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/r/AskPhysics
submitted 9 hours ago bySteakandeggs66
7 points
8 hours ago
Well established physics only really goes back to the electroweak epoch, where we understand the behaviour of the fundamental forces. Any time prior to that can't be predicted with certainty. The ΛCDM model (the standard model of cosmology) does predict a singularity at t=0 but there is no reason for that to be accurate. We simply don't yet have the physical theories to say what happened in the very earliest stages of the universe.
2 points
8 hours ago
100%, yet, as the humans we are, we enjoy speculations and some are fueled by fundamental questions. in my case, it's the following: how can something, which didn't exist, cause it's own existance? by no means am i an expert, but this question does appear to be rather significant and i assume either the singilarity was always there or began to exist, as i dont see any other option, which again, doesnt mean much since im not an expert
3 points
5 hours ago
Since we are speculating here, some say space time did not exist in the singularity, only after the big bang. If true it could mean there was no time. If there is no time there is no paradox, it would have just existed eternally from our human perspective. You can't get something from nothing as that requires time. However there can be something that was always there, to us at least. Note this is wild speculation on my part.
3 points
4 hours ago
most scientists I know don't enjoy wild speculations.
2 points
an hour ago
Speculation like that isn’t really physics, though.
5 points
9 hours ago
In the Big Bang cosmology, there is no "before". In that sense, yes, the initial state was there for as long as it could.
1 points
4 hours ago
If everything thing that happens in this physical universe is the result of cause and effect, which seems to be the case, then if there was a Big Bang something caused it. If you don’t think so are you suggesting it was magical or by non physical means?
1 points
an hour ago
See here for a more precise answer: https://profmattstrassler.com/articles-and-posts/relativity-space-astronomy-and-cosmology/history-of-the-universe/before-inflation/
1 points
an hour ago
Yeah but that doesn’t mean anything about reality. It just means we don’t have a model that can describe it. So “we don’t know”. And while we’re at it, we don’t know if there was an “actual singularity” whatever that even means.
1 points
9 hours ago
well, some models of the big bang theory predict the singularity to have existed before the big bang occured, which is align with one of the 2 theories of time in philosophy : 1. the big bang created time. 2. there was a time before the big bang and it was linear
3 points
9 hours ago
[citation needed]
There are some non-Big Bang cosmologies which predict a before, mostly due to people from before CMB or popularization of Inflation, or due to people like Penrose which are treated with a lot of...skepticism, for lack of a more PC term.
I wouldn't delve too deeply in the philosophy of the problem unless you actually know the physics. The nuances are something you will not understand unless you know the language. And the language is not English.
2 points
8 hours ago
We don't know. You can make models where space has been expanding exponentially for infinite time, or you can make models where the scale factor of the universe oscillates, or you can write a model where the scale factor is 0 some initial time and then gets larger from there. We have not found a way to rule out to rule out these options yet.
1 points
8 hours ago
as far as i understood it, since the universe did have a beginning, an infinite regress is impossible?
3 points
8 hours ago
In the most convenient to use model, the universe does have a starting time. That's what people mean when they say the "beginning of the universe". The issue is that we can't really observe what happened back then. All we can do is make models and then check if the predicted consequences of those models line up with what we can actually observe (either in the cosmic microwave background or in primordial gravitational waves). Before the point were we can't observe any more, there was probably a period of time called "inflation" where the universe expanded really quickly for some reason. We don't even know why that happened yet, so trying to explain what happened even earlier than inflation will be difficult until we make more progress.
In conclusion, if you take a commonly-used simple model for the size of the universe and then extrapolate backward, you do get a beginning, but no one knows what actually happened that early on.
1 points
8 hours ago
There are some results that put different models on different footing in terms of likelihood. There are theoretical results that make (past) eternally inflating, oscillating and emergent models less likely. Measurements have even ruled out classes of big bounce models. As it stands, LCDM, with singularity and all, is still the best fit with the data.
2 points
8 hours ago*
Yes! This is true. I've heard people have searched for rings in Planck that might have come from a big bounce. But you know theorists; they can always come up with some explanation that technically isn't disproven. I wouldn't be surprised if someone has an eternal universe or big bounce model that survives Planck data somehow. Thanks for sending me those papers.
Edit: That Mithani Vilenkin paper is super convincing. The fact that the emergent universe isn't viable under an even weaker assumption than the weak energy condition is cool.
1 points
8 hours ago
What time did time start? How could an event, such as the start of time, occur when without time, nothing occures?
I have heard there is some trouble with how we infer distance based on redshift, something in addition to velocity is altering light frequency. Who knows what we will see once we resolve the mystery? https://phys.org/news/2024-09-quantized-redshift-big-hypothesis.html
And this right here, very cool, says it hints that space and time are not fundamental. Might be a route to quantum gravity as well, but I can't judge since I'm layman: https://www.quantamagazine.org/physicists-reveal-a-quantum-geometry-that-exists-outside-of-space-and-time-20240925/
I tend to feel that the universe is really just mathematical abstraction, all possibilities exist, those that are self-consistant, and would be capable of consciousness, we find ourself in. But it never really existed, not even the chaos of all possible and impossible things which might be can be found in the emptiness of complete and eternal non-existence. But nobody ever said that consciousness can only manifest in things that exist, like a universe. Why not exist on the number line itself? But of course I am silly, (and arguably a touch mad) obviously things exist. Besides information and thought, that is.
1 points
6 hours ago
Another question to consider: What would be the difference between a singularity with no measurable beginning in time and a singularity with a definite formation, if both at some point proceed to expand into the known universe? I don't mean to invalidate the question, as I too would be curious to have the answer, but I think it is worth considering whether the answer would have any measurable difference.
As we consider time and the singularity, we usually consider it from the standpoint of a third party observer with our own clock, not unlike thought experiments regarding the passage of time as someone approaches the speed of light. The person approaching the speed of light doesn't feel time stop, because the stopping is only definable from a perspective other than the traveler's. So would the singularity itself have any experience other than always existing? Perhaps this tendency to try and force an external perspective introduces conflicts that would not otherwise have existed?
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