He might not have meant gravitational attraction in the technical sense, but more that the particle 'gravitates' towards one or the other of the slits. However, this kind of imprecision is *very* dodgy practice in Physics education.
In any case, the teacher is wrong, at least in the sense that modern QM dictates that in a two-slit (or however-many-slit) experiment the particle trajectory has no meaning - the experiment doesn't measure particle trajectory, it measures where a particle hits a detector after traversing the system.
It turns out that if you send a heap of particles through, the statistical distribution starts to look like the distribution you'd get if it were waves hitting the slits, not particles.
In that sense, there is some crossover between what we consider 'wave' and 'particle' behaviour, but it is just plain silly to wonder whether an electron, for example, is a particle or a wave. An electron is an
electron. We have very good theories that describe the behaviour and properties of electrons. Some of these properties (such as 'wavelength') happen to have similarities with classical wave properties. On the other hand, when you perform experiments on single electrons (or photons, same deal), they always look like single electrons - a single electron going through a two-slit system will be detected in *one* spot on the detector screen, not the whole screen at once. It takes a heap of electrons before the 'interference pattern' looks like an interference pattern.
There are a lot of physicists (and people who read popular science books) who have decided that particles are particles and waves are waves, and even that electrons are waves or photons are particles or whatever. The problem is, human beings were the ones who decided what waves and particles are defined to be, and the universe doesn't have to be that way.
It has been my practice, much to the chagrin of my girlfriend (also a physicist) to refer to any object described by QM as a 'quob' - a QUantum OBject, because it removes the notion that QM describes waves/particles. It describes quobs.
Ahh, now back to the thing I was intending to write about.
Feynman was fairly unequivocal about whether electrons, say, are particles or waves - he calls them particles, but what he means is quobs (
). If you're looking for a *discussion* about wave/particle duality, you might not find it in his writings.
Kane O'Donnell
