= Cosmic microwave background anisotropy
{tag=2006 Nobel Prize in Physics}
There is a slight variation in temperature of <CMB> across the sky of the order of 200 microKelvin. It is small to the ~2.7 K average temperature, but it can be measured.
If the <initial conditions> of the <Big Bang> and the <laws of physics> were perfectly symmetric, then we could expect the <Universe> to just be one perfectly uniform boring soup.
But instead some asymetry made all the fun weird things we see today happen eventually, like <galaxies> and <life>.
And the <cosmic microwave background> serves as a way for us to look back in time to the early conditions of the universe, as it was set in stone as soon as the universe became transparent to this <light> during <recombination (cosmology)>.
Or if you want to get poetic, it is the closest we can ever get to listening to the original word of <God> when he setup the <initial conditions> of the universe.
The ansiotropies of CMB is the ultimate astronomical compass we will ever have, as it is the thing with the least <proper motion>.
\Image[https://upload.wikimedia.org/wikipedia/commons/3/3c/Ilc_9yr_moll4096.png]
{disambiguate=ansiotropy}
{title=<Cosmic microwave background anisotropy> measured by the <Wilkinson Microwave Anisotropy Probe>}