Recent content by psmt

Thanks for the correction! I hadn't noticed that before. It seems strange, in a way, that treating the y-component of the field as a perturbation is OK, because it would appear that the spin-dependent force on the particle in the y direction is of the same order as that in the z-direction...

Yes - bear in mind that like any quantum theory, a quantum field theory has a state vector, although because the number of particles is not fixed, this state vector belongs in a Fock space rather than a Hilbert space. For a non-interacting theory, the particle number operator commutes with the...

The field can be inhomogeneous but in the z-direction at all times. The strength of the field depends on z.

Not in a vacuum. I would be interested to know what your teacher says "the photon's mass" is, if it can be calculated. In a superconductor, photons acquire mass, via the famous Higgs mechanism: http://en.wikipedia.org/wiki/Higgs_mechanism#Examples ... but it doesn't sound like this is what your...

I don't find it very compelling either! I don't know much at all about how this happened historically, but i think you could at least motivate the Dirac Lagrangian without any reference to charge, on the basis of trying to find out whether Nature might make use of the spinor representation of...

As i understand it, you haven't shown that the other field components are zero, you've just eliminated them from the Dirac equation - they will still contribute to the current etc (i'd have thought... can't see why not). A couple of other things: firstly, your paper appears to be on classical...

I think we should all bear in mind that there is a strong answer available from regular QFT, without having to resort to string theory. The Lagrangian for a Dirac field is invariant under a global rephasing of the field, from which a charge operator can be defined as the spatial integral of the...

That's an interesting observation. However, in the spirit of the original post, i was thinking of the non-relativistic "bog standard QM" formalism in which a single-particle wavefunction just consists of the product of a spatial part and a spin part (or a sum of such products). All i was...

What about the spin wavefunction for a spin-1/2 particle?

In the case of a von Neumann (or Pauli?) measurement of the first kind i think a) is right. For a measurement of the second kind, it looks like the answer is similar to a) but the state of the measured object after the measurement doesn't actually end up being the state you've measured, due to...

Lenz's law refers to currents set up in conductors as a result of changing magnetic fields, not to EM waves propagating in free space. EM waves in free space are solutions to the free space Maxwell's equations. Try http://en.wikipedia.org/wiki/Lenz%27s_law vs...

Yes, that's equivalent to using the correct Z.

As you saw, if you start with U = 1/2 kx^2 and differentiate once, you get the linear force law you want. Differentiate it a second time.

The quantum mechanical result has been experimentally verified, if that's what you mean.

Gamma-5 and gamma-mu are indeed all matrices, BUT the four different gamma-mu represent the Dirac algebra, whereas gamma-5 is not an element of that representation - so that's where the difference must come in. (If your question is about the number of components and the fact that really gamma-mu...