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  1. Q

    Mathematica , a simple question.

    I have a very simple issue with Mathematica, but I can't seem to find an answer for it. I solved an equation with DSolve, and I got a result as an array of the following type: Solution = { A11 -> Function[ {t} , expression1] , A22 ->Function[ {t}, expression 2] , etc } Now I want to define...
  2. Q

    Solving a matrix differential equation in Mathematica

    I want to solve a differential equation of the form d/dt (R) = B(t) where R and B are two complex matrices, with time dependent functions as their coefficients. I want to solve these 3x3 differential equations (ones on the diagonal are actually coupled) and to obtain a matrix form for R. So...
  3. Q

    Mathematica 5.0 notebook does not work in Mathematica 9.0

    1. I have managed to find the following notebook that would prove useful for me in calculating the concurrence of a 2-qubit state. http://library.wolfram.com/infocenter/MathSource/6227/ 2. The problem is that the code is for Mathematica 5.0, and try as I may, I could not make it...
  4. Q

    Switching the position of matrix elements in Mathematica

    Say I have the following matrix, written in Mathematica A := {{a11, a12, a13, a14}, {a21, a22, a23, a24}, {a31, a32, a33, a34}, {a41, a42, a43, a44}} I want to exchange the positions of a12 and a21, a14 and a23, a32 and a41 , a34 and a43. Any ideas? Thanks.
  5. Q

    A question about kaon masses and decay widths

    Homework Statement Ok, so I need to make a software that will simulate a neutral kaon system, and I only have the following data about the masses and decay widths: gammaS = 580*gammaL {S = short lived state, L = long lived state} mS - mL = 0.477*gammaS Homework Equations How...
  6. Q

    Decay Width

    What is the Decay Width of a particle and how is it related to the particle's lifetime ?
  7. Q

    Defining variables in mathematica

    I need to define some "general" variables in Mathematica 8, and I wonder if this can be done the following way. Say ta[n] and tb[m] are my variables, in turn depending on n and m. I want to define a function, for example E[ta[n]_ , tb[m]_ ] := Cos[ ta[n] ] + Sin [tb[m] ] (just a simple...
  8. Q

    Change of basis

    I have two possible bases (a,b) and (a',b'). If I also have the transformation matrix P, such that P(a,b)=(a',b'), am I correct in assuming that I can change an operator A, from the (a,b) basis to the (a',b') basis by applying A' = P_transposed * A * P ?
  9. Q

    Mathematica indices as variables

    1. I'll post here a simplified version of my problem Say you have a matrix A, and you want all its components to be functions, for example: A11 = Sin(a_n) A12 = Cos(a_n) A21 = Sin(b_n) A22 = Cos(b_n) And I want to be able to do this in mathematica so as to have the matrix A a...
  10. Q

    Yang-Mills Theory

    What exactly is a Yang-Mills Theory? Is it a general theory, based on SU(N) symmetry, which can then be applied for particular cases (ElectroWeak, Chromodynamics) ? Is it like a general mathematical model of gauge theory ?
  11. Q

    How do theoretical physicists know so much?

    I'm a PhD student in theoretical physics, and I am just amazed by how much physicists working in my field actually know. I am currently studying QFT and plan on going a bit deeper into General Relativity afterwards, but look at people like Rovelli or Susskind (just two names that came to my...
  12. Q

    A problem in deriving the interaction field equation for photons

    Well, I was doing a problem the other day, inserting the complete interaction QED Lagrangian into the Euler-Lagrange equations, in order to obtain the field equation governing the interacting electromagnetic field, with the Dirac field. The problem is that, by doing so, I got the equation, but...
  13. Q

    A Naive Question

    When you switch from Classical to Quantum Physics, as an undergraduate, there is one more thing you lose, after certainty....you lose intuitive understanding. Ok, we can obtain probability amplitudes for this or that, but is there any chance we will ever know HOW it happens? Could we have a...
  14. Q

    Haag's Theorem in QFT

    So I'm currently studying QFT, and I got to the point where I realized that the S operator, initially assumed to be unitary, is not unitary anymore, since it is assumed to act between t0 = - infinity and tf = infinity. The author of the book I'm using says this is due to Haag's Theorem, so I...
  15. Q

    How do you take notes?

