Cosmologic philosophy: what is dark matter? (Introduction)

by David Turell , Monday, February 01, 2016, 14:50 (3007 days ago) @ David Turell

A very long essay hat carefully explains what is known about dark matter and suggests it might be a superfluid formation instead of particles:-https://aeon.co/essays/is-dark-matter-subatomic-particles-a-superfluid-or-both?utm_source=Aeon+Newsletter&utm_campaign=fddf0e590c-Daily_Monday_February_1_20162_1_2016&utm_medium=email&utm_term=0_411a82e59d-fddf0e590c-68942561-:Therefore, to explain what makes up dark matter, physicists instead had to theorise about new, so far undetected, particles. The most widely used ones fall into two broad classes: weakly interacting massive particles (WIMPs) and much lighter axions, though there is no shortage of more complex hypotheses that combine various types of particles. But all attempts to detect any of these particles directly, rather than inferring their presence from their gravitational pull, have so far been unsuccessful. Instead of solving the mystery, the direct-detection experiments have only deepened it.-***-:When Liberati first learned how successful modifications of gravity are on galactic scales where cold dark matter models fall short, he immediately tried to think of ways to combine the two. ‘It made me think: maybe dark matter at small scales makes a type of phase transition,' he says. ‘Maybe it transforms into a type of fluid, in particular a superfluid. If it forms a condensate at the scale of galaxies, this really solves a lot of problems.'-:Superfluids do not exist in daily human experience, but they are well-known to physicists. They are analogous to superconductors, a class of materials that moves electricity without resistance. When cooled to temperatures near absolute zero, helium likewise starts flowing without resistance. It will creep through the tiniest pores, and even slide out of trays by moving up walls. Such ‘superfluid' behaviour isn't specific to helium; it is a phase of matter that, at low enough temperatures, can be reached by other particles too. First predicted in 1924 by Einstein and the Indian physicist Satyendra Bose, this whole class of ultra-cold superfluids is now known as Bose-Einstein condensates. -***-"We are used to thinking that quantum physics dominates only the microscopic realm. But the more physicists have learned about quantum theory, the more it has become clear that this isn't so. Bose-Einstein condensates are one of the best-studied substances that allow quantum effects to spread widely through a medium. In theory, quantum behaviour can span arbitrarily large distances, provided it isn't disturbed too much.-***-"If dark matter is a superfluid, the particles it is made of must be lightweight, much lighter than the hypothetical dark particles that have been the targets of most of the searches. The superfluid's constituents are probably too slight to show up in the experiments currently running. -"A better and unique prediction of Khoury's model is that a superfluid's quantum behaviour should leave a telltale pattern in galactic collisions. When the dark matter condensate from one galaxy runs into that of another, the collision would create interference patterns - ripples in the distribution of matter and gravity, which would affect how the galaxies settle. Superfluid dark matter also makes predictions for the friction between the dark matter components within galaxy clusters; such friction would again produce distinctive patterns of gravitational attraction. Observations of gravitational lensing could detect these fingerprints of superfluid dark matter, provided we know exactly what we're looking for."-
Comment: More quantum weirdness as the basis of the universe's reality