Recent content by jmz34

I'm slightly confused as to how we can use the picture of a 2D surface embedded in 3D space as an analogue to understand (maybe not picture!) 4D spacetime. My initial thinking was that trying to imagine a 4D spacetime isn't really possible, it's just a mathematical concept which one should not...

The example which I'll use to illustrate my problem is not a homework question but something I've found in a book and already know the answer to. The grand partition function, G, is defined as SUM(over i)[exp(-B(Ei-yNi))] where B=1/kT, y is the chemical potential and Ei is the energy of the...

Quick question, if there are n Feynman diagrams possible at first order say, is the rate proportional to n^2? I would have thought so since the matrix element is given by the expression M=M1+M2+M3+... where 1,2 and 3 are the consecutive orders. I've been looking at a few examples that say the...

OK that makes sense, thanks.

For the process (e+)(e-)->photon + photon the simplest Feynman diagram is just half of what you've drawn, but I'm confused about the propagator. I initially joined the two vertices for the above process with a line propagator (with no arrow) but in your diagram you have included arrows. I...

But a photon has an EM field? So is what I said about the electron interacting with the EM field correct?

I'm just beginning to learn about Feynman diagrams and wanted to make sure I've got the correct basic understanding of QED. This is what I believe to be true right now: QED allows us to describe the interaction between an EM field and light/matter. The QED vertex is composed of a photon and...

Homework Statement If we have the following partial decay chain: N1 -> N2 -> N3 where N1 is the number of nuclei of species 1, etc. and N1 -> N2, not via a decay but by the reaction such as N1 + neutron -> N2 + photon and we know this rate of formation of N2, say 'a'. I then get the...

If we have the following partial decay chain: N1 -> N2 -> N3 where N1 is the number of nuclei of species 1, etc. and N1 -> N2, not via a decay but by the reaction such as N1 + neutron -> N2 + photon and we know this rate of formation of N2, say 'a'. I then get the following rate...

Ofcourse. Thanks again.

Thanks a lot for your help. The question does say that Psi varies over a length scale that is approximately the same as the region which I'm supposed to be analyzing. Does that somehow mean I can take the RHS as constant?

I was trying to solve del^2(Psi)=Ae^(Psi) in spherical polars, for the radial component. Checking over my algebra I'm pretty sure it's correct.

Using this method I did this: d/dt(0.5*(r')^2)=(-GM/r^2)r' then integrated once and simplified to get (dr/dt)^2=2GM/r solving this for t gives: t=(1/3)*SQRT(2/GM)*Ro^(3/2) If you could have a quick look at my method I'd be very grateful. Thanks alot.

Homework Statement Solve ODE of form y''+(2/x)y'=C*(e^y) where C is a constant Homework Equations The Attempt at a Solution I don't really see how to approach this one, so a point in the right direction would be great. Thanks,

Homework Statement A stellar wind behaves as a steady adiabatic spherical outflow of a perfect monatomic gas (gamma=5/3) from the surface of the star, so at radius 'a' the density is 'p0' temperature 'T0' and outflow velocity 'u0'. If the fluid motions are dominated by the star's gravitational...