Clearly seeing nothing

By Daniel Holz | May 4, 2010 3:02 pm

The Xenon collaboration posted a paper today on the arXiv with their latest results. No, they haven’t seen dark matter. This is a preliminary data set, and the main point of the paper is to show that the detector is working as planned, and that the background (read: anything other than dark matter) is at a remarkably low level. This bodes well for their future constraints.

Xenon dark matter detectorThe New York Times has a brief article on the results, with one of the more amusing lines I’ve seen: “…the clarity with which they saw nothing spurred hopes that such experiments are approaching the rigor and sensitivity necessary to detect the elusive gravitational glue of the cosmos.” This is perfectly accurate: they have developed a way to see nothing very, very clearly. What this means is that, if they ever actually see anything, we’ll know it’s not nothing. And this is precisely the challenge with dark matter detection. Part of the point of these latest Xenon results is that they are saying the DAMA results (which claim a detection, and which have been quite controversial) are even more likely to be nothing. In this case, clearly seeing nothing is really something.

  • Brian137

    Speechless about nothing. Thanx, though, for the update, which is most welcome and certainly merits some insightful comments. Maybe the witty and perspicacious one-liner from the Times has exhausted the subject. I think I’ll go eat dinner while I ponder this.

  • Ixnu

    These (lack of?) results immediately reminded me of the The Michelson–Morley experiment.

  • pheldespat

    They haven’t seen dark matter because there is no dark matter.

  • thomas

    pheldespat, what’s going on with the gravitational lensing in the bullet cluster?

  • Bee

    “There’s nothing I hate more than nothing
    Nothing keeps me up at night
    I toss and turn over nothing
    Nothing could cause a great BIG fight

    Hey — what’s the matter?”
    -Edie Brickell, Nothing


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  • Bjoern

    @Ixnu: There is one clear difference to the Michelson-Morley experiment: in the latter one, the magnitude of the expected effect was quite clear, and it was also clear in advance that the measurement apparatus should easily be able to “see” an effect of the expected size. With dark matter, on the other hand, it is not clear at all how big the effect should be which we would like to observe, and hence we can’t know in advance if our measurement apparatus is sensitive enough!

  • Brian137

    Ixnu and pheldespat,

    If you google a Xenon100 or comparable website containing graphs of regions excluded by current experiments superimposed on regions predicted by various theories of supersymmetry, you will see that our current experiments bite off only a small portion of the favored part of the parameter space. But, of course, dark matter particles need not be supersymmetric and may not even interact via the weak force at all. Xenon100 may be looking in a completely unrealistic place, but I find their search exciting just on the off-chance that they might strike gold.

    Then there is the fact that some of the smartest people on the planet have spent decades trying to imagine alternative explanations of the best available data. One little stipulation, though – the explanation must be consistent with what by this time has become quite a large set of observations.

    One possibility for such an alternative seemed to to lie in some modifications of gravity or other aspects of Newtonian dynamics. Accumulating evidence, such as that mentioned by thomas in post #4 above from the Bullet Cluster, became harder and harder for MOG/MOND to account for, so theorists came up with a deluxe version called TeVeS. Now, however, TeVeS also seems to be in trouble as per this link:
    If either of you can think of a consistent alternative to dark matter, we will all be fascinated, perhaps a bit jealous, and, in fact, almost reverent.

  • Jeremy Chapman

    While the XENON100 results are encouraging, there is more politics in it than meets the eye. For example, the limit that they show makes assumptions about the light yield of low energy nuclear recoils that is not consistent with other experiments. XENON100 is a well made detector, but does not perform quite as well as advertised.

  • Sean

    Juan Collar, one of our previous guest-bloggers, has pointed out some sketchy kinematical assumptions in the Xenon100 paper.

    This isn’t the only source I’ve heard this from. I suspect Jeremy is right, and the real limits aren’t quite as restrictive.

  • Eugene


    Juan and Dan’s comment is pretty harsh.

  • Phil

    The second version of their comment is worth looking at (a cryptic footnote not so cryptic anymore).
    Is there a dead fish rotting inside the XENON100 shield?

  • Thomas Larsson

    @7 Bjoern: According to Wikipedia,neither Michelson nor Morley seem to have been convinced by their experiments – Michelson et al repeated it as late as 1929. So even if you know that their 1887 should should easily have seen ether wind, maybe the verdict was not as obvious to the active physicists of the time.

