Cocktail Party Physics

demon spawn

There's an obscure science fiction short story by William Morrison (a.k.a., Joseph Samachson), called "A Feast of Demons," in which a scientist creates a hardy little band of so-called "Maxwell's demons," capable of changing the temperature of various objects, and even reversing or accelerating the aging process in humans. (Naturally the demons run amok and weak havoc on an unsuspecting civilization. Otherwise there would be no plot!) The story is included in a collection edited by Ken Kesey, The Demon Box; in fact, all the stories explore similar themes, based on one of the most famous physics thought experiments of the 20th century (second only to the infamous Schroedinger's cat), devised by a Scottish physicist named James Clerk Maxwell.

It all started with that pesky second law of thermodynamics, a.k.a., "thermogoddamnics" to those who fight a losing battle against entropy -- i.e., everyone, whether they realize it or not. That's the one that says, basically, not only can you not have a closed system that puts out more energy than you consume, but you're always going to lose a little bit of energy in the energy conversion process. We're talking about converting potential energy into kinetic energy. One of the neat things about thermodynamics is that if you can create a large enough differential -- for example, a big difference in temperature between, say, two compartments -- you've got yourself a handy energy source to tap into should the need arise.

Refrigerators work on this simple concept, known as the Carnot cycle. Gas (usually ammonia) is pressurized in a chamber, said pressure causes that gas to heat up, this heat is then dissipated by coils on the back of the appliance, and the gas condenses into a liquid. It's still highly pressurized, sufficiently so that the liquid flows through a hole to a second low-pressure chamber. That abrupt change in pressure makes the liquid ammonia boil and vaporize into a gas again, also dropping its temperature -- thereby keeping your perishable foodstuffs nicely chilled. The cold gas gets sucked back into the first chamber, and the entire cycle repeats ad infinitum -- or at least as long as the appliance is plugged in. That's always the catch, you see. The refrigerator is not a truly "closed system": it gets a constant influx of energy from the wall outlet that enables it to operate continuously. Left on its own, without that crucial influx, and the interior would cease to be nicely chilled, and all the food therein would perish.

So that's the second law of thermodynamics, and frankly, it's pretty unyielding. But while it can't be broken, perhaps it can be bent by a cunning infusion of energy that escapes detection by all but the most perceptive eye. James Clerk Maxwell proposed the most famous evasion of thermodynamics back in 1871, dubbed "Maxwell's Demon." Maxwell was one of those kids who liked to know how things worked, taking things apart and trying to put them back together again -- one assumes not always successfully, which must have been quite trying for his parents. He ended up earning a degree in mathematics and taking a chair in natural philosophy at King's College in London, where he formed his famed equations for electromagnetism that are still in use today.

But he was equally fascinated by thermodynamics, notably the fact that heat cannot flow from a colder to a hotter body. And one day Maxwell had an idea: what if hot gas molecules merely had a high probability of moving toward regions of lower temperature? He envisioned an imaginary, tiny creature who could wring order out of disorder to produce energy by making heat flow from a cold compartment to a hot one, creating that all-important temperature difference. The imp guards a hypothetical pinhole in a wall separating two compartments of a container filled with gas -- similar to the two chambers in a refrigerator -- and can open and close a shutter that covers the hole whenever it wishes.

Now, the gas molecules in both compartments will be pretty disordered, with roughly the same average speed and temperature (at least at the outset), so there's very little energy available for what physicists call "work": technically, it's defined as the force over a given distance (W=fd), and it means that you'll spend the same amount of energy carrying a heavy load over a short distance, as you will carrying a feather over a very long distance. But I digress. It Maxwell's thought experiment, the atoms start out in a state of thermodynamic equilibrium. But they're still jiggling around all the time, as atoms are wont to do, so over time, there are small fluctuations as some molecules will start moving more slowly or more quickly than others, balance will soon be restored, since the excess heat will be transferred from hotter to colder molecules until they are all once again in equilibrium.

Ah, but then Maxwell's little demon interferes. Whenever it spots a molecule moving a bit faster in the right compartment and start  to move towards the pinhole, he opens the shutter just for a moment so it can pass through to the left side. It does the same for slower molecules on the left side, letting them pass to the right compartment. So what happens as time passes? The molecules in the left compartment get progressively hotter, while those on the right side get colder. The creature creates a temperature difference, and once you have that, well, it's a trivial matter to harness that difference for work. Entropy has been outwitted -- or so it would seem. (You can embrace your inner science imp and play a nifty online game of Maxwell's Demon here.)

Maxwell was too clever by half: in reality, his thought expression was a trick question. Maxwell himself supplied two reasons why his clever little demon couldn't exist in the physical world. First, it's statistically impossible to sort and separate billions of individual molecules by speed or temperature; Nature just doesn't do this. You can't throw a glass of water into the sea and expect to get back the exact same glass of water, right down to the last single molecule.

Okay, perhaps hypothetically you might be able to do this, provided you knew the exact speeds and positions of each and every molecule (at the quantum level, of course, this is an impossibility thanks to the Uncertainty Principle). But you'd have to expend a huge amount of energy to collect that detailed information, far more than the energy you'd get out of the system once you'd succeeded in creating the crucial temperature difference. And that's the catch. (There is always a catch. Energy is never "free.") Just like the refrigerator, Maxwell's mischievous little imp also requires energy to operate. There is no such thing as a perfect heat engine; you'll always lose some heat in the process. That's the bane of every researcher striving to develop alternative energy sources, and they have to be cost-competitive as well as energy-efficient.

That hasn't kept physicists from playing around with the concept of Maxwell's Demon experimentally in the ensuing 130+ years, and it's been a busy year in this area so far. First, a January 31, 2008, article in Physics World described a nifty manmade molecular machine created by another Scotsman, David Leigh, and his colleagues at the University of Edinburgh. Most biological processes involve driving chemical systems away from thermal equilibrium, so Leigh devised a chemical "information ratchet" that performs much the same role as Maxwell's hypothetical demon: creating a temperature difference out of thermal equilibrium, thereby seemingly "reversing" entropy. To quote from the article:

"To perform the feat, they use 'rotaxane,' an assembly of molecules comprising a dumbbell-shaped axle on which a ring can slide, hindered only by a gate located part way along. By shining light on rotaxane, the ring absorbs photons and transfers energy to the gate, which then temporarily changes shape to let the ring pass. Once the ring has passed, however, it cannot transmit energy back to the gate, and is therefore stuck -- or ratcheted -- in place."

It still requires an extra influx of energy to operate the chemical "ratchet," according to Leigh, but nonetheless, it's definitely another step towards the practical realization of manmade molecular machines similar to those found in Nature.

Then, in the March 7 Physical Review, a paper appeared by Mark Raizen and Gabriel Price of the University of Texas at Austin, describing their experiments with a laser-based cooling trap combined with a magnetic trap, divided by a barrier beam. The setup  is a little complicated-- you can read the details here -- but in essence, one laser beam serves as the "barrier" while another excites certain atoms of specific frequencies. The end result is a "sorting" of atoms, such that eventually all the atoms end up on one side of the barrier.

Raizen and Price first conceived of the device in 2005 as a means of cooling gases to very low temperatures, perhaps even just a few degrees above absolute zero. Laser cooling has been around in some form or another since the mid-1980s, when Stanford physicist Steven Chu first wove a "web" out of infrared laser beams to create what he called "optical molasses." The beams keep bombarding the atoms with a steady stream of photons -- a bit like hail constantly hitting you in the face -- tuned to specific wavelengths so that they will only be absorbed if they collide head-on with an atom. This causes the atoms to slow/cool down.

Laser cooling was combined with evaporative cooling in the 1990s to produce the world's first Bose-Einstein condensate (BEC), an exotic state of matter first predicted by Albert Einstein and the Indian physicist Satyendra Bose in the 1920s. Get atoms cold enough, they reasoned, to a few billionths of a degree above absolute zero, and they will be packed so densely that they'll coordinate themselves like one big "superatom." It took 70 years, but by gum, physicists succeeded. The work earned Carl Wieman, Eric Cornell, and Wolfgang Ketterle the Nobel Prize in Physics in 2001, and the honor was justly deserved. But BECs to date have only been achievable with specific kinds of gases, like rubidium or cesium. That's why Raizen and Prize's method was so intriguing. Not only would this enable physicists to study even more exotic states of matter, it might also give us new types of atomic clocks (which currently use cesium atoms, mostly, for keeping time).

And now a paper has just appeared in the June 20 Physical Review Letters describing another innovation on the laser-based Maxwellian demon concept, this one devised by Daniel Steck of the University of Oregon in Eugene. It's another laser barrier set-up in which the beam lets atoms pass through only in one direction, such that they all eventually end up on a single side, chilled to extremely low temperatures. Steck created a "box" out of laser light/electromagnetic fields, and then added two parallel lasers that together serve as the "trapdoor." The beam on the right is the barrier, and the one of the left is the "demon," responsible for the "sorting." In concept, it's similar to Raizen and Price's method and the secret, according to Science News' Davide Castelvecchi, is a subtle one:

"Like all lasers, Steck's pumping beam is an orderly arrangement of photons, all traveling in the same direction. And a photon increases the energy level of a rubidium atom by scattering off of it. 'But the scattered photon goes in a random direction,' Steck observes. So while the atoms get a little more order in their lives, the pumping laser ends up with a little less."

