Archive for March, 2009

Congratulations to Matt Der and Anna Parker!

Monday, March 30th, 2009

The 2009 Goldwater Scholarships were announced today.  I’m pleased to announce that two University of Richmond students were recognized: Matt Der was awarded a scholarship, and Anna Parker received an honorable mention.  In both cases, the honor is extremely well-deserved.  If you know these two students, please make sure to congratulate them.

Correlation is not causation

Tuesday, March 10th, 2009

although it is correlated with it.

Correlation vs causation

(I saw this on the Freakonomics blog.)

The Economist should know better

Monday, March 9th, 2009

I generally think of the Economist as having excellent science reporting, but I have to admit that I only read it sporadically these days, so maybe my information is out of date.  This article on some recent experiments in the foundations of quantum mechanics is way, way below the standard I’d expect from them.

The article claims that

Now two groups of physicists, working independently, have demonstrated that nature is indeed real when unobserved.

Your skepticism level should spike whenever you read an article claiming that experimental results have  confirmed some deep-sounding-yet-vague philosophical idea.

When the article gets down to details, it says a bunch of things that are just wrong:

In the 1990s a physicist called Lucien Hardy proposed a thought experiment that makes nonsense of the famous interaction between matter and antimatter€”that when a particle meets its antiparticle, the pair always annihilate one another in a burst of energy. Dr Hardy's scheme left open the possibility that in some cases when their interaction is not observed a particle and an antiparticle could interact with one another and survive.

This makes no sense.  It’s quite common for a particle and its antiparticle to interact without annihilating each other.  There’s nothing paradoxical about that.

Later on, we have

The stunning result, though, was that in some places the number of photons was actually less than zero. Fewer than zero particles being present usually means that you have antiparticles instead. But there is no such thing as an antiphoton (photons are their own antiparticles, and are pure energy in any case), so that cannot apply here.

Where to begin?  First, I don’t believe the statement that the researchers measured “less than zero” (or even “fewer than zero”) photons.  Did they have a photomultiplier tube that clicked -17 times? The actual articles by the two experimental groups contain no claims of anything that could be described in this way.

Second, the idea that fewer than zero particles means antiparticles isn’t really true.  There was a theory due to Dirac a long time ago in which positrons (the antiparticles of electrons) were regarded as “holes” that were sort of like negative numbers of electrons, but that theory doesn’t really fit into modern particle physics in any nice way as far as I know.

Finally, can we please ban the phrase “photons are pure energy”?  There’s no meaningful sense in which that’s true.

Now I know that science journalists have a tough job, particularly when reporting on very abstract things such as quantum physics.  I have no objection at all to their simplifying things to make them clearer.  But the above statements aren’t simplifications; they’re just wrong.

These experimental results seem to be a confirmation of a “paradox” in which joint probabilities of two quantities don’t obey the rules that you’d expect classically. Like other similar paradoxes, it’s a nice example of the ways in which quantum mechanics is “spooky,” but I don’t see how the results say anything new about whether reality exists when you’re not looking (whatever that even means).

There’s a common problem in journalism about the foundations of quantum mechanics.  As my friend John Baez said a long time ago,

Newspapers tend to report the results of these fundamentals-of-QM experiments as if they were shocking and inexplicable threats to known physics. It’s gotten to the point where whenever I read the introduction to one of these articles, I close my eyes and predict what the reported results will be, and I’m always right. The results are always consistent with simply taking quantum mechanics at face value.

The Economist article goes pretty far (if not all the way) down this route.  It takes a clever and interesting experimental result and blows it up into something much spookier than it is. The result does follow precisely the pattern Baez describes: it’s exactly what standard quantum mechanics predicted all along.

Please note that I’m not criticizing the experimenters here: as far as I can tell, they’ve done a difficult and very interesting experiment and described their results accurately.  I don’t see anything in their papers that would justify the silly interpretation placed on it by the Economist.

