Cocktail Party Physics

birds of a feather

Let me clarify, for the benefit of any concerned readers, that my post over the weekend bidding a fond farewell was not a departure from the blogosphere, but from my tenure as Journalist in Residence at the Kavli Institute for Theoretical Physics (KITP), the pretty peach-colored building in the photograph. It was a terrific experience, although not 100% comfortable -- which I consider a good thing, because if one is not pushed beyond one's comfort zone once in awhile, one never makes any significant developmental progress. Not only was much of the subject matter unfamiliar (and often incomprehensible) to me, but I was compelled to crystallize my various random thoughts and approaches to science communication into a workshop-type format that would appeal to theoretical physicists (or at least some of them). Did I succeed? Sometimes. The only flat-out failure was my attempt to use PowerPoint Karaoke to jump-start a discussion about communicating across disciplinary boundaries. Talk about a deflating experience. In retrospect, I think I "framed" it incorrectly for my target audience. Next time, it will take place in a local bar and feature copious amounts of alcohol. That seems to have worked very well for the PowerPoint Karaoke event organized by this group of Australians from McCann Sydney.

Anyway, after my final workshop (a post on that is forthcoming later this week), I jumped into my shiny red Prius and navigated my way one last time from Santa Barbara to Los Angeles, just like a homing pigeon seeking to reunite with its avian equivalent of a Spousal Unit. I relied on past experience and my trusty GPS display to find my way home, but apparently, birds use the earth's magnetic field to help them navigate. According to a recent entry on the physics arXiv blog maintained by the mysterious "KFC," "A growing body of evidence points to the possibility that a weak magnetic field can influence the outcome of a certain type of chemical reaction in bird retinas involving radical ion pairs." In fact, it's possible to confuse the navigational abilities of birds by zapping them with magnetic fields that, apparently, disrupt this reaction.

KFC explains that while this proposed mechanism has substantial experimental evidence, to date, it's been a little incomplete theoretically. The ion recombination effect that gives rise to a preferred chemical reaction happens far too quickly to allow for any influence from earth's magnetic field -- and yet, the experiments indicate that this field does play a vital role. Hmmm. In a recent paper posted to the arXiv, Iannis Kominis at the University of Crete has outlined an intriguing idea about how to resolve the paradox, namely, by evoking another one: arguably one of the most famous paradoxes in quantum physics, known as the quantum Zeno effect. Per KFC, "It states that the act of observing a quantum system can alter its evolution in a way that maintains the state for longer than expected." A more colloquial phrasing would say, "A watched quantum pot never boils."

Say what? There are quantum teapots? Well, no, not literally. But it's a useful analogy if one takes a bit of extra time to bone up on the broader context. And that means hopping into the Way-Back Machine for a brief visit to ancient Greece. Zeno was a Greek philosopher who logically constructed an argument to prove the (clearly) nonsensical assertion that motion is impossible. (Philosophers often like to play devil's advocate and argue for the impossible.) Zeno envisioned an archer shooting an arrow from his bow. Imagine Legolas Greenleaf from The Lord of the Rings doing just that. Assuming he shoots directly in front of him -- it's tradition in physics to hypothesize idealized situations -- the arrow will travel in a straight line indefinitely until it is stopped by an opposing force,  ideally, by piercing the heart of an evil Orc.

Zeno asked what would happen if you divided the distance the arrow must travel to its target into an infinite number of increasingly smaller increments, halving the distance every step of the way. He argued that this would mean the arrow would get closer and closer to its Orc-target but would never be able to reach the creature's heart. All motion would seem to stop. This sort of thing doesn't happen in the macroscopic world of our daily experience, of course: eventually Legolas' arrow will find its mark, and the Orc will perish. (Good riddance!) Zeno's abstract argument rests on the notion that the progression will continue for infinity, but in physical reality there is always some kind of limit. An endless series can still have a finite sum. There's lots of ways to describe the notion of a limit -- it's a key concept in modern calculus -- but just from a practical standpoint, the arrow has a fixed length (at least over the distance it travels). The distance the arrow must travel would eventually be subdivided to the point where the increments would be smaller than the arrow itself. And at that point, the arrow would hit its mark.

But the quantum world is a much weirder place, governed not by exact absolutes but by probabilities and uncertainty. On the subatomic level, something akin to Zeno's paradox actually happens. Physicists have argued for decades over the nature of a measurement or observation and its implications for quantum mechanics, ever since Werner Heisenberg first proposed his Uncertainty Principle. That's the one that says we can never know the precise momentum (or the precise velocity) associated with a particle, or we can know its exact location, but we can't know both at the same time. The very act of making the measurement changes the state of the atom.

It sounds like magic, but it's really not; it's the result of an actual physical force. We measure and observe atoms via electromagnetism, i.e., light of varying wavelengths. But how much we can see depends on the wavelength (and energy) of the light -- a photon's energy is inversely proportional to its wavelength, so the shorter the wavelength of light, the higher the energy of its constituent photons. And the smaller the object we wish to observe, the higher the energy of light we must use in order to get the resolution we need to see that object. An atom is really, really tiny. To locate its precise position, we'd need to hit it with a photon of such high energy that significant amounts of that energy would be transferred to the atom itself, thereby altering it (changing its speed or direction). Basically, we know where the atom was, not where it now is, because our ham-fisted "observation" has knocked it out of its prior position.

Ergo, Heisenberg concluded that the mere act of observation can determine the outcome of a quantum experiment. But experimental measurements are made in single, fixed, brief moments in time. What if it were possible to continuously observe an experiment? And at what point does observation become continuous? Scientists actually know the answer to both questions. Back in 1977, researchers discovered that a radioactive atom would never decay if it were "observed continuously." And the critical transition point is one measurement every four-thousandths of a second.

We have that precise figure thanks to the work of scientists at the National Institute of Standards and Technology (NIST) in Colorado. In 1989, they trapped 5000 charged beryllium atoms in a magnetic field and then tried to "boil" them by zapping them with a radio frequency field to raise their temperature. They expected the atoms to absorb the extra influx of energy and jump to higher ("hotter") energies. But this only happened if they didn't make any further measurements in the interim. The more often, they tried to measure the energy state of the atoms, the fewer of those atoms would reach the higher energy level. And at the rate of one measurement every four-thousandth of a second, no atoms at all jumped to the higher energy state. They just wouldn't heat up. It still happened even when the scientists used an automated measuring device.

Why does this happen? Blame it on uncertainty: the act of measurement interferes with the atoms' ability to absorb extra energy. The Spousal Unit once penned a classic blog post about this topic, employing quantum puppies to discuss the notion of quantum interrogation, which explains things beautifully even if the cuteness of the puppies tends to overpower all else. 

I like to think of it in the more concrete terms of Legolas' arrow. Let's imagine that this arrow is imbued with some elfin magical property by which it can grow longer over short intervals of time. That's a pretty decent analogy for what's happening to the uncertainty associated with two atomic energy states. At some point the uncertainty becomes large enough to bridge the two energy states -- akin to lengthening Legolas' arrow to the point where it can reach an Orc's heart -- the atom shifts to the higher energy state (and the arrow downs the evil Orc). The "uncertain arrow" then collapses back down to its original length and the whole process starts over again.

