According to a new study, an invisible ‘mirror world’ of particles that interacts with the universe purely through gravity could be the key to solving a crucial cosmological problem – the constant Hubble problem.
The Hubble constant is the current rate of cosmic expansion, but the rate predicted by the standard model of cosmology is much slower than the rate discovered by the most accurate local observations. Many cosmologists have attempted to resolve this difference by modifying the current cosmological paradigm.
The goal is to do this without compromising the consistency of the Standard Model predictions with many other cosmological phenomena, such as the cosmic microwave background.
The question that researchers like Francis-Yan Cyr-Racine, assistant professor in the Department of Physics and Astronomy at the University of New Mexico, Fei Ge, and Lloyd Knox of the University of California, Davis, have sought to answer is whether such a cosmic scenario exists.
Cosmology, according to NASA, is the scientific study of large-scale features of the universe. Cosmologists study topics such as dark matter and dark energy, as well as whether there is only one universe or a multiverse. Cosmology encompasses the entire cosmos, from conception to death, and is full of mystery and intrigue.
Cyr-Racine, Ge, and Knox have now identified a previously overlooked mathematical feature of cosmological models that, in theory, could allow for a faster rate of expansion without affecting the other more accurately proven predictions of the traditional cosmological model.
Most dimensionless cosmic observables are substantially invariant when gravitational free fall rates and photon-electron scattering rates are scaled uniformly.
Basically, we’re pointing out that a lot of the observations we make in cosmology have an inherent symmetry when rescaling the universe as a whole. This could provide a way to understand why there seems to be a discrepancy between different measurements of the expansion rate of the Universe..
Francis-Yan Cyr-Racine, Assistant Professor, Department of Physics and Astronomy, University of New Mexico
The study was published in Physical examination letters.
This finding suggests a new way to reconcile measurements of the cosmic microwave background and large-scale structure with high values of the Hubble constant H0 by discovering a cosmological model in which scale transformation can be demonstrated without violating measurements. values not protected by symmetry.
This effort paved the way for a new approach to meeting a difficult challenge. The development of additional models could standardize the two remaining constraints: the inferred primordial abundances of deuterium and helium.
Researchers are led to an incredibly intriguing conclusion if the universe somehow exploits this symmetry: there is a mirror universe that is remarkably identical to ours but invisible except by the gravitational influence on that world.
The dark sector of the “mirror world” would lead to efficient scaling of gravitational free-fall velocities while maintaining the accurately calculated average photon density now reported.
“In practice, this scale symmetry could only be achieved by including a mirror world in the model – a parallel universe with new particles that are all copies of known particles. The idea of the Mirror World first emerged in the 1990s, but was not previously recognized as a potential solution to the ongoing Hubble problem.said Cyr-Racine.
He further explained:It may seem crazy at first glance, but such mirror worlds have great physics literature in a completely different context because they can help solve important problems in particle physics. Our work allows us to connect, for the first time, this vast literature to an important problem in cosmology.”
The researchers also ask if Hubble’s constant deviation could be caused in part by measurement errors, in addition to looking for missing elements in the current cosmological model.
While this remains a possibility, it should be noted that the disparity has grown in importance as better quality data has been included in the analysis, suggesting that the data is not to blame.
According to Cyr-Racine,It went from two and a half Sigma to three Sigma and from three and a half to four Sigma. Right now we’re pretty much at the five sigma level. That’s the key number that makes it a real problem because you have two measurements of the same thing, which if you have a consistent picture of the universe should just be completely consistent with each other, but they differ by a very statistically significant amount.”
He concluded, “That’s the premise here and we thought about what could be causing it and why are these measurements divergent? So it’s a big problem for cosmology. We just don’t seem to understand what the universe is doing today.”
Cyr-Racine, F., et al. (2022) Symmetry of cosmological observables, a dark sector of the mirror world and the Hubble constant. Physical examination letters. doi:10.1103/PhysRevLett.128.201301.
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