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Newton's Second Law, Revisited 171

Posted by Zonk
from the my-favorite-law dept.
eldavojohn writes "Dust off your fundamental physics books, an aspiring astrophysicist by the name of Alex Ignatiev has published a paper that proposes testing special cases of Newton's Second Law on earth's surface. His goal is sort of ambitious. The time he has to test his theory is only 1/1000th of a second, twice each year, in either Greenland or Antarctica. What would he look for? Spontaneous motion. From his interview with PhysOrg: 'If these experiments were to take place, Ignatiev says that scientists would look for what he calls the SHLEM effect. This acronym stands for static high latitude equinox modified inertia and would be noticed in a condition where the forces of the earth's rotation on its axis, and of the orbital force of the earth as it moves around the sun, would be canceled out ... In the end, if Newton's Second Law could be violated, he would be forcing physicists to reevaluate much of what we understand derived from that law — which is quite a bit.'"
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Newton's Second Law, Revisited

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  • by lecithin (745575) on Friday March 30, 2007 @11:25PM (#18552999)
    Or is it?

    Reminds me of what Patrick Moore did:

    Stolen from

    http://en.wikipedia.org/wiki/Patrick_Moore [wikipedia.org]

    Eccentric personality

    Due to his long-running television and xylophone playing career, eccentric manner, distinctively rapid speech delivery and in later years his ever-present monocle, Moore is widely-recognised and well-respected in the United Kingdom, even by those with no interest in astronomy. This was used to great advantage for a 1976 April Fool's joke on BBC Radio 2, when Moore announced that at 9.47 am a once-in-a-lifetime astronomical event was going to occur: Pluto would pass behind Jupiter, temporarily causing a gravitational alignment that would reduce the Earth's own gravity. Moore informed listeners that if they could jump at the exact moment that this event occurred, they would experience a temporary floating sensation. The BBC later received hundreds of phone calls from listeners claiming to have felt the sensation.

    Moore joined the Flat Earth Society as an ironic joke though many have taken this seriously.
  • by edwardpickman (965122) on Friday March 30, 2007 @11:26PM (#18553005)
    Law breakers should be punished to the fullest extent of the physical law.
    • by orkysoft (93727)
      It doesn't look like they're going to settle...
    • by Anonymous Coward on Friday March 30, 2007 @11:50PM (#18553139)
      "Fall heavy towards the moon, and the moon falls also towards you." -- Nietzsche

      Hammer and feather are dropped simultaneously from equal heights (as measured by distance from the center of the moon), separated laterally by a distance substantially less than the moon's diameter. Both hammer and feather experience force from the moon's gravity proportional to their mass, and hence both accelerate at the same rate. Meanwhile, the moon is also accelerating towards the other two objects, but unevenly so: the hammer exerts a greater gravitational pull due to its greater mass. The moon is therefore subject to a torque, causing it to accelerate more rapidly towards the hammer.

      The hammer is first to hit the ground.

      Anyone who denies this truth is a spatially absolutist lunocentric whose refusal to recognize the validity of hammer/feather mechanics places him wholly beyond the help of Galilean metaphysics. Such hammer/feather rejectionists ought to be banished from planetary space, for their own good and for the good of not only hammers and feathers but all subjugated smaller objects, everywhere, who find themselves victims of this scientifically perpetrated emassculation.

      --
      a756f345ec354225c08ff1a10a43162a
  • So, what law is this person using to calculate the cancellation of the forces?
    • Re:violate what law? (Score:5, Informative)

      by demeteloaf (865003) on Friday March 30, 2007 @11:55PM (#18553161)

      Currently, there is a discrepancy between the rotations of galaxies, and what newtons law says should happen. If you look at large galaxies, at a bunch of different radii, all the stars orbits are at about a constant orbital velocity, which since there is less force acting on them from gravity, shouldn't happen.

      The most common physical explanation of why this happens is that there is a ring of dark matter around the galaxies that is also producing a gravitational force, and that when you add in the force from the dark matter, the equations work out, and you calculate that the orbital velocities should be constant.

      However, there are some physicists who don't like the idea of dark matter, and in order to explain how galaxies orbit, introduced a new version of newton's second law. F = m * f(a/a0)*a, where a0 is a new fundamental constant describing a small acceleration level where these new Newtonian dynamics hold. and f(x) is a function that equals x when x > 1. This theory describes the constant angular orbit speed of galaxies without the need for the existence of dark matter, however, the theory has problems when applied to relativistic systems.

      What it looks like this new paper proposes to do is find a place on earth where the acceleration from the coriolis effect, the centripital acceleration and the acceleration from the sun will all cancel out, and then create a really small force and see if the modified second law works for a very small absolute acceleration.

      • by GryMor (88799)
        Uhmm... what acceleration from the sun? Or does this hypothosis thats attacking Newton forget that Newton allready fell to GR? How would this not be dominated by the 1g acceleration of the ground pushing up on you?
        • by mstahl (701501)

          Newton's second law of motion, not Newton's law of gravitation. General relativity won out against Newton, yes, but nobody's yet disproven that F=ma./P.