In other words: it's a tradeoff. I told you energy is never free. Note, also, that all of these experiments emphasize that they cool the atoms to fractions of a degree above absolute zero (technically defined as minus 495 degrees Fahrenheit), without ever actually reaching that fundamental limit. That's the unofficial "third law" of thermodynamics. All atoms vibrate to some degree. How fast they vibrate depends on heat: the hotter they are, the faster they vibrate, the colder they are, the more slowly they vibrate. But they never cease to move entirely and exist in a state of absolute rest, so to the best of our knowledge to date, absolute zero is impossible to achieve.

Physicists devised this handy mantra summing up the basics of thermodynamics: you can't win, you can't break even, and you can't get out of the game. Now that is truly demonic.

manga from the master

Science fiction author Roger Zelazny was a huge fan of the Japanese artist and printmaker Katsushika Hokusai -- so much so, that in between a plethora of classic sci-fi series, he also penned a Hugo-Award-winning short story "24 Views of Mt. Fuji, by Hokusai." The title refers to the Japanese master's greatest work, Thirty-Six Views of Mount Fuji (circa 1831), including his most famous creation, The Great Wave of Kanagawa. (It's one of my favorite artworks -- yeah, I know, how original...) Zelazny's protagonist tours the region surrounding Mt Fuji, stopping at each location painted by Hokusai -- or most of them, at least. The set includes 46 prints; ten more were added to later additions.

Why am I bringing up Hokusai? This past weekend, the Spousal Unit and I were in Santa Barbara for a joint speaking engagement, and decided to stay an extra day and wander around downtown for a bit. As we meandered down State Street, we happened upon an oriental antiques shop called Mingei (the shop has no Website, but it's at 736 State Street, for anyone who's interested), filled with tansu chests, antique netsuke (some dating back to the 1700s), Japanese teapots, calligraphy tools, and various objets d'art, and some lovely Hokusai prints, nicely framed.

Then we found a stack of bound paper books, pages uncut, filled with small sketched images dotted about at random. The proprietor, Michael Mundy, told us the books were reproductions of Hokusai's manga -- not manga as in the graphic novels we know today (with tie-ins to Japanese anime), but these collections of sketched figures, primarily used by master artists to train their students. We bought one of the bound volumes, and frankly, the only reason we could afford it is because they weren't the original master sketches, but printed reproductions, unearthed by a local resident, who didn't know what to do with them and wound up bringing them to Mundy. ("They literally just walked in the door," he chuckled, still delighted at the serendipity of his find.)

The original sketchbooks (or manga) constituted some 15 bound volumes, containing thousands of largely unconnected images. The first volume appeared n 1814, when Hokusai was 55, and the last three were published after his death, although the final volume is controversial. Apparently some of the images in it aren't really the artist's, but were drawn by his students. Art historians really hate that. Anyway, copies of the sketchbooks have been circulating throughout the Western World since the 1850s or so.

When I say "published," I'm talking not about modern printing methods, of course, but of traditional Chinese woodblock printing as it existed in Hokusai's day. The earliest method for reproducing texts in human history was to just copy them out by hand, except this tended to lead to accumulated errors over time. Copying is a tedious, thankless task, after all, and even the most dedicated scribe is bound to let his attention wander now and then. Around 175 AD, the Chinese emperor Ts'ai Yung got fed up with all the errors. He had authorized versions of six classic Chinese tests carved into stone outside the gates of the state academy. People could make exact copies by placing a sheet of paper over the carved inscription and rubbing it with ink. (It's also a useful archaeological tool in a pinch. Movie fans may recall that Indiana Jones makes a rubbing of the engraving of a knight's tomb in The Last Crusade.)

Woodblock printing first made its appearance in China sometime between the fourth and seventh centuries AD, possibly deriving from the ancient Babylonian seals used to stamp impressions into wax or clay as authenticating marks. By the end of the ninth century, printed books are quite common all over China, at a time when most of Western Europe was stuck in the comparatively illiterate Dark Ages, waiting for Johannes Gutenberg to get around to inventing the printing press in 1455.

You might be surprised to hear that Gutenberg did have a predecessor in China: an alchemist who lived in the mid-11th century named Pi-Sheng, who invented his own form of moveable type. He fashioned small blocks from an amalgam of clay and glue, and carved a Chinese character in relief on each, then baked the blocks to harden them. He could then glue each individual piece of type onto an iron plate, coat it with a mix of resin, wax and paper ash, then hat and cool the plate to set the type. It was then a simple matter to detach the type when done by reheating the plate. Pi-Sheng's invention might even have caught on, if there weren't some 30,000 individual ideograms required to make a complete font.

Creating individual woodblock prints was only slightly less labor-intensive, just enough for the method to flourish well into the 18th and early 19th centuries, particularly for works of art. Hokusai's greatest work, for instance, was part of the Ukiyo-e tradition: a genre of woodblock prints mainly created for townspeople who couldn't afford to purchase original art. Since the Ukiyo-e could be mass-produced, such prints were thus affordable.

First, the artist created a master drawing in ink. Then an assistant (hikko) would create a tracing (hanshita), for reasons which will become obvious momentarily. Craftsmen then glued the tracing face-down onto a block of wood, and cut away the areas where the paper was white (i.e., unpainted). When they were done, all that was left was the drawing in relief (and in reverse). Unfortunately, this process destroyed the tracing -- which is why originals were never used. But near-exact copies could then be made by inking the block pressing it to paper. The artist would request a test copy (kyogo-zuri) before approving an actual "print run." It was even possible to make multi-colored block prints by inking the blocks with different colors. By inking the sheets more than once, it was even possible to vary the depth of the colors.

Even with the advent of modern moveable type printing methods, there was still a need for fast, cheap and highly efficient copying techniques of printed pages. A physicist turned patent clerk named Chester Carlson came to the rescue. Carlson earned a degree in physics from Caltech just as the Great Depression hit, and found himself unable to find work. He finally landed a job in the patent department of an electronics firm in New York, and quickly tired of the tedium of making sufficient copies of patent documents for inter-office distribution. He could send the patents out to be photographed, or type each copy individually. Neither option sounds very appealing, does it?

Carlson didn't think so, either.  There was a device called the hectograph in the 1870s that used a gelatin pad to absorb ink form an original. Blank sheets could then be pressed against the pad to produce impressions, like a modern stamp pad (although it's similar in concept to woodblock printing, too). Thomas Edison tried his hand at it in 1887, introducing the mimeograph. A waxed stencil was wrapped around an inked drum, which could be rotated to transfer an image to the paper. Finally there was the "spirit duplicator," introduced in the 1920s, a precursor to the old-school "ditto" machines used in many schools through the mid-1980s or so. Create a master sheet with the desired text or images, wrap it around a drum shaped like a cylinder, and coat the master with duplicating fluid as the drum turns. Then you just have to press paper against the drum to make the copies.

It was a pretty decent device, actually, capable of making as many as 500 copies before the print became too faint to read. Too bad it was such a messy process. Also a smelly one. I have dim memories of various teachers throughout my early education handing out freshly printed dittos with ink-stained fingers, the purple ink on the pages reeking to high heaven and sometimes bleeding onto one's crisp white blouse. Carlson wanted a dry, versus a "wet" duplicating process, and who could blame him? He found the answer in something called photoconductivity.

Although each precursor mentioned above played a part in subsequently technological developments, we owe modern Xerox machines to both Carlson and a Hungarian physicist named Paul Selenyi. The latter discovered that certain materials, like sulfur, conduct electricity in light, but act as insulators in the dark. Basically, the electrons don't move until the light hits them; the energy from the photons makes the  layer of sulfur (or other such material) conduct. So if you projected an original document onto a photoconductive surface, current would flow only in those areas that had been exposed to light, while anywhere there was print would remain dark. Voila! A copy of the original!

Carlson then spent many years figuring out how to get dry particles to stick to a charged plate in the pattern of the original image. He conducted experiments in his own kitchen until his wife became fed up and kicked him out, and continued his work in a rented room in Astoria, Queens, assisted by a young German physicist named Otto Kornei. They finally succeeded in making the first Xerox copy on October 22, 1938, using a sulfur-coated zinc plate, a glass microscopic slide printed with India ink, and common fingerprint powder (their equivalent of toner).

The story doesn't end there; initially nobody wanted the machine. It took another decade before Carlson sold his invention to a small company called Haloid -- today, it's known as the Xerox Corporation -- and frankly, that first machine had some problems (you needed 11 separate steps and a good 45 seconds after that to make a single copy, for starters). But each subsequent version improved on its predecessors, and today we can walk into any Kinko's and get several thousand copies of just about any printed matter in an hour or so. Thank you, Chester Carlson. We're happy to report that after all his travails, he ended up being a very rich man. (You can read all the gory details about how a modern Xerox machine works here, for the technologically curious. Laser printers work much the same way, except a laser beam replaces the reflected light used in an ordinary copier.)

