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Math Science

Emergent Gravity Disproved 102

Posted by timothy from the what-does-this-guy-know? dept.
kdawson writes "A paper up on the ArXiv claims to disprove the gravity-from-entropy theory of Erik Verlinde, which we discussed soon after he introduced the idea in a symposium late in 2009. Archil Kobakhidze says that experiments measuring the effect of gravity on quantum particles (neutrons in this case) match results expected from classical Newtonian gravity, not Verlindian entropic gravity. Here is Kobakhidze's paper (PDF)."
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Emergent Gravity Disproved More

Emergent Gravity Disproved

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  • In his Giant Star novels, if I recall correctly. The great breakthrough in physics by the aliens was the understanding that gravity was a consequence of particles decaying rather than through the standard Einstein model. Kind of puts a torpedo through that aspect of the books.

    • Re: (Score:1)

      by Anonymous Coward

      That was only a glossover explanation to explain their gravity control. Technobabble with a small root in contemporary science.

      Still, great series using medium-hard science and a fun reveal chain. Mod up parent, Inherit the Earth!

  • Here we go again (Score:5, Informative)

    by Anonymous Coward on Saturday August 27, 2011 @12:27PM (#37228428)

    Kdawson, could you please try to have the first clue about something that you submit? This is a non-peer-reviewed article, fresh on the arXiv. It's a followup to an earlier article which was widely criticized within the community as being full of holes, and the arguments in this article are very very weak. At best it's an argument against entropic gravity, but it is a LONG way from a proof that entropic gravity is wrong.

    The way that neutron states are treated here is questionable - see http://arxiv.org/abs/1104.4650 [arxiv.org] for a summary of what's wrong with them.

    Disclaimer: I am a gravitational theorist. I think gravity ISN'T entropic. However this paper is nowhere near sufficient to show that. I'd wait a LOT longer for the dust to settle on this one before making a strong statement one way or the other.

    • Re:Here we go again (Score:5, Funny)

      by Zedrick ( 764028 ) on Saturday August 27, 2011 @12:33PM (#37228462)
      > I am a gravitational theorist.

      I don't even understand what that title means, but it sounds very cool.

    • Re: (Score:1)

      by Anonymous Coward

      This is a non-peer-reviewed article ... and the arguments in this article are very very weak.

      I wish they would hurry up and peer-review it so it would be correct.

      • There's nothing to peer review, because the 'paper' doesn't publish a new theory. All it says is that resulting forces require a statistical 'average' of a couple of forces and that statistical analysis resulst doesn't match with what the entropic force theory calculations predict, but does match with Newton gravity.

        That doesn't disprove entropic gravity, but merely sais that the current formula's not correct.

      • This is a non-peer-reviewed article ... and the arguments in this article are very very weak.

        I wish they would hurry up and peer-review it so it would be correct.

        Note that "and" is not the same as "thus".

    • This is a non-peer-reviewed article

      I was under the impression that a peer-reviewed article was more likely to be paywalled and thus inaccessible to those Slashdot readers who had already graduated.

    • Let me explain this to you... (Score:1)

      by Anonymous Coward

      ...in very simple words:

      Exciting headlines get page hits.

      A statement like "some data gathered might suggest gravity isn't entropic" will get very few page hits, and hence generate very little ad revenue.

      A completely wrong but much more interesting statement like "Emergent Gravity Disproved" will get more hits, and hence more money.

      So, Kdawson has every incentive to state the title wrongly, whether he understands it or not.

      Complain all you want, the nature of the beast does not change.

      • Re: (Score:2)

        by Old Wolf ( 56093 )

        I guess you didn't actually read the linked paper.. the paper itself explicitly does claim to disprove the Verlinde theory of emergent gravity

        • Yes, and for emergent gravity to be disproved the (claim made in the) paper would have to be correct. The grandparent of your post (which, I guess you missed) gives convincing arguments towards the contrary.

    • Re: (Score:2)

      by tloh ( 451585 )

      Kdawson, could you please try to have the first clue about something that you submit?

      Those are fighting words, mate! It almost sounds like you're gunning for a newly vacated position [slashdot.org]. In which case you probably should have worked up the courage to post as someone identifiable rather than AC.