          • by jZnat (793348) *
            You mean F = dp/dt. Just imagine how hard it would be to calculate the acceleration of an object whose mass is changing (e.g. anything that burns fuel to provide energy).
      • by loganrapp (975327)
        What it looks like this new paper proposes to do is find a place on earth where the acceleration from the coriolis effect


        Everyone knows it's the cornwallis [youtube.com] effect. Pfft.

      • by Plutonite (999141)
        an interesting question to ask would be: even if the said forces "cancel out" in a particular coordinate plane somewhere on earth, forces acting in directions other than those considered(e.g gravitational curvature) would interfere with his oh-so-delicate measurements, no? Indeed, it would seem a NASA investigation during a space-mission would be even better, but I think it would be hard to convince NASA to get it's astronauts to do a 10-min off-course acceleration with a shuttle in some pointless direction
        • "forces acting in directions other than those considered(e.g gravitational curvature) would interfere with his oh-so-delicate measurements, no?"

          Well, yeah, but as I understand it their order of magnitude would be such that measurements would remain meaningful, which is not the case when the major nearby forces are acting on the system.
      • However, there are some physicists who don't like the idea of dark matter, and in order to explain how galaxies orbit, introduced a new version of newton's second law. F = m * f(a/a0)*a, where a0 is a new fundamental constant describing a small acceleration level where these new Newtonian dynamics hold.

        You're describing Modified Newtonian Dynamics (MOND), which can equally (and more justifiably) be interpreted as a new version of Newton's law of gravity (see here [umd.edu]). In particular, relativistic versions of MOND are interpretable as modified gravity and not as modified inertia.

  • by RyanFenton (230700) on Friday March 30, 2007 @11:41PM (#18553081)
    Yes, it only takes one demonstration to a render invalid a scientific theory. But that does not validate any other theories by doing so, unless they can accurately carry the same predictive weight as the previous theory, plus comply with the improved observations.

    A hole in Newtons second theory in any case doesn't mean scientists throw out their physics books, it generally means they add and exception to the theory and work on finding a more unified algorithm to describe the newly revised observations. Here's hoping this somewhat exotic set of observations leads eventually to a stronger set of theories, rather than just more false controversy about 'mavericks' and 'closed minded skeptics' - everyone's a skeptic AND a maverick, closed minded and radical - focusing only on the extremes of that, especially in terms of science sort of ignores the whole point of science, to use biased viewpoints to paint a larger picture.

    Ryan Fenton
    • troll toolbox (Score:1, Insightful)

      by Anonymous Coward
      Template #183
      Category: Instant karma
      For: new scientific theory proposed

      Yes, it only takes one demonstration to a render invalid a scientific theory. But that does not validate any other theories by doing so, unless they can accurately carry the same predictive weight as the previous theory, plus comply with the improved observations.

      A hole in $SCIENTIFIC_THEORY in any case doesn't mean scientists throw out their $SCIENTIFIC_FIELD books, it generally means they add and exception to the theory and work on fin

  • by bcrowell (177657) on Friday March 30, 2007 @11:42PM (#18553097) Homepage
    I think it's odd that MOND's enthusiasts are so eager to push it as an alternative to dark matter, now that we've entered the era of high-precision cosmology. We know a hell of a lot about cosmology that we didn't know ten years ago. We know the age of the universe to two significant figures. We know that the universe is expanding at an increasing rate. We know the spectrum and angular distribution of the cosmic microwave background to high precision. We've found out that neutrinos have mass. I can see how MOND would have some appeal back in 1981, when it was first proposed, but so much has changed in the last 26 years. The evidence has accumulated that we live in a universe that's much stranger than we'd believed. I think that's cool.
    • Re: (Score:3, Insightful)

      by amRadioHed (463061)

      The evidence has accumulated that we live in a universe that's much stranger than we'd believed. I think that's cool.
      And what about that rules out MOND?
    • I disagree (Score:3, Insightful)

      by khallow (566160)

      We know the spectrum and angular distribution of the cosmic microwave background to high precision.

      This is the only statement that is correct since it is the only conclusion derived directly from observation. A lot depends on how accurate our models of the universe and physics are. I think MOND is unlikely to last, but the theory is yet viable. Your claims about the age of the universe, mass of neutrino, etc are likely to be correct, but it would be embarrassing if these observations turn out to be depe

      • Re: (Score:3, Informative)

        by Ambitwistor (1041236)

        This is the only statement that is correct since it is the only conclusion derived directly from observation.

