Recent content by Ratzinger

I just like to say this was the last time I visited site!

Kurdt, are serious? Let's assume you are. Again, I was posting this in the general discussion forum: <Quote deleted by Moonbear...if we deleted the text before, it isn't allowed here either.> ZapperZ deleted this, send me a warning where he accused me of advertising this firm, and then two...

Could please other mentors than ZapperZ look at this thread https://www.physicsforums.com/showthread.php?t=195503&page=2 starting post 25 and tell me what I did wrong? thanks

hello? There is this book by Anthony Zee "QFT in a nutshell", where the author couples a free quantum field to a classical source, gets a propagator and integration goes over all momentum. No pertubation theory, no Feynman diagrams, but off-shell, 'virtual' particles. Why the claim of...

a question why do people say virtual particles come (only) from pertubation calculation, what about free fields? In the free propagator the integration goes over the whole momentum as well, including 'off shell' momentum.

great video on how turning a sphere inside out http://video.google.com/videoplay?docid=-6626464599825291409 enjoy!

many thanks meopemuk!

thanks meopemuk! But the generator of time translation (the Hamilton) consists of differential operators, so do the generators of space translation and angular momentum. Does not that mean an infinite dimenensional Lie algebra?

Is U(t)=exp(-iH/th) a Lie group? Is it an infinite dimensional Lie group? To what 'family' of Lie groups does it belong? thank you

A question: if the curvature is positive, is projective space RP^3 possible?

More precise:localizing ( by scattering, putting in a box) a particle below Compton wavelength leads to particle creation. Asking for the position of a particle below its Compton wavelength is a unphysical question. Those are not my words, but those of Sidney Coleman, made in his...

When going below Compton wavelength of a particle, energy uncertainty is big enough that particle creation occurs. So asking for the position of a particle in relativistic quantum theory does not make sense. In QFT position is no longer an observable, but becomes a parameter to...

When quantizing a static force field, say a Coulomb field, we get off mass shell, virtual particles and we say they transmit the force between two charges. They say the exchange of particles produces a force. It's a very profound and important concept in physics. But then, as I read many...

http://www.youtube.com/watch?v=r4kgxbTqz_Y&mode=related&search=

This metric is often written in an alternative form, here called the curvature normalized way. Unfortunately I can't follow how they rewrite it, could someone hint me how it is done or tell me a text where it is shown in more detail? thanks