Monday, June 15, 2009

Mad Science Monday, 6/15/2009

It's Monday, and scientists are still studying strange things. Today (probably not for the last time) I bring you a paper on quantum entanglement, what Einstein called "spooky action at a distance."

Mad Background: Quantum entanglement involves creation of two particles with linked quantum states. It's all very complicated (I don't understand it completely, and the explanation of it depends on what turns out to be the correct explanation of quantum behavior as a whole). The "spooky" part about all of this is that it appears that information can be transmitted instantaneously between two entangled particles, regardless of distance, which defies the speed-of-light barrier.

The other important piece of background for this is the "Schrödinger's cat" thought experiment. One of the hard-to-grok concepts implied by quantum mechanics is that a system exists with all possible states of the system until that system is "observed" (by a human or by other particles interacting with that system); this is called quantum superposition. Schrödinger devised an experiment in which a cat is placed in a shielded box with a "diabolical mechanism" that poisons the cat under certain quantum conditions. Until the box is opened, if superposition is correct, the cat is both alive and dead.

Mad Reference:* "Entangled mechanical oscillators." Jost, Home, Amini, Hanneke, Ozeri, Langer, Bollinger, Leibried, & Wineland. Nature 459, 683-685 (4 June 2009).

Mad Observation: Researchers have created entangled particles, such as photons and individual atoms. The way this paper words the observation that led to their experiments is what makes this science mad:
Hallmarks of quantum mechanics include superposition and entanglement. In the context of large complex systems, these features should lead to situations as envisaged in the "Schrödinger’s cat" thought experiment (where the cat exists in a superposition of alive and dead states entangled with a radioactive nucleus). Such situations are not observed in nature.
In other words, things equivalent to Schrödinger's thought experiment should happen. Why don't we see any of that quantum strangeness in the natural world? What stops us from setting up a Schrödinger's cat experiment?

Mad Hypothesis: According to the authors, there are two possible explanations for why we can't have alive-dead cats: technical and physical. It could be that we haven't been able to isolate things sufficiently to see this strangeness (technical), or there could be some undiscovered mechanism that "prevents the formation of macroscopic entangled states" (physical). With that in mind, these researchers decided to test the hypothesis that something stops systems with more degrees of freedom than single particles have from becoming entangled (ie, they sought to set up a pair of more complicated entangled systems).

Mad Experiment: The lead author on the paper has a couple very helpful videos over at his portion of the National Institute of Standards and Technology page. Basically, a pair of interacting atoms can form a mechanical oscillator. If you could make two of these pairs, and entangle one atom in each, the oscillators would be entangled if nothing stops them from becoming entangled.

They All Laughed, But: They succeeded in setting this up, thus moving us one step closer to macroscopic entanglement. This should eventually make mad engineers very happy.

Mad Engineering Applications: There are several possibilities envisioned for quantum entanglement, but the idea that fascinates me the most is something I first read about in the science fiction books of Orson Scott Card (who, more and more, I hate to recommend, but dammit his Ender's Game books are good; check them out of a library or buy them used, so he doesn't get anything for it). In Ender's Game, Card explained that the military communicated over the long distances needed for space combat using systems of entangled particles; when the sender changed something, it was immediately experienced by the receiver's half of the entangled pair, thus transmitting the distance instantaneously. I assumed that was just science fiction science when I first read it, but it might actually be possible. That might not seem very mad engineery, but if you set your sights high enough for even a multi-planet empire (let alone multiple star systems), you need faster-than-light communication to keep your subjects in line. If you don't hear about uprisings until after they occur (possibly even years after they occur), you'd have to trust your underlings to take care of them, and that hardly seems like a winning proposition.

Oh, and quantum entanglement would also allow for faster computers and more secure communications. Those aren't entirely mad, though, unless of course you make those faster computers self-aware.

That's it for this week. Next week it looks likely that I'll either be discussing brains or branes. Stay tuned to find out which!

* I almost called this "Mad Props," but couldn't bring myself to do that. Back to where you were.

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