Recent content by fermi

Finny, you have several good comments, but I think you are making a mistake by putting Spain and Portugal at the same level of a problem for EU as Greece is. It is true that all three countries were not fully prepared to enter EU initially. It is also true that all three countries have...

Thank you "bohm2" for the web links to these two interesting reports. Interesting in the sense that there is a good deal of data and analysis, but no clear-cut solution is proposed. I wonder why Greece is not considering selling some very large assets, like and island or two. I would not be...

I can't believe Germany's gullibility. Remember the cliche "fool me once, shame on you, fool me twice shame on me". Well, Greece already fooled Germany (and the rest of EU to a lesser degree) three times previously, and with this new round of bail-out Greece made it four! Fools or not...

I have a somewhat mathematical and abstract answer, I hope you find it useful. The Lorentz Group SO(1,3; R) is a real, simple, and non-compact group. Since it is a simple group, it cannot be written as the direct product of two other Lie Groups. However, all of that changes when you complexify...

I think you got two good replies, but I have one more point to add to completely kill the classical view of two protons and and two neutrons vibrating in some fashion inside the nucleus. Had that been even approximately true, the Helium-4 nucleus will exhibit an electric dipole moment, which...

I am happy to get an answer in terms of a power series if a closed form answer cannot be found. However, the power series you suggested has a problem for n=0 term in the series. For n=0, the integral: $$ \int_{0}^\infty \frac{k^{2n+2}}{(k^2+s)^{\frac 3 2}} dk $$ does not converge. This sort...

I tried integration by parts to isolate the exponential in a definite integral; that did not work. I also tried to change variables from k to z, with k=sqrt(s) * tan(z), which greatly simplifies the expression and gets rid of the nasty square root, but this time I have a trigonometric...

The integral given below is to be computed as a function of real variables x and s. Even a partial answer only for s>0 is very useful. Here is the integral: $$\int_{0}^{\infty}{dk \frac{k^2 e^{-k^2 x^2}}{(k^2 + s)^{3/2}}}$$ Thank you for your help.

Special Relativity states that a ruler flying by at near the speed of light will appear to be shortened as observed by a stationary observer in the lab frame. This is, of course, exactly what happens to macroscopic objects. The question is how far can we push this into microscopic realm...

There are many good treatments of the classical central force problem in many undergraduate and graduate textbooks. But I was unable to find a similar treatment of the retarded central force problem. I am looking for the classical treatment of the potentials of type: \delta(t'-t +...

Thanks Demystifier! I was not aware of the previous thread of a similar discussion. I agree with you that Weinberg's statement is a little careless (at best). Indeed your restatement in post#7 is almost exactly what I believe the right wording may be.

Recently a student brought the following to my attention from Weinberg’s Quantum Theory of Fields, Volume I, from page 177, which I must admit that it stumped me. Here Weinberg introduces the concept of Cluster Decomposition: “It is one of the fundamental principles of physics (indeed, of all...

An extremely light Higgs (less than < 1ev) would be a catastrophe in astrophysics. Top amongst many other problems, it would destabilize stars like our own Sun.

Thank you for the reference, I will check it out.

Ahh well, we all have to learn new tricks, don't we? Getting old is no excuse for not doing so. :smile: