(ORDO NEWS) — A curved and stretched sheet of graphene lying on top of another curved sheet creates a new pattern that affects how electricity moves through the sheets.
The new model suggests that similar physics could emerge if two neighboring universes were able to interact.
Physicists sometimes come up with crazy stories that sound like science fiction. Some of them turn out to be true, such as the fact that the curvature of space and time described by Einstein was eventually confirmed by astronomical measurements. Others remain only a possibility or a mathematical curiosity.
JQI researcher Victor Galicki and JQI graduate student Alireza Parkhiskar explored the fantastic possibility that our reality is only one half of a pair of interacting worlds.
Their mathematical model could provide new insights into the fundamental features of reality – including why our universe expands the way it does, and how that relates to the smallest lengths allowed by quantum mechanics.
These topics are critical to understanding our universe and are part of one of the greatest mysteries of modern physics.
A pair of scientists stumbled upon this new look while studying graphene sheets – individual atomic layers of carbon in a repeating hexagonal pattern.
They realized that experiments examining the electrical properties of stacked sheets of graphene produced results reminiscent of small universes, and that the underlying phenomenon could extend to other areas of physics.
In stacks of graphene, new electrical properties emerge from interactions between individual sheets, so perhaps unique physics could similarly emerge from interacting layers elsewhere perhaps in cosmological theories about the entire universe.
“We think it’s an exciting and ambitious idea,” says Galicki, who is also a professor in the Department of Theoretical Physics at the Chesapeake Physics Department.
In a way, it’s almost suspicious that it works so well, naturally “predicting” the fundamental features of our universe, such as inflation and the Higgs particle, as we described in the subsequent preprint (link is external).”
Graphene’s exceptional electrical properties, and the possible connection that our reality has a twin, are due to the special physics created by patterns called moiré patterns.
Moiré patterns are formed when two repeating patterns – anything from the hexagons of atoms in graphene sheets to grids of window screens – are superimposed and one of the layers twists, shifts or stretches.
The patterns that arise in this case can be repeated over huge lengths compared to the basic patterns. In graphene stacks, new patterns change the physics that happens in the sheets, in particular the behavior of electrons.
In a special case called “magic angle graphene,” the moiré pattern repeats over a length that is about 52 times longer than the pattern of individual sheets, and the energy level that governs the behavior of the electrons plummets, allowing new properties, including superconductivity, to manifest.
Galicki and Parkhiskar realized that the physics of two sheets of graphene could be rethought as the physics of two two-dimensional universes in which electrons periodically jump from one universe to another.
This inspired the pair to generalize the math to apply to universes made up of any number of dimensions, including our own four dimensions, and to explore whether similar phenomena resulting from moiré patterns could show up in other areas of physics.
This marked the beginning of a study that brought them face to face with one of the fundamental problems of cosmology.
“We discussed whether we can observe the physics of moiré, when two real universes merge into one,” says Parkhizkar. “What do you want to look for when you ask this question? First of all, you need to know the length scale of each universe.”
The length scale – or physical quantity scale in general – describes what level of precision is appropriate for what you’re looking at. If you approximate the size of an atom, then ten billionths of a meter counts, but this scale is useless if you measure a football field, because it is on a different scale.
The theories of physics impose fundamental restrictions on some of the smallest and largest scales that make sense in our equations.
The scale of the universe that Galitsky and Parkhizkar worried about is called the Planck length (inaccessible link – link), and it defines the smallest length that is consistent with quantum physics.
Planck’s length is directly related to a constant called the cosmological constant(link not available), which is included in the Einstein field equations in general relativity(link not available). In these equations, the constant affects whether the universe will expand or contract outside of gravitational influence.
This constant is fundamental to our Universe. So in order to determine its value, scientists, in theory, just need to look at the universe, measure a few details, such as the speed at which galaxies are moving away from each other, plug everything into the equations, and figure out what the constant should be.
This simple plan runs into trouble because our universe contains both relativistic and quantum effects. The effect of quantum fluctuations in the vast vacuum of space should influence behavior even on cosmological scales.
But when scientists try to combine Einstein’s relativistic understanding of the universe with theories about the quantum vacuum, they run into problems.
One of these problems is that whenever researchers try to use observations to approximate the cosmological constant, the value they calculate is much smaller than what other parts of the theory would expect.
Moreover, the value changes drastically depending on how much detail they include in the approximation, instead of coming to a constant value. This protracted problem is known as the cosmological constant problem, or sometimes the “vacuum catastrophe”.
“This is the biggest – far from the biggest – discrepancy between the measurements and what we can predict with the theory,” says Parkhiskar. “That means something is wrong.”
Since moiré patterns can create drastic differences in scale, the moiré effect seemed like a natural lens to look at the problem.
Galicki and Parkhiskar created a mathematical model (which they called moiré gravity) by taking two copies of Einstein’s theory of how the universe changes over time and introducing additional conditions into the mathematics that allow the two copies to interact.
Instead of looking at energy and length scales in graphene, they looked at cosmological constants and lengths in universes.
Galicki says the idea came about spontaneously while they were working on a seemingly unrelated project funded by the John Templeton Foundation (link is external) that aims to study hydrodynamic flows in graphene and other materials to model astrophysical phenomena.
By playing with their model, they showed that two interacting worlds with large cosmological constants can cancel out the expected behavior from individual cosmological constants.
The interaction results in behavior driven by a common effective cosmological constant, which is much smaller than the individual constants.
Calculating the effective cosmological constant circumvents the problem that researchers face when their approximations fluctuate because over time the influences of the two universes in the model cancel each other out.
“We never claim that this solves the problem of the cosmological constant,” Parkhizkar says. “It’s a very presumptuous statement, to be honest.
It’s just a good idea that if you have two universes with huge cosmological constants – 120 orders of magnitude more than we observe – and if you combine them, there’s still a chance that you can get a very small effective cosmological constant out of them.”
In preliminary follow-up work (link is external), Galicki and Parkhiskar began to develop this new perspective by diving into a more detailed model of a pair of interacting worlds, which they called “b-worlds”.
Each of these worlds is a complete world in itself by our usual standards, and each of them is filled with appropriate sets of all matters and fields. Since the math allowed this, they also included fields that live in both worlds at the same time, which they called “amphibious fields”.
The new model produced additional results that the researchers consider intriguing. As they collected mathematical calculations, they found that part of the model is similar to important fields that are part of reality.
A more detailed model still suggests that two worlds can explain the small cosmological constant, and provides detailed information about how such a bi-world could imprint cosmic background radiation, light that has survived from the earliest times of the universe.
This signature may or may not be noticed in real world measurements. So future experiments may determine whether this unique graphene-inspired perspective deserves more attention or just an interesting novelty in physicists’ toy basket.
“We haven’t explored all the effects – it’s hard to do, but the theory is experimentally verifiable, which is very good,” Parkhizkar says.
“If it is not falsified, then it is very interesting, because it solves the problem of the cosmological constant and at the same time describes many other important parts of physics. Personally, I do not hope so – I think it is too much to be true.”
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