Column: Looking for New Forces

By Sean Carroll | November 4, 2011 1:00 pm

While my first column for Discover was on the multiverse, the second one is more down to Earth (as these things go): searching for new forces. Of course we are searching for new short-range forces at the Large Hadron Collider and in other particle-physics experiments, but here I’m talking about long-range “fifth forces.” While there are plausible motivations for searching for such forces, and the experimentalists have done an heroic job in constraining them, I argue that the most impressive thing is how we can say what forces are not out there — in particular, anything that would have any important effect on everyday life. There probably are more forces than we know about, but they’re only going to be of direct interest to physicists, I’m afraid. No tractor beams.

  • David Brown

    “There are probably more forces than we know about, but they’re only going to of direct interest to physicists …”
    “We see in galaxies phenomenological laws that are as robust as Kepler’s laws were, when they were recognized in the solar system, and which are universal. Does it make more sense to deduce that such regularities somehow resulted from a complicated and haphazard formation history of galaxies, or to accept that they are inevitable consequences of some appropriate underlying dynamics?” — Mordehai Milgrom, “DM or MD?”, p. 14 “MD or DM? Modified dynamics at low accelerations versus dark matter” by M. Milgrom, 2010, Proceedings of Science The MOND pages (McGaugh) Pavel Kroupa: Dark Matter, Cosmology and Progress
    I claim that the -1/2 in the standard form of Einstein’s field equations should be replaced by -1/2 + sqrt((60±10)/4) * 10^-5 but this is merely part of my theory. (See “Dark matter: why should Rañada and Milgrom win the Nobel prize” at nks forum applied nks.)
    Rañada-Milgrom Gravimeter Hypothesis: The Rañada-Milgrom effect is so large that it shall revolutionize the science of gravimetry, even for commercial devices.

  • Artume

    Actually, Tractor Beams are pretty possible. NASA has just awarded $100k worth of grant to investigate three different versions of tractor beams, two of which have already been done in laboratory setting.

  • Chris

    @1 David Brown
    You may want to see Sean’s feelings on MOND

  • Torbjorn Larsson, OM

    David Brown didn’t get the message.

    Just a few weeks after DM models are conclusively confirmed by remodeling the universe to ever better precision (Bolshoi simulation) and, most importantly, galaxies consistently for the first time (Eris simulation) and buried modified gravity forever …

    Been there, done that. Didn’t work, won’t work.

  • Tom

    @Torbjorn: Not a single serious observer believes “Bolshoi” and “Eris” have solved any of the true problems of galaxy formation. Btw how many times have these problems already been solved according to past press releases? Been there, seen that, too. Ah, ‘press release science’, always sounds impressive, ends up as being as secure a Nature paper can be… ask astronomers whay they think of the scientific value of it… But of course one extreme should never be swapped for another, and the “Ranada gravimeter theory” is not going to convince anyone apart from humorists and/or perhaps, Ranada-David Brown himself 😀

  • goldy

    @Artume: In case anyone is looking, here is the NASA press release:
    Of course, they do it using the disappointing four known forces. What a letdown :-)

  • David Brown

    @6 Chris: I think that Sean is correct in suggesting that TeVeS is wrong. My guess is that TeVeS is completely wrong.
    Professor Antonio Fernandez-Rañada in his Jan. 2005 paper entitled “The Pioneer anomaly as acceleration of the clocks” says that the frequency of photons increases uniformly and adiabatically because of the expansion of the universe and his phenomenological theory; whereas, I say that the frequency of the photons increases uniformly and adiabatically either because of my physical interpretation of modified M-theory with Wolfram’s automaton or because of my physical interpretation of Seiberg-Witten M-theory with neutralino physics. “The Pioneer anomaly as acceleration of the clocks”
    By assuming that Fernandez-Rañada’s basic idea and Milgrom’s non-relativistic MOND are correct, I arrive at the Rañada-Milgrom effect. I also guess the following:
    Milgrom Denial Hypothesis: The main problem with string theory is that string theorists fail to realize that Milgrom is the Kepler of modern cosmology.
    Is Milgrom the Kepler of modern cosmology? If he is not, then all my ideas are wrong. However, I predict that there is a 99% probability that Milgrom will win the Nobel prize within 5 years.

