The oldest electromagnetic signal that we can analyze is the cosmic background radiation, a testimony that comes from 13.8 billion years ago at the time of the Big Bang. Here’s what it is and why it’s so important
One of the most fascinating things about the universe is that at any moment we are literally immersed in a sea of photons of electromagnetic radiation that comes from the Big Bang. Just think that even today we continue to feel some of that warmth that was there at the beginning. If you turn on a radio, for example, a small part of the static noise is due to the cosmic background radiation, which we also talked about in a previous article. But what exactly is it and why is it so important for science?
The echo of the Big Bang
To understand this we need to go back to approximately for a moment 300 thousand years after the Big Bang. In the universe, at the time, there was nothing like what we see today. There were no stars, no galaxies, just protons and electrons. There were also helium nuclei made up of two protons and two neutrons and small traces of other light nuclei. Most of the matter, however, was composed of protons: many scientists believe there were also neutrinos and perhaps traces of dark matter particles that we still cannot explain exactly.
Then there were photons. They are the particles that make up light and any other type of electromagnetic radiation. In short, in the universe, at the time, there was so much light and so much heat. Normally protons and electrons tend to bond together to form hydrogen atoms, but in a situation like that they couldn’t, because there were too many photons and the temperature was too high. Among other things, photons interact with electrically charged particles such as electrons, so they could not travel freely.
The discovery of cosmic background radiation
If you were there, you would have seen nothing but glowing fog, a bit like being inside a star. We know, however, that the universe was expanding and electromagnetic radiation was also affected by redshift. So the frequency of electromagnetic radiation lowered, its energy decreased, and at a certain point, when the universe was about 380 thousand years the temperature was low enough that it could no longer break apart the hydrogen atoms. Protons and electrons bonded together to form hydrogen atoms, light was released and photons began to propagate throughout the universe.
Let’s put ourselves in the shoes of these photons that begin to travel in empty space for 13.8 billion years. At a certain point one of these ends up being captured by an antenna located in New Jersey (USA). It is the antenna thanks to which astronomers Penzias and Wilson discovered for the first time, in 1964, the existence of cosmic microwave background radiation. It is one of the most important discoveries in the history of science, giving us direct proof that the universe was hot and dense in the past. Which is exactly what the Big Bang model says. The fact that this radiation is very uniform also tells us that there are no special points in the universe and that every point in space is equivalent to all the other points. It’s amazing to think of being immersed in this at every moment sea of radiation which comes from the primordial universe.
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