Quantum theory against gravity

How to reconcile two contradictory pillars of modern physics: quantum theory and gravity? For a long time, scientists believed that sooner or later science recognizes one or another theory of the dominant, but the reality as always turned out to be much more interesting. New research claims that gravity can arise because of random fluctuations at the quantum level.

Among the two fundamental theories explaining the reality surrounding us, quantum theory appeals to the interaction between the smallest particles of matter, and the general theory of relativity refers to gravity and the largest structures in the entire universe. Since the time 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 with how the quanta of light, photons themselves, represent an electromagnetic wave. So far, scientists have not had enough data to confirm this assumption, but Antoine Tilloy (Antoine Tilloy) of the Quantum Optics Institute. Max Planck in Garching, Germany, tried to describe gravity by 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 in a particular point of space. Before the measurement itself, it is not clear not only where the particle is located, but also whether it exists. The very fact of measurement literally creates reality, “destroying” the wave function. But quantum mechanics rarely turns to measurements – that’s why it is one of the most controversial areas of physics. Remember the paradox of Schrodinger: you can not solve it until you make a measurement, open the box and find out if the cat is alive or not.

One solution to such paradoxes is the so-called GRW model, which was developed in the late 1980s. This theory includes such a phenomenon as “flares” – spontaneous collapse of the wave function of quantum systems. The result of its application is exactly the same as if the measurements were conducted without observers as such. Tilloy modified it to show how it can be used to solve the theory of gravity. In its version, a flash that destroys the wave function and causes the particle to be in the same place also creates a gravitational field at this moment in space-time. The larger the quantum system, the more particles in it and the more frequent flashes, thereby creating a fluctuating gravitational field.

The most interesting is that the average value of these fluctuations is the gravitational field described by Newton’s gravitation theory. This approach to combining gravity with quantum mechanics is called quasiclassical: gravity arises from quantum processes, but it remains a classical force. “There is no real reason to ignore the semiclassical approach, in which gravity is classical at the fundamental level,” Tilloy says.

The phenomenon of gravity

Klaus Hornberger from the University of Duisburg-Essen in Germany, who did not participate in the development of the theory, treats her with great sympathy. However, the scientist points out that before the concept becomes the basis of a unified theory that unites and explains the nature of all the fundamental aspects of the world around us, it will be necessary to solve a number of problems. For example, the Tilloy model can exactly be used to obtain the Newtonian gravity, but its correspondence to the gravitational theory still needs to be checked with the help of 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 under consideration: for atoms and for supermassive black holes, the rules can be very different. However, if the tests reveal that Tillroy’s model really reflects reality, and that gravity is indeed a consequence of quantum fluctuations, then this will allow physicists to comprehend the reality around us at a qualitatively different level.