If everything is moving away from each other....

[bendiddley]

... how come the andromeda galaxy is heading towards us and other galaxies are merging? Watched the horizon program last night which said that because the universe is expanding everything is moving away from each other. Left me a bit confused on this one, can anyone explain?

[JamesF]

Because once you get enough mass close enough together (and close can be quite a long way in human terms), gravity beats four aces.

James

[bendiddley]

Because once you get enough mass close enough together (and close can be quite a long way in human terms), gravity beats four aces.

James

So andromeda is coming towards us because of the gravity of the milkyway? Sorry still a bit confused.

[JamesF]

Well, the gravitational attraction is mutual, but yes. The two galaxies are moving towards each other because of the gravitational attraction between them.

James

[x6gas]

Generally speaking, things are moving away from each other because the universe is expanding following the Big Bang (probably!). Imagine to dots drawn on the surface of a balloon; as the balloon is inflated the dots will move further away from each other. But now imagine an ant on the surface of the balloon walking from one of the dots to the other. So long as the ant is travelling faster than the dots are moving apart (due to the expansion) he will manage to walk from one dot to the other. So Andromeda and the Milky Way are heading towards each other because their mutual gravitational attraction is pulling them together faster than the universe is expanding.

Hope that makes sense!

[bendiddley]

Ok I get it now, that makes sense, thanks

[Monty]

So really speaking I'm not actually getting fat, it's just the universe expanding?

[JamesF]

Sadly I don't think it works that way once gravity gets involved.

James

[NGC 1502]

So really speaking I'm not actually getting fat, it's just the universe expanding?

This is supposed to be a serious conversation

All the clothes in my wardrobe keep shrinking

Cheers, Ed.

[Monty]

This is supposed to be a serious conversation

All the clothes in my wardrobe keep shrinking

Cheers, Ed.

So in that case, there must be a critical point where my mass reaches a big enough point so gravity takes over and makes me skinny?

I love science!