Physicists have been trying to reconcile relativity and quantum mechanics for a century. And they have good reason

Reconciling the description of very large and very small is not easy. In fact, theoretical physicists flirt with the idea of ​​unifying general relativity and quantum mechanics For a little more than a century. Practically from the same moment that the two branches of physics saw the light at the beginning of the twentieth century. They haven't gotten it yet. And they don't because we face what many researchers consider to be the greatest challenge to modern physics.

General relativity is broadly concerned with describing the interaction between matter (or energy) and the space-time continuum. From this theory of the gravitational field published by Albert Einstein in 1915, it is clear that matter bends space-time, changing its geometry, which in turn determines the path of both moving objects and light. This theory was revolutionary at the time, and although it had been tested many times, it remained valid and intact.

Quantum mechanics, on the other hand, deals with very small things. From the world of particles and the interactions to which atomic and subatomic structures are exposed. Most of these rules are radically different from the laws we know. Richard Feynman Other physicists have argued strenuously that trying to understand this branch of physics is a futile effort. Its laws are so different from those we are accustomed to observing in the microscopic world that they escape our understanding.

Perhaps the long-awaited reconciliation between the two most beautiful theories is near

General relativity and quantum mechanics are beautiful. Ideal in itself, but incompatible. Each of them gives us a rich and consistent, yet partial, view of the universe. This is the main reason why physicists have spent so many decades trying to reconcile them. Without a unifying description of the rules governing the behavior of the very large and the very small, our view of the universe of which we are a part will remain partial. incomplete.

The strategy that most theoretical physicists have chosen so far when trying to reconcile general relativity with quantum theory has been to argue that the theory developed by Albert Einstein should be modified to make it “commensurate” with quantum theory. Actually, that's what Two quantum theories of gravity Currently supported: String theory and loop quantum gravity. The problem is that neither has been able to prove whether this is true, although both have had some notable successes.

However, there are more options. Jonathan Oppenheim, a professor of quantum theory at University College London, suggests modifying the latter so that it is able to coexist with general relativity while respecting the mechanisms that regulate the interaction between objects with mass and the space-time continuum. However, the assumption on which Oppenheim based his model is very original. The post-quantum theory of classical gravity defends the possibility that the space-time continuum cannot be described using quantum theory, so, in fact, its description would be quite classical.

Curiously, Einstein himself gave up trying to unify gravity and the other three fundamental forces of nature (electromagnetism, the strong nuclear interaction, and the weak nuclear interaction) into one His unified field theory. But there is still hope. More researchers are working in this field today than at any time in the past century. In addition, they are better trained and have more tools than their predecessors, so with a little luck, it's possible that the long-awaited theory of everything isn't as far-fetched as it might seem.

It is even possible that some of the theories we have just discussed briefly may serve to strengthen their validity. In the meantime, it's still worth turning to neutrinos as one of our best options when it comes to understanding the mechanics of quantum gravity a little better. These elusive particles are a great help in studying the structure of the space-time continuum and testing the basic principles of quantum mechanics. No more, no less.

Image | INCENT/A. Mueller (California Institute of Technology) via SMC

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