Lights Out for Dark Matter Claim?

Last November, data from a balloon-borne particle detector circling the South Pole revealed a dramatic excess of high-energy particles from space--a possible sign of dark matter, the mysterious substance whose gravity seems to hold our galaxy together. But satellite data reported today stick a pin in that claim. Researchers working with NASA's orbiting Fermi Gamma-ray Space Telescope say they do not see the purported excess. The observations don't disprove the existence of dark matter, but they put a damper on hopes that physicists had already begun to see it.

For decades, astrophysicists have known that galaxies don't contain enough ordinary matter to keep themselves from whirling apart. So they assume that some form of dark matter pervades each galaxy and provides the extra gravity needed to keep it whole. But physicists have never directly observed particles of dark matter, which are supposed to interact very weakly with ordinary matter.

One way to spot these particles might be to look to the skies. Some popular theoretical models suggest that if two lingering particles of dark matter collide, they should annihilate to create an ordinary particle and an antiparticle, such as an electron and a positron, which can be observed. Those particles should emerge with a definite energy determined by the mass of the dark energy particles, leading to a sharp peak in the energy spectrum of electrons and positrons from space.

That's why the results from the NASA-funded Advanced Thin Ionization Calorimeter (ATIC) balloon experiment sparked interest last fall (Science, 21 November 2008, p. 1173). ATIC observed that the number of electrons and positrons hitting Earth peaked sharply between about 300 billion and 800 billion electron volts. That dramatic excess appeared to be consistent with dark-matter annihilations.

But the new satellite measurements, from the $690 million Fermi telescope, don't reveal such an excess. Launched in June and designed to detect high-energy photons called gamma rays, Fermi is actually a sophisticated particle detector that serves just as well to detect electrons and positrons. It detected more than 4 million electrons and positrons from August through January--compared with ATIC's thousands--and Fermi researchers precisely measured the particles' energy spectrum.

The data do not reproduce ATIC's peak, Fermi researchers announced today at the annual April Meeting of the American Physical Society in Denver, Colorado. "We have much better statistics and can tell you that we do not see so extreme a feature" as was seen by the balloon-borne experiment, says Steven Ritz, a Fermi team member from NASA's Goddard Space Flight Center in Greenbelt, Maryland.

However, ATIC researchers aren't willing to concede that the Fermi result rules theirs out. Fermi has much poorer energy resolution, says John Wefel, an astrophysicist at Louisiana State University in Baton Rouge and leader of the ATIC team. That would turn any peak into a much less dramatic broad bump, and the Fermi spectrum does seem to show some sort of a gentle upwelling. "The difference comes down to something in the instrumentation," Wefel says.

Even if the Fermi results put the kibosh on hopes that dark matter has already been detected in a clean and simple way, there's still a chance physicists have seen subtler signs of it, says Neal Weiner, a theorist at New York University. He notes that the Italian PAMELA satellite last year reported an increase in the ratio of positrons to electrons at lower energies, which could hint at some manifestation of dark matter. And, as Wefel notes, the Fermi spectrum seems to include more high-energy electrons than expected, which could also be evidence of the mysterious substance.

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“The reality is nobody knows why galaxy rotation curves are wrong, and the idea it can be patched with a DM hypothesis has all the hallmarks of an epicycle hunt. A more straightforward statement would be that our present gravity theories are not confirmed on galactic scales. “

There are LOTS of ways dark matter can be hiding. Interstellar gas, unobserved black holes, and large objects obscured by gas are just three quick ways to add DM. There is NO competing gravitational theory with the general theory of relativity, which has been experimentally confirmed many times and never refuted.

“Since they also aren't confirm on lots of other scales and in lots of other ways, it is at least as likely our present theory of gravity is wrong - only approximately correct at some scales, just like Newton's was - as that there is any “DM” to look for.”

That's a possibility—but when doesn't the General Theory of Relativity work?

False on both scores. Structures seen in CMB are compatible with just about anything. There are zero observations confirming DM. Meanwhile, here is the train wreck piled up against gravity -

(1) the pioneer spacecraft aren't where they are supposed to be. Extra net force direction sunward on both, constant acceleration with a discrepancy growing with time, for both spacecraft, traveling in different directions.

(2) galactic rotation curves are wrong. Way wrong. Solid rotation with the core area and then constant velocity once past EM-connectivity breakdown is is a better description of the actual velocity curve.

(3) the masses calculated for galactic center objects based on immediate red and blue shift speed measures for matter closest to the center, and based on the hypothesis that stars in the whole central region are gravitationally bound, come out different. Factor of 2 or more different.

(4) DM clumps posited to fix the rotation curves are more diffuse than the galaxies, but theoretically experience gravity but not EM interaction. Gravity is contractive, EM repulsive, on galactic scales. Material that interacts by only the first should be more clumped not less.

(5) DM profile needed for the distant rotation curve and for the central region are different. Also, *any* observed rotation profile is compatible with the present theory of gravity on some, sufficiently bizarre, posited DM distribution. The hypothesis immunizes the theory against observational falsification, a distinct methodological no-no.

(6) the closest thing to an extra-AU scale observation confirming gravitational waves predicted by the current theory of gravity, is the spin-down of pulsars, but dozens of other energy-loss processes can readily predict those observations, which have plenty of parameter wiggle room.

(7) direct search for gravitational waves have been fruitless. The detectors have increased by over 10 orders of magnitude in sensitivity over the last 20 years, but despite endless promises that the next 2-3 orders would see stuff, they haven't seen squat.

(8) gravitational lensing effects typically cited as great large scale confirmation of gravity would be seen for any plausible gravity theory. Not "tuned".

(9) projections based on gravity for things like redshift to distance appear to show very old galaxies as soon as observations can be made. The expected imbalance toward exclusively younger types in deep fields was not seen.

(10) DM projections to cosmic rather than galactic scales are wrong again with the sign of the error in the opposite direction, requiring the "dark energy" hypothesis to patch the non-existent extra attraction the DM hypothesis hypothesizes.

(11) gravity is un-quantizable. The answers to every question on small scales comes back "infinity", which is wrong empirically.

(12) gravity is mathematically inconsistent with QM, our most successful physical theory by miles. The underlying topologies and signatures don't even match. Even Witten has admitted as much. The epicycle hunt required to stuff them into the same theory now needs 10^500 different possible physical theories with no explanation for why ours occurs.

(13) the theory of gravity is really pretty, mathematically. It was created by a famous man and learned as a great accomplishment by several generations of physicists. These are all common features of theories adhered to stubbornly long after observation has left them in the dust.

If this theory were associated with anyone less than Einstein, we'd have thrown it already.

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