        No, you could introduce weird mechanisms that distort the true spectrum of the CMBR, which is about as plausible as the other scenarios you put forth.

        perhaps Type IA supernovas are different in the early universe than they are now (even though physical law is the same, there are substantial differences like elemental composition)

        You would then have to explain how these different supernovas still manage to produce the same characteristic light curves as modern supernovas. Possible in principle, but not plausible.

        perhaps we're incorrect about our local gravity environment (eg, we're deeper in a gravity well) and this effects our perception of the temperature of the cosmic background

        The temperature of the cosmic background isn't really that important in this context, and moreover, I can't imagine what kind of "gravity well" you could think that we were

        • by khallow (566160)

          No, you could introduce weird mechanisms that distort the true spectrum of the CMBR, which is about as plausible as the other scenarios you put forth.

          No "weird mechanism" (aside from some sort of NASA hoax) is going to change the fact that the observation was made and very precise data was collected. Nor does that statement depend on any observer biases that might be present.

          The temperature of the cosmic background isn't really that important in this context, and moreover, I can't imagine what kind o

          • No "weird mechanism" (aside from some sort of NASA hoax) is going to change the fact that the observation was made and very precise data was collected. Nor does that statement depend on any observer biases that might be present.

            You can say the same about the CMBR temperature. Yet you propose some kind of global gravity well that distorts our measurements and causes us to infer the wrong things from it. The same can be said of the CMBR angular power spectrum: there could be some astrophysical phenomenon out there distorting everything in some unknown way. You can't criticize CMBR temperature measurements for being potentially distorted by unknown processes, and at the same time insist that the CMBR angular power spectrum is a

          • I think I'm going way overboard as a devil's advocate here, but my point is that I don't think we have good reason to be so confident about phenommena either that we haven't directly observed, is based on very recent data, or depends on models that we already know aren't entirely valid in the regime in which the phenomena are observed.

            Which models do we know aren't valid in the regime in which they're being applied?

            By the way, here [wordpress.com] is a blog post with a slide from a talk by Roger Blanford listing "radical possibilities" for ways in which our cosmological inferences could be wrong. (I think most of them are very unlikely, although still more likely than "we're in a giant but unknown gravitational well".)

            • by khallow (566160)

              Which models do we know aren't valid in the regime in which they're being applied?

              The regime in question is subatomic scale and smaller with considerable precision and gravity. We already know QCD as it is for starters, and most other QFTs don't apply at this scale especially when gravity is taken into account. Perhaps when we've mapped out the full series of QCD (assuming the current perturbation theory approach to constructing QCD terms works) and glued it somehow to relativity, this will change. Stri

              • The regime in question is subatomic scale and smaller with considerable precision and gravity. We already know QCD as it is for starters, and most other QFTs don't apply at this scale especially when gravity is taken into account.

                QFT does too apply at those scales; you don't even need to do QFT in curved spacetime (which you can do if you want). The Planck scale of quantum gravity is not relevant for any of the questions you've mentioned; at best it could be relevant to very early-universe cosmology.

                Perhaps when we've mapped out the full series of QCD (assuming the current perturbation theory approach to constructing QCD terms works) and glued it somehow to relativity, this will change.

                We know quite a bit about the nonperturbative regimes of QCD as well, by the way, and it is fully consistent with special relativity. Compatibility with general relativity, once again, is irrelevant: at very large scales, QCD is uni

                • by khallow (566160)

                  You're being ridiculous. We don't even need to take the existence of the Virgo supercluster into account. Any significant redshift due to that would require very obvious zeroth-order modifications to gravity which would show up, basically, everywhere we look. That, or completely ridiculous modifications to the masses of galaxies which would, again, change all the orbital dynamics we see.

                  Eh, glancing around, it appears to me that the necessary adjustment would have to be one or two orders of magnitude gr

    • by 3waygeek (58990)
      The evidence has accumulated that we live in a universe that's much stranger than we'd believed.

      Haldane [wikipedia.org] figured that out 80 years ago, without benefit of modern cosmology.
  • by Essequemodeia (1030028) on Friday March 30, 2007 @11:56PM (#18553169)
    Maybe he's wrong, maybe he's not right. But damned if I don't admire a scientist who is willing to destroy a potentially promising career over a tiny hunch. Maybe god will take pity and alter gravity for just such an instance. I think he's getting bored with Iraq.
  • by Anonymous Coward
    http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/cr ls.rxml [uiuc.edu]

    The link above explains the Coriolis force. Among other things, this is the force that causes water to spiral down the drain in different directions on different sides of the equator. It also manifests itself such that if you fly at sufficient speed travelling past 63 deg. North Latitude, you will feel a slight bump. This is easily measured and confirmed by placing an accelerometer on the aircraft. There is almost always a slight acceleration. O
    • by Alex Belits (437) *
      No. Coriolis force exists. Phenomena you have mentioned don't.
    • by julesh (229690)
      The link above explains the Coriolis force. Among other things, this is the force that causes water to spiral down the drain in different directions on different sides of the equator.

