One of the most intriguing questions in cosmology is why our universe is expanding at an accelerating rate. Different methods of measuring this expansion have yielded inconsistent results, leading to a puzzle known as the cosmic tension problem.
Some researchers have proposed various solutions, such as modifying gravity or introducing new forms of dark energy. But a recent paper suggests a more radical idea: what if there is a mirror universe that interacts with ours through gravity?
The paper, published in the journal Physics Review Letters, is based on the work of a team of physicists from the University of New Mexico and the University of California, Davis.
They noticed that when they adjusted some cosmological models to fit the observed expansion rates, some dimensionless parameters remained constant. This implied that there was a hidden symmetry in the universe that could be explained by the existence of a mirror world.
A mirror world is not a new concept in physics. It has been proposed before to account for the imbalance between matter and antimatter in our universe.
According to this idea, there is another universe that is identical to ours, except that everything is reversed: left and right, matter and antimatter, time and space. The two universes would only interact through gravity, which would be weaker than in each individual universe.
“We find that a uniform scaling of the gravitational free-fall rates and photon-electron scattering rate leaves most dimensionless cosmological observables nearly invariant,” the researchers write in their study’s abstract.
Therefore, they add, “A “mirror world” dark sector allows for effective scaling of the gravitational free-fall rates while respecting the measured mean photon density today.”
The authors of the paper applied this idea to the cosmic tension problem and found that it worked remarkably well. By introducing a mirror world with its own dark sector, they were able to reconcile the two measurements of the expansion rate without violating any physical laws or principles.
They also showed that their model could be tested by future observations of gravitational waves and cosmic microwave background radiation.
The idea of a mirror universe is provocative and faces many challenges. For one thing, it requires a fine-tuning of the initial conditions of both universes to ensure their symmetry.
For another, it raises many philosophical questions about the nature of reality and identity. If there is a mirror universe, does it have its own inhabitants? Are they aware of us? Do they have free will? Are they our evil twins or our soulmates?
These questions may seem far-fetched, but they are not irrelevant for cosmology. As our understanding of the universe grows, so does our need for new frameworks and perspectives to interpret it.