But every time we make a measurement of an atom's energy, or the length of Legolas' magic arrow -- and no, that is not a euphemism! Get your minds out of the gutter and back onto the curb with the rest of us! -- we reduce uncertainty, so it can't increase. Every time someone tries to measure Legolas' magic arrow, it becomes just a little bit shorter (oh, stop it!), to the point where it's never long enough to reach the Orc's heart. That's what happens to the energy states of atoms in the quantum Zeno effect. Uncertainty gets smaller with every measurement, because each measurement yields new information about the atoms, reducing the "fuzziness" of their energy states. Make those measurements often enough, and uncertainty never becomes sufficiently large to enable to atom to heat up. So a "watched" quantum pot never boils.

I know -- it's really weird, and utterly counter-intuitive. That's quantum physics for you. By now you're probably wondering what the hell any of this has to do with birds and their navigation skills -- assuming folks have even read this far. But according to Kominis in Crete, it is indeed relevant! Let's recap: scientists think that a weak magnetic field (like that of the earth) influences "the outcome of a certain type of chemical reaction in bird retinas involving radical ion pairs," but the sticking point is that the ion recombination happens too quickly for earth's magnetic field to have an actual impact. And yet it really does seem to influence the avian navigational process.

Per KFC, Kominis knew that it's "possible to slow down the rate at which molecules convert from ortho to para isomers when they are constantly involved in collisions." Something similar, he believes, happens in birds, namely, "The presence of a geomagnetic field extends the lifetime" of that recombination process, thereby giving the magnetic field more time to influence the outcome of the recombination. This really could turn out to be an extraordinary insight, since it means that birds have a built-in quantum sensor -- roughly akin to a GPS chip, perhaps, or at least a compass -- that determines their macroscopic behavior (i.e., navigation). It would also explain why birds occasionally are afflicted by a 30-degree "heading error," and why these built-in "compasses" only seem to be sensitive to a certain type of magnetic field strength.

Kominis even speculates that a similar mechanism might play a role in photosynthesis. It could be a brave new world out there, indeed, if it turns out that quantum effects can impact macroscale behavior. As KFC rightly notes, in his trademark style: The quantum consciousness people are going to be all over this like freshmen at a sorority party." Let the arguments begin!

a fond farewell

it's just a flesh wound

Martial arts and personal injury seem to go hand in hand. In my decade or so of jujitsu training, I broke two toes, dislocated my wrist, endured countless bruises and sprains, fractured my right elbow, and had my back thrown seriously out of whack thanks to a powerful guillotine choke administered by an over-enthusiastic ex-Marine. Most notably while practicing self-defense techniques against a long bo (actually a stickball bat) for my black belt test, I miscalculated during a duck-under technique, came up too soon, and received a nasty thwack! on the forehead that dropped me to one knee. It didn't actually hurt; I was mostly stunned. Then the blood began to gush, and I realized mat time was over, and I'd be spending several hours in the ER instead. The slash went clear down to the skull cap, and required 14 stitches to close. I still have a jagged scar across my forehead, although few people notice unless I point it out. (Also? No need for future botox treatments in that area, since the tiny muscle that causes frown wrinkles got sliced clean through. I literally cannot frown in that portion of my forehead.)

And I still loved every minute of my training. It's just part of the rite of passage when one is seriously studying the martial arts, but to outsiders, it can seem a bit, well, extreme. (A friend of mine became so upset at the perceived brutality of my black belt test, he literally had to leave the room at one point.) I was reminded of my halcyon days sweating and bleeding with my fellow jujitsu practitioners when I received an email from my friend Jim D., who started training in Tae Kwon Do a few years ago with his teenaged son, and recently passed his brown belt exam. Jim fractured his wrist this past week when he agreed to hold six pine boards while his instructor attempted to break them with a kick. Apparently, the instructor missed the central target area and the full force of his kick landed off to the side, so all that kinetic energy (or should one say momentum? Terminology can be so confusing!) went into Jim's wrist instead of into the board. Ouchie! At least he has a very impressive looking cast with which to impress the laydeez:

Anyway, Jim took the injury in stride, like any respectable martial artist. But he's the curious sort, so he emailed me asking if I knew anything about what went on from a physics standpoint to bring about his injury. I've done lecture/demos on the topic, focusing on broad concepts as opposed to specific calculations, so I knew a little, even though I never featured board-breaking in any of my lectures. Frankly, I've never understood the point of such an exercise. I'm an adherent of the Bruce Lee philosophy, immortalized in Enter the Dragon: "Boards don't hit back."

Except in the strictest physics sense, they kinda do. Per Newton's third law, momentum is conserved, and that translates into the well-known maxim of equal and opposite reaction. Many of us remember this from our introductory physics classes (or the equivalent thereof): If an object exerts a force on another object for a specific length of time, the second object will react by exerting an equal but opposite force for the same amount of time. So a board does "hit back" in that sense. The force generated by Jim's instructor created a reaction force in the opposite direction when his foot made contact with the boards; the boards gained exactly the amount of momentum the instructor's foot lost, or almost as much; some would have been lost via conversion into heat or noise energy, for example. The boards accelerated in the opposite direction in response to the kick.

A board will break when the part that is hit -- ideally the center -- is infused with more energy than its structure can handle, causing it to crack and/or break. But not every part of the board accelerates uniformly. The part that took the brunt of the kick -- again, ideally the center, although unfortunately for Jim, in his case it was off to the side -- accelerate much more than the surrounding piney-parts. This produces a localized strain, and if the strain becomes too great, the board will crack in that locale. As for how much force went into Jim's poor wrist, I could only offer the grossest generalities. For someone weighing 140 pounds, traveling at a final velocity of about 10 MPH when s/he hits the target, that person's body would have about 504 joules of energy. But that's assuming a full-tilt run and putting one's entire body mass behind a kick. Chances are, only a portion of one's body mass will be used -- although a TKD instructor, one assumes, would have excellent technique, and would therefore employ a greater percentage of his/her overall body mass than the average untrained kicker.

I told Jim if he wanted a truly thorough answer to his question, rather than the generalities I could offer, he should contact Jearl Walker, physics professor at Cleveland State University in Ohio, longtime contributor to Scientific American, and general all-around daredevil scientist, trying his hand at firewalking, lying down on a bed of nails, and investigating the physics of the martial arts. (He has a book -- and a Website -- called The Flying Circus of Physics detailing various real-world illustrative examples of physics concepts, as well as a blog.)

Per Walker, the force required to break a standard single 3/4-inch pine board is about 3000 Newtons; the force required to break a solid pine block of the same thickness as six stacked standard pine boards is astronomically higher: six times higher, as one might expect (6 x 3000 Newtons), [CORRECTION: I didn't read my hastily scrawled notes correctly: that should be 6 CUBED x 3000 Newtons. Yowza! 6 pine boards would be about 18,000 Newtons and change.] although there are numerous variables, such as whether the boards are warped, how many have knots (which make them harder to break), and how much space is between each board. Still, that's a pretty good ballpark figure. To phrase it in slightly different units, it takes about 5 joules of energy to break one board, and about 30 joules to break six. And a large fraction of that energy went into Jim's wrist instead of into the board. (Also per Walker, it was the focused shock wave that broke Jim's arm, not a static wave of energy.)