  • Brian137

    Well, a bit of a spat seems to have broken out between the Xenon100 and the CoGeNT and DAMA collaborations:

    Three different targets, three different technologies. Maybe the Xenon group should restrict their conclusions to the ramifications of the results for the Xenon collaboration’s own investigation rather than claiming that those results invalidate the results from DAMA and CoGeNT. There may be factors involved that we do not understand. Let’s enter terra incognita with a bit of humility. That was my opinion before the response from Juan Collar and others. I have high hopes for all three experiments, even though I am somewhat frustrated watching DAMA pile up the sigmas without addressing concerns about the source of the apparent signal.

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  • SpearMarktheSecond

    Well, the `natural’ scale for weakly interacting dark matter has been bypassed already, at least for masses near the weak bosons. Weakly interacting dark matter that is related to SUSY has lots of epicycles to tune, and 5 or so more orders of magnitude in sensitivity are really needed for direct dark matter experiments to singlehandedly eliminate the SUSY/Weak/DM conjecture… in absence of assistance from the LHC.

    In the days of Michelson-Morley, there was no industry of theorists inventing alternatives, and no response of opportunistic experimentalists to keep arguing for new initiatives to test the alternate theories. Hard to say if there is anything wrong with the current situation… recall that neutrino oscillations/mass have evolved in an amazingly huge parameter space, with all kinds of productive interplay between the theory and experimental industrial complexes, that has lead to fairly interesting new physics and perhaps the only clear hint of beyond-the-Standard-Model physics.

    The same might happen with direct dark matter, or, it could be a wild goose chase. But it would be a lot more fun if Rita Bernabei, Juan Collar, Elena Aprile, etc, had better senses of history and humor.

  • Peter Fred

    What ultimately killed the hunt for the ether was a decent, believable theory which was
    Einstein’s theory of Special Relativity. We think we have no decent theory to explain the need for the dark matter and so the hunt for it goes on and on. But we do have a decent, believable theory that in Einstein’s word will make the dark matter “superfluous” . It comes from considering possibility that the heat emanating from mass attracts other mass.
    I have five experiments which show that when a test mass is placed between a hot source and and a cold source the weight of the test mass will change by 1.9%, -4.9%, 8.9%, 9.6% and 16%. They suggest that it is the sun’s heat and not its mass that attracts the planets. Or that it is the earth’s heat and not its mass that attracts the moon. To see these experiments go to . Just because I am an amateur (read crack pot) that does not invalidate the results of these experiments.
    It was the experiment of the amateur Leon Foucault that finally proved the the earth rotated on its axis. It is time to consider the possibility that we have been duped by a misleading artifact due to the close association between mass and luminosity for the past 300 years just as the Geocentrists were duped for 1500 years by the artifact of the earth rotating on its axis which misled them into thinking that that all the objects in the sky rotate around the earth in a 24 hour period.

  • Brian137

    It may be the cold more than the heat. I have observed a similar, though perhaps even more pronounced, phenomenon with leftovers placed in my refrigerator. I have also suspected that this difference in weight may be related to luminosity, but I have had difficulty checking whether the light stays on when the door is closed. I thought to leave my cat in there for a while and check the dilation of her pupils afterward, but when I opened the door, she spat at me and left in a really foul mood.

  • Peter Fred

    Bryan137 @ “It may be the cold more than the heat”
    I found this to be true in my experiments. In Fig. 3 of my paper at where I observe a 4.9% decrease in weight of test mass, the temperature of the test mass only dropped a several tenths of a degree Celsius while at the same time its weight changed by 54 gm. This is the largest gram-change of weight that I observed in all of the five experiments. In the other four experiments, where I observed an increase in weight, and hence an increase in temperature of the test mass, the temperature of the test mass had to be increased by 300 to 400 degrees Celsius. This is a favorable outcome if one is interested in harnessing the gravitational force which is a near impossibility if mass rather than heat mediates the gravitational force.

  • Brian137

    My cat seemed both colder and less attracted until later on when she warmed up and apparently got hungry.

  • Alex Ross

    “For the listener, who listens in the snow,
    And, nothing himself, beholds
    Nothing that is not there and the nothing that is.”

    – Wallace Stevens

  • Nano Drv

    I want you peple to know you make me feel like a complete moron, I hope you are happy.
    Why can’t you figure out a way to get oil which is lighter than water to flow to the top of a sea, accumulate and jump into oil tankers instead of spreading all over the gulf?
    Why can’t you explain to people that dispersants are just more polution?
    There has to be a way to explain that it’s all just so many $1000 bills!!


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