Saddle Up the Horses Into the Wide Open Universe

It is difficult to visualize this open universe of infinite extent. The closest two-dimensional approximation is the surface of a saddle, curved up in one direction and down in the other—and extending out to infinity. In an open universe, beams of light that were initially parallel would diverge. Our current estimate of the density of the universe and the recent results from distant supernovae suggest that this is the type of universe we inhabit.

With precisely critical density, by the way, it becomes a flat universe, albeit still infinite in extent. In what we call flat space, parallel beams of light would remain parallel forever. For this reason, flat space is sometimes called Euclidean space.

Images from the BOOMERANG mission. The scale size of the temperature fluctuations in the microwave background can tell us about the geometry of the universe. A flat universe should have fluctuations with scale sizes of about 1 degree. In a closed universe the fluctuations would be larger, and in an open universe, they would be smaller. Along with other evidence, the BOOMERANG data strongly suggests that we live in a universe with a flat geometry.

(Image from NASA and University of California, Santa Barbara)

Telescopes Mastery

Telescopes Mastery

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