  • Valdis Kletnieks

    Of course, currently the leading theory for the Pioneer “anomaly” is the failure to properly account for infrared radation from the power sources hitting the big dish antenna that’s pointing towards earth. Once you actually account for that radiation pressure, there’s no “anomaly” left…

  • David Brown

    @8Valdis: If the Pioneer anomaly (consistent for 2 different spacecraft) is merely a failure of properly modeling the thermal recoil forces, then why should the Pioneer anomaly be approximately in the acceleration range of non-relativistic MOND? Why are the flyby anomalies roughly in the range of the Pioneer/MOND acceleration? If you believe the Gravity Probe B (GP-B) science team’s theory of malfunctioning gyroscopes, then the Rañada-Milgrom effect is disconfirmed. However, if the GP-B gyroscopes functioned within design specifications, then the GP-B results qualitatively match what the Rañada-Milgrom effect predicts.

  • Phil

    @ David Brown, #9. “…then why should the Pioneer anomaly be approximately in the acceleration range of non-relativistic MOND?”

    Coincidence. Got a problem with that?

  • David Brown

    @10 Phil: There is no doubt that coincidence can create false confidence in a hopeful theorist. However, I claim that the empirical evidence for MOND (as opposed the standard model of cosmology) looks very good. Is non-relativistic MOND empirically invalid? Is Einstein’s general relativity theory 100% correct? Is the Lambda CDM model (LCDM) 100% correct?
    I quote Prof. Dr. Pavel Kroupa from a recent e-mail,
    “My criticism is not based on me not liking dark matter, but is a result of rigorous hypothesis testing such that, from a strictly logical and scientific point of view, LCDM is definitely not a viable model of cosmological reality. I do not write such statements because I do not like LCDM and its ingredients, but because every test I have been involved with falsifies LCDM. At the same time, the tests of MOND we performed were done on the same footing as the LCDM tests. The MOND tests yield consistency so far. I am not more “fond” of MOND or any other alternative, but the scientific evidence and the logical conclusions cannot be avoided. And it is true, I must concede, that MOND has an inherent beauty which must be pointing at a deeper description of space time and possibly associated quantum mechanical effects which we do not yet understand (compare with Kepler laws and the later Newtonian dynamics).”

  • Phil


    Is the universe relativistic? Yes, every experiment shows this. Is MOND relativistic? No. Therefore, MOND disagrees with experiment.

  • David Brown

    @12 Phil: “Is the universe relativistic?” The answer to this question might be “yes” — unless spacetime breaks down. Spacetime might have 2 possible failures: the Seiberg-Witten doom or the Fredkin-Wolfram build-up from Wolfram’s hypothetical automaton underlying quantum theory. I claim that non-relativistic MOND is an approximation to general relativity theory with the Rañada-Milgrom effect by means of an easy scaling argument. I conjecture that the Rañada-Milgrom effect means that dark matter is D-brane reinforcement of the Einsteinian gravitational signal.
    In the book “The Meaning of Relativity” (5th edition, Princeton U. Press, 1956), on pages 83-84, Einstein discusses the problem of finding a differential tensor completely determined by three conditions. At the top of page 84, we find
    (3) Its divergence must vanish identically.
    Einstein writes that the “first two of these conditions are naturally taken from Poisson’s equation. Since it may be proved mathematically that all such differential tensors can be formed algebraically (i.e. without differentiation) from Riemann’s tensor, our tensor must be of the form”
    F(a), where F is some function and a is some constant.
    Einstein writes, “Further it may be proved that the third condition requires a to have the value -1/2.”
    In Einstein’s field equations, only the constant a and the cosmological constant give a simple form of wiggle room. If a is not equal to -1/2, then we get an insane violation of Einstein’s equivalence principle. The big question is: Is this insanity really occurring in nature, and, if so, what explains it?

  • Phil

    David Brown,

    Your very use of the word “spacetime” implies special relativity, i.e. relativistic physics.

