Is Dark Matter a Superfluid?
In between marking exams and project reports I’ve been doing a little bit of reading in preparation for a talk that I’m due to give next week, which prompted me to share this talk by Justin Khoury of the University of Pennsylvania, which is about framework that unifies the claimed success of Modified Newtonian Dynamics (MOND) on galactic scales with the that of the standard ΛCDM model on cosmological scales. This is achieved through the physics of superfluidity. The dark matter and MOND components have a common origin, representing different phases of a single underlying substance. In galaxies, dark matter thermalizes and condenses to form a superfluid phase. The superfluid phonons couple to baryonic matter particles and mediate a MOND-like force. This framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not): dark matter has a higher temperature in clusters, and hence is in a mixture of superfluid and normal phase. The rich and well-studied physics of superfluidity leads to a number of observational signatures, discussed in the talk.
The idea that dark matter might be in the form of a superfluid is not new (see e.g. this paper) but there has been a recent surge of interest driven largely by Khoury and collaborators. If you want to find out more, can find a review paper about this model here.
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In the Dark 
May 22, 2018 at 5:39 pm
Dark matter is a supersolid that fills ’empty’ space and is displaced by visible matter. What is referred to geometrically as curved spacetime physically exists in nature as the state of displacement of the dark matter. The state of displacement of the dark matter is gravity.
The supersolid dark matter ripples when galaxy clusters collide and waves in a double-slit experiment, relating general relativity and quantum mechanics.
May 22, 2018 at 9:14 pm
3 possible choices:
1- DM has no EM counterpart, no EM interaction, it has no friction at all and it is a superfluid.
2- DM has its own EM field separated from our matter EM field so it has friction but not with ordinary matter. This is the most complex case. It is possible to have more than one type of DM.
3- DM has only a weak interaction with the EM field.
I think that case 1 is impossible because the EM interaction is essential to get a proper mass. I could be wrong.
May 22, 2018 at 10:41 pm
… and never forget the 4th Occams razor option – that somewhere there is a tiny error in a theory or observation and Dark Matter doesn’t exist at all….
[now expecting flames!]
Chris
May 23, 2018 at 3:44 pm
4a. Dark matter fills ’empty’ space and is displaced by visible matter. What is referred to geometrically as curved spacetime physically exists in nature as the state of displacement of the dark matter. The state of displacement of the dark matter IS gravity.
4b. There is evidence of dark matter every time a double-slit experiment is performed, as it is the medium that waves.
May 23, 2018 at 4:08 pm
It’s correct.
Dark matter ripples when galaxy clusters collide and waves in a double-slit experiment, relating general relativity and quantum mechanics.
May 23, 2018 at 6:37 pm
It’s not even wrong.
May 23, 2018 at 6:50 pm
Curved spacetime = geometrical representation of gravity.
Displaced dark matter = physical representation of gravity.
May 23, 2018 at 6:56 pm
OK then can you please tell us what equations describe this representation of gravity?
May 23, 2018 at 6:59 pm
The equations of GR describe gravity. Curved spacetime is a geometrical representation of what physically exists in nature as the state of displacement of the dark matter.
‘NASA’s Gravity Probe B Confirms Two Einstein Space-Time Theories’
http://www.nasa.gov/mission_pages/gpb/gpb_results.html
“Imagine the Earth as if it were immersed in honey. As the planet rotates, the honey around it would swirl, and it’s the same with space and time”
Honey has mass and so does the supersolid dark matter. The swirl is the state of displacement of the dark matter connected to and neighboring the Earth.
The supersolid dark matter displaced by the Earth pushing back and exerting pressure toward the Earth is gravity. What is referred to geometrically as curved spacetime physically exists in nature as the state of displacement of the dark matter. The state of displacement of the supersolid dark matter is gravity.
May 23, 2018 at 6:59 pm
Equations please.
May 23, 2018 at 7:03 pm
https://en.wikipedia.org/wiki/Einstein_field_equations
May 23, 2018 at 7:04 pm
Replace ” that describe the fundamental interaction of gravitation as a result of spacetime being curved by mass and energy” with ” that describe the fundamental interaction of gravitation as a result of dark matter being displaced by mass and energy”
May 23, 2018 at 7:19 pm
”that describe the fundamental interaction of gravitation as a result of dark matter being displaced by visible matter and its associated energy”
May 23, 2018 at 7:23 pm
If the hang-up is “curved” vs. “displaced”:
”that describe the fundamental interaction of gravitation as a result of dark matter being curved by visible matter and its associated energy”
May 23, 2018 at 9:55 pm
Neutrinos are coupled to the EM field via the weak interaction. The neutrinos are still mostly unknown particles. There is no proof that any particle has truly zero residual local charge. The residual charge could be as small as one planck length divided by the compton wavelength of the elementary particle.
May 23, 2018 at 10:11 pm
All known matter particles are coupled to the EM field anyway. For example. neutral pions decay to 2 photons or electron-positron pairs…
May 23, 2018 at 10:15 pm
Wrong. Neutrinos don’t interact via electromagnetic forces because they’re not charged.
They’re not ‘unknown’ either. Neutrino physics is a very big field!
May 24, 2018 at 2:28 am
Yes, but neutrinos still interact weakly. And the neutrino mass has no theoretical explanation, it is still unknown why and how.
May 23, 2018 at 2:25 pm
What a fun idea! I hadn’t heard of this before, Peter. Thanks!
May 23, 2018 at 5:18 pm
Peter , its heartening that people are taking the successes of MOND at galactic scales seriously and constructing DM model which reproduces its successes at galactic scales.
Otherwise as Dave Merritt write in his paper last year , more than 30 cosmology textbooks have completely ignored the observational success of empirical MOND laws at galactic scales
May 24, 2018 at 10:08 am
`An idea is not responsible for the people who believe in it.’
May 24, 2018 at 10:17 am
I remain convinced that the problem is with baryons. If they weren’t around to mess everything up the universe would be a lot more comprehensible.
May 26, 2018 at 5:00 am
Philip: Can you tell me specifically what problems you saw with the Merritt paper? It was not a paper on history of cosmology.
Also Meritt has also made seminar contributions to Dark matter paradigm. So its ludicrous to call him “MOND friend”. do you deny that the 30 odd textbooks he listed make no mention about empirical success of Milgroms’s laws at galactic scales or failure to detect WIMP dark matter? Also that the goal posts in SUSY dark matter have moved?
May 24, 2018 at 8:52 am
I’m never sure what I admire more about Sabine – her clear, well reasoned blog posts or that she’s still sane after moderating her comments section.
May 24, 2018 at 9:56 am
I’ve never actually met Sabine, but will do so on Monday as she is giving a talk at this meeting (at which I’m also speaking).
May 26, 2018 at 5:05 am
Peter: baryons lead to dissipative phenomenon. Its hard to see how they can explain a_0, MADR, baryonic Tully-Fisher relation, Renzo’s law extremly well, despite the diversity of galaxies. Btw people can look at the debates in a recent dark matter conference at Santa Barbara. http://online.kitp.ucsb.edu/online/cdm-c18/
May 26, 2018 at 6:07 am
Baryons lead to lots of things.