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Home Topics in Depth Science And Environment Emergent Gravity theory may explain galaxy rotation without dark matter

  • arendt (1035 posts)
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    Emergent Gravity theory may explain galaxy rotation without dark matter

    New theory of gravity as an emergent phenomenon in the universe: first tests look interesting

    The outer regions of galaxies, like our own Milky Way, rotate much faster around the center than can be accounted for by the quantity of ordinary matter like stars, planets and interstellar gasses. Something else has to produce the required amount of gravitational force, so physicists proposed the existence of dark matter. Dark matter seems to dominate our universe, comprising more than 80 percent of all matter. Hitherto, the alleged dark matter particles have never been observed, despite many efforts to detect them.

    In his new paper, Verlinde showed how his theory of gravity accurately predicts the velocities by which the stars rotate around the center of the Milky Way, as well as the motion of stars inside other galaxies. At first glance, Verlinde’s theory presents features similar to modified theories of gravity like MOND (modified Newtonian Dynamics, Mordehai Milgrom). However, where MOND tunes the theory to match the observations, Verlinde’s theory starts from first principles. “A totally different starting point,” according to Verlinde.

    One of the ingredients in Verlinde’s theory is an adaptation of the holographic principle, introduced by his tutor Gerard ‘t Hooft (Nobel Prize 1999, Utrecht University) and Leonard Susskind (Stanford University).According to the holographic principle, all the information in the entire universe can be described on a giant imaginary sphere around it. Verlinde now shows that this idea is not quite correct—part of the information in our universe is contained in space itself.

    This extra information is required to describe that other dark component of the universe: Dark energy, which is believed to be responsible for the accelerated expansion of the universe.

    This experiment is merely the tip of a twenty year long iceberg of research on alternative theories of gravity. These theories first appeared around 1995, in reaction to some of the inconsistencies in the theory of black holes (Hawking). Those theories introduced the idea that black holes had entropy. In trying to quantify the entropy, people (t’Hooft, Susskind) came up with the idea that reality lives on the 2D surface of the black hole, not the 3D interior – it was a way to avoid the issue with the singularity at the center of the black hole. People then took this explanation and used it outside of black holes, by drawing non-existent spherical boundaries in space and asking what the entropy of the points of matter enclosed might be.

    The new theory makes an analogy to the well-known (to physicists) ability of statistical mechanics (a theory at the atomic level) to explain the laws of thermodynamics (a theory at the macroscopic level). In this theory, gravity is something like temperature – an emergent phenomenon. That is, you can’t really talk about the temperature of one atom. Temperature is not only a bulk (macroscopic) property. To have a temperature, a collection of atoms must be in thermal equilibrium with each other. When that equilibrium is reached, the property of temperature “emerges”.

    The new theory says that gravity emerges from behind these fake spherical boundaries, that it is property of bulk matter, not indivdual atoms. It says that gravitational force is an entropic phenomenon: in trying to reach a gravitational equilibrium (in order to maximize their entropy) gravity emerges. The idea resembles osmotic pressure.

    As I mentioned, there is a twenty year literature on this stuff. It is mainstream science, not some kooky nonsense. I was surprised to hear about this stuff, because dark matter has gotten all the attention. But this explanation is so elegant, so cool. Did I mention that they have no free parameters? The holographic theory has generated a whole bunch of analogies that are being explored under the rubric of “conformal field theories”. Although this first result is non-relativistic (they selected galaxies with minimal red shift), the theory has been extended to cover General Relativity.

    You might notice that I am blown away, not by this experiment, but by the underlying 20 years of mainstream physics that I managed to miss. I would love to hear from other physics-oriented JPR folk.

    HIP56948, like this

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15 replies
  • Eggar (1150 posts)
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    1. so, it's like popping a zit

    and then releasing said zit – let’s just say with ointment covering. So when released, one would hope that the ointment gets sucked back into the vacant pore. eh?

    .

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    • arendt (1035 posts)
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      3. Sigh. I ask for physics folk, and I get stand-up comedy.

      Well, thanks for responding, I guess. And, points for creativity, even if its gross.

       

      • Eggar (1150 posts)
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        5. hehe….

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        .

  • faultindicator (571 posts)
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    2. Briefly reading this and the provided link stirs some thoughts

    It is always necessary to approach new theory, and those twenty years in the making, from assuming the conditions exist that are to be proven possible. So, to start, do galaxies rotate in that manner? This we are told – a first assumption, okay, I’ll bite and agree. Also agree to debunk dark matter.

    gotta get back to work for now – next item?