Today's modern machines are huge, with loads of advanced complicated features that most of us will never need. As such, until one learns the ropes, they can be a little daunting to even a brilliant mind: I once walked into the copy room of the old American Physical Society headquarters in New York City and found three Nobel laureates standing around the machine, stroking their beards (those who had beards) and conferring about how best to go about this little task: "So... should we press START?" They figured it out pretty quickly, actually -- not surprising, given the collective brain power in that little room -- but it was a charming, very humanizing moment, nonetheless.

Even a hundred thousand perfect Xerox copies are only as good as the original, Hokusai would no doubt say. As an artist, he cared deeply about the quality of his original sketches. In fact, he was quite the perfectionist, insisting, in his postscript to a second landscape series, One Hundred Views of Mount Fuji (he had a thing for Mount Fuji), that while he had been sketching nature since he was six, it wasn't until he was 73 that

"... I began to grasp the structures of birds and beasts, insects and fish, and of the way plants grow. If I go on trying, I will surely understand them still better by the time I am 86, so that by 90 I will have penetrated to their essential nature. At 100, I may well have a positively divine understanding of them, while at one hundred and thirty, forty or more I will have reached the stage where every dot and every stroke I paint will be alive. May Heaven, that grants long life, give me the chance to prove that this is no lie."

He was trying to make the most perfect copy of Nature itself: so much so, that the images were "alive." For me, Hokusai's art already seems alive, metaphorically speaking: each line, every brushstroke, is so exquisitely precise, rendering the figures with the least possible number of strokes need to capture their essence. It's artistic minimalism at its finest. (Interesting side note: several years ago, a researcher named Richard Voss analyzed numerous ancient Chinese landscape paintings from various historical periods at the Metropolitan Museum of Art in New York City. He determined the dimension of brushstrokes in each painting -- a tricky task! -- and found that those considered superior by art historians -- i.e., the earlier landscapes -- had fractal dimensions comparable to those of typical coastlines: 1.25 and 1.33. The significance of this, if any, is still being debated: can you really give a number to aesthetic value judgments? But it might say something about the kinds of patterns we humans prefer.)

Like all geniuses, the artist himself was never 100% satisfied, and wanted to live long enough to reach unprecedented levels of mastery of his art. Indeed, he never stopped painting, completing Ducks in a Stream at age 87. But human mortality wins out every time, and Hokusai died on April 18, 1849, at 89 years of age. Legend has it that even on his deathbed, he exclaimed, "If only Heaven will give me just another ten years... Just another five more years, then I could become a real painter."  Heaven, alas, had other plans for one of Japan's most gifted artists. His work is what lives on.

if you could see what i hear

For every major Hollywood hit film that smashes box office records, there's a thousand modest little gems that get passed over and forgotten. One of those is an independent biopic from the 1980s called If You Could See What I Hear, a fictionalized retelling of the college years of Tom Sullivan, a blind man who went on to become a successful author, musician, occasional actor and (today) motivational speaker. The most refreshing thing about the film -- and Sullivan himself, frankly, who golfs, skis and sky-dives in addition to be being an avid runner -- is that it doesn't present him as a victim. He just happens to be blind.

His roommate, Will Sly, far from tip-toeing around the subject, cracks jokes with the fictional Sullivan about his lack of sight. In perhaps the funniest scene, Sullivan, Will, and a couple other pals are pulled over by a policeman, who notices the erratic driving -- erratic because Sullivan is at the wheel. The officer is understandably incredulous:

Officer: Your friend is blind?
Will: More or less. Yeah.
Officer: Then why the hell is he driving?
Will: 'Cause he's the only one who's sober!

Sullivan then does a backflip over the car, and Will deadpans, "See?" Later in the film, Sullivan falls in love with a black woman, and while things don't work out between them -- his being literally "color blind" can't overcome the very real social issues surrounding inter-racial dating back in those days --  he does save his girlfriend's little sister from drowning in a pool, locating her by listening for the sound of air bubbles. Like any fictional biopic, the episode is based on an actual event, except it happened many years later, and the infant girl Sullivan saved from drowning was his very own daughter. And yes: he located her by listening for air bubbles, an impressive example of human echolocation at work.

We normally associate echolocation with animals like bats or dolphins. But there are a few humans who can echolocate very well, most notably James Holman, an early 19th-century British adventurer known as the "blind traveler." While serving in the Royal Navy, he contracted an illness that first affected his joints, then robbed him of his sight at the age of 25. In recognition of his service, he was awarded a lifetime grant of care. He could have simply lived out his days in leisure, but instead, he took multiple leaves of absence, the first to study medicine and literature at the University of Edinburgh. Then the travel bug bit.

From 1819 to 1821, Holman took a Grand Tour through France, Italy, Switzerland, parts of Germany, and the Netherlands, and later toured Russia (where he was accused of being a spy by the czar -- yep, a blind spy -- and deported), Austria, Saxony, Prussia, and Hanover. Near the end of his life, he journeyed through Spain, Portugal, Moldavia, Montenegro, and Turkey. I suspect he and Sullivan would have got along very well.

Holman used the sound of a tapping cane to navigate his environment. Teenager Ben Underwood makes frequent clicking noises with his tongue and listens to the returning echoes to get his bearings and identify objects around him, augmented by a tapping cane. (This video clip shows him correctly identifying things like a fire hydrant and garbage cans.) Underwood was diagnosed with retinal cancer when he was 2, requiring the removal of his eyes a year later. By age 5, he'd discovered echolocation, developing the ability under the tutelage of another blind echolocator, Daniel Kish, who regularly leads blind teenagers on hiking and mountain-biking expeditions.

It's very much a learned ability, apparently; most of us just don't face the necessity of acquiring such skills, and even so, some people prove to be better at it than others. For those of us without our own built-in sonar-sense, researchers at Boston University have developed a prototype device that can enhance auditory cues while navigating an environment -- designed, naturally, to assist the blind. The device repeatedly emits an inaudible (to humans, which means it might the family dog a bit crazy) ultrasonic cluck several times per second, and each click reflects off any objects in the environment. The reflections are then detected by special head-mounted microphones. Computer processing does the rest, converting the ultrasonic signal into audible signals. The person wearing the device can then hear those signals over custom open-ear earphones.

The result? An "auditory image" in which objects in the environment seem to emit sounds to the user. Objects of different shapes and textures emit subtly different sounds, such that the user can distinguish between them. Per BU researcher Cameron Morland (who kindly answered my emailed queries), the unique acoustic characteristics of the reflections enable the user to better distinguish the location and size "surface" properties of various objects. For instance, sounds emitted by an object to the left will arrive at the left ear a bit sooner and louder -- an effect acousticians call interaural time difference and interaural level difference. Morland will present the group's findings at the upcoming meeting of the Acoustics '08 meeting in Paris, the annual meeting of the Acoustical Society of America (ASA), running June 30th through July 4th.

Also, sounds reflect off the body, the head, and the outer ear (pinna), modifying the spectrum of the signal.  At normal frequencies -- within the range of human hearing -- this kind of spectrum shaping is what enables us to determine elevation of an object, according to Morland: "We can then synthesize this to make it sound 'in front'." Unfortunately, the new device uses high-frequency pulses, so users won't get those elevation cues. But who knows? Future prototypes might resolve the issue.

It just so happens you can tell a lot about your surroundings, if you just know how to listen to aural cues. Sweeping the device over an object's surface while remaining the same distance from it will produce a refection with no changes in velocity if that surface is flat. If the surface is tilted so it moves closer to the user, it will sound higher in pitch; if tilted the other way, it will sound lower in pitch, thanks to our old friend the Doppler shift. A roughly textured surface will have some regions that are closer, and others that are further away, and users can be trained to recognize the resulting pattern of increased and decreased pitch. "Venetian blinds sound quite different than a flat surface, or a bookshelf packed with different-sized books," says Morland. You can more fully appreciate these Doppler shift effects by watching the short movies at Morland's website.

The BU team's prototype device is capable of simple detection of objects and open spaces. Preliminary tests show that most people can echolocate a little using the device, and improve quickly with practice. (As with anything else, practice makes perfect, or at least Most Improved.) Morland and cohorts are now refining their prototype so that it can help users get in touch with their inner bat and navigate effectively in more acoustically complex, real-world environments.

A few years ago, Peter Meijer, a research scientist in the Netherlands, developed a similar system he called the vOICe, enabling the user to "see" using sound. (There's an entire project devoted to this area of research, actually, called Seeing with Sound.) It's basically a tiny head-mounted camera, a laptop, and headphones; the camera collects visual data and the computer converts the video input into soundscapes, presented to the user in stereo. And again, with practice, users can learn how to relate the features of a given soundscape with objects of features in their real-world environment. For those who found the laptops a bit cumbersome, camera cell phones came to the rescue: users can now download the simplified version of the software and just point their camera phones in any direction they'd like to "see." The image at right is a "soundscape" of a face, based on one second of sound, giving a sense of what vOICe users are "seeing": ghostly grayscale images, a bit fuzzy in terms of resolution, but frankly, not far off from what a sighted person would "see."

