We do not know where the matter that gave rise to the Big Bang came from. What is considered the Big Bang model that explains the evolution of our universe and what we observe today fail to explain exactly the beginning of the cosmos. Why is it so? Well, because the description is based on the equations of general relativity that explain gravitational interactions. That is, they explain why the cosmos expands. But it is a classical description, that expansion of the universe depends on its content of matter and energy. As you know, in the relativistic description, energy and matter are interchangeable concepts. What happens is that the rest of the interactions between particles, when we go over very small distances, do have a quantum description, but gravity does not.
So because of that lack of a quantum description of gravity, when we get closer to that initial instant when everything is there in a very small volume, very hot, very dense, and very close to time equal to 0—which is what same as saying very close to the initial singularity—we think that the quantum effects of gravity have to play a role, but there is still no theory that describes it.
What the Big Bang model assumes is that what we see today, the entire structure of the universe made up of the fundamental particles, was already there from the beginning. What we don’t have is the answer to your question, where do they come from. We don’t know. What we do know is that they were there, so when we model the origin of the universe, we put them there. But we don’t have any theory that explains where they came from. What does exist are different hypothetical alternatives to explain it. One of them is that the universe is cyclical without beginning or end. But these are not theories, they are some ideas that have been proposed.
The problem with knowing what happened at that initial moment of the universe is that we are limited when it comes to observing it. With the technology that we currently have, we still do not have direct or indirect access to those initial moments. That is why we are not capable of developing a theory that can describe that initial moment and that singularity and, therefore, that allows us to know where the matter that was there at that first moment came from. We think that quantum corrections to gravity are going to play an important role in explaining it, but we still don’t know what those quantum corrections to gravity are.
But the truth is that little by little we are getting closer to that moment, so presumably there will come a day when we will be able to describe it. For example, the James Webb Space Telescope, which was launched two years ago, is now giving a wealth of information about the initial moments at which stars began to form. Oddly enough, we did not have access to that part of the evolution of our universe until now. With direct observations, the farthest we can go back is to the time when the background microwave radiation was decoupled. And now, for several years, what we have are observations of gravitational waves.
With these observations, so far the collision of black holes has been seen. But if quantum corrections to gravity or some other phenomenon like a certain period of inflation that we also assume took place at that first instant gave rise to gravitational waves, the goal is to be able to observe them, which would give us insight into that first instant. . This is not going to happen in the very near future, but science is like that, we ask ourselves the right questions and look for the answers. So it is possible that at some point we can answer your question.
Mar Bastero Gil She is a tenured professor and researcher of the High Energy Theoretical Physics Group (FTAE) at the University of Granada.
Question submitted by Alfredo Javier Navarro Cortes
Coordination and writing: Victoria Bull
we answer is a weekly scientific consultancy, sponsored by the Dr. Antoni Esteve Foundation and the program L’Oréal-Unesco ‘For Women in Science’, that answers the doubts of the readers about science and technology. They are scientists and technologists, members of MY T (Association of Women Researchers and Technologists), which answer those questions. Send your questions to [email protected] or by Twitter #werespond.
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