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Evidence
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That's nonsense. You think some massive amount of matter just materialized from nothing into a singular point? How do you think all the stuff managed to get there in the first place?
Not just matter but time as well. That's what they were referring to. There is no "before time".
Regarding your rethorical question: go find an answer and you're sure to win the Nobel Prize.
Absolutely nothing is a reliable constant except the speed of light.
But the speed of light changes. It can be slowed down. It just doesn't change while moving through outer space (a vacuum). The maximum speed is the constant.
It's only something we can speculate about. It represents a limit to our ability to gather any evidence that might validate those speculations. We can't say what happened before it, because time itself was one of the things that popped out of the big bang. What would "before" even mean if time didn't exist?
Even if time and matter did exist in some sense, we can't get any evidence for it. We can't make any kind of useful theory about it. At best, we can make wild guesses.
We could also just say "we don't know what it was like". Russell's Teapot suggests we should instead say there was nothing, because we can't prove there was anything.
There's no evidence to point to the big bang as being the very beginning, though. There may well have been a billion big bangs before this one. Each one taking so long to reset and start anew that to us, it might as well be seen as about infinity. Humanity outright doesn't have the knowledge of what happens on extremely large or extremely small scales. We don't really have a clue for what actually made space start to expand in the first place, so we don't know if it's ever happened before, or even if it happened anywhere else at any other time but outside of our observable universe.
The works of Roger Penrose have shown that it's conceivable or potentially even provable that at the very largest scales of time and space, there is no meaningful difference between the accelerating "cold" end of our universe and the collossal expansion that began the universe as we know it, and in fact those two states are perpetually cycling, birthing new universes from the explosion of old ones. This is based on the idea that when there is no more physical mass in the universe, you can look at the universe from a reference frame that only looks at the geometry of the energy expanding through space and it's identical to the beginning states.
I would recommend PBS Spacetime youtube channel for a lot better explanations of conformal cyclic cosmology than my feeble mind can try to relate.
Maybe there were other big bangs, but we need evidence of that, and that evidence doesn't exist.
Jyst saying "but we don't know" isn't a replacement for evidence.
There's no evidence that time started at the big bang, either. So it's silly to say.
Not how it works.
"Time exists" is a positive statement. We need evidence for positive statements. There is no evidence of time until the big bang.
It wasn't matter that did the banging, it was space-time itself. Have you heard how we know that the universe is expanding? Well we can extrapolate backwards and find the point in time where space-time was just a point: "the big bang". Not only was there no space-time for matter to exist in before the big bang, there was no concept of "before" because that word only makes sense in the context of spacetime. So yeah, the person you're replying to is right, "before the big bang" is a nonsense phrase.
They keep finding inconsistencies to that. Groupings and radiation and gap distances that don't line up with the expansion expectations.
Then the other more applicable point is that what makes you think "the big bang" was the first big bang? You think mass and entropy and radioactive decay and all this shit in the nothingness of space all started with "the big bang" but it only happens once and then in a ridiculously long time from now when everything reaches absolute 0 and there's no energy left anywhere, that it's just done? A one trick pony?
Well what if it all eventually manages to head back to its origin point after that and it makes another big bang that kicks off again?
Well, again you're using terms of time to describe the birth of time, so no that's not what I think because that statement doesn't make sense. But I'm being pedantic, I'm sure you meant "what if our's wasn't the only big bang?" And to that I can confidently say "maybe?". It's an interesting question but it's just not a scientific question. According to big bang theory, our universe, space-time and all the matter and energy in it, began with the big bang and we still exist inside it. Other big bangs, if they exist in some higher medium, are simply outside our scope. We just can't design tests to answer those questions. Best we can tell scientifically is where our universe started.
Again maybe? You're kinda putting words in my mouth. Idk if our universe is the only one, it's impossible to know. My original point was that time as defined by general relativity could not exist before the big bang because it was itself a product of the big bang.
What I meant by "what if it wasn't the first big bang?", was that what if it wasn't the first of our own universe? I mean what if space will at some point stop expanding and start contracting. Pull everything back close together again. Then theres another expansion just like what we're currently in now. The best scientists, physicists, and mathematicians haven't been able to work out a lot of major thing about our universe or how it works or even if it's flat or folded in on itself yet. The data and tests/measurements don't exist yet. So until that can get worked out into a theory, it's silly to say time began at the expansion.
Last I heard scientists were leaning more toward the ever-accelerating expansion "heat death" theory then the expansion-to-contraction "big crunch" theory, but it's not set in stone yet. But even if "big crunch" came out on top, assuming that the life of the universe is cyclical is pure conjecture. It could be right, but it's unprovable, so we'll never know.
As for the existence of space-time before the big bang, I don't know what to tell you, I'm just quoting theory. By definition, the big bang is when space-time came to be. If the big bang was the result of an ancestor universe's big crunch, we can't assume that the same space-time carried over, let alone that the ancestor universe even had something analogous to space-time. Barring some insanely massive breakthrough, it's simply unknowable.
Based on the comment you're replying to, I assume they would say "no, nothing materialized from nothing because there wasn't a 'before' in which nothing could have existed"
What makes anyone think "the big bang" has only happened once?
I'm not a physicist, I don't know one way or another. But it's possible that there's a leading explanation for the formation of the universe based on a mathematical model that predicts exactly one big bang.
Physicists don't even know why it started expanding to begin with. We also don't know if there's anything outside of our own universe. We also don't know if our universe is curved and folded in on itself, which would make several mathematical calculations for the size of the universe and what was going on with expansion a bit easier to try and work out (I'm also not a physicist. These are just things ive read about) or if it's flat. Their best measurements right now is that it's flat. But they still aren't sure, because they don't know how big space actually is right now. If it's big enough, it could still be curved in on itself, but we just can't measure the flatness of two points far enough apart from each other to notice the curve. An example I given was that it would be like trying to show the earth was round by measuring an area of a sandbox.
You're still thinking like a meat-monkey. There are stranger states out there than one can imagine, and that's not hyperbole. There was no causality before expansion, because there was no meaningful interactions or spacetime in which interactions can occur.
You're always going to have a hard time imagining this, because again, you are a human. We all are, none of us can imagine states of the universe without time and space.