Expanding Universe & Red Shift

ChrisXenon · May 21, 2009

We hear that the universe is expanding, and this accounts for red shift as all objecsts are accellerating away from eachother.

But I have also heard that it is the space itself, of which the universe made, that is expanding - not that things are moving in that space.
If so, then the distances between objects as measured in this expanding space is presumably constant, since the "rulers" would also be expanding in that same space.
And in this case, there would be no red shift.
Clearly, I'm wrong, and I'm hoping someone can straighten my out on this.

This might relate to another puzzle I have.
I am told not only that things are moving away from eachother, but that things are accelerating away from eachother.
Since these objects are isolated, what is the constant force which is causing this acceleration?
Or, if we are way beyong Newton at this point, how is this accelleration caused?

Thanks again, Chris

mathman · May 21, 2009

Rulers are not expanding.

The acceleration of expansion (discovered about ten years ago) is due to something given the name "dark energy". No one knows what it really is, although it seems to be related to the "Cosmological Constant" in general relativity.

Chronos · May 22, 2009

The Perlmutter study injected dark energy into the mix. See
http://physicsworld.com/cws/article/print/31910

qraal · May 24, 2009

ChrisXenon said: ↑

We hear that the universe is expanding, and this accounts for red shift as all objecsts are accellerating away from eachother.

But I have also heard that it is the space itself, of which the universe made, that is expanding - not that things are moving in that space.
If so, then the distances between objects as measured in this expanding space is presumably constant, since the "rulers" would also be expanding in that same space.
And in this case, there would be no red shift.
Clearly, I'm wrong, and I'm hoping someone can straighten my out on this.

Bound systems - held together by gravity or electromagnetic forces - can oppose the expansion so they don't change. At least for now.

This might relate to another puzzle I have.
I am told not only that things are moving away from eachother, but that things are accelerating away from eachother.
Since these objects are isolated, what is the constant force which is causing this acceleration?
Or, if we are way beyong Newton at this point, how is this accelleration caused?

Thanks again, Chris

Newton still holds, but we presently don't know what is causing the observed acceleration. There are lots of theories, but no definite answers as yet. That's why we're still making bigger and better telescopes to study it further. If we knew why, then the need for the scopes would be less.

Beware of physicists with too many answers. They might be trying to sell you something ;-)

Dex · May 24, 2009

universe is expanding. maybe not! think if the photons ,we see in Hables telescope, are with more or less energy they change colors spectre - so if in middle of universe is huge super-massive black hole , which evidence universe , then on its way photon loose energy and we see it as red or violet or blue..

qraal · May 24, 2009

Dex, check out Professor Ned Wright's discussion of why "Tired Light" models don't work to explain the red-shift.

Dex · May 24, 2009

uh thanks!!! thats help a lot....
anyway - do we have thread - how universe is made?

btw it was idea i made myself - that i liked ;(

qraal · May 24, 2009

Dex said: ↑

uh thanks!!! thats help a lot....
anyway - do we have thread - how universe is made?

btw it was idea i made myself - that i liked ;(

Start that thread yourself over in the https://www.physicsforums.com/forumdisplay.php?f=69".