Morland & Company's device is a tremendous achievement (as are similar technologies), even with its current limitations, if one stops to consider how sophisticated a bat's system for echolocation actually is. The upcoming ASA meeting in the City of Lights also features some of the latest research on bat sonar. For instance, Cynthia Moss of the University of Maryland says that bats can control both the distance and direction of their acoustic "gaze." Not only does the bat use the returning echoes from its ultrasonic pulses to build a 3D acoustic "image" of its surroundings, but it adapts its behavior in response.

Moss's team recorded a bat's 3D flight path with high-speed stereo IR video and recorded its sonar signals with a microphone array. This way, they could build their own "acoustic image," reconstructing the emission. They found that the big brown bat (Eptesicus fuscus) "points" its sonar beam in different directions to inspect objects in its environment. The bat's beam is pretty wide, falling within a 60 to 90-degree cone, and this width is sufficient to enable it to gather information about closely spaced objects -- what Bat People like Moss consider a complex environment -- simply by  directing its beam in the general direction of those objects. However, the bat doesn't really do that: instead, the bat "points" the center of its beam sequentially at these objects. 

Moss interprets this to mean that the bat is carefully analyzing acoustic information separately for closely spaced objects. The bat also modifies the duration of its calls to avoid overlap between its vocalizations and returning echoes. When the bat encounters objects that are at a close distance, it produces shorter sonar calls than when it encounters objects that are further away. For instance, in Moss's latest study, the bat being tested encountered an obstacle that was closer to it than an edible food reward, and the animal made adjustments in the duration of its calls. This indicates, say the researchers, whether or not it was paying attention to the near or distance objects.

But even bats aren't perfect; they still have to compensate for so-called "ranging errors," according to Marc Holderied of the University of Bristol, who studies that very thing. Ranging errors are especially risky when flying in those "complex environments" filled with closely spaced objects. Bats depend on the accuracy of their auditory images, especially in determining the distance between them and an object, which they figure out "measuring" the time delay between call and echo. But accuracy can get a bit shaky during flight. Bats are moving around as they emit their pulses and receive echoes back, for starters, and their changing position must be accurately accounted for by the animal's echolocation "system." Those echoes can also be modified by Doppler shifts.

At the ASA meeting, Holderied will report on new results from his studies of how 18 different species of bat (to date -- his research is ongoing) control the spatial distribution of ranging errors via their signal sweep rate. He found that objects at one particular distance from the bat might have zero ranging errors --a kind of echolocation "sweet spot," if you will -- while ranging errors will increase for closer or more distant objects. Apparently bats can adjust their signals so that the "sweet spot" distance shifts to whatever distance they need it to be (within reason, of course) -- similar to how our eyes will readjust their focus as we move around an environment (accommodation in vision, distance of focus). Holderied used 3D tracking techniques combined with 3D laser scans of bat habitats to study their adaptive calling behavior. And he can cite specific examples of actual distances of focus for different bat species in different behavioral contexts: search flight, obstacle avoidance, and target approach, specifically.

What the bats are doing is probably not all that different from how echolocating humans adapt  acoustically to their environment as they navigate. Yet another paper at the upcoming ASA meeting will focus on a study demonstrating that if humans are motivated and/or determined enough, they most certainly can learn to "hear" silent objects, just by listening to reflected and ambient sounds. You can read about some of the particulars here.

Not surprisingly, the University of California, Riverside, researchers also say their results confirm that there's really no such thing as "true" silence, apart from those we create artificially, like soundproof booths. There is always some ambient noise. Psychology professor Lawrence Rosenblum, who participated in the study, pointed to what we hear when we hold a seashell up to our ears as an example: something that sounds like the distant roar of the ocean. In fact, the seashell is merely amplifying the specific frequencies of ambient sound, which, to our hears, sounds like the ocean.

Kinda makes me want to go back to the Paris for the ASA meeting, frankly, just to hear firsthand about all the nifty research going on in echolocation. I like acousticians. They see the world just a little bit differently from the rest of us, precisely because they're so attuned to sound. If only we could see what they hear -- we might learn to view our familiar world in a fresh new way, too.

tripping the light fantastic

One of the best things about blogging is the stuff you stumble upon while researching something else. Take, for instance, my recent Google search on optical fiber sensors. It led me, rather improbably, to the official Website and blog of Jean-Michel Jarre, a French composer, performer and music producer who has sold some 80 million records worldwide, making him one of the most successful musicians I've never heard about. (Jen-Luc Piquant, on the other hand, has far more wide-ranging tastes and has been savoring the YouTube videos of Jarre's live performances for quite some time.) Why did Jarre's name come up? Well, while reading about optical fiber sensors, I stumbled upon a mention of the laser harp: an electronic musical instrument that uses numerous laser beams, blocked at various lengths, to produce audible sounds. Jarre is the most prominent musician to use this instrument in his music. (He also uses various other cutting-edge synthesizers and electronic instruments, including the theremin.)

Laser harps have been around since 1976, when the first working prototype was invented by Geoffrey Rose, who built it out of a matrix of 5x5 laser beams in an octagonal frame. The laser harp is usually connected to synthesizer or computer to produce audible notes. The instrument only needs a single laser, although some of the newer versions employ multiple lasers that can be individually controlled by pulsing on and off. In the single-laser version, the beam is split into an array of parallel beams, usually spreading outward like a fan. (See this YouTube video of Jarre in concert to get an idea of how it looks and sounds. There have been rumors that the instrument is fake, but Jarre has just as many defenders. Regardless, the visual impact is pretty impressive!)

Whenever a beam is blocked, the change is detected by a photodiode connected to the electronics, and the computer activates the relevant note. (That's in the frameless version favored by Jarre. The framed laser harp usually has an array of photodiodes embedded in the upper part of the frame.) By matching the timing of the reflected beam, the computer can determine which beam is being blocked, and therefore which note needs to be played.

Not just any old laser can be used to build a laser harp. You need one with at least 20 mW of power just to produce visible beams, but to get the best results, a laser with 500 mW of power or more is best. This means there's a high risk of suffering skin or eye damage unless one takes precautions: Jarre for instance, wears gloves when "plucking" the "strings" of his laser harp, and other users have been known to don protective glasses. Artist Jen Lewin has been known to use laser harps in her art installations. most notably at at Lincoln Center in 2000 and Burning Man 2005. And for those interested in perhaps building their own photonic instrument,, there are several online resources available.

Why on earth was I Googling optical fiber sensors in the first place? You might ask. Well, sometime last year, I came across a group of scientists at the Ecole Polytechnique de Montreal in Quebec -- led by a professor there named Raman Kashyup --who've created a novel musical instrument based on optical fiber. They call it a "photocello." It's not something that seems to have captured much attention in the scientific community -- I wasn't able to find hardly any mention of the photocello on the Intertubes -- but I still find the concept charming. The photocello employs a vibrating optical fiber to reproduce vibrations that mimic those of a stringed acoustic musical instrument (like a normal cello, for instance). Rather than several different strings, the photocello just needs the one optical fiber, and one common detector (a photodiode).

Optical fiber sensors are used in lots of different applications these days: to measure strain, temperature, pressure, or other useful parameters. These sensors detect a change in one of the properties of the optical fiber, and then translate that detected change into a signal that can be "read" or otherwise used in some way. For instance, optical fiber sensors are used in hydrophones used in seismic or SONAR applications; they are also used to measure temperature and pressure in deep oil wells -- an environment that is not especially hospitable to standard semiconductor sensors. And the Boeing 767 uses an optical fiber as a sensor in its optical gyroscope.

The Montreal scientists exploited an intriguing feature of optical fiber: a single one can represent the "richness of the multitude of harmonic frequencies," which is why the photocello only needs a single optical fiber sensor instead of several different strings. The optical fiber "string" can produce many different notes depending on which section of the stretched fiber one chooses to focus on. Perturbing a stretched optical fiber -- by plucking it, or otherwise causing it to vibrate, in any given segment -- creates a change in the interference pattern, which can be detected by the photodiode and then, through computer processing, demodulated into a reproduction of the harmonic vibrations one would find a stringed musical instrument. The sound is barely audible, although it can be easily amplified to recreate specific musical notes.

Kashyup has also built a photonic guitar, replacing the nylon strings on the frame of a standard acoustic guitar with a multimode optical fiber. Hit one string, and it generates a wave, which can then be transformed into an electrical signal using a photosensor. As with the photocello, the signal can then be sent to a typical audio system with amplifiers and speakers to produce audible notes.

Kashyup is certainly a prolific inventor. Fresh on the heels of his photocello -- which was recently featured in a Quebecois business newspaper called Les Affaires -- he has developed a new scheme to increase substantially the output power of a fiber amplifier. Apparently, the amplification takes place in the doped fiber cladding, not in the core (which is how it's done in the usual method). More specific details weren't available (at least not easily), probably because there's a patent pending.

