Double Slit Experiment: Particles, Interference & Measurement

[Strafespar]

The first question is, how does a single particle(say a photon) interfere with itself? Next, how does measuring it interfere with the interfering pattern? Need help on those please! Thanks!

 

[unusualname]

It has a wave property associated with it which causes the interference.

Measuring its position causes the wave to collapse to another wave localised at one of the slits and thus the wave can no longer interfere with itself (since it doesn't travel through both slits)

It may be possible to construct sufficiently delicate measurement techniques so as not to destroy the interference. The Copenhagen Interpretation says this is not possible but I'm not so sure it isn't.