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Natural Science Forum / Physics / General Physics / June 2008Has anyone tested MOND?
If F=ma breaks down at very low accelerations as claimed by MOND, has any experiment been done to test its validity? It seems to me that it would not be a very difficult experiment to conduct. Fred > If F=ma breaks down at very low accelerations as claimed by MOND, has > any experiment been done to test its validity? > > It seems to me that it would not be a very difficult experiment to > conduct. It may not be possible to do inside Earth's gravity, since the acceleration of Earth's gravity is much larger than MOND's a_0, and it would inundate the experimental results. Yousuf Khan > fred.zak...@gmail.com wrote: > > If F=ma breaks down at very low accelerations as claimed by MOND, has [quoted text clipped - 8 lines] > > Yousuf Khan But if the applied force is perpendicular to the earth's gravity, can't the effects be separated? Fred. > But if the applied force is perpendicular to the earth's gravity, > can't the effects be separated? But aren't you specifically interested in testing the acceleration due to gravity, rather than just any old acceleration? If so, then testing acceleration that's due to perpendicular forces is not testing acceleration due to gravity, is it? Yousuf Khan >> If F=ma breaks down at very low accelerations as claimed by MOND, has >> any experiment been done to test its validity? [quoted text clipped - 7 lines] > > Yousuf Khan MOND is Dead? ...most likely http://www.astro.ucla.edu/~wright/density.html#MOND http://www.astro.ucla.edu/~wright/old_new_cosmo.html 22 Oct 2002 - The Chandra X-ray Observatory presented evidence against the MOdification of Newtonian Dynamics (MOND) alternative to dark matter theories. The August 2002 Scientific American has a long article about MOND. The hot X-ray emitting gas around the galaxy NGC 720 forms an ellipsoidal cloud, which requires an ellipsoidal gravitational potential well. While an ellipsoidal cloud of dark matter could provide such a well, MOND would necessarily give a spherical potential well. In general MOND works well on the scale of individual galaxies, but not for clusters of galaxies. So why is MOND only maybe dead? Its supporters like Milgrom are persistent and clever, and they may come up with a MONDian explanation for NGC 720. More on Dark Matter http://www.astro.ucla.edu/~wright/cosmolog.htm#News 21 Aug 2006 - NASA announced updated information about the "bullet cluster" 1E0657-56 today. Two clusters of galaxies have recently collided in this X-ray source. This cluster is filled with hot gas so X-ray observations by the Chandra X-ray Observatory show where the ordinary matter is located. 90% of the ordinary matter (the "baryonic" matter) is hot gas. The new results [Clowe et al., Bradac et al.] use gravitational lensing of background galaxies to show where the sources of gravity are located. The sources of gravity in the cluster are not located where the ordinary matter is located, so this cluster is a counter-example to MOND. All of this was known in 2003 but with less precision. Sean Carroll has a nice post about this at Cosmic Variance. The Matter of the Bullet Cluster http://antwrp.gsfc.nasa.gov/apod/ap060824.html Explanation: The matter in galaxy cluster 1E 0657-56, fondly known as the "bullet cluster", is shown in this composite image. A mere 3.4 billion light-years away, the bullet cluster's individual galaxies are seen in the optical image data, but their total mass adds up to far less than the mass of the cluster's two clouds of hot x-ray emitting gas shown in red. Representing even more mass than the optical galaxies and x-ray gas combined, the blue hues show the distribution of dark matter in the cluster. Otherwise invisible to telescopic views, the dark matter was mapped by observations of gravitational lensing of background galaxies. In a text book example of a shock front, the bullet-shaped cloud of gas at the right was distorted during the titanic collision between two galaxy clusters that created the larger bullet cluster itself. But the dark matter present has not interacted with the cluster gas except by gravity. The clear separation of dark matter and gas clouds is considered direct evidence that dark matter exists. > MOND is Dead? ...most likely > > http://www.astro.ucla.edu/~wright/density.html#MOND > http://www.astro.ucla.edu/~wright/old_new_cosmo.html Yeah, and Dark Matter Theories were killed off by the Abell 520 cluster. So what? Battling articles, you show me an article that kills MOND, and