So, last night the Time Lord and I participated in the San Diego Science Festival with a conversation about "Exploring Your Inner Geek." We organized the discussion around the topic of "The Pleasure of Getting Things Right," which included chatting about our experiences at the intersection of science and Hollywood. I bring it up because science fans who didn't catch last week's episode of Bones missed another fantastic episode showcasing nifty real-world science — on a par with the time Jack Hodgins and Zack dropped a frozen turkey from the second floor. In this case, a blizzard hits the DC area and the fictional Jeffersonian Lab loses power — right in the middle of a time-sensitive murder investigation. How can the team do the required tests without electricity or their usual high-tech equipment? Well, necessity is the mother of invention and all that, so… they improvise! And they draw on all kinds of cool science tricks in the process.
They crush up Hodgins' beetles (to his great distress) to create a makeshift dye capable of highlighting small fissures along the bones being studied. And to get the most recent numbers dialed off the murder victim's dead cell phone, the team gathers a bushel of potatoes and hooks them all together to create a battery. This is one of the most basic science experiments in the book, and it was a very inventive way to incorporate it into the story line. Apparently, someone once built a 500-pound potato battery to power his sound system: "The potato provides phosphoric acid, which enables a chemical reaction causing electrons flow from copper to zinc. The zinc came from galvanized nails and copper came from small pieces of copper."
You can also build a makeshift battery from a lemon, or a pickle — Gil Grissom once made use of the latter trick in an episode of C.S.I. Pickles contain salt water, which is rich in charged particles (ions). Triggering a chemical reaction will turn this classic sandwich garnish into a makeshift battery, causing it to glow as it heats up, and probably smoke a bit as it gets hot enough.
There's lots of variations on the basic experiment, including this one, courtesy of San Francisco's Exploratorium science museum, which uses a pickle, a pencil and a piece of aluminum foil (along with a couple of alligator-clip leads) to set off a simple buzzer. The aluminum and the graphite in the pencil chemically react with the ions in the pickle, triggering a flow of electrons between the two materials.
Regardless of your choice of foodstuff, the fundamental physics at work is the same. Just like any other battery, the pickle (or lemon, or potato) uses two metals suspended in an ion-rich liquid to separate electrical charge, and converts chemical energy into electrical energy by a spontaneous transfer of electrons between them, which can be harnessed to perform some useful task, like illuminating a standard household light bulb.
My favorite part of the episode was the Bones scientists' solution to not being able to x-ray one of the victim's bones in particular using the standard equipment. Instead, they drew on a pretty recent (2008) scientific paper on triboluminescence (a.k.a., "the Wint-O-Green Life Saver Effect") observed in scotch tape. The simplest explanation of this phenomenon is that when molecules are crushed or torn asunder, electrons are forced from their atomic fields and start colliding with nitrogen molecules in the air. The collisions cause a transfer of energy from the electrons to the nitrogen molecules, which begin to vibrate (an "excited state"). The nitrogen molecules want to get rid of the excess energy so they emit light, usually in the ultraviolet range, but there's usually a small amount of visible light as well.
Or, as Wikipedia succinctly puts it: "electrical fields are created, separating positive and negative charges than then create sparks while trying to reunite." It's rather like a lightning strike, in fact. The effect is usually observed with asymmetrical crystals; when those materials are scratched, crushed or rubbed, the chemical bonds are broken and a small flash of light is emitted. Hence the name triboluminescence from the Greek tribein ("to rub") and the Latin lumen ("light").
And sometimes the light that's emitted is in the x-ray regime! I blogged about this back in November 2008, when physicists at UCLA first announced that unspooling a simple roll of Scotch tape produces sufficient X-rays to make clear images of their fingers. Seth Putterman and several students constructed a device to unspool the 3M brand Scotch adhesive tape at a steady rte of about 1.3 inches per second, and placed it in a vacuum. They measured emitted light and X-rays.
Surprisingly, the tape did not emit X-rays continuously, but in short bursts — enough energy to produce an X-ray image of a finger in a second. (A dental X-ray takes about one-third of a second.) As you can see, it's not a very detailed image, whereas the Bones contingent achieved an excellent x-ray of the bone in question — that's fiction for you.
The next step for the UCLA team is to build a device that brings two pieces of tape together, and then rapidly separates them — at a rate of around 1000 times per second — using a piezoelectric device. The idea is control the effect, and hopefully miniaturize it for potential applications.
Something similar happens with cloth tape, which displays a glowing line where the end of the tape is being pulled away from the rest of the roll. Putterman's team found most brands of clear adhesive tape also give off x-rays, albeit with a different spectrum of energies. Duct tape does not, and at the time, they hadn't gotten around yet to testing masking tape. Apparently you also get triboluminescence when you tear off the piece of tape at the end of a roll of photographic film.
Potential applications for this unusual discovery include nucelar fusion. The idea is that energy from the breaking adhesive could somehow be directed away from the electrons to heavy hydrogen ions that would be cunningly implanted into the tape. Those ions would accelerate and (hopefully) collide with sufficient force that they could fuse, emitting energy in the process. But fear not! Ripping off a piece of Scotch tape is not exposing us to dangerous radiation on a daily basis in the workplace — unless you happen to work in a vacuum. Air molecules otherwise intercept the X-rays, rendering them harmless pretty quickly.
A more realistic possibility is finding some way to exploit the phenomenon in simple medical devices to destroy tumors with bursts of x-rays. Putterman's UCLA group is eying a potential application to detect x-ray emissions from composite materials as they start to fatigue (i.e., become more prone to cracking); current methods, which work very well with metals, don't always reveal weak areas in composites in time to prevent a crisis. Since composite materials are increasingly used to build airplanes, I, for one, would support any new technology capable of telling ground crews whether or not the plane I'm boarding is likely to break into pieces mid-flight, 37,000 feet in the air.
The point of all this is, getting the science right (with a few minor liberties) on Bones isn't 100% necessary for the writers to build a successful episode. But they care about those kinds of details; they take pride in their work. Also, it adds to the verisimilitude of this fictional world, and helps viewers engage in the willing suspension of disbelief. And it also sheds light on the characters: you just know Hodgins et al. were science fair nerds who followed their passion all the way through grad school. And now they're working scientists who are helping put criminals behind bars, and bring closure to the families of the victims, thereby making the world a better place. What better inspiration could there be for today's young people to seek to emulate?