# 4 the question related to double slit experimetn

#### drphysica

Yep I have seen that movie! :)
Ok I am crazy enough to explain, “how Q.M. actually works”. Lets start with simple explanation of wave-particle duality, which actually states that the light has a dual nature: It exhibits both wave and particle characteristics (& that is a FACT). In early 20th century Albert Einstein has won a Nobel prise for his famous experiment, which we know as photoelectric effect. This experiment states that the incident photon possesses nature of particles or quanta which has energy given by E = hf where h is Planck’s constant and f is the frequency of radiation. And from Optics or E.M. theory we know that light is variation of electric and magnetic fields, which poses the nature of waves. So here arises question which model is correct? Is light a wave or a particle? The answer depends on the phenomenon being observed (note the word observed). Some experiments solely can be explained with photon model and others with a wave model. In 1923, here comes the Louis de Broglie and postulates that: because photons have both wave and particle characteristics, perhaps all forms of matter have both properties. Guess what? He was right! From classical theory we know what we need to describe a particle, we need to know its energy and momentum which are given buy E = mc2 = sqrt[p2*c2+m2*c*4] (relativistic energy) => p = E/c so using these equations and E = hf we can find that p = h/l where l is the wavelength of particle oscillating. Therefore l = h/p = h/(mv) (non-relativistic) this basic formula suggests that you me and all matter in the universe are also waves. By using this formula you can calculate your wavelength, which will be very small, much, much smaller than the atom its self. So the question is how can you observe that you are wave if the oscillation is infinitely small. So we all define our selves as I (particle, whatever) and yet we all posses the wave nature. Ok here comes my favourite topic (welcome to my world) Quantum Mechanics. Now before I go into this I want to assure you of that if you don’t understand anything you are on the right track. It is impossible for human who is attuned to everyday experience to understand quantum world. In my 3rd year one of the students in my class said that the QM is easy and he understands it, my lecturer took it very personally and was upset with that person. If you meet some one who said that they understand QM, it is most definitely that they saying that out of they ignorance and that they don’t understand it. Anyways the way I and most physicist “understand” QM is through mathematics, this is as good as it gets but don’t worry I will not go into proofs and theorems. The understanding of photon being a particle and the wave at the same time we can bring an example of free particle in QM theory. When we solve Schrodinger wave equation for a free particle (very complicated stuff if no advanced mathematical background) we find the Fourier transform which describes free particle being a wave and particle at the same time. A person must be crazy to even try to visualise how quantum world works (it’s madness) so here a mathematical or graphical description of a particle.

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#### dtfroedge

drphysica:
. Now lets get back to your question about the double slit experiment, this is very deep question in physics, which has yet to be answered. ).
Thanks for the history lesson. but I don’t think throwing up our hands and saying we can't understand it is the right approach. There is a big distinction between the math which works great, and the physical descriptions, which basically suck, for all the reasons you cited. The problem is that physicists don’t understand the physical phenomena, and it’s hard to explain something you don’t understand. The physical description is the subject that needs work. I would draw your attention to a thread discussing a likely error in Dirac’s thinking on the physical phenomena as an example.