This question is connected with the so-called wave-particle duality. We know experiments which can be explained only if we assume that the quantum objects are waves. However, are there experiments which can be explained only if we assume that the quantum objects are particles?
The fact that on a photographic plate a quantum object leaves a single spot, is not a convincing argument that we have to do with a particle. People can say that the wave-function collapsed.
But I consider another argument, as follows: let a source of, say, yellow photons, be open for 0.1 picoseconds. (This is the coherence time of a down-conversion photon.) Assume that the wave-packet contains only a few photons, and that we can record the time at which each photon impresses the detector with precision of femto-seconds. I think that we will find that some photons impressed the detector in the beginning of the wave-packet, others toward the end of the wave-packets, and most of the photons, in between. This is not a wave picture, it is a particle picture, i.e. that a photons has at a certain time a position better localized than the entire wave-packet.
However, for relying on this argument I need a datum: how long takes to a photon to impress a detector, e.g. to kick out an electron from an atom?
In the order of pico seconds, I guess.
It is definitely thought that particles are also part of QM, appear as points on screens, registered as clicks in geiger counters, marks on cathodic tubes, etc
Juan Weisz
Juan, where from do you guess so? If you can tell me precise things you are GREAT.
Please see, a photon belonging to the visible range lasts cca 0.1picoseconds. For passing through a sensitive material of 1mm thickness, a photon needs 0.1/3×1010 ≈ 3picoseconds. However, it seems to me that for interacting with an atom in the detector, is needed less than the duration of the photon. In other words, for the interaction photon-atom is NOT necessary that the entire wave-packet of the photon pass through the atom.
Good question, may I suggest to apply the uncertainty principle? How long it really takes is out of reach, but the shortest time the total absorption can be measured is accessible according to the Kopenhagen interpretation.
This measurement time is limited by Delta t > hbar / Delta E
Delta E is the energy of the photon, i.e. h * f or h * c/lambda, so we obtain
Delta t > lambda / (2*pi*c)
lambda is the wavelength of the photon, c the speed of light
Green light is at about lambda = 530nm so we obtain Delta t > 530*10^-9m / (6*3*10^8m/s) ~ 3*10^-16s ~ 0.3fs
What do you think?
Best greetings!
Claus Fütterer
Unfortunately, you cannot apply the unsertainty principle here. ΔE Δt helps you to find the length of the wave-packet, Δt, of the quantum particle if you know the uncertainty in the energy, ΔE.
Juan Weisz
My dear Juan, you'd do me a great service if you'd try where you saw this evaluation. I need it as an argument in an article. I don't think it's of the order of pico-seconds by of the order of femto-seconds. You see, a down-convesion photon is as long as cca 100 femto-seconds. I have reasons to think that for detecting the photon it is not needed that the entire wave-packet pass through the detector.
Another thing: would you have a loook again at my article for the conference?
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With best regards
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