The universe was born from nothing? At the beginning of everything, there was no matter and it appeared as a consequence of the evolution of the cosmos. Something we are still trying to understand.

Even though matter didn’t always exist in the universe, it must have been created very early on. I’m amazed by this, so naturally, my first question is: Where did it come from? What was the process? We are not talking about anything philosophical or religious, but simply about pure physics.

To try to understand this we must focus on one of the most surprising discoveries of modern cosmology: the acceleration of the expansion of the universe. To try to understand this we must focus on one of the most surprising discoveries of modern cosmology: the acceleration of the expansion of the universe. The projection of this result is that the expansion is forever and with a uniform velocity. But for this to happen, a critical density is necessary. This is the density that the universe must-have for the expansion to be effectively uniform and with constant velocity, which is currently about 14 hydrogen atoms per cubic meter.

Therefore, we must consider the following relationship: if the energy density in the universe is just enough for it to expand at a constant velocity, then the energy associated with that motion is equal to the energy associated with the distances between particles. In other words, the kinetic energy is equal to the potential energy. Now, since the energy of a material system is the sum of these two energies, then the total energy must be exactly zero. In other words, “the universe is born from nothing.” Amazing, isn’t it?

This result is not only one of the solutions of Einstein’s equations but also the one preferred by theoretical and observational astrophysicists. This is because all observational and theoretical evidence points in that direction.

## The universe was born from nothing

This result is not only one of the solutions of Einstein’s equations but also the one preferred by theoretical and observational astrophysicists. This is because all observational and theoretical evidence points in that direction.

If we now go into detail, there are three possible solutions to Einstein’s equations. The first option says that if the density of the universe is greater than the critical density, everything would (eventually) collapse into a black hole and we would decay into elementary particles. The second says that if the density is less than the critical density, everything would move away from everything and we would no longer see stars and galaxies in the sky, i.e. darkness. The third – the most popular at present – says that the universe has a critical density and total energy of zero. Don’t you find it incredible that the total energy of the universe is zero and here we are?

Much of the astrophysical activity of the last 20 years has focused on testing all of these points. All kinds of experiments and observations have been developed, huge telescopes and extremely sophisticated instruments have been built to measure the density of the universe. Very sophisticated methods have even been used; some use the kinematics or motion of galaxies, others the properties of background radiation or the remnant of the Big Bang, others large-scale structure, etc. All of these results agree that the density of the universe is the critical density, which means that the total energy of the universe is zero. This is not trivial to accept!

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