Physicists can come up with crazy stories that sound like science fiction. Einstein's description of the space and time he observed eventually came to be seen by astronomy. Some linger on as mathematical curiosities.
JQI Fellow Victor Galitski and JQI graduate student Alireza Parhizkar wrote a paper about the possibility that our reality is only one half of a pair of interacting worlds. Their mathematical model may provide a new perspective for looking at fundamental features of reality, including why our universe expands the way it does and how that relates to the most minuscule lengths allowed in quantum mechanics. One of the great mysteries of modern physics is the importance of these topics.
The pair of scientists stumbled upon this new perspective when they were looking into research on sheets of Graphene, a single atomic layer of carbon in a repeating hexagonal pattern. Experiments on the electrical properties of stacked sheets of Graphene produced results that looked like little universes, and the underlying phenomenon might generalize to other areas of physics. New electrical behaviors arise from interactions between the individual sheets, so maybe unique physics could emerge from interacting layers elsewhere in the universe.
It is almost suspicious that it works so well because it is an exciting and ambitious idea.
The special physics produced by patterns called moiré are what lead to the amazing electrical properties of stacked graphene. Moir patterns form when two repeating patterns, anything from the hexagons of atoms in Graphene sheets to the grids of window screens is twisted, offset, or stretched.
The patterns can repeat over long lengths compared to the underlying patterns. The new patterns change the physics that plays out in the sheets. The pattern repeats over a length that is about 52 times longer than the individual sheets, and the energy level that governs the behaviors of the electrons is allowed to drop.
The physics of two two-dimensional universes where electrons occasionally hop between universes could be interpreted as the physics of two sheets of Graphene. This inspired the pair to generalize the math to apply to universes made of any number of dimensions, including our own four-dimensional one, and to explore if similar phenomena might occur in other areas of physics. This started a line of inquiry that brought them face to face with one of the major problems in the universe.
When two real universes coalesce into one, what do you want to look for? You need to know the length scale of each universe.
A length scale or a scale of a physical value can tell you what level of accuracy is relevant to what you are looking at. If you are approximating the size of an atom, then a ten-billionth of a meter matters, but if you are measuring a football field, it is not on a different scale. Some of the smallest and largest scales make sense in our equations because of the fundamental limits put on them by physics theories.
The smallest length that is consistent with quantum physics is defined by the scale of the universe. Einstein's field equations of general relativity include a constant that is 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- The constant influences whether the universe expands or contracts in the equations.
Our universe is based on this constant. To determine its value, scientists just need to look at the universe, measure several details, plug everything into the equations and calculate what the constant must be.
Our universe has both quantum and relativistic effects. The effects of quantum fluctuations on the vacuum of space should have an influence on behaviors. When scientists combine theories about the quantum vacuum with theories about the universe, they run into problems.
One of the problems is that when researchers try to use observations to approximate the cosmological constant, the value they come up with is much smaller than they would expect. The value jumps around a lot depending on how much detail is included in the approximation. The challenge is known as the cosmological constant problem orvacuum catastrophe.
This is the largest discrepancy between measurement and what we can predict by theory.
Since patterns can produce dramatic differences in scales, effects seemed like a natural lens to view the problem through. Two copies of Einstein's theory of how the universe changes over time were taken by Galitski and Parhizkar to create a mathematical model. They were looking at the constants and lengths of universes instead of looking at the scales of energy and length.
When they were working on the seemingly unrelated project that was funded by the John Templeton Foundation, they came up with this idea.
They showed that two interacting worlds with large cosmological constants could change the behavior of individual cosmological constants. The interactions produce behaviors governed by a smaller effective cosmological constant than the individual constants. The problem researchers have with the value of their approximations jumping around is solved by the calculation of the effective cosmological constant.
Parhizkar says that they don't claim to solve the constant cosmological problem. There is still a chance that you can get a very small effective cosmological constant if you combine the two universes that have huge constants.
In preliminary follow up work, Galitski and Parhizkar have started to build upon this new perspective by diving into a more detailed model of a pair of interacting worlds. Since the math allowed it, they also included fields that lived in both worlds.
The researchers find the new model intriguing. They found that part of the model looked important in reality. The model still suggests that two worlds could explain a small cosmological constant, and that they could cause a signature on the Cosmic Background Radiation.
In real world measurements, this signature could be seen or not seen. Future experiments could determine if this perspective inspired by Graphene deserves more attention or if it is just an interesting novelty.
The theory is a good thing, but we haven't explored all the effects. I think it is too big to be true, and I don't have my hopes up for that.
More information: Alireza Parhizkar et al, Strained bilayer graphene, emergent energy scales, and moiré gravity, Physical Review Research (2022). DOI: 10.1103/PhysRevResearch.4.L022027Alireza Parhizkar, Victor Galitski, and Moir are related.
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