WIMPy Physics. [Built on Facts]
Some of you may have heard in the news recently about a possible detection of the particles that may make up dark matter:
Detectors in the mine, part of the Cryogenic Dark Matter Search experiment, were tripped recently by what might be weakly interacting massive particles, or WIMPs. WIMPs are among the most popular candidates for dark matter, the invisible material that scientists think makes up more than 80 percent of the mass in the universe. Recently detectors in the mine recorded two hits with "characteristics consistent with those expected from WIMPs," according to a statement posted on the Cryogenic Dark Matter Search Web site. There is a one-in-four chance, however, that the particles detected are not dark matter but ordinary subatomic particles such as neutrons, the team cautions.
Long story short, thanks to careful observations of the motions of stars within galaxies, we know that there's a lot more mass distributed within and around galaxies than can be accounted for by the stars themselves. After decades of work, most of the obvious possibilities have been eliminated. The main suspect left standing is very weakly interacting particles. Because their interactions are so weak, they're very difficult to detect. Numerous experiments are in progress searching for these particles, but because the universe is also filled with lots of particles that do strongly interact it's difficult to tease the tiny signal from the occasional WIMP from the background noise. We don't know much about WIMPs though since we've never seen them, and the possible properties they might have could easily render them invisible to these less-sensitive detectors.
But this current iteration of experimentation has detected two possible candidates for WIMP interaction events. The expected background count (ie, false positives) is about 0.6. So it's a close-run thing, and both events could well be illusory.
The research team's statistical methods are very solid. They deliberately set up their calibrations and detection criteria before the data collection period in order to have a "double blind" test - making sure to avoid the possibility of biasing the calibration criteria to include specific events. Though it hasn't been publicized as much, there are in fact four events that might plausibly be WIMP detection, where two of the events fall just outside the rejection criteria. Including them would mean 4 events of an expected ~1.5, though this is not scientifically acceptable since selection bias in the criteria is no longer definitely eliminated. (Widening the criteria farther doesn't buy any more events until the criteria are really implausibly wide.) Still, it's an interesting sign.
So on the Mythbuster scale of Confirmed/Plausible/Busted, I'd rate this detection event Plausible. The team conducting the research stresses that this is only a hopeful first step and not anything close to conclusive. Further data runs, including new data runs with better equipment in even better shielded locations, will help move the WIMP detection into the Confirmed or Busted category.
It would really nice to be able to bag a WIMP. The dark matter mystery has been an open question for a long time, and finally putting it to bed will be a tremendous victory.
UPDATE: Ethan of Starts with a Bang (a very excellent physics blog) has a scathing and well-argued contrary take that you should read. He thinks 2 events out of 0.6 is a load of bull. And he's got a point. But while a bracing dunk in cold water is always good for science, in this case I think the CDMS data is a little more suggestive than he gives it credit. "Plausible" in my Mythbuster ranking means just what is does on the show - just maybe, given further testing. In either case both of us are in complete agreement with the CDMS experimenters: "We estimate that there is about a one in four chance to have seen two backgrounds events, so we can make no claim to have discovered WIMPs."
"A Tantalizing Hint of Dark Matter?" No. [Starts With A Bang]
One of the reasons I write here on ScienceBlogs is because of our associations with the New York Times, a journalistic news source that I'm proud of on most days.
Today is not one of those days.
It isn't just the Times, either, the BBC is busy botching this story, so is the Telegraph, the Daily Mail, and pretty much everyone else, except for TG Daily, which got it right.
If you go down to the bottom of Soudan Mine in Minnesota, you'll see an usual site for a mine: a group of giant physics experiments! Why? At the bottom of mineshafts, you have up to hundreds of feet of Earth protecting you from all the particles and radiation coming from the Sun, from space, and from terrestrial sources. This way, when you're looking for a very rare physical event, you can be confident that what you're seeing isn't contaminated by other, mundane processes.
Perhaps the most important experiment going on down there is the Cryogenic Dark Matter Search (CDMS), which searches for Dark Matter particles by hoping that they bounce off of their detectors (above). When a dark matter particle bounces off, you can detect the recoil of other particles.
But there's a problem here: other things bounce off your detector, too, despite your best attempts at shielding it. You cannot stop neutrinos, you cannot stop radioactive particles inside the Earth from decaying, and you cannot stop some cosmic rays (like muons) from getting through. These all hit your detector also, and create what we call "background" events. You can calculate what your expected background is; anything you see above that is likely your signal.
