Stretching the Waves

There is another interesting way to think about the observed redshift in galaxy spectra. The photons emitted by a receding galaxy are like elastic bands in the fabric of the universe, and expand with it. In this sense, the redshift we measure from distant galaxies is nothing less than a direct measurement of the expansion of the universe.

We have seen where the universe and all that is within it have come from. Now we turn finally to where it is all going, where it will end. Will the universe expand forever? Or will it turn back in on itself and end in a final collapse? As it turns out, it all depends on gravity.

Depending on how much mass there is in the universe, it will either expand forever or collapse back in on itself in the opposite of a Big Bang: a Big Crunch. Recent observations of high-redshift supernovae and the cosmic microwave background suggest that a Big Crunch will never happen. The universe appears doomed to expand forever.

The Least You Need to Know

V The redshift of galaxies and the presence of a cosmic microwave background are two clues that the universe had a beginning.

V The cosmological principle holds that the universe is homogeneous (uniform in structure on large scales) and isotropic (it looks the same in all directions). This principle allows us to generalize from local observations.

V The leading theory of the origin of the universe is the Big Bang, which holds that the universe began as an explosion that filled all space.

V For the first 300,000 years after the Big Bang, the universe was opaque due to its own radiation. Once the universe was cool enough for electrons and nuclei to combine, it became transparent.

V All matter in the universe was created at the moment of the Big Bang. Since that time, stellar fusion and supernovae have converted the hydrogen, helium, and lithium into all of the elements of the periodic table.

Telescopes Mastery

Telescopes Mastery

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