Universe finite more likely now

[Martin]

this paper came out 10 january 2005

http://arxiv.org/astro-ph/0501171

it makes it seem more likely (than say a year ago) that the universe is finite

 

To keep in touch with current developments in cosmology it can be helpful to check Ned Wright's "News of the Universe" at his website.

Ned is one of the top halfdozen cosmologists in the world and teaches at UCLA and is one of the directors of WMAP (satellite now mapping the cosmic microw. backgrd)

 

http://www.astro.ucla.edu/~wright/intro.html

 

Ned gives the reference to this paper (48 authors, Sloan Survey) and then he comments. His comment may be easier to understand than the paper

 

Ned Wright featured this article in his "News of the Universe" for 11 January 2005:

 

http://www.astro.ucla.edu/~wright/cosmolog.htm#News

 

he references astro-ph/0501171, and has this to say

 

"Cosmic Ripples Seen by Galaxy Surveys

 

11 Jan 2005 - Both the Sloan Digital Sky Survey and the 2 Degree Field Galaxy Redshift Survey reported the discovery of features in the distribution of nearby galaxies that correspond to the oscillations seen in the anisotropy of the Cosmic Microwave Background for several years. The overall statistical significance of this result is good but not great: 3.5 standard deviations. But observations of these ripples provide two valuable new constraints on cosmological models, and verify the current Lambda-CDM model of the Universe. The detection of these ripples is shown at right in a version of Figure 3 from a technical paper describing these results. It gives a matter density in gm/cc that agrees with the value found by WMAP. Both WMAP and the SDSS measure this density to a precison of 8% and their values agree to within 5%. Combining the CMB and SDSS data gives an improved limit on the total density of the Universe: Omega_tot = 1.01 +/- 0.009. If Omega_tot = 1, the Universe is flat; if Omega_tot > 1 the Universe is closed; while if Omega_tot < 1 the Universe is open."

 

"Figure 3" which Wright reproduced is on

page 5 of the paper.

 

When Wright says "if Omega_tot > 1 the Universe is closed" he doesn't mean by closed that it eventually must collapse in a Big Crunch. (that used to be the way people thought, but no longer)

what closed means in this context is spatially finite. this does not make collapse inevitable.

a closed universe with positive cosm. const. can continue expanding.

 

what Wright is pointing out in his "news of the universe" blog is that if we accept the finding of this new paper the error bar for Omega is now

1.001 to 1.019

 

the Omega = 1, spatially flat, case is no longer in the likely range

[aguy2]

When Wright says "if Omega_tot > 1 the Universe is closed" he doesn't mean by closed that it eventually must collapse in a Big Crunch. (that used to be the way people thought' date=' but no longer)

what closed means in this context is spatially finite. this does not make collapse inevitable.

a closed universe with positive cosm. const. can continue expanding.

[/quote']

 

I couldn't find Wright's reasoning on why Omega>1.0 would not indicate a Big Crunch condition.

 

aguy2

[Martin]

I couldn't find Wright's reasoning on why Omega>1.0 would not indicate a Big Crunch condition.

 

aguy2

 

dark energy AKA positive cosmological constant

 

since 1998, working cosmologists have assumed some percentage (like 70 percent) dark energy and therefore have no math proof to imply that Omega > 1 necessarily implies crunch.

the old proof breaks down because of the new term in the Friedmann eqn.

 

So Wright didnt have to supply reasoning because a typical reader of his webpage would not assume that Omega > 1 necessarily implies crunch

and there is nothing he needs to explain to the typical informed reader.

 

but maybe YOU think that that Omega > 1

necessarily implies crunch. Why then, what are your reasons?

You must have some math to back it up.

 

the math that used to imply crunch broke in 1998.

 

BTW if you know differential equations, the real answer is in the Friedmann equation when you put in a positive Lambda (cosm. const.) terms. you see permanent expansion. A copy of the friedmann eqns. are in the Astr. and Cosm. "sticky" thread