So what you do is reduce your background (which is bad) as much as you can. You try to catch all the muons and block all the radioactivity, and you find a way to try and tell light, fast-moving neutrinos apart from heavy, slow-moving WIMPs. At CDMS, they got their background down so far that, over two years of looking for these dark matter particles, they expected about one background event.
They saw two. What's the appropriate response to that, Matt Foley?
That's right, when you expect to see one and you see two, it doesn't tell you anything conclusive. On Monday, I went through a hypothetical situation about CDMS, and now here's the revised version -- as best as I can reconstruct it -- based on CDMS' released results.
Looking for dark matter is like playing a one-in-a-million lottery. There are two interesting ways to play it for you: you can either buy a whole bunch of different tickets for one drawing, which gives you the best chance of winning exactly once, or you can buy tickets one-at-a-time for a bunch of successive lotteries.
CDMS, based on how long they waited (two years) and what their detector size was (30 hockey-puck-sized detectors), had the equivalent of about 900,000 tickets. If you could buy 900,000 tickets and you bought them all at once, you'd have a 10% chance of not winning and a 90% chance of winning once. CDMS can't do that; each particle at each moment is an entirely different lottery drawing. When you work out the math for that, you find that:
- 40.66% of the time, after two years, you observe 0 events.
- 36.59% of the time, after two years, you observe 1 event.
- 16.47% of the time, after two years, you observe 2 events.
- 4.95% of the time, after two years, you observe 3 events.
- 1.11% of the time, after two years, you observe 4 events.
- 0.22% of the time, after two years, you observe 5+ events.
That's what you expect to see from your background alone. The fact that CDMS saw two events? That doesn't even count as a "hint" for dark matter; you would've needed to have seen four event to scientifically count as a hint, and you would've needed about 8 events to have some very good evidence.
The scientists who released these results are good, and they said as much in their release (emphasis is mine):
We estimate that there is about a one in four chance to have seen two
backgrounds events, so we can make no claim to have discovered WIMPs.
That's right. What we saw? It's probably background, and there's no evidence at all that what we saw is anything more than that.
This doesn't mean dark matter doesn't exist, and it doesn't mean that dark matter isn't made of WIMPs either. But it means that we haven't detected it yet, either, and stating that these two events mean anything other than this is just unscientific wishful thinking.
100 Billion, 3 Degrees [Casaubon's Book]
You've got to give our Secretary of State credit - she knows how to make an entrance. Show up at the door with 100 billion and people can't look away. Of course, she didn't promise 100 billion from the US, but to raise it collectively with some unspecified other folk by 2020, but still, it is an impressive number, and it isn't wasn't a bad way to get attention. That doesn't change the fact that the rich world is still trying to blame the poor, or that the climate talks are still failing.
Meanwhile, a new UN report released confirms what we already knew - that everything presently on the table is totally insufficient:
Later in the day, reporters obtained a confidential UN analysis stating that current emissions-cut pledges now being proposed at Copenhagen would lead to a temperature rise this century of 3 degrees C (5.4 F), surpassing the 2 degree C (3.6 F) target that negotiators set as an acceptable limit to global warming. The report by the UN Climate Change Secretariat said the current emissions reductions offered by the U.S., the European Union, China, Japan, Australia, and other nations would mean pouring up to 4 billion tons more carbon dioxide into the atmosphere by 2020 than the level needed to hold temperature increases to 2 C. That increased amount of CO2, coupled with significant levels of carbon dioxide emitted in later decades, would mean that atmospheric concentrations of CO2 could rise from the current 387 parts per million to roughly 550 parts per million in a century or so. Those concentrations would likely lead to a 3 C rise, the UN report said.
Look, any reduction in C02 levels is good. Abd 100 billion dollars to developing countries to preserve rainforest and replace obsolete technologies is a good idea - assuming, of course, we actually pay it (we've reneged before) and that such a coalition could be formed (not at all clear). But the central issue is very much not on the table - dealing with climate change as it actually exists. And it probably won't ever be - because the kind of cuts that are required are simply inconsistent with growing economies and the fantasy of eternal wealth.
Of course, so is global warming. But enough people care more about the short term than the long - what none of the countries can do is deal with the painful reality - that our economic system is on the table. Clinton can make quite an entrance - but it is the exits that will matter in the end, and those aren't looking so good.
Sharon
Privacy vs knowledge [Applied Statistics]
Wired reports a great new opportunity to make money online by suing internet companies for revealing the data:
An in-the-closet lesbian mother is suing Netflix for privacy invasion, alleging the movie rental company made it possible for her to be outed when it disclosed insufficiently anonymous information about nearly half-a-million customers as part of its million contest to improve its recommendation system.
