I have been trying to understand "wave-particle duality" and other cases related to it. I am currently a college level student. I have few question which I am not getting answers clearly.
In double slit experiment, A particle behave like a wave, then how is "wave-particle duality" explained? I mean, If the particle behave like wave, then is it generating a wave or behaving as a wave? Is that wave going horizontally through slits (Double Slit Experiment) or vertically up and down or in which direction/axis the particle is vibrating to have a specific frequency? How does light behave as waves in it? and how does observer modify the experiment?
I may be thankful to you, If you clear my problems. I have read the theories on Wikipedia and other informational sites and tried to understand it.
Best Answer
The demonstration shown in the answer of another respondent, with the time frames showing how the interference patern builds up over time, is one of the best pieces of evidence we have about the wave particle duality of matter at the quantum scale. An intersting aspect in all these mysteries of nature, that I would like to express my opinion about, is the following:
Let us talk about photons, because they are the most missunderstood objects in quantum mechanics discussions.
Wave or particle? Photons are particles every day of the week, not some days they are waves and some other days they are particles. They are as much particles as the electrons are. We know that from the distinct clicks we hear in our detectors when sufficiently low intensity light arrives at them. The wave property of the photon, or any other particle, is the wave function, and I assume we are familiar with the interpretation given to it, as the probality to observe the photon (or any other particle) at some position $x$ at some time $t$. That is to say that there is no way to tell were actually the photon is before we observe it. The wave function in the mean time occupies the whole of the space that is available for the photon to be in. It is important to undestand that photons of the same colour are all identical (they have the same energy).
Two slit experiment: Now let us see what happens when a photon approches the two slits. The wave function that represents the photon will pass through the slits like waves do. It will split into two waves and recombine to interfere on the aray of detectors on the other side. The maxima corespond to high probability, the minima to zero probability. The consequence of this is that the photon is most like to show up in one of these maxima and will only hit one detector, but we don't know which one. Likewise, we don't know which slit it has gone through. An interesting point to make here is this, there is no way that one photon will hit two detectors at a time. Any attempt, or trick we might do to determine which slit the photon has gone through, destroys the interference pattern as all wave properties are removed!
Conclussion: The interference pattern people had seen in the Young experiment when they did it, they observed the pattern forming instantly because they used high intensity light. But we discover the reality when we use very low intensity light. It is like you turn down the water tap, and you start getting droplets instead of that continuous flow you had when the tap was fully open. And we know that if we look closer we will see molecules of water.
For a deep discusion on all these, try to google: Richard Feynman's lectures at the university of Auckland, New Zealand, First Lecture. Very entertaining too! Try this link: http://vega.org.uk/video/subseries/8