One of the versions of the origin of our Universe is the Big Bang theory. It is based on a simple thought – the universe had a beginning. T&R, together with the author of the podcast “The Theory of the Big Beard”, Anton Pozdnyakov, explains the theory in simple terms and tells how the “explosion” took place.

What is the essence of the Big Bang theory?

The Big Bang Theory is a cosmological model that describes the early stages of the universe. It is based on a thought that until recently was not at all obvious – our universe had a beginning.

At the beginning of the 20th century, astronomers discovered that galaxies distant from us scatter in different directions. It follows from this that our Universe is not static, but expanding. And if expansion occurs over time, then sometime in the past it should have begun. It is the moment from which the expansion of the Universe began that is now called the “Big Bang”. According to modern estimates, this happened 13.8 billion years ago.

Talking about what happened before the Big Bang is not entirely correct. According to modern physical concepts, the very concept of time, in our understanding, did not exist then. There was no “before”, no “after” or “during.” The Big Bang theory describes the early stages of the expansion of the Universe, that is, the events that took place immediately after the Big Bang.

How the Big Bang happened

All processes after the Big Bang were because the Universe was gradually cooling down and becoming less and less dense. As we know, the temperature is a measure of how particles move. The temperature drops – the particles slow down. The slower the particles move, the easier it is for them to connect. As the universe cooled down, at first, separately flying quarks were able to combine into protons, neutrons, and other hadrons and leptons. Then the already obtained particles, continuing to slow down, began to form the first nuclei of the atoms familiar to us.

The period of formation of the first atoms in the Universe is called primary nucleosynthesis. It lasted about 20 minutes after the Big Bang. During this period, the entire Universe was heated to the state that we observe today inside the stars. During this period, the nuclei of hydrogen and helium were mainly formed in a ratio of 3 to 1. We still observe such fractions of hydrogen and helium, the two most common elements in the Universe.

One of the most frequently asked questions is where exactly did the Big Bang take place? After all, if there was an explosion, there must be an epicenter. But in fact, this is a delusion that comes from the not entirely correct term “explosion”. The fact is that our Universe does not have a center (approximately how it is impossible to designate a center on the surface of a sphere). It would be more correct to imagine that the Big Bang happened everywhere at once, in all points of the Universe at the same time.

After the end of the primary nucleosynthesis, and new atomic nuclei were almost not formed, the Universe was still hot enough that the matter in it was in a state of plasma. In it, electrons flew separately from the nuclei. And thanks to free-flying electrons during this period, the Universe was opaque to light. The photons constantly collided with electrons and could not fly straight, as if they were blocked in a mirror maze. Therefore, by the way, you cannot see them through a fluorescent lamp or our Sun. They, too, are composed of plasma and therefore are opaque.

The universe continued to cool, and about 300,000 years after the Big Bang, the temperature dropped enough for electrons to attach to the nuclei of atoms, and as a result, the universe became transparent. This moment is called recombination. The photons, which filled everything around, no longer saw obstacles in the form of electrons and were able to fly straight. Moreover, from everywhere and in all directions at once.

Actually, it is precisely those photons that were “released” at the moment of recombination that we see today. More than 13 billion years later, they reach us in the form of relic radiation  – the microwave cosmic background that we register with modern telescopes.

The detection of the CMB is one of the main confirmations of the Big Bang Theory. Its important feature is uniformity. It is the same no matter which direction we look. It also indirectly confirms that the universe does not have a certain direction. Wherever we look, on a large scale, the universe is the same in all directions.

Today there are many confirmations of the Big Bang Theory. We observe the expansion of the Universe and see how galaxies and intergalactic structures were formed at different stages of the evolution of the Universe, we observe the predicted ratio of helium and hydrogen in the latter. They all agree with the current ideas about the early stages of the formation of the Universe, which TVB describes.

In the theory itself, some inaccuracies will need to be eliminated by furthermore accurate and detailed astronomical observations and the development of more perfect physical models. But the amount of independent cross-sectional data that modern cosmology already has in its hands allows us to say with confidence that the Big Bang, which became the starting point for the expansion of the Universe, really happened, and everything around us is its direct consequences.

More information about the Big Bang theory can be found in the  release of a podcast, “The theory of the big beard.” Its host talks in simple words about science and space communicate with guests from the scientific world and examines concepts from the scifi world.