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id10tothe9
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I hear about the balloon analogy, and that there is no need to say that the universe has a boundary, but is that the only reason or would it be problematic to assume that space-time has a volume and a boundary?
id10tothe9 said:I hear about the balloon analogy, and that there is no need to say that the universe has a boundary, but is that the only reason or would it be problematic to assume that space-time has a volume and a boundary?
id10tothe9 said:I hear about the balloon analogy, and that there is no need to say that the universe has a boundary, but is that the only reason or would it be problematic to assume that space-time has a volume and a boundary?
phinds said:What would happen to physics as we know it at the boundary? How could our physics possibly deal with an "edge" to the universe?
id10tothe9 said:But wouldn't having a boundary be in conflict with the isotropy, ie. the assumption/measurement (which is it?), that the relative velocity of matter would look the same any where in the universe and that there is no center of the universe?
phinds said:basically you pretty much lose your mind trying to figure out how do model a boundary.
QuantumHop said:The expansion of space causes a natural boundary.
Any objects separated in space by a distance that the expansion between them exceeds speed c then they become causally disconnected. In short our visible universe is surrounded by a collapsing event horizon beyond which the known laws of nature cannot communicate.
phinds said:I don't think that's what the OP was asking about at all. I'm not arguing w/ your statement, just saying that it is irrelevant to this discussion.
bcrowell said:Yes, "boundary" has a technical definition here http://en.wikipedia.org/wiki/Manifold_with_boundary#Manifold_with_boundary , and whether the OP knew it or not, #1 was using the term in a way that was consistent with that definition.
HallsofIvy said:An interesting question would be- what would the boundary be made of?
id10tothe9 said:I hear about the analogy, and that there is no need to say that the universe has a boundary, but is that the only reason or would it be problematic to assume that space-time has a volume and a boundary?
PeterJ said:Would I be right in thinking that a boundary to the universe is an absolute, and that physics does not deal with absolutes.
Okay. But I'm assuming it wouldn't be observable for reasons already given.Drakkith said:Any boundary, if it were observable, would be dealt with by science. *Breaks out the shotgun* I'm going to deal with it right now actually.
audioloop said:Friedmann–Lemaître–Robertson–Walker cosmology requieres a connected universe hence a non-trivial topology.
id10tothe9 said:thnx didn't see there is already a second site for , got to look into that..
Tim13 said:A balloon expands against the atmosphere. If the atmospheric pressure were to increase the balloon would shrink.
So what is the universe expanding against? And if there is nothing to expand against wouldn't that mean a rapidly accelerating rate of expansion?
Tim13 said:I agree that the balloon analogy is too simplistic. Like you say it doesn't explain the physics driving the expansion of the universe. And it is potentially misleading because a balloon has a latex "boundary" while the universe may not have a measurable boundary.
id10tothe9 said:But wouldn't having a boundary be in conflict with the isotropy, ie. the assumption/measurement (which is it?), that the relative velocity of matter would look the same any where in the universe and that there is no center of the universe?
PeterJ said:I'm shooting the breeze, by the way, not proposing anything. But I have read clear statements from a few physicists about this, and unless I am misreading them, which is perfectly possible, then we cannot simply take it for granted that extension is real for an fundamental ontology, and would have to bear this in mind when considering the size of the universe and its boundaries.
When we imagine we are seeing into an infinite three-dimensional space, we are falling for a fallacy in which we substitute what we actually see for an intellectual construct. This is not only a mystical vision, it is wrong.
In Leibnitz’s view, the ultimately real, something that depends on nothing else for its existence, cannot have parts. If it had parts, its existence would depend on them. But whatever has spatial extension has parts. It follows that what is ultimately real cannot have spatial extension, …
Tim13 said:I agree that the balloon analogy is too simplistic. Like you say it doesn't explain the physics driving the expansion of the universe. And it is potentially misleading because a balloon has a latex "boundary" while the universe may not have a measurable boundary.
cepheid said:You misunderstand the balloon analogy completely if you think that it has a boundary. The balloon analogy is a 2D analogy for the universe. In other words, the 2D surface of the balloon represents the expanding universe in this model. The 2D surface, of course, has no boundaries, and no centre.
A boundary in the universe refers to a physical or conceptual limit or edge that defines the extent of the universe. It is the point at which the universe ends and something else begins.
Currently, there is no scientific evidence to suggest that the universe has a boundary. In fact, the prevailing theory in cosmology is that the universe is infinite and has no boundary.
Assuming that the universe has a boundary can lead to inconsistencies and paradoxes in our understanding of the universe. For example, if the universe has a boundary, what lies beyond it? How can something exist beyond the boundary of the universe? This raises philosophical and scientific questions that have yet to be answered.
It is currently impossible to definitively answer this question. Our understanding of the universe is limited by our technology and current theories, and it is possible that future advancements may provide new insights into the nature of the universe and whether it has a boundary.
The Big Bang theory does not necessarily imply a boundary in the universe. It simply describes the expansion of the universe from a singularity, but does not address what may lie beyond the observable universe. Some theories suggest that the universe may be part of a larger multiverse, but this is still a subject of debate and speculation.