How to reconcile the two conflicting pillars of modern physics: quantum theory and gravity? For a long time, scientists believed that sooner or later science would recognize this or that theory as dominant, but the reality, as always, turned out to be much more interesting. New research suggests that gravity can arise from random fluctuations at the quantum level.
Among the two fundamental theories that explain the reality around us, quantum theory appeals to the interactions between the smallest particles of matter, while general relativity refers to gravity and the largest structures in the entire universe. Since the days of Einstein, physicists have tried to bridge the gap between these teachings, but with varying success.
One way to reconcile gravity with quantum mechanics was to show that gravity is based on indivisible particles of matter, quanta. This principle can be compared to how the quanta of light themselves, photons, represent an electromagnetic wave. Until now, scientists have not had enough data to support this assumption, but Antoine Tilloy (Antoine Tilloy) of the Institute of Quantum Optics. Max Planck in Garching, Germany, tried to describe gravity with the principles of quantum mechanics. But how did he do it?
Quantum world
In quantum theory, the state of a particle is described by its wave function. It, for example, allows you to calculate the probability of finding a particle at one point or another in space. Before the measurement itself, it is unclear not only where the particle is, but also whether it exists. The very fact of measurement literally creates reality by "destroying" the wave function. But quantum mechanics rarely addresses measurement, which is why it is one of the most controversial areas of physics. Remember Schrödinger's paradox: you cannot solve it until you take a measurement by opening a box and finding out whether the cat is alive or not.
One solution to these paradoxes is the so-called GRW model, which was developed in the late 1980s. This theory includes such a phenomenon as "flares" - spontaneous collapses of the wave function of quantum systems. The result of its application is exactly the same as if the measurements were carried out without observers as such. Tilloy modified it to show how it can be used to arrive at a theory of gravity. In its version, a flash that destroys the wave function and forces the particle thereby to be in one place also creates a gravitational field at this moment in space-time. The larger the quantum system, the more particles it contains and the more frequent flares occur, thereby creating a fluctuating gravitational field.
The most interesting thing is that the average value of these fluctuations is the very gravitational field that Newton's theory of gravity describes. This approach to uniting gravity with quantum mechanics is called quasi-classical: gravity arises from quantum processes, but remains a classical force. “There is no real reason to ignore the quasi-classical approach, in which gravity is fundamental at a fundamental level,” says Tilloy.
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The phenomenon of gravity
Klaus Hornberger of the University of Duisburg-Essen in Germany, who did not take part in the development of the theory, treats it with great sympathy. However, the scientist points out that before this concept forms the basis of a unified theory that unites and explains the nature of all fundamental aspects of the world around us, it will be necessary to solve a number of problems. For example, Tilloy's model can definitely be used to obtain Newtonian gravity, but its correspondence to gravitational theory still needs to be verified using mathematics.
However, the scientist himself agrees that his theory needs an evidence base. For example, he predicts that gravity will behave differently depending on the scale of the objects in question: for atoms and for supermassive black holes, the rules can be very different. Be that as it may, if tests reveal that Tillroy's model really reflects reality, and gravity is indeed a consequence of quantum fluctuations, then this will allow physicists to comprehend the reality around us at a qualitatively different level.
Vasily Makarov