How did the Universe begin? News-thread


Our growing knowledge of physical laws has allowed us to rewind the tape of the universe, tracing its evolution back to a fraction of a second after the Big Bang. Here, however, when the sum total of matter and energy coalesces into a ball of infinite density and temperature, the equations of general relativity break down.

As a theory, “the Big Bang omits the explosion,” writes physicist Brian Green in The fabric of the cosmos. What happened at that instant, let alone before that moment, is anyone’s (well-reasoned) guess, and there is no shortage of guesses about how the universe began.

What happened before the Big Bang?

First, a word of caution: Many experts argue that the word “before” misses the mark. It assumes that there was some pre-existing time separate from the universe, when in reality, time and space may have arisen. outside the universe.

From this point of view, the question: “What came before the Big Bang?” – is literally meaningless. Stephen Law, Oxford philosopher it suggested in interviews that what we need is not an answer to these types of questions, but “a kind of therapy, an explanation that makes us realize why it is time to stop asking the question.”

The idea pushes human language and intuition to its breaking point, but we can try to make sense of it with a favorite analogy from the late physicist Stephen Hawking: Asking what happened before the Big Bang is like asking what lies south of the South Pole. It is not even accurate to say that there is nothing further south; the point is that the question itself doesn’t make sense. We’re trying to pin down something that just doesn’t exist.

How did the Universe begin?

That answer may seem intellectually unsatisfactory. surely the universe came of something. How can all this bewildering beauty and complexity come from…nothing?

One solution, dating. back to Aristotle, is that there was no origin for the movement in the universe, it has always existed. Newton, Einstein, and others of their caliber believed that the cosmos was eternal and static, until astronomer Edwin Hubble discovered in the 1920s that all galaxies are expanding away from each other. That implied a starting point, the famous “singularity”.

So where did the uniqueness come from? Mocking Aristotle’s need for a “first cause,” some physicists today reply that our notions of causality are irrelevant in the extreme conditions of the Big Bang. We must take a closer look at scientific theories of how the universe began.

Read more: Could the Big Bang be wrong?

A quantum mechanical solution

Quantum mechanics has shown that even seemingly empty space is filled with fluctuating virtual particles that, through a process known as tunneling, can generate matter. We only see that behavior on an ultra-small scale, but the universe was just the right size back then.

A leading proponent of this perspective is Alexander Vilenkin, a cosmologist at Tufts University. In a 1982 paperwritten for an audience of professional physicists, he admitted that “the concept of the universe being created out of nothing is crazy.”

However, he argued that the laws of physics alone could have given rise to everything we see around us. (Physicists have even considered whether it is possible create a universe in a laboratory.)

Like MIT physicist Alan Lightman has described it“The entire universe could have ‘suddenly’ appeared from where things originate in the impossible-to-understand haze of quantum probabilities.”

Still, you might suspect that this “nothing,” if it was compatible with the creation of reality as we know it, was “something” after all.

A universe from nothing

David Albert, philosopher at Columbia University, has argued exactly that: “If what we previously took for nothing turns out, on closer examination, to have protons and neutrons and tables and chairs and planets and solar systems and galaxies and universes in it, then it is it was not nothing, and that I couldn’t they have been nothing, in the first place.

When it comes to understanding the concept of a universe out of nothing, there is an important difference between philosophical nothing and physical nothing. That is, the latter still includes the laws of nature required for cosmic genesis.

However, even conceding Albert’s point, we’re just kicking the can down the road. Whatever the origin of our universe, that must have come from something else as well (at least by the common-sense expectations of weak-brained humans).

In other words, it is “turtles to the bottom,” as some scholars say. So, bringing up that topic, let’s delve into some theories a little less steeped in philosophy.

The multiverse and eternal inflation

When we try to imagine the Big Bang, the best we can do is visualize an event of extraordinary force and grandeur, the fireworks display to end them all, or start them all. But what if, from the perspective of a cosmological landscape, it was just another Tuesday?

For example, we could be descendants of a larger proto-universe, which continually generates new ones. This concept, known as perpetual inflationit was developed in the 1980s, primarily by physicists Alan Guth, Andrei Lind, and Paul Steinhardt.

Under the right conditions, they believe, quantum fluctuations can cause “pocket universes” to expand outrageously quickly. That process could continue indefinitely, leading to a potentially infinite multiverse. However, despite the name of the theory, inflation can only be eternal in the future, not in the past; how it started remains a mystery.

Cyclic universe theory

It is also possible that the Big Bang was not the beginning of our universe, but rather a transition from some earlier state.

It could be that the cosmos has infinite cycles, each phase ending where the next begins, making the interval between the two more of a bounce than an explosion. The theory of the cyclical universe supports the idea of ​​the eternal universe, with all its comforting logic (ie, they don’t try to make something out of nothing), while still accounting for cosmic evolution.

According to one version of this story, the ekpyrotic modelour universe began in a collision between two “branes”: unconfirmed theoretical objects that exist in as many as 10 or 11 dimensions, depending on which version of string theory you subscribe to.

The idea is that we live inside a three-dimensional brane, which routinely collides with a second parallel brane, the two separated by a space of higher dimension. The energy produced by their meeting causes them to expand, then contract, and finally come together again in the next clash.

Read more: Did the Big Bang happen more than once?

C.formally cyclical cosmology

Another alternative is conformal cyclic cosmologythe controversial brainchild of Nobel Prize-winning physicist Roger Penrose, who was inspired by a striking similarity between the predicted birth and death of the universe.

In the unimaginable course of a googol of years (1 followed by 100 zeros), black holes will gobble up every last bit of matter and then evaporate in a process known as Hawking radiation, leaving behind a sea of ​​massless photons. Surprisingly, that cool, quiet ending is mathematically equivalent to the hot, energetic Big Bang: they’re essentially the same thing, suggesting one could blend in with the other.

In 2020, Penrose even claimed to have detected the imprint of a previous “cosmic eon” on our own, although many physicists are not convinced.

Until scientists find the long-sought unified theory, which would combine Einstein’s gravitational ideas with the mind-boggling mechanisms of the quantum world, our picture of the Big Bang will likely remain blurry.

As strange as these scenarios are, the truth may be even stranger. Meanwhile, lucky for us, physicists love to speculate about how the universe began.

Read more: Scientists try to map the multiverse


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