Part of the  

Chip Design Magazine


About  |  Contact

Casimir over Cocktails

It’s been said that any good explanation you truly understand. you should be able to deliver in five minutes over cocktails. I’ll add a 2000’s caveat that you should also be able to type the first draft on a cell phone keyboard after consuming said cocktails. So, after having two Irish whiskys, pressed into my hands by my father-in-law, (I have the best father-in-law), and while quietly waiting for our one year old to drift off to sleep, I begin. Two weeks ago it was all the rage on the internet that Eagleworks had been funded. by NASA and was hot on the trail of a viable warp drive solution(pdf, search for ‘quantum vaccum’ within). Their solution utilized a number of avant-garde physics theories (at least they were avant-garde in the ‘40s), including the Casimir effect. Since this effect can be observed at nano-tech scales, let’s start there.

Fans of Stargate, (I’ve always been a fan of MacGyver and our  kid loves watching the show to unwind after a hard day at daycare), will recognize the term Zero Point Module. Well, that utilizes the same energy as the Casimir effect. If you want to wow your friends, here’s the skinny on the ZPM, (Casimir effect.). For a variety of reasons I won’t go into here, in the 1940′s a lot of smart guys figured out that electromagnetic radiation behaved like a harmonic oscillator (think about a friction-less ball oscillating back and forth. on a friction-less parabola), and that the fields energy wad quantized in units of (n+1/2) times the frequency times Planck’s constant, (where n is any integer greater than or equal to zero and Planck’s constant is a very small number). What that means for you and me is that even when n equals zero, even in a complete vacuum, there’s still energy(it’s the fault of that one the equation). Even when nothing is going on, there’s a sort of cosmic backwash of every frequency of EM radiation you can think of.

So, that’s your so called zero point energy, but what does it have to do with the Casimir effect, and for that matter, what is the Casimir effect anyway? In 1948, Casimir predicted that when two conducting plates were brought very close together, (think on the micron scale,), they would suddenly attract each other. It’s no so much though that they’re attracting each other as that they’re being pushed together. Due to certain physical boundary conditions, defined in your undergraduate EM class, only certain frequencies of the zero point energy can exist between the two conducting plates. Outside the plates, every frequency of radiation can still exist and does. The difference in the amount of radiation between the plates and outside the plates causes an energy pressure differential and the excess radiation outside the plates pushes the plates together. We began to see experimental verification of this as soon as the 1970s.

by Thomas Eakins, Philadelphia Museum of Art

There’s a macroscopic analogy to all of this. For centuries, sailors have warned that two ships shouldn’t pass too closely to each other or they would suddenly be smashed together for apparently no good reason. The same mechanism is at work here. As the ships near each other, there are fewer wavelengths of ocean waves that can exist between them than are available for the entire ocean outside the ships. The pressure differential in the waves between the ships compared to the waves outside of the ships results in the two ships being pushed together. Don’t believe it? Some students at the Naval Postgraduate School demonstrated it experimentally with two plates in a beaker of water. If you’re near a university you can read about it in a back issue of the American Journal of Physics, specifically (B. Denardo, J. Puda, A. Larraza, “A Water Wave Analog of the Casimir Effect”, American Journal of Physics, 77, (2009), 1095).

Speaking of oceans, if you want to fully explain warp drive technology, you’re going to need to know about Dirac’s “infinite sea of electrons”. This one’s a doozy.  That’s where we’ll pick up next time.

Interesting lesson learned while drafting on a cell phone:  While Casimir is not known by the auto-complete feature, MacGyver is!


One Response to “Casimir over Cocktails”

  1. The Week in Space 10/13/2012 | The Canonical Hamiltonian Says:

    [...] Post navigation ← Previous [...]

Leave a Reply