the universe, cannot be infinite, if it had a beginning, or will have an end. of that, we do not know. we have many theories, some more valid than others, depending on your perspective.
to say the universe is infinite, would be to say that it is static, an infinite object has no beggining, or end, it just
is.. einstein took years of thought to realize that the universe is a very dynamic place.... the idea gave him many problems with his theory of relativity. but to put it as simple as possible, in observable terms, its kind of like this-
it the universe wasn't accelerating away from a central point in space-time (aka The Beginning, the big bang...) then it would simply collapse under its own gravity. just like objects are sucked into a black hole.... sooner or later, everything would collapse into a central blackhole.
this evidence of a beginning would also suggest the evidence of an ending, because as of date, the only infinite object we know, is the mathematical expression for it: ∞
an interesting question though, is our observable universe really 'the' universe, by definition?
or is it just another formation, as particles form atoms that form molecules that form stars that form planets that form solar systems that form galaxies that form galaxie clusters that form our visible universe.... could be our entire visible universe is just a particle in another formation, yet to be observed.
mind freak!
[video=youtube;aAJql0P8QYY]http://www.youtube.com/watch?v=aAJql0P8QYY[/video]