I think it would be a bit more difficult to determine the force of impact of my old head injury, although if any of you are bored over the weekend and care to give it a shot, we'd all be interested in hearing what you came up with. The mass of the stickball bat could probably be estimated, along with the respective body masses of me and my friend Jordan, who was swinging the stick. Then we'd need to estimate the speed of the swing (Jordan's pretty big, and strong, and to his credit, respected me enough to not pull his punches, so to speak), and how fast the stickball bat was traveling when it struck my head. The hardness of my head might also be a factor; all materials have their own varying degree of elasticity, after all. Complicating matters is the fact that both Jordan and I were moving when the injury occurred, and because of that, it was more of a sharp, glancing blow that slashed across my forehead at a downward angle. That's probably why I escaped without a concussion or more serious skull fracture.

Of course, like most head wounds, it bled like crazy. There are a lot of arteries, veins and capillaries in the head, since the brain requires a constant supply of oxygen- and glucose-rich blood to function properly. Also, I'd been exercising for a good hour by then, so the blood was really pumping. Funny side story: My chief instructor was chatting with a visitor to the dojo when my head injury occurred, his back to the mat. The visitor, gazing at the gushing blood in horror, mentioned that I'd been hurt, and really, oughtn't someone to do something? My instructor was used to people worrying about my welfare (there were very few women in my chosen style, and a hard fall from, say, a judo throw can look much worse than it really is). So he just waved it off and said, "It's okay -- she gets back up." Quoth the guest, "But... but... she's bleeding all over the mat!" That got his attention. He swung around, and immediately warned, "Don't you bleed on my mat!" Too late!

Ironically, when I examined my gi upon getting home, there was hardly any blood on it at all, just a bit of staining around the collar when the ER doc rinsed the matted blood from my hair. It had spurted outward in impressive gushes, hitting pretty much everyone in the vicinity except me -- just like the Black Knight's arterial sprays in Monty Python and the Holy Grail. ("It's just a flesh wound!") That's not what I would have expected.  Granted, we aren't talking about arterial spatter of the sort one sees routinely these days on C.S.I. Still, the blood pumping through my head at that point was clearly moving at a high enough pressure to cause an arterial-like spurt. Which meant I didn't need to soak my gi in bleach for two days, like a few of my unfortunate fellow students. (One guy -- who kindly administered pressure to my wound to stem the bleeding while waiting for the ambulance to arrive, and thus had my blood all over him -- just gave up bought a new gi. Thanks, Vito!)

The C.S.I. franchise certainly has its critics when it comes to how it depicts forensic science, but in fact, there is such a thing as bloodstain pattern interpretation that can be used to piece together the events that gave rise to a particular pattern of spatter or bloodstains. Experts trained in this approach consider such qualities as the viscosity of blood, the specific gravitational forces acting upon it, and the role of surface tension. (For instance, a bit of blood that falls off a pricked finger will round out into a sphere because surface tension acts to reduce surface area to the absolute minimum possible.) Here's some fun facts I learned about blood spatter (illustrated by some handy photos) from this excellent Website:

* Blood cast from a moving source will make smaller droplets than blood cast from a stationary source.

* Blood follows the same basic laws of physics as any projectile in motion. (This means it should be possible, in principle, to calculate the trajectory of the blood spurting from my head wound and predict where it would land on the mat, so everyone could steer clear of that spot.)

* The terminal velocity of a falling blood drop depends on its size: smaller drops have a lower terminal velocity and reach that point after a shorter fall distance that larger droplets (which accelerate over a greater distance and thus reach a greater terminal velocity).

* The shape of the blood spot depends in part on the texture of the surface on which it calls. If it falls on smooth glass, it will be circular and fairly uniform in shape. If it calls on a textured surface, such as paper, or wood (or a judo mat), the shape won't be nearly as regular. In general, the harder the surface, the less spatter there will be. If a blood drop hits a surface that is both hard and smooth, it will break apart upon impact into smaller droplets -- and those offspring droplets will continue to move in the same direction as the parent drop.

* The angle of impact also determines a blood drop's final shape. For instance, a vertical drop onto a smooth target tilted at 90 degrees results in a circular stain, and as the angle decreases, the stain becomes more elongated, and its length-to-width ratio increases accordingly.

* Finally, blood spatter patterns are classified according to the velocity with which the blood struck a given surface. For instance, spatter patterns occur when blood is projected at a velocity greater than the force of gravity, such as what occurs when blood is cast off a weapon. (Per the site, "The direction and origin of the backswing is often clearly discernible.") Low-velocity blood spatter is basically what happens when the stuff just drips downward from a cut. A blow with a baseball bat would constitute medium-velocity blood spatter, producing spots of about 4 mm in diameter, while a gunshot will produce high-velocity spatter and a "fine mist" of spots less than 1 mm in diameter. Arterial spurting is a category all its own.

The Black Knight would have been fascinated, I'm sure, to hear King Arthur ruminate on these matters (far more interesting than determining the air speed velocity of an unladen sparrow, both African and European varieties). There's much, much more to do with the science of blood spatter, and the physics of the martial arts (judo throws are a specialty all their own), but I suspect I've grossed everyone out enough for one day.

let me explain

I found myself chuckling in amused recognition on Sunday while reading Rebecca Solnit's Op-Ed in the Los Angeles Times, "Men Who Explain Things." Solnit, for those unfamiliar with her work, is the author of A Field Guide to Getting Lost and River of Shadows: Eadweard Muybridge and the Technological Wild West, among other tomes. Her Op-Ed is a wry commentary on a familiar phenomenon, per the subhead: "Every woman knows what it's like to be patronized by a guy who won't let facts get in the way." She opens with the story of an upscale party at a chalet in Aspen; most of the guests were old enough that she, in her 40s, was considered quite young. So perhaps it shouldn't have been surprising when the host mentioned he'd heard she'd written a couple of books, and condescendingly asked what they might be about, "in the way you encourage your friend's 7-year-old to describe flute practice."

Solnit has actually written six or seven books, but rather than give him a laundry list -- correctly guessing he was less interested in her work than in figuring out how he could use the topic to jump-start his own literary soliloquy -- she started to tell him about the latest book (published in 2003), on Muybridge. In record time, her host interrupted and proceeded to expound at length on the "very important" Muybridge book that had been published that year, which she really must read if she was interested in Muybridge, and launched into a summation of that revered tome for her edification. His soliloquy was delivered "with that smug look I know so well in a man holding forth, eyes fixed on the fuzzy far horizon of his own authority." (That Solnit has quite a way with words, doesn't she?) Not even the news that Solnit had written the "very important" book he was pontificating about was enough to dissuade him for long, beyond a moment of ashen-faced embarrassment. Small wonder he couldn't remember her name. He had not, it turned out, actually read the book on which he was holding forth with such authority. He'd merely skimmed an article about it in The New York Times Book Review.

