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An Experiment Could Determine Whether Gravity Is Quantized ( 134

TheAlexKnapp writes: Physicist Brian Koberlein explains an experimental proposal by Großardt et al, which would attempt to determine whether gravity is quantized. "Their idea," explains Koberlein, "is to take a charged disk of osmium with a mass of about a billionth of a gram and suspend it an electric field. This is small enough that its energy levels in the electric field would take on quantum behavior when cooled to temperatures a fraction of a Kelvin above absolute zero, but its also massive enough that its gravitational pull would affect the quantum behavior."

The two primary approaches to a quantum gravity, the "perturbative approach" and "the semi-classical method," predict different results from this type of interaction. So the results of the experiment, could, in principle, elucidate the right approach for developing future theories of quantum gravity.

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An Experiment Could Determine Whether Gravity Is Quantized

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  • arXiv links (Score:5, Informative)

    by Anonymous Coward on Saturday October 17, 2015 @10:44AM (#50749439)
    Proposed experiment: arXiv:1510.01696 [].
    More detailed theory: arXiv:1510.01262 [].
    See also blog post [].
    • I'm curious about the choice to use osmium. Sure, it is the densest element, but iridium is almost the same density and osmium easily forms toxic compounds while iridium doesn't (easily, I mean).
      • by HiThere ( 15173 )

        While there may be problems with fabrication, I don't think toxic compounds are going to be a problem. They want it to be small enough that they're going to need to shield it from atmospheric contact anyway. No dust, no water condensing, no chemical reactions. They need to avoid all of those in an experiment this sensitive.

        I might wonder about the choice of osmium, though, as it *IS* difficult to work, and the techniques for working indium are far more developed (due to it's use in LEDs).

        Still, even if i

        • by Mr.CRC ( 2330444 )

          He said iridium, not indium! Geez, I hope you aren't a pharmacist!

          Besides, indium as used in LEDs isn't fabricated into anything as metallic, elemental indium, but rather as part of compounds with other elements, aka, InGaN, InGaAs, etc.

          • by HiThere ( 15173 )

            Sorry, i did misread. And it didn't matter to the major point. The thing is not going to be exposed where it would have any chance of having chemical reactions.

      • by myowntrueself ( 607117 ) on Saturday October 17, 2015 @03:39PM (#50750557)

        I'm curious about the choice to use osmium. Sure, it is the densest element, but iridium is almost the same density and osmium easily forms toxic compounds while iridium doesn't (easily, I mean).

        Its very small and no one is going to eat it.

      • osmium goes superconducting at 0.66 K, while indium 0.11 K

        That's much harder to achieve

    • So we'll finally get a transformative hermeneutics of quantum gravity?
  • Not much gravity ... or anything else on Forbes

    • Why don't editors catch such shenanigans?
    • by Bengie ( 1121981 )
      Same thing with all of my computers and browsers. Ohh wait... I just went to their home page,, then clicked on the link in /. and it suddenly worked. Probably a broken cookie or something.
      • Forbes and LA Times are 2 sites I never visit as their pages don't render for me. There are also a few other newspaper sites that don't work, I suspect they're all owned by the same billionare.

        For the newspapers, by not work I mean I get a blank page for a couple seconds, then a normal page for about 1/10 of a second, blank page for a couple seconds, repeat forever.
  • by Manywele ( 679470 ) on Saturday October 17, 2015 @10:49AM (#50749463)
    There's a good explanation by a physicist who thinks about experimental validation of quantum gravity here [].
    • by H3lldr0p ( 40304 )

      THANK YOU! That actually makes sense instead of the gibberish installed as the "article" above.

      • by KGIII ( 973947 )

        You've been here longer than I. However, in this case, I was actually thinking that this was, oddly, one of the summaries that made sense to me. Maybe I've just acclimated to the lack of proper editing?

    • by Anonymous Coward

      Sabine Hossenfelder said...

      You're more than welcome trying to construct a consistent theory of semi-classical gravity. I am sure you'll be the one to succeed where 80 years of work by the brightest minds on the planet have failed. Good luck!

      The tone of this comment leads me to think that social considerations, including the assumption that nature has to be consistent, are more important here than any real search for truth.

      • by Megol ( 3135005 )

        I don't understand - are you complaining that she points out the truth?

