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Here’s an interesting one for the books. In the continuing debate over the widely-accepted cold-dark-matter theory, a new study of the dwarf galazies surrounding the Milky Way has found that their arrangement appears to simultaneously require and refute the presence of dark matter.
More exactly, the orbital dynamics of the dwarf galaxies are consistent with what would be predicted by the cold-dark-matter theory ... but their arrangement indicates that they were formed by collision with other galaxies, a mechanism that — according to dark matter theory’s predictions of the properties of dark matter — precludes them containing any dark matter.
“The fragments produced by such an event can form rotating dwarf galaxies,” Metz said. But there is an interesting catch to this crash theory, “theoretical calculations tell us that the satellites created cannot contain any dark matter.” This assumption, however, stands in contradiction to another observation. “The stars in the satellites we have observed are moving much faster than predicted by the Gravitational Law. If classical physics holds this can only be attributed to the presence of dark matter.”
Doubt has been shed on the cold dark matter theory before. This is the first time, however, that an observation has been found for which assuming dark matter creates a paradox. If the dark matter theory is assumed to be correct, then dark matter is the only explanation for their orbital dynamics, yet their arrangement precludes the possibility of dark matter being responsible for their orbital dynamics.
How to resolve this?
Or one must assume that some basic fundamental principles of physics have hitherto been incorrectly understood. “The only solution would be to reject Newton’s classical theory of gravitation,” adds Kroupa. “We probably live in a non-Newton universe. If this is true, then our observations could be explained without dark matter.” Such approaches are finding support amongst other research teams in Europe, too.
Mordechai Milgrom’s MOND — Modified Newtonian Dynamics — theory has long been proposed as an alternate explanation for the observations used as evidence for cold dark matter. But there are hard scientific reasons why MOND cannot be correct if the rest of our understanding of the Universe is correct — specifically, MOND is not consistent, and cannot be made consistent, with relativity. A greatly more complex approach to the problem is Jacob Bekenstein’s TeVeS, tensor-vector-scalar gravity. TeVeS, unlike MOND, is consistent with relativity; but it has been argued that TeVeS cannot simultaneously account for both galactic dynamics and gravitational lensing. Both TeVeS and dark-matter theory are also unable to completely explain the Bullet Cluster observations without postulating additional factors; TeVeS requires the presence of dark matter as well to fully explain the observations, while dark matter theorists have found it necessary to invoke not only both dark matter and dark energy but a possible fifth basic force in order to fully explain them. A related theory, STVG (scalar-tensor-vector gravity), takes a slightly different approach from TeVeS, and is able to successfully explain galaxy rotation curves, galaxy cluster mass profiles, gravitational lensing, the Bullet Cluster observations, and the accelerating expansion of the Universe without requiring the presence of either dark matter or dark energy. Another very recent theory (to which I’m unable to find a reference right now), based on M-theory, posits that gravitons are weakly bound to the brane and can drift off of it and diffuse away into the bulk, resulting in a net gravitational force that follows the Newtonian inverse-square law at “normal” distances, is slightly stronger at huge distances as required by MOND and TeVeS to produce the effects which CDM theory explains via dark matter, and on truly vast scales becomes weaker than inverse-square again, in order to explain universal expansion without dark energy.
We don’t know yet which, if any, of these theories may be correct, and new theories are being proposed all the time. However, with this finding, particularly if it can be confirmed, the holes in cold dark matter theory are beginning to become larger and more evident.
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As noted above, one of the problems I have with CDM is that it doesn't point us to new information. As CDM theorists are fond of saying about competing theories, CDM theory is purely descriptive. It adds no new information. It just says "These anomalous explanations could be explained if 90% of the universe were made of magic invisible stuff that behaves in this defined way. We can't tell you what it is or why it should behave like that, but we need it to do so. Oh, and we need this other magic repulsive force, too, but we have no explanation for why that should exist either, we just need it to exist and behave like this to make the math work." The public declarations I have seen from some CDM theorists that studying any other explanation is a complete waste of time lead me to feel that CDM theory is beginning to actively obstruct studying the questions. To touch on other recent discussions, it seems to be verging dangerously close to "A wizard did it."
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I am not ready to be picking a loser either. Simplicity is a plus with any theory, even if it is not perfectly represented by all the data, as long as it increases our understanding and gives us new directions to look. I don't have anywhere near your specific knowledge of the subject. What I have read (and understand) implies that CDM theory is not the monster that it appears to you as. We are still wrapping our heads around the implications of several theories. I don't think we understand what our suppositions imply well enough to throw CDM out, yet.
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