      Erm, yes. But the Coriolis force (actually not a force at all, but an effect of inertia in an accelerating reference frame) is (a) perfectly consistent with newton's second law, (b) not what the author of the paper, which you clearly didn't even look at the abstract of, was talking about and (c) doesn't cause water to spiral d
  • A big IF (Score:5, Insightful)

    by Ibag (101144) on Saturday March 31, 2007 @12:11AM (#18553229)
    "In the end, if Newton's Second Law could be violated, he would be forcing physicists to reevaluate much of what we understand derived from that law -- which is quite a bit.'"

    In the end, if the second law of thermodynamics [or any other law of physics] could be violated, it would force physicists to reevaluate much of what we understand derived from that law - which is quite a bit. However, given that what we have derived from our laws generally fits with experimental observation (which is why we call them laws), the odds of him disproving Newton's second law with this experiment are about as good as me disproving the second law of thermodynamics by accidentally building a perpetual motion device.

    Experiments disproving longstanding laws have happened before. People don't have reason to care about them until afterwards, though.
    • Re: (Score:3, Insightful)

      by blank axolotl (917736)
      The key is that our experimental observations only cover the cases we have thought to test - he would be testing the law in a new way.

      In fact, we already know that newton's second law is wrong from special and general relativity, but you only see so at high velocities/high curvature of space. It was only once we had the theory that we knew how to test it properly. Here he is testing the law in the case of very small accelerations, based on a theory which tries to explain an astrophysics observation that is
      • ...Newton's second law is wrong from special and general relativity...
        Not if you state it in the form:

        F = dp / dt
        where F is the force on an object, p is the momentum of the object, and t is time; ie. the force is the time differential of the momentum. (And for completeness, p and F can be vectors.) Only with classical simplification do you get "F = ma".
        • The actually stated in the article,

          Using momentum in the terminology (which would never have occurred to Newton) is a latter-day revision of the law to bring it into correspondence with special relativity.
          But after reading that, I'm left wondering where the heck the rocket equation came from. and fluid dynamics. And whether a smart man is trying to blow smoke where smoke does not belong in the hopes of appearing even smarter for the purpose of getting grant money.
        • by blank axolotl (917736) on Saturday March 31, 2007 @04:18AM (#18554129)
          You're right that you can still use an equation that looks like F = dp/dt in GR, but I still think the original second law is wrong with all the quantities defined as they were. Writing it your way, it is then the definition of momentum which is wrong (or going on, the definition of velocity as dx/dt not dx/dTau). (Also in GR F= dp/dTau, not dp/dt if t is the time coordinate). The symbols in GR just happen to look and act quite like the newtonian symbols, but are interpreted differently.

          Anyway, it is the error in predicted motion that is interesting here, where 'F=ma' gives the newtonian motion,
          but this becomes like 'F = ma + m Gamma Vi Vj' in GR. You can't clearly see the different motions each theory gives in F = dp/dt.
      • Re:A big IF (Score:5, Insightful)

        by Ibag (101144) on Saturday March 31, 2007 @03:04AM (#18553889)
        A few quick comments. First, relativity does not conflict with Newton's second law. It only needs to be changed from F=mA to F=dp/dt where p is momentum. Second, nobody said that general relativity was the pinnacle of physical theories. People have been trying for a while to find a grand unified theory that incorporated all the known forces in the universe and worked at both small and large scales. This appears to have nothing to do with the article, though. Third, while our experimental observations may only cover the cases we have thought to test, our laws are further verified every time the world behaves like we expect it to, every time we use GPS satellites with relativistic corrections, and every time we use devices that rely on quantum effects to work. The odds that everything holds except for 2/1000 of a second each year in two places on earth is unlikely. Maybe the experiment will work. That is science. However, it doesn't hurt to be skeptical until the experiment is done. I'm not saying that it won't happen, just that it seems premature to talk about rewriting textbooks just yet.
    • idea for ya.

      The universe blows up, expands, shit forms, eventually everything comes back, collapses, and another big bang happens. Repeat countless cycles, yet it keeps happening.

      If you want to get into it, I'd argue that the universe, as open as it is, is a closed system without energy loss. But, this only works with the Big Bang theory.

      As it stands, we'll NEVER know in our lifetimes. So, I just present something for you to think of - the perpetual motion machine could exist, but it's on such a scale that
  • by AaxelB (1034884) on Saturday March 31, 2007 @12:12AM (#18553231)
    that Newton's Laws are actually just flawed theories? In that case, sign me up for the new "Intelligent Force" theory. Everything accelerates because something smarter than me decided it would, and there's no point asking questions. No more physics equations for me!
  • by BlackGriffen (521856) on Saturday March 31, 2007 @12:16AM (#18553247)
    I mean, NSL only applies in the case of slow moving/low acceleration objects because it assumes infinite propagation speed of the force carrier.

    If he finds this it will be interesting not because of NSL concerns but because it would be an observation of the finite propagation speed of gravity. A fact that would serve as indirect (or perhaps direct) evidence of gravitational waves.
    • by Plutonite (999141)

      Speed of Light Breaks it Already, Doesn't It?

