Who lit the fuse: what happened to the Universe before the Big Bang
The Big Bang is usually considered the beginning of everything that exists today: about 13.8 billion years ago, the observable universe began to grow and develop. But what was it like before the Big Bang? What happened and whether it happened at all? There are a lot of theories on this subject, each of which has its own scientific justification.
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The first thing to understand is what the Big Bang really is. "This is a moment in time, not a point in space," says Sean Carroll, a theoretical physicist at the California Institute of technology. It is possible that the universe was tiny at the time of the Big Bang, Carroll continues. Well, seriously, there's no way to look back in time at things that we can't even see today. All we really know, or rather we want to believe that we do, is that the universe at this moment was very dense, the size of a peach or less, and at a temperature of more than four billion degrees Celsius. Then very quickly it began to lose density. As a consequence of this theory, there is really nothing outside the Universe, because the universe is, by definition, everything.
It is believed that until the first second after the Big Bang, when the universe cooled enough for protons and neutrons to collide and stick together properly, there was a process of exponential expansion, an increase called inflation — just as rapidly as prices are now rising, our universe once grew. This process smoothed out the matter of space-time, which is why the same matter is so evenly distributed in the Universe today.
There is a theory that before the Big Bang, the universe was an infinite band of ultra-thin, dense material that remained stable until, for some reason, the Big Bang occurred. This super-dense universe may have been governed by quantum mechanics, physics on an extremely small scale. For Stephen Hawking, this moment was all that mattered: before the Big Bang, he said, events are immeasurable and therefore undefined. Time and space, according to Hawking, are finite, but they have no boundaries, starting or ending points, just as the planet Earth is finite, but has no boundaries.
According to another, even more, confusing theory, the Big Bang is not the beginning of time, but rather the moment of symmetry. In this idea, before the explosion, there was another universe identical to our own, but with entropy growing toward the past, not the future. A kind of mirror image. Proponents of this theory also suggest that other properties would also be inverted in this mirror Universe. Physicist David Sloan from the University of Oxford published a scientific paper in which he claims that the asymmetries in molecules and ions (so-called chiralities) in the Mirror Universe are the opposite of those in our Universe.
The concept of a "Big bounce" suggests that there may be infinite Big bangs as the universe expands, contracts, and expands again. The problem with these ideas is that there is no explanation for why or how an expanding universe will shrink and return to a low-entropy state.
In 2004, physicists suggested that perhaps the universe as we know it is the product of a parent Universe from which a little space-time has escaped. This is similar to the decay of a radioactive core: when the core decays, it spits out an alpha or beta particle. The parent universe can do the same, except that instead of particles, it spits out the child Universes endlessly.
If all this sounds rather strange, it is because scientists have not yet been able to look back even at the time of the Big Bang, much less at what happened before it. But no matter how far-fetched these or other theories may sometimes look, there is no way without them. "We don't even know what we're looking for," Sean Carroll said, " until we have a theory."