You should remember that the old TV used to receive satellite signals by antenna. When we tune in, sometimes there will be no program screen full of snowflakes, accompanied by the sound of ho ho. In this case, everyone knows that the signal is disturbed or in the state of no signal, but few people know that the snowflake screen we see at this time is actually from the big bang.
The big bang took place 13 billion years ago. At that time, human beings did not exist. The big bang was very violent, but the heat it emitted has not completely dissipated. The heat of the big bang was initially ultra-high temperature X-rays. As the temperature dropped and the wavelength stretched, they turned into visible light, and moved from the blue end to the red end, and then turned into microwave, and finally into radio waves and radio waves Waves radiate all the time in the universe and also to the earth, which is called cosmic microwave background radiation. This is the echo of the Big Bang itself and the afterglow of the shock wave when the universe was born.
With the appearance of satellite communication system on the earth, the TV antenna can receive the microwave radiation and show it on the TV screen. If human beings can have a pair of eyes that can see the microwave, then we can see the spread of the big bang every night.
As we all know, light has speed. According to the exact calculation, the sun we see now is actually the sun eight minutes ago. When we look deep into the universe, the stars we see may be in the state of stars ten years ago or more. Then we can see the snowflake screen, which is also the continuation of the big bang. It comes from the past, from the cosmic microwave background radiation, because all radiation will not disappear, but will only be spread farther away. When it radiates to the receiving antenna of our TV, it will be translated into this kind of image (snow screen). Of course, this image comes from all kinds of clutter in the circuit, but it can be determined that 1% of it really comes from cosmic microwave background radiation.