Saturday, July 31, 2010

A cool application and more travel

Apologies for the long break between posts.  It's been an incredibly hectic summer, and I'm about to go on a last big trip before the school year starts (and I get to teach honors intro mechanics to ~ 90 frosh - should be exciting, at least).

Before I go, I wanted to point out a very cool application of micromachining and computing power.  There are many consumer electronic devices now that contain within them a little 3-axis accelerometer made by micromachining techniques, like this one.  The basic gadget consists of a micromachined "test mass" (typically a block of Si) suspended on (silicon) springs.  When the whole device is accelerated, the test mass "lags behind" because of its inertia, just as you get pushed back into the seat of your car when the car accelerates forward.  Through (often) capacitive sensing, the displacement of the test mass can be transduced into a voltage that the chip then outputs.  If the displacement can be detected along three axes, voila, you have a 3-axis accelerometer.  This is the widget that tells the Nintendo Wii how you've been swinging the controller, and it tells iPhones and other similar toys how to orient their displays.  With added sophistication, it's also possible to make micromachined gyroscopes.  They aren't true gyros that spin.  Rather, they're micromachined resonators (like tuning forks of particular shapes), and rotation leads to Coriolis forces that twist the resonator in a way that can be detected.  (For Wii aficionados, that is how the "Wii Motion Plus" works.)  Then you can get angular accelerations, too.

What is the point of this discussion?  Well, some people at Microsoft Research had a great insight.  You can put a sensor like this on a digital camera.  If the acceleration data is logged when a picture is snapped, then it is possible to retroactively unblur photos (at least, pictures that were blurry because the camera was moving).  This is the slickest thing I've seen in a while!     

Thursday, July 22, 2010

Why there has been no Carl Sagan or Brian Greene of condensed matter physics

It's impossible to be a condensed matter physicist that cares about outreach and scientific literacy, and not think about why condensed matter physics has taken such a back seat, comparatively, in the popularization of science.  It is easy to argue that condensed matter physics has had more direct impact on the daily lives of people living in modern, technological societies than any other branch of physics (we could get into an argument about the relative impacts of the transistor and the laser, but I think the CM folks would win).  So, how come there are specials and miniseries on PBS and Discovery Channel about string theory, the LHC, cosmology, and astrophysics with considerable regularity, people like Stephen Hawking, Brian Greene and Neil DeGrasse Tyson show up on The Daily Show, and the closest condensed matter gets to the public consciousness is a BBC special from several years ago about the Schon scandal?  Is it just that there is no charismatic, telegenic champion of the cause?  I think it's more than that.

First, there is the issue of profundity.  High energy physics makes an obvious play toward people's desire for answers to Big Questions.  What is mass?  What is everything made out of?  How many dimensions are there?  How did the Universe begin, and how will it end?  Likewise, astrophysics talks about the history of the entire Universe, the birth and death of stars, the origin of galaxies, and literally heaven-shaking events like gamma ray bursts.  Condensed matter physics has a much tougher sell.  In some ways, CM is the physics of the everyday - it's the reason water is wet, metals are shiny, diamond is transparent and sparkly, and the stuff in sand can be used to make quasimagical boxes that let me write text read all over the world.  Moreover, CM does look at profound issues (How does quantum mechanics cross over into apparently classical behavior?  How do large numbers of particles interacting via simple rules give rise to incredibly rich and sometimes amazingly precise emergent properties?), just ones that are not easy to state in a five word phrase.

Second, there is the problem of accessibility.  CM physics is in some sense an amalgam of quantum mechanics and statistical mechanics.  People do not have everyday experience with either (at least, the vast majority don't realize that they do).  It's very challenging to explain some of the very nonintuitive concepts that crop up in condensed matter to lay-people without either gross oversimplification or distortion.  There can be a lot of overhead that must be covered before it's clear why some CM questions really are interesting.  An awful lot of CM issues literally cannot be seen by the naked eye, including atoms.  Of course, the same can be said for quarks or colliding neutron stars - this is not an insurmountable problem.

Third, there is perceived relevance.  This is complementary to profundity.  People are naturally interested in Big Questions (the origins of the stars) even if the answers don't affect their daily lives.  People are also naturally interested in Relevant Questions - things that affect them directly.  For example, while I'm not that into meteorology, I do care quite a bit about whether Tropical Storm Bonnie is going to visit Houston next week.  Somehow, people just don't perceive CM physics as important to their daily existence - it's so ubiquitous that it's invisible.  

These issues greatly constrain any attempt to popularize CM physics....

Tuesday, July 20, 2010

Wow - look what I missed!