    A malfunction causes an FI (fault indicator) to light up on the dash. It flashes in code saying what to fix. Simple and straight forward. Just like this place - causes and solutions without the bullshit.
    • arendt (1035 posts)
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      4. If you have physics background, and some time, the original Verlinde paper…

      is sorta readable. (I assume that when you say “next item”, you mean “do you have another reference?”)

      https://arxiv.org/pdf/1001.0785.pdf

      However, I gotta say that without knowing a lot of other background stuff, it seems like he is just pulling one rabbit after another out of a hat. But, if you have some physics context, you can sorta follow.

       

      • faultindicator (571 posts)
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        9. Is it even possible to observe the rotation of a galaxy in the short time that

        we have been told of their existence? I think not. We can no more tell if objects in a galaxy are spinning like a pinwheel or like objects in an eddy. That is my first point. The second is the lack of any evidence of dark matter, especially to the extent that currently accepted theories cannot mathematically reason it’s existence without the cosmological constant, basically a fudge factor. It is speculated that the dark matter is plausible in M theory or string theory, both of which argue that it’s direct proof is unobtainable because we cannot measure anything smaller than a planck-length.

        To successfully argue for the ability of one’s theory to be true outside an observable universe, it is only necessary for another, any other, consciousness to concur that the theory is true and understood on the merits of it’s presentation, thus becoming reality in one of any number of unlimited ranges of possibilities. I do not believe in dark matter as it is suggested to exist, thus dismiss the entire theory.

        A malfunction causes an FI (fault indicator) to light up on the dash. It flashes in code saying what to fix. Simple and straight forward. Just like this place - causes and solutions without the bullshit.
        • arendt (1035 posts)
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          10. Googled that

          First: Just googled “how do we know galaxies rotate” and got this:

          One of the easiest way to show that galaxies rotates are Doppler observations of atomic or molecular lines. For example, if the observed galaxy is seen edge-on and rotates clockwise, the left side of the galaxy is going away from you, and is then Doppler-shifted in the red. The right side, going toward you, is Doppler-shifted in the blue.

          This kind of observations was realized already in the ’60, in radio.

          The spiral patern observed in spiral galaxies is also a clear signature of their rotation. Note that spiral are linked to density waves in the galactic disk (see for example Lin & Shu 1964).

          Second, I don’t buy dark matter either. That is why this research interests me. I think high energy physics has wasted the last thirty years with string theory, for which you need an accelerator the size of a solar system to do any definitive experiments. Ditto all this dark matter, dark energy stuff. People speculating about stuff that it is darn near impossible to prove. Of course, the two groups reinforce each other and point to each other’s theories as support, in a circular reasoning chain from hell.

          To successfully argue for the ability of one’s theory to be true outside an observable universe,

          Not sure what this refers to. Don’t want to speculate. Could you please rephrase this so I know which theory (emergent gravity, dark matter, string theory) you are referring to. Thanks.

          • faultindicator (571 posts)
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            11. No need to rephrase, we said the same thing –

            you using groups to reinforce one another, me using individuals. In cases like quantum physics or a unified theory, etc, I prefer to look upon it as an unending quest. Everything is built from a preceding chapter or book. We as individuals jump into the fray at some point, and dis/agree as much or little as we like. Not being a professional making a living in the field, but rather a polar opposite finding its’ value more as entertaining and relaxing. It is my belief that this unaccounted for matter and energy does not exist as dark, but exists in an alternate direction of time. A particle that attains a state now, at this very moment, did not yet exist in this state at the instant the observation was made, therefore not visible. An extreme example would be a particle moving through time towards its creation, unlike us who are moving away from the time of creation; That particle may be becoming younger in a sense, younger in that in our future its existence will be a gluon, quark, string, etc., and we will be older than dirt.

            A malfunction causes an FI (fault indicator) to light up on the dash. It flashes in code saying what to fix. Simple and straight forward. Just like this place - causes and solutions without the bullshit.
  • so far from heaven (7342 posts)
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    6. From what is presented, this is a macro descriptive theory.

    Just like Statistical Mechanics and Solid State.

    There are a couple things that need to be addressed as a FULL theory of gravity, which lie outside the premise so it’s going to run into real trouble in those parts.

    Gravity is an intrinsic property of mass, at any level including the absolute micro physics realm, quantum physics. The biggest problem with General is the fact that quanitization of gravity has eluded everyone, including the individuals that discovered the quantum and relativistic physics world.

    The reason that conformal theory has some serious problems to overcome lies in the fact that the universe isn’t actually isotropic nor homogeneous. It has structure that is small but observable. Macro theories ‘gloss’ over these inconsistencies to give an overall picture, not the underlying picture. It also neglects the actual source of the thing we call gravity, studying how that thing acts on very large scale only.

    To show the difference you need only look at a few things. How would conformal gravity describe the big bang? Gravity is one of four known forces and has dominant influence after the other three forces have ‘frozen’ out. How does this theory describe the underlying symmetry breaking of the mass portion throughout the known universe? And last but by far not the least is the question of the origin of gravity (a force) itself. This last question is a quantum structure problem and outside the theory itself as far as I can tell.

