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Two Universes: What if “this solves cosmological constant problem”?

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Physicists occasionally come up with bizarre science fiction stories. Some of them turn out to be true, such as Einstein’s theory of the curvature of space and time, which was later confirmed by astronomical measurements. Others linger as hypothetical possibilities or mathematical puzzles.

Victor Galitski and graduate student Alireza Parhizkar have investigated the speculative possibility that our reality is simply one half of a pair of interacting universes in a new bit published in Physical Review Research. Their mathematical model could offer a fresh view on fundamental aspects of reality, such as why our universe expands the way it does and how it links to quantum physics’ smallest lengths. These themes are critical to comprehending our universe and are part of one of contemporary physics’ big mysteries.

When the two scientists were researching graphene sheets—single atomic carbon layers arranged in a hexagonal pattern—they came across this unique perspective. They found that research on the electrical properties of graphene stacked sheets yielded findings that appeared like miniature universes, and that the underlying phenomenon might be applied to other fields of physics. New electrical behaviors develop from interactions between individual graphene sheets in stacks, thus possibly distinct physics could emerge from interacting layers elsewhere as well—perhaps in cosmological ideas about the entire universe.

“We think this is an exciting and ambitious idea,” said Galitski. “In a sense, it’s almost suspicious that it works so well by naturally ‘predicting’ fundamental features of our universe such as inflation and the Higgs particle as we described in a follow up preprint.”

The curious physics produced by moiré patterns gives stacked graphene its extraordinary electrical characteristics and a possible connection to our world having a twin. When two repeating patterns—from the hexagons of atoms in graphene sheets to the grids of window screens—overlap and one of the layers is twisted, offset, or stretched, Moiré patterns emerge.

When compared to the underlying patterns, the patterns that emerge can repeat over large distances. The novel patterns in graphene stacks alter the physics that occurs in the sheets, particularly the behavior of electrons. The moiré pattern repeats across a length 52 times longer than the pattern length of the individual sheets in the particular case known as “magic angle graphene,” and the energy level that governs the behaviors of the electrons decreases dramatically, permitting unexpected behaviors such as superconductivity.

Galitski and Parhizkar found that the physics of two graphene sheets may be understood as the physics of two two-dimensional universes with electrons hopping between them on occasion. This prompted the researchers to extend the math to worlds with any number of dimensions, including our own four-dimensional universe, and to see if comparable moiré patterns may appear in other fields of physics. This sparked a line of inquiry that led them to one of cosmology’s most difficult challenges.

“We discussed if we can observe moiré physics when two real universes coalesce into one,” Parhizkar added. “What do you want to look for when you’re asking this question? First you have to know the length scale of each universe.”

A length scale, or a scale of a physical value in general, specifies the level of precision applicable to whatever you’re looking at. A ten-billionth meter matters for calculating the size of an atom, yet that scale is worthless when measuring a football field because it is on a different scale. Some of the lowest and largest sizes that make sense in our equations have fundamental restrictions imposed by physics theories.

The Planck length is the smallest length that is consistent with quantum physics, and it is the scale of the universe that troubled Galitski and Parhizkar. The Planck length is proportional to the cosmological constant, which is contained in Einstein’s general relativity field equations. The constant in the equations determine whether the cosmos tends to expand or contract outside of gravitational effects.

This is a fundamental constant in our universe. So, in principle, scientists only need to look at the cosmos, measure a few details, such as the speed at which galaxies move away from one other, plug everything into equations, and calculate what the constant must be.

This simple approach runs into difficulty since our universe has both relativistic and quantum influences. Even at cosmological sizes, the effect of quantum fluctuations over the immense vacuum of space should influence behavior. However, when scientists try to merge Einstein’s relativistic view of the cosmos with quantum vacuum theories, they run into difficulties.

One of these issues is that anytime researchers try to estimate the cosmological constant using observations, the result is substantially lower than what they would predict based on other aspects of the theory. More crucially, instead of homing in on a stable value, the value fluctuates dramatically depending on how much data they include in the approximation. The cosmological constant problem, sometimes known as the “vacuum catastrophe,” is a persistent problem.

“This is the largest—by far the largest—inconsistency between measurement and what we can predict by theory,” Parhizkar said. “It means that something is wrong.”

Moiré effects felt like a suitable lens to view the situation through because moiré patterns can yield remarkable scale variations. Galitski and Parhizkar devised a mathematical model (dubbed moiré gravity) by combining two copies of Einstein’s theory of how the world develops over time and adding extra mathematical elements to allow the two copies to interact. They were looking at cosmic constants and lengths in universes rather than the scales of energy and length in graphene.

Galitski claims that the idea came to them when they were working on apparently unrelated research financed by the John Templeton Foundation and aimed at simulating astronomical phenomena using hydrodynamic flows in graphene and other materials.

They demonstrated that two interacting worlds with enormous cosmic constants might overcome the expected behavior of the individual cosmological constants by playing with their model. The interactions result in behaviors that are governed by a common effective cosmological constant that is significantly less than the separate constants. Since the influences from the two worlds in the model cancel out over time, the computation for the effective cosmological constant avoids the difficulty that academics have with the value of their estimates hopping around.

“We don’t claim—ever—that this solves cosmological constant problem,” Parhizkar said. “That’s a very arrogant claim, to be honest. This is just a nice insight that if you have two universes with huge cosmological constants—like 120 orders of magnitude larger than what we observe—and if you combine them, there is still a chance that you can get a very small effective cosmological constant out of them.”

Galitski and Parhizkar have begun early follow-up work on this new perspective by delving into a more thorough model of a pair of interacting worlds, which they refer to as “bi-worlds.” As far as our conventional standards are concerned, each of these worlds is a whole planet in its own right. These “amphibian fields” were created because of the fact that arithmetic allowed them to exist in two different worlds at once.

The new model yielded additional findings that academics are particularly interested in discussing. They discovered that part of the model looked like crucial fields in reality as they put the math together. The more precise model still suggests that two worlds may explain a modest cosmological constant, as well as information on how such a bi-world might imprint a distinct mark on cosmic background radiation—light that lingers from the universe’s beginnings.

In real-world measurements, this signal may or may not be visible. Future tests could determine whether graphene’s unique perspective needs greater attention or is just a fun novelty for physicists to play with.

“We haven’t explored all the effects—that’s a hard thing to do, but the theory is falsifiable experimentally, which is a good thing,” Parhizkar added. “If it’s not falsified, then it’s very interesting because it solves the cosmological constant problem while describing many other important parts of physics. I personally don’t have my hopes up for that— I think it is actually too big to be true.”

Image Credit: Getty

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