Saturday, December 19, 2009

Searching for Unusual Hay in a Haystack: The Case of CDMS

Over the past two weeks, rumors have swirled around the web that the CDMS collaboration had discovered particles of "dark matter". [I have not yet written a promised post on dark matter, but there is this.] It all started with a single blog post which contained "facts", such as the statement that there was a paper in press at the journal Nature, which turned out to be false. One very connected person tweeted about the post, and it spread like wildfire. Soon the Nature editor sent the blogger a snarky letter denying the claim, which the blogger posted. Others speculated that the Nature editor was just trying to throw them off track. The next day the Nature editor posted a comment on the blog apologizing for the snarky nature of the letter, but again refuting the claims. Still rumors shot around the net about what result there might be.

So there was much anticipation Thursday when the CDMS collaboration gave two simultaneous talks announcing their results.
I watched a live stream of one of them. It proceeded in a halting fashion from the strain of the web traffic. Then, when the speaker got to the point of announcing their results, the stream froze for ten solid minutes. When it recovered, it zipped straight to her conclusions (how many of you were assuming the speaker was male--come on admit it), and I was left to guess a number of the details. But the bottom line is this: they saw 2 events with a background of 0.8. What does that mean, you ask?

The experiment looked for a very rare signal: that a particle of dark matter, which rarely interacts with anything, leaves a small ripple in the detector. The detector is located at the bottom of a mine to shield it from most cosmic rays. But there are still background events: interactions in the detector from particles which come from radioactive elements in the rock or particles which somehow survive going through hundreds of meters of rock. There are telltale signatures of dark matter particles (such as the energy and timing of the event) which help distinguish them from background particles, but occasionally a background particle mimics those signatures by chance. In the CDMS experiment, they calculate that over two years of running, that happened on average 0.8 times ( it took heroic efforts to keep it this small) . Maybe this helps: if they ran for 20 years with the same detector, i.e. 10 times longer, then they'd expect it to happen 8 times.

Now they saw 2 events. So what is the chance that those events are really signals of dark matter particles? Well, it is easier to ask "what is the chance they are background events?". If you ran for 20 years, what is the chance that 2 of the background events happened in the first two years. Using something called the Poisson distribution, they find that there is about a 1/4 chance those 2 events are both just background events. That's not a strong signal. As good as their efforts were at reducing backgrounds, it was not enough. If there were no dark matter particles and you ran the experiment for 20 years and divided them into ten two year periods, about two or three of those ten periods would happen to have 2 background events in them.

Still, if the events do turn out to be really from dark matter, it will begin to explain one of the great mysteries of science. So we await future experiments with more signal and less background.


Saturday, November 28, 2009

Why the rising star of Sarah Palin troubles us

This post is directed at fans of Sarah Palin (if there are any amongst my readers!). It may help you to understand why the rest of us are so appalled at her success. I've tried to think objectively about why I find her rising star disturbing.

It is not because she is "folksy", which I suspect is a big aspect of her appeal. Nor does it have anything to do with her being a working mom--many of us admire the ability to balance work and family. No, it is because of her overt incompetence and shallowness. After having just lived through the worst presidency of modern times, that of Geroge W. Bush, where decisions were made on a political basis without regard for competence ("heck of a job Brownie") and as if the world were black and white, it is disturbing that another politician with very limited knowledge and ideological blinders could gain such popularity. It is also disheartening to have such a polarizing figure rise in prominence now. Whatever you think of President Obama, he has made an effort to restore thoughtful dialogue to our national debates. We can disagree, but let us not disagree with the gleeful venom of Sarah Palin.

Whatever you think about Sarah Palin's politics, or her ability to raise children while working, or whatever you perceive as positive, please recognize that she is not fit to be President of the United States. I don't know if she really believes what she says, or she is just an opportunist, but the scariest thing is that her ambitions seem to greatly exceed her abilities.


Monday, November 16, 2009

Trip to Hawaii Big Island

I attended a conference in Hawaii held jointly by an American and a Japanese physics society. Where else are you going to hold it? It was an incredible trip. This post is about the stuff I did before, after and during breaks in the conference. Here's the list of places I went on the Big Island:

• Waipio valley
• Akaka falls
• Kiluea caldera & lava fields
• Inside the Keck observatory atop Mauna Kea
• Kohala waterfall hike
• Underwater in a sub near Kailua-Kona

I was staying in Waikaloa Village on the west coast of the Big Island. Here is a sunset from a restaurant there:

Here is a dolphin in their lagoon:

