1,689 reputation
615
bio website markbeadles.com
location Columbus, OH
age 47
visits member for 2 years, 11 months
seen Jan 28 '13 at 17:55

Feb
2
comment Energy required to reach 1 wavelength
Thanks, @Community♦ for catching my error in the sign of the exponent.
Feb
2
comment Energy required to reach 1 wavelength
As @Martin alludes to above, it's not correct to think of photons as "using" or "needing" energy to travel. They always travel; that's what they do, and always at the speed of light. A photon doesn't need to "reach" a frequency: when it is emitted, it already has that frequency. It's not like a mechanical wave. Photons essentially are energy. And absent hitting something, a photon will keep travelling to infinity.
Jan
31
comment What experiment would disprove string theory?
I like the metaphor of the extension of the positive integers to the signed integers as a model for the extension of relativity+quantum theory to string theory. But I think a better metaphor is the extension of Euclid's axioms. It turned out there were multiple consistent (even "correct") extensions of the axioms. But of course, only one extension is "true" (or "real) for any given universe. This is rather the question being asked here: is there any experimental way to know which extension reflects reality?
Jan
31
comment What experiment would disprove string theory?
Your indication of the importance of quantum gravity to this question is a great point.
Jan
29
comment How can I measure the conductivity of a copper rod?
Well, you could always measure the length and the resistance with a ruler and ohmmeter, and just calculate $\sigma=1/(\rho * l $)
Jan
29
comment Why does electron-positron annihilation prefer to emit photons?
Thanks for the clarification, that is helpful.
Jan
29
comment Why does electron-positron annihilation prefer to emit photons?
OK, it was not clear from your question that this was what you were asking, as opposed to the more general question.
Jan
27
comment What is the inertial frame that explains the Foucault Pendulum?
I'm making a statement. :) Sorry, not trying to talk at cross purposes. As the wikipedia article also states, the Foucault pendulum is not in an inertial frame. It is rotating, by an angle of −2π sin(φ) per day where φ is the latitude. At the poles the pendulum indeed does not rotate.
Jan
27
comment What is the inertial frame that explains the Foucault Pendulum?
@JohnRennie the triangle you describe rotates with the Earth. Consider the point on that plane, which is on the ceiling where the pendulum is attached. This point is in a building attached to the surface of the earth and therefore rotates with a period of 24 hours. Therefore that plane is itself rotating around the center of the earth as well.
Jan
27
comment What is the inertial frame that explains the Foucault Pendulum?
The sidereal day is 23.93447 hours.
Jan
26
comment What is the inertial frame that explains the Foucault Pendulum?
@JohnRennie What you say is true only at the poles. Elsewhere the pendulum must rotate.
Jan
26
comment What is the inertial frame that explains the Foucault Pendulum?
@Vam'çá it's not gravity that is causing the apparent rotation. I say "apparent" rotation because that's what it is. We are seeing the effect of a combination of real and fictitious forces that, when observed from our viewpoint as stationary with respect to the accelerating Earth, looks like rotation.
Jan
26
comment why is there no ninth gluon?
@mbq thanks for checking it for me!
Jan
26
comment why is there no ninth gluon?
See also this question and its answer on "colorless" gluons.
Jan
25
comment why is there no ninth gluon?
Interesting - it postulates that the color symmetry is broken $U(3)$ instead of $SU(3)$ and that the broken symmetry gives an extremely massive singlet gluon.
Jan
23
comment Earth's stationary iron core
@RonMaimon Of course you are right and I spoke loosely. Sorry.
Jan
23
comment Earth's stationary iron core
In physics when we say "stationary" we must always ask "stationary relative to what?"
Jan
23
comment Earth's stationary iron core
Great links, Adam - in particular I'm fascinated by the discovery that the core is asymmetrical.
Jan
22
comment What is the meaning of speed of light $c$ in $E=mc^2$?
Possible duplicate of this question; you may want to take a look at that.
Jan
19
comment Does a perfect mirror behave the same as a blackbody radiator?
This paper addresses your question, I believe, but I do not have access to full text from here. "Radiation from perfect mirrors starting from rest and the black body spectrum"