Of all the concepts and topics discussed, the Big Bang is the most controversial concept. Of course, this is a fairly old scientific theory, present since the 1940s, and since the 1960s there has been a myriad of evidence to support it. The idea is simple: the universe had a beginning. It was her birthday. There was a day that didn't have "yesterday" when matter, radiation and the expanding, cooling Universe we know didn't exist until a certain point in time. And yet we are here. Which causes a flurry of questions from any inquiring mind. One of our readers just has such a mind, and he wants to know: Are there theories or experiments that can calculate and prove our location in space relative to the point of the Big Bang? I think that since our observing capabilities are very limited in terms of the location of our planet,it will not be easy to determine the curvature of space. Why do we think that the Big Bang happened at some point in three-dimensional space? Why do we think the universe is a sphere?
These are very good questions, and they all demonstrate a common understanding of the universe by people. But are these views correct?
We often think that the Big Bang was a real explosion. And the universe really resembled a huge, energetic and expanding fireball in its earliest stages.
It was filled with particles and antiparticles of various types, as well as radiation. All this expanded and all particles, antiparticles and radiation quanta moved away from each other. All of this cooled and slowed down as it expanded.
It really sounds like an explosion. In fact, if you could be transported into those first moments, and somehow protected from all this energy, there would even be a sound that you can hear thanks to the following video:
But it's not without reason that I use the word "expansion" instead of "explosion" when describing this phenomenon. An explosion is something that happens at one point in space, from which debris is scattered. A supernova is an explosion; a burst of gamma rays is an explosion; detonation of a bomb is an explosion; a grenade is an explosion.
But Big Bang is not an explosion [in English Big Bang, Big Bang, literally means "Big Bang" - approx. transl.]. When we talk about a "hot Big Bang", we mean the very first moment at which the Universe can be described as a state containing particles, antiparticles and radiation. From that moment on, the Universe began to expand and cool according to the laws of General Relativity, and we followed the path of the destruction of antimatter, the formation of atomic nuclei and neutral atoms, and, as a result, stars, galaxies and large-scale structures visible today. The key to the first question is to understand exactly what the universe was doing at that moment: at a moment that we can describe for the first time, based on this platform of the hot Big Bang.
Promotional video:
As far as we know, there was no particular starting point. There was no "source" from which the universe began. All the evidence speaks of a counterintuitive, but no less true conclusion: the Big Bang happened everywhere at the same time. There is plenty of evidence for this, and the Universe itself gives them to us. The Universe, judging by the large-scale structures, clusters of galaxies, the appearance of the Big Bang afterglow, the average density of areas of space over several hundred million light years in size, etc., gives us two important observable facts. Its properties are the same everywhere, and it looks the same in all directions. Physically speaking, the universe is homogeneous and isotropic.
Such characteristics of the universe cannot be obtained with an explosion - period. In an explosion, the fastest moving fragments are the most distant, but also the most dispersed in space. The greater the distance, the less there should have been galaxies per unit volume - but this is not the case in the Universe. In the event of an explosion, it would be possible to explicitly indicate its starting point. The universe works in such a way that this point would be only a few million light-years from the Milky Way, on the border of the local group. Statistically, the chances of such a point, given the presence of more than 170 billion galaxies in the Universe, are 100 times worse than winning the Powerball or Mega Millions lottery.
The fact that the universe is homogeneous and isotropic suggests that the Big Bang happened at the same moment, about 13.8 billion years ago, and is the same in all places. But we cannot see him in all places. We see him only where we are. Our review is limited. Therefore, you can often find such illustrations: how our Universe is seen from our point, with us in the center.
But this does not mean that the universe is a sphere! We can actually measure the shape of the universe, and put some restrictions on it. If you go outside and send your two friends in two different directions so that you can see each other, you three will form a triangle. Each of you will be able to measure the apparent angle between the other two. Then you can add those angles and you get 180º - this is the sum of the angles of the triangle.
Any triangle in flat space.
But the space doesn't have to be flat! It can have a negative curvature like a saddle surface when the sum of the angles is less than 180º. It can be curved positively, like the surface of a sphere, when the sum of the angles is greater than 180º. If you stand at the equator in South America, one of your friends stands at the equator in Africa, and the other at the North Pole, you will find that the angle difference will be large. The sum of the angles will turn out to be closer to 270º than to 180º. We don't have friends in space, but we have something just as good: fluctuations in background radiation. Depending on the curvature of the space, they should look completely different.
We made observations and found something amazing: The universe, as far as we can tell, is flat. Very, very flat. Recent evidence from the Planck experiments and the Sloan Digital Sky Survey suggests that if the universe is curved - positively or negatively - it is noticeable on a scale at least 400 larger than the part of the universe that we observe. And we can see a part of it with a diameter of 92 billion light years.
So, the Big Bang happened everywhere simultaneously, 13.8 billion years ago, and our universe is spatially flat according to our best measurements. The Big Bang did not occur at some point, and we can judge this by the extreme isotropy and homogeneity of the universe. These properties are so accurate that when we come across an inhomogeneity with a deviation of 0.01% of the mean, we already think that something is wrong. So if you claim that the Big Bang happened exactly where you are, and you are standing right in the center of everything that happens, no one will object to you. It's just that everything and everything, in the entire Universe, can say the same about itself.