Young's Double Slit Experiment and the properties of light.

_Dubh_

I try to get myself away from the wave/particle duality of light in a way that I agree that light has properties of both but I try to visualise it as a new and different phenomenon.

My point I would like to put forward for discussion is what exactly happens after the light passes through the two slits???.....are there actually photon waves or probability waves etc...and how come the interference pattern can be easily collapsed by placing a detector on the other side of the slits?

Does anyone have their own way of visualising light and what is going on here? Please discuss.

For those unfamiliar with this experiment:

http://en.wikipedia.org/wiki/Double-slit_experiment

Thankyou

dudara

A scientist called Afshar conducted an experiment in 2004 which demonstrated simulataneously both the wave and particle nature of light. Clicky

It was fascinating reading when I read about it in the New Scientist, because you've traditionally been taught that while light is both wave and particle, you can only measure or observe one aspect. However, this guy knocked that on the head

Son Goku

My interpretation of what happens can be split into two circumstances:
(a)No detector:
The "wavicle" that is the photon propagates through both holes and interferes with itself.
The wavefunction tells us the probabilities of finding the photon in a given volume, as well as other things. Basically it gives us a description of the photon.
The Schrödinger Equation then lets us follow the evolution of the wavefunction over time, allowing us a description of the photon "at all times".

(b)Detector:
The Famous "Wavefunction Collapse". The wavefunction randomly jumps to another wavefunction which isn't predicted by the Schrödinger equation.
What we get is a selection of wavefunctions it can possibly jump to, given to us by the Measurement operator.
My basic opinion is that the Measurement operator "hides" the physical reality of what occurs when the photon is measured.
As Quantum Mechanics stands there is almost no way to "dig out" what actually happens.
There are many interpretations, about twelve last time I counted, but in essence there is no way to know for now.

dudara wrote:

However, this guy knocked that on the head

I wouldn't confident about that. Peer Review found certain possible flaws in what he did and it has been difficult to reproduce.

_Dubh_

Fascinating reading there.

Previous experiments I believe placed detectors at one or each of the slits.
To me this experiment is different. I do this laser experiment at home regularly (I think the interference pattern on the wall is eerily beautiful). Whenever I do this experiment, I can't help but stare at the empty space between the slits and the wall/screen and ask myself "What in the Jaysus is happening in this space?"

Now this guy focuses the light in 2 directions producing images of the 2 pinholes and monitors the flashes at each hole. (Presumably this is the photon going through the slit and touching off the edge slightly? ! ?)
I'm not 100% on the flash thingy.

So he basically places wires (which might aswell be called detectors) in the place where we know there should be no (or very little) light, i.e. the mimima of the interference pattern. Okay. To me this is acceptable because there has been nothing interfering in the space between the slits and the lens.
Only the wires are placed where we 'expect' not to see any light... That is okay...I can walk over to my wall and put my little finger in the minima part of my interference pattern and nothing will happen......I wonder what would happen if the wires were placed at the maxima?

Say our screen is 12 meters away from the slits.....in the classic experiments, does it matter how far away the detector is from the slits?

nesf

Interesting, will read up on this if I get a chance. My quantum is a bit rusty

dudara

Son Goku wrote:

I wouldn't confident about that. Peer Review found certain possible flaws in what he did and it has been difficult to reproduce.

Agreed that it has been difficult to reproduce, but it has provided much food for thought, and when you think about it on a very simple level, why is it that we can't measure both wave and particle properties simulataneously?

I think that the problem lies in the fact we're not asking the right questions just yet

Son Goku

dudara wrote:

Agreed that it has been difficult to reproduce, but it has provided much food for thought, and when you think about it on a very simple level, why is it that we can't measure both wave and particle properties simulataneously?

I think that the problem lies in the fact we're not asking the right questions just yet

True.
Although in essence even if he is correct, it doesn't strictly go against QM only interpretations.

nesf

Son Goku wrote:

True.
Although in essence even if he is correct, it doesn't strictly go against QM only interpretations.

Exactly

The mathematics of QM (for the most part iirc) stand alone seperate from the Copenhagen Interpretation.

The Copenhagen Interpretation is just the most popular way to visualise and explain what happens. We know what happens mathematically, it's just very very odd.

Although an invalidation of even part of the C. I. will force a major rethink on the whole QM in the conceptual side of things. Most of the "examples" are really dependent on it.

The maths won't change, but our assumptions as to why the maths works will.

Still to be fair, they did call it just an Interpretation in the first place. It was just turned into dogma by the next generation so to speak.

Bear in mind, this isn't my field of study/research so I might not be exactly correct in my views here. Quantum never really interested me that much, so I never spend the time on it necessary to have a very solid understanding of it and it's history. It (like most areas of physics) needs to be studied "outside" of just formal education to really get your teeth into it.