h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Get this if the universe is expanding then whats it expanding into?

a) You might be better off posting this at <./>askh2g2</.>

b) It's not expanding into anything. It's the 3-dimensional surface of a 4-dimensional 'hypersphere'. The usual analogy is with two little men drawn on the surface of a balloon. They only have 2-dimensions; they live in a 2-dimensional world. But we can inflate the balloon in 3-dimensions. The men get further apart, but from their point of view there is no 'in' or 'out' 3rd dimension. Extrapolate that into 3-dimensional galaxies on a 4-dimensional balloon, and that's pretty much what's going on. Humans cannot visualise a 4th dimension, because its axis is time, rather than space. So there's no space for the Universe to expand into, but it is expanding in the 'time' direction. Of course, Stephen Hawking thinks that the Universe is saddle-shaped, rather than balloon-shaped, but the principle still applies.

B

Sounds a bit like rubbish to me

The universe, the theory or the way rubbish also expands, apparently from nowhere, to fill more space than is available?

That theory also applies to women's handbags.

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yea, but if you blow up a balloon, it expands in to the air around it does it not? the men drawn on the balloon may get further apart but its still expanding in to an existing air space.

The balloon is only an analogy - a simple picture for simple people. You are picking at the inadequacies of the analogy and not at anything fundamentally wrong with the real theory.

And the point I was making is that the Universe in NOT expanding into space. Space is 3-dimensional, and the Universe is expanding along the line of the 4th dimension.

B

Traveller in Time philosophical
"The Universe is expanding into _nothing_.

Nothing seen as 'the void of nothing' that already existed before the universe. The universe is not replacing 'the nothing' and nothing is not shrinking as it was nothing already. "

Whatever it is expanding int(or not) It,s beautiful,It,s great to be a small part of it. Might as well enjoy, the alternative's not in sight.

oh i see not expanding outwards into stuff, but expanding in time. right i see