      Yes, many of us have pointed this out, but apparently the man is proposing that relativistic form of the equation be revisited, which is a whole-nuther story. We're just nitpicking to be frank with you ;)

      If he finds this it will be interesting not because of NSL concerns but because it would be an observation of the finite propagation speed of gravity.

      I haven't done enough gravity to touch on advanced things like G waves, so I don't follow you. What I do know, as I posted somewhere below, is that cornerstone relationships like E=mc2 would very much go to hell, and quantum electrodynamics would have to be written from scratch. Relativity still holds as

  • Perhaps there's a force that hasn't been taken into account in his calculations...
    • by SEWilco (27983)
      Did he include the force of enough money for him to vacation at lovely polar locations?
    • Perhaps there's a force that hasn't been taken into account in his calculations...
      What kind of force? A bangy force? A pushy force? A growy force? A forcy force force? A magic man dunnit [scienceblogs.com].
  • by r00t (33219) on Saturday March 31, 2007 @12:40AM (#18553367) Journal
    Think it'd be cool to visit Greenland?

    1. be a prof
    2. propose theory that must be tested in Greenland
    3. profit
  • Why Not in Space? (Score:2, Interesting)

    by vertigoCiel (1070374)
    Am I missing something, or would this be a hell of a lot easier to do in space? From TFA I gather that he's looking for an instance of no outside force, and, since orbit is essentially free-fall, this would be easily accomplished on the ISS. Granted, I might be missing the point entirely, or I don't get his strange "I've got to do this on the surface of the Earth!" fetish.
  • That's a cute little paper. If other physicists think it makes sense, that little experiment is worth doing, even though some people will have to go up to the northern tip of Greenland to do it.

  • Dangerous? (Score:3, Insightful)

    by Plutonite (999141) on Saturday March 31, 2007 @12:50AM (#18553399)
    Newton's law underwent some serious revisiting in 1905 when a chap called Einstein realised that masses are not constant/absolute but in fact relative, and this is why the modern relativistic notation differs quite a bit from the original F=ma. Now if this new guy is not joking (Russian timezones, April 1st, bit early..etc) then not only is our understanding of momentum going to be radically different, but in fact E=mc2 might have to be revisited as well (must read part 10 of this historical paper by Einstein [fourmilab.ch] to understand). That happens to be a very ground breaking idea if it were true, and would change lots of things we supposedly know about fundamental physics.
    • by julesh (229690)
      Now if this new guy is not joking (Russian timezones, April 1st, bit early..etc)

      The paper was published in December. That's a lot early.
    • Newton's law underwent some serious revisiting in 1905 when a chap called Einstein realised that masses are not constant/absolute but in fact relative, and this is why the modern relativistic notation differs quite a bit from the original F=ma.

      Not so. Even in Einstein's relativity, mass is invariant [ucr.edu].
      • by Plutonite (999141)
        Read the notes you linked to carefully (they are some of the best on the web). Mass/inertia is no longer invariant when a body is moving with respect to a frame. This is why the term "relativistic" mass is used. Invariant mass is the so called "rest" mass which results from the mass being stationary with respect to a frame of reference, and this is the typical, implicit nomenclature for non-relativist applications. Because we need to consider the relative mass in moving systems, F=ma (which is just m*dv/dt)
    • by XchristX (839963)
      A few conceptual corrections. The concept of "relativistic mass" is an entirely unnecessary construct designed to make Einstein's famous "E=mc^2" look simple (actually, it's better stated as E^2=p^2c^2+m^2c^4 where m is the so called "rest mass"). If we do away with the redundant concept of "relativistic mass" altogether and only stick to the Lorentz-invariant "rest mass", then there is no need to muck about with the whole "mass depends on velocity" stuff. Relativity remains perfectly consistent without tha
      • by Plutonite (999141)

        actually, it's better stated as E^2=p^2c^2+m^2c^4 where m is the so called "rest mass"

        Yes, now may I ask what the "p" in that equation represents? It is (Lorentz factored)momentum, which incorporates the concept of relativism in mass. The word relativistic mass is not merely a simplification of the equation by substitution - it is a real effect of energy content on the inertial mass of the body (it's resistance to an accelerating force). When bodies gain energy (through motion or otherwise) they also gain "mass" by a factor of L/c^2, and the same for energy loss. Hence when bodies are trav

        • by XchristX (839963)
          [quote]
          Yes, now may I ask what the "p" in that equation represents? It is (Lorentz factored)momentum, which incorporates the concept of relativism in mass.
          [/quote]

          I disagree. Momentum can be defined irrespective of mass. Momentum is simply the generalized velocity derivative of the Lagrangian, or the generator group of the group of all possible motions (remember that photons have momentum but no mass)

          Momentum and mass are 2 different and largely unrelated ideas.

