hey guys i have read the centre of the universe thread and was left with some questions if some one culd answer them it wuld be much appreciated

how do we know the universe is expanding ?

is it from observing galaxies ?

if the galaxies are moving do they move in a linear fashion or unpredictably "outwards" .... ?

if they move linearly can we not find a trajectary angle to focus on the centre of the universe or is that subject to relativity or is that just a stupid logical thoery that holds no ground ?

Because of the movements of galaxies generally seen as moving away from one another.

Yes

The whole of space seems to be expanding so I am not sure it is entirely linear because space itself inflate AND the galaxies might have other proper motions, but generally it should be close to linear as viewed (and this is the important bit) from ALL vantage standpoints in the universe.

Not sure this is valid, every point in the universe is expanding in relationshipg to each other, so I am not sure how you would define a center when all referentials, and the fabric of space-time itself is expanding...

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The impossible often has a kind of integrity which the merely improbable lacks.

The best analogy I've heard is imagine that the universe is the surface of a balloon and the stars and galaxies are dots on the surface. Now put more air in the balloon. The galaxies are moving away from each other as the universe expands, but since we are only looking at the surface of the balloon, there is no "center".

By the way, welcome to BAUT paca_ts

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One Earth, One Sky - IYA 2009
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Paca : for the expansion of the universe the support is in the red shift of light from stars and galaxies. Swift's reply explains the different speeds relative to us between nearby and far-away galaxies.

For the INCREASING expansion of the universe the support is found in supernova data from extreme remote supernovae and in the cosmic background radiation data.

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First there was nothing. Than even that exploded ....

I've never liked that analogy, too two-dimensional. I guess the pudding/cake/whatever with the raisins in it expanding offers a better approximation

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The impossible often has a kind of integrity which the merely improbable lacks.

thanks for the replies

i dont care much for that balloon idea if we are all expanding we must be expanding from a piont by definition
if we are just simply moving then we are simply moving but if all galaxies with reference to us are travelling "away" maybe not at a constant speed but angle surely theres something ...

maybe im being to ideal in an un-ideal enviroment thanks again for the answers very helpful

We don't know that it is expanding, but we do think that it is expanding (for appropriate definitions of "we"). The primary observational impetus for such an idea is the interpretation of galactic ("cosmological") redshifts as an indication of relative motion. But the real reason for believing that the universe is expanding is the combination of that interpretation, along with the constraints of general relativity, which does not easily permit a static universe. This combination of observation & theory make an expanding universe the most elegant & simple explanation for a host of observational characteristics of the universe.

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The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell

The galaxies are all moving away at a velocity roughly proportional to their distance to us. There's something special about that kind of proportionality. It means that, to us, it looks as though we're the center of the expansion. But it also means that, if we were to work out what the universe would like to someone in a distant galaxy, we can tell that they would see all the galaxies rushing directly away from them. In fact, any point you pick will look like it's the "center" of the expansion if you're observing from that point.So as far as that goes, it looks like every point in the universe is equally the center from which the universe is expanding.

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Conserve energy. Commute with the Hamiltonian.