A colleague and I drove around the island past gorgeous Waipio valley,

stopped at Akaka falls, the tallest in Hawaii,

and Halema'uma'u crater (big circle) inside the Kiluea caldera (huge circle that goes beyond the edge of the photo):

The sulfur dioxide streaming up with the steam made the air quality poor, and several areas were shut down. Nothing grows in the caldera. Lava flows underneath it via a lava tube to the sea. We went on the lava field at night, and you can make out the lava in the distance (as close as one is allowed to go):

Then several of us took a trip to the top of Mauna Kea, which from sea floor to summit is the tallest mountain in the world. Here are the twin domes of the Keck observatory, the most powerful in the world. Their main mirrors are 10m (30ft) in diameter! (the mountain way in the distance is Haleakala on Maui)

We were honored to receive a tour from a friend of a friend of the inside. This is the secondary mirror of one of the telescopes. You can see the dome opening in the background.

The main mirror is hard to see. It is the honeycomb structure just to the left of the blue girders (the pipes which seem to be on it are actually a reflection):

Then I went on a waterfall hike (the water was cold!)

and finally a submarine trip off the coast of Kailua-Kona:


Tuesday, August 4, 2009


Mere words cannot describe this. Watch it.

[thanks N.J.]


Sunday, May 17, 2009

The Two Cultures

Fifty years ago, C. P. Snow lamented in his famous lecture, The Two Cultures, that there was a rift in understanding  between the sciences and the humanities.  He noted that ignorance of the laws of thermodynamics is akin to never having read a work of Shakespeare, and that such scientific illiteracy could prove harmful to society.  How can our leaders solve our problems if they don't understand them?

So it was with great interest that I went last Saturday (9 May) to the New York Academy of Sciences, at the top of the world, to attended a conference exploring the current state of the Two Cultures and what could be done about it.   There were many fascinating people there.

The 192 year old NY Academy of Sciences now resides in the gleaming new building at 7 World Trade Center.  Forty stories up, there is a panoramic view of Manhattan, and an overlook on the unimproved hole of ground zero.  

Actually, one feels the presence of 9/11 as soon as one steps in the elevator.  Each wall of the elevator is roughly polished metal, so that one's reflection is distorted  as it is bounced back and forth, and one is surrounded by ghostly images.

There were two main topics discussed: the nature of the divide between scientists and nonscientists (both in the humanities and the general public), and what one could do to bridge the gap.
E. O. Wilson, the famous biologist, described his idea of consilience, and argued that the walls between fields were illusions because of the interdisciplinary bridges which already exist.  He is a hardcore reductionist who believes that complex sociological behavior can be mapped to chemical reactions in the brain.  On the other hand, the historian Ann Blair argued that having walls between fields was important so they can flourish independently.

But most of the day was spent discussing how to bridge the gap between science and the larger society (such as you, dear reader).   There was a panel on "How to more effectively communicate science issues to the public," with the executive producer of Nova, Paula Apsell, and the host of Science Friday, Ira Flatow.   There was a panel on science and politics with the founders of Science Debate 2008.  And there was a concluding keynote address by Segway inventor, Dean Kamen.  I have to say that I was impressed with his organization, FIRST, which sponsors a robot competition that makes science cool for kids.  In just 20 years, it has gone from a handful of people, to something which won't fit in the Houston Astrodome!

Science is  increasingly important for our society.  For democracy to work in such an environment, it is essential that the average citizen be at least somewhat scientifically literate.  For example, everyone should have some vague idea why a perpetual motion machine can't work (thermodynamics says, "there ain't no free lunch").  So I hope we can all work on bridges of understanding between ourselves.


Tuesday, May 5, 2009

Report from the 'April meeting'

Scientific conferences have personalities. They shift locations and take on the color of the locale, but the canvass of a given conference is the same. I write this from a hotel room in Denver, CO, site of my society's annual meeting. It does not matter that it is in Denver, or that it's May, it is still the 'April meeting'.  The April Meeting is not a cozy specialized meeting, nor is it a zoo that the largest meetings become. It covers just the subjects of particle physics, nuclear physics and astrophysics. So it is a chimera of the small and the large, the specialized and the very broad.

There is the same rhythm of expansive plenary talks in darkened ballrooms, and frenzied cryptic parallel session talks in small rooms which either are empty or overfull. There are talks on science and society. There are all the organizational meetings. There are the booths and posters. Yet at 1400 people it feels sparse.

