Before the formation of the first stars, the Universe was already filled with light. But how?

Light believes that he is the fastest, but he is mistaken: no matter how fast the light flies - the darkness is already in place and is waiting for it.
- Terry Pratchett

If we look at the Universe, we see dots of light scattered over the vast empty darkness of the sky: stars, galaxies, nebulae, and so on. But in the distant past there was a time before all these objects were formed and shortly before the Big Bang, when the Universe was filled with light. This week, Professor of Chemistry Fabio Gochcho was unable to answer one question and sent him to our rubric:

I try to keep students informed about what's going on using your blog. Recently, during the discussion of the Big Bang, a good question was asked: where did the photons come from at CIPI ? As I understand it, they appeared as a result of the annihilation of pairs of particles / antiparticles, resulting from quantum fluctuations after inflation. But wasn’t this energy supposed to “return”, since they were initially “borrowed” to create particle / antiparticle pairs?

Some things in the question of Fabio are very precisely formulated, but there are also delusions. Let's first take a look at KMFI and the question of its origin in the distant past.
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In 1965, a duet from Arnaud Penzias and Robert Wilson worked at Bell's laboratory in Holmdel, New Jersey on calibrating a new antenna for transmitting radar signals from satellites. But no matter where they directed their antenna, they received noise. He was not associated with the Sun, other stars or planets, or even the plane of the Milky Way. It continued day and night, and its power did not change from direction.

After a long confusion about the nature of the noise, they learned that a team of researchers, literally 30 miles away, at Princeton, predicted the existence of such radiation, not the result of anything happening on our planet, in the Solar System or the Galaxy. The radiation was to be born in a hot dense state in the early Universe: at the moment of the Big Bang.



For decades, we measured the radiation with increasing accuracy and found that it was not at 3 degrees above absolute zero, but at 2.7 K, then 2.73 K, then 2.725 K. And perhaps the greatest Of all the achievements concerning this residual luminescence, there was a measurement of its spectrum, which showed the spectrum of an ideal black body. The result is consistent with the Big Bang theory and not consistent with other theories, such as reflected starlight or tired light theory.




A little later, we even measured - based on the absorption and interaction of this light with gas clouds - that the temperature of this radiation increases the more we look back in time (and in the direction of the red shift).

With expansion, the universe cools down, and when we look further into the past, we see a smaller, denser, and hotter universe.



And where does this light - the first light of the universe - come from? He did not come from the stars, because he is older than them. It was not emitted by atoms, because it appeared before atoms were formed. If we continue to extrapolate back to higher and higher energies, we will find out a lot of strange things: thanks to Einstein E = mc ² , these light quanta can interact with each other and spontaneously generate particle / antiparticle matter and antimatter vapors!



And this, as Fabio correctly pointed out, is not virtual pairs of matter and antimatter particles, existing a fraction of a second due to the Heisenberg uncertainty principle and the inequality ΔE Δt ≥ ћ / 2, but quite real particles. As two protons colliding in a LHC can create a large number of new particles and antiparticles (possessing sufficient energy), two photons in the early Universe could create everything that they had enough energy for. Extrapolating back in time, it can be concluded that, shortly after the Big Bang, in the observable Universe contained about 10 ⁸⁹ particle / antiparticle pairs.

If any of you are interested in how the Universe turned out to be filled with matter (and not antimatter) - there must be some process that creates slightly more particles than antiparticles (in a ratio of about 1 in 1,000,000,000) from the initially symmetric state , leading to the fact that the universe now contains 10 ⁸⁰ particles of matter and 10 ⁸⁹ photons.



But this does not explain where all the matter, antimatter and radiation came from. Entropy is large, and a simple explanation of “the Universe began with this” will be unsatisfactory. But if we turn to solving a completely different set of tasks - problems of the horizon and problems of flatness - the answer to the first question will appear itself.



Something had to happen to set the initial conditions of the Big Bang and this is something — cosmic inflation, or a period when the most energy in the Universe was contained not in matter (or antimatter) or radiation, but in the energy inherent in the space itself, in the early, superintensive form of dark energy.

Inflation straightened the Universe, set the same initial conditions everywhere, scattered all of the initially existing particles or antiparticles and created germinal fluctuations where in the Universe density is now increasing or decreasing. But how to understand where all these particles, antiparticles and radiation come from? They came from one simple fact: to get our today's Universe, inflation had to end. In terms of energy, inflation occurs when you slowly descend into a potential hole, but when you have already descended into the valley below, inflation stops and converts this energy (accumulated on top) into matter, antimatter and radiation and generates what we call the Big Bang .



Here's how to imagine it.

Suppose we have a huge, endless surface of cubes pressed together and held together by an incredibly large force of gravity. A heavy bowling ball is rolling along them. In most places, the ball will not make large disturbances, but in some weak points the ball will leave dents. In one happy place the ball will break through a few blocks, and they will fall. What happens after that? The loss of several blocks will lead to a chain reaction due to the absence of tension and the whole structure will crumble.



Falling cubes on a very distant surface will mean the end of inflation. And there the energy inherent in the space itself is transformed into real particles. Due to the fact that the density of space energy was so high during inflation and a large number of particles, antiparticles and photons created at the end of inflation appear.

This process, the end of inflation and the appearance of the Big Bang, is known as re-cosmic heating, and as the universe cools and expands, the particle / antiparticle pairs annihilate, creating even more photons and leaving behind a small amount of matter.



When the universe continues to expand and cool, nuclei, neutral atoms appear, and then stars, galaxies, clusters, heavy elements, planets, organic molecules and life. And all this time, those photons left after the Big Bang, traces of the end of inflation, which started this whole process, fly through the Universe, gradually cooling down, but not completely disappearing. When the last star of the universe goes out, these photons — long ago shifted to the radio band and dispersed to the density of one piece per cubic kilometer — will still be present in the same amount as they were trillions and quadrillions of years earlier.

This is where the first light in the universe came from and how it came to today's state. Thank you for the wonderful question that allowed you to tell an amazing story, Fabio! Send me your questions and suggestions for the following articles.