Official "Science News" Thread

[kladner]

Originally Posted by ewmayer

Rare Record of Chinese Classics Discovered: Muddy bamboo strips, dating from about 300 B.C., turn out to contain texts as important to China's history as ancient Greek or Latin texts are to the West.

They also could be compared to the Dead Sea Scrolls. It sounds like they have the same potential to upset commonly held notions.

[science_man_88]

Space-Time Loops May Explain Black Holes

Physics cannot describe what happens inside a black hole. There, current theories break down, and general relativity collides with quantum mechanics, creating what's called a singularity, or a point at which the equations spit out infinities

and don't even bother with newton it gives different densities to be an electron black hole versus a quark black hole etc.

[ewmayer]

"Physics cannot describe what happens inside a black hole."

Wrong.

[xilman]

Originally Posted by ewmayer

"Physics cannot describe what happens inside a black hole."

Wrong.

Correct, in at least two ways. (You're correct, that is.)

First, current mainstream physical theories predicts that the event horizon is not particularly unusual. A galactic mass BH has an event horizon located where the (classical, i.e. Einsteinian) theory says that the geometry is quite well described by Newtonian gravity. Some, more speculative, theories suggest that the event horizon may be the surface of a fuzz ball; others include the prediction that it's the location of a surface at the Planck temperature.

Second, it's a truism that physics describes essentially everything. Where current physical theories do no describe something properly or fully, the theory is either wrong or misunderstood.

[ewmayer]

More or less what I meant ... specifically:

There is no good reason not to believe that the classic Schwarzschild metric solution (and its extensions to e.g. rotating black holes) of the Einstein equations does not apply through the event horizon and until the spatial/energy-density scales get small enough to make quantum gravitational effects likely to be significant. (More on the latter shortly). Hawking's theory of quantum-mechanical blackbody radiation from black holes - unproven, but believed likely to be true - shows that non-negligible quantum effects may occur even at the event horizon, but note the time scales of said radiation to carry away an appreciable mass fraction of a multi-solar-mass-style classic BH is enormously large. Thus, as deep inside the BH, we have reason to believe that quantum effects are significant only at small-space/large-energy-density scales. Hawking's model implies radiation as a blackbody with temperature inversely proportional to the black hole's mass, i.e. the radiation becomes more intense as the BH mass gets smaller:

A black hole of one solar mass has a temperature of only 60 nanokelvin (60 billionths of a kelvin); in fact, such a black hole would absorb far more cosmic microwave background radiation than it emits. A black hole of 4.5 × 10^22 kg (about the mass of the Moon) would be in equilibrium at 2.7 kelvin, absorbing as much radiation as it emits. Yet smaller primordial black holes would emit more than they absorb, and thereby lose mass.[11]

The above Wikipedia article describes several QM-inspired models of what may occur in and around black holes (by "in" I mean inside the event horizon), thus it seems clear that physics *can* describe such things. Whether any current theories *do* is another issue - and due to "observational validation issues" here, it is unclear whether any kind of experimental validation is possible for such phenomena.

----------------------------

Related: I recall going to a seminar by one of my UMich math professors around 20 years ago. This professor had a special interest in the mathematics of various modifications/extensions to the Einstein equations; in the talk in question he described some topologically "interesting" solutions of the so-called Einstein-Yang-Mills equations. He gave the talk the rather bold title "Refutation of the No-Hair Hypothesis." I was apparently the only member of the audience-of-roughly-a-dozen who had a background more weighted toward physics than pure-maths, because there was general surprise and no small amount of consternation when I pointed out during the ensuing Q&A session that even if his theory were true, it implied no externally visible effects, i.e. was not subject to validation. (And thus was not in fact a refutation of Mr. Wheeler's famous no-hair hypothesis.)

Note that I intend no slight by this discourse - he was a good man and a fine teacher, but fundamentally a theoretical mathematician, not a physicist (nor even a mathematical physicist).

[xilman]

Originally Posted by ewmayer

shows that non-negligible quantum effects may occur even at the event horizon, but note the time scales of said radiation to carry away an appreciable mass fraction of a multi-solar-mass-style classic BH is enormously large. Thus, as deep inside the BH, we have reason to believe that quantum effects are significant only at small-space/large-energy-density scales. Hawking's model implies radiation as a blackbody with temperature inversely proportional to the black hole's mass, i.e. the radiation becomes more intense as the BH mass gets smaller:

The Planck temperature claim to which I alluded makes the point that anything radiated arbitrarily close to the event horizon is red-shifted by an arbitrarily large amount before it is seen by a distant observer. That is, the radiation is cooled by an arbitrarily large amount. The conclusion is that the temperature approaches the Planck temperature at the horizon to allow a distant observer to measure a non-zero temperature as Hawking predicts.

Fuzz balls are an entirely different member of the zoo.

[science_man_88]

Scientists find how 'obesity gene' makes people fat

Using a series of tests, a British-led research team said they had found that people with the variation not only had higher levels of the "hunger hormone" ghrelin in their blood but also increased sensitivity to the chemical in their brains.

[xilman]

Unexplained high power radio bursts

[ewmayer]

Originally Posted by xilman

Unexplained high power radio bursts

Apparently distant civilizations have talk-radio-demagoguery and Monday-morning-quarterbacking, too.

Whether this is proof of "intelligent life" is open to debate, there as here.

[bsquared]

http://news.yahoo.com/video/worlds-s...170700340.html

[xilman]

Mimicking cactus spines to produce a mechanism for separating oil and water.