What causes light to diffract in the double slit experiment?

[Ivanov]

I was studying the double slit experiment and started wondering what exactly does happen to the wave when its in the slit that makes it diffract or not? I toyed around with http://www.falstad.com/ripple/ but could not figure what exactly goes on that makes things as they are.

While trying to answer myself two additional questions came up:
Does light require an EM field to travel through or does it create its own?
Is light nothing more than a ripple through the EM field and if so how do we quantise it? Wouldnt it have a continuous nature (I know it doesnt) because of that?

 

[DrChinese]

I was studying the double slit experiment and started wondering what exactly does happen to the wave when its in the slit that makes it diffract or not?

I assume you mean what causes the interference pattern? It is not the slit per se. It is the effect from both slits.

 

[Ivanov]

I assume you mean what causes the interference pattern? It is not the slit per se. It is the effect from both slits.

Well that would be something I don't know as well, but my question is what happens in a single slit when a wave passes through it? Why is it that when the wavelength is shorter than the slit a tight cone is observed on the other side and if its a longer wl it spreads out and we observe diffraction?

 

[atyy]

I was studying the double slit experiment and started wondering what exactly does happen to the wave when its in the slit that makes it diffract or not? I toyed around with http://www.falstad.com/ripple/ but could not figure what exactly goes on that makes things as they are.

While trying to answer myself two additional questions came up:
Does light require an EM field to travel through or does it create its own?
Is light nothing more than a ripple through the EM field and if so how do we quantise it? Wouldnt it have a continuous nature (I know it doesnt) because of that?

A light wave is an excitation of an EM field.

You can think of (free) quantum field theory as a theory of an infinite number of particles.

 

[mike1000]

I was studying the double slit experiment and started wondering what exactly does happen to the wave when its in the slit that makes it diffract or not?

During my investigations I stumbled upon this description of the double-slit experiment. According to this description, interference is a natural by-product of the fact that the state of the photon in the double slit experiment is a superposition of two states. The part I find interesting is the description says the interference is caused by the relative phase difference caused by the differing distance the photon is from each of the slits. Here is the description.

One example of a quantum interference phenomenon that arises from superposition [of pure states] is the double-slit experiment. The photon state is a superposition of two different states, one of which corresponds to the photon having passed through the left slit, and the other corresponding to passage through the right slit. The relative phase of those two states has a value which depends on the distance from each of the two slits. Depending on what that phase is, the interference is constructive at some locations and destructive in others, creating the interference pattern. By the analogy with coherence in other wave phenomena, a superposed state can be referred to as a coherent superposition.
https://en.wikipedia.org/wiki/Quantum_state#Superposition_of_pure_states