    Does MOND explain the bullet cluster observations? Does MOND explain why decaying particles take longer to decay when they are moving at close to the speed of light than when they are at rest?

  • David Brown

    @14 Phil: “Does MOND explain the bullet cluster observations?” If non-relativistic MOND is valid and M-theory in some form is also valid, then my guess is that the only hope is to replace the -1/2 in the standard form of the field equations by -1/2 + dark-matter-compensation-constant.
    “There is a tremendous amount of evidence for dark matter. Yet all this evidence is based on the assumption that Newton’s theory can be safely applied to the scales of galaxies.” — Stacy McGaugh “Mond over matter”, 2002
    “By using both wide-field ground-based images and HST/ACS images of the cluster cores, we create gravitational lensing maps showing that the gravitational potential does not trace the plasma distribution, the dominant baryonic mass component, but rather approximately traces the distribution of galaxies. … In the absence of dark matter, the gravitational potential will trace the dominant visible matter component, which is the X-ray plasma. If, on the other hand, the mass is indeed dominated by collisionless dark matter, the potential will trace the distribution of that component, which is expected to be spatially coincident with the collisionless galaxies. Thus, by deriving a map of the gravitational potential, one can discriminate between theses possibilities.” — Clowe, Bradač, Gonzalez, Markevitch, Randall, Jones, & Zaritsky “A Direct Empirical Proof of the Existence of Dark Matter”, 2006
    Have critics of Milgrom’s MOND made an epistemological error in assuming that gravitational lensing maps based upon Newtonian gravitational theory are empirically valid? MOND challenges Newtonian gravitational theory; therefore, refuting MOND might require extreme care in terms of considerations of gravitational theory. MOND
    Consider the Rañada-Milgrom apparent-or-real effect, which is that the -1/2 in the standard form of Einstein’s field equations should be replaced by -1/2 + dark-matter-compensation-constant, where this constant is approximately sqrt((60±10)/4) * 10^-5 . (If virtual mass-energy obeys the equivalence principle, then the effect is apparent and not real; in this context the word “apparent” means that the dark matter appears to empirically satisfy the modified field equations.)
    CLAIM 1: At low gravitational accelerations, empirical evidence confirms MOND and, by the introduction of a scaling factor, the Rañada-Milgrom effect.
    CLAIM 2: At high gravitational accelerations, empirical evidence for gravitational lensing confirms that the Rañada-Milgrom effect is approximately correct.
    CLAIM 3: If new physics is the explanation for the OPERA neutrino anomaly, then, as suggested by Fernandez-Rañada, anomalous gravitational acceleration of clocks is the reason that neutrinos might seem to be traveling faster than the speed of light in a vacuum. Thus the OPERA experiment might confirm the Rañada-Milgrom effect. If new physics is not the explanation for the OPERA neutrino anomaly, then the Rañada-Milgrom effect is disconfirmed. “Scientists Question Faster-Than-Light-Neutrinos” | Wired Science, Sept. 23, 2011

  • David Crawford

    May I contribute two points. The first is to remove one force, namely gravity.
    I and many others have argued that gravity both Newtonian ans Einstein
    is an acceleration and not a force. The second point is that my theory of
    “Curvature Cosmology” agrees with observations much better than the
    standard Big Bang model with its many ad hoc extensions. Both points are
    expounded in the paper “Observational evidence favors a static universe.”
    A major aim of the paper is to show that the evidence in favour
    of an expanding universe is not as strong as most would believe.
    A second aim is to provide a complete exposition of my alternative
    theory “Curvature Cosmology” (CC) and to show its excellent agreement with
    nearly all cosmological observations. It is a tired light cosmology
    where the redshift arises from an interaction of photons with
    curved space-time (curvature redshift). The other major hypothesis
    is Curvature Pressure which stabilises the static universe. I believe
    that the model is in complete agreement with general relativity
    and quantum physics. Except for the modelling of different
    cosmological objects The theory only has one free parameter-
    the average density.

