Why is the universe considered to be flat?

[Meron]

Hello!
I've read somewhere that the universe is flat and this can be proven by the fact that CMB is homogenous.

I still don't get the idea. So, can anyone explain it to me in more detail?

Please do correct me if I'm wrong.

Thank you.

 

[phinds]

The universe is not known for sure to be flat but it IS known to be flat to within the margin or error of the measurements we have been able to make and that is now down to .4%

http://en.wikipedia.org/wiki/Shape_of_the_universe

 

[wabbit]

Homogeneity of the CMB alone is neither necessary (there are flat anisotropic models, see Luminet's work) nor sufficient (a curved homogeneous space would also have a homogeneous CMB) to prove this though, I believe it comes as a result of the fitting of the LCDM model to a host of observations.

 

[Chronos]

The combination of CMB measurements and the HST key project provide some of the most compelling evidence the universe is flat. They are based on unrelated observations that correspond to different ages of the universe, yet they are in close agreement. For discussion see http://ned.ipac.caltech.edu/level5/March04/Page/Page3.html.