          [quote]
          The word relativistic mass is not merel
          • by Plutonite (999141)

            I disagree. Momentum can be defined irrespective of mass. Momentum is simply the generalized velocity derivative of the Lagrangian, or the generator group of the group of all possible motions (remember that photons have momentum but no mass)

            Ah, and therein the confusion lies. This is a great chat by the way, the issue has been debated formally in journals before. I agree perfectly with what you've said in both posts, it's just that classicaly the concepts of momentum and mass have been tied together, and that is why people use terms like "relativistic mass" to account for the variation in the time component of the four vector, which is very different from the "actual" or "rest" mass. Books still have F = d(mv)/dt, even though the m here is ve

            • by XchristX (839963)
              So the consensus is that concepts like "relativistic mass" are constructs largely directed towards a popular audience that likes to "perceive" human behaviour in natural phenomena (ie anthromorphism), and comes about as a result of historical associations between mass and momentum (very historical, since the Poynting Vector was discovered in 1884, and that alone shows momentum without mass).

              [quote]
              Whereas today we define (real, rest, invariant)mass only through energy equivalence
              [/quote]

              There are several pr
              • by Plutonite (999141)
                1. This is the reverse of the infinite/inifitismal - the infinite is defined but undetermined, not the other way round. You can define an infinite set, but you will never be able to "determine" all it's elements. It is rather dangerous playing with infinity also, because it can be argued that the lack of determinism is axiomatic i.e the definition is the lack of determination. Scary stuff, and not really relevant.

                2. Yeah, I thought about the circular definition issue for a while. The problem is that if you
        • by XchristX (839963)
          [quote]
          When bodies gain energy (through motion or otherwise) they also gain "mass" by a factor of L/c^2, and the same for energy loss

          [/quote]

          Sorry I forgot to add in my last post that mass-energy equivalence is not destroyed if we abandon the concept of relativistic mass. Rest mass itself can be "converted" to photons (as happens in nuclear fission and decay processes). You go to a frame when the nucleus is at rest (so p=0) and you get E=mc^2 where m is the "rest mass" and, when the nucleus breaks off into
  • So for this thousandth of a second in a remote location at 80 degrees of latitude, is he proposing that we build an entire testing facility to see if an uncharged particle wiggles a little bit for some reason by some mechanism that no one has really figured out?
    Are we also to believe that because the mathematical calculations work out such that all first- and second-order gravitational forces are cancelled, if we observe some motion, that motion is a clear violation of Newton's Second Law by assuming that
    • by toby34a (944439)
      It seems that he's got ideas for mobile testing locations. Now, 80 degrees N/S doesn't seem like that great of a place to go, but it's somewhere where we don't have to put it on a rocket, which would require more funding. The materials (from TFA) that he proposes wouldn't be too terribly expensive to cart to Greenland/Antartica versus launching it onto the ISS.

      Again, it's probably worth setting up some theoretical physicists up on top of a glacier just for the hilarity of it. But most of them are probabl
  • One thing about this is at least it can be tested for, and right here on Earth. But even if it's observed, that doesn't automatically prove his theory true. It would only add evidence to it.
  • Oh yeah? (Score:5, Funny)

    by HardCase (14757) on Saturday March 31, 2007 @01:48AM (#18553597)
    You can take my gun from me...oh, wait, wrong 2nd law...
  • by thrawn_aj (1073100) on Saturday March 31, 2007 @01:49AM (#18553601)
    What laypersons should realize is that when a flaw is discovered in a well-established physical theory, it usually reduces the domain of validity of the theory, but RARELY makes that theory useless as a calculational tool (it just tells us when the theory will break down, as ALL current theories eventually do - the triumph of modern physics is to push those breakdown points to the farthest reaches of the imaginable). In this, physics has been an unqualified success - a fraction of the predictive power that we have today would have been enough to condemn several "soothsayers" to a grisly demise at one point in history :P. To digress for a moment here, it amuses me greatly that people can be obsessed with psychics and the contemptible Nostradamus while taking such exquisitely detailed predictions as tomorrow's weather for granted. It's rather like being impressed with a mythical flying superman while thinking of an airplane as mundane.

    An example to illustrate the breakdown of theories: the Special theory of Relativity modified Newtonian mechanics on a fundamental level. However, for speeds much less than the speed of light (which is what most of us experience in daily life), it is STILL Newtonian mechanics that we use, even in several cutting edge research fields. The rule of thumb in research is: never use a full model when an approximate one is just as accurate in the domain of interest. In much the same way, even if MOND were true, any deviations from Newton would kick in at EXTREMELY LOW accelerations (of the order of 10^-20 m/s^2 which is about 10^-21 g, something next to impossible to duplicate in a lab because of ambient vibrational noise which is usually MUCH higher (say, about 10^-9 g is a VERY quiet environment)). This is the reason why the paper (which attracted our group's attention a few weeks ago) proposes an experiment at such well-defined times and locations. To put it bluntly, this is an ad-hoc modification in the sense that there is just no justification for the modification. Of course, I don't even think MOND would replace the Dark Matter hypothesis. One might even argue that this modification is simply a way of expressing the effect of Dark Matter (just a thought).

