# Search results

1. ### Autocorrelation of a wiener process

ok, so can I say <e^{\phi(t)+\phi(t+\tau)}>=<e^{\phi(t)+\phi(t)+\phi(\tau)}> since W(t+\Delta t)=W(t)+W(\Delta t). Next we can say <e^{\phi(t)+\phi(t)+\phi(\tau)}>=<e^{2\phi(t)}><e^{\phi(\tau)}> because <\phi(t)\phi(\tau)>=0
2. ### Autocorrelation of a wiener process

Let \phi(t) be a Brownian Walk (Wiener Process), where \phi\in[0,2\pi). As such we work with the variable z(t)=e^{i\phi(t)}. I would like to calculate E(z(t)z(t+\tau)) This is equal to E(e^{i\phi(t)+i\phi(t+\tau)}) and I know that E(e^{i\phi(t)})=e^{-\frac{1}{2}\sigma^{2}(t)}, where the...
3. ### Brownian motion solves Laplace's Equation?

There seems to be a curious connection between Brownian Motion, stochastic diffusion process, and EM. http://en.wikipedia.org/wiki/Stochastic_processes_and_boundary_value_problems I was hoping to share and to have someone add some insight on on what it means that the Dirichlet boundary...
4. ### LaTeX Custom Mathematica Shortcut: Copy as LateX

This can be very useful, so I thought i'd share. If you edit the > Wolfram Research\Mathematica\8.0\SystemFiles\FrontEnd\TextResources\Windows\MenuSetup.tr file you can make Strl+Shift+C copy not plain but in LateX format. Very useful. Look for the line in the file that says "&LaTeX"...
5. ### Quantum Numbers of Spin 1/2

this sounds like a question that should be answered somewhere, but i cant find it. how many quantum numbers does it take to specify the state of a spin 1/2? 1. if it points along z, then just 1: the eigenvalue of Sz will do (up to global phase) A. whether or not in a B field B. if...
6. ### What is Information?

im not sure thats any better. just because 200 years ago we could not "point to" or manipulate say cooper pairs or atoms, doesn't mean they dont exist and don't have an effect. this is a real problem in physics, how do we see and manipualte, people are discovering new ways every so often...
7. ### Complex Conjugate: just replace i by -i even in denominator or inside argument?

so i think it works for any function with a taylor expansion (~analytic), because conjugation carries through addition and multiplication and so through powers and thus exponents 1. (z1 +z2)* = z1*+z2* 2. (z1 z2)* = z1* z2* 3. (z1^n)* = z1*^n 4. \left(\frac{1}{\text{z1}}\right)^* =...
8. ### SHO Ladder Method missed states?

Thanks a lot!
9. ### What is Information?

yes, you are saying that information is a human construct and does not exit beyond us, like the alphabet or the idea of the color green. this is true, the concept of information is 'artifical' in the sense that as a concept it is not ontological (does not exist), but like all human concepts...
10. ### Complex Conjugate: just replace i by -i even in denominator or inside argument?

this is very good, that is what i was asking! Thank you, so it works almost all the time. do you know when, in what cases i should be careful when using it? ie anytime i dont use fractions and logs, and exponetnials and trig funcs?
11. ### Complex Conjugate: just replace i by -i even in denominator or inside argument?

see my post right above yours, i know that the complex conjugate is only equal to the complex # itself when the number is real, i am asking how to get the complex conjugate
12. ### What is Information?

i agree, i think this is the essence of heisengber uncertainty and infromation. for something to be ontological (that it can exist), it must have effect, and must be also epistomological (knowable), we must be able to know about it, to learn it is there. we can only deal with things we...
13. ### SHO Ladder Method missed states?

this is all true, and is a summary of grifits derivation, but it it doesn't tell you that the raising and lowering operators take you between nearest orthogonal states. what is they raised and lowered by two quanta of energy, how do you know what the smallest quanta of energy is?
14. ### Complex Conjugate: just replace i by -i even in denominator or inside argument?

