The Cosmic Microwave (CMB)Background RadiationModern satellite measurements show that the CMBdi tiCMB radiation is extremely uniform inuniform in all directions. The radiationThe radiation comes from a time about 400,000 years after the Big Bang, when theIf we look carefully there are tiny fluctuations in theabout 400,000 years after the Big Bang, when the universe’s temperature had cooled to about 3000 K.If we look carefully, there are tiny fluctuations in the CMB (1 part in 100,000)—the beginnings of galaxies.
ushdThe Expanding Universe•Today we see all galaxies flying away from usToday we see all galaxies flying away from us.•The farther away a galaxy is, the faster it ismovingmoving:A galaxy that is 2 × farther moves 2 × fasterA galaxy that is 3 × farther moves 3 × faster
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ushfThe Beginning of Time•The motion of galaxies is what we would expectfrom an explosion—a “Big Bang”•Extrapolating backward we find all galaxies were“on top” of each other 13.7 billion years ago.M ttddi tik d tthd•Matter and radiation was packed together andvery hot.