The Standard Model of particle physics is the most successful theory in science because it predicted the building blocks and properties of the universe with such accuracy. The common model of mathematics and physics describes the fundamental interactions and the particles that mediate them. For electromagnetism, the photon; for the strong interaction that holds atomic nuclei together, the gluon; for the weak interaction, the W boson and the Z boson.
The fourth fundamental interaction is gravity, but its mediator, the graviton, has not yet been observed. Gravity is the weakest interaction of all, it only appears with very large masses, and has no effect at the microscopic level. This may be one of the reasons why deep down inside us there is a serious theoretical contradiction between general relativity, which describes the entire universe, and quantum theory, which studies the smallest units of existence. Thus, it is questionable whether gravity is among the fundamental interactions at all, and whether the graviton even exists.
If it exists, its mass is very small, one billionth of an electron, and one billionth lighter. Accordingly, measuring it is extremely difficult, but not impossible, so scientists have not given up even after a century of trying.
The sound of weight
Igor Bykovsky, a professor at Stockholm University and an employee of the American Stevens Institute of Technology, is working on this case, and in columns in the journal Nature Communications, he and his colleagues propose a method that would finally make the mysterious particle discoverable.
The idea of the measurement is based on an experiment demonstrating the photoelectric effect. Albert Einstein's measurement in 1905 proved the existence of photons, and in 1921 he was awarded the Nobel Prize in Physics for it (as is well known, he did not receive the Nobel Prize for the theory of general relativity, because his theories were confirmed by observations decades later).
Our solution mimics the photoelectric effect, but we use acoustic resonators on the gravitational waves that reach the Earth. This is called the “acoustic gravity” effect.
German Tobar, a PhD student at Stockholm University, explained in his statement.
The researchers cited as an example the operation of the LIGO observatory, the first detector to detect gravitational waves, and also a Nobel Prize winner in physics, which, with its laser arms, can measure space-time waves 10,000 times smaller than gravitational waves, the diameter of a proton.
The proposed detectors are based on two-ton aluminum cylinders, which would be cooled to a temperature close to absolute zero in order to reduce their quantum energy to the lowest possible level. The cylinders would resonate with the incoming gravitational waves, and if there was a sufficiently strong wave, some of the wave's energy would remain—observing a quantum energy jump, the absorption or emission of a graviton would become visible (as the energy from the photon was then seen as a quantum jump).
The resulting detector, compared with data from LIGO or other gravitational wave observatories, will show that what was measured was indeed the result of a gravitational wave.
The researchers acknowledge that a relatively strong wave is necessary for success, but according to their calculations, something similar to this has already been measured once, in 2017, during the merger of two neutron stars. Such a wave would carry enough gravitons to have a good chance of absorbing one in the resonator.
Designing and manufacturing aluminum cylinders and their associated quantum sensors is neither easy nor cheap. If successful, the successful discovery of the graviton would be a major step toward the theoretical unification of physics.
(Interesting engineering, Popular Mechanics, Stockholm University)
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