades.

Undoubtedly, every piece of evidence and data collected over the years by cosmologists points toward the possibility that it all might have started with a ‘big bang.’ But what if there is more?

Table of Contents

What Is The Big Bang Theory? A Brief Introduction

In 1927, Belgian astronomer Georges Lemaitre proposed the theory of an expanding universe (later confirmed by Edwin Hubble). He theorized that an expanding universe could be traced back to a singular point, which he termed the “primeval atom,” back in time. It laid the foundation for the modern Big Bang theory.

The Big Bang Theory is an explanation, based mostly on mathematical models, of how and when the Universe came into existence.

The cosmological model of the Universe described in the Big Bang theory explains how it initially expanded from a state of infinite density and temperature, known as the primordial (or gravitational) singularity.

This expansion was followed by cosmic inflation and a massive temperature drop. During this phase, the Universe ballooned at a much faster rate than the speed of light (by a factor of 10 26 ).

Subsequently, the Universe was reheated to a point where elementary particles (quarks, leptons, and so on) before a gradual decrease in temperature (and density) led to the formation of the first protons and neutrons .

A few minutes into the expansion, protons and neutrons combine to form primordial hydrogen and helium-4 nuclei. The estimated radius of the observable Universe during this phase was 300 light-years. The earliest stars and galaxies appeared about 400 million years after the event.

A crucial piece of the Big Bang model is the cosmic microwave background (CMB), which is the electromagnetic radiation left from the time when the Universe was in its infancy. CMB remains the most definitive proof of the Big Bang.

While the theory remains widely accepted across the scientific spectrum, a few alternative explanations — such as steady-state Universe and eternal inflation, have gained attraction over the years.

Below, we have discussed seven of the most popular alternatives of the Big Bang, explaining the origin of the Universe.

8. Quantum Fluctuation Theory 

According to quantum mechanics, particles and antiparticles can spontaneously appear and annihilate in empty space. While doing so, they create temporary fluctuations in energy called vacuum fluctuations. 

The quantum fluctuation theory proposes that our universe might have formed from one of those vacuum fluctuations. Image a very small space where an energy fluctuation occurs. Instead of quickly annihilating, this fluctuation could potentially increase and develop something more substantial. 

This theory suggests that the initial fluctuation expanded rapidly, which eventually led to the birth of our universe. This rapid expansion can be associated with comic inflation. 

As our universe expanded and cooled, the energy from the initial fluctuation might have transformed into particles and antiparticles. These particles would ultimately become the building blocks of matter throughout the cosmos.

Although the concept seems intriguing, it is just a theoretical framework. The precise details of how our universe formed from a quantum fluctuation remain a subject of active research. Scientists continue to study and refine this theory to get deeper insights into the origin of the universe. 

Reference Sources –

Spontaneous creation of the universe from nothing, arXiv :1404.1207

Massive galaxy clusters hint at primordial quantum diffusion, Physics Review Letters  

7. Theory of Eternal Inflation

The concept of the inflationary universe was first introduced by cosmologist Alan Guth in 1979 to explain why the Universe is flat, something that was missing from the original Big Bang theory.

Though Guth’s idea of inflation explains the flat Universe, it creates a scenario that prevents the Universe from escaping that inflation . If this were the case, reheating of the Universe wouldn’t have taken place, and neither would the formation of stars and galaxies.

This particular problem was solved by Andreas Albrecht and Paul Steinhardt in their “new inflation” model. They argued that rapid inflation of the Universe happened just for a few seconds before ceasing. It demonstrated how the Universe can go through rapid inflation and still end up getting heated.

Based on the previous works of Steinhardt and Alexander Vilenkin, Andrei Linde, a professor at Stanford University, proposed an alternative to Guth’s inflation theory called chaotic inflation or ‘eternal inflation theory.

The theory argues that the inflationary phase of the Universe goes on forever; it didn’t end for the Universe as a whole. In other words, cosmic inflation continues in some parts of the Universe and ceases in others. This leads to a multiverse scenario, wherein space is broken into bubbles. It’s like a universe inside a universe.

In a multiverse, different universes may have different laws of nature and physics at work. So, instead of a single expanding cosmos, our Universe might be an inflationary multiverse with many small universes with varying properties.

However, Paul Steinhardt believes that his ‘new inflation’ theory doesn’t lead to or predict anything and argues that the multiverse notion is a “fatal flaw” and unnatural.

Eternal inflation and its implications, arXiv :hep-th/0702178

Inflationary paradigm in trouble after Planck2013, arXiv :1304.2785

6. Conformal Cyclic Model

The conformal cyclic cosmological (CCC) model speculates that the Universe goes through repeated cycles of the Big Bang and subsequent expansions. The general idea is that the ‘Big Bang’ was not the beginning of the Universe but rather a transition phase. It was developed by renowned theoretical physicist and mathematician Roger Penrose.

The theory suggests that the universe goes through a series of cycles, each involving a Big Bang followed by expansion, contraction, and another Big Bang. These cycles are infinite, which means the universe goes through this process repeatedly with no end. 

This concept is often compared with a spring oscillation, where the universe expands and contracts periodically. 