Now, this sort of unmasked literary pretension is quite common in certain pseudo-intellectual circles, and is not gender-specific per se. (Frankly, certain women can be just as preening and pretentious, with the same need to hold center stage. They can also be absolutely brutal when it comes to the art of diminishing the stature of perceived rivals via the subtly condescending put-down.) Solnit is very careful to point out that she is not describing all men, only a particularly annoying sub-species, and acknowledges that "my life is well-sprinkled with lovely men... Still, there are these other men, too." Explaining Men are the in-your-face embodiment of what Solnit decries as a much broader "archipelago of arrogance." It bespeaks an underlying attitude towards women as "empty vessel[s] to be filled with their [i.e., men's] wisdom and knowledge," and the worst part is, women themselves often buy into this skewed under-assessment of their relevance and abilities.

"Men explain things to me, and to other women, whether or not they know what they're talking about.... Every woman knows what I mean. It's the presumption that makes it hard, at times, for any woman in any field; that keeps women from speaking up and from being heard when they dare; that crushes young women into silence by indicating... that this is not their world. It trains us in self-doubt and self-limitation just as it exercises men's unsupported over-confidence. This syndrome is something nearly every woman faces every day, within herself too, a belief in her superfluity, an invitation to silence...."

My own experiences with Explaining Men are a bit more complex, in part because I am a science writer, and thus quite often I want someone to explain something esoteric to me, and welcome the attempt at edification. (It helps that I am naturally curious, too.) In the male-dominated field of physics, that explainer is usually going to be a man -- although the percentage of women is inching upwards every so slowly with each passing decade -- and for the most part, those men have been very decent about it, with a few rare exceptions.

That's not what Solnit is describing, however. She's talking about the sort of patronizing condescension that pervades all kinds of daily interactions between men and women; Men Who Explain Things are among the more benign examples. So I tend to agree in principle with Solnit when she writes, "Most women fight wars on two fronts, one for whatever the putative topic is, and one simply for the right to speak, to have ideas, to be acknowledged to be in possession of facts and truths, to have value...." This harsh reality hit me full force with the publication of my first book a few years ago, and my very first radio interview to promote it: an hour-long call-in program in San Francisco. Something about a former English major thinking she could effectively communicate physics concepts to a general audience stuck in the craw of one cranky male physicist, who called in specifically to harangue me on the air for my chutzpah is daring to presume to "speak for physics" (a claim I never made). He didn't actually call me uppity English major scum, but the implication was clear.

"But surely that had nothing to do with your gender," some of you might be thinking. I suspect it did. After all, he didn't merely take issue with the substance of what I said (the cornerstone of any healthy debate); he questioned my right to say anything publicly on the topic at all.

A similar incident occurred about two months later when I appeared on a radio call-in show in Washington, DC. Another male physicist called in, highly irate, to take issue with my off-the-cuff summation of the uncertainty principle. It was a nitpicky technical point, plus, it was a live show, so for all I knew, I could have mis-spoken, and said so. I hadn't, as it turns out; I'd simplified the explanation for the public radio audience, but within those constraints, it was a perfectly acceptable summation. A couple other male physicists of my acquaintance who heard the show were incensed that the caller had attacked me for no good reason -- and, frankly, a bit disappointed that I hadn't defended myself more aggressively. Mea culpa. I let self-doubt hold sway. The caller claimed to be a physicist, and I was just a first-time author, and a girl at that. Some small part of me just assumed I'd made a mistake, rather than concluding that he was being a jerk.

I have a lot more confidence these days in my right to speak and be heard; now, I'd come out swinging and make mincemeat out of that irate Explaining Man. But three years ago, I was still a bit lacking in confidence, despite all the hard work I'd done to research the book, running all the sample chapters past PhD physicists to check for technical accuracy, and so forth. Even Solnit, a far more seasoned writer, has fallen victim to this phenomenon: "There was a moment there when I was willing to believe Mr. Very Important and his overweening confidence over my more shaky certainty." And it was her book he was pontificating about!

Would I have been attacked so vigorously had I not been a young woman, with a degree in English, daring to speak about the caller's pet topic? Everyone mis-speaks occasionally when talking off-the-cuff, including the Spousal Unit. But he's a man, with a PhD in physics, so when he mis-speaks, it's assumed that he's made an honest error. When I mis-speak, it's usually assumed I am ignorant. Or sloppy. Or both. At least by men. Honestly, there were times, during the year of the First Book, when it felt less like I was being interviewed about a book I'd written, and more like I was being grilled before some self-appointed Inquisition of Popular Physics Writing to make sure I had earned the right to even be there in the first place. Generally speaking, the women who interviewed me (or reviewed the book) were interested and friendly (even if they had criticisms); several men were condescending at best, harshly critical and combative at worst.

Don't get me wrong: I'm not one of those writers who thinks her words are sacred; I rely on thoughtful, constructive criticism to improve my skills, and deliberately seek it out. I'm also a bit of a perfectionist. Like most writers, I'd dearly love to rewrite portions of that first book, so it could benefit from everything I learned in the process of writing it. That sort of input is not the same thing as a subtle power play, an attempt to put the little lady in her place, thinly disguised as helpful criticism, the better to puff up one's own ego and sense of superiority. (Jen-Luc Piquant acidly comments that if you take such faux-criticism otherwise, you're denounced as clearly "over-sensitive." Hey, must be "that time of the month!" Insert deprecating chuckle here. Cut her some slack. She's still bitter over a recent confrontation with a pompous Lacanian Avatar Who Explains Things about deconstructing Jane Eyre.)

Sometimes I envy Explaining Men this over-weening confidence in their own authority -- even when they actually know very little about the particular topic at hand. In this era of superficial dialogue, the appearance of knowledge is often all that's required.  Then again, the constant reminders of my own supposed irrelevance have made me stronger, more confident with each storm I weather that yes, I do deserve to be here, and to be heard.  All those years as a struggling writer have given me a hard-won expertise that no patronizing Explaining Man can take away from me.

Maybe I'm more appreciative of the freedom to speak because I had to fight so hard to find my voice in the first place. These days, I'm more inclined towards rueful amusement when encountering Men Who Explain Things. But as Solnit points out, that's because we've had to learn to publicly stand our ground as authors; millions of other women don't get that particular boost, and never learn to push back. That's the underlying tragedy of what would otherwise be an amusing oddity of social discourse. Per Solnit: "The battle with Men Who Explain Things has trampled many women... [including] the countless women who came before me and were not allowed into the laboratory, or the library, or the conversation, or the revolution, or even the category called human."

Certainly, throughout the ages, women have not enjoyed many exalted positions in intellectual circles, especially in math and science. Usually, they had to teach themselves, unless they came from wealthy and/or noble families. Such was the case with an 18th century Italian mathematician named Maria Gaetana Agnesi. The eldest of 21 children -- I was relieved to learn her father married three times, since the thought of one woman enduring that many pregnancies boggled the mind -- Agnesi was very much a child prodigy, known in her family as "the Walking Polyglot" because she could speak French, Italian, Greek, Hebrew, Spanish, German and Latin by the time she was 13.

Agnesi had the advantage of a wealthy upbringing; the family fortune came from the silk trade. And she also had a highly supportive father, who hired the very best tutors for his talented elder daughter. Unfortunately for the shy, retiring Agnesi, he also insisted she participate in regular intellectual "salons" he hosted for great thinkers hailing from all over Europe. The young Maria delivered an oration in defense of higher education for women in Latin at the age of 9 (she had translated it from the Italian herself and memorized the text).

