Finite vs Infinite Universe!?

Question

I have heard from a lot of people that the universe has been PROVEN to be finite... but thats not true. I have an article that sums up the edge of the debate pretty well, please read.

http://www.newscientist.com/article.ns?id=dn4250

If you have any other articles that pertain to this subject please post.

Answer 1

The only things that has been "proven" is that the universe is not smaller than what we actually see.

The universe could be wrapped onto itself.  Like the surface of a sphere, it could be finite in size, but unbounded (no ends, no edges).

On thought was that it could be wrapped so tight that its size could be smaller than the 14 billion light-years radius we see in proper distance (approximately 78 in comoving distance).

The probe WMAP, sent to collect data on the Cosmological Microwave Background radiation, was looking for telltale signs of such tight wrapping and did not find them.

Therefore, the only thing we know for sure is that the entire universe is AT LEAST 28 billion light-years in diameter (in proper distance -- equivalent to approximately 156 billion light-years in comoving distance).

It could still be infinite.

If it is infinite, it should be overall, "flat".

On a flat surface, all triangles have their inner angles add up to 180 degrees.  Whatever the size of the triangle.  On a positively curved surface (e.g., a sphere), the inner angles add up to more than 180, in a proportion that is relative to the triangle's size.  It is called the spherical excess.

If you can draw a large enough triangle on Earth, and carefully measure the angles, you could prove that the Earth is a sphere and even give an idea of its size.

However, if you are only using your backyard, the triangle will be much too small for the accuracy of the instruments and you will not be able to prove anything.

That is our problem.  Plus we have to do this in 3 dimensions (not 2 as we do for surfaces).

The other thing that does not help us is that space-time itself is curved (because of the finite speed of light and of the expansion:  the further out we look, the smaller the universe was).

Unfortunately, I cannot post the papers.  They are in the scientific journal "Nature" and they don't let us see them for free.

---

A flat Universe from high-resolution maps of the cosmic microwave background radiation

P. de Bernardis, and others. Nature 404, 955-959 (27 April 2000)

They are talking of the universe being flat at the "moment" of decoupling (when the CMB radiation was emitted).

---

Evidence for a positive cosmological constant from flows of galaxies and distant supernovae

by Idit Zehavi and Avishai Dekel, Nature 401, 252-254 (16 September 1999)

---

However, the best one I found is a letter (not a paper):

"Dodecahedral space topology as an explanation for weak wide-angle temperature correlations in the cosmic microwave background"

by Jean-Pierre Luminet, Jeffrey R. Weeks, Alain Riazuelo, Roland Lehoucq, Jean-Philippe Uzan.

Nature 425, 593 - 595 (09 Oct 2003)

Quote: The current 'standard model' of cosmology posits an infinite flat universe forever expanding under the pressure of dark energy. First-year data from the Wilkinson Microwave Anisotropy Probe (WMAP) confirm this model to spectacular precision on all but the largest scale.

They use the first year results as published in the Astrophysics Journal Supplement of 2003.

Here, the issue is with the word "but" near the end of the quote.

Apparently, waves from the Big Bang at all wavelengths should fill the entire universe.  "But" very long wavelengths seem to be missing, implying that the universe does have a finite size (the universe not being long enough to support these waves).

What they do is give example of how the universe could be flat AND finite (in at least some dimensions, if not all).

The simplest example I can think of is a 2-dimension surface, wrapped as a cylinder.  The "up-and-down" dimension could be infinite, but the "let-and-right" dimension would have a finite length (the horizontal vector crossing its starting point over and over again).

Such a surface is "flat" (angles in triangles add up to 180).

Of course, their 3-dimension example is far more complicated.  But the idea is that they do come up with a model where the universe is flat AND finite in all directions.

---

I still prefer the flat and infinite universe.  However, I must accept that proving "flatness" is not, by itself, a sufficient proof.

Answer 2

We can't tell with current technology whether the Universe is finite or infinite.  You can find lots of information on it just by doing a search.

I know these aren't links that you can click on.  You will have to copy and paste, but they are just examples of some of the info out there on this subject.

curious.astro.cornell.edu/question.php... - 11k -

www.astro.ucla.edu/~wright/infpoint.ht... - 3k -

Answer 3

The article does no such thing as you insist. If anything, the article suggests that the Universe is not as small (70 billion light-years) as may have been thought previously. It could be either infinite or very large (but finite).

Interestingly, the article mentions the Cosmic microwave background radiation, but has no comment regarding the expansion of the Universe. This expansion (proven by the CMBR itself, as well as the Hubble constant) rules out the possibility of seeing mirror images of distant galaxies, or traveling back to your starting point by going in a continuous straight line, as the article indicates. Check Google for 'The Horizon Problem' for more on that.

My own opinion is that the Universe is 'finite but unbounded'. The article suggests there's lively debate about that idea, but I fail to see where it's been disproven.

Answer 4

Current observations do not discriminate between an infinite universe and a finite but unbounded universe.