Unlike the standard Big Bang theory that postulates a singular beginning of the universe, the Cyclic Universe theory avoids the singularity problem by suggesting that our universe had no initial singularity but has always existed in this cyclical pattern. 

As a basis for his model, Penrose used multiple FLRW (Friedmann–Lemaître–Robertson–Walker) metric sequences. He argued that the conformal boundary of one FLRW sequence could be attached to the boundary of another.

The FLRW metric is the closest approximation of the nature of the Universe and a part of the Lambda-CDM model . Each sequence begins with a big bang, followed by inflation and subsequent expansion.

The cyclic or oscillating model, wherein the Universe reiterates over and over in an indefinite cycle, first came into the spotlight in the 1930s, when Albert Einstein investigated the idea of an ‘everlasting’ universe. He considered that after reaching a certain point, the Universe starts collapsing and ends with a Big Crunch before going through the Big Bounce.

Right now, there are four different variations of the cyclic model of the Universe, one of which is the Conformal Cyclic Cosmology.

Read: Does Universe Iterate Through Infinite Numbers of Big Bangs?

This theory has been studied extensively, but it faces some serious challenges in terms of observational evidence. One of the major challenges has been detecting remnants of past cycles in our current universe. 

5. Black Hole Mirage

A study conducted by a group of researchers in 2013 speculated that our Universe might have originated from the debris spewed out of a collapsed four-dimensional star or a black hole.

According to the cosmologists associated with the research, one of the limitations of the Big Bang theory is to explain the temperature equilibrium found in the Universe.

While most scientists concur that the inflationary theory gives an adequate explanation of how a small patch with uniform temperature would rapidly expand to become the Universe we observe today, the group found it implausible due to the chaotic nature of the Big Bang.

To solve this problem, the team proposed a model of the cosmos, in which our three-dimensional Universe is a membrane and is floating inside a four-dimensional ‘bulk universe.’

They argued that if the 4-D ‘bulk universe’ has 4-D stars, it’s likely they will collapse into 4-D black holes. These 4-D black would have a 3-D event horizon (just like the 3-D ones have a 2-D event horizon ), which they named ‘hypersphere.’

Read:  11 Biggest Unsolved Mysteries in Physics

When the team simulated the collapse of a 4-D star, they discovered that the ejected debris from the dying star was likely to cast a 3-D membrane around that 3-D event horizon. Our Universe might be one such membrane.

The ‘4-D black hole’ model of the cosmos does explain why the temperature is almost uniform throughout the Universe. It may also give valuable insights into exactly what triggered the cosmic inflation a few seconds after its genesis.

However, a recent observation by ESA’s Planck satellite has uncovered small variations in the cosmic microwave background (CMB) temperature. These satellite readings differ from the proposed model by about four percent.

4. Plasma Universe Theory

Our current understanding of the Universe is mostly influenced by gravity, specifically Einstein’s General Theory of Relativity, through which cosmologists explain the nature of the Universe. Coincidentally, just like most other things, an alternative to gravity has also been entertained by scientists over the years.

The plasma cosmology (or plasma universe theory) speculates that electromagnetic forces and plasma play a much more important role in the Universe than gravity.

Although the approach has many different flavors, the basic idea remains the same: every astronomical body, including the sun, stars, and galaxies, results from some electrical process.

The first prominent plasma universe theory was proposed by Nobel laureate Hannes Alfvén in the 1960s. He was later joined by Swedish theoretical physicist Oskar Klein to develop the Alfvén–Klein model .

The model is built around the assumption that the Universe sustains equal amounts of matter and antimatter (that’s not the case according to modern particle physics). The boundaries of these two regions are marked with cosmic electromagnetic fields. And thus, interactions between the two would produce plasma, which Alfvén named ‘ambiplasma.’

According to the theory, such plasma would form large sections of matter and antimatter throughout the Universe. Furthermore, it theorized that our current location in the cosmos must be in a section where the matter is much more abundant than the antimatter – hence solving the matter-antimatter asymmetry problem.

Read:  Could Life Form In a Two-Dimensional Universe?

3. Slow Freeze Theory

Decades of mathematical modeling and research have led cosmologists to a valid conclusion that our Universe started from a single point of infinite density and temperature called the singularity. The subsequent expansion of the cosmos allowed it to cool, which led to the formation of galaxies, stars, and other astronomical objects.

However, as we know, the standard Big Bang model has not gone unchallenged, and one such challenging theory was proposed by Christof Wetterich, a professor at Germany’s Heidelberg University.

Wetterich argued that the Universe we know today might have actually started as cold and sparse, awakened from a long freeze. Over time, the fundamental particles in the early Universe became heavier while the gravitational constant decreased.

Furthermore, he explained that if masses of the particles have been increasing, radiation from the early Universe could make space appear hotter and move away from each other even if it wasn’t the case.

The basic idea of Wetterich’s Slow Freeze cosmic model is that the Universe has no beginning and no future. Instead of a hot Big Bang, the theory advocates for a cold and slowly evolving Universe.

According to Wetterich, the theory explains density fluctuations in the early Universe (primordial fluctuations) and why our current cosmos is dominated by dark energy.