    It seems that lots of physics students, even graduate students have a problem with finding the most effective way of learning by themselves. So...how do you do it? Here's the situation: you have 1 book, 1 chapter, say around 30 pages, divided into subchapters, and some problems at the end...
  16. Q

    LQG Resources ?

    If you search major book retailers on the internet, you can find lots of new and very good books on string theory, for both novice and more advanced students. However, for loop quantum gravity, you can't really find anything. Is there an introductory book that takes you from QFT to LQG ? Where...
  17. Q

    Symmetry Groups

    I have a question regarding symmetry groups. I've often heard that the Standard Model is a SU(3) x SU(2) x U(1) theory. From what I understand these groups contain the symmetries under which the Lagrangian function is invariant. If so, what does every one of the 3 groups above contain (what...
  18. Q

    Schools Universities with PHD programs in Quantum Information Theory

    I will finish my Master studies in theoretical physics next year, and I want to do a PHD in Quantum Information (my main interest). I want to apply to universities in the UK and Germany (right now I restrict myself to these two countries). What are the universities you know of, that have Quantum...
  19. Q

    Question regarding the flux of a field.

    I'm currently studying Classical Electrodynamics, and I see everywhere that the flux of a field through a surface is defined as the normal component of the field times the surface area. They interpret this in a physical way as the net charge flowing through the surface in the unit of time. My...
  20. Q

    Is this a realistic goal ?

    Ok , so I have to finish a classical electrodynamics book ASAP... I absolutely hate it when I have to study with a deadline, but that's how it goes. Here's the book: https://www.amazon.com/dp/0805387331/?tag=pfamazon01-20&tag=pfamazon01-20 Here's my question : Is it realistic to set...
  21. Q

    A problem in electrostatics

    Homework Statement Ok, so I have a charge inside a conducting sphere. I managed to calculate the electric potential inside the sphere, and also the surface charge distribution, on the interior surface of the sphere. Homework Equations How can I calculate the charge distribution on the...
  22. Q

    A problem with a series expansion

    Homework Statement Ok so I have to expand in a power series of ({\alpha} Z)^{2}, the equation E_{nj}=mc^{2}\left\{ \left[1+\left(\frac{Z{\alpha}}{n-(j+1/2)+\sqrt{(j+1/2)^{2}-\alpha^{2}Z^{2}}}\right)^{2}\right]^{-\frac{1}{2}}-1\right\} Homework Equations I know that a series expansion...
  23. Q

    Relativity and Electrostatics

    Say you have to equal charges q1 and q2 and a distance r between them. We know from electrostatics that the force exerted by one charge on the other is inversely proportional to the square of the distance between them. If you place a massive object at the middle of the segment connecting the...
  24. Q

    Why does the electron jump ?

    I've been bothered by this question. Say we have an electron in it's ground state. According to quantum mechanics, that is a stationary state. Then we excite the atom and the electron jumps into a higher energy level. That is also a stationary state. The question is: Why does the electron jump...
  25. Q

    A good problem book in undergraduate mathematics

    Does anyone know a good problem/exercise book in general undergraduate mathematics, the stuff covered by Arfken&Weber of Riley, Hobson and Bence: basically, vector algebra, analysis (real and complex),differential equations, algebra, vector analysis and maybe some geometry (analytical and...
  26. Q

    LASER effect

    I did not quite understand the "stimulation" part. How does the photon coming near the excited atom force this atom to emit another, identical (from the physical properties point of view) photon? More precisely, how do the stimulating photon and the atom interact?
  27. Q

    Entanglement and String Theory

    I'm a physics undergraduate (2nd year), and I'm just learning the basics of Quantum Mechanics. As you would expect, I've been fascinated by the elegance and.....paradoxes involved. My question here is about the phenomenon of entanglement. I know the mathematics of it, but when I asked my...
  28. Q

    System of linear equations with complex coefficients

    1. You have a system of equations of the following form: x + iy = 0 -ix + z = 0 y - z = 0 or -2Sqr(5)x - iy = 0 ix - 2Sqr(5)y + 2iz = 0 -2iy -...
  29. Q

    A Good Atomic and Nuclear physics book?

    Could anyone tell me a good book on Atomic and Nuclear physics?
  30. Q

    How much do you work daily?

    I don't know if this post is related to Academic Guidance, but it seems to fit here. So the question is simple, how much do you work daily/weekly/monthly? (choose what period of time you like). How long does it take for you to finish a book of...say 600 pages. (I know that different books take a...
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