    • Re:Here we go again (Score:4, Interesting)

      by Freddybear ( 1805256 ) on Saturday August 27, 2011 @12:52PM (#37228566)

      For more discussion of Kobakhidze's paper, and for criticism of the paper by Chaichian cited above, go here:
      http://motls.blogspot.com/2011/08/once-more-gravity-is-not-entropic-force.html [blogspot.com]

      Motl also responds directly to Verlinde here:
      http://motls.blogspot.com/2010/01/erik-verlinde-why-gravity-cant-be.html [blogspot.com]
      The discussion of a two-slit interference experiment in a gravitational field is clear enough that even I can almost understand it. ;)

    • This guy sounds pretty convinced and pretty much closes the chapter at the end of the blog entry http://motls.blogspot.com/2011/08/once-more-gravity-is-not-entropic-force.html [blogspot.com]

      • I admire the entropic gravity theory, from what little I can understand about it, though I am not sure I buy it.

        That said, I am not sure I buy Lubos Motl Pilsen's rebuttal, either. He makes two two points that seem weak to me.

        Instead of accepting the usual potential force as found by Newton, one must adopt an entropic force that depends on a temperature and an entropy. The temperature should be associated with the Unruh temperature which depends on the gravitational acceleration. This assumption is very pro

    • Re:Here we go again (Score:5, Informative)

      by bcrowell ( 177657 ) on Saturday August 27, 2011 @02:10PM (#37228922) Homepage

      Kdawson, could you please try to have the first clue about something that you submit?

      There's no reason to be so rude. In fact, I would consider the summary pretty accurate, although maybe not the title.

      This is a non-peer-reviewed article, fresh on the arXiv.

      Totally irrelevant. New research typically appears on arxiv first. That doesn't mean it's wrong.

      It's a followup to an earlier article which was widely criticized within the community as being full of holes, and the arguments in this article are very very weak.

      I'm not a specialist in this field (my specialty is experimental nuclear physics), but the impression I get as an outsider is that this is inaccurate. Actually many people in the field seem to find Kobakhidze's arguments very strong. I think the most fair summary would be that right now, the whole thing is controversial. Verlinde never claimed that he had a worked-out theory. It's always just been a rough heuristic. Even if it's right, it's wrong. What I mean by that is that it's at best a provisional picture (historically analogous to the Bohr atom) which needs to be reworked into a real theory (analogous to quantum mechanics). Just as there were no clear criteria for judging whether the Bohr model was a good idea or a dead end in 1915, there are no clear criteria for judging whether this idea is good or a dead end in 2011.

    • Re: (Score:3)

      by JamesP ( 688957 )

      From the bottom of my heart, a huge thank you

      This is the way science should go. Not "disproving theories" with barely acceptable arguments just because it's against the current theory.

      Oh, btw (not for you), Einstein's General Relativity is not a theory OF gravity, it's a theory of how things behave in a gravitational field, it doesn't matter if it's a field, particles, entropy or bunnies causing gravity.

    • I think gravity ISN'T entropic

      Could you elaborate on that? What are your reasons for thinking that? It seems to me that emergent gravity is an obvious conclusion from the holographic principle. I'm not a gravitational theorist and I don't claim to fully understand these things. But as far as I understand it, the holographic principle basically says that a really complicated theory with explicit gravity is exactly equivalent to a much simpler theory without explicit gravity. Given that, it seems obvious to conclude that the simpler

    • Re: (Score:2)

      by MrLint ( 519792 )

      Its just a theory. I advocate intelligent shoving ;)

    • Disclaimer: I am a gravitational theorist. I think gravity ISN'T entropic. However this paper is nowhere near sufficient to show that. I'd wait a LOT longer for the dust to settle on this one before making a strong statement one way or the other.

      You can determine that by reading it? I can't imagine what complexities are involved, but how long did you spend on the paper, and also are there gravitational, like... experimentalists? You know, guys who take these theories and do experiments?

  • Motl comments (Score:5, Informative)

    by Sara Chan ( 138144 ) on Saturday August 27, 2011 @12:43PM (#37228522)
    Lubo Motl [wikipedia.org] has some additional, supportive, thoughts on his blog:
    Once more: gravity is not an entropic force [blogspot.com]

  • It's great that something can be disproved in physics these days, it means that physics it's still alive as a science. I hope it's true.

  • Gravity again? (Score:5, Funny)

    by The Creator ( 4611 ) on Saturday August 27, 2011 @01:16PM (#37228666) Homepage Journal

    I thought that we decided to go with intelligent falling?

    • Of course. You know, information is neg-entropy. So if entropic gravity is disproved, then obviously information gravity is proved. Now information comes from intelligence, therefore we have intelligent gravity, i.e. intelligent falling.

