looking towards robotic undulatory locomotion

A coral snake (credit: http://animals.nationalgeographic.com)

Have you ever been walking in the woods and come upon a snake (startling both you and it), only to see it slither away with incredible speed? I know I have. How is it possible for the massive bulk of a whale to travel thousands of miles underwater without eating? As is often the case, the efficiency (and beauty) of nature’s solutions to common problems far supersede those we’ve developed ourselves.

A recent review by Netta Cohen and Jordan Boyle of the University of Leads (UK) to be published in Contemporary Physics has a nice discussion of the fluid mechanics involved in different models of undulatory locomotion, as presented by various organisms. What becomes clear to someone (me) not in the field, is that for something seemingly as simple as getting around in a fluid, we know pretty much exactly how the most efficient organisms do it but are a good ways from being able to replicate it well ourselves.

Towards the end of the paper, the authors discuss the emerging technologies of undulatory robotics, on both the meter scale (robotic snakes for searching for people in building rubble) and on the micrometer scale (robotic worms to swim through an artery to image tissue injury or healing progress). These applications are an interesting glimpse at an area of research ripe for development.

The propeller (which itself is of biological origin) on the back of a boat has gotten us a good, long way, but it has a number of limitations. For one, it’s quite inefficient compared to biological undulation; although, it’s significantly simpler to implement mechanically. As our material science and coordination of many mechanical movements (think how many independent muscles a fish must move to flap its body once) continues to improve, our ability to implement this form of locomotion will improve. (Perhaps in 100 years I’ll be able to take a ride in a flagella-powered boat.

A tangent
At the risk of being cliche, I’m again struck by the resourcefulness of evolution in using the tools it has available to perform a task, rather than trying to reinvent the wheel every time. So, the cells in your bronchiole tubes would like a way to move mucus and dirt up and out of the lungs? Well, why not just use oar-like cilia that many paramecium use? A less practical builder (us, perhaps) would expensively go about designing an entire new apparatus. In fact, many of the tools used by evolution (if random chance can be given some agency) are imperfect (for example, the skeletal structure of bat wings vs. bird wings), but they work well enough. This imperfect-but-good-enough usage of biological tools, by the way, is one of the best arguments (if you entertain the argument at all) against so-called intelligent design.

the relationship between lightning and rain

(credit: Wikimedia)

Last night a huge thunderstorm woke me up in the middle of the night. For some reason I realized then that I had no good idea of why rain almost always accompanies lightning (and thunder). What about the two processes makes them work together as they do? A bit of internet research yielded a logical if not entirely complete picture.

HowStuffWorks.com has a very thorough discussion of lightning. We all know that lightning is the discharge of an electric potential built up between either two clouds or a cloud and the ground. Interestingly enough, though, we don’t completely understand how those clouds get charged in the first place. The current (and best supported) hypothesis is that, within the cloud, rising and condensing water vapor collides with falling ice crystals and loses a few electrons in the process. These electrons fall down with the ice to the bottom of the cloud, causing the lower region to become negatively charged and thus the upper region to become positively charged. As the lower region of a cloud becomes negatively charged, it also causes the ground to become positively charged. At a certain point, these electric potentials become so large that they discharge in the form of lightning.

Through this collision theory of cloud-charging, the relationship between precipitation and lightning become more clear. The more precipitation moving around in a cloud, the more separation of charge occurring. Thus, thunderheads that produce a lot of lightning must have had a lot of precipitation in them to create that electric potential. And that much precipitation rarely stays up in the cloud.

A number of climate scientists have actually tried to correlate lightning strikes and rainfall in storms. Vladimir Rakov and Martin Uman, in their book Lightning: physics and effects, discuss some of these efforts. While some scientists seem to have a bit of consistency. Rakov and Uman present data (the numbers are in kg of rainfall per ground flash) from a large number of studies that ranges in four orders of magnitude. It seems that specific types of storms (especially in the same area) yield far more consistent results than generalized storms.

Again, I return to a familiar theme of mine. So many commonplace things operate in ways we don’t entirely understand. The next time you see lightning, think of those colliding water and ice particles.

the forces between grains of sand

If I asked you what makes water form into droplets, you might say surface tension, perhaps (for the more sciency) intermolecular forces like dipoles and hydrogen bonding. Most of us are comfortable with these strange little forces acting on the tiny, molecular level, but then how can we explain these clips:

This above clip is a high-speed video of falling sand, where the camera is falling at the same speed of the sand and thus can capture the “drops” of sand that form from the thin stream. The below clip shows an iron ball falling into sand.

A recent study by the Jaeger group at U. Chicago in Nature investigates (that Mark Trodden of Cosmic Variance summarizes) the interactions of sand particles. Jaeger’s group demonstrated the existence of surface tension forces roughly 100,000 times less strong than those of normal liquids on the sand and nanoNewton forces between the particles.

