Recent content by BucketOfFish

Ah great, Feynman always catches the interesting stuff.

Thanks, Truecrimson! This is exactly what I was thinking of!

I don't think I'm describing a motor. For one thing, there is no alternating current in my model, which is required even in a permanent magnet motor. I'm proposing to just dangle a block of some material in midair and then to apply an extremely strong stationary magnetic field. I know the field...

I know that magnetic fields can align objects with spin. In that case, if we suspend an object and turn on a magnetic field such that a significant number of electrons become aligned with the field, could we observe a macroscopic change in angular momentum?

Sometimes when studying I'll run into a derivation that seems unclear, unmotivated, or which seems to require outside information. What do you do in those cases? Search online? Bang your head against the equations? Look for another book? I'm specifically asking about learning things on my own...

Homework Statement Given that ##x_\mu x^\mu = y_\mu y^\mu## under a Lorentz transform (##x^\mu \rightarrow y^\mu##, ##x_\mu \rightarrow y_\mu##), and that ##x^\mu \rightarrow y^\mu = \Lambda^\mu{}_\nu x^\nu##, show that ##x_\mu \rightarrow y_\mu = \Lambda_\mu{}^\nu x_\nu##. Homework Equations...

I'm an experimentalist, so go easy on me... What does it mean for a particle to either couple or not couple to a field? I haven't taken a class in QFT yet, so please try to explain the general idea without any details or equations!

I was looking up plastic injection molders for a project, and I noticed that while benchtop injection molders can be very small, industrial ones weigh several tons and take up an entire room! What accounts for this difference in size? Is it simply the capability to apply more pressure, or is it...

Thanks for the reply, Matterwave. I think I understand the path integral formulation, but I'm still confused as to how Feynman thought up the contribution amplitude for each path. For example, in problem 2.6 of the same book, he states that relativistic particles have a different path...

In chapter 2.2 of Feynman's book on QFT, he states that the probability amplitude of a particle going from a to b is the sum of contributions from all paths, and that each path contributes the same amplitude, but with a different phase. My question is, why does Feynman state that this is the...

Thanks a lot for the link, it was really interesting!

Thanks for the reply. So it seems then that maybe physicists a hundred years ago would have spent their undergrad years learning the basics in more detail then we do now, and maybe even delving into the frontiers of modern research on their own? It seems to me that with all the new advances we...

Before quantum mechanics and relativity were incorporated into the physics curriculum, what did physicists go to grad school for? It seems like classical mechanics, thermodynamics (I believe stat mech was not well developed at the time), and electromagnetism were the only things that were...

Wow thanks Newton! That was a really great answer!

Thanks for the answers! Leveret, you say that it's not physical to have particles in constant motion in a material, but from what I know about superconductors, they can hold constantly circulating currents for very long periods of time without any energy input. Do you know what is happening in...