15 July 2010

The double slit experiment

Here's a fun link to an explanation of the classic two slit experiment, courtesy of the University of Colorado.

Start there, click on the green button to see the pattern, then follow the explanation as you're directed to next panel.

The gist of it is that we have to think of electrons as waves in order to make any sense of the interference pattern.

Here's another link, to another "take" on the older form of the same experiment, using light waves (or particles known as "photons") rather than matter.

"Modern photodetectors (which exploit the photoelectric effect explained by Einstein) can show individual photons plinking against the screen behind the slits in a particular spot at a particular time-just like particles. But as the photons continue striking the screen, the interference pattern gradually emerges,a sure sign that each individual photon went through both slits, like a wave."

So the same wave/particle duality appears in both matter and energy. So what? Didn't I learn this at school, decades ago, and mentally shrug it off like everybody else?

Yes, but I was callow. Here is the point. As Horgan stresses, paraphrasing John Wheeler of Princeton, it is a "physicist's choice of apparatus" that "forces the photon [or the electron] to choose" whether it is acting at a given moment as a wave or a particle. Think about that. A mindful creature, a conscious experimenter, determines the nature of the building blocks of reality by the way in which the experimenter seeks to measure said blocks.

This is fatal to reductionism. It is simply incoherent to say that A is "nothing but" B unless B itself can be understood without reference to A. What if we string them together? A is nothing but B, which is nothing but C, which is nothing but D. This string becomes incoherent if we end up using A-dependent terms in our discussion of D.

Yet that is exactly the situation we face in the relations among the sciences. If we say "mind is nothing but a particular manifestation of life, life is nothing but a particular manifestation of matter, matter is nothing but the way certain very tiny particles interact," then we ought in principle to discuss the interactions of those tiny particles without intrusive talk about "decisions" or "knowledge" or other mind stuff. Yet we can't. We end up saying things like this (Horgan quoting a scientist at the University of Rochester), "The quantum state reflects not only what we know about the system but what is in principle knowable."

Since this epistemic circle plainly does exist, the once-dreamt-of reduction has failed, and it is the case that there is more to this world than particles bouncing around and various manifestations thereof. We are of course free to speculate about the nature of that "more."

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Knowledge is warranted belief -- it is the body of belief that we build up because, while living in this world, we've developed good reasons for believing it. What we know, then, is what works -- and it is, necessarily, what has worked for us, each of us individually, as a first approximation. For my other blog, on the struggles for control in the corporate suites, see www.proxypartisans.blogspot.com.