Infinite Regress | Why is everyone telling me I am wrong?

  • Thread starter Thread starter iDimension
  • Start date Start date
  • Tags Tags
    Infinite
Click For Summary
The discussion centers on the concept of whether the universe is infinite or finite, with the original poster arguing that if the universe encompasses everything, it must be infinite. Friends counter that infinite regression leads to paradoxes, suggesting that if the universe is contained within something else, it creates an endless chain of layers. They emphasize that the universe may be finite and still be unbounded, similar to the surface of a sphere, which is finite yet has no edges. The conversation also touches on the limitations of human comprehension regarding higher dimensions and the nature of space. Ultimately, the debate reflects ongoing philosophical and scientific questions about the universe's structure and boundaries.
  • #31
Thread closed for Moderation...
 
Space news on Phys.org
  • #32
The thread is reopened with a reminder to keep the conversation courteous.
 
  • #33
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.

But how is this possible sinse we are not on the surface of the universe, we are in the universe. If you are inside a finite object and travel in a direction, you can't come back to where you started right?

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?
 
  • #34
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?
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.
Everywhere in this thread where dimensions were mentioned, they were meant to be purely spatial.
 
  • #35
iDimension said:
If you are inside a finite object and travel in a direction, you can't come back to where you started right?
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?
 
  • #36
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.

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.

iDimension said:
we are not on the surface of the universe, we are in the universe

There is no "surface of the universe". That's the point. The universe, spatially, is just a 3-dimensional space without a boundary. It could have a finite volume, in which case it is topologically a 3-sphere, or it could have infinite volume, in which case it is topologically what we ordinarily think of as "3-dimensional space". But either way there is no boundary and no "surface".
 
  • #37
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.
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.
 
  • #38
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.

Hi Peter

When one of the spaceships reaches radius of sphere what happens? (Like the asteroids game does it come back in at the opposite point?)
 
  • #39
Imager said:
When one of the spaceships reaches radius of sphere what happens?
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.

A 3-sphere is a 3D manifold with no boundary and with a positive curvature which is uniform everywhere. There is no radius in the 3-sphere.
 
  • #40
Imager said:
When one of the spaceships reaches radius of sphere what happens?

When you fly halfway around the Earth what happens? Do you reach a boundary?

The case of a spaceship flying around the universe is the same, just in a 3D sphere instead of a 2D sphere. The spaceship can fly in the same direction indefinitely and will never encounter a boundary: eventually, it will return to its starting point, having circumnavigated the universe.

Imager said:
(Like the asteroids game does it come back in at the opposite point?)

Not in a 3-sphere. If the universe had a different topology, called a 3-torus, then this would happen (or at least, this would be one way of describing what would happen). The asteroids game takes place in a 2-torus (or the computer representation of one, anyway).
 
  • #41
DaleSpam said:
I don't think that you understand the geometry being described.

You are right, I wasn't even close! One look at wiki was a mindblower! I think it is time for a beer or three...
 

Similar threads

  • · Replies 20 ·
Replies
20
Views
1K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 36 ·
2
Replies
36
Views
6K
  • · Replies 41 ·
2
Replies
41
Views
4K
  • · Replies 11 ·
Replies
11
Views
2K
Replies
3
Views
2K
  • · Replies 22 ·
Replies
22
Views
5K
  • · Replies 17 ·
Replies
17
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 58 ·
2
Replies
58
Views
7K