The discussion centers on the concept of the universe's boundedness and the implications of infinite regression. The original poster argues that if the universe is defined as everything that exists, it must be infinite; otherwise, it would imply that the universe exists within something else, leading to an infinite chain of containment. Participants highlight that the standard cosmological view, particularly post-Big Bang, suggests that space itself is all there is, challenging the notion of the universe being inside something else. The conversation concludes with the assertion that the observable universe is finite, despite the philosophical implications of infinity.
PREREQUISITESAnyone interested in cosmology, philosophers exploring the nature of infinity, and students of physics seeking to understand the complexities of the universe's structure and dimensionality.
Drakkith said:That's extremely unlikely. The most plausible explanations are that you will either never run into any wall and continue on forever, or you will eventually come all the way around the universe and end up back where you started.
This is it, more or less. It's what we've all been saying all this time. Only with the caveat that the fourth dimension needen't actually exist as anything physical.iDimension said:Or do you mean that the Earths 2D shape lives on a 3D object and our 3D reality lives on a 4D object? Btw the 4th dimension is time or?
You have already been given several examples where you can, such as a ring, a sphere, and their higher-dimensional versions. A ring is a finite 1D object, and if you travel in either direction far enough you do in fact come back to where you started. Do you not understand that?iDimension said:If you are inside a finite object and travel in a direction, you can't come back to where you started right?
Bandersnatch said:This is it, more or less. It's what we've all been saying all this time. Only with the caveat that the fourth dimension needen't actually exist as anything physical.
iDimension said:we are not on the surface of the universe, we are in the universe
I know. I don't think I said we have. I pointed out the analogy was proper, as it gives the meaning to the shape of the 2D surface without it having boundaries, but that the embedding is not required for this to work. A 2-sphere will remain a 2-sphere whether there exists a 3rd dimension or not.PeterDonis said:But the caveat means it isn't what we've been saying all this time; we have not been saying that our universe is embedded in a higher-dimensional space.
PeterDonis said:No. No boundary means no boundary, period.
For example, suppose our universe were, spatially, a 3-sphere. (And suppose, for purposes of this thought experiment, that the universe is not expanding, so the size of the 3-sphere is constant.) Then we could, in principle, send out spaceships to explore the entire 3-sphere, and measure its finite 3-volume, and none of those spaceships would ever encounter a boundary.
I don't think that you understand the geometry being described. A normal sphere that you are used to thinking of is a 2-sphere. It is a 2D manifold. As a 2D manifold it has no boundary, and the radius doesn't even exist in the 2D manifold. I.e. there is no point in the 2D manifold where you would say that you have reached the radius. All that exists in the 2D manifold is a positive curvature which is uniform everywhere. All "spaceships" are always at the radius in a 3D embedding space where the radius would exist.Imager said:When one of the spaceships reaches radius of sphere what happens?
Imager said:When one of the spaceships reaches radius of sphere what happens?
Imager said:(Like the asteroids game does it come back in at the opposite point?)
DaleSpam said:I don't think that you understand the geometry being described.