# Problems in cosmology

by bill alsept
Tags: cosmology
 P: 124 Is there a current list of the major problems or conflicts with the standard cosmology models?
P: 534
 Quote by bill alsept Is there a current list of the major problems or conflicts with the standard cosmology models?
Here are some:

http://en.wikipedia.org/wiki/List_of...ems_in_physics

PF Gold
P: 10,793

## Problems in cosmology

Lol, that's the link I just gave him Yenchin!
 P: 534 LOL. Guess I was beaten by a few seconds :-P
 P: 111 Here's one. The Hubble space telescope can see 12 billion light years of distance in most directions, more in some directions. This can only mean that 12 billion years ago the, (visible to us), universe had a diameter of at least 24 billion light years. And yet it is said to be "only" 13.7 billion years old. Something of a paradox there!
P: 1,498
 Quote by Peter Watkins Here's one. The Hubble space telescope can see 12 billion light years of distance in most directions, more in some directions. This can only mean that 12 billion years ago the, (visible to us), universe had a diameter of at least 24 billion light years. And yet it is said to be "only" 13.7 billion years old. Something of a paradox there!
Only if you completely ignore the expansion of the universe.
Astronomy
PF Gold
P: 22,679
 Quote by Peter Watkins Here's one. The Hubble space telescope can see 12 billion light years of distance in most directions, more in some directions. This can only mean that 12 billion years ago the, (visible to us), universe had a diameter of at least 24 billion light years. And yet it is said to be "only" 13.7 billion years old. Something of a paradox there!

Peter, for Heaven's sake learn a little about the heavens.

We see glowing hot gas at a redshift of 1100.

That material will have long since cooled and condensed into galaxies and stars. It is now at a distance of about 45.5 billion lightyears. So that's essentially how far we can see (with a microwave antenna telescope, not the Hubble telescope.)

Distance in astronomy often means the distance NOW---if you could freeze the expansion process at this moment to give yourself time to actually make the measurement. It is not in any simple relationship to the light travel time, or socalled "lookback time."
Popular accounts are often unclear what kind of distance measure they mean---a real instantaneous distance at some moment, or maybe on the other hand a travel time.
Mentor
P: 21,886
Ok then: please explain what the paradox is that you see. Because I see no paradox in those two pieces of information. They do not contradict each other.
 Sci Advisor PF Gold P: 9,096 The projected age of the universe gives us a radius, not a diameter. And keep in mind the universe has been expanding during the entire time those ancient photons have been journeying to meet our detectors.
 P: 111 If the universe is expanding then to look back in time, via distance, would be to see a smaller universe. But we don't! The further back in time we look, the larger it can be seen to have been. To expand to a diameter of at least 24 B.L.Ys. in only 1.7 B.Ys. would seem to me to be a problem with our picture of the universe and its evolution.
P: 1,498
 Quote by Peter Watkins If the universe is expanding then to look back in time, via distance, would be to see a smaller universe. But we don't! The further back in time we look, the larger it can be seen to have been. To expand to a diameter of at least 24 B.L.Ys. in only 1.7 B.Ys. would seem to me to be a problem with our picture of the universe and its evolution.
No, it's a problem with your understanding of cosmology. What exactly do you mean by "The further back in time we look, the larger it can be seen to have been." What specific cosmological observation are you referring to here? To calculate the distance to the edge of the observable universe (the particle horizon, $d_H$), one must compute the integral
$$d_H = a(t)\int_0^{t_0} \frac{dt'}{a(t')}$$
where $a(t)$ is the scale factor of the universe and $t_0$ is the present time. It's not a matter of simply multiplying the age of the universe by the speed of light, since that assumes a static universe (the point I made earlier that you decided to ignore). See this FAQ for more information,
http://http://www.astro.ucla.edu/~wr...gy_faq.html#DN

 P: 111 How on earth is the original question ignoring the expansion of the universe?
Astronomy
PF Gold
P: 22,679
 Quote by Peter Watkins If the universe is expanding then to look back in time, via distance, would be to see a smaller universe. But we don't! ...
I have to go to a family get-together today but when I get back I want to try something, Peter. I am going to take a different tack and interpret every question of yours as thoughtful, well-motivated, and intelligent. I'm going to assume that all the critical reaction to your questions is due to a purely verbal misunderstanding (on one side or the other). It could just be due to a mismatch of verbal concepts.

When we look back in time the OU (the matter we see now out to the surface of last scattering) was actually much smaller---radius about 41 million LY, if you could have frozen it back then at the time it emitted the light.

You can get that from the Morgan calculator. I have a dim memory of your telling me you had "been there done that" with her "cosmos calculator". Is that right? You have spent some time playing around with it?

So it should be clear that what we see when we look back IS much smaller.

And the physics we see is of something that small, with the hot gas that dense, so that we can see even evidence of sound waves that were traveling thru it at that moment.

So you may find that reassuring. You seemed worried that we look back the OU is very large. No, what we see back then is small and is evidently behaving as a relatively small hot concentrated gas world. We see its image in the sky and measure its temperature. As it was back then.

But I have to go. When I get back I will try to reassure some of your worries. In the meanwhile I hope you hang in there and listen to the criticism cheerfully. It is well-informed and well-intended, for sure.

And there may be issues of substance (not just semantics) that do call for critical attention.
Anyway, I'll check in later.

OOPS I just saw your name crossed out. Well that's that. It was probably inevitable
 P: 694 Marcus perhaps you could give Peter that great online calculator link you gave me that helps to visualise and put different numbers on these sizes and speeds. Peter if you are still around this might help: http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html
 P: 1 Bill, is this what you're after ? http://metaresearch.org/cosmology/BB-top-30.asp

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