By the way, I got the Baez quote above from a web page by Matt McIrvin which quotes Baez.  I can’t find this quote on Baez’s own web site, not that I looked all that hard.  Matt has great things to say about the interpretation of quantum mechanics, by the way.  If you’re at all interested in this subject, please read this page in addion to — or better yet instead of — the many silly things that have been written on the subject.  John Baez has said a bunch of really smart things on the subject in various newsgroup posts over the years as well.  He collected some of them here, but as far as I know he hasn’t written up anything more polished.

Who’s the audience?

Sunday, March 8th, 2009

 My friend Walter makes the following very sensible point about my recent article on evolution and the second law of thermodynamics:

The paper about thermodynamics and evolution is neat. Though of course it will not convince any creationists as their argument was never truly science based anyway.

This is certainly true.  I don’t harbor any hope that even a single creationist will read the article and see the error of his ways.   So then who is this article written for, and what’s the point of writing it? There are actually a few answers.

1. The people who are most likely to read the article are people with an interest in the teaching of physics.  It’ll appear in the American Journal of Physics, which is kind of a funny journal: it publishes some articles explicitly about physics education research (comparing different instructional techniques, etc.), but its main emphasis is articles about physics, written in a way that are of interest to physics educators. The main reason I wrote the article is because I think that it raises some interesting physics points that educators may find useful.  In particular, I like the fact that you can use back-of-the-envelope estimates using standard undergraduate statistical mechanics techniques to get an answer to this interesting question.  I wish I’d worked all this out before the last time I taught statistical mechanics: I would have liked to use it in my class.  I expect I’ll get another chance.  Anyway, I hope that other statistical mechanics instructors find it useful.

2. My article is a followup to an earlier article, which I really liked but which had an unfortunate error in it. I wanted to set the record straight.

3.  Despite Walter’s correct assertion that I’m not going to win any creationist hearts and minds with this article, I do hope it fits in in a tiny way to the ongoing arguments on this subject.  Walter’s quite right that fundamentally the creationists’ argument is non-scientific, but on the other hand creationists do frequently try to make scientific (or scientific-seeming) arguments in support of their beliefs.  In particular, the claim that there is a conflict between evolution and the second law is a scientific claim, and the right way to refute it is scientifically.

When creationists make scientific claims, they like to use the traditional signs of scientific authority to bolster these claims.  For instance, they prominently refer to the academic degrees and positions held by their advocates.  Moreover, they use the peer-reviewed literature, and prominently note that they’re doing so.  I’m not criticizing them for doing this: peer review (for all its flaws) is the main way that scientific quality is evaluated.  But this does suggest that, when a claim is made in the creationism/evolution debates that has the form of a scientific argument but is scientifically incorrect, it’s worthwhile to have an authoritative, peer-reviewed refutation of it. When a creationist tries to use the authority of the peer-reviewed literature to make an incorrect point, a scientist can fight fire with fire.

Another tactic used by creationists (and other people who reject well-established science) is to claim that scientists are unwilling to even look at arguments that go against the standard orthodoxy.  That’s another reason it’s worthwhile to examine the creationist argument and take it seriously enough to show why it’s wrong.

The intended audience is not the already-convinced creationist, of course, but the innocent bystander who may not know much about the subject and who hasn’t made up his mind.  I don’t expect such a person to read the article (although if they’ve had enough undergraduate-level physics, it’d be great if they did); I want scientists and science teachers who are talking to such people to be able to say, “Yes, scientists have looked carefully at this argument, taken it seriously, and shown why it’s incorrect.”

Good luck to Kepler!

Sunday, March 8th, 2009

NASA successfully launched the Kepler satellite, which will spend 3-4 years surveying nearby stars to look for Earthlike planets.  We’ve discovered lots of giant planets so far, but we know relatively little about how common smaller planets like ours are.  Assuming that life elsewhere is most likely to have evolved in environments similar to our own (a reasonable guess, although it’s important to bear in mind that we don’t really know it’s right), this is obviously a really important piece of information to acquire.