I'll show you one that kills Dark Matter. Dark matter mystery deepens in cosmic 'train wreck' "Astronomers have discovered a chaotic scene unlike any witnessed before in a cosmic “train wreck” between giant galaxy clusters. NASA’s Chandra X-ray Observatory and optical telescopes revealed a dark matter core that was mostly devoid of galaxies, which may pose problems for current theories of dark matter behavior." http://www.innovations-report.de/html/berichte/physik_astronomie/bericht-89116.html And let's not forget all of the other new theories coming up that could replace either MOND or DM, such as Dark Fluid: SPACE.com -- New Cosmic Theory Unites Dark Forces "Zhao has also tested his model against the bullet cluster of galaxies, where a massive collision appears to have stripped hot gas from its dark matter envelope. This "naked" dark matter was seen as iron-clad proof for traditional dark matter theories, but Zhao claims that his fluid can reproduce the same effect." http://www.space.com/scienceastronomy/080211-mm-dark-unification.html Even if MOND is just a curve-fitting theorem, at the very least it could be one of those theories that could be right for the wrong reason. If no Dark Matter particles are found in the LHC, then it can only be a joke. Yousuf Khan > > MOND is Dead? ...most likely > > > http://www.astro.ucla.edu/~wright/density.html#MOND > > http://www.astro.ucla.edu/~wright/old_new_cosmo.html > > Yeah, and Dark Matter Theories were killed off by the Abell 520 cluster. Why? The dynamics that are supposedly really unlikely are model based, and the whole /setup/ that we are observing is unlikely. I haven't seen anything that really approaches nail-in-coffin level of dark matter refutation. Worst case, we have to re-evaluate how dark matter interacts Is there anything reasonably recent on Abell 520? As I recall, there was one article about a supposed dark force, and the literature was silent ever since. Either I missed the followups... > So what? Battling articles, you show me an article that kills MOND, and > I'll show you one that kills Dark Matter. MOND is utterly excluded by lensing observations. That is slightly more compelling than "numerical simulations raise some eyebrows". [...] > And let's not forget all of the other new theories coming up that could > replace either MOND or DM, such as Dark Fluid: [quoted text clipped - 5 lines] > for traditional dark matter theories, but Zhao claims that his fluid can > reproduce the same effect."http://www.space.com/scienceastronomy/080211-mm-dark-unification.html Negative billion points for even mentioning ether. I hate popularizations - they never have arXiv links or communicate a worthwhile level of accuracy. > Even if MOND is just a curve-fitting theorem, at the very least it could > be one of those theories that could be right for the wrong reason. If no > Dark Matter particles are found in the LHC, then it can only be a joke. Remember the history of the neutrino. > Yousuf Khan > MOND is utterly excluded by lensing observations. That is slightly > more compelling than "numerical simulations raise some eyebrows". And yet, the Milky Way's tidal effect on neighboring dwarf galaxies are better predicted by MOND than Dark Matter. Battling articles again. Do Dwarf Galaxies Favor MOND Over Dark Matter? "When MOND is applied to the population of dwarf galaxies, one effect is that tidal forces from the Milky Way, which have a negligible effect in classical Newtonian Mechanics, can actually make a big difference. This is particularly significant for the dwarfs orbiting our Galaxy most closely." http://www.sciencedaily.com/releases/2008/04/080402202332.htm >> And let's not forget all of the other new theories coming up that could >> replace either MOND or DM, such as Dark Fluid: [quoted text clipped - 10 lines] > I hate popularizations - they never have arXiv links or communicate a > worthwhile level of accuracy. [0804.1588] Dark Fluid: Towards a unification of empirical theories of galaxy rotation, Inflation and Dark Energy http://arxiv.org/abs/0804.1588 >> Even if MOND is just a curve-fitting theorem, at the very least it could >> be one of those theories that could be right for the wrong reason. If no >> Dark Matter particles are found in the LHC, then it can only be a joke. > > Remember the history of the neutrino. Yeah exactly, as I recall, the neutrino was first theorized to explain a bit of missing energy in particle physics /equations/. It was eventually discovered by particle physics /experiments/. Dark Matter is used to explain some missing numbers in /cosmology/. So