accelerating expansion of the universe doesn't fit

[RideFree]

Thanks, had me worried for a minute!

 

[jALLAD]

Originally posted by: Chiropteran
Let me put this another way. Ignore distance.

thats the whole point u cant do that. u r comparing different objects in different positions in space at different points in time.

when the galaxy a billion light yrs away reaches a distance 2 billion light yrs, it will have a redshift 2x instead of what used to be x. this comes from the fact that the expansion of the universe is a non-local event. there is no centre of the expansion. its same and uniform everywhere and in every direction.

 

[PolymerTim]

Originally posted by: silverpig

Originally posted by: Chiropteran
Let me put this another way. Ignore distance.

All the sources 1 billion years ago have x redshift
All the sources 2 billion years ago have 2x redshift
All the sources 3 billion years ago have 3x redshift
All the sources 4 billion years age have 4x redshift

Translate redshift into velocity, and the pattern is very clear:

Everything was moving away from us much faster in the past, and it is slowing down as we look at examples more recently. That shows a linear deceleration over time.



So. Based on that observed data, why do scientists claim that the opposite is actually the case, and the velocities are accelerating rather then decelerating with time? All the data indicates deceleration.

Read my post.

Also, if you calculate velocities equivalent to those redshifts, then figure out a deceleration and strength of gravity, there isn't enough mass to slow everything down that much.

I have to admit I don't know enough about astrophysics to understand in theory why the OP's claim is false, but I think this response hits closest for proof for me. I'm guessing that if you just do a few simple calculations on the actual velocities required to obtain the observed redshift assuming no expansion of space-time then you would get unreasonable numbers.

This gets back to the earlier post that if you measured the redshift of the star from very close, there would be no significant redshift. I think if you proved this by something like the above-mentioned method, that would satisfy me and the OP better.

-Tim

 

[firewolfsm]

This is a good article for someone with a little more technical knowledge, I'm not really sure how much of it I understood, but I think I've got a hold on his concepts. It explains some of the reasoning and evidence for acceleration that doesn't just stem from what we see from ancient light (what the OP had problems with.)

http://arxiv.org/PS_cache/astr...pdf/0310/0310342v2.pdf

 

[bwanaaa]

Chiropteran

I understand and agree with your argument. In fact, one might say that the very recent theory of hyperinflation is support for your argument. As I understand hyperinflation, it occurred at the very beginning of this universe when the matter was expanding faster than the speed of light(as it is measured today). This begs the question as to whether there has been an observable change in the speed of light over the brief time that we have been able to measure it (and there has not). Finally, if one is to go off into fantasy land and ignore occam's razor, one might postulate that dark matter is acting like a lens and slowing down the speed of light-over greater distances, lightspeed delay will increase and if you are not aware of it and account for it in your calculations, then more distant objects will appear to be moving away faster.

 

[erskogly]

I don't know where the OP found his original quote, but it seems to me there is a lot lacking in that explanation. I've found a slightly more thorough explanation, but a full explantion seems to be somewhat hard to come by on the internet!! I've only ever seen a good explanation of this in a book, and it requires quite a bit more than five lines to explain fully - but the shortest explanation which does a half-way decent job of explaining it follows. This from a FAQ on cosmological questions:

The evidence for an accelerating expansion comes from observations of the brightness of distant supernovae. We observe the redshift of a supernova which tells us by what the factor the Universe has expanded since the supernova exploded. This factor is (1+z), where z is the redshift. But in order to determine the expected brightness of the supernova, we need to know its distance now. If the expansion of the Universe is accelerating due to a cosmological constant, then the expansion was slower in the past, and thus the time required to expand by a given factor is longer, and the distance NOW is larger. But if the expansion is decelerating, it was faster in the past and the distance NOW is smaller. Thus for an accelerating expansion the supernovae at high redshifts will appear to be fainter than they would for a decelerating expansion because their current distances are larger.

The part in bold at the end is what was missing from the OP's original quote. It is the correlation between redshift, apparent brightness and actual distance that is used to determine that the expansion is accelerating, not just the redshift.