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Testing for no dark matter

You might recall a while back physicsworld.com reported on a prediction for peculiar event that takes place on the two equinoxes. On the 20 March and the 22 September (or thereabouts) at two places on the Earth’s surface, many of the gravitational forces in the Milky Way should cancel out.

Such a quiet time in the turmoil of our galaxy provides an ideal opportunity for a ruthless test of Newton’s laws of motion. Some physicists think that if there were any deviation in the laws at very low accelerations it would mean dark matter — the elusive substance thought to make up around 95% of the universe’s mass and the dream catch of experiments worldwide — does not exist. Instead, all the phenomena associated with dark matter could be explained by a slight alteration in the laws known as modified Newtonian dynamics (MOND).

When Alex Ignatiev from the Theoretical Physics Research Institute in Melbourne, Australia, came up with the idea for the equinoctial experiment, there were a couple of problems with his proposal. First, there was a worry that stray icebergs at high latitudes where one of the experiments would have to be performed might give a false gravitational signal. Second, Ignatiev did not know the exact time that the desired signal would occur.

Now, in a new paper, he has resolved both of these. He has shown that even the biggest icebergs would not produce a signal big enough to confuse the data. And he has also shown how to predict the exact signal times.

One of the referees for Ignatiev’s paper has given a rich endorsement to the proposal: “MOND is the leading alternative to cosmic dark matter. It has passed a surprising number of astronomical tests and is desperately in need of laboratory tests. The author’s idea for testing MOND in a terrestrial setting is the only viable suggestion I’ve ever heard for such a possibility. This is an incredibly important problem, and deserves to be explored just as much as CDMS and the many other dark matter search experiments.”

Posted by Jon Cartwright on May 19, 2008 10:24 AM |

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Comments (2)

  • 1 Zephir May 28, 2008 10:00 PM

    If I remember well, MOND theory has started its existence like typical phenomenological theory, which has converted itself into relativistic description of Universe expansion. This is strong point of theory, because of hidden paradox in space-time dilatation by my opinion:

    This expansion is considered as omni-directional in general, which effectively means, not only the more distant object retreats by increasing speed with increasing distance. If we're observing some sufficiently large source of light and/or gravity, the omni-directional expansion would mean, the light and/or gravity force should spread by the decreasing speed. These interaction would appear effectively "frozen" in expanding space, like during passing of cloud of more dense vacuum of finely spread matter around center of radiation.

    As the result, the large galaxies are rotating like single objects due the limited speed of gravity spreading from center of mass: the gravity isn't sufficiently fast to follow space-time expansion. Note that such expansion can be interpreted as a gradual increasing of vacuum density, followed by phase transition by Aether Wave Theory: it leads to vacuum "clumpiness", which can be observed like streaks of so called dark matter, which are analogous to foamy density fluctuations inside of condensing supercritical fluid.

    http://www.chem.leeds.ac.uk/People/CMR/images/scco24.jpg

  • 2 Thomas D May 30, 2008 1:04 PM

    This is depressing proof of ignorance on the part of Physical Review editors and referees and even the author. For a start MOND is not even relativistic, it doesn't reach the level of correctness in the Solar System that is required to explain the perihelion shift of Mercury, gravitational lensing by the Sun, and several other precision tests of GR. Why should we consider a precision experiment to 'test' a theory that is already ruled out multiple times?

    In order to make any sense you need a relativistic version of MOND, for example Bekenstein's tensor-vector-scalar theory, that behaves in a similar way for galactic rotation. This will typically have quite different predictions for the 'equinox' effect Ignatiev is hoping for - if indeed there is any effect at all in a properly formulated theory.

    Also, the main reason for considering that dark matter exists is *not* galaxy rotation curves. It is the existence and statistics of the large-scale structure of the Universe, galaxy clusters and superclusters, which cold dark matter fits very well but MOND completely fails with. The statement

    "all the phenomena associated with dark matter could be explained by a slight alteration in the laws known as modified Newtonian dynamics"

    is simply untrue with respect to clusters and large scale structure and I am surprised that a physics graduate could come out with this. Even MOND advocates agree that clusters require some sort of dark matter. Just call up Carlos Frenk in Durham and ask him why he thinks cold dark matter is necessary.

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