Here is something else that may amuse you taken from Paul Dirac when speaking about
 this same double slit experiment...

QUOTE (http://en.wikipedia.org/wiki/Theoretical_a...dinger_equation)
 
Some time before the discovery of quantum mechanics people realized that
 the connexion between light waves and photons must be of a statistical character.
 What they did not clearly realize, however, was that the wave function gives information
 about the probability of one photon being in a particular place and not the
 probable number of photons in that place. The importance of the distinction 
can be made clear in the following way. Suppose we have a beam of light consisting
 of a large number of photons split up into two components of equal intensity.
 On the assumption that the beam is connected with the probable number of
 photons in it, we should have half the total number going into each component.
 If the two components are now made to interfere, we should require a photon
 in one component to be able to interfere with one in the other. Sometimes these
 two photons would have to annihilate one another and other times they would have
 to produce four photons. This would contradict the conservation of energy
. The new theory, which connects the wave function with probabilities for
 one photon gets over the difficulty by making each photon go partly into each
 of the two components. Each photon then interferes only with itself. Interference
 between two different photons never occurs. 

Theoretical and experimental justification for the Schrödinger equation

—Paul Dirac, The Principles of Quantum Mechanics, Fourth Edition, Chapter 1 


(my emphasis)