Hubble scale

[sanctus]

This is just a basic question, what does sub and super hubble scale mean?

Is sub-hubble scale the scale at which there can be causality and super where there can't?

[CraigD]

This is just a basic question, what does sub and super hubble scale mean?

I’m not sure what the terms sub and super Hubble scale refer to.

 

Does they refer to density parameter ([math]\Omega[/math], which I’ve encountered under the term “Hubble number”) being less than or greater than 1?

 

Or do they refer to points in space relative to an observer that are less or more distant than the Hubble limit, the distance at which, classically, Hubble’s law predicts objects will be receding at greater than the speed of light?

[Jay-qu]

I think it would have something to do with the scale at which there is noticeable expansion..

[Dov Henis]

Take a look at:

http://cfa-www.harvard.edu/~huchra/hubble/

[coldcreation]

Take a look at:

http://cfa-www.harvard.edu/~huchra/hubble/

 

Yup, just checked out your link. It's not called the Hubble scale.

 

It's called the Hubble Law. That really does not matter though. Just terms. As far as sub and super, I didn't read that far. I imagine it is either faster or slower than the standard model predicts.

 

What did catch my eye was this passage: "...Olber's paradox --- that the sky is dark at night, as one of the cornerstones of modern cosmology."

 

Olber's paradox is worse than bad joke. That it is a cornerstone of modern cosmology is revolting.

 

Perhaps, at first glanse this has nothing to do with your question set out in the first post, but it does.

 

Olber's paradox has come to imply; if the universe were not expanding, the sky at night would be ablaze, bright like the surface of the sun.

 

That is the bad joke.

 

Part of the reason that Hubble's Law was accepted as a Law (which it is absolutely not, the reason for which may be beyond the scope of your thread) is because of the paradox (see the above link, second line down, I think).

 

Olber's paradox, its implications are simply not true, i.e., it is untenable, and it is no paradox. A stationarey, static, non-expanding universe would look precicely as does the night sky right now, dark, with all the objects in it as we see them.

 

I may also add, the observed redshift of extra-galactic objects, interpreted as a change in the scale factor to the metric (expansion, according Hubble's Law) would also be precisely identical in a stationary rest frame (in a non-expanding universe redshift z would still be observable).

 

Someone should start a thread about Olber's paradox, it's a great thing to trash. I would do it but I would hate to have the Coldcreation name attached to it on a search engine.

 

Don't fight the chill

 

CC

[Dov Henis]

Dear CC,

 

-The link refers also to the HST Key Project on the Extragalactic Distance Scale, see

 

http://www.ipac.caltech.edu/H0kp/

 

- I have only a scant informal background in astronomy. If asked why the sky is dark at night plain common sense will direct me to suggest the distances from us of the sources of light and maybe also the rate of expansion of the universe.

 

- Maybe someone more familiar with astronomy can explain what makes the "dark night question" a "cornerstone of modern cosmology"...

 

DH

[sanctus]

SO i asked now my professor about the difference between sub- and super- hubble scale and sub- and super-horizon.

 

The Hubble scale gives the limit distance of an two events connected by causality in the case of a non-inflanatory universe (ie one which never had a period of inflation). The horizon is the limit distance of causality for an inflanationnary universe, which can be bigger than the hubble scale!