Uncertainty and the Two-slit Experiment

My current understanding of physics and the double slit experiment is 1)Photons in vacuum travle at c which is konstant 2)You can tell when you ¨fire¨ a photon and when it hits your photoplate by the recoil and momentum it will apply. 3)You can allso tell atleast roughly where the photon hit the plate. 4)You cannot know which slit the photon went trough without collapsing the wave function, and saying that it had a tredjectory is nonscenceical. If any of these statements are wrong then please correct me, however i will now assume that they are legitimate. From 1,2 and 3 it seems obivous that you can tell which slit the photon went through, by finding the distance each of the straigthest tredjectories through each of the slits and induvidually deviding by c and finding which one matches with delta t. However i cannot imagine this collapsing the wave fucnction seeing as i do not interfere with the photons ¨during flight¨ , thus im contradicting 4. Some clarification would be much appreciated.
- David. S (age 21)
Kristiansund, Norge

The problem is with your statement (2). You can only approximately tell when the photon was emitted or arrived. There's a frequency-time uncertainty relation. In order to get good interference fringes, you need a fairly narrow range of frequencies. That requires a large spread in times. So the timing can't be used with enough precision to determine which slit the photon traveled through.

Mike W. 

(published on 03/23/2014)