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Our future, our universe, and other weighty topics

Monday, October 20, 2014

New Results Consistent with Dark Matter, and Also Astrology

Some excitement has been raised recently about a scientific study involving solar x-rays. The popular press has been gushing forth with statements like this: “British scientists believe that they may have finally found the first direct evidence of dark matter.” But such statements are exaggerations.

The new study does not give direct evidence for dark matter. Direct evidence for a new type of particle is found at places like the Large Hadron Collider, which produced evidence for the Higgs boson particle. The new study was something completely different, a study of solar x-rays. The authors detected a seasonal variation in solar x-rays, one that is anomalous. As we normally think of the sun, it is something that goes about its business without the slightest knowledge of earthly seasons – so how could there be such a seasonal variation?

sun face
Sun face: another type of solar weirdness (credit: NASA)

There are a variety of possible explanations that the authors can think of, which are listed in Table 4 at the back of their paper. The explanations include solar wind charge exchange, “galactic background, local bubble,” residual soft proton flux, keV electron flux, Earth aldebo, and Compton-Getting effect/X-ray dipole. But the authors seem to prefer a different explanation – that their observations are caused by a type of undiscovered particle called axions. Their suggestion is that the sun may be producing these axions, that they may be interacting with our planet's magnetic field, and that this may be the explanation for the seasonal variability.

It's the same old story we see again and again these days. First, scientists make a modest statement, which in this case is the statement made in the scientific paper, which merely says that “potential axion signatures” have been found. Then science writers (eager to announce something important that gets more web hits) inflate this into something much bigger, in this case “the first direct evidence of dark matter.” For one thing, the new study does not provide direct evidence for any type of matter, either dark or normal, because it is a study of energy not matter (X-rays being a form of energy). For another thing, as I mentioned above there are quite a few alternate ways of explaining the observations without assuming the existence of axions.

Moreover, even if axions do exist, that does not confirm the theory that dark matter is a key component of the universe. Axions are merely a candidate dark matter particle. If we knew that the sun produced some axions, that still would not tell us whether dark matter plays a major role in the universe, as we still wouldn't know about how much of a relation there is between dark matter and axions, how many axions there are, how much dark matter there is, and so forth.

The scientists say, “We have discovered a seasonal signal in this X-ray background, which has no conventional explanation, but is consistent with the discovery of axions.” The phrase “consistent with” means little. Here are four levels of scientific assertion, from weakest to strongest:

X is consistent with Y. This means very little. It does not mean that Y is true, nor does it necessarily imply that Y is probably true. A hundred and one weird conspiracy theories are consistent with the assassination of John Kennedy, but it doesn't mean that any of them are true or probably true.

X suggests Y. This is a stronger statement, but basically all that it says is that X brings to mind Y, without asserting Y's likelihood. Lots of things suggest other things that aren't really there, as when you look at a cloud in the sky and see a face.

X is evidence for Y. This is a still stronger statement, which pretty much indicates that Y is likely. But since evidence can be misleading, it still leaves the door open that Y may not be true.

X proves Y. This is the strongest assertion, which asserts that Y is definitely true.

I may note that while the new X-ray observations may be consistent with dark matter or axions, they are also consistent with something radically different: astrology! The authors have provided evidence suggesting a weird unexplained connection between the sun and the seasons. I can imagine an astrologer's reaction: why, of course, they're all connected along with the zodiac and your birth sign, just as we astrologers have been saying for centuries. Don't get me wrong: I am not a believer in astrology. I merely mention this to point out that it means quite little to say “X is consistent with Y,” because X may also may be consistent with a hundred and one other things you don't want to believe in or never thought of.

As you can probably figure out, I am still skeptical about dark matter. I regard it as a possibility, but do not think its likelihood has been demonstrated. One of the reasons I am skeptical is the severe problem of reconciling dark matter theory with observations of dwarf galaxies, as discussed here and here. Another reason I remain skeptical is that scientists keep changing their story about dark matter. Six days ago an article on space.com said, “Scientists have found that the Milky Way galaxy holds half as much dark matter...as scientists had previously thought.” Beware of a claim when someone keeps changing his story. If someone knocked on your door one day offering to sell you a jewel that he claimed was worth 2000 dollars, you wouldn't exactly have confidence in him if he appeared the next day claiming the jewel was actually worth 1000 dollars.