    • This was funny. If I knew what a mod point was and had one, I would have used it here.
  • Considering the bunk and completely unproved concepts that physics is using currently ie. Dark Matter, Dark Energy, String Theory, Supersymmetry and the Higgs Boson. Even IF there is a Higgs particle, the Higgs does NOT explain gravity. Emergent Gravity is a VERY compelling concept. It could also explains Mass, Inertia AND the 2nd law of thermodynamics.
    Currently it is obvious that physics has been stuck in a rut for decades. The discovery of virtual particles has yet to be fully incorporated into other th

    • Considering the bunk and completely unproved concepts that physics is using currently ie. Dark Matter, Dark Energy, String Theory, Supersymmetry and the Higgs Boson.

      You are mixing together very different things here. For one, I don't think anyone is using string theory. And I bet you are not qualified to call even one of the concepts you mention "bunk".

      Even IF there is a Higgs particle, the Higgs does NOT explain gravity.

      As far as I know, nobody ever claimed it would.

      • And I bet you are not qualified to call even one of the concepts you mention "bunk".

        I don't need to be. It is widely know they all the concepts I mentioned are UNPROVEN THEORIES.

        • And I bet you are not qualified to call even one of the concepts you mention "bunk".

          I don't need to be. It is widely know they all the concepts I mentioned are UNPROVEN THEORIES.

          So you think that every unproven theory is bunk? In that case I want to inform you that I don't have a proof of the theory that your IQ is above 70. So I guess that theory, being unproven, is bunk, and therefore I'm safe in assuming that your IQ doesn't exceed 70.

          • So you think that every unproven theory is bunk? In that case I want to inform you that I don't have a proof of the theory that your IQ is above 70. So I guess that theory, being unproven, is bunk, and therefore I'm safe in assuming that your IQ doesn't exceed 70.

            I think it's obvious who the child is here.

    • Virtual Particles, Vacuum Energy and Gravity. http://en.wikipedia.org/wiki/Vacuum_energy [wikipedia.org] Quoted from the Wiki page:

      Vacuum energy is an underlying background energy that exists in space even when the space is devoid of matter (free space). The concept of vacuum energy has been deduced from the concept of virtual particles, which is itself derived from the energy-time uncertainty principle. The effects of vacuum energy can be experimentally observed in various phenomena such as spontaneous emission, the Casimir effect, the van der Waals bonds and the Lamb shift, and are thought to influence the behavior of the Universe on cosmological scales.

      The vacuum energy also has important consequences for physical cosmology. Special relativity predicts that energy is equivalent to mass, and therefore, if the vacuum energy is "really there", it should exert a gravitational force. Essentially, a non-zero vacuum energy is expected to contribute to the cosmological constant, which affects the expansion of the universe. In the special case of vacuum energy, general relativity stipulates that the gravitational field is proportional to -3p (where is the mass-energy density, and p is the pressure). Quantum theory of the vacuum further stipulates that the pressure of the zero-state vacuum energy is always negative and equal to . Thus, the total of -3p becomes -2: A negative value. This calculation implies a repulsive gravitational field, giving rise to expansion, if indeed the vacuum ground state has non-zero energy. However, the vacuum energy is mathematically infinite without renormalization, which is based on the assumption that we can only measure energy in a relative sense, which is not true if we can observe it indirectly via the cosmological constant.

    • Re: (Score:2)

      by rtb61 ( 674572 )

      Of course if you want to have real theoretical fun, consider a black hole (important in Entropic gravity theory) no longer as a collection of compressed molecules, but as an oversized atom, where gravity, compression and extreme energy levels has forced a fundamental change in the arrangement of the subatomic particles that make up a black hole. Similarly that neutron stars and pulsars are attempting to behave like a very large transitional state molecule.

      It is worthwhile to keep in mind that interaction

  • To be fair, the article only addresses one formulation of emergent gravity from a single hypothesis. To say the whole idea of emergent gravity is wrong is a little disingenuous. My pet theory (hey, a boy needs a hobby) is that gravity is emergent from a universe where the physics, the actual computation, has to be done to make anything happen. Apple falls to the ground? The universe has to perform the calculations to make it happen. If there's a processor limit then it would manifest as the speed of li

    • Re: (Score:1)

      by nu1x ( 992092 )

      Interesting.

      Thanks for the insight; I also found interesting the point that centrifugal force and inertia are so gravity-like. So my intuition would say that gravity is heavily dependent on motion, maybe not only of macro objects, but also of micro objects (particles and their interactions, which may be why bigger particle conglomerations are more gravitic).

      I am still working on this one tho, but I really think that gravity is motion (and by connection, time, which is the emergent property of motion) depend

  • At first pass I read the headline as "Emergency Gravity Disallowed".

    My thought was, "Wow, this Hurricane Irene hysteria has really gotten out of hand. People are even afraid the gravity's going to get knocked out."

  • -You're flying!

    -How?

    -Gentoo! [xkcd.com]

    # emerge antigravity

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