This diagram features the surface of the cosmic microwave background at a distance of one degree in angular size, which corresponds to around 380,000 light years in size:
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The fact that the CMB is so uniform is very puzzling..
An angular distance of one degree is roughly equal to a lump that is 380,000 lightyears across, which means that, as the universe itself was only 380,000 years old, light from one particular lump would not have had enough time to reach another and, subsequently, information would not have been able to be communicated between distant regions of the universe.
Therefore, there is no reason to expect the CMB to be so uniform.
This implies that some form of order preceded creation of the CMB.
In relation to our search for a method for measuring the curvature of the universe, we only need to take a look at the size of the primordial lumps present in the CMB.
This is because the largest lumps that could possibly form would have been 380,000 light years across, as, due to the age of the universe, if they were any larger gravity would not have been able to act on them and therefore they would not have been able to collapse.
Now, the apparent angular distance of a lump 380,000 light years across (1 degree), is dependent on the curvature of the universe.
In an open universe, light rays would bend outward as time reverses, therefore the lumps would appear smaller than it actually is, such as 0.5 degrees.
Likewise, in a closed universe light rays would bend inwards as time reverses, therefore the lumps would look larger, say 2 degrees.
However, in a flat universe light rays travel in a straight line and therefore the lumps would appear to be approximately 1 degree.
Therefore, all one has to do is simulate universes featuring lumps of 0.5, 1 and 2 degrees respectively, and then compare them with the image of the CMB.