Theoretical scientists in Warsaw and Potsdam have reached a ground-breaking conclusion that the symmetries present in elementary particles at the most basic level are radically different from what scientists have thought thus far. Their new theory unifies all forces of nature in a way that explains all existing observations. Also, the scientists pose the plausibility of the existence of new particles that may be present in our immediate environment.
For the past 50 years, physicists have been working on explaining all four forces of nature – electromagnetism, weak interaction, strong interaction and gravity -- with one unifying theory. Such a theory would also have to incorporate the existing known elementary particles and predict the existence of new particles.
The best predictive model thus far has been the Standard Model of particle physics. However, it doesn’t cover the gravitational force, and it leaves some phenomena unexplained. In their new paper in the Physical Review Letters, Prof. Krzysztof Meissner from the Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, and Prof. Hermann Nicolai from the Max-Planck-Institut für Gravitationsphysik in Potsdam, present a new scheme for the Standard Model that includes gravitation and applies a new kind of symmetry that has previously not been applied to elementary particles.
Symmetry in physics refers the unchanging laws of physics with respect to shifts in time or space. For example, an apple drops from a tree in the same way the next apple drops; it drops from a tree of the same height in the same way as the first. Prof. Meissner explains: "Symmetries play a huge role in physics because they are related to principles of conservation. For instance, the principle of the conservation of energy involves symmetry with respect to shifts in time, the principle of the conservation of momentum relates to symmetry of spatial displacement, and the principle of the conservation of angular momentum relates to rotational symmetry.”
Dating back to the 1970s, physicists have worked on theories to describe symmetries between elementary particles – fermions (the matter and antimatter particles that include quarks, leptons, antiquarks and antileptons) and force particles responsible for interactions among fermions, bosons.
"The first supersymmetric theories tried to combine the forces typical of elementary particles,” says Meissner. “The symmetry between the bosons and fermions was still global, which means the same at every point in space. Soon thereafter, theories were posited where symmetry was local, meaning it could manifest differently at each point in space. Ensuring such symmetry in the theory required for gravitation to be included, and such theories became known as supergravities."
Professors Meissner and Nicolai solved the problem of incorporating gravity into the Standard Model in 2015, after the presented an adjustment to the existing symmetry. “The approach proved to be very different from all other attempts at generalizing the symmetries of the Standard Model…That would explain why all previous attempts at detecting new particles,” says Meissner. He adds: "For the first time, we have a scheme that precisely anticipates the composition of the fermions in the Standard Model—quarks and leptons—and does so with the proper electric charges. At the same time, it includes gravity into the description. If further work confirms the role of this group, that will mean a radical change in our knowledge of the symmetries of nature.”
What does the new theory mean in terms of practical applications? It is possible that new particles exist, and that they can be detected with the modern equipment available today. The new take on the Standard Model also better explains the fundamental structure of matter: that everything in the universe is made from a few basic building blocks called fundamental particles, and that everything is governed by the four fundamental forces. Will this knowledge help humanity explore more of the universe? Time will tell.