Skulls in the Stars

The tally of death and devastation in China in the aftermath of the earthquake continues to grow; now the official death toll is 22,000, with 14,000 still buried under rubble. In addition, repeated aftershocks are hitting the region.

Numerous eyewitness videos have been posted online since the event. This one in particular caught my eye, which shows a group of students outdoors experiencing the quake firsthand. It is a bit chilling to see their enthusiasm, knowing the devastation that was being wrought far away, but the students clearly felt that they were experiencing a small local quake, and had no idea that they were in fact 500 miles from the epicenter.

The part of the video that caught my eye was the sloshing of the water in the small pond. I believe this could be considered a small-scale version of a relatively little-known water wave phenomenon known as a seiche.

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In the May 1st issue of Optics Letters, a Korean research group has demonstrated another interesting application of surface plasmon resonances: the optical measurement of neural activity. Though I’m not sure how useful this technique will be in the long run, it shows that surface excitations can be used in sensors in many situations when an ordinary optical wave is not sensitive enough. A description after the fold…

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Update: In my haste to finish this “monster” post, I neglected to include an introduction to standing waves, an explanation which is crucial to understanding the experiment.  That oversight has been corrected.

A couple of weeks ago I issued a “challenge” to my fellow science bloggers: find, read, and blog about a classic, (preferably pre-WWII) scientific paper. There’s so much interesting historical context and methodological information hidden away that’s worth a second look.

For my part in the challenge, I chose an 1890 paper by Otto Wiener, “Stehende Lichtwellen und die Schwingungsrichtung polarisirten Lichtes,” Ann. Phys. Chem. 38 (1890), 203-243. Loosely translated, the title is, “Standing light waves and the oscillation direction of the polarization of light.”

The experiment that Wiener performed, as we will see, is conceptually simple and elegant. I foolishly thought that this would “translate” into a short, easy to cope with paper. As one can see from the citation above, no such luck: the paper is 40 pages of somewhat antiquated German! I accepted my fate, though, and soldiered on. A description begins below the fold…

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Right after “challenging” my fellow science bloggers to find and write about an old scientific paper, I take a hypocritical turn and write about some recent results in the theory of extraordinary optical transmission!

In a paper that came out recently in Nature*, authors Haitao Liu and Philippe Lalanne present a new model for the phenomenon now known as “extraordinary optical transmission”. The relatively simple pen-and-paper model they’ve developed provides results which are quantitatively in agreement with exact numerical simulations, and promises to be a powerful tool in the study of plasmonic nano-optical systems.

But what is extraordinary optical transmission, what are plasmons, and what is the relevance of both to nano-optics? Before I describe the results of the recent publication, I give a background on these questions, and others related to nano-optics.

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A couple of years ago, a number of physicists made international news (some descriptions here and here) by proposing that “cloaking devices” were theoretically possible to construct. Two papers appeared consecutively in Science Magazine in May 2006, one by U. Leonhardt of the University of St Andrews, Scotland (Science 23 June 2006: Vol. 312. no. 5781, pp. 1777 - 1780), and the other by J.B. Pendry of Imperial College, London and D. Schurig and D.R. Smith of Duke University (Science 23 June 2006: Vol. 312. no. 5781, pp. 1780 - 1782). Both papers describe how, with the proper materials, one could create devices which ‘guide’ light around a central core region without distortion, effectively making the cloak, and whatever sits in the core, invisible. This idea is illustrated by the figure below, from the Pendry paper, which shows how light rays could be guided around the core:

These papers have generated so much interest that it is fair to say that they have created their own subfield of optical science, what one might call ‘invisibility physics’, and numerous research groups are busy concocting their own invisibility schemes or attempting to construct a Leonhardt/Pendry-style device.

It is interesting to note, however, that the study of objects which are in some sense ‘invisible’ is not really new, and in fact there is a century-long history of scientists studying objects which may be considered, one way or another, undetectable.

I happen to know a lot about the history of such objects, so I thought I’d start yet another long-running series of posts, this one on invisibility physics. We start today with a discussion of what may be the first paper of this type, written by none other than the remarkable physicist Paul Ehrenfest.

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Wandering through StumbleUpon.com’s science links often looks more like a drunken stagger through the realm of crackpot science. The previous one I found, using Coulomb’s law to get free energy, I passed along to Tyler to deal with as it deserved. The latest contender, which is getting a lot of recent attention, is a so-called ‘whipmag’ device, which uses neodymium magnets to supposedly accelerate a disk to a high rate of rpm with no external energy input. The video below the fold…

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When I wrote my ’speed of light’ post, I had to do a lot of searching to find Fizeau’s original paper. Fizeau, as I mentioned, produced the first terrestrial measurement of the speed of light, using a rapidly rotating toothed wheel to break a light signal into continuous pulses whose speed could then be estimated. Since I’ve managed to find, after some effort, Fizeau’s paper, I thought I’d do the physics community a service and post it in a more easy to find place: my blog!

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When I was an undergraduate, one of my professors told the following funny (and probably apocryphal) anecdote (recalled from memory):

A court case was being tried in New Mexico. A group of pornographers were charged with smuggling pornography from Mexico by projecting it across the border to a camera. The defense argued that nothing physical was transported, and in the end the argument boiled down to this: if light moved at a finite speed, the films were being transported; if it moved at infinite speed, the defense was correct. A physicist was brought in to discuss the speed of light but, after a number of figures were presented, the judge interrupted. “When I put my hands over my eyes, the light stops coming immediately, and when I move my hands, it reappears instantly. The speed of light is infinite - the defendants are not guilty!”

The reason I suspect this story is apocryphal is that science has accepted that the speed of light is finite - albeit very large - for centuries. The value, usually denoted c, is approximately meters/second, or 186,282 miles/second. In fact, as we will see in later posts, light is the fastest thing in the universe. The topics we address in this post: a brief history of measuring the speed of light, and how these measurements led inexorably to Einstein’s special theory of relativity.

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In a previous post, I discussed recent research which demonstrated the creation of an artificial ‘event horizon’ in a fiber optic cable. In that post, I described how a river speeding up as it goes towards a waterfall has an event horizon: waves that are created past the horizon have no possibility of escape. This was illustrated by the figure below:

As you can see, I’ve drawn the wavefronts created by rocks dropped in the water as ellipses, which seems like the obvious solution: waves will be ’stretched out’ along the flow of the river, while they will spread normally perpendicular to the flow. Being a nitpicky sort of guy, though, I wanted to demonstrate that this is the case mathematically, which I do below the fold… (warning: algebra and calculus follow!)

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My mind works in rather silly ways sometimes. Posting about skydiving soon after posting about avalanches on Mars, I got to thinking about how cool it would be to skydive off of a Martian cliff. Then I started to wonder: could you? What would be a skydiver’s terminal velocity in freefall on Mars? Well, with a little prior knowledge and some physics, we can actually make a rough estimate of this!

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