    Bite me Deadpool.     "When you're in jail, a good friend will be trying to bail you out. A best friend will be in the cell next to you saying, 'Damn, that was fun.'" -Groucho Marx
    • arendt (1035 posts)
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      7. Fuck. Fifteen minutes of comments blown away by a glitch. Too tired to reproduce

      get back to you later.

      Stupid editor flagged me for no title. Then it hung. When I tried to back out, all my work vanished.

    • arendt (1035 posts)
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      8. Yes. It is a macro theory. But it denies the primacy of the micro theory.

      You say:

      Gravity is an intrinsic property of mass,…the question of the origin of gravity (a force) itself. This last question is a quantum structure problem and outside the theory itself as far as I can tell.

      Well, the theorist will definitely argue that point. His claim is that gravity is only an emergent, macroscopic phenomenon. The theory is like thermodynamics because it is an extension of the thermodynamically based theories about black holes. Just as we cannot say what goes on behind an event horizon, this theory claims it does not care (not sure about ‘cannot know’) what goes on beneath the level of the theory. They make a lot of references to renormalization group, which I was always a little fuzzy on. (Sorry, bad physics pun.)

      You say:

      Macro theories ‘gloss’ over these inconsistencies to give an overall picture, not the underlying picture. It also neglects the actual source of the thing we call gravity, studying how that thing acts on very large scale only.

      That is your interpretation. Their interpretation is that the source of gravity is nothing more than the entropy of the arrangement of bits of matter in space. They discard the details because, in their theory, the details are not the source of gravity. Entropy is.

      All quotes here from the 2010 Verlinde paper:

      information about the location of particles is stored in discrete bits on the screens. The dynamics on each screen is given by some unknown rules, which can be thought of as a way of processing the information that is stored on it. Hence, it does not have to be given by a local field theory, or anything familiar. The microscopic details are irrelevant for us. …

      As opposed to you, they find coarse-graining to be essential, not to be some disqualifying defect.

      Space emerges at a macroscopic level only after coarse graining. Hence, there will be a finite entropy associated with each matter configuration. This entropy measures the amount of microscopic information that is invisible to the macroscopic observer. In general, this amount will depend on the distribution of the matter. The information is being processed by the microscopic dynamics, which looks random from a macroscopic point of view. But to determine the force we don’t need the details of the information, nor the exact dynamics, only the amount of information given by the entropy, and the energy that is associated with it. If the entropy changes as a function of the location of the matter distribution, it will lead to an entropic force.

      You say:

      Gravity is one of four known forces and has dominant influence after the other three forces have ‘frozen’ out. How does this theory describe the underlying symmetry breaking of the mass portion throughout the known universe?

      Well, they point to “dualities between closed string theories that contain gravity and decoupled open string theories that don’t”. Then they claim that their theory is consistent with open string theory. So, their answer to your question seems to be: see open string theory.

      6.2 Implications for string theory and relation with AdS/CFT.
      If gravity is just an entropic force, then what does this say about string theory? Gravity is seen as an integral part of string theory, that can not be taken out just like that. But we do know about dualities between closed string theories that contain gravity and decoupled open string theories that don’t. A particularly important example is the AdS/CFT correspondence.
      The open/closed string and AdS/CFT correspondences are manifestations of the UV/IR connection that is deeply engrained within string theory. This connection implies that short and long distance physics can not be seen as totally decoupled. Gravity is a long distance phenomenon that clearly knows about short distance physics, since it is evident that Newton’s constant is a measure for the number of microscopic degrees of freedom. String theory invalidates the ”general wisdom” underlying the Wilsonian effective field theory, namely that integrating out short distance degrees of freedom only generate local terms in the effective action, most of which become irrelevant at low energies. If that were completely true, the macroscopic physics would be insensitive to the short distance physics.
      The reason why the Wilsonian argument fails, is that it makes a too conservative assumption about the asymptotic growth of the number of states at high energies. In string theory the number of high energy open string states is such that integrating them out indeed leads to long range effects. Their one loop amplitudes are equivalent to the tree level contributions due to the exchange of closed string states, which among other are responsible for gravity. This interaction is, however, equivalently represented by the sum over all quantum contributions of the open string. In this sense the emergent nature of gravity is also supported by string theory.

      This stuff is not my speciality. I am just winging my answers based on a skim of this paper. I am willing to be educated. Can you comment on what he says about effective fields:

      String theory invalidates the ”general wisdom” underlying the Wilsonian effective field theory, namely that integrating out short distance degrees of freedom only generate local terms in the effective action, most of which become irrelevant at low energies. If that were completely true, the macroscopic physics would be insensitive to the short distance physics.
      The reason why the Wilsonian argument fails, is that it makes a too conservative assumption about the asymptotic growth of the number of states at high energies.