I still think the photocello concept is pretty cool, as is the photonic guitar. You can listen to a sample of Kashyup "playing" the latter instrument here. It's a bit rougher-sounding than an acoustic guitar, but who knows? Kashyup might be the harbinger of the future of musical instruments. Jean-Michel Jarre could be working the photocello into future live performances as I type -- it should complement the laser harp quite nicely.

the skull beneath the skin

"Webster was much possessed by death
And saw the skull beneath the skin;
And breastless creatures underground
Leaned backward with a lipless grin."
-- T.S. Eliot, "Whispers of Immortality"

Eliot's classic poem alludes to the great Jacobean tragedian, John Webster (of Duchess of Malfi fame), who did indeed have a predilection for the macabre, but the Indiana Jones film series arguably has an element of that as well. The Spousal Unit and I finally went to see Indiana Jones and the Kingdom of the Crystal Skull Sunday night (he was decidedly underwhelmed, I was moderately entertained). All the usual tropes were present: the mystical objects (loosely based on historical artifacts and legend), the drawn-out chase scenes, inventive stunt work, sly witticisms (this installment is less witty than others), attacks by creepy-crawlies, the double-crossing "ally", the power-mad villain(ess), and the almost laughably absurd supernatural climax -- in this case, bringing in shades of The X-Files. (The Spousal Unit bemoaned the silliness of the ending; it was silly, but not any sillier than any of the previous three installments.) Of course, there's also loads of mucking about underground in ancient archaeological sites, strewn with dusty cobwebs, booby traps, and lots and lots of decaying corpses grossing out delighted filmgoers with their "lipless grins."

Admittedly, the film suffers from a formula that's getting a wee bit tired, and what appears to be laziness on the part of the filmmakers in terms of character development, dialogue, and pacing. Everyone's in such a hurry to get to the next stunt or special effect, hurtling towards the climax, that they forget to let the audience savor those little throw-away moments that made the first and most successful Indy film so much fun. The cheesy props don't help matters -- could the crystal skull of the title look any sillier? paging CGI! -- but really, when has Indiana Jones ever been about anything except far-out fun? Cue my usual mantra about how it's unrealistic to expect film and television to be very true to life when it comes to facts about science, history, blah, blah, blah. (NOTE: There may be a few unintentional spoilers below for those who haven't yet seen the film.)

Except in this case, I'm starting to think the thin line between fiction and reality really might be getting a bit too blurred. Last month the Archaeological Institute of America -- the oldest and largest nonprofit organization in the US devoted to archaeology -- elected actor Harrison Ford to its Board of Directors in recognition of his role in "stimulating the public's interest in archaeological exploration," according to AIA president Brian Rose. I'm happy for Ford, who does seem to have an genuine interest in the field; any celebrities who care to lend their name in support of science get mega-points with me. But, well, Dr. Jones is a pretty glamorized version of your typical archaeologist. The National Science Foundation was sufficiently concerned to issue a special report highlighting the differences and similarities between the worlds of science and Indiana Jones. Per the press release accompanying its release:

NSF-supported archaeologists do discover "lost cities." They try to figure out what happened to "vanished civilizations" and whether what caused their collapse may have relevance to contemporary problems. They seek rare and precious artifacts that tell important stories about the past, even if those artifacts are minute snails and the scrapings of ancient teeth and not golden idols. They "deal with Native peoples," though with respect, as partners in the process of learning about the past, rather than with weapons. And certainly, as jokingly noted in the latest Indiana Jones adventure, teaching is an important part of what they do.

Being tall is also an important part of what archaeologists do, not to mention breaking into song when locating ancient Sumerian artifacts from the 3rd dynasty -- at least according to Monty Python (h/t: Afarensis). Harrison Ford's got the tall part down, at least, even if the NSF report failed to mention it.

Most of the press related to the new film, however, has focused on the legends and myths surrounding the crystal skulls. Yes, Virginia, there really are crystal skulls -- 13 of them, to be exact -- and the film even identifies the most famous one by name: the infamous Mitchell-Hedges skull, a.k.a., "the skull of doom." It was supposedly discovered by 17-year-old Anna Mitchell Hedges and her father in either 1924 or 1927 (they never did get their stories straight on the year) under the altar of a Mayan temple in a ruined city in Belize, although there is documentary evidence that in fact, Anna's father bought the skull at a Sotheby's sale in 1943. (Anna herself later came up with an "explanation" for that bill of sale.") Her father, a British "adventurer" named F.A. Mitchell-Hedges, claimed the clear quartz crystal skull was "at least 3600 years old, and according to legend was used by the High Priest of the Maya when performing esoteric rites. It is said that when he willed death with the help of the skull, death inevitably followed. It has been described as the embodiment of all evil."

The other skulls include "Max," the "Texas crystal skull," supposedly from Guatemala; "ET", supposedly discovered in 1900 (notable for its pronounced overbite); "Ami," an amethyst crystal skull, supposed to be Mayan; "Sha-na-ra," a clear crystal skull that moonlights as a member of an a capella doo-wop group whose owner claims to have found it in Mexico; the British Museum crystal skull (also mentioned in the film), made of cloudy quartz; the Paris Skull, thought to be Aztec, currently housed in the Musee de l'Homme in Paris; and an Aztec crystal skull anonymously sent to the Smithsonian's Museum of Natural History in 1992, which also had a smaller crystal skull in its possession for many years.

The real crystal skulls look nothing like the hulking prop used in Kingdom of the Crystal Skull. For starters, they're a lot smaller; some of them measure as little as an inch across, most likely having been carved out of authentic pre-Colombian beads in the 19th century, when museums first began collecting crystal skulls. There are exceptions: the one in the British Museum is life-sized, and  the crystal skull mysteriously mailed to the Smithsonian in 1992 weighs a whopping 30 pounds; the anonymous sender claimed it was of Aztec origin.

Not so, sez Jane MacLaren Walsh, a Smithsonian anthropologist who has studied several of the skulls extensively, including the most recent acquisition. In a recent cover story in Archaeology magazine, she insists, "These exotic carvings are usually attributed to pre-Colombian Mesoamerican cultures, but not a single crystal skull in a museum comes from a documented excavation, and they have little stylistic or technical relationship with any genuine pre-Colombian depictions of skulls, which are an important motif in Mesoamerican iconography." (You can find a preliminary report on her study of both the Smithsonian and British Museum crystal skulls here.)

Walsh is featured in an upcoming documentary for the Smithsonian Channel, The Legend of the Crystal Skulls, airing July 10th. (You can see clips/video footage, and find quite a bit of background information about the skulls, here. And if you want to own your very own crystal skull, you can buy one here, although many of the most popular models are currently sold out -- no doubt boosted by the current Indiana Jones craze. They also offer clear stone phalluses, which if nothing else would make for an interesting conversation piece at dinner parties.)

There are some wacky sorts out there who attribute the crystal skulls with special psychic powers, and even some murmurings of possible alien provenance (rumors that started with F.A. Mitchell-Hedges). An art restorer named Frank Dorland claimed to hear ringing bells and the sound of a choir singing and could see images when he gazed into the Mitchell-Hedges skull -- which he studied for about six years, becoming one of its staunchest devotees. Anna claims her skull has been used for healing -- disputing her own father's characterization of the artifact as "the embodiment of evil." The owner of "ET", a smoky crystal skull, believed it healed her brain tumor. These claims have been handily debunked, of course, but certainly the notion that the skulls have special powers captures the imagination: an episode of Stargate SG-1 memorably featured a crystal skull that enabled characters to travel between worlds.

The most popular legend has it that when all 13 of the crystal skulls are brought together in a certain configuration -- and no doubt at a specific place and time, just to make it as unlikely as possible -- they will "divulge their secret and prevent a terrible calamity." LucasFilms Ltd. picked up that premise and ran with it in their latest blockbuster, although they got a bit confused at the end about what calamity, exactly, the skulls were supposed to prevent. (The destruction of an entire Mayan city might strike some as a calamity.)

So where did the skulls come from? The consensus seems to be that they emerged in the late 19th century, part of a wave of pre-Colombian fakes that found their way into various museums around the world. While visiting Mexico City in 1884, the Smithsonian archaeologist W.H. Holmes warned about the burgeoning number of "relic shops" on every street corned filled with fakes, prompting him to write an article for Science on "The Trade in Spurious Mexican Antiquities." One wonders, then, how the Institute was taken in a mere two years later, when, in 1996, the Smithsonian purchased a small crystal skull from a man who had been Emperor Maximilian's secretary in Mexico at the time. In part, museums began collecting rock-crystal skulls at this time because existing knowledge about real artifacts was pretty scarce, making it easy to pass off fakes as the real deal.

Walsh tracked down several of the skulls to one Eugene Boban, a French art dealer in the late 19th century. At least three of the 13 famed crystal skulls can be traced directly back to Boban, who served as the official "archaeologist" in the Mexican court of Maximilian, as well as being a member of the French Scientific Commission in Mexico. After Maximilian's execution by the army of Benito Juarez, Boban found himself back in Paris, where he opened an antiquities shop. Even at the time (1885), one of his second-generation crystal skulls was denounced as a fake when he tried to sell it to Mexico's national museum as a bona fide Aztec artifact. Eventually he found himself in New York City, where he managed to sell the skull at auction to Tiffany's for $950. (This skull is the one that was later sold to the British Museum.)

