What came before the Big Bang? what happened before the big bang? Since time is thought to have started at the big bang, asking what happened “before” is like asking what is North of the North pole? It may have no meaning. But there are three good theories.

One is the idea of a cyclic or ‘bouncing’ universe, where the Big Bang is just the latest of many beginnings, in an eternal series of cosmic expansions and contractions. The universe begins from an initial tiny state (a singularity?) in which all the matter and energy of the universe is contained in an infinitesimally small volume. The universe then expanded, and after 13.8 billion years is at its current state. It will keep expanding for perhaps billions more years, and then it will contract for another long period or time until it is tiny again. And then the cycle repeats itself over and over again for eternity.

But the current rate of expansion of the universe is not slowing down. It would need to stop and reverse at some time in the future. But that’s not what we observe. If the lambda cdm model is incomplete, then the cyclic model could be correct.

Another hypothesis about what came before the Big Bang is a multiverse, where our universe is just one bubble in a frothy sea of universes, each with its own laws of physics. There are many types of multiverses, but this one stems from the theorized concept of eternal inflation.

The idea is that there exists an infinite spacetime that is expanding faster than the speed of light. This is what we call inflation. Inflation is believed to have occurred in our universe shortly after the Big Bang for an extremely short period of time But in this short time, the universe expanded by a factor of 10^78 in size. Since quantum mechanics ensures that there will always be some randomness, it’s possible that inflation could last a bit longer or shorter than expected in different parts of the universe.

In the 1980s, Paul Steinhardt, Andrei Linde and Alexander Vilenkin realized that the exponential expansion of cosmic inflation, although it stopped in our part of the universe, could continue in other unobservable parts of the universe. And if that’s the case, then the universe we are familiar with, may be a very small fraction of all that exists. It could have stoped in other parts of the universe, forming other bubble universes. This could go on for eternity. Our universe would be nothing but a very tiny part of an unimaginably larger whole.

Another theory is that our universe could have come from nothing. At the subatomic level in empty space, particles are popping in and out of existence all the time. These are virtual particles. They borrow energy from the vacuum and give it right back so quickly that no conservation laws are violated. Energy is conserved.

Cosmologists have speculated that even in a universe where no matter, space or time exists, as long as the laws of quantum mechanics exist, spacetime itself could have emerged in a quantum fluctuation, because in quantum mechanics, anything that is not forbidden by conservation laws necessarily happens with some finite probability. If we live in a closed universe, like a sphere is a closed universe, then all the positive energy of matter is perfectly balanced by gravity, which has negative energy. So, just like with virtual particles, no net energy is created.

Just as virtual particles come in and out of existence without breaking any conservation laws, a small empty space could come into existence probabilistically due to quantum fluctuations. And since time is connected to space, time would follow in this nucleation.

A scientific paper authored by 3 Chinese physicists, titled “spontaneous creation of the universe from nothing,” was published in 2014, which showed a mathematical proof of how this could happen.

Why can’t we turn the clock back just a little bit further and figure out what happened just a tiny fraction of a second before the Big Bang? because current understanding of physics breaks down at the singularity, the moment that predates the Big Bang.

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