What is behind dark energy – and what links it to the cosmological constant introduced by Albert Einstein? Two physicists from the University of Luxembourg point to a way to answer these open questions in physics.
The universe has a number of strange properties that are difficult to understand through everyday experience. For example, matter as we know it, made up of atoms, molecules, and other particles, apparently makes up only a small fraction of the energy density of the universe. The largest contribution, more than two-thirds, comes from “dark energy” – a hypothetical form of energy whose background physicists are still at a loss for.
Moreover, not only is the universe expanding steadily, but it is also doing so at an ever faster pace. Both properties appear to be connected, since dark energy is also considered a driver of accelerated expansion. Moreover, it can unite two powerful physics schools of thought: quantum field theory and the general theory of relativity developed by Albert Einstein. But there is a catch: the accounts and notes are far from identical. Two researchers from Luxembourg showed a way to solve this 100-year-old puzzle in a research paper they published Physical review letters.
The effect of virtual particles in a vacuum
“Dark energy arises from the equations of quantum field theory,” explains Alexandre Tkachenko, Professor of Theoretical Solid State Physics at the University of Luxembourg’s Department of Physics and Materials Sciences. This theory was developed to combine quantum mechanics and general relativity, which are incompatible in fundamental aspects.
Its main advantage: unlike quantum mechanics, the theory considers not only particles but also matter-free spheres as quantum objects. “In this framework, many researchers consider dark energy to be an expression of what is called vacuum energy,” says Tkachenko, a physical quantity that results, in vivid form, from the continuous appearance of pairs of particles and their antiparticles, such as electrons and positrons — in what is actually space. empty.
Physicists speak of the comings and goings of virtual particles and their quantum fields as fluctuations in a vacuum, or zero point. As the pairs of particles instantly vanish into nothingness again, they leave behind a certain amount of energy. The Luxemburg scientist notes that “this vacuum energy also has meaning in general relativity.” “It manifests itself in the cosmological constant, which Einstein inserted into his equations for mathematical reasons.”
Unlike dark energy, which can only be deduced from the equations of quantum field theory, the cosmological constant can be determined directly by astrophysical experiments. Measurements with the Hubble Space Telescope and the Planck space mission have yielded close and reliable values for the fundamental physical quantity.
On the other hand, dark energy calculations based on quantum field theory lead to results consistent with the value of the cosmological constant being 10120 times greater—which is an enormous contradiction—although, according to the prevailing view of physicists today, both values should be equal. The contradiction that exists is instead known as the “enigma of the cosmological constant”. “It is without a doubt one of the greatest contradictions in modern science,” says Alexander Tkachenko.
Unconventional way of interpretation
Together with his Luxembourg research colleague Dr. Dimitri Fedorov, he has now brought the solution to this mystery, which has been open-ended for decades, an important step closer. In a theoretical paper, which they recently published their findings, the two Luxembourg researchers propose a new explanation for dark energy. Zero point fluctuations are assumed to result in vacuum polarization, which can be measured and calculated.
“In hypothetical pairs of particles with an electric charge, they arise from the electrodynamic forces that these particles exert on each other during their very short time of existence,” explains Tkachenko. Physicists refer to this as self-interaction, and polarization in such particles is a characteristic of the reaction to it. “It leads to an energy density that can be determined with the help of a new model,” says the Luxembourg scientist.
In collaboration with research colleague Fedorov, he developed and first presented this model in 2018, originally used to describe atomic properties, for example in solids. Since it is very easy to measure geometrical properties experimentally, polarization can also be determined via these transformations.
“We transferred this procedure to operations in a vacuum,” Fedorov explains. To do this, the two researchers looked at the behavior of electrons and positrons, which they treated as fields according to the principles of quantum field theory. Fluctuations of these fields can also be characterized by equilibrium geometry, the value of which is already known from experiments.
“We incorporated it into our model formulas and in this way we finally obtained the polarization force of the vacuum,” says Fedorov. The final step then was to mechanically calculate the energy density of the self-interaction between electrons and positrons. The result obtained in this way is in good agreement with the measured values of the cosmological constant: this means: “dark energy can be traced back to the energy density of the self-interaction of quantum fields,” emphasizes Alexander Tkachenko.
Consistent values and verifiable expectations
“Our work thus offers an elegant and unconventional approach to solving the mystery of the cosmological constant,” the physicist concludes. “Moreover, it provides a verifiable prediction: that quantum fields such as those of electrons and positrons do indeed possess a small but ever-present polarization.”
The discovery points the way for future experiments to detect this polarization in the lab as well, say the two Luxembourg researchers, who now want to apply their model to other particle-antiparticle pairs. “Our conceptual idea must be applicable in any field,” emphasizes Alexander Tkachenko. He sees the new results obtained with Dimitri Fedorov as a first step towards a better understanding of dark energy – and its relationship to Albert Einstein’s cosmological constant.
Tkatchenko is convinced: “Ultimately, this will also shed light on the way quantum field theory and general interaction theory intertwine as two ways of looking at the universe and its components.”
Alexander Tkachenko et al., Kasimir self-interaction energy density in quantum electrodynamic fields, Physical review letters (2023). DOI: 10.1103/PhysRevLett.130.041601
Provided by the University of Luxembourg
the quote: A New Approach to Solving the Mystery of Dark Energy (2023, January 24) Retrieved January 25, 2023 from https://phys.org/news/2023-01-approach-mystery-dark-energy.html
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