frogprince - Toe Rag's statement is an interesting one. It could mean a number of things.

What does "the greatest thing imaginable" mean? It could mean different things to different people. One person might see it as the largest single physical object we can imagine...in which case, it could be a huge star...or it could be the whole Universe (a collection of objects).

Another might see it as bigger than the observable Universe.

Another might see it as "all that is" (which would include, theoretically, not just the observable Universe, but all other dimensions and universes, all thoughts, all energies, etc).

Some religions and philosophies do see God as "all that is". If that's the way you see it, then no one can deny the existence of all that is, can they? It's self-evident.

So it depends on how you define "God".