Recent content by diracbracket

Does a photon have a mass? Yes it does. Energy and mass are the same thing, which is the reason physicists coined the term mass-energy. Historically "mass" has been the name given to an amount of mass-energy when it is in the form of matter, i.e. atoms. In this case it is measured in kg...

Let me see, \newcommand{\mean}[1]{{<\!\!{#1}\!\!>}} \newcommand{\braket}[2]{{<\!\!{#1|#2}\!\!>}} \newcommand{\braketop}[3]{{<\!\!{#1|\hat{#2}|#3}\!\!>}} \braket{\phi}{\psi} \equiv \int \phi^*(x) \psi(x)\,dx This LaTeX code doesn't work when I hit 'preview post'. There's no way to check it's right.

That is differentiation under the integral sign, actually. The answer is log(4/3). How do you do mathematical formulae on the messageboard?

Thanks guys. I get the gist of it. Someday I hope I'll be able to re-read Pervect's reply and understand it. I'm working though track 2 of Wheeler, Misner and Thorne at the moment. It's been mostly only differential geometry so far. In the meantime here's another one I've long wondered about...

Hi, everybody. Can anyone settle this question that I've been puzzling about? If an object with a small rest-mass, say, an apple, were to whiz very close past you in space with a relative velocity so great that its mass, as measured in your own inertial frame, was comparable to the rest-mass...