New Theory Challenges Need For Dark Matter

New submitter elsurexiste writes "An Italian Physicist came up with a strange way to explain anomalous galactic rotations without dark matter, instead relying on the gravitational effects of faraway matter. The article explains, 'Conceptually the idea makes little sense. Positioning gravitationally significant mass outside of the orbit of stars might draw them out into wider orbits, but it’s difficult to see why this would add to their orbital velocity. Drawing an object into a wider orbit should result in it taking longer to orbit the galaxy since it will have more circumference to cover. What we generally see in spiral galaxies is that the outer stars orbit the galaxy within much the same time period as more inward stars. But although the proposed mechanism seems a little implausible, what is remarkable about Carati’s claim is that the math apparently deliver galactic rotation curves that closely fit the observed values of at least four known galaxies. Indeed, the math delivers an extraordinarily close fit.' As usual, these are extraordinary claims that divert from the consensus, so keep a healthy skepticism. The paper is available at the arXiv (PDF)."

Comments

"Solves" one issue of dark matter only

[thegreatemu]

Disclaimer: I do experimental searches for dark matter for a living, so I may be biased in my judgement of these types of papers that crop up so often. There was a similar paper a few weeks ago from someone claiming that quantum vacuum polarization could account for dark matter PhysOrg link.

The issue with both of these explanations, is that they only address galactic rotation curves. Those are among the first and easiest to explain indications of the need for something like dark matter, but are not the strongest by a long shot. For instance, this guy's explanation can't explain things like the famous Bullet cluster , nor can they explain the evolution of structure formation or the spectrum of fluctuations in the cosmic microwave background which, in the field, are considered much stronger constraints.

The Cold Dark Matter (CDM) theory of cosmology fits all of the astrophysical measurements reasonably well, and has a nice tie-in to supersymmetric particle physics, which is one of the current leading theories. No one in the field will take any new theory seriously until it can reproduce ALL the phenomena at least as well as the current model (which of course is exactly how the scientific process is supposed to work!)

Re:Wow.

[jd]

Not sure about the summary, but the paper is extremely simple. I'll summarize it:

It is commonly assumed that galaxies are evenly distributed. This would mean that if you picked any galaxy at random, you could pick other galaxies whose gravitational pull totally balanced out the effect of the first one. So, overall, no distant galaxy would ever affect anything.

What is observed is that galaxies are NOT evenly distributed. There is, indeed, left-over gravitational pull. Provided the distribution of galaxies is self-similar (which is what they mean by "fractal", since "fractal" itself has no meaning here) AND a few other constraints are valid, THEN the left-over gravitational pull would be enough to explain the rotation of the stars and gasses within the galaxy. The author's analysis of the galaxies over a relatively nearby region of space suggests to him that the distribution is indeed self-similar.

(Summary off, analysis on)

Is this a new theory? As a replacement for Dark Matter, yes. In any other context, no. Shepherding moons/asteroids dominate our own solar system, creating a dynamic that would be utterly unstable without them. Shepherding galaxies and super-galaxies is a new one, but if the physics is observed in other systems then the physics must be considered sound. The only question I see here is whether the distribution of galaxies is indeed self-similar. If it isn't, the theory is wrong. If it is, then dark matter - as it is currently understood - must be wrong because you now have left-over gravity and you have to alter the dark matter theory to allow for it.

Doesn't the dark matter theory fit things well as it is? No it doesn't. Dwarf galaxies and globular clusters exhibit NONE of the signs assumed to indicate the presence of dark matter. Some don't have high-speed rotation at all. Dark matter theory cannot explain either of these and the usual answer is to say that dark matter "isn't uniform" without ever explaining why it should be missing only with certain classes of structure and not others. It's actually much easier to say that "excess" rotational velocity is a function of residual gravity and that where you have little residual gravity you have no excess rotational velocity. It is also entirely plausible to argue that "null points" are backwaters and that this explains why you get relatively few major galaxies appearing at such points but do get minor multi-stellar structures.