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My question is the same as the title 'Is there a boundary present for our universe?'
Are there actually any models that use a boundary? (and to be clear, I don't mean being bounded)Shyan said:But whether there is actually some boundary to the universe, we still don't know. Different cosmological models make different assumptions and so we can just work with different answers and see what will come out!
Actually I was using "model with a boundary" interchangeably with "a model suggesting a bounded universe".Bandersnatch said:Are there actually any models that use a boundary? (and to be clear, I don't mean being bounded)
Wouldn't that contradict the notion of universality? Set containing all elements? What would a point outside of the universe even be? Multiverse stuff?Bandersnatch said:Having boundary means that you can name points that lie outside the set - i.e., in 3D space you go one way until you reach the "end" of the universe, beyond which there is something else.
Shyan said:Actually I was using "model with a boundary" interchangeably with "a model suggesting a bounded universe".
I'm not that much into cosmology and can't name different models but I know there are models saying universe is infinite and others saying its finite. So I was referring to this. I thought having a boundary is the same as being bounded. I mean, its the definition of boundary to bound something, right?(or wrong?)
You're mixing the dimensions.elusiveshame said:Correct me if I'm wrong, but couldn't you have an unbounded universe that has a boundary, similar to a balloon (has boundary, but if you go straight, you'll just end back up at the starting point)?
I'm not sure of the various models, but I thought I've seen that mentioned somewhere on PF.
Bandersnatch said:You're mixing the dimensions.
A balloon's surface (a 2D space) is without a boundary and bounded. It's volume (3D) has a boundary and is bounded. Infinite 3D space minus the volume of the balloon is unbounded and has got a boundary.
When used as an analogy to visualise the expansion of the universe, only the 2D surface of a balloon is being considered.
Bandersnatch said:Apologies, I can't quite follow your question. I think there's still some confusion, and not unexpectedly so, considering the nomenclature.
Bounded means basically the same as "finite". Unbounded is then infinite. As in, we don't know whether the universe is bounded or not = we don't know if it's finite or infinite.
Boundary means the same as "edge". E.g., the observable universe is bounded = it's got an edge (beyond which we can't see), but the Universe as a whole doesn't.
Perhaps we should stick to "in/finite" and "edge" as they are less prone to getting confused with each other.
Could you try and reword your question using those terms?
(mind you, this is all talking about space, not space-time)
That is, it has a start and an end? I was of the impression time got way complicated in early-universe stuff so that the question of "before that" becomes too difficult or even pointless.Chronos said:All evidence suggests the observable universe is temporally bounded
The boundary of our universe is not yet fully understood. Some theories suggest that the universe is boundless, while others propose that it has a finite boundary. Currently, there is no concrete evidence to support either theory.
Scientists use various methods, including observations of cosmic microwave background radiation and studying the expansion rate of the universe, to try to determine if there is a boundary to our universe. However, these methods have not yet provided a definitive answer.
This is a difficult question to answer as it is currently beyond the scope of scientific understanding. Some theories suggest that there may be other universes or dimensions beyond our own, but there is no way to confirm this at present.
The Big Bang theory suggests that the universe began as a singularity and has been expanding ever since. This theory does not require a boundary, as the universe can continue to expand infinitely without reaching a boundary. However, some theories suggest that the universe may have a boundary that is constantly expanding with the universe's expansion.
The presence or absence of a boundary in the universe has significant implications for our understanding of the universe. It could change our understanding of the beginning and end of the universe, the laws of physics, and the possibility of other universes or dimensions. However, until there is concrete evidence, it remains a topic of speculation and ongoing scientific research.