Physicists have proposed a new interpretation of dark energy. As his two perspectives on the universe and its elements, we can gain insight into the interconnection between quantum field theory and general relativity.
What’s behind dark energy, and what ties it to the cosmological constant introduced by Albert Einstein? Two physicists from the University of Luxembourg answer these open questions showing you how.
The universe has many strange properties that are difficult to comprehend in everyday experience. For example, matter as we know it consists of elementary particles and composite particles that make up molecules and matter, and seems to constitute a small part of the energy of the universe. The largest contribution, about two-thirds,dark energy– a hypothetical form of energy that background physicists are still puzzled by. Moreover, the universe is not only expanding steadily, it is expanding faster than ever before.
Both features appear to be related. dark energy It is also thought to be a factor that accelerates the expansion. In addition, there is the possibility of reuniting his two powerful schools of physics: quantum field theory and general relativity developed by Albert his Einstein. But there are pitfalls. So far, the calculations and observations do not agree. Two of his researchers in Luxembourg have shown a new way to solve his century-old mystery in a paper published in the journal. physical review letter.
Trajectories of virtual particles in vacuum
“There is energy in the vacuum. This is a fundamental result of quantum field theory. University of LuxembourgThis theory was developed to link quantum mechanics and special relativity, but quantum field theory seems to be incompatible with general relativity. Its essential feature is that, in contrast to quantum mechanics, the theory regards not only particles but also matter-free fields as quantum objects.
“Within this framework, many researchers see dark energy as a representation of the so-called vacuum energy,” says Tkatchenko. This physical quantity is caused in sharp images by the constant appearance and interaction of pairs of particles and their antiparticles. — electrons, positrons, etc. — is actually empty space.
Physicists call this back-and-forth between virtual particles and their quantum fields vacuum or zero-point fluctuations. The pair of particles quickly disappears into nothingness again, but their existence leaves a certain amount of energy behind.
“This vacuum energy also has implications for general relativity,” said the Luxembourg scientist.
huge mismatch
Unlike the vacuum energy, which can only be estimated from quantum field theory formulas, the cosmological constant can be directly determined by astrophysical experiments. Hubble Space Telescope and Planck Space Mission measurements have yielded reliable values close to the fundamental physical quantity. On the other hand, dark energy calculations based on quantum field theory yield results corresponding to values of the cosmological constant up to 10.120 Twice as big – a huge discrepancy, but in today’s worldview of physicists both values should be equal. The discrepancy found instead is known as the “cosmological constant mystery”.
“This 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. Dmitry Fedorov, he has taken an important step forward by bringing a solution to this puzzle that has been open for decades.In their recently published theoretical study, the results physical review letterTwo researchers from Luxembourg propose a new interpretation of dark energy. We hypothesize that zero-point fluctuations lead to vacuum polarizability, which can be both measured and calculated.
“For pairs of oppositely charged virtual particles, it arises from the electrodynamic forces that these particles exert on each other during their very short existence,” explains Tkatchenko. Physicists call this vacuum self-interaction. “It leads to an energy density that can be determined with the help of new models,” says the Luxembourg scientist.
Together with his research colleague Fedorov, they developed a basic model of the atom several years ago and published it for the first time in 2018. This model was originally used to describe the properties of atoms, in particular the relationship between atomic polarizability and equilibrium properties. of certain non-covalently bound molecules and solids. The geometric properties are very easy to measure experimentally, so the polarizability can also be determined from those equations.
“We transferred this procedure to a vacuum process,” explains Fedorov. To this end, the two researchers focused specifically on the behavior of the quantum field, which represents the ‘back and forth’ of electrons and positrons. These field fluctuations can also be characterized by the equilibrium geometry already known from experiments. “We inserted it into the model formula and thus finally obtained the strength of the intrinsic vacuum polarization,” reports Fedorov.
The final step was to quantum mechanically calculate the energy density of the self-interaction between electron and positron fluctuations. The results obtained in this way are in good agreement with measurements of the cosmological constant. This means that “dark energy can be traced to the energy density of self-interactions in the quantum field”.
Consistent values and verifiable predictions
“Thus, our work provides an elegant and unconventional approach to solving the mystery of the cosmological constant,” the physicist summarizes. “Furthermore, it provides a testable prediction: that quantum fields, such as those of electrons and positrons, do indeed have a small but ever-present intrinsic polarization.”
The findings point the way for future experiments to detect this polarization also in the laboratory, say the two Luxembourg researchers. “Our goal is to derive the cosmological constant from a rigorous quantum-mechanical approach,” emphasizes Dmitry Fedorov. “And our work includes the recipe for making this happen.”
He sees the new results, obtained with Alexandre Tkatchenko, as a first step toward a better understanding of the relationship between dark energy and Albert Einstein’s cosmological constant.
Finally, Tkatchenko is convinced that:
See: “Casimir Self-Interaction Energy Density of Quantum Electromagnetic Fields”, Alexandre Tkatchenko and Dmitry V. Fedorov, 24 January 2023, Available here. physical review letter.
DOI: 10.1103/PhysRevLett.130.041601