Quote:
Originally Posted by snas
I've been reading about various possible universes. One question that seems to come up frequently is, is the Universe finite or infinite? As I am not an astrophysicist, I may be missing something here. But, it seems to me that if the BB occurred when a "singularity" containing all of what now makes up the Universe suddenly underwent a period of massive, rapid expansion, then surely the original singularity had an edge,a boundary. If so, it was finite. So how would a growing universe get from a finite singularity on day one of the new Universe, to an infinite state. Surely a finite thing cannot become infinite.
Stuart
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Stuart,
Mathematically the visible Universe is finite, the entire Universe is infinite. This is based on the visible Universe being flat or having a zero curvature. We know nothing beyond the boundaries of the visible Universe so an infinite Universe is a speculation.
An analogy which puts a physical perspective on the concept of infinity and how it relates to a flat visible Universe, is to think of the entire Universe as being a sphere. Our visible Universe is an area on the surface of the sphere.
If the radius of the sphere is small we can discern that the surface has a definite curvature. Increase the radius and the surface appears flatter.
Mathematically there is a relationship between radius and curvature, increasing the radius reduces the curvature of the surface.
When the radius becomes infinitely large, the curvature is zero and the surface of the sphere is flat.
With regards to the singularity it's one of those unfortunate timings that the science of Cosmology predated Quantum Mechanics. The singularity is an artefact of assuming that the laws of physics (in this case General Relativity) extends all the way down to the smallest scales.
In the very early history of the Universe, the Universe was small enough to obey the laws of Quantum Mechanics instead of General Relativity.
Singularities don't exist in Quantum Mechanics as space time is "smeared".
Regards
Steven