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'''{{PAGENAME}}''' radiation describes the [[electromagnetic wave]]s that propagate through our entire universe. It is thought to be left over radiation from the [[Big Bang]], but its true origin is unknown.

'''{{PAGENAME}}''' radiation describes the [[electromagnetic wave]]s that propagate through our entire universe. It is thought to be left over radiation from the [[Big Bang]], but its true origin is unknown.

Some believe that the cosmic microwave background contradicts [[relativity]]; it provides a way to irrefutably define what is moving and what is not moving. Since the cosmic microwave background is made of electromagnetic waves, a moving observer will observe a [[Doppler shift]] of the cosmic microwave background, whereas a stationary observer will not. Since the frequency of the cosmic microwave background is known (160.2 GHz <ref>http://www.physorg.com/tags/cosmic+microwave+background/</ref>), the velocity of the observer can easily be calculated. Our very Earth sees a Doppler shift in the cosmic microwave background.

Some believe that the cosmic microwave background contradicts [[relativity]]; it provides a way to irrefutably define what is moving and what is not moving. Since the cosmic microwave background is made of electromagnetic waves, a moving observer will observe a [[Doppler shift]] of the cosmic microwave background, whereas a stationary observer will not. Since the frequency of the cosmic microwave background is known (160.2 GHz <ref name="physorg">http://www.physorg.com/tags/cosmic+microwave+background/</ref>), the velocity of the observer can easily be calculated. Our very Earth sees a Doppler shift in the cosmic microwave background.

The thermal black-body spectrum of the cosmic microwave background is 2.725 K. <ref>http://www.physorg.com/tags/cosmic+microwave+background/</ref>

The thermal black-body spectrum of the cosmic microwave background is 2.725 K. <ref name="physorg" />

==Notes==

==Notes==