New research both proves and disproves ... wait, what?

[unixronin]

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.

Comments

Re: bah. stupid 4300-character comment limit again. (Part 2)

[unixronin.livejournal.com]

Frankly, I'm also bothered by the idea that CDM theory requires 75% to 90% of the entire universe to be made of what amounts to "magic invisible stuff whose existence and nature we can't explain." It strains credulity, and smacks far to much of the Far Side cartoon where the middle of the blackboard reads "And then magic happens", with a group of scientists standing around and the caption "I think you need to be a bit more specific here."

I'll place a little more trust in CDM theory when the theorists comes up with some actual evidence for the existence of dark matter, or at least comes up with some plausible and logically consistent explanation of what dark matter and dark energy are, why they should exist, and most importantly, why they should behave as CDM requires that they do. But so far, they haven't. It's handwavium. Not that the non-Newtonian gravitational theories aren't also handwavium to varying extents, though TeVeS and STVG seem at least to be built on a sound mathematical footing; but the non-Newtonian gravity theories say "We have these anomalous observations, here's a possible theory to explain them," while CDM says "We have these anomalous observations, here's a theory that explains them, oh and by the way all those other theories are bunkum because they don't have a mechanism", skipping over the inconvenient fact that the last time I heard, CDM theory doesn't have one either. (And for that matter, the weakly-bound-graviton theory — to which I'd post a link if I could find it again — does propose a single, simple, plausible mechanism underlying the observed gravitational anomalies, and if correct would make both dark matter and dark energy unnecessary.)

I'm not positing that any of the non-Newtonian gravitational theories is necessarily correct either (though the weakly-bound-graviton theory does have an appealing elegance from the viewpoint of Ockham's razor). We simply don't know enough yet to be declaring a "winner". It bothers me the way CDM theory insists that it's the One True Way and all other theories are flawed, but then when flaws (or possible flaws) in CDM theory are pointed out, such as its own lack of any proposed causal explanation, the answer too often seems to amount to "Pay no attention to the man behind the curtain." It particularly bothers me when I have heard CDM theorists say that even considering any possible explanation other than CDM is a complete waste of time. It betrays a closed mind that I don't believe is conducive to an objective approach to the problem.

I'm not ruling out CDM. I simply feel that CDM has flaws that are too often being simply ignored or wallpapered over, and that it has thus far failed to convince me. I think it's too early in the race yet to be putting all our money on one horse.