what makes anyone think that Dark Matter is going to pop out of /particle physics/ experiments? The answer to Dark Matter lies out in cosmology where it is an equation in need of solving. Yousuf Khan | > MOND is utterly excluded by lensing observations. That is slightly | > more compelling than "numerical simulations raise some eyebrows". [quoted text clipped - 9 lines] | closely." | http://www.sciencedaily.com/releases/2008/04/080402202332.htm Ads by Google Advertise here -------------------------------------------------------------------------------- On-line Game: DarkOrbit Conquer unknown galaxies in a space on-line game: Play now! www.darkorbit.com Date Singles into Fitness View Photo Profiles. Local Singles into Fitness. Join Now for Free. www.Fitness-Singles.com Galaxy in Greece Book here now and save up to 70% at the Galaxy in KalambakaMeteora www.TravelRepublic.co.uk/Galaxy Galaxy black Nero Assoluto £34.04 + vat in stock Galaxy black £38.29 + vat in stock www.rock-revelations.co.uk Buy: Cornelia Parker Signed, numbered, limited editions exclusively at The Multiple Store www.themultiplestore.org --------------------------------------------------------------- So much for that crap. > If F=ma breaks down at very low accelerations as claimed by MOND, has > any experiment been done to test its validity? > > It seems to me that it would not be a very difficult experiment to > conduct. Galactic rotation motivated MOND. The Bullet galaxy pretty much killed that. The Pioneer anomaly motivated MOND. Alas, http://arxiv.org/abs/0710.2656 1/3 modeled away Let this be a lesson to theorists: Curve fitting does not prove proximity is causality. The next big hit is the Higgs not showing at the LHC.  SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 > Let this be a lesson to theorists: Curve fitting does not prove > proximity is causality. The next big hit is the Higgs not showing at > the LHC. Long faces in Berne. Bob Kolker >> Let this be a lesson to theorists: Curve fitting does not prove >> proximity is causality. The next big hit is the Higgs not showing at [quoted text clipped - 3 lines] > > Bob Kolker Many of the scientist will be overjoyed to finding anything new and I suspect that is exactly what will happen! > Let this be a lesson to theorists: Curve fitting does not prove > proximity is causality. The next big hit is the Higgs not showing at > the LHC. What are the implications, if Higgs boson not seen? -- Rich On Jun 25, Uncle Al <Uncle...@hate.spam.net> wrote: > Let this be a lesson to theorists: Curve fitting does not prove > proximity is causality. The next big hit is the Higgs not showing at > the LHC. What are the implications, if Higgs boson not seen? -- Rich Keep looking, of course. Too much money spent not to find it. Higgs sunt dracones. If you can't find a real dragon there's always a T-Rex skull to substitute. Higgs will be found, it's a dragon to be believed in. Or build an even bigger accelerator. > If F=ma breaks down at very low accelerations as claimed by MOND, has > any experiment been done to test its validity? > It seems to me that it would not be a very difficult experiment to > conduct. It's actually quite hard. For MOND to be self-consistent, the breakdown has to occur at small accelerations in the galactic reference frame (or the reference frame of the local group of galaxies), not the laboratory frame. But the Earth's acceleration in the galactic reference frame is already quite large compared to the MOND scale. There are actually brief periods in which various accelerations cancel at special locations, at which MOND could be tested on Earth. One computation, for instance, predicts such a situation this August at a location in Greenland and another in Antarctica. You can find a discussion of possible experimental tests in papers by Ignatiev, http://arxiv.org/abs/gr-qc/0612159 (Phys.Rev.Lett. 98 (2007) 101101) and http://arxiv.org/abs/0802.1599 (Phys. Rev. D77 (2008) 102001). The experiments are, unfortunately, not at all easy. Steve Carlip > > If F=ma breaks down at very low accelerations as claimed by MOND, has > > any experiment been done to test its validity? [quoted text clipped - 19 lines] > > Steve Carlip We could be especially naughty and conjecture that dark matter is instead a tangle of Weyl tensors. That obtains gravitation without mass. What would an experimentalist detect as a discrete validating event? SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 > We could be especially naughty and conjecture that dark matter is > instead a tangle of Weyl tensors. That obtains