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awktrc
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How do we know that the Big Bang did not expand into a preexisting void?
What is the justification for this knowledge/belief?
What is the justification for this knowledge/belief?
If you examine what a universe would look like "from the outside", so to speak, it would look like a black hole. Because the new universe looks like a black hole from the outside, it is unable to expand into the pre-existing universe. But it has no trouble expanding from the perspective of somebody within the new universe.awktrc said:How do we know that the Big Bang did not expand into a preexisting void?
What is the justification for this knowledge/belief?
granpa said:lets assume that it did expand into a preexisting space. Then where did that space come from? Another Big Bang? Did that Big Bang expand into a preexisting space?
At some point there had to be a Big Bang that created space itself.
Chiclayo guy said:If cold is the absence of heat, and dark is the absence of light, why can’t an infinite and eternal space be the absence of matter? To me asking the question where did space come from doesn’t make any more sense than asking where did dark or cold come from. There does not seem to be consensus on this forum as to whether space existed prior to or was created by the bb.
Okay…back to lurk mode for me.
Tom
zhermes said:The BB didn't expand "into" anything (in the way you're suggesting). Space(-time) itself is what was expanding, not just the matter in it. It doesn't make sense to describe it as expanding "into" something.
awktrc said:How do we know that the Big Bang did not expand into a preexisting void?
Chronos said:Painting on a canvas is a classical argument - suggesting matter must be superimposed over a preexisting 'space'. There is no valid theoretical or observational evidence supporting that premise.
justwondering said:And it still may safely be assumed that no information could 'pass' through the Big Bang event.
Dmitry67 said:Oldfart, our universes our 4 dimensional, so they can coexist in higher dimensional space without any intersections. That hypotetical super-space is called BULK. However, let's wait for TOE to get clearer picture.
For the classification of types Universes in Multiverse (I, II, II and IV) google Max Tegmark Mathematical Universe Hypotesis.
twofish-quant said:If the universe was spreading into a void, you'd see the effects of the void. You don't.
Chronos said:There is a word they use in physics for anything that is entirely uninteractive - nonexistent.
twofish-quant said:Let me rephase that to something stronger. The observations say that for the parts of the universe we have any data of, that the universe is not spreading into a void. If the universe was spreading into a void, you'd see the effects of the void. You don't.
Chronos said:It makes more sense if you picture expansion creating its own space as it evolves, and that space is created in the vast gulfs between galactic clusters. Empty space is endowed with a peculiar property called dark energy, and this dark energy is accelerating the expansion of the universe.
bcrowell said:Our observations can only reach out to a certain distance. If all we know is that we don't see a surrounding void, that doesn't seem like a very strong argument to me, since maybe we just don't see the surrounding void because it's too far away.
On the other hand, nobody has ever found a model *with* a preexisting void that fits 1, 2, and 3. That makes us suspect that there is no preexisting void.
In particular, if GR is correct, then timelike world-lines can't be extended backward through that singularity.
I think we should distinguish logically between a large but finite void and the case where there is an infinite, preexisting, asymptotically flat void. The latter is really what the OP was asking about.twofish-quant said:Who is "us"? All I can say is that with our current knowledge of the universe, there are no detectable anisotropies and inhomogeneities within 60 billion light years. There could very will be massive voids 1.2 trillion years out.
It is certainly easier to do calculations with an assumption of homogeneity and isotropy, but it's also impossible to cut and paste a Big Bang singularity into an infinite, preexisting, asymptotically flat void. A BB singularity, which we know exists because of the Hawking singularity theorem, has geodesic incompleteness, so it can't arise out of a preexisting void.twofish-quant said:I can also say that when I do my GR calculations I *assume* that there are no voids at all, because it makes the math easier.
True. Everything I'm saying is in the context of classical GR.twofish-quant said:The trouble is that it is known that GR is wrong once you get to Planck's length.
Chronos said:If the universe is surrounded by an infinite void, it is difficult to explain why the cmb intensity is identical in every direction.
Chronos said:If the universe is surrounded by an infinite void, it is difficult to explain why the cmb intensity is identical in every direction.
This doesn't actually make a difference. The thing is, space-time is not some absolute thing, so even if you have two big bang events born within some other space-time separated by some distance, those two big bang events still can never interact in any way, shape, or form. The new space is generated within each individual event, and cannot effect either the parent universe or anything else.nunogirao said:Imagine you have two BigBangs in the preexisting void, separated by a distance greater than the actual size of our universe.
Chalnoth said:This doesn't actually make a difference. The thing is, space-time is not some absolute thing, so even if you have two big bang events born within some other space-time separated by some distance, those two big bang events still can never interact in any way, shape, or form. The new space is generated within each individual event, and cannot effect either the parent universe or anything else.
However it started, space most definitely expanded. It may have started from a pre-existing space-time, as I mentioned. But entirely new space is produced as the universe expands. The expansion of the new universe cannot ever possibly be observed in the old universe.nunogirao said:I don't know if the space-time was created in the BB or if it is something that ever existed (and there we go to the «when/why» it was created).
From what we know of high energy physics today, it definitely appears that different regions of space-time, both within a universe and between them, may well have different low-energy laws of physics. We really can't say much at all about the extent of this variation just yet. For now, the only variation from place to place that we have at least some confidence of is the electroweak symmetry breaking event, which appears to have a particular parameter that is random and varies from place to place (as in it is likely different some place far from our observable universe, but is the same everywhere we can see).nunogirao said:And, could it be possible that different types of universes (with different rules) populate the same void?
Well, unless you want to talk about higher-dimensional theories like string theory, it just isn't sensible to talk about another universe existing transverse to our own. In General Relativity, our space-time is self-contained and cannot overlap with any other universe.nunogirao said:Could a «neutrino type» universe exist that just transverse our universe, without influencing it?
awktrc said:How do we know that the Big Bang did not expand into a preexisting void?
What is the justification for this knowledge/belief?
awktrc said:How do we know that the Big Bang did not expand into a preexisting void?
What is the justification for this knowledge/belief?
Chronos said:If the universe is surrounded by an infinite void, it is difficult to explain why the cmb intensity is identical in every direction.