Physics Towards a theory of everything: the first quantum measurement of gravity

Let us return to one of the great mysteries of 20th-century science, namely the construction of the “most beautiful of theories,” one that is able to unify the major laws of physics by identifying a common matrix. Yes, because once the new road was identified, experimental confirmation arrived for the “old” one, which didn’t seem to work at all.

In theorizing that “norm of everything” on which the most brilliant theoretical physicists of our time and of the last century labored, there was always a very high wall to overcome: to bring together Albert Einstein’s general relativity (which explains gravity through the curvature of space-time) and Werner Karl Heisenberg’s quantum mechanics ( which controls the smallest particles in the universe). For unification, it was hypothesized that Einstein’s theory of gravity had to be modified, or “quantized”, to fit quantum theory. However, this system did not work, leaving the theory of quantum gravity, created in the 1980s, at a dead end.

Recently, a new theory, developed by Professor Jonathan Oppenheim (UCL Physics & Astronomy), has been presented to the international scientific community, which takes an alternative approach suggesting that space-time, which is mathematically quite classical, cannot be governed at all by quantum theory, which uses discrete algebra, is not continuous. Instead of modifying spacetime, the new theory—called the “post-quantum theory of classical gravity”—modified quantum theory and posited an internal collapse of predictability mediated by spacetime itself. “Quantum theory and Einstein’s general theory of relativity are mathematically incompatible, so it is important to understand how this contradiction is resolved. Should spacetime be quantized, or should we modify quantum theory, or should we find something completely different?,” Oppenheim said.

However, it seems that it was during these hours that an important confirmation regarding the theory of quantum gravity came which, precisely because of its fragility, seemed to end up in a drawer. In fact, it was discovered how to measure gravity the Heisenberg way. Demonstration in an experiment carried out by physicists at the University of Southampton in collaboration with European scientists, published in the journal Scientific advances. Experts have never fully understood how the force discovered by Isaac Newton works in the tiny quantum world. Even Einstein was puzzled by quantum gravity and said in his theory of general relativity that there was no realistic experiment that could show a quantum version of gravity. But now, thanks to a new technique, physicists have successfully detected a weak gravitational pull on a small particle. According to scientists, this could open the way to the discovery of the elusive theory of quantum gravity. Scientists have used levitating magnets to detect gravity on microscopic particles small enough to enter the quantum realm.

“The results could help experts find a missing piece of the puzzle in our picture of reality,” said Tim Fuchs of the University of Southampton and lead author of the paper describing the experiment. “For a century, scientists have tried and failed to understand how gravity and quantum mechanics work together,” Fuchs noted. “Now that we have successfully measured the gravitational signals at the lowest recorded mass, we are one step closer to finally understanding how they work. work in tandem,” the scientist added. “From there, we will use this technique to shrink the source down until we reach the quantum world on both sides – concluded Fuchs -. By understanding quantum gravity, we could solve some of the mysteries of our universe, such as its origin, what happens inside black holes or the connection of all forces into of one grand theory.’

The rules of the quantum world are not yet fully understood by science, but microscopic-scale particles and forces are believed to interact differently than normal-sized objects. The Southampton researchers carried out the experiment together with scientists from Leiden University in the Netherlands and the Institute for Photonics and Nanotechnology in Italy, with funding from the EU Horizon Europe EIC Pathfinder grant. The study used a sophisticated setup, including superconducting devices, known as traps, with magnetic fields, sensitive detectors and advanced vibration isolation. The scientists were able to measure a weak attractive force of just 30aN on a small particle weighing 0.43mg, levitating it at sub-freezing temperatures one-hundredth of a degree above absolute zero, about minus-273 degrees Celsius. “The results open the way for future experiments between even smaller objects and forces,” emphasized Hendrik Ulbricht, professor of physics at the University of Southampton. “We are pushing the boundaries of science, which could lead to new discoveries about gravity and the quantum world,” Ulbricht elaborated. “Our new technique, which uses extremely low temperatures and devices to isolate particle vibrations, is likely to prove the way forward for measuring quantum gravity,” he noted. “Unraveling these mysteries will help us uncover more secrets about the very structure of the universe, from the smallest particles to the largest cosmic structures,” concluded Ulbricht.


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