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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38 Responses to “Is Dark Matter a Superfluid?”

  1. 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.

  2. Michel C. Says:

    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.

    • … 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

    • “I think that case 1 is impossible because the EM interaction is essential to get a proper mass. I could be wrong.”

      Not sure what you mean here. Before neutrinos were shown to have mass, then every massive elementary particle was charged, but not anymore (though all charged elementary particles are massive).

      • Michel C. Says:

        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.

      • Michel C. Says:

        All known matter particles are coupled to the EM field anyway. For example. neutral pions decay to 2 photons or electron-positron pairs…

      • telescoper Says:

        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!

      • Michel C. Says:

        Yes, but neutrinos still interact weakly. And the neutrino mass has no theoretical explanation, it is still unknown why and how.

    • 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.

      • Repeating something doesn’t make it true, even if you add detailed section numbers.

      • It’s correct.

        Dark matter ripples when galaxy clusters collide and waves in a double-slit experiment, relating general relativity and quantum mechanics.

      • telescoper Says:

        It’s not even wrong.

      • Curved spacetime = geometrical representation of gravity.

        Displaced dark matter = physical representation of gravity.

      • telescoper Says:

        OK then can you please tell us what equations describe this representation of gravity?

      • 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.

      • telescoper Says:

        Equations please.

      • 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”

      • ”that describe the fundamental interaction of gravitation as a result of dark matter being displaced by visible matter and its associated energy”

      • 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”

  3. What a fun idea! I hadn’t heard of this before, Peter. Thanks!

  4. There is a discussion at Sabine Hossenfelder’s blog about this. She is usually quite (healthfully) sceptical, but, for what it’s worth, agrees with me that this is an interesting idea. Khoury gave a talk about this at the last Moriond cosmology meeting, and I was not alone in thinking that it was the most interesting talk.

  5. Shantanu Says:

    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

    • I think that anyone who has looked at the data with no agenda takes MOND phenomenology seriously. This includes James Binney, who literally wrote the book on galactic dynamics.

      The main problem the MOND camp has are papers like the one by Merritt which you mention. There are few papers I have read which are worse than this one. He demonstrates an extremely limited grasp of the history of cosmology—which is OK if he weren’t trying to use the history of cosmology to make his point. He also attacks a straw-man version of the standard model which is an unbelievably naive caricature. It doesn’t matter if he actually believes this or not. With friends like these, MOND needs no enemies.

      Yes, some of the points he makes are valid. But he would be more convincing if he would stick to the facts and not stoop to caricaturing his opponents.

      I would like to see some MOND people distancing themselves from this sort of rhetoric. “The enemy of my enemy is my friend” is rarely a good strategy.

      • telescoper Says:

        `An idea is not responsible for the people who believe in it.’

      • True. The biggest fool can say that the Sun will rise tomorrow, but that doesn’t make it dark. Still, people who are interested in MOND and think that more people should look at at least the MOND phenomenology would be well advised not to refrain from criticizing someone just because he likes MOND. 😐

      • telescoper Says:

        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.

      • Many claim this, but few can back up their claims. Yes, some say “MOND phenomenology falls out of our simulations”, but since they require millions of hours of CPU time, they are not easy to check. (And if confirmed, many journals wouldn’t publish the confirmation, even though this would be very important.) Another approach is to explain exactly what goes into the simulation and what comes out and to what extent it was tuned or not. Since there are no PEM* cosmological simulations, without understanding exactly what approximations etc are made it is a tough call.

        MOND enthusiasts predicted many phenomena which were later observed, all based on one parameter determined from observations. Have cosmological simulations predicted anything which was later observed, as opposed to being tuned to reproduce observations?


        *PEM: primitive-equation model, a mathematical model which is based on fundamental physical equations the validity of which are not in doubt.

      • Shantanu Says:

        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?

      • “Can you tell me specifically what problems you saw with the Merritt paper?”

        I gave a summary above; I could literally write an entire paper pointing out what is wrong with Merritt’s paper; perhaps I will.

        “It was not a paper on history of cosmology.”

        No, but where he does mention history he should get it right.

        Also Meritt has also made seminar contributions to Dark matter paradigm. So its ludicrous to call him “MOND friend”.

        In this paper he obviously comes across as a very strong proponent of MOND. What he did before is not really relevant.

        “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?”

        No, I don’t deny it. There are, however, a huge number of issues which are not mentioned in introductory textbooks. I reviewed one recently where MOND is mentioned, so his list is at least incomplete.

        “Also that the goal posts in SUSY dark matter have moved?”

        Yes, but this hardly strengthens the case for MOND or against dark matter. At best, it says something bad about SUSY.

  6. Shantanu Says:

    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/

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