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Photo Source: Pixabay according to the prediction of quantum field theory, our universe should have a very large cosmological constant, which will push the universe to expand so rapidly that light from neighboring celestial bodies will not have time to reach Earth. However, the actual observation is 120 orders of magnitude less than the prediction of quantum field theory. How to resolve this conflict? Some physicists have proposed a novel model: two universes with very large cosmological constants interact with each other and a very small cosmological constant can be obtained as a whole. Will our universe be half of all reality?

In the previous push, we talked about the history of several ups and downs of cosmological constants. Today, physicists generally accept the existence of this term in the Einstein field equation of general relativity and try to use it to explain the accelerated expansion of the universe, whose real counterpart is the famous "dark energy". The nature of dark energy determines the future evolution of the universe, but there is no consensus in academic circles on what this mysterious energy is and how to describe it in physics.

However, this is not the most troublesome problem, and what is even more troublesome for physicists is that quantum field theory independently gives the predicted value of the cosmological constant, which is 120 orders of magnitude less than the actual observation, which is definitely a disaster in physics. Physicists have put forward many solutions to this "cosmological constant problem". Recently, two physicists took inspiration from bilayer graphene and gave a novel explanation: two universes with very large cosmological constants can show very small cosmological constants as a whole through some kind of interaction. If this explanation is true, it means that we live in a universe that is only half the size of the complete world.

The vacuum energy of disaster in quantum field theory, there is a kind of energy that can play the role of dark energy, which is "vacuum energy". Quantum physics does not allow absolute "nothingness". Even in a seemingly empty vacuum, there will be fluctuations of energy: a large number of virtual particles are rapidly produced and annihilated, contributing to the vacuum energy. This kind of energy is everywhere in the universe and will also promote the expansion of the universe.

Even in a vacuum, there are virtual particles that quickly generate and annihilate in pairs (photo: Ahmed Neutron / Wikipedia) since quantum field theory has a ready-made source of cosmic expansion energy, why is dark energy a mystery? The reason is that the value of vacuum energy calculated by quantum field theory is too different from the actual observation. Back in the 1920s, in the early days of quantum mechanics, physicist Wolfgang Pauli estimated that the vacuum energy was so large that the universe expanded so rapidly that the light emitted by neighboring celestial bodies could not catch up with the expansion rate of the universe, and the entire observable universe could not even reach the current lunar orbit. In 1967, the Soviet physicist Yakov Zedovich (Yakov Zeldovich) formally calculated the vacuum energy in quantum field theory, which is reflected in Einstein's field equation as a cosmological constant. However, the value of the cosmological constant in this version of quantum field theory is 120 orders of magnitude different from that obtained by astronomical observation.

In fact, quantum physics is not compatible with the universe depicted by general relativity, which is nothing new. There are conflicts between the two theories on many basic physical problems. Therefore, some physicists regard the cosmological constant problem as another manifestation of this conflict, and believe that in order to solve this problem, we need to wait for a better physics in the future. These physicists are developing different theories of quantum gravity. In the new theory, spacetime will also show quantum effects and thus fluctuate like particles. This effect is likely to eliminate the influence of the huge cosmological constants in the existing quantum field theory. However, the establishment of the theory of quantum gravity is a huge project, which involves all aspects of physics. At present, the field of physics is still in the exploratory stage and there is no recognized theory.

So what else can be done to solve the problem of cosmological constants other than the new physics that pinning its hopes on the future? In a study published in physical Review KuaiBao in May, researchers used a new cosmological model to provide a solution: if two universes interact like bilayer graphene, they exhibit new properties as a whole, including a cosmological constant of the right size.

The two-universe model is presented by Viktor Galitsky (Victor Galitski) and Arireza Parritzkal (Alireza Parhizkar) of the University of Maryland, and their inspiration comes from a field that seems to have nothing to do with cosmology-bilayer graphene.

Graphene is a two-dimensional material with carbon atoms arranged in a hexagonal lattice. If two layers of graphene are stacked together in a special way-for example, the two layers of graphene are staggered at an angle, or the lattice sizes of the two layers of graphene are different, an interference pattern is produced, which is called the "Moir é pattern". This interference pattern changes not only the appearance of bilayer graphene, but also the energy band distribution of the material, which in turn changes the behavior of electrons. Some bilayer graphene staggered at a specific angle will show superconductivity, ferromagnetism and other properties that monolayer graphene does not have, so they are also called "magic horn graphene".

Two striped plates are stacked at a certain angle to form a moire pattern (image source: P. Fraundorf / Wikipedia) Galitzki and Parizkar borrowed the physical model of bilayer graphene and modified it to make it suitable for cosmology. In this model, known as Moir é gravity, two separate and complete universes evolve according to the laws of general relativity, but some of their matter fields are common, the so-called "amphibious fields" (amphibian field). This means that some fermions tunnel between the two universes, just like electrons in bilayer graphene. In this two-universe model, each universe has a very large cosmological constant, as predicted by quantum field theory. But under the interaction between the two universes, a very small cosmological constant is obtained as a whole, which is close to the observed value of our real world. In other words, the reason why the actual observation is so different from the prediction of quantum field theory is that we miss the observation of another universe.

So can another universe in the model be verified by observation? The researchers say that if another universe does exist, it should leave a mark on the microwave background radiation of our universe. However, the researchers added that they did not claim to solve the cosmological constant problem-it was too arrogant, and they hoped the two-universe model would provide a new perspective and inspire physicists to look for the relationship between everyday materials and the real universe.

Original paper:

Https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.4.L022027

Reference:

Https://phys.org/news/2022-05-bilayer-graphene-two-universe-cosmological.html

This article comes from the official account of Wechat: global Science (ID:huanqiukexue), written by Bai Defan revision: Wang Yu

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