      It seems to me that this whole local vs at-a-distance argument is the crux of the matter; and I am missing too much of the debate of the last 20 years to appreciate exactly what he is pointing at here.

      I appreciate your feedback.

      Note: adS/CFT = anti-de Sitter space/conformal field theory

      • so far from heaven (7342 posts)
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        12. YEs, I know what asS/CFT is.

        I can only approach this via my research and specialty which is high energy physics.

        What I am asking the authors to discuss, which they haven’t, is the underlying symmetry loss from an assumed homogeneous and isotropic initial state to a state with ‘lumps’ and ‘tendrils’ almost immediately after initialization of the system. Everyone, not just this branch,  has glossed final state structure showing this breakage via ‘if we make the thing big enough we can ignore it’. And the breakage from isotropy keeps getting bigger and bigger all the time via better and better observation for both matter dominated and vacuum regions.

        This is only the start of my questions.

        That breakage, as well as the baryon abundance symmetry break are extremely important when coupled with the mass of the higgs.

        And, as far as I know, string theory can’t tie it’s own shoelaces yet, but I know, give it time.

        Bite me Deadpool.     "When you're in jail, a good friend will be trying to bail you out. A best friend will be in the cell next to you saying, 'Damn, that was fun.'" -Groucho Marx
        • arendt (1035 posts)
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          13. You have bad manners.

          I’m sorry, but I was only trying to help. You act as if it was condescending to flesh out an obscure acronym.

          I asked you to comment on Wilsonian effective fields. You said nothing.

          I gave answers to many of your questions. You have given me nothing but demands that the authors explain something.

          Look. I am not the authors. Take it up with them.

          We are done here.

          • so far from heaven (7342 posts)
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            14. Sorry if I am coming off that way, but

            you asked for science type people to weigh in on the story.

            So, I tried to give a brief overall picture or the entire story, not just the results from this particular study.

            When put into the context of the complete physics of all field forces, there are two physics ‘realms’ at the very least. One is macro the other quantum. There are two realms of relativity, the dynamic and the forces. The universe is a composite of the latter expanding to the prior. Unfortunately there are a few outstanding unknowns that need to be addressed, starting with the ‘essence’ of the nature of the origination of the forces themselves. At present this is glossed over by noting that they are intrinsic to the particles. It is always helpful to develop simpler and more elegant theories. This particular theory reduces an unknown observed in the non-newtonian rotational curves of galaxies without the complication of unknown physics such as dark matter. I just wanted to keep it in context.

            However, the concept of dark matter may be far more important than fixing the rotation velocity problems if it turns out that it can accurately reproduce the structure of the distribution of visible mass. We’re just getting our feet wet on all of these ‘quandries’.

            Like I tried to point out: let’s give these studies a little breathing room and time. There is always the fundamental idea that the entire universe can be developed from one elegant all encompassing theory, sometimes nicknamed the ‘theory of everything’ and perhaps this is a start to address one section of that. The notion of an all encompassing theory is usually referred to as Grand Unification Theory, GUT. GUT starts at the beginning, the singularity where all forces are unified into a single force, that freezes out as the temperature of the universe declines, creating the observed universe we see today.

            Bite me Deadpool.     "When you're in jail, a good friend will be trying to bail you out. A best friend will be in the cell next to you saying, 'Damn, that was fun.'" -Groucho Marx
            • arendt (1035 posts)
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              15. Closing thoughts

              you asked for science type people to weigh in on the story.

              That I did. But I was hoping for responses to specific questions I raised instead of even more new information that I am not equipped to evaluate.

              Unfortunately there are a few outstanding unknowns that need to be addressed, starting with the ‘essence’ of the nature of the origination of the forces themselves. At present this is glossed over by noting that they are intrinsic to the particles. It is always helpful to develop simpler and more elegant theories. This particular theory reduces an unknown observed in the non-newtonian rotational curves of galaxies without the complication of unknown physics such as dark matter. I just wanted to keep it in context.

              To be honest, I can’t tell from this if you agree or disagree with this new theory. The bolded sentence starts out saying that the theory is doing something useful, but ends in midair, without a judgment as to whether or not that is some kind of advance. You could be agreeing that the theory is not inconsistent with known physics,  and simultaneously saying it does not answer the question you want answered.

               

              Like I tried to point out: let’s give these studies a little breathing room and time.

              Just a little feedback: before this, I never got that you were willing to entertain this theory, rather than just dismiss it as not addressing basic interactions.

              Anyway, thanks for participating. Clearly not a topic that draws many viewers at JPR.