Quantum Astronomy: The Double Slit Experiment:
So light is both a particle and a wave. OK, kind of unexpected (like Jell-O) but perhaps not totally weird. But the double slit experiment had another trick up its sleeve. One could send one photon (or “quantumâ€? of energy) through a single slit at a time, with a sufficiently long interval in between, and eventually a spot builds up that looks just like the one produced when a very intense (many photons) light was sent through the slit. But then a strange thing happened. When one sends a single photon at a time (waiting between each laser pulse, for example) toward the screen when both slits are open, rather than two spots eventually building up opposite the two slit openings, what eventually builds up is the interference pattern of alternating bright and dark lines! Hmm… how can this be, if only one photon was sent through the apparatus at a time?The answer is that each individual photon must – in order to have produced an interference pattern — have gone through both slits! This, the simplest of quantum weirdness experiments, has been the basis of many of the unintuitive interpretations of quantum physics. We can see, perhaps, how physicists might conclude, for example, that a particle of light is not a particle until it is measured at the screen. It turns out that the particle of light is rather a wave before it is measured. But it is not a wave in the ocean-wave sense. It is not a wave of matter but rather, it turns out that it is apparently a wave of probability. That is, the elementary particles making up the trees, people, and planets — what we see around us — are apparently just distributions of likelihood until they are measured (that is, measured or observed). So much for the Victorian view of solid matter!
Funny story. A couple years ago (spring of ‘02) I was walking to the bus stop with a girl from my Renaissance history class. At one point through our conversation I looked at her sternly and asked: are you pro or anti matter? She actually tried to come up with an answer and reasoning to it.
I think she works at NASA now.