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Cosmic Microwave Background

In 1964 two astronomers were studying microwave signals from space and noticed that there was a constant background signal coming from all points in space. The type of signal was consistent with the radiation emitted by an object which was at a temperature of about 2.7 K.

Figure 15.4: Microwave background
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This background is (nearly) uniform in intensity across the sky. The big bang model theoretically predicts that such background radiation would be present in the universe today some 12 or so billion years after the initial big bang.