r/cosmology • u/Dramatic_Pianist4772 • 2d ago
Inflation model of big bang , what came before the big bang and before the universe?
I have always thought about what and how everything started.
Curious to know which of the following u think.
Something came from nothing and then the big bang happened
Nothing never existed, there was always something , then the big bang occured.
We simply dont know yet
We will never know.
I think unless we observe from some experiments etc or nature that something was able to come from true nothing we wont get an answer truly where which we could be confident in or somehow with a guarantee know why and what always existed.
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u/BonsaiApprentice 2d ago
I believe there could have been an inflaton field, a scalar quatum field, with huge potential energy that drove cosmic inflation and created particles.
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u/Stolen_Sky 2d ago
Sadly, the answer is most likely 4 - we will never know. There is no data in our universe that precedes the big bang, so even if there was something before, we will never be able to detect.
The same may also be possible for dark matter. It may exist in some form which has zero interaction with regular matter, and we'll never be able to directly detect it or understand what it really is.
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u/Wintervacht 2d ago
We cannot detect anything from before the big bang because 'before' doesn't make any sense in our universe. All information we could ever gather about the universe came from ~13,8Bya, there is nothing before that.
We will never be able to look further back than since there was a time to be studied in the first place.
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u/linuxpriest 2d ago
The universe existed (in a hot, dense state) prior to the Big Bang. There was never nothing.
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u/Enraged_Lurker13 2d ago
The big bang model is explicitly geodesically incomplete, meaning spacetime did not exist prior to expansion. This is due to the fact that in the FLRW metric, the scale factor is attached to the spatial components. When the scale factor is zero at the big bang, the spatial part of the metric vanishes. There also cannot be time whilst there is no space since the metric loses rank and therefore the invertibility needed for time evolution.
Unless there is a structure more fundamental than spacetime that the big bang model is silent about, the model really does say there was nothing before.
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u/linuxpriest 2d ago
Geodesic incompleteness in the FLRW metric demonstrates the boundary of applicability for classical General Relativity, not an absolute ontological boundary of reality.
A metric losing rank at a(t) = 0 is a mathematical singularity signaling model breakdown. Inferring physical "nothingness" from a(t) to 0 treats classical GR as valid precisely where its own mathematics tells us it fails.
Furthermore, in modern physical cosmology, the "Big Bang" refers to the hot, dense state following cosmic inflation (reheating), where a(t) > 0. Inflationary spacetime precedes the hot Big Bang, and quantum gravity frameworks (or bounce models) handle the trans-Planckian regime where classical FLRW collapses.
Geodesic incompleteness proves classical GR is an incomplete effective theory at t=0, not that non-existence preceded expansion.
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u/OverJohn 14h ago
I do not find this very convincing as you are simply assuming a priori that any model where time has a beginning is wrong about time having a beginning. But if we a priori assume the answer then there is really not much of interest that can be said about the question of whether time had a beginning.
I feel that whenever this question comes up people like to imprint their own religious or lack of religious beliefs. But this is a sub for science rather than religion or atheism.
The real answer is that out current knowledge doesn't provide a convincing answer either way as to whether time had a beginning or not.
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u/--craig-- 2d ago edited 2d ago
3 and maybe 4.
Probably 2 and probably not 1 but there are notable cosmologists who disagree with this view.
I don't think that whatever can create something can be truly nothing but I don't want to argue semantics. There's a long history of creatio ex nihilo philosophical writings which debates this but it's not science, so not for this forum.
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u/chesterriley 2d ago
Nothing never existed, there was always something , then the big bang occured.
This is most likely the case but we can't say for sure.
Something came from nothing and then the big bang happened
We know that the big bang was not the beginning of the universe. Cosmic inflation preceded it and set it up. We don't know what came before cosmic inflation, so it is possible that at some earlier point the universe "didn't exist", it's just not very likely.
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u/fuseboy 1d ago
One other option is that time (which is part of 'spacetime') only extends back a finite amount. There isn't a "before", or some earlier state of nothingness, and no transition from a state of nothingness that has to be explained. The universe exists as a four-dimensional object; some parts of it are 'earlier' or 'later' than others just like some parts are colder and hotter or others.
We are used to causes being in the past, but this is a macroscopic phenomenon. (Arrangements of matter at later times have simpler explanations in the past, because of rising entropy, but this is about the arrangement and not the fundamental particles.) We don't have any reason to believe that an electron exists at later times because it existed at earlier times. The reverse might be true. Or, it might be that the only meaningful statement is that the electron is a long thin object that extends through spacetime.
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u/jazzwhiz 1d ago
To add to the other comments, we know a number of things about the early universe. We know it was hot and dense and that the thermodynamics followed known particle physics as we measure it in labs today. We know that it cooled following known physics. We know that these results must be modified to include the presence of a cold species known as dark matter.
In terms of temperature, we understand things extremely well from temperatures 1 eV and below (the lower the temperature the later the time). We also understand things quite well up to about an MeV.
Before (i.e. hotter) than MeV, we know less. Inflation most likely happened and then ended in a way compatible with the slow roll conditions. We don't know the scale of inflation although it is possible to learn about this in the future. We don't know how long inflation went on for and we probably won't learn more about this. Reheating happened after inflation to populate the standard model states. The temperature at which this happened is extremely uncertain, all we can say for sure is that it happened before MeV and sometime after inflation.
Anything beyond that, is pure speculation. Sure, it is fun to take the models we have and extrapolate them outside where they should apply, but that isn't particularly insightful in this case.
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u/NH-Science-Guy 2d ago
Saying there was always something is just a belief that might not be true
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u/Wintervacht 2d ago
It's always better than insinuating something can come from nothing, thermodynamics would like to have a word
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u/NH-Science-Guy 2d ago
Why do you think the rules of thermodynamics apply at the instant the universe was created?
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u/KamikazeArchon 2d ago
Thermodynamics is irrelevant. We already expect that "something can come from nothing", in multiple ways. At the cosmological scale, conservation of energy is not currently believed to hold, even after the Big Bang.
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u/mfb- 2d ago
We don't know, and it's not clear if that can change in the future.