        • "You seriously think you're smarter than us, you uppity little shit? Fuck you, eat my snark. SNARK SNARK SNARK"

          Yeah, he's complaining that she's pointing out the truth.
  • It's not about gravity, it's investment advice. Long osmium?

  • shut up and do the experiment already!

  • by mark_reh ( 2015546 ) on Saturday October 17, 2015 @11:04AM (#50749519) Journal

    Physicists are quantized, so they want everything else to be quantized.

  • Just google it.
  • Mass is quantized, therefore gravity has to be as well.

    • by cnettel ( 836611 )
      Even if mass would be quantized, the Newtonian equation is m1m2/r^2. Even with discrete mass quanta (which is also false, see other replies), you would get a continuous spectrum of resulting forces. Inserting relativity here changes the expressions, but it would really just muddle things. So, no, there is no specific reason to believe gravity to be quantized - outside of an actual theory of quantum gravity.
      • by Bengie ( 1121981 )
        Kind of an interesting discussion. One of the interesting things that have come out of the whole blackhole information paradox is that tossing an elementary particle into a blackhole increases its spherical surface area by exactly one square planck. They said if you run that backwards, it means you can store at most 1 bit(explicitly state binary bit of "data") of information in a cubic planck. That is the density of a blackhole.

        It seems that the current set of elementary particles are the highest density
  • Not trying to poop on it, far from it. But could someone explain just what this should prove or show? What insights will this give us?

    • by cnettel ( 836611 ) on Saturday October 17, 2015 @12:02PM (#50749745)
      Well, electron states being quantized has helped us to (truly) understand chemistry and create transistors as well as LEDs. By realizing that things are only allowed to make certain transitions under certain conditions, you can "cheat" and build up high-energy states that are far more stable than they really should be. I am not saying we would get macroscopic anti-gravity or a "Faraday cage for gravity", but this is kind of the space where we would get more specific explanations for how you might be able to accompish those things in theory. For very delicate experiments (similar to the one described!) and possibly sub-nanoscale manufacturing procedures, an understanding of a quantized nature of gravity influences might be useful, if only for better understanding the noise in measurements and tolerances.
      • We'll understand why and how molecules form and why they do it in the way they do? Did I get that right? That's awesome!

      • I really like this explanation, as a general motivation for about learning about constraints. I think it can be applied to all of technology -- e.g. 'by realizing things are only allowed to make certain transitions under certain conditions, you can "cheat" and build up high-energy states that are far more stable than they really should be' might well be said for GMO, for example.

    • by ganv ( 881057 ) on Saturday October 17, 2015 @12:14PM (#50749801)

      It would open up the possibility of observing the effects of quantization of gravitational interaction in the low field limit. Up to now, no one has observed any quantization of gravity. This is a really tiny effect, so you might argue that you don't care, but it would be a small clue in the big mystery of how to reconcile quantum mechanics and general relativity. In the history of physics, this has happened before. We had quantum mechanics in the 1920s through 1940s, but we didn't know how to quantize the electromagnetic field. We simply used classical interactions between charged particles and quantized their motion since we didn't know how to quantize the electromagnetic fields themselves. Then in the late 1940s and early 1950s, Schwinger, Feynman, and Tomonaga figured out how to quantize the electric and magnetic fields. It made only tiny changes in the predictions of quantum mechanics for atoms, but it has turned out to be critical to modern precision measurement and definition of the units we use. Their Quantum Electrodynamics has proved to be one of the great triumphs of theoretical physics.

      Now quantization of gravity is a much much smaller effect in conditions that we can study on earth. This proposes that we might be able to observe some effects. Unfortunately, in this low field limit, I think most physicists expect that perturbative methods will give the right answer. In this case, the experiments will not be much help in building a self-consistent quantum gravity theory because perturbative methods are known to fail in the high field regime where the inconsistency between quantum mechanics and general relativity becomes important. But we definitely should make these measurements to see if the effects can be observed. Precision measurements often yield new insights, often unexpected ones.

      • I doubt that we will see any effects that are noteworthy because of our frame of reference. We are in the frame of reference of the planet Earth, which is in the frame of reference of the star Sol, which is in the frame of reference of the black hole Sagittarius A*.

        Due to galactic rotation curves not being understood (Dark matter? Matter that does not interact with anything but gravity? It is to laugh.)

        I do hope that this experiment does shed more light on what we call gravity.