Read: All Interesting Facts About Black Holes and White Holes

2. Hindu Cosmology

Religion and science have been the best of enemies since at least the time of Copernicus and Galileo. There is perhaps no room for science when we talk about religion and vice-versa. However, there is one religion whose cosmological beliefs sit well with the current model of the Universe.

Creation theories in Hindu mythology are widely considered one of the most ancient and significant of all other religious counterparts.

Over the years, prominent physicists and cosmologists, including Carl Sagan and Niels Bohr, have admired Hindu cosmological beliefs for its close similarity with the timelines in the standard cosmological model of the Universe.

According to Hindu mythology, the Universe follows an infinite cyclic model. It means that our current Universe will be replaced by an endless number of universes. Each iteration of the Universe is divided into two phases, ‘Kalpa’ (or the day of Brahma) and ‘pralaya’ (the night of Brahma), and each is 4.32 billion years long.

According to Hindu mythology, the age of the Universe (8.64 billion years) is more than the currently estimated age of the solar system.

1. Steady State Universe

The Steady-State model asserts that the observable Universe remains the same at any place and time. In the Universe, which is forever expanding, matter is continuously created to fill the space.

The idea of the steady-state theory was first proposed in 1948 by cosmologists Hermann Bondi, Fred Hoyle, and Thomas Gold. It was derived from the perfect cosmological principle, which itself states that the Universe is the same no matter where you look, and it will always be the same.

According to the model, galaxies and other large astronomical bodies near us should appear similar to those that are far away. However, the Big Bang tells us that distant galaxies should look younger than those at close proximity (when observed from the Earth) since light takes much longer to reach us.

The Steady-State theory gained widespread popularity in the early and mid-20th century. However, by the 1960s, it was mostly discarded by the scientific community in favor of the Big Bang after the discovery of the cosmic microwave background.

Interestingly, according to a 1931 manuscript that was discovered by researchers in 2014, Albert Einstein was working on an alternative to the Big Bang theory. It was identical to Fred Hoyle’s Steady State model, proposing that the universe has expanded steadily. However, the idea was shortly abandoned by Einstein.

More to Know

How old is the universe.

The universe is nearly 14 billion years old (13.78 billion, to be exact). Scientists have reached this conclusion after extensive studies of the cosmic microwave background and analyzing data from the Plack Space Observatory, WMAP, and other space probes.

However, a team of researchers in 2019 calculated the age of the universe to be a couple of billion years younger than the age predicted by the Plank study. The team used the movement of galaxies and stars to estimate how fast the universe is expanding. A higher expansion rate means that the universe reached its current size faster, and thus, it must be younger.

To put an end to the discrepancy, an international team of astronomers analyzed the data from the Atacama Cosmology Telescope (ACT) in Chile in 2020 to find out the approximate age of the universe.

The team determined the age of the universe to be 13.77 billion years , give or take 40 million years, which is in line with the estimate from the Plank research team.

What is the Age of the Sun?

The estimated age of the Sun is about 4.56 billion years. How did they reach this number? Well, it is a combination of nuclear cosmochronology and simulations of the stellar evolution model.

8 Biggest Black Holes In The Universe | As Per Their Solar Masses

15 Brightest Stars In The Sky | Based On Apparent Magnitude

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Varun Kumar

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Leave a reply cancel reply.

In reference to the big bang, you never explain where all the material in the universe derived from. No matter what thoughtful possibility, Where did all the material derive from? It cannot come out of nothingness. Where is your explanation. What are you saying that I already said that? Is that any excuse for not being able to explain?

Its easier and more plausible that : (a) The universe has ALWAYS existed and WILL always exist. And that : (b) Is always subject to change dispite long periods of static in some regions. (c) contains an amount of energy which is infinite and dispite chemical interactions, remains the same. And (d) is composed of elements and particles, atoms and sub-atomic particles which can be known and are limited thou thier by-products may be unlimited. AND : (e) Life and living beings almost d i dont happen at all and so is unlikely to exist elsewhere at least anywhere near where we are. (f) 99.9 % of space is freezing cold and 0.001% is way hotter than any life form could ever tolerate. And percentages of infinite amounts are abstract. (g) the human mind and brain is the most complex thing in the known universe. (h) the universe is mainly harmless. (i) always take a towel !

Just came across your comment. I have searched for the words to extract your very questions, not really knowing just how to express such inquiries. I now have reference material to go forward. Yours. LOL.

Thanks for putting the words in my mouth. Brilliantly said.

do you have evidence about the theory of Steady State??

I’ve read it all, and I can see a preference for the big bank theory, in some version or other. What I cannot seem to find, in any writings, is a definition of the place at which the bang started, be it a point, line, or plane. If the universe is expanding, there are a lot of theories about it. But no one seems to be able to tell me from where?