this is basically the answer to my question, but i do need to unravel its meaning: 1. holomorphic - basically well behaved, has derivatives. 2. phi(z) is real for z in reals, this is a hard condition, because often the form of the expression is not such, but i have found that the trick...
15. ### Complex Conjugate: just replace i by -i even in denominator or inside argument?

to get a Complex Conjugate of a #, is it ok to just replace i by -i even in denominator or inside argument?
16. ### Mathematica Mathematica: Fourier Transform by hand of sin

Hi, i do not understand why i can find the FT of sin in mathematica using the built in function but not by integrating, even thoiugh they should be the same: Integrate[Exp[i(ω-ω0) t,{t, -∞, ∞}, Assumptions ->ω0 el Reals && ω el Reals] but the statment FourierTransform[Sin[ω0 x]...
17. ### Is Energy the Glue of Entanglement?

can you summarize that paper to answer the question? i do not directly find the answer in the paper
18. ### Question on wave functions

your question is very fundamental and basic, check the wiki on wavefunction. the wavefucntion is a function of the phase space -> like position the interpertation is not agreed upon but you can think of it as probabily density of finding the particle (matter) at some position. yes it obeys the...
19. ### SHO Ladder Method missed states?

Following Griffiths derivation on pg 44 of the eigen-states of SHO Hamiltonian, he says that we can now find all eigenvalues, but doesnt say how he knows that a and a dagger will indeed take you between nearest neighboring orthogonal states. in other words, how do we know the ladder operators...

thank you
21. ### Photons in amorphous glass slow because?

well there is some interaction b/w the photon and the phonons, like in ion trapping, where you get dressed states of the phonon ladder and the qubit (some transition in say Yb+ (Monroe research)) which atomic transition (qubit) the light field can interact with. on the other hand this is...
22. ### How is light absorbed/reflected?

ok! so if you have a linewidth on your state (eg a non-ground state) then you can also transition within the linewidth with some small probabily, which would be incoherent and inelastic. the reason this is called spontaneous Raman scattering is because it only occurs sometimes?
23. ### How is light absorbed/reflected?

-usually? maybe you can be a bit more explicit about what you mean by coherence? i was imagining that the phase and polarization of the outgoing photon is the same as the ingoing one - this makes sense to me if i believe the that for processes on short time scales the effective...
24. ### Photons in amorphous glass slow because?

what do you mean? they are localized dispersion relations for different zones, corresponding to some small order?
25. ### Photons in amorphous glass slow because?

In solids it is the interaciton b/w the phonons and photons that give a lower effective speed. not absorption & re-emmision. (see ZapperZ's post: https://www.physicsforums.com/showthread.php?t=511177 [Broken]) but in amorphous glass there are [B]no[B] phonons. So why does light 'slow down'...
26. ### How is light absorbed/reflected?

ok that makes a bit more sense Cthugha, thank you. so there are 2 scattering processes for an atom in free space: 1. the linear abs/emit 2. quadratic a, a-dagger combinations for the light field that emit a photon of the same energy but in a random direction? (should be quasi-random right...
27. ### How is light absorbed/reflected?

to be honest im very confused now, is there any way you can describe the process to someone unfamilar with virtual photons but in a physics phd program
28. ### Which Quantum Interpretation could make a difference?

ok that is more strictly true since it modifies the SHE. but it also sheds some light on measrument and decoherence treating them as wavfunciton leaking from system with small #dof to a system with large #dof again see the post by zpower
29. ### Which Quantum Interpretation could make a difference?

If you are [I]really[I] interested in the subject i just found a great review article on decoherence and interpretations: Decoherence, the measurement problem, and interpretations of quantum mechanics Rev. Mod. Phys. 76, 1267–1305 (2005) http://rmp.aps.org/abstract/RMP/v76/i4/p1267_1
30. ### What is Information?

Great Question!! I've been puzzling over this myself. I think we are talking about physical information, as in one spin can contain 1 bit of information. it is either up or down. (or is it two since it also has direction?). When we measure it, to know it is there, must we be recieving...