## flatness of the universe, boomerang

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Theoretischer
Posts: 26
Joined: Sat Jan 31, 2009 5:59 pm

### flatness of the universe, boomerang

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Last edited by Theoretischer on Sun Feb 15, 2009 4:28 pm, edited 1 time in total.

pqortic
Posts: 398
Joined: Fri Aug 29, 2008 9:24 am

### Re: flatness of the universe, boomerang

what does this topic have to do with prospective Ss? it should be followed in lounge maybe.

coreycwgriffin
Posts: 249
Joined: Fri Nov 07, 2008 1:28 am

### Re: flatness of the universe, boomerang

Yeah...definitely the wrong place for this.

twistor
Posts: 1530
Joined: Thu Apr 13, 2006 2:47 pm

### Re: flatness of the universe, boomerang

Extremely interesting.

Did you read up to the end of the article? It explains that a flat universe theory predicts peaks in the microwave background to occur at specific places. That's how you can measure the geometry.

And let the mods worry about whether this post is in the right place or not.

gnatman
Posts: 10
Joined: Wed Feb 04, 2009 12:09 am

### Re: flatness of the universe, boomerang

It all depends on the energy density of the universe. There is a critical density, where if that's exactly how much energy we have, then everything is flat.

If we're over or under, than we get a closed sphere or an open saddle.

The thing that boomerang did was measure the anisotropies in the CMB, and those small deviations are heavily dependent on the energy density of the universe.

I found an article which gives a great explanation of it all here:
http://physicsworld.com/cws/article/print/601

nathan12343
Posts: 249
Joined: Sat Dec 20, 2008 9:34 am

### Re: flatness of the universe, boomerang

BOOMERANG was the first instrument to measure fine details in the CMB. WMAP was able to do the same thing, except using data covering the whole sky:

It turns out that the power in the CMB at various angular scales (the spatial Fourier Transform of the CMB map, more or less), is distributed into so-called 'acoustic peaks'. Here's a plot of the acoustic power spectrum of the CMB:

If you've seen a colloquium or talk on cosmology in the last 5 years or so, you've probably seen this data.

Anyway, the red fitted line in the plot is the prediction for a universe in which the total energy budget is approximately 70 percent cosmological constant, 25 percent cold dark matter, and about 5 percent normal 'baryonic' matter (e.g. protons and neutrons). This plot can also be used to find the total energy density by measuring where the first, big peak occurs. You can see in the plot that the peak is at about 1 degree of angular separation, and looking at the data by eye you can see that most of the structures are separated by distances of about a degree. A 1 degree angular separation corresponds to a universe which has exactly the 'critical' energy density and exhibits no spatial curvature. The measurement errors are small, less than 1 percent.