If the Big Bang theory is correct and if the red-shift/ blue-shift theory is correct, they would lend credence to the idea of all expanding or outward flow of stars and galaxies all being red ( going away) vs blue ( coming in towards us). Under this scenario – trajectories at various galaxies and stars could be calculated to determine a point of origin of where the Big Bang started from. Is that spot then to be found void of all matter …? To date … blank spaces seem to hold much intrigue following Hubble’s highly successful 12 day synchronized stare into one of those many blank spaces, and most astronomers do not come away disappointed upon seeing developed plates of those blank spots. Every cubic light-year is chocked full of matter. So with this theory one could say …”bye – bye Big Bang theory”…

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“Cosmic Lighthouses” – Webb Unlocks the Secrets of the Universe’s First Light

By Adrienne Berard, Penn State University March 31, 2024

Utilizing data from NASA’s James Webb Space Telescope, scientists have unveiled the earliest starlight spectra, revealing low-mass galaxies’ central role in the universe’s dawn. Credit: SciTechDaily.com

Groundbreaking JWST observations reveal the pivotal role of low-mass galaxies in the early universe’s reionization, challenging existing cosmic evolution theories.

Scientists working with data from NASA’s James Webb Space Telescope (JWST) have obtained the first full spectra of some of the earliest starlight in the universe. The images provide the clearest picture yet of very low-mass, newborn galaxies, created less than a billion years after the Big Bang , and suggest the tiny galaxies are central to the cosmic origin story.

The international team of researchers, including two Penn State astrophysicists, published their results recently in the journal Nature . The spectra reveal some of the first visible light from a period in the universe known as reionization, which was powered by the arrival of the earliest stars and galaxies.

Deep field images from NASA’s James Webb Space Telescope provided the first glimpses of ultra-faint galaxies that researchers identified as strong candidates for the objects that sparked the reionization of the universe. Credit: Hakim Atek/Sorbonne University/JWST

The Primordial Universe: A Transition From Darkness to Light

Normal matter in the universe started as a hot, dense fog made almost entirely of hydrogen and helium nuclei, explained Joel Leja, assistant professor of astronomy and astrophysics at Penn State and author on the paper. As it expanded and cooled, lone protons and electrons started bonding, forming neutral hydrogen for the first time. Then, roughly 500 to 900 million years after the Big Bang , that neutral hydrogen — which predominated in the early universe — began to separate again into ionized gas, spurring the creation of stars and galaxies and lifting the primordial fog so light could travel unimpeded through the cosmos for the first time.

“Something turned on that started pumping out very high energy photons into the intergalactic void,” Leja said. “These sources worked like cosmic lighthouses that burned off the fog of neutral hydrogen. Whatever this was, it was so energetic and so persistent, that the entire universe became re-ionized.”

Galactic Pioneers: The Role of Low-Mass Galaxies

By analyzing the spectra of young, low-mass galaxies, the scientists demonstrated that small galaxies were strong candidates for the “something” that sparked the reionization of the universe by heating the dense primordial gas around them and ionizing the once-neutral hydrogen.

“If the other low-mass galaxies in the universe are as common and energetic as these, we think we finally understand the lighthouses that burned off the cosmic fog,” Leja said. “They were incredibly energetic stars in many, many tiny little galaxies.”

The majority of galaxies in the early universe are expected to be relatively small, making studying their frequency and their properties extremely difficult, Leja added. Thanks to a technological feat made possible by the unique combination of JWST sensitivity and the gravitational lensing effect of the Abell 2744 cluster — nearby galaxies that act like cosmic magnifiers, distorting space and amplifying the light of background galaxies — it is now possible to determine the abundance of small galaxies and their ionizing properties during the first billion years of the universe.

“We found that small galaxies outnumbered massive galaxies by about a hundred to one during this epoch of reionization of the universe,” Hakim Atek, astrophysicist at Sorbonne University, researcher at the Paris Astrophysics Institute and first author on the paper said in a release. “These novel observations also reveal that these small galaxies produced a considerable amount of ionizing photons, exceeding by four times the canonical values usually assumed for distant galaxies. This means that the total flux of ionizing photons emitted by these galaxies far exceeds the threshold required for reionization.”

Charting the Cosmic Evolution: Future Directions

The Penn State team led the modeling for the UNCOVER survey, which targeted the large foreground galaxy cluster that lensed the tinier, more distant galaxies. The Penn State researchers analyzed all the small points of light in the survey to understand the object properties as well as their likely masses and distances. That analysis was then used to guide later, more detailed JWST observations that drove this discovery, Leja explained.

Prior to these findings, there were number of hypotheses that identified other sources responsible for cosmic reionization, such as supermassive black holes; large galaxies with masses in excess of one billion solar masses; and small galaxies with masses of less than 1 billion solar masses. Researchers said confirmation of the hypothesis relating to low-mass galaxies proved particularly difficult, given their low luminosity, but the new findings offer the clearest evidence to date that low-mass galaxies played a central role in the reionization of the universe.

The researchers now want to extend the study to a larger scale to confirm that the particular location they analyzed is representative of the average distribution of galaxies in the universe. Beyond the reionization process, their observations provide insight into the process of early star formation, how galaxies emerged from the primordial gas — and how they evolved into the universe we know today.

