Since when does spacetime exist?

This new galaxy was generated just a few hundred million years after the Big Bang.

The spacetime described by current physics began just after the Big Bang. But let's go by parts, space-time as science understands it is a model that combines both concepts as a single inseparable continuum in which all physical events in the universe occur. As for the Big Bang, it is the great explosion with which the cosmos began. But the Big Bang is what in science we know as a singularity, which means that physics, as we know it, does not work there. So we can't even talk about spacetime at that point.

But we can do it from an infinitesimal fraction of a second later. And that is so because from then on we already have a language to talk about it. That language is physics and mathematics that allow us to explain it, model it, and discuss it. There, after that infinitesimal fraction of a second after the Big Bang, space-time began. To understand everything a little better, one must understand that, in the singularity, the universe was very, very small. It was so small that classical physics does not help us to analyze it, we need quantum physics. At the same time it was also very massive, it contained everything we know of the cosmos today and everything that the cosmos will always contain. To understand the appearance of space-time we need Einstein's theory of general relativity. But here we have a problem, we cannot combine both physical theories, quantum and general relativity, under the conditions of the universe at that time. The two theories do not match and we do not have what is called a unified theory, that is, a model that unites them.

The conditions of the cosmos at the time we are talking about, if we look at its size, it would be 0.00000000000000000000000000000000001 meters (0, followed by 34 zeros and a one) which was the space that the cosmos occupied in the fraction of a second when it started space time. In terms of time, this occurred at 0.0000000000000000000000000000000000000000001 seconds after the Big Bang (0, followed by 42 zeros and one).

We do not yet have a well-defined theory, but we do have enough indications to think that in that interval space-time was very extended, so much as to reach the approximate size of an orange

Between that time and 0.00000000000000000000000000000001 seconds after the Big Bang (0, followed by 31 zeros and one) we have strong indications that a super accelerated expansion occurred. We do not know well the physics of this expansion, we do not yet have a well-defined theory, but we do have enough indications to think that in that interval the space-time extended a lot, so much as to reach the approximate size of an orange. From that moment on, we do have a very good description of everything that has happened to the cosmos in the 13.8 billion years that have elapsed since then.

So to answer your question I will tell you that space-time began after that tiny fraction of a second after the Big Bang occurred.

Licia Verde is a cosmologist and theoretical physicist, ICREA professor at the Institut de Ciències del Cosmos of the University of Barcelona.

Question sent via email by Luis Soto

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