    A major difference between cosmologies in an expanding universe
    and that in a static universe is time dilation. Whereas a tired
    light process could explain the energy loss of photons it cannot
    produce the effect of time dilation on the rate of arrival of photons.
    In an expanding universe cosmology the equations for the distance
    modulus and for the angular size include a term, (1+z), to allow for
    time dilation. Since the similar equations for a static-universe
    cosmology do include this term its presence (or absence) makes
    a suitable test for determining whether the universe is expanding.

    Recently I have published three papers in the Journal of Cosmology
    that investigates this proposal. The editor required that I split the
    original paper into three parts and the references are: : 2022, JCos, 13, 3875-3946 : 2022, JCos, 13, 3947-3999 : 2022, JCos, 13, 4000-4057

    A single file version that is essentially identical to the three papers
    is available at arXiv 1009.0953:
    It includes a table of contents, hyperlinks and several minor corrections.
    Be warned it has 96 pages and is about 1MB in length.
    It is also available on my website:

  • Lord

    It is not whether any of these have any important effect on everyday life, but whether they could have any important effect that is important. It is not life as it is that is important, but life as it could be.

  • James Gallagher

    “How can we be so sure there aren’t other forces that we just haven’t yet been clever enough to find?

    The answer is, we can look for them. We know where to look, and indeed we have looked. Other forces are not out there, at least not to any significant extent. Any new force we might someday discover must be so impotent over everyday distances that there’s no way it can affect the macroscopic world. If it could, we would already have found it.”

    Or even more convincingly, evolution has looked for them! If any other useful forces existed on everyday scales/energies evolution would surely have utilised them. This is also a simple way of debunking parascience and other nonsense – we don’t have telepathic cats and levitating birds because such things are not possible in nature at everyday Earth conditions – ie Evolution has probed nature exhaustively at this scale.

  • S

    Evolution has only probed the low-energy EM part of the parameter space, and even then, you can’t rule out telepathic cats without experiments. Seriously. Although cats right now aren’t telepathic, there is no physical reason or law (unlikely as that may be) that sometime in the future cats, wombats or even plants won’t develop biological radio transmitters via some random mutation that is beneficial for natural selection.

    Granted, it’s far more likely that the time required for such a biological telepathic mutation to develop is far longer than the survival time of a species. Unless that is… the cats become smart enough to cheat like we humans do, with technology.

  • Penelope

    “An heroic” is just plain bad english. Do you say “An house”? The rule is to use “an” in front of words with a soft h, and “a” in front of words with a hard h. “Heroic” has a hard h.

    This rule would eliminate the current craze of “an historic”, found everywhere, unfortunately.

    Of course, by the rule that good english is defined by usage, “an historic” might squeak by because of its increasing occurrence on mainstream programs like NPR’s “All Things Considered”.

    However, “an heroic” certainly stretches the usage rule to new bounds.

  • Charles Z

    Huh? No fifth force? What about the force that is pushing the galaxies apart and also speeding up? I have seen this force described as a sort of variant of gravity, but it seems more like gravity’s opposite. What about it?

  • ohwilleke

    Honestly, the prospects for a force that works at long ranges but is not discernable at short ranges, in the nature of some component of dark energy, dark matter, dark flow, or what have you have a lot more theoretical wiggle room than short range forces, because the experimental constraints are nearly so great.

    In a nutshell, until we have a more definitive dark matter model and an identified dark matter particle, we have lots of wiggle room in the experimental constraints, since experiment and GR as best calculated to date without dark matter do not coincide, since CDM models make contrafactual predictions that WDM (warm dark matter) theorists have identified, and since there is no plausible dark matter candidate supported by any experimental evidence and the direct detection experiments mutually contradict each other. Also, a lot of dark matter cosmology is being done without updating their calculations to reflect the elipitcal galaxy baryonic matter surveys done in the last couple of years showing that the amount of baryonic matter in the universe relative to ordinary matter is closer to 1:1 than 3:1 because the amount of baryonic matter in eliptical galaxies from low brightness objects was drastically undercounted.

