Background or relict radiation of the Universe falls every second in a continuous flow to the surface of the Earth. Only a tiny part of the Universe's radiation is visible to the naked eye, though if we could see the whole electromagnetic spectrum, the sky would burn with this original radiation both day and night. There is no need to think that part of this hidden light is a very inexpressive glow.
The long-wavelength universal glow - the cosmic microwave background or relict radiation - shows the changes that have occurred. The cosmic microwave background carries in itself an image of our Universe as it was right after the birth, and this discovery has given us proof that the beginning of the Universe was really put by the Big Bang.
Radio waves - messengers with information
The Namib Desert stretches along the west coast of South Africa. It is the oldest desert in the world; its landscape is a volatile sea of sand, stretching over 77,700 square kilometers and changing every minute. It is the driest desert on the planet that has not seen moisture for more than 50 million years. It is a sun-molded world. Its energy drives the wind, which collects tiny grains of sand into magnificent dunes, and the colors hidden in its light paint the landscape dark orange. But even when the sun sets, the desert continues to shine with light and color, but the human eye cannot see it.
Visible light represents a tiny fraction of the light of the universe. Outside of red, the electromagnetic spectrum extends far beyond the waves that are too long for our eyes to see. In the Namib desert, you can feel this light if you bring your hands to the sand. The dunes store heat for a long time after sunset, and this residual heat is nothing more than longwave light. A scientist would call it infrared light: the wavelength of infrared light is longer than the wavelength of visible light. Traveling further across the entire spectrum, bypassing infrared light, we arrive at the microwave: the spectrum flows smoothly into the radio wave region, the length of which is the size of a mountain.
When you monitor the radio, you do not tune in to sound waves - you collect information encoded in the electromagnetic spectrum. There is a lot of visible, non-artificial light in the universe, and there are natural microwaves and radio waves. These are messengers who carry detailed information about distant places and times all over the universe and send it to our technologically created artificial eye.
The Big Bang Echo
If you walk the old radio on the air, you can hear static noise between the stations. About 1 percent of it is music for the ears of the physicist because with this sound we perceive how the radio waves that have been traveling through space since the beginning of time are stretched.
Deep down in the statics, the Big Bang echoes. These radio waves were once visible light, but this light came about 400,000 years after the Big Bang. Prior to it, the Universe being born was much smaller and hotter than it is today. Its temperature was 273 million degrees Celsius, which is much hotter than in the center of the star, so hot that the nuclei of hydrogen and helium could not keep their electrons in the atoms. Matter that laid the beginning of the universe was a superheated ball of naked atomic nuclei and electrons, that is, it was a plasma. Light cannot move far away in dense plasma because it is reflected from electrically charged subatomic particles.
Only when the Universe has expanded and cooled down enough for electrons to be combined with hydrogen and helium nuclei into atoms - only then can light move freely. Scientists call this episode of evolution of the universe recombination. Before the birth of the universe was about one-thousandth of its current size and cooled down to 3000 degrees Celsius. This is close to the surface temperature of the red giants, so that the whole set of matter, energy and space glowed with visible light, as huge stars.
Since then relic radiation of the Universe began to extend freely in Space.
The whole space has become colder and more spacious, and some of these "wandering messengers" - the stretched waves of light we "collect" today by means of radio monitoring. However, as the Universe expands, so does Cosmos. The same thing happens to light, so much so that it goes beyond the visible part of the spectrum. It has gone beyond the infrared part of the spectrum, and now we can only "see" it in the microwave and radio wave parts of the spectrum.
These weak, long waves of universal glow - the cosmic microwave background or the relict radiation of the universe - were discovered in 1964 by American physicists Arnaud Penzias and Robert Wilson and became the key proof that the whole body of matter, energy, and space began with the Big Bang. Penzias and Wilson were awarded the Nobel Prize in 1978 for this discovery.
Nowadays, the science of astronomy and cosmology is studying the large-scale whole evolution of the universe.