Reference: “Most of the photons that reionized the Universe came from dwarf galaxies” by Hakim Atek, Ivo Labbé, Lukas J. Furtak, Iryna Chemerynska, Seiji Fujimoto, David J. Setton, Tim B. Miller, Pascal Oesch, Rachel Bezanson, Sedona H. Price, Pratika Dayal, Adi Zitrin, Vasily Kokorev, John R. Weaver, Gabriel Brammer, Pieter van Dokkum, Christina C. Williams, Sam E. Cutler, Robert Feldmann, Yoshinobu Fudamoto, Jenny E. Greene, Joel Leja, Michael V. Maseda, Adam Muzzin, Richard Pan, Casey Papovich, Erica J. Nelson, Themiya Nanayakkara, Daniel P. Stark, Mauro Stefanon, Katherine A. Suess, Bingjie Wang and Katherine E. Whitaker, 28 February 2024, Nature . DOI: 10.1038/s41586-024-07043-6

Bingjie Wang, a postdoctoral scholar in astrophysics, is the other Penn State co-author on the study. A full list of authors and their respective institutions is available on the published paper. The researchers acknowledge funding and support from CNES, the Programme National Cosmology and Galaxies, CEA, the Cosmic Dawn Center, the Danish National Research Foundation, the Australian Research Council, the NOW, the European Commission’s and University of Groningen’s CO-FUND Rosalind Franklin program, the United States-Israel Binational Science Foundation, the U.S. National Science Foundation (NSF), the Ministry of Science & Technology, Israel and NOIRLab , which is managed by the Association of Universities for Research in Astronomy under a cooperative agreement with the NSF.

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2 comments on "“cosmic lighthouses” – webb unlocks the secrets of the universe’s first light".

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How one year or a billion years was calculated before the formation of earth. Billion years after big bang refers to what sort of time period

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What Can A Total Solar Eclipse Teach Us About Our Universe?

The total solar eclipse on April 8 will be a once in a lifetime opportunity to witness a truly awesome cosmological marvel. You don’t need a scientific background to appreciate its stunning visual beauty, but astronomers and astrophysicists at The University of Texas at Austin have used these rare phenomena to help answer fundamental questions about our universe.

In 1919 two British scientists conducted an experiment intended to verify Albert Einstein’s controversial theory of general relativity. This physical theory, that had been published four years prior, proposed the universe is four-dimensional and that massive objects like the sun actually warp the very fabric of spacetime. According to general relativity, this warped spacetime is what we feel as gravity.

Of course, Einstein’s theory was purely theoretical. So another physicist, Arthur Stanley Eddington, believed observing a total solar eclipse might support the validity of Einstein’s radical thesis. Since Einstein had predicted that gravity would bend the path of light near massive objects like the sun, curving spacetime itself, Eddington realized that during a total solar eclipse, the moon blocks the sun’s light, allowing stars near the sun to be visible. By photographing the positions of stars near the sun during the 1919 total solar eclipse, Eddington’s experiment proved to be a landmark result, helping establish general relativity as the prevailing theory of gravity over Sir Isaac Newton’s previous model.

Disprove Me Right!

Science is as much about disproving as it is proving hypotheses. Always looking for that fatal flaw in Einstein’s theory, several amateur and professional scientists sought to reproduce Eddington’s results in the coming decades. In fact, the last experiment conducted using photography was performed by a team from the U.S. Naval Observatory, Princeton University and UT Austin.

“I was actually on that team,” said Richard Matzner , professor of physics at UT’s College of Natural Sciences. “In 1973, myself and the rest of the group traveled to an area in Mauritania, Africa. There we witnessed a total solar eclipse that lasted for six minutes and 10 seconds, a very long time for an eclipse.”

Using improved visual photographic technology than what Eddington would’ve had at his disposal in 1919, Matzner and his colleagues found reasonable proof to corroborate Einstein’s theory once more.

Riding The Gravitational Wave

At UT Austin’s Center for Gravitational Physics , researchers are expanding on the pioneering work of Eddington and his team by helping to explore one of the other exciting predictions of  Einstein’s theory of general relativity that observers were unable to verify for an entire century, namely, the existence of gravitational waves.

Simply put, these ripples in spacetime – caused after massive space events, such as two black holes colliding – are the messengers of gravitational information. In the same way electromagnetic radiation (light) provides us with information from the sun, we also get gravitational wave information from objects.

However, it took a long time for gravitational waves to be welcome at the spacetime party. “Gravitational waves were one of Einstein’s predictions that even he was uncomfortable with for a while,” said Deirdre Shoemaker , Director of the Center for Gravitational Physics.

Shoemaker is nonchalant when discussing gravitational waves. However, just a decade prior, they still hadn’t been directly confirmed as real.

It wasn’t until 2015, a century after Einstein even posed the hypothesis, that scientists would successfully find the requisite evidence. And the UT Austin theoretical physicist was part of the international team that confirmed their existence.

“The Laser Interferometer Gravitational-Wave Observatory, or LIGO project, (of which I am a member) is a large scientific collaboration involving many researchers across different universities and countries,” Shoemaker said. “In 2015, the LIGO’s detections were the first direct observations of gravitational waves.”

(In fact, Shoemaker isn’t the only UT Austin connection to what some described as “the biggest scientific discovery of our time.” The director of LIGO at the time they found the first-ever detection of gravitational waves, David Reitze , is an alumnus who started his career as a Ph.D. candidate at UT Austin.)

There are two LIGO observatories located in the United States – one in Washington and another in Louisiana. Each uses lasers and mirrors arranged in an “L” shape to precisely measure the distance between the mirrors.

