Ever since humans started asking questions, they’ve been popping up. descriptions, hypotheses and explanations who tried to answer them, to make sense of what we observed around us. From why a stone fell or why the fire burned, to how living things work, why they get sick and die or why there is so much diversity in them. And during those thousands of years we’ve learned, countless theories that they are gone being improved or that have been discarded when a better explanation was found, one that predicted more or the same phenomena but with greater accuracy.
A very clear example of one of these theories is that of Universal Gravitation, Newtonwhich at the beginning of the 20th century was replaced by the more complete, accurate and “correct” one (we put this term in quotation marks because it has many nuances, which perhaps are outside the scope of this article) Einstein’s theory of general relativity. Both describe the severity, the gravitational attraction between different bodies, but Einstein’s theory predicts its consequences more accurately. This was demonstrated shortly after the formulation of that theory, measuring the light deviation coming from distant stars when it passed close to the Sun, or by measuring the precession of Mercury’s orbit around the star king. Both theories were able to explain these phenomena and predict the importance they should have, but it was Einstein’s theory that was more in line with reality, with the measurements of our experiments. Therefore, general relativity replaced universal gravitation.
Something similar happened at about the same time. O quantum mechanicsalso developed at the beginning of the 20th century, was able to explain concepts and observations that were not understood by any other theory at the time, so that this new physics replaced classical physics. Quantum physics is not really a single concrete theory that applies to one part of physics, but rather a tool kit with which to build theories, so what was replaced were these tools.
Today these two theories work side by side to help us understand the universe that we inhabit the quantum field theory for example, is the result of the union of quantum mechanics with special relativity, and in our cosmological models we take into account the predictions of general relativity, but also of the different theories that use quantum field theory to describe how fundamental particles interact.
However, although these theories are among the most accurate that science has provided, predicting some properties of, for example, the electron accurately within a billionth of a part, there are still some discrepancies between experimental observations and theoretical predictions that they are not able to solve. One is known as “cosmological constant problem”considered one of the biggest mistakes in the history of physics.
The cosmological constant is a concept introduced by Einstein shortly after proposing his theory of General Relativity, which would serve to counteract gravity and create a static universe, which neither expanded nor contracted, as that was the conception of the universe at the time. Just over a decade later Edwin Hubble showed that really the universe was expanding, since he measured how the galaxies were moving away from the Milky Way and that they were also doing so with a speed proportional to the distance that separated us. After this discovery Einstein discarded its cosmological constant but some six decades later it had to be recovered with the discovery that the universe is expanding rapidly. Currently, the person responsible for this accelerated expansion would be what we call “dark energy”whose simplest form would be that of a cosmological constant.
From quantum field theory, this constant is understood to be the empty space energy. The different fields that would represent the different particles and the interactions that govern them would permeate all of space, concentrating on those points where we would classically say that a particle exists. All these fields would have fluctuations that would contribute to the energy of a region of space. Although these change over time and are different for each field, a kind of average contribution can be calculated, which would give us the energy corresponding to each point in space that we consider empty. O theoretical prediction what we arrive at in this way is a value 120 orders of magnitude greater than experimental measurement of vacuum energy. That is, the theoretical result has 120 more zeros than the experimental result. Such a discrepancy is, in principle, irreconcilable.
Although some modern calculations are capable of reducing this difference to approximately 60 orders of magnitude, with more precise considerations it is evident that there is something that we are not taking into account. That’s why this difference is known as one of the biggest problems in physics today.
Bengochea, GR; Leon, G.; Okon, E; Sudarsky, D (January 11, 2020). “Do quantum vacuum fluctuations really solve the cosmological constant problem?”. The European Physical Journal C. 80 (18), doi:10.1140/epjc/s10052-019-7554-1