What are the true verifiable ramifications of the double slit experiment?

I have often found conflicting and confusing information in textbooks and on the internet regarding the famed double slit experiment. I've seen it with light in class, I've never seen it with electrons or atoms. In the literature I've seen, the test apparatus is never described very well, and the idea of placing a detector at the slit is often glossed over.





The conclusions people reach are sometimes wacky, implying that human observation effects physics, which seems ridiculous to me.





Can anyone point me to some really good sources of information on the web regarding this fundamental element of quantum physics?What are the true verifiable ramifications of the double slit experiment?
The double slit experiment is one of those tricky little processes. It is often one of the first things introduced in any quantum course. In your first year of quantum, it seems counter intuitive. By your second year it seems obvious (given that you trust the math), but by your upper years it seems complicated again.





What we think we know: All matter exists as waves, and has a non-zero possibility of being at any point (given there isn't an infinite potential). Think of this as being a continuous and infinite superposition (since wavefunction occur in continuous L2(R)). However, by the postulates of quantum mechanics, when we ';measure'; such an object, it collapses to one of its eigenstates. The photodetector is considered such a measurement. If we measure the particle to see which slit it entered, we've destroyed the superposition before it can self-interfere.





The types of measurements used to detect the particle at the slit are called ';non-destructive measurements'; and usually involve detecting some variation of an electric/magnetic field as the particle passes through. Even if the particle isn't charge, it's spin creates a magnetic dipole moment that can be detected. Try google/wiki for more results.





The point is that as all things are in superposition, but this is a very delicate state (coherence). The act of measurement results in the system decohering, and collapsing into an eigenstate. It need not be human observation, just a measurement in general.





What is a measurement? This is a very deep question, one that is still an active area of research in quantum foundations. Is it just an apparatus and ancilla? Or perhaps must we consider the human and apparti as quantum elements as well and consider the combined space? It's actually a very deep question.





For a good source of info, there is of course the standard textbooks. Sakurai may be too complicated for newcomers, and Griffiths is too simple for a deeper understanding. You may wish to try the website www.am473.ca, which is essentially an entire upper-year undergraduate course on advanced quantum theory.What are the true verifiable ramifications of the double slit experiment?
There are some quantum text books such as Modern Physics by serway et al. that describe the double slit experiment in detail. Like you said I also don't think some of the stuff on the web is very credible





The most important part of the apparatus is the detector. All detectors are basically a collection of particles which traveling electron will hit and this in turn would reveal which slit the electron came through. The problem is however these detector also alter the momentum of the electron when it collides with the detector particles. Now after all this the conditions required to form an interference pattern violates the uncertainty principle.
What happens when you put light through a very small slit (nanometers) is that the light creates fringes. These are due to a property of all waves known as defraction where you get areas of relatively high intensity and low intensity. They found that when you do this with only one wave of light you still get multiple fringes which gives proof to the Hisenburg uncertainty principle which says that something can be in two places at once.
Let's start with the last comment first...that observation affects the physics. This is of course the crux of the Heisenberg Uncertainty Principle. The problem is that, we cannot ';see'; something unless something is coming from or rebounding off it and into our detectors.





Case in point, you cannot see this text unless photons come from it and enter your eyes. Mere existance of an object is a necessary but not sufficient condition for observation. Something has to be coming from that object for us to observer it. And that something affects the object's location and/or momentum.





So as soon as we probe an object with oh I don't know...light, X-rays, gamma rays, BBs...anything...that object takes on the momenta of that probe. And, voila, you no longer really know the real momentum of that object you probed. [BTW: I mention BBs because they are used often in HS/college physics labs to demonstrate how we discern the shape of subatomic particles by scattering effects.]





The uncertainties found at the subatomic level fade away as we move up into the macro world...the one you and I see daily. That results because the probes we use to see these macro objects are way way smaller than the objects themselves. So the affects on the large object locations and/or momenta are very very tiny. This is a good thing, because if the uncertainties remained large, this text would be bouncing all over the place from the photons used to probe it.





Now to the 2 slit experiment. Makes no difference (except in dimensions like focal length and slit separation) what particles we send through the slits...photons or electrons...the results will be similar. That is, we will see constructive and destructive interference rings on the projection screen. This result deomonstrates the wave nature of the particles.





Let's see if I can drow the 2 slit from above:





......................|...............鈥?br>

......................x...............鈥?br>

X--------------------|................鈥?br>

......................x...............鈥?br>

......................|...............鈥?br>




Best I can do given Answers editing limits. Anyway the source (electrons or photons) is at X. At each x, the slits, the wave fronts act as though they were two separate sources. But they are in sync with their respective phases. That is, over time, the wave front above and the wave front below are oscillating up and down together.





They are still going up and down in sync when they hit the screen. But...this is important...because some waves travel a short distance directly to the screen (right in front of the slits) and others travel a longer distance to either side from the slits, when the waves from the two sources (each x) overlap (inteference), some of them are out of phase with each other.





That is, as we move away from directly in front of the slits, there will be alternating bands of dark (where the waves from the two sources are 180 degrees out of sync (crest to trough)) with bands of light (where the two source waves are in sync (crest to crest). The dark bands occur where destructive interference takes place and the light bands are where there is constructive interference.





Whether the bands are destructive or constructive depends on the geometery. So if one wave travels just a bit farther than the one it is interfering with, it might be 180 degrees out of phase with that other one and the interference would be destructive. If it travels even farther, so more time is taken, it would find itself back in phase with the other wave...constructive. And there you are.





';The Elegant Universe'; by Brian Greene, PhD, has an excellent section on the 2 slit, including why we still get interference bands even when we push one electron or photon through at a time....rather than a group of them at a time.