Illustration of a quantum experiment to study the force of gravity on a small scale (University of Southampton)

Four forces govern the pattern of interactions between matter in the universe, and they are called "the four fundamental forces of nature": the strong nuclear force, the weak nuclear force, the electromagnetic force, and finally the gravitational force, which is completely different from the others.

The force of gravity in its origin is nothing but the effect of the curvature of the cosmic fabric or space-time on matter, so to speak. For this reason, gravity does not lend itself to merging with the rest of the three forces that are all united within the framework of quantum theory.

The effect of gravity is basically weak when compared to other things, and appears clearly only at the level of large objects or macroscopic scales (which can be observed with the eye), while quantum theory (quantum mechanics) deals with atoms and subatomic particles, and this means that physicists are unable to know what It affects the force of gravity at subatomic levels, where quantum effects dominate.

Quantum effects are unusual phenomena that occur at the level of small particles such as atoms and molecules, such as fusion, dispersion, and interference between particles.

These effects are completely different from what classical physics suggests, and quantum effects today play an important role in computer science, communications, and other scientific fields.

In a recent study published in the peer-reviewed scientific journal Science Advances, entitled “Measuring Gravity with Suspended Masses in Milligrams,” researchers have identified a way to measure gravity at microscopic levels, which will hopefully lead them to a broader understanding of the theory of “quantum gravity,” which will be the gateway to solving some of the greatest mysteries. Universe.

Relativity is described by Einstein's field equations in general relativity, while quantum theory is described by equations such as the Schrödinger equation or quantum field theory equations such as the Dirac equation or the Klein-Gordon equation (Shutterstock)

Relativity physics and quantum physics

While quantum theory provides scientists with the best description of the universe on microscopic scales, Albert Einstein's theory of general relativity provides the best description of physics on massive cosmic scales.

After 100 years have passed since the emergence of the two theories, there is still a missing link that connects them into a single entity that explains the mechanism of operation of the universe as a whole, noting that both theories have proven correct within the scope assigned to them.

One of the most basic reasons preventing the union of the two theories is that gravity lacks a quantum theory to describe it, while the other three forces have quantum descriptions.

The research team has made progress in addressing this defect by detecting a weak force of attraction on a small particle using modern techniques, and the researchers believe that this experiment may be the first step that will ultimately lead them to the theory of quantum gravity.

Tim Fox, a member of the research team and a doctor at the University of Southampton, points out that scientists have failed for a century to understand how gravity and quantum mechanics work together, despite their diligent attempts.

By understanding quantum gravity, there is a glimmer of hope for solving some of the complex mysteries of the universe, such as how it began, and what happens inside black holes, or perhaps this is the link that unites the theory of relativity and quantum mechanics.

Quantum entanglement... “a suspicious relationship at a distance”

Einstein, the author of the theory of relativity, was not accommodating to quantum theory in any way, and he was even cynical about it, because he believed that there was an aspect of the theory that bothered him, which was the phenomenon of “quantum entanglement,” which describes an entanglement in some way between atomic particles such that the properties of the particle change. To change the properties of the particle entangled with it simultaneously, even if the two particles are separated by the beginning and the end of the universe.

Einstein called this a “dubious and frightening relationship at a distance” because it violates the “principle of locality.”

Scientists believe that quantum gravity will establish a unified framework that accommodates the theories of relativity and quantum theory (Shutterstock)

The principle of locality, in brief, urges that a body is only directly affected by its surroundings, and that bodies always have specific properties that interact with what is around them, provided that they are governed by distance and the speed of light, which is the cosmic limit that Einstein assumed as a basis in his special theory of relativity.

Despite Einstein's own objection, quantum physicists have already proven entanglement and other strange phenomena that occur in the world of quantum physics in particular.

Many experiments have provided evidence of this, including the recent pioneering experiment that brought the 2022 Nobel Prize in Physics to physicists Aline Aspect, John Clauser, and Anton Zeilinger.

Preparing the experiment

In the recent quantum experiment, researchers from the University of Southampton and Leiden University used devices similar to superconducting magnetic traps to measure the force of weak gravity on the smallest possible mass on which this experiment was previously conducted.

Scientists raised the small particle in the magnetic trap at temperatures of about negative 273 degrees Celsius, which is a few fractions away from absolute zero, which is the hypothetical temperature at which the movement of atoms stops completely.

The very cold temperature was chosen to reduce particle vibrations to a minimum.

The team was able to measure an attractive force of 30 “tonnewtons” on the particle (a newton is a unit of force in the metric system, equal to one quintillionth of one newton, and the number reflects how small the gravitational force acting on the particle in the experiment).

Fox says that their success now is to measure gravitational signals at the smallest mass ever recorded, and by using this technique and repeating the experiment over and over until scientists reach the level of the quantum world, that is, they are one step closer to understanding how gravity interacts at smaller levels.

Hendrik Ulbricht, a member of the team and a scientist at the University of Southampton, said: This experiment paves the way for conducting tests with smaller masses, and thus reaching the measurement of smaller gravitational forces.

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