Yup, photons do behave strangely. In college I was
shown the famous double slit experiment, wherein a
laser forms a horizontal spread, as you called it. You
>can send photons through double slits, and form
>a pattern of high and low illumination on the wall behind.
>This is explained by wave interference. But now you
>can turn the power to the laser so low, that the photons
>pass through *one at a time*. If you do that, you can
>observe that the pattern does not go away. Therefore, each
>photon must be somehow splitting into a wave, waving
>through *both* slits, interfering with *itself*, creating
>the interference pattern on the back wall. QM is weird
>stuff, James. spike
David Deutsch has used wave-particle duality to justify the Many Worlds Interpretation. In fact, he claims he's proved it, and after reading his book "The Fabric of Reality" I concur.