The most exciting results this year are from the Fermi Gamma-ray Space Telescope (formerly called GLAST). Launched in June 2008, it is already changing our view of the high-energy sky. Its main instrument, the Large Area Telescope, or LAT, has made a precise measurement of ultra-high energy electrons and positrons. A previous experiment had shown indications of an excess in number of particles detected, which was hard to explain with known physics. LAT has shown that that "bump" was likely just a statistical fluctuation. Alas, this is what usually happens--most coincidences are actually just coincidences. LAT also showed that there is some new source of high-energy positrons out there, which will surely launch a thousand papers.

Fun anecdote: One of the talks was given by a senior physicist  (he received the Nobel prize for work done in 1964). He admitted that he had a habit of showing data before the large collaboration of which he is a part was ready to release it. After his talk, someone asked a question about the composition of the cosmic rays his collaboration had detected. He excitedly jumped to a slide he'd prepared because he "knew someone would ask that question". He explained that the collaboration would release the data soon, after further analysis, but he'd show the figure now. When the figure popped up there was a big "X" in place of the plot. He was astonished and confused and wondered aloud how it could have happened. Then one of his collaborators raised her hand and admitted to have hacked into his talk. She said, "we knew you might show this but we're not ready to release it yet".   He laughed at being thwarted.


Monday, February 16, 2009

Evolution in a Nutshell

Sorry I haven't been writing much lately.  My personal life has been evolving.  More on that later.  But I would be remiss if I didn't have some kind of post for Charles Darwin's 200th birthday, which was on February 12th, 2009.  To celebrate, let me give you evolution in a nutshell.  I want to take a slightly different tack than most other treatments.  I want to argue that Darwin's central brilliant idea is so close to a tautology that it can't be wrong.

There are two things which determine whether a creature reproduces: the traits it was born with and the environment it lives in.  This is true even if you believe (which I don't) that a deity has an active hand in forming the creature, or in affecting its environment.  Now, given a bunch of creatures in that same environment, some will have inborn traits that make it more likely they will survive and reproduce, and some will have traits which make it less likely they will survive and reproduce.  For example, if there are a bunch of feral cats in Minnesota, those with heavy fur are more likely to survive than those with very light fur.  But if they are in Mexico, those with light fur are more likely to survive (all other things being equal).

Well, Darwin's central idea is Natural Selection by Survival of the Fittest.  Those creatures which are most suited to the given environment are the ones which are most likely survive.  It is almost tautological, because what else can "fittest" mean than "most likely to survive?"   And what does the "selection" entail other than "having survived"?  Nothing.  Darwin simply pointed out the obvious.  If you have a population of creatures, the ones best suited for the environment are the ones most likely to survive and reproduce.   And how can you tell which creature are the ones best suited for the environment?  Because they are the ones which survived!

So, then,  what's the big deal if it has to be true, almost by definition, that the "fittest" are "selected"?    The answer is that this simple mechanism, which as we have shown has to be true almost by definition, is enough to explain the evolution of life.  How did drug-resistant bacteria arise?  There were some bacteria in the huge population of bacteria which were resistant, and they took over in the patient because they were the fittest (they survived the drugs).  How did polar bears get such thick fur? Because their ancestors who had thinner fur did not survive as well.

Some people are fine with the above until one gets to major changes in species or complicated organs like a wing.  It would take me too long to delve into all possible considerations here, but the central answer is TIME.  Creatures have been roaming the Earth for a very long time, so even very slow change can have a dramatic effect.  Suppose each generation of creatures changes in some attribute by just 0.01%.  Then after 10,000 generations, they could have changed that attribute completely.  Even to take the human value for a generation, 20 years, that would take only 200,000 years.  That may sound  like a lot of time, but life has been on the planet for almost 4 billion years, which is 20,000 times 200,000 years.

So in summary, there has been a selection process going on for millions of generations of life, picking out creatures who are fittest for their environment. That process can explain the diversity of life we see now and in the past, and that is why, despite being essentially a tautology, Darwin's theory of evolution is the cornerstone of biology.  

Happy Birthday Darwin!


Thursday, January 8, 2009

Inauguration Ticket Essay Contest

The Obama campaign is giving away 10 tickets to the Presidential Inauguration via an essay contest phrased as, "what does the inauguration mean to you?"   Here is my entry:

Exclamation Point
Once in a great while, a nation alters its course through history, casts off its shackles of fear, and turns resolutely to face the challenges of the past, present and future.  As its people wake from a nightmare of illogic, indifference and intolerance, they assemble, shoulder to shoulder, ready to overcome old divisions and new obstacles, with reason, determination and humanity.  Celebrating their power to chart a new course, they gather as one, having reached an exclamation point. Yes we can!

[photo: March on Washington (Program), 08/28/1963; Bayard Rustin Papers; John F. Kennedy Library; National Archives and Records Administration.]