How do we determine that the size/shape of “hot/cold spots\ in the CMBR tell us anything about curvature?
It’s hard to draw the picture here, but here’s the idea: if the universe is closed (), two parallel light beams will eventually cross; if the universe is open (), light beams will diverge. Consider looking at a CMBR blob representing a temperature fluctuation. If the universe is flat, you will see the blob to have its actual size. If the universe is closed, light rays coming from the opposite edges of the blob will bend towards each other: the image you see will then look larger. If the universe is open, light from opposite edges of the blob will give an image that looks smaller. The upshot is that curvature of spacetime distorts the sizes of the blobs, and the specific pattern that is observed corresponds to a flat geometry.
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- How do we determine that the size/shape of ``hot/cold spots\ in the CMBR tell us anything about curvature?