There is evidence from contemporary accounts that Agnesi loathed this sort of thing and hated being put on display, even though her erudition earned her much admiration. One contemporary, Charles de Brosseslde Brosses, recalled, "she told me that she was very sorry that the visit had taken the form of a thesis defence, and that she did not like to speak publicly of such things, where for every one that was amused, twenty were bored to death."

Unlike the men in her father's salon, Agnesi didn't much care for Explaining Things. De Brosses  admired her intellectual prowess greatly, and expressed his horror upon learning that she wished to become a nun. What a waste! was the implied sentiment. And perhaps it was. But I'm thinking maybe she was far too intelligent for her own good; she just couldn't take the self-aggrandizing intellectuals of her father's acquaintance seriously. And perhaps she realized that she would always be proving herself, and that her accomplishments, no matter how impressive, would always be treated with some degree of patronizing amazement. ("Look at the smart woman discoursing in Latin!")

Agnesi did, eventually, become a nun, but not before spending 10 years writing a seminal mathematics textbook, Analytical Institutions, which was published in 1748. (Most biographies, while admiring, feel compelled to note that the tome contained "no original mathematics.") She was also the first woman to be appointed as a mathematics professor at a university -- the University of Bologna -- although there's no record she ever formally accepted the position. She died a pauper in 1799, having given away everything she owned. At least there's a crater on Venus named in her memory. And she need never be forced to perform like a trained circus monkey again, or listen to any more Explaining Men eager to find some means to edify such a prodigy. She can just let her life's work speak for itself.

I'll give Solnit the last word, since she writes so eloquently:

"Men explain things to me still. And no man has ever apologized for explaining, wrongly, things that I know and they don't. Not yet, but according to the actuarial tables, I may have another 40-something years to live, more or less, so it could happen. Though I'm not holding my breath."

these boots weren't made for walking

Every now and then, shoe-frenzy makes a cameo appearance the blogosphere. Okay, it's omnipresent in blogs dealing with fashion and shopping, but most of us (male and female) have to shop for footwear at some point. And some of us feel compelled to blog about our particularly noteworthy finds, at least in passing. You know, like the incomparable Heather Armstrong at Dooce, who has waxed ecstatic about silver-metallic ballet flats (dismissed by her husband as "elf shoes"), and once wrote this wonderful paean to the joy of finding the perfect pair. Armstrong is known for detailing the minutiae of her daily life on her blog, but that doesn't mean the rest of us don't occasionally bliss out over an especially nifty pair of pumps. Which is exactly what happened in comment threads this week over at Bitch PhD and Shakesville. (Fair warning to the easily offended: why are you clicking on a link to a blog called Bitch PhD in the first place? Because you thought it would be about knitting while sipping mint juleps and nibbling cucumber sandwiches? Duh!)

Ah, but there are lots of killjoys out there on teh Internets, no doubt wearing too-tight or ill-fitting shoes (or, worse, clunky "sensible" shoes), which might explain why they're so cranky, and why they feel compelled to spoil other people's fun. Apparently some people criticized Shakesville's Melissa McEwan for departing from her usual hard-hitting feminist political fare to focus on something as trivial as shoes. I'm guessing this is something women scientists face as well. We aren't allowed, it seems, to take pleasure in the small joys of life and still be Serious Women, respected professionals in our chosen fields.

Um, screw that. I'm the patron saint of comfy sensible shoes -- I'm known for it among my female friends, in fact (who are not always complimentary about my workmanlike choices) -- but that doesn't mean I can't branch out once in awhile and be truly stylin'. Who says women can't be smart, serious, 100% professional, and still totally rock a pair of hot pink pumps if they want to? (Or asphalt-stomping Doc Martens, if that's your preference. To each his/her own.) In honor of Melissa, Bitch PhD, Heather, and all you other shoe-lovers out there, today's post will focus on the science of footwear.

First, a look at this week's featured products before we delve into the science. Bitch PhD offered these multi-colored beauties:

Then Melissa weighed in with these innocent-seeming pink pumps that launched a thousand angry comments (UPDATE: Oops! Apparently it was only a couple of negative comments, but it did inspire her to write a blog post on the topic):

Followed by these plaid ballet flats, for the more sensible-minded of her readers:

Just for good measure, since we're talking flats, here's Heather's silver ballet flats (a.k.a., "elf shoes"), which I covet greatly:

Perhaps your tastes run to more of a Goth/fetish look. A few blog posts ago, I mentioned going shoe-shopping with the Spousal Unit (who wore ostrich skin boots at our wedding, so he's a man who appreciates stylish footwear). I got some comfy low-heeled sandals for summer, a couple pairs of Skechers (for daily practical wear), and these fabulous New Rock Malicia Silver Spiderweb mid-calf-length boots:

Yeah. It's an indulgence. These boots are definitely not made for walking, although as stiletto heels go, they're surprisingly comfortable. Ergo, I bought them. That's what a well-made pair of heels does for you, and why they're worth paying a bit extra. According to a UK pal of mine, "fantasy heels" are all the rage this season for the "fashion forward." Take that, cranky Shakesville commenters! (Or, you know, the one or two commenters who complained...)

Okay, so we're fashion forward. Yay, us. But could there really be any actual science associated with sexy stilettos? "Mais oui!" Jen-Luc Piquant exclaims. "How could you doubt it?" We need look no further than Jolly Olde England. Several years ago, The Globe and Mail ran an entertaining article about a physics professor at the University of Surrey named Paul Stevenson who calculated the maximum height of stiletto heels a woman could wear without falling over, and/or cramping up in pain. He did so at the behest of a publicist at the Institute of Physics in London, who -- while watching the series finale of Sex and the City -- found herself wondering how the women in the show could possibly wear such high stiletto heels and still perambulate around the Big Apple with any measure of grace. I've never seen the appeal of the show myself (which puts me firmly in the minority among women), but must admit, it's a valid question.

Stevenson obliged by coming up with a formula for the maximum heel height you could wear without tipping over: h = Q x (12+3s/8). His formula determines how changes in foot slope increase the "tippiness" likelihood. It's based on the wearer's shoe size and something he calls the "Q" factor: taking into account sociological factors like how much pain a woman is prepared to tolerate for the sake of style. (If you're me, the Q factor is pretty low: if a shoe pinches or chafes, it's coming off, which is why those gorgeous Michael Kors sage green ballet flats I bought for half price are sitting forlornly in my closet, unworn. But a friend of mine once developed bleeding blisters walking around in ill-fitting shoes because she loved them so much.) It's hard to quantify that sort of subjective parameter, which is probably why we haven't seen Stevenson's paper on arXiv. But he made a noble attempt, figuring in things like "the probability that wearing the shoes will turn heads," how much experience (in years) the wearer has with high heels, the cost of the shoes (in British pounds), how much time has elapsed since the shoe style was all the rage, and of course, the amount of alcohol consumed by the wearer.

Going by Stevenson's handy formula, the answer is: about five inches. (Of course, that's assuming the wearer is sober; alcohol can really disrupt one's equilibrium.) It's basic Pythagorean geometry, really: much like the hypotenuse of a triangle, the sharper the angle of the foot in the shoe, the more unsteady the wearer becomes -- especially since stilettos support the wearer's weight on a relatively small area. The answer would be different for a broader heel, since the greater area would probably help the wearer remain stable at even greater heel heights.

