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?"