New research suggests an invisible “mirror world” of particles interacting with our world only via gravity may be the key to solving a major puzzle in cosmology today – the problem of the Hubble constant.
The Hubble constant is the expansion rate of the universe today. Predictions of this rate – from the Standard Model of cosmology – are much slower than the rate found by our more accurate local measurements. This contradiction has been attempted by many cosmologists to resolve by changing our current cosmological model. The challenge is to do this without destroying the agreement between the predictions of the Standard Model and many other cosmic phenomena, such as the cosmic microwave background. Determining whether such a cosmic scenario exists is the question researchers, including Francis Jan Sir Racine, associate professor in the Department of Physics and Astronomy at the University of New Mexico, and Fei Ge and Lloyd Knox at the University of California, Davis have been trying to answer.
According to NASA, cosmology is the scientific study of the large-scale properties of the universe as a whole. Cosmologists study concepts such as dark matterAnd dark energy And whether there is one universe or many, is sometimes called the multiverse. Cosmology entails the entire universe from birth to death with puzzles and intrigues at every turn.
Now, Cyr-Racine, Ge and Knox have discovered a previously unnoticed mathematical property of cosmological models that could, in principle, allow for a faster expansion rate while hardly changing other carefully tested predictions of the standard cosmological model. They find that regular measurement of the free-fall rates of gravity and the rate of photon-electron scattering leaves most dimensionless cosmological observations almost constant.
“Essentially, we are pointing out that a lot of the observations we make in cosmology have an inherent symmetry under the remeasurement of the universe as a whole. This may provide a way to understand why there is a discrepancy between different measurements of the rate of expansion of the universe.”
The research, titled “Cosmic Observation Symmetry, a Dark Sector of the Mirror World and the Hubble Constant,” was recently published in Physical Review Letters.
This result opens a new approach to reconciliation cosmic microwave background Large-scale structure observations with high values of the Hubble constant H0: search for a cosmological model in which a measurement shift can be achieved without violating any measurements of quantities that are not protected by symmetry. This work has opened a new path towards solving what has proven to be a difficult problem. Additional model construction may lead to consistency with the two conditions not yet satisfied: the inferred primordial abundance of deuterium and helium.
If the universe somehow exploits this symmetry, the researchers have come to a very exciting conclusion: that there is an inverse universe that is very similar to ours but is only visible to us through the effect of gravity on our world. This dark sector of the “mirror world” would allow an efficient measurement of gravitational free-fall rates while respecting the average photon intensity accurately measured today.
“In practice, this gradient symmetry can only be achieved by including the mirror world in the model – a parallel universe with new particles that are all copies of known particles,” said Cyr-Racine. The idea of a mirror world first appeared in the 1990s but was not previously recognized as a potential solution to the Hubble constant problem.
“This may sound crazy on the surface, but such mirror worlds have significant physical compositions in an entirely different context because they can help solve an important problem in particle physics,” explains Cyr-Racine. “Our work allows us to relate this big book, for the first time, to an important problem in cosmology.”
In addition to searching for missing components in our current cosmological model, researchers are also wondering whether this discrepancy in the Hubble constant is due in part to measurement errors. While it is still a possibility, it is important to note that the discrepancy is becoming more and more significant as higher quality data have been included in the analyses, indicating that the data may not be wrong.
“I’ve gone from one and a half sigma, to three, and three and a half to four sigma. Now, we’re pretty much at the five sigma level,” said Sir Racine. “It’s the base number that makes this a real problem because you have two measurements of the same thing, which if you have a consistent picture of the universe should be perfectly consistent with each other, but differ by a statistically large amount.”
“That’s the hypothesis here and we’ve been thinking about what could be the reason for this and why are these measurements contradictory? So this is a big problem for cosmology. We don’t seem to understand why that is. being doing today.”
Francis Jan Sir Racine et al., Correspondence of Cosmic Observatories, the Mirror Realm of the Dark Sector, and the Hubble Constant, Physical Review Letters (2022). DOI: 10.1103/ PhysRevLett.128.201301
University of New Mexico
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