Stability aside, one's weight pressing down on stiletto heels produces a huge amount of pressure. The late, great songstress Kirsty MacColl has a classic tune called "In These Shoes," wherein the heroine turns down offers from aspiring swains to take her on all kinds of far-flung adventures, in response to which she sniffs, "In these shoes? I don't think so...." In the final stanza, an Englishman asks her to walk up and down his spine in her sexy stilettos. The response: "In these shoes? I doubt you'd survive." She's not kidding. A 100-pound woman in a pair of stiletto high heels would exert pressure under the foot that is 20 times greater than that of a 6-ton elephant. (Jen-Luc cautions: Don't make Sarah Jessica Parker angry by knocking Sex and the City too loudly, lest she stomp on you with her pricey Manolo Blahnik pumps!)

Stevenson's formula was primarily concerned with balance, but the awkward angles and high pressures associated with heels has been cause for concern in some circles. For years now, orthopaedists, podiatrists and other medical sorts have been warning women about the health risks of routinely donning high heels: bunions, stress fractures, joint pain in the ball of the foot (because weight is shifted to the ball of your foot, rather than being distributed over the entire foot), corns and calluses, hammertoes, ingrown toenails, toenail fungus, and something called "pump bumps" (enlargement of the bony area on the back of the heel). High heels have been linked to injured leg muscles, lower back pain, and osteoarthritis in the knee, too, because when you wear heels, the foot slides forward, redistributes your weight and creates those unnatural pressure points. You can pretty much kiss healthy spinal alignment goodbye. 

High heels also mean your heel bones don't regularly come into contact with the ground, so the Achilles tendon can't stretch out properly while walking, and thus becomes shortened and/or tightened. Then there's a little thing called Morton's neuroma, a growth of nerve tissue in the foot -- usually between the third and fourth toes -- that arises when you wear too-tight shoes, causing sharp burning pain in the ball of your foot and a stinging or numbness in your toes. The list goes on and on. In fact, thanks to high heels, the American Orthopaedic Foot & Ankle Society estimates that women account for 90% of surgeries performed each year for common foot ailments.  That's about $3.5 billion annually in the US alone, according to this May 2007 article in the Washington Post.

Suddenly Heather's "elf shoes" are starting to look pretty good, right? Ah, but are flats really better for your feet than heels? Inquiring minds want to know. The answer is, not necessarily. Flip-flops, for example, can cause other kinds of problems, like plantar fasciitis, thanks to the repeated lifting of the heel away from the shoe surface. Ballet flats don't offer much in the way of arch support, and can still be tight and/or ill-fitting; they're not really made for walking long distances, either. So perhaps now all the folks who snickered at the practical Teva clogs I wore until they fell apart will reconsider their harsh judgment of my fashion sense. I could walk for hours in those Tevas, they were that comfortable. And having lived without a car for many years in New York City and Washington DC, I've always been an inveterate walker.

So, what should we look for in a stylin' pair of shoes? The recommendation is usually for a rounded toe, more cushioning in the sole, and good arch support (a quality that is lacking in my pretty new Skechers and languishing Kors ballet flats). If one must wear high heels, it's recommended you limit the height to 3 inches (preferably 1 or 2 inches) and not wear them for more than three hours at a stretch -- something that is not an option for, say, cocktail waitresses in Vegas. Wider heels are preferable to stilettos, and it's important to make sure shoes aren't too narrow for your feet.

The Mayo Clinic recommends shopping for shoes in the late afternoon or early evening, since the feet swell up during the day, and trying on both shoes of a pair, since many folks have one foot that is bigger than the other. Also? "There's no such thing as a 'break-in' period. Shoes should feel comfortable right away. Don't buy a pair that you think will fit well after you've worn them for awhile." (*hangs head in shame*) We have all been guilty of this... especially when I was impoverished in the Big Apple and Payless Shoe Source was the only outlet I could afford.

When I shop for "fashionable" shoes these days, I tend to avoid pointed toes as a general rule (because I have freakishly long, mutant toes), but here's something I discovered about pricier shoes: the pointed toes are actually "fake." What I mean is, they're made longer than usual, so one's toes aren't really being crunched together into that tiny space. That's certainly the case with my new Malicia spiderweb boots, and with the stunning black Dior pumps I purchased for our wedding. The downside: most of us can't afford the high price tags for high-end heels. Those prices have recently gotten way out of hand, with some of the most famous designers charging over $1000. The Los Angeles Times recently reported that many consumers have "balked" at paying those prices. Um, ya think?

The good news for women who love their stiletto heels is twofold. First, several shoe manufacturers are coming out with "healthy high heels" with more air-cushioning. For example, the Massachusetts-based Insolia has designed a line of heels with weight-shifting inserts that shift body weight off the ball of the foot, with a shape that places feet in optimal position for a high heel, thereby improving body alignment and ankle stability -- while still making sure the shoes are attractive.

But there's even better news, according to this February 12 report: "High Heels Might Boost Your Sex Life."  The same unnatural posture that wrecks your spinal alignment can also tone your abdomen and pelvic floor, according to Maria Angela Cerruto, a urologist at the University of Verona in Italy. She tested 66 women under the age of 50 and found that if they stood with feet at a 15-degree angle -- achievable by wearing three-inch heels -- the pelvic muscles were more relaxed, making them stronger and easier to contract. To counter being pushed forward by the heels, women naturally tighten the abdominal muscles and push the pelvis under. Cerruto thinks this might mean that wearing heals could reduce the need for so-called "Kegel" pelvic exercises -- associated not just with reversing the toll of pregnancy, childbirth, extra weight and such on women, but also with improving sexual response/gratification. Manolo Blahnik, for one, is thrilled at the findings, no doubt with visions of dollar signs dancing in his head.

So there you have it: the science of shoes. The upshot is, be smart about your choices, but wear the styles you like, whether it be sexy stilettos, ballet flats, platform wedges, comfy Tevas, cowboy boots, or anything in between.  After all, ever since humans began wearing shoes, the accessory has been as much about status and fashion, as about practicality and comfort. The WaPo article quotes Elizabeth Semmelhack, curator at Toronto's Bata Shoe Museum, which has some 13,000 artifacts, including one that is nearly 4500 years old. "It's absolutely clear to me... when I look at cultures that impracticality is one of the primary features among the privileged" class, she said. And the rest of us seek to emulate the privileged class. Or perhaps, as Dawn once said in an episode of Buffy the Vampire Slayer, it's just because "Everyone loves a slender ankle."

the great junkyard in the sky

Last week, I was driving home to Los Angeles from Santa Barbara along the 101, when a random piece of debris flew off a truck in the right lane and struck the hood of my shiny red Prius. It was just a little piece of rock, but at highway speeds, it carried enough kinetic energy to gouge the paint when it struck. It was most distressing, even though I realize that cars begin to depreciate the second you drive them off the lot, so you really can't get too worked up over the inevitable wear and tear. Still, it was just so random and unnecessary. Amplify my reaction about a million-fold, and you might get some sense of how NASA astronauts and engineers feel when one of their prized spacecraft or satellites gets pinged with bits of orbital debris: otherwise known as "space junk." Sure, the damage is mostly minor -- a scratch here, a barely perceptible dent there, a pinged window on the Space Shuttle -- but as bits of discarded space junk accumulate to greater densities, the risk of collisions with the potential for serious damage is increasing at an alarming rate. And that debris is traveling a heckuva lot faster than 65 MPH. (I might be down-playing the truth there, rather than admit to driving above the speed limit.)