I did some travel + have a busy period at work, and what happens?  Scienceblogs implodes, and Chad Orzel laments something I've worried about for a long time:  the difficulty of explaining the importance (and basic coolness) of condensed matter physics to a general audience.  As for the former, serves 'em right for not inviting me to participate -- kidding!  There are enough talented people involved that they'll be fine, and as Dave Bacon points out in his linked post above, mixing up new networks of people interested in communicating science is probably a net good thing.  I do think it's a shame, though, that some interesting blogs have seemed to fade away (Incoherent Ponderer, Angry Physicist, you are missed.).  Regarding the second topic, I do want to point out a previous post I made about topological insulators (the strawman topic of Chad's post), and once I dig out from under work, I'll write more about why condensed matter is particularly difficult to popularize, and thoughts on how to get around those inherent challenges.

Thursday, July 08, 2010

Symmetries and level-appropriate teaching

This fall I'm going to be teaching honors introductory mechanics to incoming undergraduates - basically the class that would-be physics majors take.  Typically when we first teach students mechanics, we start from the point of view of forces and Newton's laws, which certainly parallels the historical development of the subject and allows students to build some physical intuition.  Then, in a later class, we point out that the force-based approach to deriving the equations of motion is not really the modern way physicists think about things.  In the more advanced course, students are introduced to Lagrangians and Hamiltonians - basically the Action Principle, in which equations of motion are found via the methods of variational calculus.  The Hamiltonian mechanics approach (with action-angle variables) was the path pursued when developing quantum mechanics; and the Lagrangian approach generalizes very elegantly to field theories.  Indeed, one can make the very pretty argument that the Action Principle method does such a good job giving the classical equations of motion because it's what results when you start from the path integral formulation of quantum mechanics and take the classical limit.

A major insight presented in the upper division course is Noether's Theorem.  In a nutshell, the idea is that symmetries of the action (which is a time integral of the Lagrangian) imply conservation laws.  The most famous examples are:  (1) Time-translation invariance (the idea that the laws of physics governing the Lagrangian do not change if we shift all of our time parameters by some amount) implies energy conservation.  (2) Spatial translation invariance (the laws of physics do not change if we shift our apparatus two feet to the left) implies conservation of momentum.  (3) Rotational invariance (the laws of physics are isotropic in direction) implies conservation of angular momentum.  These classical physics results are deep and profound, and they have elegant connections to operators in quantum mechanics.

So, here's a question for you physics education gurus out there.  Does anyone know a way of showing (2) or (3) above from a Newton's law direction, as opposed to Noether's theorem and Lagrangians?  I plan to point out the connection between symmetry and conservation laws in passing regardless, but I was wondering if anyone out there had come up with a clever argument about this.  I could comb back issues of AJP, but asking my readers may be easier.  

Science and communication

I've tended to stay away lately from the arguments about scientists-as-communicators that seem to flare up periodically.  This recent editorial by Chris Mooney, about how scientists who actively listen to the general public do a better job of communicating and affecting policy, was simultaneously informative and yet blindingly obvious in some ways.   (Here's a shock:  making it clear to an audience that you're listening to their concerns and considering them seriously gets better results than talking down to them or ignoring them dismissively.)  Chad Orzel followed up with a very well-written (as usual) post about scientists and communication skills that is, like Mooney's, really common sense in the end.  (Here's another shock:  not everyone is Carl Sagan or Neil DeGrasse Tyson, and sometimes our scientific and academic institutions do not value public communication as much as they do utter dedication to scientific research.)  

Many people in the general public do have some baseline interest in science and engineering issues, even if they don't label them as such.  Lots of people watch Mythbusters.  Lots of people read about nutritional information or medical research quasiobsessively.  Many people do care about space, and climate, and the environment, and energy, and electronics, and so forth, even if those concerns are not the top of their list all the time.  There is a thirst for information, and this is all good for society.  I do want to point out one additional issue that seems to get neglected to some degree in this discussion, however.  There are people out there who either don't know what they're talking about (the MD who somehow has a column on the Huffington Post who periodically spouts off utter pseudoscientific nonsense), or actively are pushing misleading or inaccurate information (members of the TX Board of Education who grossly mischaracterize the nature of science).  Scientists can do as much as possible to "market" ourselves and communicate our enthusiasm and willingness to have an honest and open dialog about scientific issues.  However, when anti- or pseudo-science can command at least as big a bully pulpit, and when education and time make it difficult for the average person to discriminate between gold and dross, it's an up hill struggle.  Add in to this the mainstream media's love of controversy ("Some say that the earth goes around the sun, but others disagree.  Let's look at both sides of this issue!"), and the situation can get downright depressing.

Edit:  I realize I left out two other confounding factors:  (1) Scientists who end up distorting actual science beyond recognition in a misguided attempt at popularization (Michio Kaku is an example); and (2) Scientists who are so aggressively arrogant and obnoxious that they only hurt their own cause.