Recent content by gamma5772

You seem to have misunderstood my point, both in the sentence you quoted, and in the my entire post. In the sentence quoted, the "cat" is not a cat at all -- it is a photon or electron -- experiments have been performed which indicate that the photon or electron is in a superposition (humor me...

It is experimental fact, as has been pointed out, that for microscopic objects, the Schrödinger cat experiment indicates that the cat (photon, electron, what have you) actually is in a superposition. Let us for now assume that quantum mechanics does not include wavefunction collapse. We can...

The uncertainty principle is NOT tied to our abilities to observe. The uncertainty principle is \sigma_x \sigma_p \geq \hbar / 2. What this says is if you have an bunch of identically prepared states of a particle, and you go through and measure the momentum of half of them, and the...

Thank you! This was helpful. I am still confused about the symmetry business: you claim that because SO(2) ~ U(1) that two real scalar fields (endowed with SO(2) symmetry) behave as a single complex field. I understand what you mean by possession of a symmetry now, but I don't understand...

In the orthodox interpretation of quantum mechanics, the answer is yes, the uncertainty principle will still hold. The uncertainty principle is a statement that the wavefunction of a particle cannot be simultaneously localized in both position and momentum -- this has nothing to do with...

A couple questions: What precisely does it mean to "obey a symmetry?" QFT in a Nutshell and Peskin and Schroeder (If I recall correctly -- I don't have the latter on hand right now) adopt the view that \phi and \phi ^\dagger are independent variables, writing expressions such as...

In treating the complex scalar field in QFT, \phi and \phi^\dagger are treated as independent variables. I'd like to make sure I understand what this actually means: Is this the same idea as treating \phi and \partial \phi as independent variables in the Lagrangian? Formally, we view the...

Oh my. This is embarrassing -- I thought for a minute the diagram I just drew was distinct from the other two! Thank you!

Sorry if I'm being slow, but the attached Feynman diagram seems to be a u-channel diagram for the reaction e+ e- -> e+ e-. (Apologies -- I don't know how to make Feynman diagrams in latex)

I don't understand why in Bhabha scattering (e+ e- -> e+ e-) why there are only two leading order Feynman diagrams. It seems to me like there should be s, t, and u-channel diagrams. Could someone explain why I am wrong?

I don't seem to be able to fully wrap my head around the equivalence of standard QM and 0+1 QFT. In particular, I am having difficulty with the relationship between the correlator in QFT, <T\phi(t_1) \phi(t_2)> and the propagator in QM, <x', t' |x,t>. First of all, is there any relationship...

I'm wondering if there is a monotonically increasing function with a jump discontinuity at every rational (or any other dense, countable subset of the reals). Here's a specific candidate that I've come up with: Let g:\mathbb{Q} \cap [0,1] \rightarrow \mathbb{R} take the rational p/q (p and q...

What is the formula for the force between 2 charged particles? Once you know the force 1 exerts on 3 and the force 2 exerts on 3, it is a simple matter of adding them up -- but remember that force is a vector, so you must use vector addition.

This is misleading for a couple reasons. In general, under a gauge transform, A and phi can be changed and leave the E and B fields unchanged. Yet the Aharonov-Bohm effect is gauge invariant. This implies that we cannot deduce the value of A from the AB experiment, and actually, from the form...

A characteristic of massive springs is the ability to support waves. The particle striking will generate waves in the spring (unless it is traveling faster than the speed of sound in the spring), which carry both potential and kinetic energy. This is what you will find if you follow...