How did the universe come into being?
We know we live in an expanding universe. This means that the entire universe is getting bigger every day. It also means that our universe was smaller in the past than it is today.
Rewind the tape far enough, and physics suggests that our universe was once an infinitesimally small, infinitely dense point — a singularity.
Most physicists believe this point expanded in the Big Bang, but since all known physics collapses under the extreme conditions that existed in our universe’s infancy, it’s hard to say with confidence what happened in those earliest moments of the universe happened.
Related: Our Expanding Universe: Age, History and Other Facts
Back in time
For most of the history of the universe, it has been littered with similar celestial objects as they exist now – they were just closer together.
For example, when our Universe was less than 380,000 years old, the Universe was about a million times smaller in volume than it is today, and had an average temperature of about 10,000 Kelvin. It was so hot and dense that it was a plasma, a state of matter in which atoms are ruptured into protons, neutrons, and electrons. However, we encounter plasmas in many other situations in space and on Earth, so we have a pretty good understanding of how they work.
But the further we go back, the more complex the physics become. When the universe was only a dozen minutes old, it was an intense soup of protons, neutrons, and electrons, still governed by the same physics we use to understand atomic bombs and nuclear reactors.
However, if we look back even earlier, things get really sketchy.
If we try to understand the universe when it was less than a second old, we have no physical theory that can cope with the insanely high temperatures and pressures that the universe has been subjected to. All our theories of physics break down and we have no understanding of how particles, forces and fields work under these conditions.
Birth of the Singularity
Physicists can chart the growth of the cosmos using Einstein’s general theory of relativity, which links the contents of the cosmos to its history of expansion.
But Einstein’s theory contains a fatal error. If we follow general relativity to its ultimate conclusion, then at some finite time in the past our entire universe was crammed into a single, infinitely dense point. This is known as the Big Bang singularity.
The singularity is often referred to as the “beginning” of the universe: but it’s not a beginning at all.
Mathematically, the Big Bang singularity doesn’t tell us that the universe began there. Instead, it tells us that general relativity itself has collapsed, losing its predictive and explanatory power.
Physicists have long known that general relativity is incomplete. It cannot explain gravity at high magnitudes or at small scales, known as quantum gravity. In other words, to fully understand the earliest moments of the universe, we need new physics.
A question for eternity
Unfortunately, we currently lack such physics. We have several candidates for quantum gravity, such as string theory and loop quantum gravity, but these theories have not yet been fully developed, let alone tested.
But if any of these theories are correct, they can tell us interesting things about the early Universe.
In the case of loop quantum gravity, the singularity is replaced by a finite-size block of spacetime. In string theory, on the other hand, our universe emerges from a “landscape” of possible universes. It is also possible that our Big Bang exists as just one of an infinite series of universes endlessly multiplying in a multiverse. Only further advances in theoretical physics will help to clarify the ambiguity of these possible ideas.
But there is another problem: we can never know what caused the big bang. In its earliest moments, even our notions of time and space collapse. At such extreme scales, normal, everyday concepts like “beginning” and “before” might not even make sense.
Originally published on LiveScience.
https://www.space.com/how-was-the-universe-created How did the universe come into being?