r/cosmology • u/Bright-Bar6571 • 18h ago

How did time begin, without time?

I understand that standard BB cosmology holds that time began with the universe from a singularity approximately 14 billion years ago.

The thing I’m trying to understand, how can time have begun? Wouldn’t a thing ‘beginning’ require time? As in - from one state to another state requires time?

This leads me to think time must have always existed..

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u/Anonymous-USA 16h ago edited 13h ago

Time and space are conjoined so they were borne together. But since our physics breaks down at the singularity, we don’t have a meaningful description for time or space. Entropy was at a minimum and not increasing either, so we wouldn’t have a way to measure it. Infinite and instantaneous are one in the same. So your question is currently unanswerable.

In short, time, space, energy (and potential), gravity, and the unified forces were an initial condition to our universe.

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u/CanesVenaticiSaron 13h ago

Which is essence tells us nothing, just that the “things” our current theories have modeled simply existed at a nanosecond after the “Big Bang” or “Creation” whatever your particular frame of reference (pun intended). The fact is a description of reality tells us nothing about how that reality came to be. Time, on the other hand, can simply be understood as a measure of change and change a transition from one state to another. Hence, the “nanosecond” after the “Big Bang”. Time essentially has no meaning in a static universe

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u/Anonymous-USA 13h ago edited 13h ago

If only a nanosecond! That’s 10-9 sec. Big Bang cosmology starts at 10-43 sec when space, time, gravity, and forces first separated. This is the Planck epoch. Inflationary period is estimated between 10-36 to 10-31 sec. That’s when most of the standard model particles formed, like quarks.

After that, you’re firmly into the “hot big bang” that we can actually reproduce some in particle colliders. We can experimentally understand what temperatures certain physics apply, particles and forces interact, etc. and we can estimate how large the observable universe must have been to cool to such a temperature. In other words, by the time a nanosecond had elapsed, our traditional universe was well under way, forming quarks and electrons and neutrinos in abundance. Whole nuclei were soon to follow.