Decoherence and Flying Fish

“I think I can safely say that nobody understands quantum mechanics.” -- Richard Feynman

We usually assume that at any given time, all objects have a definite location.  For example, last week I was in the US; this week I am in Israel.  But quantum mechanics postulates that microscopic particles can be in two (or more) places at once.  So if I was a microscopic particle, I could be 25% in the US and 75% percent in Israel, etc.

Now here comes the weird part.  When somebody looks at (or observes, or measures) the particle, the particle chooses one of these locations, at random.  So if I was a microscopic particle who was 10% in Tel Aviv and 90% in Jerusalem, and then you called my cell phone to see where I am, there would be a 10% chance that I would be in Tel Aviv and a %90 chance that I’d be in Jerusalem.

You might ask, what is the difference between saying that a given Libicki Boson is 10% in Tel Aviv and %90 in Jerusalem, and saying that we simply don’t know where it is, but we would bet 9 to 1 that it’s in Jerusalem?  It turns out that there is a big difference.  The particle’s “superposition”, as it is called, is responsible for what is known as the interference effect, which in turn is responsible for some of the wavelike properties of microscopic particles.  See http://en.wikipedia.org/wiki/Double_slit_experiment

In my arrogant opinion, one of the most important aspects of quantum mechanics that needs to be pinned down is what counts as an observation or a measurement.  Microscopic particles are in many places at once, but if we look, they appear in only one of these places.  This choice of position then affects the future motion of the particle.  So the critical question is: what counts as looking?

The branch of quantum mechanics that tries to pin this down is called “decoherence”.  I tried reading about decoherence and it went way over my head.  There was a lot of math.  After five minutes of absolute confusion, I gave up and watched a YouTube video:

http://www.youtube.com/watch?v=gAjzH0vWSIA

Flying fish!  How cool is that?