A small finite universe and some wierd thoughts from it

In summary, the conversation discusses the concept of the universe being a 3D version of a balloon's surface and how this could lead to interesting scenarios in a small universe. The conversation also mentions a paper that explores the topology of the universe using the cosmic microwave background and the possibility of finding giant rings in the CMB sky.
  • #1
JHUK
5
0
I do not have physics education pass A-levels, yet. So what I've been thinking of should be very simple to follow. It's just so fascinating that I'm wondering if any experts could either point a logic flaw, or direct me to material that has already mused over this for me.

I understand that the answer to "what is at the edge of the universe" is something we can't know, due to the limited distance that light has traveled since the big bang. But that it's speculated that the universe is like a 3D version of a balloon's surface, that if you were to travel far enough in one direction, you'd end up back where you begin.

This brings up the very interesting and fun question, to imagine a universe like this being only the size of a small room. You're floating, what do you see? (we can assume there's light, air, etc for our convenience) Naturally you'd see the back of yourself. Now twist forward (shrink the universe a bit for this) and grab hold of "his" leg, you'd feel the same hand wrap around your own leg. There's a lot of funny things you could do here.

But on further reflection, if the universe "repeats" itself in front of you, it should also do it upwards. But likewise it should also "repeat" in any direction, which begins creating an absurd and confusing scenario, so to simplify it, imagine just a sphere.

Place this imagined sphere inside this empty and small universe. Wherever it is, we can picture that as the "center" (e.g. like placing a dot onto a balloon containing no other drawings). For our convenience, this sphere is also able to see, and emit light.

I'm going to get a sphere picture from google images, and express the rest using a crude MSpaint diagram.

pBTFv.png


You get a similar result if you picture a point on an empty sphere. If you imagine light travels over the surface like everything else, instead of flying off into space, light emitted from the point would fly around the planet and hit it's back. The point would therefore see a circle around him. Made of him.
 
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  • #2
Great post JHUK! It looks like you're having some fun with the topology of the universe. If you're interested, check out this paper:

http://arxiv.org/abs/astro-ph/9801212"

These guys seek to use the cosmic microwave background to measure the topology of the universe. Rather than a sphere, they consider the case in which the universe is a 3D torus (a cube with opposite faces identified). Now, rather than a person seeing copies of himself in every direction (as in the case of the sphere), one sees copies of himself in 4 directions. In this paper, the authors are interested in what the CMB looks like in such a universe. As you may know, the CMB is seen as a 2D sphere, called the surface of last scattering. In the paper, they imagine the case in which the distance to the last scattering surface is larger than the dimension of the cube. Then, what one sees is 4 intersecting copies of the CMB-sky:

http://member.ipmu.jp/brian.powell/cmb.jpg

The task is then to go and look for the circles of intersection -- giant rings in the CMB sky. Their study didn't find any such rings, but I think the book is still open on the topology of the universe!
 
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Related to A small finite universe and some wierd thoughts from it

What is a small finite universe?

A small finite universe refers to a universe that has a limited or finite size and is not infinite. It is a concept that is often explored in physics and astronomy.

How is a small finite universe different from an infinite universe?

A small finite universe has a limited size and is bounded, meaning it has an edge or boundary. In contrast, an infinite universe has no boundaries and is considered to be endless.

What are some implications of a small finite universe?

One implication is that if the universe is finite, it must have a certain shape or geometry, such as a sphere or torus. This also raises questions about what exists beyond the boundaries of the universe and if there could be other universes beyond our own.

Could we ever reach the edge of a small finite universe?

It is currently unknown if we could ever reach the edge of a small finite universe. The universe is expanding at an accelerating rate, and it is possible that the edge is moving away from us faster than we could ever travel.

How does the concept of a small finite universe relate to the multiverse theory?

The concept of a small finite universe is often explored in the context of the multiverse theory, which suggests that there could be multiple universes beyond our own. Some theories propose that our universe is just one of many small finite universes that make up the multiverse.

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