We should have seen this coming. Many years ago, while chatting with a few space scientists about various missions, I innocently asked, "So, how do we get all that stuff back down again once we're done with it?" The answer: we don't. It just sits up there, year after year, until various forces conspire to pull it out of orbit and back down to earth. It's not something many of us think about as we breathlessly watch each Space Shuttle launch, and marvel at the glorious images collected by the Hubble Space Telescope, Mars Rover, the Cassini mission (just renewed for another two years, so congrats!), and so forth. We certainly don't think about the potential consequences of littering the Earth's orbit with all our communication satellites: we need our GPS, our satellite radios, and our satellite TV. Those are very real, much appreciated technological benefits. But we gain them at a cost. The sad truth is, the "human footprint" in space is starting to get a bit too big to ignore. We make a mess wherever we go, it seems, and haven't been any better about cleaning up after ourselves in space as we have here on earth. It's just not "cost effective."

Well, it looks like we're now starting to pay the price for that short-sighted behavior, according to David Wright of the Union of Concerned Scientists (which maintains a satellite database), who addressed the problem of space debris at the APS April Meeting. It's not exactly a new concern: back in the mid-1990s, the United Nations deemed it a significant enough risk to implement mitigation measures aimed at reining in the proliferation of space debris, measures it re-introduced in June 2007. Mitigation worked, for awhile (throughout the 1990s), but as we continue not just to explore space, but also exploit it for commercial (and/or military) gain, the issue is fast approaching a crisis point. The big worry is supercriticality: what happens when the destruction of an orbiting object into lots of smaller fragments of debris initiates a chain reaction of satellites in nearby orbits.

"With their high speed in orbit, even relatively small pieces of debris can damage or destroy satellites in a collision,'" Wright wrote in the October 2007 issue of Physics Today. "Since debris at high altitudes can stay in orbit for decades or longer, it accumulates as more is produced. As the amount grows, the risk of collisions with satellites also grows. If the amount of debris at some altitudes becomes sufficiently large, it could become difficult to use these regions for satellites." It may already be too late: Wright cites a 2006 study by NASA's Orbital Debris Program that found certain parts of space (the 900 to 1000 km band in particular, part of the Lower Earth Orbit, or LEO) have already reached supercritical debris densities; in fact, it estimates that an active satellite in LEO will collide with a piece of debris larger than 1 centimeter every five to six years.

A one-centimeter piece of debris doesn't sound like much, but at the high orbital velocities in space, it can pack a wallop. Wright noted that orbital speeds in LEO are typically greater than 7 kilometers per second (30 times faster than a jet aircraft), and "the relative seed of a piece of debris approaching a satellite in an intersecting orbit may be 10 kilometers per second or higher." That's a lot of kinetic energy. According to the folks at Space Watch, "a tiny speck of paint from a satellite once dug a pit in a space shuttle window nearly a quarter-inch wide" (see picture). Returned solar arrays from the Hubble telescope had multiple impact craters from collisions with debris, each one counted and classified by the European Space Agency (ESA) for future reference.

No wonder the Space Shuttle chose to perform a collision avoidance maneuver with a 7-second reaction control burn to avoid colliding with debris from an old Cosmos satellite in September 1991. France wasn't so fortunate. In 1996, a collision with space debris tore off a boom from the French satellite Cerise.

Where does all that junk come from? It's a mix of things, ranging from spent rocket stages, defunct satellites, fragments from explosions of various space gear, paint flakes, dust, and so forth, all dating back to the launch of Sputnik in the 1950s, ushering in the dawn of the space age. Haven't you ever lost a glove? Astronaut Ed White did, on the very first US space-walk, except his just floated around for a weeks until it re-entered the atmosphere. Lost pliers, cameras, even jettisoned garbage bags, routinely drift around a bit, but they're not major contributors to the space debris problem because they don't stay up very long.

Usually, this re-entry isn't catastrophic. Sure, in 1996, an Oklahoma woman got hit on the shoulder by a small piece of metallic material that fell from the sky. It turned out to be part of a rocket fuel tank used to launch a satellite earlier that year. But sometimes it can wreak devastation. in July 1979, Skylab -- the 78-ton space station the US had since abandoned -- came crashing down a bit earlier than planned, raining debris all across the Australian outback. Fortunately, it's not a highly populated area, but imagine if the same thing happened along the Northeast coast, or the heart of Europe. And in 2006, wreckage from a Russian spy satellite came awfully close to colliding with an Airbus carrying 270 passengers over the Pacific Ocean. That could have been truly disastrous. (I'm told the odds are unlikely, since most debris burns up as it re-enters the atmosphere, or re-enters over water -- nearly 3/4 of the planet is wet, and there are still vast swatches of uninhabited dry land.)

It's the explosions that seem to cause most of the trouble when it comes to accumulated debris. Rockets or spacecraft with unspent fuel have been known to collide with other objects and explode, thereby producing even more bits of debris. And sometimes the explosions are deliberate: China made global headlines in January 2007 when it used an anti-satellite (ASAT) missile to destroy one of its old weather satellites orbiting about 537 miles above Earth, thereby creating the largest amount of space debris in history: more than 2300 pieces bigger than a golf ball, and over 35,000 pieces larger than 1 centimeter. 

Perhaps you're thinking, hey, no biggie. What goes up, must come down, right? Well, yes -- eventually. Aye, there's the rub. The higher the altitude, the longer the stuff stays in orbit. The debris from the Chinese test was high enough that scientists estimate that stuff won't "deorbit" for 35 to 100 years. In the meantime, any other spacecraft and satellites out there better be prepared to duck. The ESA offers the image below as a visual representation of the distribution of "space junk" in the  lower earth orbit (h/t to James H. of Island of Doubt, from whom I shamelessly snagged the image).

Thanks to these kinds of events, the amount of space junk keeps growing. In 2006, NASA scientists published a report in Science concluding that even if the global community stopped launching things into space today, it still wouldn't solve the problem. This is due to something rather grandiosely dubbed the Kessler Syndrome (a staple of science fiction by now): there's already so much aging crap in orbit, many of which may collide with existing debris and break into even more pieces, thereby compounding the clutter problem. And before you know it, we're at supercriticality. The man behind the moniker, Donald Kessler (former head of NASA's orbital debris program) told the New York Times in February that the worst-case scenario is an over-hyped exaggeration, but doesn't deny that space debris presents a very real, very worrisome problem.

So what can we do about all that junk up there? Um... not very much. There's nothing wrong with the UN's mitigation measures in principle, but such measures merely maintain the status quo, and frankly, they're more like guidelines, with no real regulatory teeth. Plus, any "gains" can be easily wiped out by one bust-up event. Wright noted that while the UN's measures caused the accumulation of debris to level off in the 1990s, last year's Chinese test of an anti-satellite mission to destroy an old weather satellite alone undid all the gains of the previous decade. Uh, thanks for nothing, China. Your little "test" is the reason NASA had to move its Terra environmental spacecraft to avoid colliding with all that debris.

