“Momentum spontaneously begins out of null-where/null-when/null-thing, and the universe exists because not existing is an unstable condition and isn’t allowed by the laws of physics.”
Here is a list of the words and phrases in that sentence that involve time—that depend on a temporal experience in order to have meaning.
The laws of physics
We are left with “null-where/null-when/null-thing”, and just naming that unthinkable concept has a context, and context is temporal, so it’s ringed in by time. Just by thinking of it, it becomes effectively a temporal concept.
It’s like the relationship of an event horizon to its black hole. What’s in the black hole is forever unknowable to us, and us to it, but the actions at its surface give it a unique physical presence in our universe. Thinking about "The Null" is temporal.
We cannot think or know anything outside of time. And non-existence of the universe is outside of time. Saint Augustine devotes about three pages of the Confessions to time and what lies outside of time, which he calls eternity. You should look it up. I don’t think we know any more today than what he said fifteen hundred years ago. His famous concluding quote is “What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know.”
So suddenly, I’m talking about time. I started with dimensions and space, and then motion, and spent all that time (ouch!) on momentum. What gives? Is time the fundamental problem?
Remember, I defined time as motion. Motion requires mass and space because something has to move and it has to have somewhere to go. Mass doesn’t exist without motion. And motion requires time. It’s all circular. Momentum is the concept that combines all four: time, mass, motion, and space.
It doesn’t matter where I start, or which one I focus on. Talking about any one of them implies all of them, implies momentum. The wholeness of the concept of momentum is what is fundamental.
So where does momentum come from?
This is where I end: We do not know and we cannot know.
Physicists can devise models that fit our observations, and we can extrapolate into the past (sort of) and define a "time" at which everything began, but philosophically it's a dead end. Momentum can't begin without time, or space, or mass, or motion. Momentum can't begin without momentum.
It’s not because we don’t have enough information or because we aren’t smart enough. We don’t know because the question we are asking is meaningless. As Stephen Hawking commented about a similar question, it’s like asking what’s north of the North Pole. Northness ends at the North Pole because everything is south from there, not because we need more information.
I know this can seem over simplistic, and I'm open to being convinced otherwise, but the concept of anything existing with time and nothing else, waiting eons for the moment that null momentum turns into plus momentum and minus momentum equals zero momentum, just seems to me to be shot through and through with our human temporal prejudice. I don't buy it. Momentum and time are one. The whole ball of wax or nothing.
So what’s the point of all this?
Per Plato again, knowing that I don’t know and can’t know means I know more than I did before...and more than most.
Note that this discussion is all about understanding, which is a particular type of knowledge. It's thinking knowledge. There are other types of knowledge that don’t ask or answer in the same way at all. We use them all the time without thinking. They help us when understanding fails. They also lead us into some of the most destructive and unwanted actions of which our species is so sadly guilty.
Why? I think it’s because we carelessly mix unthinking knowledge and thinking knowledge in unproductive ways. But…that’s for another time.