The mirror symmetry of the universe may well be in trouble if the results of some current research is confirmed. These results are based on our current understanding of the large-scale structure of the cosmos and what we know about how gravity works within it. To fix ideas, if we look at a sampling of how galaxies are distributed throughout the universe and then compare it with its mirror image, the two should be basically indistinguishable.
Consider the mirror images of the tetrahedrons (Tet 1, Tet 2) in the above graphic. What we need for cosmic isotropy to be valid is that the distributions of galaxies within each are basically the same - say based on counts using the Sloan Digital Sky survey (see e.g. my Aug. 4, 2016 post). But two recent separate analyses have now found that this principle called "parity symmetry" doesn't seem to hold. Each analysis, see e.g. this link to one by Oliver Philcox of Princeton:
[2206.04227] Probing Parity-Violation with the Four-Point Correlation Function of BOSS Galaxies (arxiv.org)
examined galaxies from the Sloan Digital Sky Survey using a technique from solid geometry, or rather a classic figure of solid geometry: the tetrahedron. In this case, the method took advantage of the fact this figure is the simplest 3D shape that can be distinguished from its mirror image. Thereby, the researchers compared all possible tetrahedrons that could be formed for a given sample of galaxies by placing a galaxy on each vertex. More specifically, to determine whether parity symmetry was violated, the researchers assigned a primary vertex for each of the galaxy-assigned tetrahedrons and then split them into two groups.
Group I: Those for which - when one looked down from the primary vertex - the sides increase in length when you move clockwise, and:
Group II: Those for which - when one looked down from the primary vertex - the sides increase in length when you move anticlockwise.
According to Zachary Slepian at the Univ. of Florida, who performed one of the 2 analyses:
"It's just like how you can't rotate your right hand and make it impossible to tell the difference from your left hand. It's the same with these pyramids of galaxies"
For the universe to obey parity symmetry, Group I and Group II should both be roughly the same size. However, neither the analysis of Philcox or Slepian found this to be the case. By way of comparison of the two teams' results, Philcox et al found a parity violation on the order of 2.9 sigma (2.9 s) which means there was only a 0.4 percent chance the pattern would show up as it did based on a statistical fluke. Meanwhile, Slepian et al found even greater violation at a level of 3.1 s in one case and 7.1 s in another. See e.g.
[2206.03625] Measurement of Parity-Odd Modes in the Large-Scale 4-Point Correlation Function of SDSS BOSS DR12 CMASS and LOWZ Galaxies (arxiv.org)
Two separate analyses of our best map of galaxies showing parity symmetry violation? In the words of one Brown University cosmologist (Stephon Alexander), quoted in a New Scientist piece: "This observation is completely shocking!" Alexander went on to note he'd have been "skeptical" if the data came from just one group, but "with two groups it's a lot harder to shake." Well, because the chances of sheer coincidence, i.e. from random distributions, recedes "into the ether" - especially given the strength of those sigma violations.
Another possible case for anisotropy comes from an international team led by astronomer Konstantinos Migkas of the University of Bonn in Germany. This work relies on new or archival data on nearly 850 galaxy clusters seen by NASA’s Chandra X-ray Observatory, the European Space Agency’s XMM-Newton satellite and Japan’s Advanced Satellite for Cosmology and Astrophysics. Migkas, for his part found anisotropy (lack of symmetry) in terms of the Hubble constant H o, with a 4 s level of symmetry violation, e..g.
What do these results mean in concert? According to Slepian (ibid.):
"If what we find turns out to be genuinely from the early universe it would mean there's a new interaction between particles that has not previously been part of our understanding of physics. Basically a new force of nature."
Well, that's a very heady statement to be sure, but fortunately, both Slepian's and Philcox's analyses are very testable. So before we admit any new particles, particle interactions or new forces of nature, you can be sure many other research teams are lining up to see if they can confirm these results. Or, as is often the case in science, invalidate them.
And as another cosmologist pointed out (ibid.), if there really is such a symmetry- breaking mechanism at cosmological scales, it ought to be evident not merely at large scale. For example, we should encounter signals in the cosmic microwave background, as well as gravitational waves.
Post a Comment