As scientific knowledge advanced in the 20th century, the crystal skulls lost quite a bit of their mystic luster, and almost all of their credibility as bona fide antiquities. Based on her research, Walsh concludes that "all of the smaller crystal skulls that constitute the first generation of fakes were made in Mexico around the time they were sold, between 1856 and 1880. This 24-year period may represent the output of a single artisan, or perhaps a single workshop."

In the 1950s, a Smithsonian mineralogist named William Foshag realized that the crystal skull it had acquired in the 1800s had been carved with a modern lapidary wheel. From then until it mysteriously disappeared in 1973, the skull was displayed in an exhibit of archaeological fakes.

Using high-end instruments like Scanning Electron Microscopy, Walsh concluded that the Mitchell-Hedges skull, for instance, shows evidence of tool marks, casting serious doubt on claims the skulls are pre-Colombian in origin, since the Maya, Aztecs or other pre-Colombian peoples just didn't have the tools to make those kinds of marks. (Aliens, though, would most certainly have had advanced tools, claim the True Believers.) Heck, even Frank Dorland said that the Mitchell-Hedges skull showed signs of "mechanical grinding on the faces of the teeth," although he was a proponent of the alien origin theory, the better to bolster his delusions about the skull's power. The Paris Skull -- which Walsh believes to be a "transitional piece," larger but similar in style to the first generation of crystal skulls -- will be undergoing extensive scientific testing with such advanced elemental testing techniques as particle induced X-ray emission and Raman spectroscopy, to determine its exact age/composition once and for all.

As for attributing special mystical powers to the crystal skulls -- or any kind of crystal, for that matter -- no doubt True Believers would say that scientists are close-minded and refuse to consider the possibility. Um, nice try, but actually, scientists know a great deal about the properties of crystals. There's an entire field of material physics (crystallography) devoted to studying those properties, and crystals -- unlike, say, soft condensed matter (amorphous solids and the like) -- are among the best understood materials today. Crystals get their properties from their atomic structure; the definition of a crystal is a solid in which the atoms, molecules and/or ions are arranged in regularly ordered, repeating patterns in all three spatial directions. It's a naturally occurring structure, wondrous in and of itself, but that's not enough for crystal aficionados, who feel the need to attribute mystical properties to these materials as well.

According to crystal skull sycophant Frank Dorland, "The crystal stimulates an unknown part of the brain, opening a psychic door to the absolute." It's a common type of argument. For instance, True Believers have been known to cite the natural piezoelectric properties of quartz crystals as evidence of their power. Now, piezoelectricity is pretty nifty: in 1880, Pierre and Jacques Curie discovered that squeezing a quartz crystal produced an electrical charge, which is why quartz is used in watches, those old car lighters, all kinds of sensors, and so forth. Granted, this is energy of a sort, but it's certainly not psychic energy, just plain old electricity. Crystals are very pretty, though, which might explain why there's so much wishful thinking surrounding the issue of whether they have healing or psychic powers.

So there you have it: the lowdown on the real-life crystal skulls, which are nothing like that depicted in Kingdom of the Crystal Skull -- but nonetheless, I think they're still pretty darn cool. And science could offer some useful fodder for future installments in the Indiana Jones saga, should Hollywood decide to build a similar series around Indy's son, Henry Jones III (Shia LeBoeuf). Over at Twisted Physics, I mentioned the use of cosmic ray detectors by archaeologists, using muons to map out archaeological sites and detect hidden tombs or chambers. I think it would make an excellent premise for the first Son of Indy flick. After all, Crystal Skulls takes place in 1957. Luis Alvarez first used cosmic ray detectors to study Egyptian pyramids around 1967, when Indy 2.0 would be around 30 (give or take a couple of years), hopefully having completed some semblance of an education at long last.

Can't you just see Alvarez teaming up with a rebel archaeologist to foil some nefarious plot or another? Ancient Egypt certainly has enough myth, legend, and mystical artifacts to fuel another wacky plotline, and Alvarez really is the sort of physicist who should be better known among the general populace. I think he'd get a kick out it, frankly. So, George Lucas, feel free to use the above suggestion as you see fit -- in exchange for just a teensy percentage of the profits from the inevitable Son of Indy franchise. Then I should be able to keep the Spousal Unit and Resident Feline in the manner to which they would like to become accustomed.

seeing the light

Over at my new blog, Twisted Physics, I wrote about the Telectroscope, a whimsical art installation linking New York City and London, ostensibly via a giant tunnel under the Atlantic Ocean connected on either end via a telescopic lens. In reality, the connection is made via fiber optic cable and a gigantic Webcam, but either way, you've got information traveling across the pond at the speed of light, enabling Londoners and New Yorkers to wave and hold up signs in greeting, pretty much in real time. It just so happens that I've also been reading George Johnson's excellent new book, The Ten Most Beautiful Experiments, this  week while recovering from some minor bug. (I swear my body breaks down on a regular basis just to force me to get some sleep.) Chapter 8 describes historical attempts to measure the speed of light, culminating with the famed Michelson-Morley Experiment in 1887 to detect something called the "luminiferous aether, a medium thought to pervade all of space to enable light waves to propagate. People might have their quibbles with Johnson's choice of experiments to include in his top ten, but I'd have to agree that Michaelson and Morley deserve to be in the pantheon -- if only because it's a prime example of how illuminating (even revolutionary) a null result can be.

Galileo first suggested a scheme for measuring the speed of light in the early 1600s: stand on a hilltop at night and flash a bright light toward a distant hill, where one's assistant would see the flash and respond by flashing back. Galileo lacked an accurate timepiece, alas -- this was the man who used his own pulse when measuring the speed of balls rolling down an incline plane, after all -- so the best he could conclude was that "if not instantaneous, light is very swift." Even back then, "really, really fast" fell a bit short of prevailing scientific standards for precision, but it wasn't until the 1670s that Danish astronomer Ole Roemer used his observations of Jupiter and its moon, Io, to arrive at a light speed of about 140,000 miles per second. (The critical observation: Io seemed to be slowing in its orbit at certain times of year, and Roemer rightly surmised that this was because as it moved farther from Earth, its light took longer to reach Earth.)

Fifty years later, English astronomer James Bradley confirmed Roemer's estimate while tracking a star called Gamma Draconis. It seemed to wander from its expected position, and eventually Bradley figured out it was because by the time the starlight reached his telescope, the Earth had shifted position. Bradley refined Roemer's original estimate to 183,000 miles per second.

Next on the scene were a pair of French physicists, Hippolyte Fizeau and Leon Foucault (of Foucault's pendulum fame). In 1849, Fizeau used two fixed mirrors to measure the speed of light, one partially obscured by a rotating cogwheel. Light projected between the spinning cogwheel's teeth would reflect off the mirror and be sent back through the wheel, and from the length of the light path and the speed of the wheel, Fizeau was able to estimate the speed of light. It was a noble effort, a more sophisticated version of Galileo's earlier approach with two lanterns, but the resulting estimate was about 5% too high (196,000 miles per second). About 13 years later, Foucault improved on Fizeau's original design and devised an apparatus that reflected light off one rotating mirror, toward a stationary mirror some 20 miles away. He refined Fizeau's estimate to about 185,000 miles per second.

And this is where Albert Michelson made his grand entrance onto the speed-of-light stage. He knew all about his predecessors' experiments. Per Johnson, I learned that Foucault's experiment produced a displacement less than a single millimeter, which was very difficult to measure accurately. Michelson figured he'd just project the beam down a much longer path than Foucault's 20 meters, resulting in a greater lag time. "The returning beam would hit the mirror later in its cycle, resulting in a larger deflection and, he hoped, a better value for the speed of light," Johnson writes. And it did! Michelson's experiment yielded the best measurement of the speed of light yet: 186,350 miles per second. (Today's accepted value is 186,282.397 miles per second, so Michelson was impressively accurate.)

Ah, but this is not the famed experiment honored in Johnson's Top Ten, impressive though it was.  After successfully measuring the speed of light, Michelson turned his attention to the question of the luminiferous aether. This was a mysterious substance believed to pervade the universe, serving as a transport medium for light. The assumption was that light, like sound, needed a medium through which to propagate.

Johnson's poetic take is that Michelson yearned for an unmoving constant, something fixed against which all things could be measured. The luminiferous aether served such a purpose, and Michelson conceived of a method of measuring the motion of the Earth against the aether by sending a light beam in the same direction that the Earth was moving around the sun. The light beam should be slowed a bit by the "aether wind" that everyone assumed would be produced as the aether flowed over the Earth as our blue planet moved through it. (It was assumed at the time that light did not travel at the same velocity in all directions.)

To make this delicate measurement, Michelson invented a truly ingenious device, later called an interferometer (scientists still use such instruments today). He sent a beam of light through a half-silvered mirror, thereby splitting it into two beams traveling at right angles to each other. The beams traveled out to the ends of long arms and bounced off small mirrors, causing them both to return to the center and recombine in an eyepiece, producing an interference pattern. Even the slightest change in the time spent to make the trip should be observed as a shift in the positions of the interference fringes.

