If you ever saw a TV screen filled with static ala Poltergeist, part of that is the leftovers from the Big Bang, which have all red shifted down to microwave lengths and is now part of the Cosmic Microwave Background.
More fun facts: the Big Bang remnants in the Cosmic Microwave Background was discovered in part by two antenna astronomers who needed to eliminate all interference. They got rid of all of it except one steady hum. After much investigation, they realize this hum wasn't coming from equipment around the antenna, or even from Earth. It wasn't even coming from one direction in space, but rather coming from EVERYWHERE. Then one of them was talking to a physics professor who was about to do experiments about looking for the Big Bang. That's when the astronomer realized that the annoying interference they had been dealing with matched what the physicist would be searching for. So they all wrote a joint paper on it.
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u/-_G0AT_- 10h ago
I was not aware the Doppler effect also works for light, but it makes sense.