No matter how we look at the Universe — at low temperatures or ultra-high energies, from our own backyard to the most distant recesses of the observable cosmos — we find that the same laws of physics apply. The fundamental constants remain the same; gravitation appears to behave the same; the quantum transitions and relativistic effects are identical. At all points in time, at least for the parts of the Universe we can observe, General Relativity (governing gravity) and Quantum Field Theory (governing the other known forces) appear to apply in the exact same form we find them appearing here on Earth. But has it always been this way? Is there a time where the Universe didn’t have the same quantum fields in it, or perhaps no quantum fields at all? That’s what Patreon supporter Chris Shaw wants to know, asking:
“When did the first quantum fields form in the universe? Have they been there since the Big Bang or even from the inflationary period before?”
Perhaps surprisingly, quantum fields are there even under conditions where you might not expect them. Here’s what we know so far.
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However, one thing that is certain is that quantum fields of some variety must have still existed during inflation. They may or may not be the same quantum fields that exist today, and there may have been additional quantum fields over and above the ones we know of and have today, but they had to exist. How do we know? Because the fluctuations that we see in the Universe, the ones that gave rise to the cosmic structure that eventually formed, match exactly the ones predicted to arise from fluctuating quantum fields that existed during inflation.
Those fluctuations, the ones that normally occur on tiny, microscopic quantum scales, get stretched across the Universe during inflation, get translated into temperature and density fluctuations at the start of the hot Big Bang, and imprint themselves irrevocably onto the Universe. The fact that we’ve observed these fluctuations and their consequences tell us, quite definitively, that those quantum fields did exist during inflation.
For as long as spacetime has existed, some version of quantum fields must have existed as well. But whatever occurred in our Universe prior to the final tiny fraction-of-a-second of inflation can never be observed or accessed from within our observable Universe. In the absence of evidence, we are bound to probe the limits of what’s known and match them up with whatever’s left as a possibility. However fun and instructive it may be to speculate, the truth is we simply don’t know.