He teamed up with a chemist named Edward Morley to refine his basic prototype apparatus. In the seminal experiment, the light as reflected back and forth along the arms repeatedly. The entire apparatus was housed in a closed room in the basement of a stone building to shut out vibrations and variations in temperature (which might cause the brass arms to expand or contract), and they placed the experiment on a large block of marble floating in a pool of mercury to further reduce vibrations. To their surprise, there were no interference effects at all. In essence, the speed of the earth through the aether was, for all intents and purposes, zero. So there was no need for an aether at all, and furthermore, the speed of light in a vacuum appeared to be independent of the speed of the observer. This experiment was refined and repeated many times up until 1929, always with the same results and conclusions.

Technically, the Michelson-Morley experiment was a failure, in that it did not measure the effect the men expected to find; quite the opposite, it disproved their basic premise, and the very existence of the aether. Albert Einstein explained the results when he published his theory of special relativity in 1905. One of the central tenets is that there is no such thing as a fixed frame of reference. (In physics, a frame of reference simply denotes where a person or object happens to be standing relative to the rest of the universe.) So there is no absolute reference frame for time against which all motion can be measured. This was a pretty radical idea at the time, although modern scientists take it as a given.

Einstein explained that this is because everything (and everyone) is constantly in motion through both space and time, and therefore has its own unique frame of reference. This has some pretty bizarre implications. For instance, two people who are moving relative to each other, wearing identical watches, will measure time differently. Time will slow down or speed up depending on how fast each is moving. This usually isn't noticeable because your average wristwatch isn't sensitive enough to measure the tiny discrepancies that appear at slower speeds. Time dilation only becomes significant at speeds approaching the speed of light, when the effects are greatly magnified.

Einstein also asserted that space and time are one. Our three-dimensional existence -- the "where" of an event -- evolves along the fourth dimension of time -- the "when" of an event -- so we live in a four-dimensional space time. Ergo, what happens to time must also happen to space. So as time dilates for an object in motion, the object's length contracts along its horizontal axis by a corresponding amount.

If one wanted to be silly -- and one might, here at the cocktail party -- one might say that a good way to look noticeably thinner is to travel at faster speeds relative to the rest of the world. After all, the faster an object moves, the more its horizontal length contracts, at least from the perspective of an outside observer. Should one approach the speed of light, one would become so thin as to appear almost two-dimensional to an outside observer -- all without giving up a single calorie. Alternatively, one could claim that one wasn't so much fat, as really, really slow. (Here's a bit more risque take: Jen-Luc Piquant once asked a male acquaintance how he felt about the possibility relativistic "shrinkage"; he  took it in stride, shrugged and replied, "That's why I try to move as slowly as possible.")

Silliness aside, while it's true that space and time are in the eyes of the beholder, the speed of light is constant, regardless of frame of reference. That's the true significance of the Michelson-Morley experiment. Scientists before Einstein had assumed that motion through space was the same as motion through time, but if space and time are one, then the two types of motion are linked. Time dilation and length contraction occur because space and time adjust with motion to ensure that two people moving relative to each other will always measure the same speed for light.  Light is the link between space and time.

It also sets the cosmic speed limit. According to Einstein, nothing can travel faster than the speed of light. And there's no such thing as an event happening at the same exact moment for two observers in different frames of reference because none of us ever sees the world as it is right "now." We can't tell something has happened until the information about that event reaches us, and there is always a delay of at least the speed of light before that happens. How much it is delayed depends upon the relative speed of whoever is observing an event.

So far, Einstein's theory is holding strong, despite the deployment of ever-more-sensitive instruments and ingenious approaches to find the tiniest hint of violation of the laws of special relativity (as well as general relativity). And the null results continue. Thus far, it seems, special (and general) relativity holds true (at least until you get down to the quantum scale).  I'll give Johnson the last word:

[Michelson] died ... in 1931, just months after meeting Einstein, whose special theory of relativity had explained the true significance of Michelson and Morley's beautiful experiment: they had proved, contrary to their expectations, that there is no fixed backdrop of space, or even of time. As we move through the universe, our measuring sticks shrink and stretch, our clocks run slower and faster -- all to preserve the one true standard. Not aether, but the speed of light.

who are you? bourne and the brain

Lee Kottner here, on assignment from Jennifer to cover at least one of the offerings the World Science Festival held in NYC last weekend. Before I get started on the one event I actually got to, let me say how hard it was to narrow it down. So many cool offerings! So little time! It was just like being presented with with a really juicy conference program and having to pick between overlapping sessions: a nerd's paradise, with the bonus that there was also a street fair, movies, and art. Definitely more fun than your average conference (unless it's the Kalamazoo Mediaevalists). This is the World Science Festival's first year, so it's a little rough around the edges yet organizationally, but the line-up is absolutely stellar, and the intersections of art and science couldn't have been more intriguing. Theatre, dance, music, and film were all represented, along with the history of science and the fields of math (or maths, for you Brits out there), physics and astronomy, evolutionary biology, environmental science, epidemiology, genetics, botany, computer science, engineering, and neuroscience. The topics ranged from creativity, space-time, longevity, climate change, and astrophysics to the science of sports, of illusions, of green building and of Disney Imagineering, and plays and films about Einstein, Richard Feynman, Hugh Everett (of the parallel worlds theory) and . . . Jason Bourne.

And yes, that's where I come in, shallow fan of action flicks that I am. But it's the neuroscience offerings as a whole that got me excited about the festival. One of my favorite science writers, neurologist Oliver Sacks, had not one but two presentations, the first on visual perception and the brain, at the Metropolitan Museum of Art, and the second on music and the brain, in conjunction with the Abyssinian Baptist Church choir. I've read most of Sacks's books for the general reader, so normally I'd jump at the chance to hear him speak. But I couldn't resist "The Brain and Bourne" (nothing like Pinky and the Brain, I assure you) with producer/director Doug Liman, psychiatrist/neuroscientist Giulio Tononi, and producer/screenwriter (oh, the multitasking!) James Schamus. (Spoiler alert for anyone who hasn't seen the movie. And, like, what's taking you so long? There are two more already!)

The movie opens with an unconscious figure in a wetsuit (Matt Damon) floating face-up in a stormy Mediterranean Sea. Hauled aboard a passing fishing vessel, Wetsuit Man is discovered (1) to be still alive, though (2) shot twice in the back and (3) to be carrying a stainless steel capsule embedded under the skin of his hip. The capsule contains a laser which projects the number of a blind Swiss bank account. Huh? Wetsuit Man comes to, understandably upset at having objects removed from his body without his consent (or anesthesia), even if they are bullets and weird implants, and discovers he doesn't know who he is. He can walk, talk, play chess, shuffle cards, do pull-ups, tie complicated knots, speak several languages and function on a day-to-day level, but he has no idea who he is or was, or where he's been for the last twenty-some years of his life. For all he knows, he's sprung from the sea like Venus on the half shell. Classic amnesia.

Or at least the Hollywood version. Amnesia of just about any type is actually pretty rare, though you'd never know it from watching soap operas or reading Gothic murder mysteries. But there are several different types of amnesia and a number of causes. The two main types are anteretrograde amnesia, the inability learn and remember new information since the time the amnesia began, and the kind our hero experiences: retrograde amnesia, which involves a lack of memory of the past preceding the time one becomes conscious again. One of the symptoms of dementia is memory problems, but unlike those suffering from, say, Alzheimer's, victims of amnesia retain their cognitive powers and intelligence. They lack only their former memories, or, in the case of anteretrograde amnesia, the ability to make new memories. Guy Pearce's character suffers from this type of amnesia in the 2000 movie Memento, and must constantly write himself notes and take Polaroid pictures to tell himself what he's been doing for the past fifteen or so minutes.

Amnesia can encompass varying stretches of memory—from all of your previous life (global amnesia, usually transient) to just the five minutes before you knocked yourself out in a bike accident—and last for varying periods of time. Its causes include stroke, inflammation (from infections like encephalitis), tumors, oxygen deprivation (from a heart attack or CO poisoning), long-term alcohol abuse, and the classic Hollywood cause: pressure from bleeding between the brain and skull, i.e., a knock on the head. It takes a fairly serious head injury, however, one likely involving a long coma and months of rehab, to induce anything but transient global amnesia.

Wetsuit Man, who eventually decides his name is Jason Bourne on the strength of the evidence he finds in his lockbox at the Swiss bank, also discovers along the way that some of the things he knows how to do are downright scary. In one very subtle scene before Bourne visits his lockbox, he tries to catch some sleep on a park bench but is rousted by the Swiss cops. One pokes him with a nightstick, which Bourne grabs reflexively. If you watch carefully, you'll see him pause and in that pause is the moment when Bourne says to himself, much like Neo in The Matrix, "Hey! I know Jujitsu!" Bourne then handily disarms and disables the cops and runs away, to live to lay movie-fu on other attackers another day. Okay, he doesn't know who he is, but he can take out two trained cops in less than 30 seconds? Wait, it gets weirder!   