    Further, the quality of our GR predictions that we match against experiment in complex multibody systems are simply not very rigorous. There are disagreements on the order of 50% over what the GR contributions relative to Newtonian gravity are in the context of systems as familiar as the Milky Way. There are non-cranky PhD physicists saying the GR contribution is negligable and others saying that it is large for the same system. GR in complex multibody situations is in much the same situation as QCD is in quantum physics; we have a very good set of equations that are hard to calculate with outside highly stylized situations.

    MOND and TeVeS by the way aren’t the only games in town. Moffat, in particular, has been plugging away with less publicity, but arguably better results, for a long time in some of the domains where MOND/TeVeS have had trouble.

    Dark energy also makes at least as much sense as part of the GR equation via a cosmological constant, which is a force explanation, as it does as a substance. There is certainly no experimental way to distinguish the two at this point.

    There are lots of proposals for short range forces in the theoretical literature, but nada in the experimental work, which doesn’t have huge discrepencies between theory and experiment. As weak as the evidence of SUSY particles may be, evidence for SUSY forcesat work is even weaker. You could call the Higgs field a force, and we do have evidence to support it (although not the boson it implies). There are proposals force technicolor forces and some sort of right handed neutrino force, but again, absolutely nothing empirical to indicate that we’ve ever seen a wiff of either of them.

  • Md Santo

    Substituting Tractor Beam with Human System Biology-based Knowledge Management (HSBKM) model framework to search the 5th Fundamental Force

    Instead of using tractor beam, a device with the ability to attract one object to another from a distance, we use our own Human System Biology-based Knowledge Management (HSBKMtm) model framework to prove the existence of Knowon, proposed as the 5th Fundamental Force representing Knowledge as the third fabric of Universe beside Matter and Energy. We coined a term of the method we used as “Inverted Paradigm” phenomenon by treating Applied Science (Knowledge Management) as “Knowledgeable Science” for the sake of the development of Basic Science (Theoretical Physics).

    The “Duo entity Graviton – Knowon” as Universe DNA across the Universe making Nature’s Laws may vary across the Universe and finely-tuned for the existence of life . To read more, goto URL

  • Arnold Lasky

    Hey folks, sorry to come so late to the party, but I would like to say that I believe Sean and Charles Z are BOTH right, in that the acceleration of the universe (and many other outstanding cosmological questions of the day) can best be addressed by proposing that dark energy/matter is mass equivalent “stuff”, which affects the force of gravity, but is also affected by a new repellent force of nature that induces, and is induced by, the attractive gravitational force, in a manner that is analogous to electromagnetism. I call this GRAVITODISPLACEMENT INDUCTION, and the new force, the DISPLACEMENT FORCE. Let us divide this proposal into its two distinct, but interelated, parts, and start with mass equivalent dark matter/energy- i.e., the stuff.
    When Fritz Zwicky described the galactic rotational anomaly, the first candidate for his “missing mass” was vacuum energy, which I would like to combine, with its equivalent virtual particles, into what I call STRINGICLES. This candidate was eventually discarded when laboratory tests of the Casimir effect indicated that vacuum energy fell orders of magnitude short of the required mass equivalence to account for such anomaly. I propose that the test result was skewed because the displacement force is strongest at the surface of any massive body, say, the earth or a galaxy, and that if this test were conducted within a galactic halo, the results would show that mass equivalent vacuum energy, as acted upon by the displacement force, possesses the required heft.
    This brings us to an explanation of the displacement force, in accordance with Sean’s three specifications: “which particles feel the force, how strong it is, and the range over which it interacts”, and let us assume: that the geometry of the universe is flat, but can vary in density, within different regions and different times, provided that all such variabilities sum to zero; that at the largest scales of time/distance, the value of omega is one; and that the expansion of the universe, and the repulsive effect, among others, can all be explained, solely as a consequence of the following corrective factor- i.e., that a quantitative equilibrium exists beween the electromagnetic energy equivalence of actual mass and the vacuum energy equivalence of virtual mass.
    Sean, I am about to publish a book, which explains the galactic rotational problem, the Pioneer anomaly, the Bullet Cluster dichotomy, and the accelerating expansion of the universe, among other things. The Nobel beckons, and if you are still interested in a mathematical collaboration in this area, please contact me at


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About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] .


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