  • by gb (8474) on Saturday March 31, 2007 @02:49AM (#18553825) Homepage
    It's worth pointing out that this paper is only publihed on a preprint server - that means it has not been through peer review, so needs to be treated with a lot of caution. There's an awful lot of totally crazy stuff on preprint servers. Not that I'm saying it's totally crazy - whilst I'm a physicist, I do condensed matter not astro - amd wouldn't describe myself as qualified to have a definitve opinion. But I would be both cautious and skeptical until proven oherwise.
    • Re: (Score:2, Informative)

      by Dr_Mic (975409)
      Indeed, it is quite a stretch to say that putting a paper up on arXiv.org is "published" in any normal sense (say onethat would be accepted by a tenure review committee). However we do have

      Is Violation of Newton's Second Law Possible? A. Yu. Ignatiev Phys. Rev. Lett. 98, 101101 (2007)

      as well as

      Mirror dark matter and large scale structure A. Yu. Ignatiev and R. R. Volkas Phys. Rev. D 68, 023518 (2003)

      Geophysical constraints on mirror matter within the Earth A. Yu. Ignatiev and R. R. Volkas Phys. Rev

  • by Phroon (820247) on Saturday March 31, 2007 @02:50AM (#18553827) Homepage
    These theoretical astrophysicists are getting good at what they do.

    The submitter of this article (and the populace of Slashdot as a whole) doesn't get the point of this article. Ignatiev isn't suggesting this experiment out of thin air, he's suggested a novel earth-based experiment to help explain the anomaly in galactic rotation (ie. Dark Matter). To explain this anomaly some theoretical astrophysicists modify Newtonian dynamics in a small way so that the galactic rotation calculations come out correct. Others introduce Dark Matter, or alter gravitation itself.

    He basically wants to observe an object smaller than 7 cm x 40 cm x 40 cm at the precise moment and the precise location on the earth such that it would experience an acceleration that is much smaller than the extra acceleration it would experience as proposed by the modified Newtonian dynamics. So any extraneous acceleration observed at this moment had to have come from modified Newtonian dynamics.

    The interesting thing about this article is that it isn't just a wild claim by a crackpot scientist, it's the proposition of an extremely accurate measurement using the most advanced technologies we have available. Of particular interest to me was that the proposed effect was two orders of magnitude larger than that observable by LIGO, a gravitational wave detector, suggesting that such an experiment is actually possible.
  • by Alex Belits (437) * on Saturday March 31, 2007 @05:50AM (#18554473) Homepage
    This article (and the whole MOND thing) would make some sense if the systems described in them were not accelerating because of gravity. Sun is subjected to the gravity forces toward the center of our galaxy, so its path relative to the center of the galaxy is not a straight line but a circle -- though a very large one. I find it to be an extremely weird oversight considering that the whole hypothesis exists to describe parameters of the very same motion of stars in galaxies. So even when a point on the Earth surface is not accelerating in the Sun's coordinate system, it still does in the galaxy's coordinate system.

    Worse yet, MOND does not explain anything about galaxies because galaxies themselves accelerate. They are not distributed evenly and uniformly in space but form clusters. Each cluster just like a galaxy itself, is pulled together by gravity, so galaxies experience some acceleration in the cluster's coordinate system because of the gravity of other galaxies.

    Obviously this acceleration is not detectable locally because it is caused by gravity -- for the same reason objects in orbit are "weightless". To find out that you are in freefall (or in orbit, what is the same thing) without looking at other celestial objects you have to throw something and observe its movement -- since gravity is not parallel and uniform everywhere, after the object will get far enough from you, it will be noticeable that its trajectory is not a straight line relative to you, as it would be if you weren't accelerating at all. However locally gravity and acceleration are indistinguishable, and at the scale of Solar system or galaxy the size of such "local" area is huge.

    MOND is talking about absolute acceleration that should be clearly distinguishable from gravity. However if we will try to find something in the universe that is really "unaccelerated" by this definition, there will be very few objects in this category, if any. Certainly it would not be massive centers of galaxies, Sun or two spots on the Earth surface the author of the article proposes as locations for his experiments.

    This is the theoretical part of the problem. Now, the practical one. In two proposed spots the conditions that article author expects to happen last for a very short time and happen once a year. The extent of effect is similar to the influence of gravity from many existing celestial bodies. Tidal waves caused by Moon and affected by the shape of oceans, condition in the atmosphere, movement of Earth crust, etc. are likely to produce more noticeable influence on any test body that may be used in the experiment. Though I didn't do any calculations, it's hard to believe that variations of tidal waves caused by changes in weather will be less than supposed effect of "modified" 2nd Newton's Law even if it worked the way that the article author's proposed. And since conditions are supposed to be so rare, there is no way to collect enough samples for any statistical analysis.

