"My god, it's empty of stars."

[unixronin]

I have a recollection of having read, some time back, an article in New Scientist which discussed the existence of intergalactic voids with regard to the opposing dark matter¹ and MOND/TeVeS theories.  The substance of the issue, with respect to voids, is that MOND/TeVeS theory allows for voids as large as the previously-known 200 million light-year Great Void, and even larger, although it predicts (not unreasonably) that larger and larger voids will become increasingly rare.  Dark matter theory, on the other hand, can accomodate the known Great Void, but predicts that it should be impossible for any such void to become significantly larger than that size.

This makes the recent discovery of such a void fully a billion light years in diameter, completely empty even of dark matter, a major problem for dark matter theory.  It should make for some interesting discussion.

[1]  And dark energy, and whatever the hitherto-unknown and so-far-unnamed fifth basic universal force is that the dark-matter theorists have found they had to invent to fully explain the dynamics of the Bullet Nebula using dark matter.

Update:

Looking back through my own past posts, I find that in fact the existence of large-scale structures was significant not to the question of cold-darm-matter vs. MOND/TeVeS, but rather to the question of a homogeneous universe (when cold dark matter is take into account) vs. a universe possessing fractal structure.  Lambda-CDM theory apparently requires that at scales not far beyond 200 million LY, the large-scale structure of the universe should smooth out and become homogeneous, and calls for the presence of dark matter in the voids.  Both the newly-discovered void and the Sloan Great Wall, assuming they are not observational artifacts (as apparently argued by the Lambda-CDM school), conflict with this prediction.  They are, however, completely in accordance with a fractal-structure model of the universe.

Comments

[smandal.livejournal.com]

I am not aware of the dark matter folks inventing a fifth force to make the Bullet Cluster data support Lambda-CDM (dark energy + cold dark matter) -- can you give a ref?

Also, dark energy shouldn't have any an effect on such a small scale.

[unixronin.livejournal.com]

Not right now, but I can see if I can dig one up tomorrow. The way New Scientist reported it, it was about like the Far Side cartoon of the scientists and the blackboard with the line "And then magic happens." No proposed mechanism, no proposed carrier, no rationalization for it in the Standard Model, just "Well, if there were a fifth elemental force that operated sort of like this, but only on dark matter, then the math would work."

And in the words of that cartoon, "I think you need to be a bit more specific here."

[smandal.livejournal.com]

The whole point of dark matter is that it's mass (so interacts gravitationally) but hardly otherwise (or only at higher energy).

A new fundamental force is not problematic per se if its consistent with particle experiment data, though adding it on top of dark matter is not very economical -- I agree that then something like MOND or TeVeS would become less un-interesting.

[unixronin.livejournal.com]

Checking back through older posts, I find that the post in which I was discussing having read in New Scientist that Lambda-CDM theorists found it necessary to postulate a fifth basic force in order to make observations of the Bullet Nebula match theory was posted on March 18 of this year (http://unixronin.livejournal.com/437177.html). This somewhat narrows down the original article source, and I tried to see if I could find the article on newscientist.com and look up the references there, but newscientist.com is apparently down for scheduled maintenance today. (I frequently seem to have difficulty logging in to it to access full articles anyway.)

I'll try to remember to check it again tomorrow.

[james-nicoll.livejournal.com]

You do know NS is the Weekly World News of science reporting, right? These are the same guys who published an excited story about a space drive which to work would have to violate things like conservation of momentum.

[unixronin.livejournal.com]

I think tarring them that badly for one bad article (however bad it was) is a bit unjust. Sure, that particular article stank like week-old dead fish, but it was an aberration for them, not business-as-usual.

(That said, New Scientist has drifted a long way from "hard science for the educated layman" towards "mass-market popular science" since I first began reading it in the mid-1970s.)

[james-nicoll.livejournal.com]

I think tarring them that badly for one bad article (however bad it was) is a bit unjust.

It's part of a general pattern of credulous sensationalism at NS. I try never to use anything that I have seen there without first tracking down the original papers, if they exist.