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Oink Honey
Does it?
No. The Big Bang Theory predicts an infinite future (and heat death) for the universe but says nothing about what might have come before inflation, so an eternal universe is possible although I believe it is considered unlikely. It would require some kind of fundamental state change, since the universe before the singularity would have to have been different in some significant way than the current universe, otherwise the singularity would not have happened (we see no singularity in the future of the current universe). I'm not widely read in this but I have never encountered a theory of an eternal universe that seemed to be anything other than pop-sci blather.Oink Honey said:Does it?
Back when I was about 2nd year in high school, my English/Spanish/History teacher knew of my interest in science, and he gave me a paperback book by Fred Hoyle on the Steady-State Universe. He said, "This is an old theory that has now been proven wrong, but it is still an interesting read". I really enjoyed the book, and it motivated me to go on and learn more about the BBT and more modern understandings.Drakkith said:I believe the historical idea of an eternal universe is one that is static, unchanging, and has no beginning and no end. The big bang theory absolutely rules this specific type of eternal universe out, as it says that at every scale the universe is neither static nor unchanging but has a very dynamic existence
Varsha Verma said:I have read
Varsha Verma said:the current model of the universe has no boundary
Varsha Verma said:That is an assumption.
Varsha Verma said:Big Bang says that the the Big Bang itself created space
Varsha Verma said:We know that matter was compacted to a tiny point.
That is a pop-sci presentation authored by a science reporter. It falls well short of the Physics Forums standards. However, the language used is closer to the mark than most popularizations.Varsha Verma said:Here is the reference for space been created by the Big Bang: https://www.space.com/52-the-expanding-universe-from-the-big-bang-to-today.html
Varsha Verma said:Here is the reference for space been created by the Big Bang:
What evidence is there to show that the the current model of the universe is specially infinite??PeterDonis said:Where? Please give a reference.
To be precise, our best current model of the universe has the universe being spatially infinite.
No, it's a conclusion based on evidence.
No, it doesn't.
No, we know that our observable universe, right after the Big Bang, occupied much less spatial volume than it does now. But our observable universe is not the entire universe.
Varsha Verma said:What evidence is there to show that the the current model of the universe is specially infinite??
Varsha Verma said:What evidence is there to show that the the current model of the universe is specially infinite??
@PeterDonis, I think you mean "no non-trivial topology" there.PeterDonis said:Spatially flat + non-trivial topology = spatially infinite.
jbriggs444 said:I think you mean "no non-trivial topology" there.
I wonder what William of Occam would make of this dilemma.bapowell said:I think people are being too heavy handed with claims that data support an infinite universe. It equally supports a closed universe with a radius of curvature much larger than the Hubble scale.
Good point. What does Bayesian model selection have to say? Do you have a good prescription for a prior on the model space?rootone said:I wonder what William of Occam would make of this dilemma.
bapowell said:a prior on the model space?
The assumption referenced by @Varsha Verma is the assumptions of homogeneity and isotropy. Together (with simple topology) they also imply the absence of a boundary, regardless of whether the universe is finite or infinite. So the lack of a boundary is indeed an assumption, but as you say the spatial infinite-ness is a conclusion based on the evidence.PeterDonis said:To be precise, our best current model of the universe has the universe being spatially infinite.
No, it's a conclusion based on evidence.
Dale said:Together (with simple topology) they also imply the absence of a boundary
Here is a picture of a torus. I can see boundaries here. Especially the 'hole' in the middle is a boundary right.PeterDonis said:Actually, I think they imply the absence of a boundary even with a non-simple topology. A flat 3-torus, for example, still has no boundary.
Varsha Verma said:Here is a picture of a torus. I can see boundaries here.
Varsha Verma said:Especially the 'hole' in the middle is a boundary right.
But space is 3 dimensional right? Why have that restriction??PeterDonis said:No, you can't. What you see are artifacts of embedding the torus in a higher dimensional space. The torus itself has no boundary. Someone restricted to moving just on the torus could cover its entire surface and never reach an edge.
No. See above.
Varsha Verma said:space is 3 dimensional right? Why have that restriction??
Varsha Verma said:Why have that restriction?
Varsha Verma said:space is 3 dimensional right? Why have that restriction??
Well there are clever math arguments that it might be more than 3 at very microscopic scale,Varsha Verma said:But space is 3 dimensional right?
You are referring to sting theory, right?rootone said:Well there are clever math arguments that it might be more than 3 at very microscopic scale,
but 3 dimensions is what is obvious. (plus time).
Asking why that is the way it is is pointless, you could ask the same question if there were 5 dimensions of observable space
I have not done even high school physics. So I can't read GR stuff.PeterDonis said:Yes. And if you go back and read my post #24 again, carefully, you will see that I said a flat 3-torus. The picture you gave was of a 2-torus. A 3-torus is a 3-dimensional manifold, like the "space" that we perceive, and it has been suggested as a possible non-trivial topology for the space that we perceive, the space of the universe.
The general definition of a manifold, and its topology, works for any number of dimensions, not just 3. It isn't a "restriction", it's a particular mathematical concept, whose definition you would do well to learn properly before you post further in this discussion.
Varsha Verma said:I have not done even high school physics. So I can't read GR stuff.
Varsha Verma said:you are saying that the 3 dimensional universe we see is not like a 3 dimensional torus or Doughnut?
Varsha Verma said:a flat 3-torus is not like a doughnut, its' a purely mathematical concept which we cannot actually visualize?
Varsha Verma said:why is it called a torus?
Wouldn't assuming a closed universe contradict the evidence that it expands accelerated which supports a open universe?bapowell said:It equally supports a closed universe with a radius of curvature much larger than the Hubble scale.