    In the end, I can add that if your experiment is to look for a black cat in a dark room, it shouldn't be a surprise if the result is negative regardless of the actual presence of a cat. However this makes no excuse for proposing that the cat is in the room when there is no reason for it to be there in the first place. Both theory and proposed experiment look extremely stupid, and if MOND can be modified to explain why it should include movement of stars within galaxies but not movement of galaxies in clusters, maybe it would be worth a second look. For now it's just that -- stupid idea with no foundation and no viable method of verification.
    • by julesh (229690)
      So even when a point on the Earth surface is not accelerating in the Sun's coordinate system, it still does in the galaxy's coordinate system.

      While movement on a galactic scale is quite rapid (in the galaxy's frame of reference), I believe the acceleration of any individual body is rather small, and can probably be ignored for any short timescale purpose.
      • by Alex Belits (437) *
        Then just compare movement of stars in galaxies with different acceleration measured against other galaxies. Dense clusters, or small galaxies orbiting larger galaxies would provide examples of higher acceleration, so if the hypothesis is true, movement of stars in them would be different from movement of stars in galaxies that are supposed to be accelerating less.

        One thing that is good about the Universe is that it has plenty of very large, weirdly shaped objects in it.
        • by julesh (229690)
          As I understand it, this observation has already been made, such an effect has been noted, and is what provoked the development of the theory that this new experiment is designed to test.
    • by ThosLives (686517) on Saturday March 31, 2007 @08:52AM (#18555217) Journal

      I don't think it has to do with acceleration of galactic centers. I think it has to do more with the effective radius used in the calculations.

      For instance, in a traditional central-body problem, you have a very basic set of equations that says the path of any body around another body will be a conic section, with modifications due to more than two bodies in a system.

      What I've never seen in literature, and I've seen the plot of angular velocity versus radius that "flattens out" for galaxies, is just what that angular velocity is? Is it angular velocities for individual stars, or an average?

      If it is just an average, then I wonder is it an effect due to observation. What I mean is this: when looking at a gas here on earth, the average temperature is a good measure for its properties. However, only a small portion of the individual molecules in the gas actually have that exact temperature. The same for a stream of exhaust from a jet - the jet has a general average velocity, but each individual particle has some other velocity that contributes to the bulk average velocity.

      I am wondering if the aggregate motion of a galaxy is like gas temperature or velocity; that is, it may be a superposition of the individual accelerations of the individual starts and nebulae in the galaxy. That is, is it possible to generate a system only with particles that obey classical (relativistic) gravity but can appear, in aggregate, to disobey the mass proportionality of Newton's Second Law? I suspect that 'galactic' measurements are like measuring bulk properties of a gas rather than looking at the kinetic model. Something perhaps like the recent storm on Saturn / water in a spinning bucket articles where simple motion of individual particles gives rise to more complex aggregate behavior.

    • All of this talk about reference frames and trying to decide what the "absolute" accelerations and velocity of everything is just makes my head spin and wonder where these physicists come from that they havn't read about about this nearly Century-old theory proposed by the crazy Swiss patent examiner named A. Einstein.

      Essentially speaking, it really doesn't matter what frame of reference you are using. From a certain point of view, everything in the Universe is gravitationally attracted to you, not the oth
  • I think the point here isn't that there's some weird hiccup that only occurs during this brief time, but rather that standard theory predicts that a certain observation over this brief period should be zero while MOND predicts a nonzero value. Testing whether something is zero or not is one of the more sensitive types of tests out there. As an example, it's a lot easier to figure out whether there is a person or not in a room than to figure out whether there are 1,000 or 1,001 people in a room. By measuring
  • Which postulates that the amount of time for a research assistant to get back from Quiznos is directly proportional to the gastric sounds of everyone else in the lab, and inversely proportional (to the second power) of the immediacy of the stuff left to do in the afternoon.

  • I read about a fascinating experiment recently which attempts to test whether the laws of physics are invariant with your frame of reference, by comparing the enthalpy of crystallisation of the two enantiomers (mirror images) of a chiral compound. If the laws of physics vary with space (i.e. there's a slight energetic preference to certain orientations in a universal "ether"), then the enthalpies of crystallisation will be different for each enantiomer as your orientation in space changes (achieved by perfo
  • Just on general principles, the idea sounds ridiculous:
    • Astrophysical theories and estimates of dark matter, miniature black holes, "wimps", "gimps", renegade neutrino varieties, and more-- the estimated magnitude of these effects can only be guessed at, and the best guesses vary by factors of two to ten.
    • Newton's law, F = MA has been tested hundreds of times, in all kinds of places, on earth, in deep mines, in the air, in space, and as far as Vger 10 has wandered. IIRC it's always passed within the preci

"Ignorance is the soil in which belief in miracles grows." -- Robert G. Ingersoll

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