gravitation without > mass. What would an experimentalist detect as a discrete validating > event? Weyl Tensors are mathematical abstractions that live in human brains. Mathematic -describes- what is Out There. It is not, itself, what is Out There. Bob Kolker > We could be especially naughty and conjecture that dark matter is > instead a tangle of Weyl tensors. That obtains gravitation without > mass. What would an experimentalist detect as a discrete validating > event? Outside matter, the Weyl tensor satisfies a wave equation -- it propagates at the speed of light. What you're describing is simply a gravitational wave background. This won't do as dark matter (it would be "hot" dark matter, not "cold," and that doesn't fit measurements). There certainly could be a stochastic background of gravitational waves, though. There are experimental restrictions at some frequencies (from, for example, observed limits on stochastic fluctuations of spacecraft trajectories); see Armstrong's article at http://relativity.livingreviews.org/Articles/lrr-2006-1/index.html, for instance. Steve Carlip > > We could be especially naughty and conjecture that dark matter is > > instead a tangle of Weyl tensors. That obtains gravitation without [quoted text clipped - 6 lines] > (it would be "hot" dark matter, not "cold," and that doesn't fit > measurements). Bummer. What about a perturbation expansion? Let sleeping turds sleep. > There certainly could be a stochastic background of gravitational > waves, though. There are experimental restrictions at some [quoted text clipped - 4 lines] > > Steve Carlip Hmpf. Brilliant, concise, and wrong. (Liberal Arts would give credit for 2 out of 3 - and extra credit for dialectic and critique after having lost sight of the goal.) SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 > There are actually brief periods in which various accelerations cancel > at special locations, at which MOND could be tested on Earth. Which reminds me I read about that in NS... http://www.newscientist.com/channel/fundamentals/mg19325974.300-equinox-challeng e-to-newtons-law.html "The key is to find a time and place when the acceleration felt by a test object would be zero. Not an easy task, since besides Earth's gravity, our planet's rotation and its motion around the sun also set up forces that accelerate objects beyond the MOND limit. However, Ignatiev's calculations show that along latitudes of about 80° north or south, passing through northern Greenland and Antarctica, at two precise times of year, these forces cancel each other out." >> There are actually brief periods in which various accelerations >> cancel at special locations, at which MOND could be tested on Earth. > > Which reminds me I read about that in NS... http://www.newscientist.com/channel/fundamentals/mg19325974.300-equinox-challeng e-to-newtons-law.html > "The key is to find a time and place when the acceleration felt by a > test object would be zero. Not an easy task, since besides Earth's [quoted text clipped - 3 lines] > or south, passing through northern Greenland and Antarctica, at two > precise times of year, these forces cancel each other out." They are way off then, They forgot (or are ingoring) the Galaxy spin. And of course the Galaxy motion around the Universe spin also. :) Not one spot in the universe except direct center of all the spinning will truly experience 0 acceleration. :) SignatureJames M Driscoll Jr Spaceman >>> There are actually brief periods in which various accelerations >>> cancel at special locations, at which MOND could be tested on Earth. [quoted text clipped - 17 lines] > Not one spot in the universe except direct center of all the spinning > will truly experience 0 acceleration. Silly. It is only necessary to eliminate the effects that are greater than the predicted MOND effect so that the latter will be detectable above background. [...] > They are way off then, > They forgot (or are ingoring) the Galaxy spin. > And of course the Galaxy motion around the Universe spin also. How remarkable of you to be able to tell what "they forgot" without even reading the paper (http://arxiv.org/pdf/0802.1599)! Or did you read it and somehow just miss equation (3.2), table I, and the footnote on page 3? Steve Carlip > [...] >> They are way off then, [quoted text clipped - 6 lines] > Or did you read it and somehow just miss equation (3.2), > table I, and the footnote on page 3? And they still got those time for 0 accelration? Wow, they are funny. maybe they were using relative timing. LOL |
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