Not that the US can really point fingers, mind you.  Nor can Russia. The oldest piece of space junk still in orbit is a the US satellite Vanguard 1, first launched in 1958. It's like the Energizer bunny, except it does nothing except drift about in orbit with no sign of falling back to earth any time soon. At least it hasn't exploded into thousands of tiny pieces. A US Pegasus rocket exploded in 1996, generating a cloud of about 300,000 fragments. That alone doubled the collision risk for the plucky Hubble Space Telescope. We did it again (oops!) just this past February, using an SM-3 missile to destroy a defective satellite carrying toxic hydrazine fuel; sure, we did it a pretty low altitude, but still -- let he who has not sinned cast the first stone. And in February 2007, a Russian booster stage exploded in orbit over Australia (what does space debris have against that continent?), producing just as much debris as the Chinese ASAT test, albeit at a lower altitude, so the debris won't be stuck up there as long.

The NASA scientists who authored the Science article advocated removal of existing large objects from orbit to "prevent future problems for research in and commercialization of space." However, they concluded, "As of now, there is no viable solution, technically and economically, to remove objects from space." Lots of things have been proposed to "sweep" space debris back into the atmosphere: laser "brooms" that "vaporize or nudge particles into rapidly-decaying orbits, or huge aerogel blobs to absorb impacting junk and eventually fall out of orbit with them trapped inside," per Wikipedia. We could also design our satellites and spacecraft with engines to direct them back to Earth, but this is really expensive (it adds considerable weight, for starters), for what is deemed to be very little benefit. People have also toyed with the notion of using ground-based lasers to disturb the orbits of defunct satellites, but the darn things are so big, it would take a huge amount of laser energy to make any kind of difference.

My personal favorite is a proposed "terminator  tether" for any future launched spacecraft or satellites, which would use electromagnetic effects to slow down a spacecraft sufficiently that it can no longer stay in orbit. Apparently France did this successfully in 2003 with one of its satellites, which is expected to re-enter the atmosphere in about 15 years. Yeah, that's considered a short-term solution. On cosmic scales, it is. On human scales? Not so much. Then there are those who think we shouldn't even bother trying to get all that stuff back down: why clutter up terrestrial landfills even more, when we have the vast expanse of space at our disposal? (Jen-Luc would like to note, for our more literal-minded readers, that this a rhetorical question, asked satirically.) Really, they think it wold be a terrific idea to gather discarded spacecraft and the larger bits of debris into a central orbital "junkyard" in some part of space we're not really using. At least not right now. Hey, we could even mine it for old parts in a pinch! That should inspire tons of confidence in future astronauts who want to come home, knowing their re-entry vehicle has undergone patched repairs with debris fragments from a few decades ago.

Personally, I hope global space agencies and their respective governments take a cold hard look at what's at stake, and ask themselves: can we really afford to keep on this path? Is mitigation really enough? And isn't a sustainable long-term solution preferable to short-term temporary "fixes" even if it means initial high capital outlays? I would like to think they would answer with a resounding "YES!" But considering the human race's historical record on mitigating global warming, extinction of species, over-fishing the oceans, over-farming land, and so forth, I'm not optimistic about that.

wimping out

Like many denizens of teh Internets, I'm a huge fan of Mr. Deity, the online satirical series of shorts (usually around 5 minutes long) about a silver-haired middle-aged deity --reimagined as the ultimate Hollywood producer -- and his two sidekicks, Jesus and Larry (not to mention his on-again, off-again relationship with Lucy, a.k.a., Lucifer). It's clever, well-written, and filled with amusing one-offs. Take this tossed-off bit from "Mr. Deity and the Really Big Favor," when Mr. Deity receives a call from Larry, who's currently in the 13th dimension overseeing the construction of the nascent universe. Larry and the construction guys are wondering "how dark do you want to go with the dark matter?" Mr. Deity responds, "Take it all the way to void and then back off a scosch..."

Dark matter was the topic du jour over the weekend at the APS April Meeting in St. Louis, which features several sessions on experimental searches for this elusive stuff. Quick recap: the current model for the actual "stuff" in the universe calls for only about 4% regular matter. That would be every visible bit in the universe, from galaxies and stars to quarks and leptons, and everything in between. The rest of the universe is comprised of the mysterious dark energy (73%), which is causing the expansion of the cosmos to accelerate, and dark matter (about 23%). Oh, and neutrinos might be 0.001% of all the stuff in the universe.

There's pretty strong indirect evidence of dark matter's existence already, most dramatically seen in the now-famous (among science geeks) Bullet Cluster image (see the Spousal Unit's excellent description of what's going in the image at right here). But nobody really knows what this stuff actually is. The two leading contenders are massive astrophysical compact halo objects (MACHOs) and weakly interacting massive particles (WIMPs). The former would be things like black holes, neutron stars, and brown dwarfs, plus any other similar objects that emit little or no radiation and therefore escape detection by our instruments. MACHOs are still technically "normal" matter. WIMPs would be something else entirely, a new type of matter that pretty much never (or almost never) interacts with regular matter -- and therefore is even harder to detect than MACHOs. They only interact through the gravitational and weak nuclear forces. Mr. Deity made the dark matter very dark indeed!

WIMPs seem to share certain qualities with neutrinos, often popularly referred to as "ghost particles" (a term that makes at least one neutrino researcher I know grit his teeth in distaste) because billions of them pass through our bodies every day unnoticed. (John Updike even wrote a famous poem about them back in the 1950s, called "Cosmic Gall.") Like WIMPs, neutrinos interact only rarely with other subatomic particles, although they're definitely a lot "chattier" than WIMPs, and scientists have gotten pretty good at finding them -- using gigantic vats of liquid and really big, sensitive detectors buried deep underground, for instance. Perhaps that explains why many facilities and detectors currently studying neutrinos can also be used to search for WIMPs. It's dual-use technology for the cosmology crowd!

The big rumor buzzing around our St. Louis hotel is an expected announcement sometime in the coming week that the DAMA-LIBRA collaboration, housed in an underground laboratory in Gran Sasso, Italy, will report confirmation of an earlier, highly controversial 2000 experiment in which they claimed to have detected dark matter. I missed all the hullabaloo eight years ago, since cosmological matters weren't my usual "beat," but it's not hard to find quite a bit of information on the controversy via Google. I won't go into too much detail here, except to say that physicists were not convinced that the original DAMA experiment had detected a clear signal for dark matter. Instead, they thought it was probably a systematic error stemming from the high degree of background noise associated with DAMA's particular experimental approach: looking for a tiny signal variation in a sodium iodide detector over the course of a year, supposedly due to the motion of the Earth through the cosmic dark matter background.

The DAMA team vehemently disagreed, and a major battle ensued in the pages of the physics journals and associated trade press -- "major" for physics, anyway. Judging from the collaboration's current home page, some of them are still a little angry about the reception their finding received: the page bears a quote from "If," by Rudyard Kipling: "If you can bear to hear the truth you've spoken/twisted by knaves to make a trap for fools,... you'll be a Man my son." (Three guesses who the "knaves" might be!) In 2002, a French underground experiment k