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

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.

Boltzmann brains

New Scientist for August 18-24 contains an article talking about Boltzmann brains and the nature of the Universe.  (The concept of the Boltzmann brain is basically this:  We know elementary particles are constantly popping in and out of existence from quantum vacuum fluctuations.  Occasionally, entire atoms pop into existence in this way.  The more complex a construct, the lower the probability of its spontaneous appearance.  Theoretically, given a sufficiently large space and a sufficiently long time, quantum fluctuations should cause complete functioning consciousnesses able to observe the Universe to spontaneously pop into being.)  Much of the thread of the article seems to center around discussion of how crucial it is that Boltzmann brains never outnumber physical human observers, because if that happened we wouldn't be typical of the Universe, and everything we know might go poof.

Oh, boy.  There's that old anthropic bugbear raising its head again.  Let us suppose that tomorrow, some theorist irrefutably proves that, 10^{10^30} years from now, Boltzmann brains will dominate the Universe.  Would his proof cause the universe as we know it to suddenly disappear in a flash of logic?  I rather doubt it.  (In fact, were we able to somehow prove that Boltzmann brains becoming the majority obeservers of the Universe would cause the end of existence as we know it, it would logically follow that, at least for now, such quantum observers do not outnumber us.)  Does it even MATTER whether we are typical observers of the Universe, or whether our little corner of it is typical?  Again, I rather doubt it.  Nothing that happens to the Universe in the deep future can possibly affect the demonstrable fact that right now, we and our little hospitable corner of the Universe exist.

I propose that we will never fully understand the Universe, so long as our theories about the nature of the Universe are unconsciously built atop a foundation that says it is necessary we remain somehow significant to the Universe, even if only by virtue of being a typically representative sample of it.  I roll to disbelieve that the Universe as a whole gives a blind tinker's damn (figuratively speaking, of course) whether we exist or not.

This, I think, is modern science's version of arguing about how many angels can dance on the head of a pin.