I wonder if anyone knows the answer to this

Rubecula

I watched a TV documentary (I think it was the Discovery Channel) and on it they made a statement.

Astronomers studying the universe were measuring the expansion of the Universe to see the rate of the expansion slowing down, but they were amazed to discover that it is actually speeding up.

Ok I get the "Doppler" effect, by which you can measure distance and speed of expansion (or otherwise). But how do they measure acceleration over such distances? Surely the Doppler effect would not show much difference over cosmic distance? Or does it? I would have thought that measurements would need to be made over a very extended period of time to see acceleration.

Obviously I am misunderstanding this, but I can't see where I am going wrong.

namloc1980

Redshift

WalterMitty

very detailed measurements can be made using light from standard candle supernovae. Recently they have discovered that the acceleration is increasing by comparing this standard light from galaxies of known distances away and discovered that the rate of stretching of the light is increasing /accelerating AFAIK.

Rubecula

Yes indeed but to know about acceleration you need to compare it to something.

How can we compare it to something without knowing what the speed of expansion was say 1000 years ago?

Am I making myself clear?

If we are speeding up we can only know that if we were going slower previously, but how do we how fast we were going back then?

The Hill Billy

I could be totally wrong, but by comparing the redshift of two or more objects at known, but different, distances it may be possible to infer the rate of accelleration of the universe relative to their distance from us.

WalterMitty

http://en.wikipedia.org/wiki/Accelerating_universe

WalterMitty

http://www.bbc.co.uk/news/science-environment-15165371

gkell1

Rubecula wrote: »

I watched a TV documentary (I think it was the Discovery Channel) and on it they made a statement.

Astronomers studying the universe were measuring the expansion of the Universe to see the rate of the expansion slowing down, but they were amazed to discover that it is actually speeding up.

Ok I get the "Doppler" effect, by which you can measure distance and speed of expansion (or otherwise). But how do they measure acceleration over such distances? Surely the Doppler effect would not show much difference over cosmic distance? Or does it? I would have thought that measurements would need to be made over a very extended period of time to see acceleration.

Obviously I am misunderstanding this, but I can't see where I am going wrong.

The idea of 'big bang' is not just wrong,it is cruel.

In a nutshell,the belief that you can see the evolutionary timeline of the Universe directly is as perverse as a belief that you can see the evolutionary timeline of anything else directly whether it is planetary development,human evolution or even you own evolutionary development from a child to adult.

The continuity between past and present which most people understand within context of their normal existence and which meshes with all other evolutionary timelines cannot be set aside.Telescopes are time machines in a way that we can take a snapshot of things that happened in the past and put them in context of motion and structure but the idea that a person can see the evolution of the Universe directly is not so much an affront to the intellectual abilities of humans as it is an affliction of the mind.