Why didn’t the universe start on its own?

Until a few decades ago, it was believed that the ultimate beginning of the universe was a Big Bang of infinite density concentrated into a single point – the singularity. It turns out, today, that concept has changed, but there is still some difficulty in publishing current theories about the origin of everything.

The Big Bang has been a theoretical prediction since the early 20th century, after a series of startling discoveries, such as the expansion of the universe. Around 1927, Georges Lemaître came to the conclusion (which seems pretty obvious today, but was still bullshit at the time) that if we went back in time, the expanding universe would become compact.

By extrapolating this back in time to the beginning of time, and knowing that time and space are the same thing, as Einstein showed, it is easy to conclude that the “zero” time of the universe was also “zero” measured space. In other words, 13.7 billion years ago (the age of the universe), everything was compressed into a single point.

A singularity is an uncomfortable topic for physicists, by its very definition: a single point of infinite density and infinitesimal size, smaller and more massive than any law of physics would allow. The problem is that general relativity allows these controversial objects to exist, so many physicists have worked to explain how they can form inside extremely dense structures, such as black holes.

For the same reason, scientists were convinced for most of the 20th century that the Big Bang was born from a singularity, in which all the matter and energy in our universe was compressed. If black holes also appear to be unique, it is tempting to imagine the Big Bang as the “mother of all black holes”.

Then, at some point, some mechanism caused this singularity to expand, releasing all that matter and energy to form the universe. This also led many physicists, such as Stephen Hawking, to speculate that the universe is cyclical: one day, the dark energy responsible for the expansion of the universe will run out and gravity will destroy everything back into a singular state. This idea is known as the Big Chunch.

The Big Bang was not a black hole

Today, although the Big Bang is still possible and verifiable through observations, physicists have another idea about the beginning of the universe. In the 1980s, the idea of ​​cosmic inflation appeared as a proposal to answer some questions that the Big Bang could not explain, and it succeeded. Since then, the cosmic inflation model has been increasingly accepted by the scientific community.

This theory shows that before the Big Bang, there was an inflationary period that served as a “preparation” for what would come next. In that time, the universe has expanded exponentially, at a very accelerated rate, forming and “stretching” all pre-existing elements – such as quantum fields and their fluctuations. This is where things get interesting, because these early formations can still be observed today.

The Big Bang singularity model shows a universe simply “born” with this set of quantum fluctuations and configurations. In the inflationary model, the Big Bang appears only after a period of cosmic inflation, which left initial quantum fluctuations ‘imprinted’ on the universe as it evolved.

Generated on the smallest of scales and extended to larger scales by cosmic inflation, these quantum fluctuations make up the defects seen in the cosmic microwave background (the fossilized light from the Big Bang). This means that the defects were already implanted by quantum fluctuations before the Big Bang.

If this is true, then there are two implications for the Big Bang: it is not the beginning of everything, and it is certainly not a black hole, let alone a unique one. Of course, 13.7 billion years ago it was still incredibly small – by the time 10 and a half seconds after the Big Bang it was only 1.5 meters. It already contained all the matter/energy (both are different manifestations of the same thing) that we see today, so with that small volume, the density would definitely collapse into a black hole.

But that couldn’t have happened with the Big Bang, because the formation of a black hole also depends on an area of ​​negligible density around it for gravity to come into play. If the density is the same everywhere, there are no differences in gravity and therefore no collapse into a black hole.

This means the following: In the proto-Big Bang model, the “black hole” would be literally in the middle of nothingness, where all space and time were compressed along with all the matter of the universe, into that unique point of infinitesimal smallness. measuring. Black holes are mostly distortions in space-time and there was neither space nor time outside of the Big Bang. Result: no crash.

But could it be that, even though it wasn’t a black hole, the Big Bang wasn’t a singularity? Well, there is one more thing that prevents this from happening: the early universe was dynamic. evolved and expanded.

The Big Bang was not a singularity

We said above that dark energy is responsible for the expansion of the universe. It is not yet known exactly what it is, but if the universe continues to expand and accelerate, then something is happening and that something called dark energy. Keeping the universe from expanding until everything collapses into a black hole requires a lot more matter than there is.

There simply isn’t enough mass in the universe to make gravity overcome the dark energy and pull everything back into a singular state. And for this very reason, the universe did not collapse again after the Big Bang, and as far as we know, it will not collapse in the future.

Finally, the inflationary model doesn’t allow you to go back in time until the universe has merged into a singularity. This is due to the very exponential nature of cosmic inflation – even if we went back to infinity of time, space would only approach the infinite size and infinite density that defines the singularity. That is, it will not actually reach these proportions.

While part of the scientific community resisted the new proposals for the inflationary model, others began to accept that if the model was validated, the Big Bang should be discarded as unique. The two things are opposites and cannot “live” in the same theory.

More and more physicists are finding evidence that the inflationary model is correct. Not only do they make observable predictions, they solve problems that a single Big Bang can’t explain. The bad news is that the nature of cosmic inflation does not allow us to know what happened before. Inflation may have gone on countless times, it may have been for a short period, or even several periods and stages.

At the moment, there is no known way to know this phase of our universe. Was there a singularity before inflation? There’s simply no way to theorize about it – at least not yet.

source: space.comAnd Big thought