    • by Anonymous Coward

      Deeper understandings of physics usually have unforeseen applications. For example, if we didn't understand quantum mechanics we wouldn't have much by way of semiconductors (cat's whisker diodes and oxide plate regulators are about all we could manage pre QM). And without GR we could kiss GPS goodbye (to get sufficiently accurate timekeeping you need to understand time dilation effects due to spacial curvature). And EM... obscure theory when Maxwell and Faraday wrote the book, indespensible now. And so

  • How the charge of a single electron was measured back in the early 1900's - good luck to these scientists.
    • by twosat ( 1414337 )

      Paraphrasing part of []

      Millikan's experiment as an example of psychological effects in scientific methodology

      In a commencement address given at the California Institute of Technology (Caltech) in 1974 (and reprinted in Surely You're Joking, Mr. Feynman! in 1985 as well as in The Pleasure of Finding Things Out in 1999), physicist Richard Feynman noted:

      We have learned a lot from experience about how to handle some of the ways we fool ourselves. One e

  • It would seem that gravity would be quantized at the level of the smallest particle having mass. Any bulk mass is ultimately made up of these smallest particles and the expression of the gravity of the bulk mass would be the sum of that of all the smallest particles making up that mass. One problem with gravity for the smallest particles is distinguishing it from the much larger kinds of interactions such as electric charge, etc.
    • That is not what's meant by gravity being quantized. Quantum gravity would mean the gravitation interaction between particles is quantized: i.e. if particle A pulls on particle B (and vice-versa), the energy exchange between them occurs in discrete packets. The alternative would be that the gravitational forces between them are a continuous interaction, so that A pulls on B to change the energy state of both constantly. To use an analogy: the former is like an object rolling down a staircase, where the obje

      • Or, to put it another way, and probably horribly inaccurately to boot, 'quantized' gravity is like constantly throwing a ball at something, only when that ball hits the object, it casues the object to move towards, instead of away from, the direction of impact.

        Non-quantized gravity is like everything being attached to everything with ropes, constantly pulling on everything.

    • by HiThere ( 15173 )

      Were that to be the case, you'd need to worry about the gravity of neutrinos, as they are currently the least massive particle known. But good luck trying to measure the mass accurately, or trying to get one to change it's speed, or even bend its path.

  • gravitons exist? (I remember reading the problem with gravitons is that they were basically impossible to detect because their interactions were so weak.)
  • Why is the site covered in cheap clickbait and list articles? Are they that desperate for clicks that they'd list "Grid Girls, Pit Girls photo collection" and "Fame Was The Worst Things That Happened To These 10 Former Child Stars" on the page?

    I think those are just advertisments that are deceptively made to look like part of the host site, which is almost worse., you're going on my blocked DNS lookups list.

  • by dfn5 ( 524972 ) on Saturday October 17, 2015 @12:33PM (#50749881) Journal
    So... a fraction of a Kelvin then.
  • "Oh dear, Watson, I just fell up!"

  • If Gravity is nothing more than a curvature of spacetime and objects moving through it fowls "straight" lines, then why do people still also say that gravity is a force? Or try to unify it with the other forces? Or tat it can be quantized?
    • Consider that this might say more about what we know about the nature of other forces...
    • All forces curve 'space-time'.

      • Go ooooon...?

      • by Anonymous Coward

        No, only momentum, pressure, and energy density in the stress-energy tensor, not forces. Forces are associated with a gradient in potential energy and fields, and those have effects on spacetime curvature (except gravitational potential energy which is excluded from the Einstein stress-energy tensor). But having a force at any given point doesn't mean spacetime there is curved, as that depends on the global structure of energy and it is possible to have a force still at a point with zero curvature.

    • I can't answer your question directly, but I can quote from my handy textbook on General Relativity which admittedly is 30 years old now ('General Relativity', Robert M. Wald, 1984). From Chapter 14, 'Quantum Effects in Strong Gravitational Fields', "As discussed in chapter 9, spacetime singularities occur in the solutions of classical general relativity relevant to gravitational collapse and cosmology. Thus, in these situations, the classical description of spacetime structure must break down. In particu

  • Like, monitor a speck of dust near a mountain. I'm convinced we don't have "gravity" here, it's just "density". But then I'm also convinced the world is flat.

    Read "Zetetic Astronomy" for convincing arguments, experiments, and proof: []