Courtesy either Douglas Adams or Terry Pratchet (in one of those sci fi books he did)
Aged about 9, I read this (paraphrased), which still has me nicely stumped in a particularly pleasing way:

1) The universe is infinite. If it's infinite, it must contain infinite possibilities (planets made of glue populated by intelligent blancmanges that speak Dutch etc).

2) This means that at one point, the universe cannot exist - because that is one of the infinite possibilities. But if there is a point where the universe doesn't exist, the universe isn't infinite.

3) But if the universe isn't infinite, the point where it stops existing must be nothingness. But this nothingness cannot be quantifiable in any way, shape or form, for it it had any kind of measurable space or time, that would mean it was simply emptiness.

If the nothingness beyone the universe is not quantifiable in space or time, it does not exist, which means that the universe must be infinite - which takes you back to step 2).

Equally, this means that the universe must have always existed, which wipes out the necessity for God quite nicely (even though if the universe is infinite, one of the infinite possibilities which must exist at some point in the universe for the universe to be truly infinite is that there is a supreme being who created the universe - just as for the universe to be truly infinite there must be a point where there is no God...)

Anyone still with me?
( TV's Nosemonkey, Fri 1 Apr 2005, 15:51, Reply)