expanding universe question

jim77

Another question for you all. What evidence for an expanding universe is there besides redshift. I am a layman and to me it seems like it would be simpler to find another explanation for the spectral shift of light as it passes through millions of light years of space (say some kind of lensing effect caused by warps in space (not that I know what that means) or the gravitational effects of the bodies from which it emanates or passes) than to throw common sense out the window and assert a universe out of nothing, inflation (why doesn't the gravity of the newborn universe collapse it into itself, I thought nothing could move faster than light,etc.) and all the other suppositions that separate you geniuses from we mortals. One more question along the same lines. I love those astronomy documentaries but I was troubled when I heard one scientist say that the universe was 13 billion years old and any scientist who disagreed was a "crackpot". Was this was just an unfortunate remark or does it reflect the consensus in higher physics? thanks again.
sincerely

skydivephil

The big bang theory which states the universe has been expanding for 13.7 bio years (according to latest measurements) relies not just on red shift but on four independent pillars of evidence.
http://physics.weber.edu/palen/Phsx1.../LBigbang.html
If you don't know what lensing or warps in sapce mean, or you dont understand inflation, I suggest reading some introdcutory astronomy texts as well as the FAQ here in cosmology forums.
A good text is this:
http://www.amazon.co.uk/Universe-Rog...ef=pd_sim_b_10

There is a consensus that the universe beganb expanding 13.7 bio years ago this is supported by the lines of evidence I linked to above. Yes I would agree that anyone that disputes that is considered a crackpot. However there is certainly a widely held belief that this picture is not wrong, but is incomplete and there may be a pre big bang history. This is currently being explored by cosmologists but no model is agreed upon yet because they haven't been tested. There are many interesting, creative and exciting ideas , this inlcudes a universe from nothing, but also includes many other ideas such as our unvierse bouncing from a previous one that contracted. But until some test can be devised and carried out they will not be considered facts in the same way the expansion history of the unvierse is considered a fact.

Lino

Phil, I've read about the four pillars previously and one interesting thing is that different people seems to quote a different set of four - always four, but not always the same four! This is the first time that I've sen Obler's paradox included. Do you normally consider it one of the four pillars?

Regards,

Noel.

skydivephil

Actually no, good point. The standard 4 should be: the Hubble relationship, the light element abundaces, galaxy evolution and the CMB (especially the fact that its a black body).
Olbert is usually carted out to show the universe cant be infinite in both time and space and static. So perhaps its come circumstantial evidence but I dont think its one of the four. in retropsect this is better:
http://en.wikipedia.org/wiki/Big_Ban...ional_evidence

bapowell

I've also not typically seen Olber's paradox included (in fact, I'm familiar with the *three* pillars, further adding to the confusion!) I don't like including Olber's paradox because as is caveated in Phil's link, there's a way around it -- a finite universe. The website goes on to state that a finite universe, however, is unsavory because we would need to be at the center of it. But this is only true if the whole of the finite universe was taken equivalent to our observable universe, and I don't know why you'd force this constraint on yourself. One can evade Olber's paradox (without accepting the big bang) by postulating a universe larger than the observable universe but still finite.

I think the pillars are best reserved for observational evidence, which I think is their intent. I've always known these to be: Hubble expansion, big bang nucleosynthesis, and the CMB.

Lino

Thanks Phil & Bapowell.

Regards,

Noel.

skydivephil

well i do think galaxy evolution is an important pillar , when we look at distant galaxies they dont look the same as nearby galaxies , this is good evidence the observable unvierse is changing.

skydivephil

Actually now I think of it,suppose you did have an infinite past and infnite space, the light from the infinite past cant go through the last scattering surface so wouldnt this be a way round Olbert's paradox?

Lino

I think that the usual 4th pillar relates to the cosmic principle (generally isotrophic and homogenius) which, though not strictly observational, is extremely important.

(Phil, good point on Obler's paradox, I like it.)


Regards,


Noel.

bapowell

Except that a static universe could be isotropic and homogeneous, no?

Lino

Mmmm ... I suppose so! I've never really thought about it from that perspective.

When you say static, how "static" are you talking about? (Evolution but no BB so just the age is different, or existed forever but no change except for those associated with collisions, or something else?)

Regards,

Noel.

bapowell

I just mean that the observation of a homogeneous and isotropic universe does not in itself imply that the universe is expanding (or that there was a big bang).

bapowell

This implies that galaxies are evolving and that the speed of light is finite, but does it necessary imply that the universe is expanding or itself evolving from an initial high density state?

Lino

But isn't that the point about the pillars? If you take any one in isolation, it does not imply that there was a big Bang / the universe is expanding, but when taken together, the weight of evidence strongly suggests / implies that there was a big Bang / the universe is expanding.

(My understanding is that: hubble expansion observations can be caused in other ways, big bang nucleosynthesis has large potential "error bars" (my clumsy words - I'm not sure how to say it explains some but not all of the related element abundances), and the CMB ... I still reading about and trying to understand this so I'm open minded about it at the moment.)

Again, and only my understanding, taken as a sum total, it strongly suggests / implies that there was a big Bang / the universe is expanding.

Regards,

Noel.

George Jones

Recently, there has been a lot of work on the observation status of this. See some of the entries in this arXiv search:

http://arxiv.org/find/gr-qc/1/au:+cl.../0/1/0/all/0/1

Lino

Thanks George. Appreciated.

Regards,

Noel.

bapowell

Maybe that's a fine interpretation. It's just that the observation of a homogeneous and isotropic universe has nothing to do with expansion. If you add it to the other three, it does not strengthen the argument for a big bang.