I'm not sure whether the litigators have read this particular section of the Netflix prize rules:
To prevent certain inferences being drawn about the Netflix customer base, some of the rating data for some customers in the training and qualifying sets have been deliberately perturbed in one or more of the following ways: deleting ratings; inserting alternative ratings and dates; and modifying rating dates.
So yes, you can match a set of reviews with someone else, but how will you know that it's really a person and not a random coincidence? The Netflix dataset contains almost half a million anonymous users, and there is plenty of opportunity for a false positive match (an example of which is the birthday paradox). Netflix learned from AOL's data release disaster, which resulted in a few people getting fired.
But this theme is important. Many internet companies provide free services in return for the ability to employ user data for profit. Andrew Parker looked at which companies make profit out of user data. Usually, the data is never given away, but just used to make other people's lives easier. Let's say that you bookmark a particular page - others won't see that you've done it directly, but they will see indirectly that there are people that find that page worthy of saving. Because it's worthy, it can be listed on the first page of search results.
A more problematic area is medicine. Wired reports that there is a market out there for medical records, and that anonymity protection isn't very secure.
Keeping medical data public would allow massive advances in medicine. For example, the Personal Genomes project seeks to analyze a number of volunteers in a lot of detail (see, for example, Steven Pinker's medical record). If a few million people did that, we'd know so much more about disease, risks, factors affecting it, effectiveness of drugs, diet, the effects of genome.
One-sided disclosure gets many people worried - their insurance rates might go up, they might not get a job. It would help if everyone was doing that: nobody feels well being naked when others wear swimsuits.
But we should also ask ourselves as a society - what is insurance? Is insurance a protection against uncontrollable risk or is it an instrument of equality? Is genome our destiny or an uncontrollable risk?
Some previous posts on this topic: EU data protection guidelines, Privacy vs Transparency.
Blogosauruses and bad bad bad bad science TV [Neuron Culture]
I wanted to rig up an electrified fence around the falsehood to keep the producers from sneaking back to it
Carl Zimmer on just how damned bad much science TV is. I've not advised programs, as Carl has, but the times I've seen subjects I'd written about covered on TV -- DBS for depression, and Williams syndrome, which I'd written about for the Times Mag and both of which were subsequently covered by 60 MInutes -- the TV results were truly appalling. And that was the hallowed supposedly best-of TV 60 Minutes.
It's nice when you see it done better. Too bad it's so rare.
The 10xs the Price=10xs Crappier Rule Hits the Healthcare Bill [Casaubon's Book]
A while back I argued that there's a rule - when the US spends a whole lot more and uses a whole lot more than everyone else, what we usually get back isn't just less than everyone else gets for the same buck, it is dramatically worse. I called it my rule of 10 times the price = 10 times crappier. It applies to an astonishing range of American actions - from our military budget and its results to the oil we invest in agriculture.
Back then, one of my examples was healthcare, which I pointed out was at least 4 times crappier (and at least 10xs or more for those who can't get it at all, an increasingly large percentage of the populace) for more than double the price of the average European nation's health insurance.
Well, we seem to be well on the way to achieving the 10-10 rule with the current healthcare bill. Without a public option, its function will be to force many people to give private industry their money, without dramatically lowering prices. This is an enormous boon for the healthcare industry, who get billions of dollars without actually reforming their practices, and a boon for a percentage of the population that can afford healthcare but can't get it because of pre-existing conditions. It is an enormous sucky hell for the large number of people who can't afford healthcare - particularly the struggling folks just over the edge for subsidies.
So the question comes around - does one support this piece of shit legislation or not? The argument in favor is this - if healthcare fails again, it will be a long, long time before it comes around again. With more than 2 out of every 5 Americans with no healthcare, and Medicare expected to be broke in 7 years, we can't afford to wait another decade. On the other hand, this is so obviously screws so many people and benefits exactly the wrong ones.
I'm not convinced at all that once in place, it will be reformed. On the other hand, I am convinced that if we don't say yes, a lot more medical bankrupcies and early deaths will result. In the long term, I fear that the coming breaking of the Medicare budget will result in the casting off of baby boomer seniors into the arms of the private insurers as well, with this as a precedent.