As the movie progresses, it's clear that Bourne is not just a martial artist with lightning reflexes (and that he fights dirty as hell), but he knows all about surveillance techniques, weapons, and being followed. Sitting in a truck stop on the way to Paris, he says to his new accomplice, Marie, "I can tell you the license plate numbers of all three cars out front. I can tell you that the waitress is left-handed and the guy at the counter weighs two-hundred and fifteen pounds and knows how to handle himself. I know that the best, first place to look for a gun is the cab of that grey truck outside.  I know that at this altitude I can run flat out for half a mile before I lose my edge. I knew that you were my first, best option out of Zurich.  How do I know all that?  How can I know all that and not know who I am?  How is that possible?"

Excellent question, Mr. Bourne. Is this just another example of Hollywood mangling scientific truth? Well, no, it's not for a change, though I wouldn't have known it without going to this talk. James Schamus started it off by asking Dr. Tononi if this kind of amnesia was actually possible. Surprisingly, the answer is yes, but it is more likely if it has a specific cause. In Robert Ludlum's original book, it's the classic blow on the head that gives Bourne his case of amnesia. Liman, in his research before making the movie, discovered this was unlikely to cause the kind of amnesia Bourne suffered from. Liman twisted the plot a bit and, though Bourne does suffer a break of consciousness after he's shot and falls (is tossed?) overboard with two bullets in his back, his amnesia is purely psychological in nature, arising from an internal conflict.

Psychogenic amnesia, it turns out, acts just like physically induced amnesia in many ways, but without the trauma. Dr. Tononi studies consciousness and its disorders, so this is right up his alley. True to the nature of the talk, he came prepared with a PowerPoint presentation, the first slide of which showed two PET scans of amnesiacs, one caused by encephalitis, one psychogenic. In both, the right temporal lobe (the yellow bit in the diagram at right) is inactive in almost exactly the same areas, though one brain is completely uninjured. Unsurprisingly, this is the part of the brain that is most closely involved with memory, mostly the storing (the hippocampus is thought to be mostly closely involved with making memory). Recent studies in brain mapping and neuroscience have shown that our brains generally parcel tasks into regions. Our memories are concentrated in one area; our skills, some of which involve muscle memory (proprioception) in another; our pattern recognition in another, and so on. Knowledge and personal memory are not the same thing, either. Our knowledge about a subject is static and factual, while personal memory tends to encompass a linear sense of time and other sensory impressions. Memory, like dreams and oddly like the movies, as Schamus pointed out, is a limnal state: ambiguous and untrustworthy as cops and prosecutors well know.

We tend to think of our memories as fixed and visual. The research of Dr. Tononi and others has shown that consciousness is a process, not just a location, and that our memories are not representational but rely more on reconstruction than recall. There's no rewind or replay button in your head, in other words. When we ask ourselves "Who am I?" or "What happened?" we're not going to get a picture, but a narrative, a story. This story includes not just our memories, but who we tell ourselves we are—our interpretation of those memories. If there's a clash between who we think we are and our memory, guess what loses? Then we become our own unreliable narrator.

In the case of Jason Bourne, as the other two sequels to this movie show, the internal conflict is between the kind of person Bourne thinks he is (one of the good guys who doesn't just randomly kill people) and the things his memory tells him he has done (not-so-randomly kill people). What sparks the conflict is a mission to assassinate a dictator in exile and finding him on his boat with his children in the same room. Bourne can't bring himself to shoot the man while he's holding his daughter and his other children are asleep in chairs around him. Instead of a blow to the head, guilt is the trauma, and Bourne conveniently forgets what he does for a living when he wakes up. It's too awful to contemplate otherwise.

In effect, Bourne becomes the person he thinks he is. Tononi pointed out that people with dissociative disorders, including multiple personalities, don't share the memories, even on a PET scan, that their "others" have. People in dissociative fugues can suddenly forget who they are (usually because of some emotional trauma) and wander off. But unlike Bourne, they generally don't know they've lost something, and will assume another identity, not try to find their old one. This separation can also occur in sleep states, such as the infamous case of Kenneth Parks, who killed his mother-in-law and seriously injured his father-in-law when he was sleepwalking, but had no memory of it. Bourne is in the process of writing a new story for himself, reconciling what he did with who he is now, and in doing so, recovers the memories of who he was. Like Kenneth Parks, until he regains his full memory, Bourne is conscious but not self-conscious.

Originally, this was a big problem for Liman, as a director. Usually, when characters are introduced in a story, the audience is cued on how to relate to them by seeing them in the context of their life: with friends, relatives, their dog, their boss. Bourne has no one and nothing to cue his audience. He's a blank slate. It's only in his journey, in the reconstruction of a new personality, that he becomes interesting and fully aware.

Now, imagine not only having your past be a blank slate, but not being able to imagine a future. Tononi also mentioned the case of Clive Wearing, a British musicologist who developed total amnesia after a viral infection. Although he still knows how to play the piano and conduct music, he has no other personal memories and cannot form new ones, like the character in Memento. Only Wearing's memory is of even shorter duration than Guy Pearce's character. Wearing has none. Most of his waking time is spent "rebooting" his consciousness from moment to moment. His diary consists of the consecutive statements "I am alive! I'm awake now. I am alive!" If that's the entirety of one's self-consciousness, is there a self? Bourne, at least, does manage to find or make a new one, as well as recover his past. But not everyone does.

Cue The Who. Oh wait. That's CSI. I forgot.

meta musings

It's rare when we indulge in navel-gazing at the cocktail party, mostly because there's so much cool stuff to be seen by gazing outward -- really, who has time to gaze inward? But even we can get a bit reflectively "meta" sometimes. Today is one such time, because we have a couple of special announcements. First, for those in the Los Angeles area, I'll be speaking at the LA Center for Inquiry on Sunday, June 15th -- yes, it's Father's Day, so feel free to make it a family outing! -- about "The Rules of the Game: Finding the Physics in the Buffyverse." I'll be showing a few clips from the TV series, and showing off the spiffy new replica crossbow I found in Paris, in one of those sci-fi/fantasy shops that also carry items like Lady Arwen's elfin pendant from The Lord of the Rings trilogy, as well as fake Arthurian swords and katanas. I don't care if my crossbow is a replica: it blends nicely with my miniature cannon, catapult, and guillotine. It also makes a killer prop for talks. The catch and release mechanism works, making it ideal to demonstrate potential and kinetic energy in Buffyverse weaponry, plus it comes with a nifty stake-like wooden arrow should any errant vampires happen to stop by.

It's hard to top the whole crossbow thing for sheer excitement. But I have an even bigger announcement. Long-suffering regular readers are all too familiar with my chronic long-windedness when posting; the sheer length of the posts is one reason why I generally only blog two or three times a week. Sometimes I get helpful emails from random readers, offering advice for making the blog more "readable" -- at least for them -- and invariably, "write shorter posts" is at the top of the list. Like any self-respecting iconoclastic blogger, I remain true to myself and ignore said advice.

Until now! Relief is at hand for the groaning masses who, honestly, would love to read my little blog if only they had the time to wade through all that excess verbiage. This week marks my debut blogging for Discovery News, with a completely new blog, Twisted Physics. (I realize there are a few people who think that's the name of Cocktail Party Physics, but it isn't. It's just in the Typepad domain name, and now I can't change it without screwing up all my links.) I'll be posting there three times a week: Mondays, Wednesdays and Fridays. The posts are shorter, sharper, and focused on topics like astrophysics, particle physics, relativity, cosmology, and who knows? Maybe even a bit of string theory or loop quantum gravity if I'm feeling frisky.

Discovery News actually hosts several science blogs, so after you're done checking out Twisted Physics, feel free to browse some of the others as well. For instance, here's my fellow new space-related bloggers debuting this week:

Next Generation: Student scientists in the field with David Chandler
Cosmic Ray: Ray Villard explores planets and distant worlds
Free Space: Irene Klotz looks at what's happening beyond Earth.
Space Across the Pond: Chris Lintott gives us the European view of the universe.
Space Disco: It's Dave Mosher's party and he'll dance if he wants to.
What's Up: Touring the night sky with Alan Dyer.

And in case you missed them: Tracy Staedter has an excellent technology and materials science blog called Material World, while fans of mummies and other archaeological pursuits ("Ooh! Ooh! Moi! Moi!" chirps Jen-Luc Piquant) might enjoy perusing the most excellent Archaeorama.

Rest assured, Cocktail Party Physics isn't going anywhere. It will continue much the same, staunchly independent and wheezily long-winded. How could I give up my bloggy haven? More and more, my other writing outlets are opting for shorter, sharper formats to appeal to ever-shorter attention spans. There's absolutely nothing wrong with that, but be honest: don't you sometimes get a hankering to really sink your teeth into a subject? The cocktail party is the only place where I have the freedom to ramble on about whatever topic catches my fancy on that particular day, for as long as I want. And sometimes the effort pays off: occasionally a post will lead to an article for a magazine, or a new book. Case in point: I am currently writing my third book for Penguin, inspired by a series of blog posts here at the cocktail party about my clumsy foray into teaching myself calculus.

The way I see it, I'm getting the best of both worlds: a chance to branch out a bit and explore what blogging is like for normal, less long-winded folks, while still preserving my online writing laboratory. Who knows? I might decide I like getting to the point occasionally. It's a crazy, twisted blogosphere out there; anything could happen.