Monday, January 21, 2013

The Quantum Moment

2012’s NYI included a seminar on the metaphors of quantum physics.  Why are quantum physics metaphors (like Schrodinger’s Cat, Heisenberg’s Uncertainty Principle, Parallel Worlds) surprisingly common, more than you’d expect since quantum physics is relatively obscure subject matter for the public at large?  This is the question we tried to tackle with Robert Crease, the author of a book on this, called The Quantum Moment.

This post is background for another post on Uncertainty and Relationships. 

Perhaps one of the most surprising findings in quantum physics is from the so-called double-slit experiment.  Understanding the results will alter your entire understanding of reality.

If you’re not familiar with it, an illustrated explanation is here.  Very briefly, if you shine a laser at a card with two parallel slits cut in it, you would expect to see two corresponding lines of light behind it (say, on a piece of paper), representing the two lines cut in the card. 

But what you actually get is a pattern of interference: packets of light going through one slit interfere with the ones going through the other slit (and vice versa), and so you get multiple bands of dark and light, where they cancel each other out or add on to each other.  So the light behaves not like “particles” (each going through its own slit) but like “waves” (like ripples from a rock dropped in a pond).

Where things start blowing your mind is that this happens even if you shine only one packet of light at a time: that one packet goes through both slits and interferes with itself! 

However, if you try to be clever and add a detector, to find out which slit the light goes through before it goes through the slits, this stops happening and you get the two lines of light that you would have expected originally. 

The upshot is this: until you observe the packet of energy, it is in all places at once (with varying probabilities).  Then it interacts with something else, and of all the possibilities one ends up being the case.  This is the case for everything, not just packets of light!  Remember high-school chemistry, where the electrons orbit the nucleus at certain levels?  In some sense, each electron is in all places in that orbit at once (remember the “electron cloud”?).

This forms the basis of the Schrodinger’s Cat thought experiment: a cat is in a closed box with an apparatus that might kill it (with 50% probability).  In some sense, until you open the box to check what happened, the cat is simultaneously alive and dead.

One of the questions we were to answer:

"[W]hy does the image [of Schrodinger’s cat] still seem as packed with creative force as ever?"

I think perhaps there are two—dare I say, complementary—reasons for the endurance of these quantum physics metaphors and this one in particular.

One is simply the way our understanding of reality is turned on its head by this idea of probabilistic uncertainty: that reality isn’t what it seems, until we observe that “seemingness”, so to speak. That there’s more to this reality—and perhaps life itself—than meets the eye. That we can't truly understand—or even define—our existence.

In tandem with this is, perhaps, the tantalizing hope it gives us: both possibilities are available until we make a decision; indeed, perhaps both choices exist in separate “realities”, and one can perhaps take solace that things turned out better for “oneself” in that alternate reality. Will Grayson, Will Grayson touches on the first part of this, i.e. "decisions yet unmade":

“Well, that’s not all, actually. It turns out to be somewhat more complicated.”

“I don’t think I’m smart enough to handle more complicated,” I say.

“Don’t underestimate yourself,” she says.

The porch swing creaks as I try to think everything through. I look over at her.

“Eventually, they figured out that keeping the box closed doesn’t actually keep the cat alive-and-dead. Even if you don’t observe the cat in whatever state it’s in, the air in the box does. So keeping the box closed just keeps you in the dark, not the universe.”

“Got it,” I say. “But failing to open the box doesn’t kill the cat.” We aren’t talking about physics anymore.

“No,” she says. “The cat was already dead – or alive, as the case may be.”

“Well, the cat has a boyfriend,” I say.

“Maybe the physicist likes that the cat has a boyfriend.”

“Possible,” I say.

“Friends,” she says.

“Friends,” I say. We shake on it.

--Will Grayson, Will Grayson, pp. 197-98

…and indeed I myself had made a very similar comparison in the face of relationship ambiguity of my own the year before.

A separate possibility is perhaps the simple intractability of this paradoxical idea—the inability to truly wrap one’s head around it, though one continually bounces tantalizingly close to understanding it—gives it staying power. A similar question is posed by music: why do we enjoy hearing a piece of music more than once—perhaps even increasingly so—with repeated exposure? Why don’t we get bored of it? One theory is the unbreakable cycle between tension and release that comes with melodic progression, a sort of “feedback loop”, and perhaps a similar notion that drives us to continually ponder “that damned cat”, as Schrodinger later dubbed it (perhaps apocryphally):this simultaneous understanding and yet bafflement; a fitting response to the paradox, after all.

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