My first choice would be to lock the entire American Congress in with a selection of the angrier, larger and healthier friends and family members of millions of people who can't get decent healthcare, and wait until a better bill emerges. Given that that's not going to happen, I'm caught between two visions - the middle class family that was almost making it until the shitty healthcare bill forced them to buy insurance, and the person with a medical diagnosis who is skipping dinner to pay for her medications. I don't like what this does to either of them, but I'm going with the impoverished person with a medical diagnosis. So I guess I'm for it, assuming arranging for the big men with borrowed canes to change the minds of our government isn't a choice.
Sharon
Friday Flotsam: Undersea volcanism revisited and a Mayon update [Eruptions]
Finals day for me, so I'll be grading grading grading ... but first, a little news:
The May 2009 eruption of West Mata. Image courtesy of NSF and NOAA.
- I covered it in May, but the popular press is now all over the West Mata undersea eruption - mostly thanks to the media boost that AGU can give you. It is worth checking out the new articles on the eruption in the Lau Basin near the Marianas, mostly because of the nifty video of the eruption. In the video, you can clearly see both an explosive component of the eruption as gas "burps" out through a cooled carapace and a more effusive pillow lava component coming down the right side of the vent. I've been scratching my head at exactly how you have explosive volcanism at 4,000 feet / 1,200 meters below the ocean surface - the pressure should be too high - but this lava must be full of volatiles to produce an eruption like this. There is tons of information on this eruption on the Vents Program website.
- More lava, more ash, more signs of a bigger eruption at Mayon in the Philippines. The volcano is now racking up hundreds of earthquakes a day and PHIVOLCS is saying that a
"major eruption" could be coming in the next week and may move the volcano up to Level 4 status. However, it hasn't stopped people from already returning to their farms on the slopes of the volcano - which is leading to more forced evacuations and a curfew in Albay Province.
Stress is an old, old companion [Neuron Culture]
A nice short piece on "The Prehistory of Stress" by Matt Ford at Ars Technica (newly designed site worth checking out).
I have heard people say, on multiple occasions, that they think stress is a modern, Western phenomenon. While the psychological phenomenon known as stress has only had a formal name for just over 80 years, knowing when it was first suffered by our ancestors is a daunting task. Was life really better in the past? Is stress an entirely modern phenomenon?
Using modern forensic technology and a decidedly modern understanding of biochemistry, researchers from The University of Western Ontario have taken a look at stress levels in pre-Colombian Peru; their findings are summarized in an upcoming edition of the Journal of Archaeological Science. They found that stress has plagued humanity for at least 1500 years. The researchers were able to get the dead to give up not only their final secrets, but an understanding of their life for a few years before they shuffled off this mortal coil.
When humans get stressed, our bodies release a chemical known as cortisol, which appears in our blood, our urine, and even our hair. Of those three, hair is only one stands the test of over 1000 years of time, and provides a short history of the last years that its owner had. By examining hair strands from 10 individuals at five different dig sites in Peru, the researchers were able to determine how stressed people were, using the levels of cortisol in segments of their hair.
The team found that the time just before the individuals passed away was a stressful one--not an overly surprising result. But the majority of the individuals had lived through stressful periods in the years leading up to their death, suggesting that stress was a regular part of life in the pre-modern period. Perhaps this can be filed under "the more things change, the more they stay the same."
This shouldn't be a surprise. Yet, like Ford, I am surprised at how many people assume that life in earlier times was less stressful. This colors our view of our typical reactions to stress -- withdrawal, aggression -- which we tend to see as anomalous and define as maladaptive. But as the orchid or sensitivity hypothesis suggests, it makes much more sense to view these reactions as adaptive in many situations and maladaptive in other situations. Their value depends on their context. Quitting school and doing a youth gang, for instance, can be a pretty adaptive move considered from a local context -- one's prospects in the immediate neighborhood and social structure -- but a lousy move considered from a broader societal context. And all sorts of behaviors that are considered maladaptive within the particular constraints and values of our culture make sense when viewed with more sensitivity to human history.
The paper, by Emily Webb and others at the University of Western Ontario, is at the Journal of Archeological Science. You can find some other write-ups here.
Tag Heuer to drop Tiger ads in some markets (Reuters)
CHICAGO, Dec. 18, 2009 (Reuters) -- Swiss watchmaker Tag Heuer said on Friday it would not use Tiger Woods, who has admitted to marital infidelity, in its advertising in "certain markets" to respect the golfer's desire for privacy. ... > read full story
California gay marriage trial takes national stage (Reuters)
SAN FRANCISCO, Dec. 18, 2009 (Reuters) -- The biggest U.S. gay rights battle next year is brewing in a California federal court as raucous fights over same-sex marriage in state legislatures and at state ballot boxes subside. ... > read full story