Not only is this research just plain cool, but it also illustrates how we’re still learning about seemingly everyday things like sand. Most often people see current scientific developments as incredibly specialized and unapproachable. Research like this reminds us of the science that we interact with even when we’re not looking for it.

update: communication and entanglement

After talking with my physics friend, I have learned that it’s basically impossible to communicate via entangles particles. So, the idea that as I, on earth, measure the spin of an electron, thus determining the spin of an entangled electron on Mars, doesn’t actually help us at all in communicating with Mars. The person on Mars still has to measure the spin of the electron (or whatever), but the problem is that he doesn’t know whether he’s looking at an electron that’s already determined or whether he’s looking at it (and its partner on Earth) for the first time and thus determining the Earth electron’s spin.

Thus, a physicist might say, the distinction between instantaneous determination (across the galaxy in an instant) and speed of light determination between two entangled particles is irrelevant because we could never confirm a successful communication faster than the speed of light.

Ok, but let’s consider the following experiment:

We entangle 10 sets of particles and then send one half to Mars and keep the other half here on Earth. We set out a timetable saying that we’re going to measure the spin of each particle one second apart, which is not enough time for us to communicate with Mars at the speed of light (about 3 minutes minimum). After finishing the experiment, the people on Mars fly back to earth, and we compare our results. If we find that all of the times an Earth particle’s spin was measured “up,” the correlated Mars particle’s spin was measured “down,” it would seem that the particles are communicating their “determinism” instantaneously, because that behavior is very improbable (i.e. impossible) for a large number of pairs of just any two particles.

If we find that when measured so closely together, the particles, don’t behave as an entangled pair, that’s certainly interesting and seems to contradict the idea of entanglement as distance-independent (which, as I understand, it’s thought to be).

Even if we prove that the entanglement-communication is instantaneous, that still doesn’t get us very far because we’ll never know (faster than the speed of light) whether a particle is determined or non-determined when we measure it. And, at this point, we have no way of setting a particle’s spin, only measuring it, so we can’t really communicate anything anyways.

Another difficulty, which I’ve hitherto overlooked, is determining when, exactly, the person on Earth and the person on Mars are going to measure their particles. Since the person on Mars had to increase his velocity relative to Earth a bit to get to Mars, his conception of “time” is a bit (not very much, though) different from that of the guy on Earth due to relativity. Perhaps this is a small difficulty, perhaps a large one.

At this point, your brain is probably hurting a lot. What’s interesting is that this kind of discussion doesn’t bother most physicists at all. It’s first year graduate coursework at most. Because physics has taken such a non-intuitive bend in the past hundred or so years, physicists are quite comfortable (because they have to be) talking about things that seem crazy in our “normal world” but actually make a good deal of sense in theoretical physics world. Thus, physicists can talk about the idea of multi-universes–in which every instant in “our” universe, another universe “branches off,” weaving an alternate path through history–because it helps explain where the collapsed states of Shrodinger’s wave equation go.

Very seldom in science–I’d say really only in physics–does the theory not make intuitive, real-life sense on some level or another. This is why we hold physicists on such a pedestal even though their work won’t actually help us in any way for at least a few hundred years.

what entanglement means for philosophy

A depiction of entanglement (credit: Nature Physics cover, Volume 2, No 10)

The most recent issue of Nature reports a new study involving entanglement. For those not familiar with or a bit hazy on entanglement, here’s my best description:

The basic idea is that we can entangle two quantum particles, like electrons, such that one or more of their properties are inextricably related. This means that if I have two entangled electrons, and I measure the spin (think of it like planetary rotation on its axis) of one electron, the spin of the other electron necessarily becomes the other direction. This property means that if I measure the spin one electron here on earth to be “up,” immediately (not sure if it’s truly instantaneous or at the speed of light–asking a particle physics Ph.D on this, who’s going to get back to me) an entangled electron on Mars would have a spin of “down”.

What’s interesting about this new research is that it involves the mechanical oscillation of ions (beryllium). Previous experiments with entanglement have only been done with electrons and particles of that size (and ions, or atoms, are tens of thousands of times more massive than electrons), and none have dealt with a mechanical property like moving back and forth.

But what’s really interesting about this whole phenomenon is that it’s basically like a new way of communicating without radio waves or any other type of electromagnetic radiation. I can imagine cool Sci-Fi scenarios in which we have entangled communication devices that allow us to talk efficiently with people and their devices in other galaxies (although, again, the whole instantaneous or speed of light question comes back into play over large distances).

The process of entanglement also raises much more profound metaphysical questions. Most of us (I believe) think of objects–an apple, my computer, a person–as distinctly different things, all objects in the world, yes, but distinct objects nonetheless. An idea called monism, holds that (very simplistically) everything is really part of one thing. Just like individual waves in the ocean are really just wrinkles in one thing, the apple, computer, and person are wrinkles of a large thing, that contains every seemingly (but not really) individual thing in the universe.

Now, I recognize that this idea seems kind of crazy, but the existence of entanglement makes it seem much less crazy. If things in our universe are really completely distinct, why should they be able to influence each other millions of miles away form each other? Keep in mind that there’s no type of electromagnetic radiation or other normal “communication” between the two particles. If seemingly separate things are actually little wrinkles of one thing, this relationship between entangled particles makes much more sense.

Monism is still a bit too far out there for me to accept it at the moment, but more evidence of increasingly complex entanglement really makes me consider monism seriously as a way of understanding our universe.