Gravitational waves passing through the observatories cause tiny changes in the distances between the mirrors. By measuring any differences in the distances using the lasers, LIGO can detect these gravitational waves. This allows scientists to study cataclysmic events in the universe like black hole and neutron star collisions.

Black Hole Sun

Since total solar eclipses can only be seen about every 400 years from any one place on the surface of the Earth, Shoemaker studies gravitational waves by observing the more dependable black hole – also large enough to warp spacetime.

Choosing the empty nothingness of a black hole over the sun doesn’t appear to have been a compromise for the NSF Career award winner and fellow of the American Physical Society.

“Black holes are beautiful because they don’t contain any messy matter,” she said. “They’re just curved space time.”

And, since they can form in pairs, and even binary pairs that eventually merge into one bigger black hole, they are excellent sources of gravitational waves.

“Black holes are our strongest source,” said Shoemaker. “We see them with the detector all the time. We’ve observed almost 90 individual gravitational waves coming from black holes since 2015.”

Texas Sunsets Meet Their Match

Of course, one doesn’t need to retain any of the above information to enjoy the total solar eclipse on April 8, 2024. It will be just as spectacular to watch for the non expert as it will be for the most zealous of gravitational physicists.

But as Arthur S Eddington demonstrated over a century ago, the eclipse on April 8 is an opportunity for those now carrying the gravitational torch to find answers to other questions about our universe. You just have to know what to look for.

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Confirmed! We Live in a Simulation

We must never doubt Elon Musk again

By Fouad Khan

Sean Gladwell Getty Images

Ever since the philosopher Nick Bostrom proposed in the Philosophical Quarterly that the universe and everything in it might be a simulation , there has been intense public speculation and debate about the nature of reality. Such public intellectuals as Tesla leader and prolific Twitter gadfly Elon Musk have opined about the statistical inevitability of our world being little more than cascading green code. Recent papers have built on the original hypothesis to further refine the statistical bounds of the hypothesis , arguing that the chance that we live in a simulation may be 50–50 .

The claims have been afforded some credence by repetition by luminaries no less esteemed than Neil deGrasse Tyson, the director of Hayden Planetarium and America’s favorite science popularizer. Yet there have been skeptics. Physicist Frank Wilczek has argued that there’s too much wasted complexity in our universe for it to be simulated. Building complexity requires energy and time. Why would a conscious, intelligent designer of realities waste so many resources into making our world more complex than it needs to be? It's a hypothetical question, but still may be needed.: Others, such as physicist and science communicator Sabine Hossenfelder , have argued that the question is not scientific anyway. Since the simulation hypothesis does not arrive at a falsifiable prediction, we can’t really test or disprove it, and hence it’s not worth seriously investigating.

However, all these discussions and studies of the simulation hypothesis have, I believe, missed a key element of scientific inquiry: plain old empirical assessment and data collection. To understand if we live in a simulation we need to start by looking at the fact that we already have computers running all kinds of simulations for lower level “intelligences” or algorithms. For easy visualization, we can imagine these intelligences as any nonperson characters in any video game that we play, but in essence any algorithm operating on any computing machine would qualify for our thought experiment. We don’t need the intelligence to be conscious, and we don’t need it to even be very complex, because the evidence we are looking for is “experienced” by all computer programs, simple or complex, running on all machines, slow or fast.

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All computing hardware leaves an artifact of its existence within the world of the simulation it is running. This artifact is the processor speed. If for a moment we imagine that we are a software program running on a computing machine, the only and inevitable artifact of the hardware supporting us, within our world, would be the processor speed. All other laws we would experience would be the laws of the simulation or the software we are a part of. If we were a Sim or a Grand Theft Auto character these would be the laws of the game. But anything we do would also be constrained by the processor speed no matter the laws of the game. No matter how complete the simulation is, the processor speed would intervene in the operations of the simulation.

In computing systems, of course, this intervention of the processing speed into the world of the algorithm being executed happens even at the most fundamental level. Even at the most fundamental level of simple operations such as addition or subtraction, the processing speed dictates a physical reality onto the operation that is detached from the simulated reality of the operation itself.

Here’s a simple example. A 64-bit processor would perform a subtraction between say 7,862,345 and 6,347,111 in the same amount of time as it would take to perform a subtraction between two and one (granted all numbers are defined as the same variable type). In the simulated reality, seven million is a very large number, and one is a comparatively very small number. In the physical world of the processor, the difference in scale between these two numbers is irrelevant. Both subtractions in our example constitute one operation and would take the same time. Here we can clearly now see the difference between a “simulated” or abstract world of programmed mathematics and a “real” or physical world of microprocessor operations.

Within the abstract world of programmed mathematics, the processing speed of operations per second will be observed, felt, experienced, noted as an artifact of underlying physical computing machinery. This artifact will appear as an additional component of any operation that is unaffected by the operation in the simulated reality. The value of this additional component of the operation would simply be defined as the time taken to perform one operation on variables up to a maximum limit that is the memory container size for the variable. So, in an eight-bit computer, for instance to oversimplify, this would be 256. The value of this additional component will be the same for all numbers up to the maximum limit. The additional hardware component will thus be irrelevant for any operations within the simulated reality except when it is discovered as the maximum container size. The observer within the simulation has no frame for quantifying the processor speed except when it presents itself as an upper limit.