Congratulations to Alicia Soderberg

Thursday, March 5th, 2009

Alicia Soderberg is the winner of the 2009 Annie Jump Cannon award.  This very prestigious award is given by the American Astronomical Society to a female astronomer, at most 5 years post-Ph.D., for “outstanding research and promise for future research.”

I taught Alicia when she was an undergraduate at Bates College.  In fact, I think I was nominally the advisor for her senior thesis or something.  I say “nominally,” because I really had little or nothing to do with it: her thesis work was with a group at Harvard, and she  really worked with them, not me.   (Even so, I’m a bit embarrassed that I can’t remember for sure whether I was her advisor: I don’t think that there are any other students about whom I’m unsure whether I was  their research advisor!)

By the way, if you don’t know who Annie Jump Cannon was, you should read about her.  She did very important work in astronomy, figuring out the classification of stars that is still used today, at a time when women were largely excluded from science. Despite the importance of hr work, she was denied full recognition, only receiving a proper academic appointment very late in her career.

McCain tweets about astronomy

Thursday, March 5th, 2009

This news is a few days old, but in case you haven’t heard, John McCain has apparently been making fun of various earmarks in the current spending  bill on his Twitter feed.  One recent tweet:

$2 million "for the promotion of astronomy" in Hawaii – because nothing says new jobs for average Americans like investing in astronomy.

I agree that that earmarks are a lousy way to allocate funding.  But it really bothers me that complaints about earmarks so often take the form of contemptuous mocking of science.  For the record, astronomy jobs are jobs, and astronomy is a significant industry in Hawaii.  Yes, the average American doesn’t work in the astronomy industry, but the average American doesn’t work in, say, road construction either. 

This post from the Cosmic Variance blog (a very good science blog, by the way) says it all much better than I can.

Accepted

Sunday, March 1st, 2009

Two papers I submitted a while ago were accepted for publication by the American Journal of Physics this week, within minutes of each other as a matter of fact.  To be precise, they were “conditionally accepted,” meaning that they’ve successfully passed the review by external referees and the science content been deemed acceptable.  There’s a further review by the editors for style, clarity, etc., before they’re  finally accepted.  Because AJP is a journal with a pedagogical slant, they place a heavy emphasis on clarity, which is probably why they have this “conditional acceptance” stage.

Both of these are less technical than the usual research paper: they’re intended for readers who know some physics but are not necessarily specialists in any particular field.  The first one requires a bit of knowledge of relativity (students who took my Physics 479 course should be fine) , and the second one requires just undergraduate-level thermodynamics and statistical mechanics.

The first article is on the correct interpretation to place on the observed redshifts of galaxies in the expanding Universe.  I blogged about it when we originally submitted it.  These redshifts are usually described as being due to the “stretching of space,” but David Hogg and I argue that this conceptual model is misleading.  We claim that, contrary to what you often see in introductory textbooks,  it’s correct to think of the redshift as being due to a plain old Doppler shift.

Here’s the revised version of the paper.  It  doesn’t differ all that much from the one we originally submitted, although some aspects of the argument are expanded and clarified a bit in response to the referees’ comments.

The second article is on the relationship between entropy and the second law of thermodynamics.  It’s a response to a very nice paper by Daniel Styer, which attempts to show quantitatively that the entropy production due to sunlight is more than enough to account for the entropy reduction required for biological evolution (contrary to claims often made by creationists).  The original article had a serious gap in it: it depended on an assumption that was unjustified and, I argue, almost certainly wrong.  My paper presents an argument that doesn’t depend on that assumption.  The new argument shows quite rigorously that there is no conflict between evolution and the second law.

I blogged about the original Styer article and about my response a while back.  Here’s the revised version of the paper.  Thanks to the referees, I think the new version is much clearer than the original.  It’s also much longer.  I was thinking of the original as just a comment on Styer’s earlier paper, but the new version reads more like a stand-alone article.