Is it Bernardo vs Riff or Bernardo vs Tony?
Category Archives: Cool stuff
The Photon Push-Me Pull-You
A few weeks ago, over at Built on facts, I threw Matt a bit of a knuckleball in the comments.
[C]onsider a solid bar of the same index [as water]. You send in the pulse of light (assume a really good AR coating so there’s no reflection). What happens to the speed of the bar?
This was sneaky because it is one of the unsolved issues in physics (I feel no remorse for doing this, and Matt realized that something was up) — the theory is complicated enough that it’s really easy to miss out on some of the subtleties and end up with an invalid answer. There are two schools of thought: Minkowski, who had taken the approach that the photon’s momentum in the medium should be nE/c, and Abraham, whose approach gave the momentum as E/nc. Clearly, the results are at odds, and this came to be known as the Minkowski-Abraham momentum controversy.
I found a number of articles on the topic, but perhaps the best one is a review article from Reviews of Modern Physics. Momentum of an electromagnetic wave in dielectric media by Pfeifer et. al, No. 4, October–December 2007 pp. 1197-1216. (link is to a pdf file) The article points out that this isn’t a simple problem, because a photon in a medium can’t be naively treated as just a photon — both solutions have merit, but must include the interactions with the medium, which are obviously different depending on the approach you take — in the end there can be only one you can only have one answer for the momentum of the system.
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Waterfalls
There is something about waterfalls that fascinates me.
Can't . . . Avoid . . . Collision
Remember the conservation-of-momentum problem you did in 1st semester physics, where the projectile breaks into two pieces at the apex of its flight? Now multiply by Avogadro’s number (and then an additional order of magnitude or more)
Momentum’s conserved, even in slo-mo.
Relax!
. . . and hit me with that laser beam. Or rather, hit Al, and rip it apart, in slow motion.
Way to go, Frankie.
And The Beat Goes On
Cool musical step sequencers that use optical input.
What, No Half-Pipe?
Google’s Zurich office
Infrared Swan
The temperature range in these images (and others on the site) mean that these were taken with a thermal imaging camera; 300-310K blackbody spectra peak somewhere between 9 – 10 microns, rather than a regular ol’ digital camera with the IR filter disabled.
Frankly, though, most of the other birds and mammals in the menagerie have more interesting IR spectra associated with them, like yappy dog.
Please Don't Do This to My Windshield
Making Lichtenberg figures. First video seems to be with an external discharge
This video is using an internal charge. Mind you, absolutely anyone who has a large particle accelerator at their disposal can do this.
(HA! Take THAT, Cool Chemistry!)