I Expansion of the Universe question

[feddz]

If the galaxies we see are as they were a few million years ago, then how do we know that the universe is expanding since we don't know their current velocities?
Hubble's graph shows a linearly proportional relationship between velocity and distance but the fact that the further a galaxy is, the further in the past we are looking at isn't taken into account supposedly?

This has been torturing my brain a lot lately!

 

[Ibix]

If the galaxies we see are as they were a few million years ago, then how do we know that the universe is expanding since we don't know their current velocities?

Why would they stop?

the fact that the further a galaxy is, the further in the past we are looking at isn't taken into account supposedly?

Where did you read that? It's wrong - scientists are very well aware of the implications of a finite speed of light.

 

[Orodruin]

Hubble's graph shows a linearly proportional relationship between velocity and distance

This is only true for relatively nearby galaxies.

the fact that the further a galaxy is, the further in the past we are looking at isn't taken into account supposedly?

Why would you think that in generations of cosmologists doing this for a living, nobody would have thought of this? Obviously such effects are taken into account.

 

[UlkMulken]

This is only true for relatively nearby galaxies.Why would you think that in generations of cosmologists doing this for a living, nobody would have thought of this? Obviously such effects are taken into account.

Then try to explain carefully, because I am as interested as the thread author, but also an noob amateur.

As I see it there are two main theories. 1) The old theory: The universe will collapse upon itself by the force of gravity (the big crunch). 2) The new theory: The universe expands, and the expansion increses. This is due to a mysterious force called dark energy, since nobody knows what it is.

Now to the empirical evidence: From my amateur perspective the scientific data seems to show that galaxies further away are traveling away from us at higher speeds than galaxies closer to us. This measured by red shift of the light.

My first question is how this empirical evidence can prove the new theory about dark energy? From my perspective it seems like the evidence could support the old theory as well as the new. If the universe was expanding a lot in the past and is now in a phase of slowing that expansion, then you would get the result that the galaxies that are further from us are expanding fastest while the galaxies close to us expands slower. However, you could also argue that the galaxies further away are accellerating due to the expansion of space (the balloon analogy), thus as support for the new theory.

My second question is which assumptions are needed for the new theory of dark energy? It seems to me, that in order to finally prove the theory of dark energy and increasing expansion you would essentially need to observe both the galaxies close and further away at the same time (which is impossible). Is it correct that an assumption for this theory is that the relation of galaxies traveling speed as comparative proxies to each other since they cannot be measured at the same time? It seems like the theory of dark energy need assumptions in order to handle the fact that the different galaxies are measured at different points in time.