If we live in a simulation, then our universe should also have such an artifact. We can now begin to articulate some properties of this artifact that would help us in our search for such an artifact in our universe.

The artifact is as an additional component of every operation that is unaffected by the magnitude of the variables being operated upon and is irrelevant within the simulated reality until a maximum variable size is observed.

The artifact presents itself in the simulated world as an upper limit.

The artifact cannot be explained by underlying mechanistic laws of the simulated universe. It has to be accepted as an assumption or “given” within the operating laws of the simulated universe.

The effect of the artifact or the anomaly is absolute. No exceptions.

Now that we have some defining features of the artifact, of course it becomes clear what the artifact manifests itself as within our universe. The artifact is manifested as the speed of light.

Space is to our universe what numbers are to the simulated reality in any computer. Matter moving through space can simply be seen as operations happening on the variable space. If matter is moving at say 1,000 miles per second, then 1,000 miles worth of space is being transformed by a function, or operated upon every second. If there were some hardware running the simulation called “space” of which matter, energy, you, me, everything is a part, then one telltale sign of the artifact of the hardware within the simulated reality “space” would be a maximum limit on the container size for space on which one operation can be performed. Such a limit would appear in our universe as a maximum speed.

This maximum speed is the speed of light. We don’t know what hardware is running the simulation of our universe or what properties it has, but one thing we can say now is that the memory container size for the variable space would be about 300,000 kilometers if the processor performed one operation per second.

This helps us arrive at an interesting observation about the nature of space in our universe. If we are in a simulation, as it appears, then space is an abstract property written in code. It is not real. It is analogous to the numbers seven million and one in our example, just different abstract representations on the same size memory block. Up, down, forward, backward, 10 miles, a million miles, these are just symbols. The speed of anything moving through space (and therefore changing space or performing an operation on space) represents the extent of the causal impact of any operation on the variable “space.” This causal impact cannot extend beyond about 300,000 km given the universe computer performs one operation per second.

We can see now that the speed of light meets all the criteria of a hardware artifact identified in our observation of our own computer builds. It remains the same irrespective of observer (simulated) speed, it is observed as a maximum limit, it is unexplainable by the physics of the universe, and it is absolute. The speed of light is a hardware artifact showing we live in a simulated universe.

But this is not the only indication that we live in a simulation. Perhaps the most pertinent indication has been hiding right in front of our eyes. Or rather behind them. To understand what this critical indication is, we need to go back to our empirical study of simulations we know of. Imagine a character in a role-playing game (RPG), say a Sim or the player character in Grand Theft Auto. The algorithm that represents the character and the algorithm that represents the game environment in which the character operates are intertwined at many levels. But even if we assume that the character and the environment are separate, the character does not need a visual projection of its point of view in order to interact with the environment.

The algorithms take into account some of the environmental variables and some of the character’s state variables to project and determine the behavior of both the environment and the character. The visual projection or what we see on the screen is for our benefit. It is a subjective projection of some of the variables within the program so that we can experience the sensation of being in the game. The audiovisual projection of the game is an integrated subjective interface for the benefit of us, essentially someone controlling the simulation. The integrated subjective interface has no other reason to exist except to serve us. A similar thought experiment can be run with movies. Movies often go into the point of view of characters and try to show us things from their perspective. Whether or not a particular movie scene does that or not, what’s projected on the screen and the speakers—the integrated experience of the film—has no purpose for the characters in the film. It is entirely for our benefit.

Pretty much since the dawn of philosophy we have been asking the question: Why do we need consciousness? What purpose does it serve? Well, the purpose is easy to extrapolate once we concede the simulation hypothesis. Consciousness is an integrated (combining five senses) subjective interface between the self and the rest of the universe. The only reasonable explanation for its existence is that it is there to be an “experience.” That’s its primary raison d’être. Parts of it may or may not provide any kind of evolutionary advantage or other utility. But the sum total of it exists as an experience and hence must have the primary function of being an experience. An experience by itself as a whole is too energy-expensive and information-restrictive to have evolved as an evolutionary advantage. The simplest explanation for the existence of an experience or qualia is that it exists for the purpose of being an experience.

There is nothing in philosophy or science, no postulates, theories or laws, that would predict the emergence of this experience we call consciousness. Natural laws do not call for its existence, and it certainly does not seem to offer us any evolutionary advantages. There can only be two explanations for its existence. First is that there are evolutionary forces at work that we don’t know of or haven’t theorized yet that select for the emergence of the experience called consciousness. The second is that the experience is a function we serve, a product that we create, an experience we generate as human beings. Who do we create this product for? How do they receive the output of the qualia generating algorithms that we are? We don’t know. But one thing’s for sure, we do create it. We know it exists. That’s the only thing we can be certain about. And that we don’t have a dominant theory to explain why we need it.

So here we are generating this product called consciousness that we apparently don’t have a use for, that is an experience and hence must serve as an experience. The only logical next step is to surmise that this product serves someone else.

Now, one criticism that can be raised of this line of thinking is that unlike the RPG characters in, say. Grand Theft Auto, we actually experience the qualia ourselves. If this is a product for someone else than why are we experiencing it? Well, the fact is the characters in Grand Theft Auto also experience some part of the qualia of their existence. The experience of the characters is very different from the experience of the player of the game, but between the empty character and the player there is a gray area where parts of the player and parts of the character combine to some type of consciousness.

The players feel some of the disappointments and joys that are designed for the character to feel. The character experiences the consequences of the player’s behavior. This is a very rudimentary connection between the player and the character, but already with virtual reality devices we are seeing the boundaries blur. When we are riding a roller coaster as a character in say the Oculus VR device, we feel the gravity.

Where is that gravity coming from? It exists somewhere in the space between the character that is riding the roller coaster and our minds occupying the “mind” of the character. It can certainly be imagined that in the future this in-between space would be wider. It is certainly possible that as we experience the world and generate qualia, we are experiencing some teeny tiny part of the qualia ourselves while maybe a more information-rich version of the qualia is being projected to some other mind for whose benefit the experience of consciousness first came into existence.  

So, there you have it. The simplest explanation for the existence of consciousness is that it is an experience being created, by our bodies, but not for us. We are qualia-generating machines. Like characters in Grand Theft Auto, we exist to create integrated audiovisual outputs. Also, as with characters in Grand Theft Auto, our product mostly likely is for the benefit of someone experiencing our lives through us.

What are the implications of this monumental find? Well, first of all we can’t question Elon Musk again. Ever. Secondly, we must not forget what the simulation hypothesis really is. It is the ultimate conspiracy theory. The mother of all conspiracy theories, the one that says that everything, with the exception of nothing, is fake and a conspiracy designed to fool our senses. All our worst fears about powerful forces at play controlling our lives unbeknownst to us, have now come true. And yet this absolute powerlessness, this perfect deceit offers us no way out in its reveal. All we can do is come to terms with the reality of the simulation and make of it what we can.

Here, on earth. In this life.

New Inside Out 2 Trailer Confirms Major Pixar Shared Universe Theory

After many years of speculation and rumors, the new trailer for Inside Out 2 just confirmed the Pixar shared universe theory.

Inside Out was initially released back in 2015, and now, fans are looking forward to seeing the sequel, Inside Out 2 , which is set to hit theaters on June 14.

The teaser trailer for the upcoming Pixar film teased that a new emotion (Anxiety) will be on full display alongside the other emotions introduced in the first title, which were Joy, Sadness, Anger, Fear, and Disgust.

How Inside Out 2 Confirms the Pixar Shared Universe Theory

In the new trailer for Inside Out 2 , a subtle easter egg appears in one of the shots, finally confirming the Pixar shared universe theory.

For those unfamiliar, this theory (created by Jon Negroni and popularized by the Super Carlin Brothers ) states that every single Pixar film happens in the same universe and that elements from each film influence the others, from Brave (which takes place somewhere around the year 1300-1400) to Monsters Inc . (4500-5000).

However, Inside Out 2 's new trailer is the first time that one of the films acknowledges the fact that the different titles are all in the same universe, and it does so by subtly revealing a poster on the wall.

In the trailer, Riley ( Inside Out 's main character) is in her bedroom. Behind her, a poster of a band called 4*Town is hung on the wall.

This band was present in Pixar's recent Turning Red movie , which means that Riley's having a poster of them on her wall definitively places Inside Out and Turning Red in the same universe.

Turning Red is set in 2002, and the first Inside Out is set in 2007, so the latter's sequel likely takes place a few years later. So, although Turning Red and Inside Out 2 are likely roughly around eight years apart, it still seems as though the 4*Town band is still together. More importantly, it confirms and continues the Pixar shared universe theory.

Diving Deeper Into the Pixar Shared Universe Theory

The original Inside Out movie has its own connections to Jon Negroni's Pixar Theory. In a post on his official website , Negroni stated that a rat in Inside Out looks strikingly similar to Remy from Ratatoullie , and Carl and Ellie's wedding from Up can be seen in a memory.

However, Negroni also presented the idea that Riley's imaginary friend, Bing Bong, was a monster from the Monsters Inc. world who began as her personal monster.

Negroni revealed that this would explain why Bing Bong has animal-like features from cats, elephants, and dolphins because the monsters in Monsters Inc. have animal characteristics themselves.

The Super Carlin Brothers explained in a YouTube video how Turning Red connects to the wider Pixar shared universe. In that video, Jonathan "J" Carlin dives into how the witch from Brave is Boo from Monsters Inc. , who is also the mother of Meilin's friend, Abby, in Turning Red .

In Brave , there is a carving of Sully in the witch's hut, and she has dozens of wooden bears that she has carved out because she always remembers Sully.

J Carlin described that Boo could have learned a lot about bear magic from Meilin's family in Turning Red and also could have learned about time travel from the Lightyear movie, which she would have been able to use infinitely to make sure that Sully is never forgotten.

Since the witch can turn people into bears in Brave , this theory also suggests that Boo could have traveled back in time to utilize that magic in the past as well.

Inside Out 2 will be released in theaters on June 14.

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