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location Boulder, CO
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visits member for 3 years, 11 months
seen Sep 1 at 17:01

I'm a physics graduate student at UC Boulder


Jun
19
comment Why can't a rope be pulled completely straight?
$\cos(\theta)$ does not go to zero as $\theta$ goes to zero, it goes to $1$.
May
19
comment What is negative about negative energy states in the Dirac equation?
If you go back to the post he references, it is a bit more clear that he is mixing and matching the two pictures (electrons/holes, positron/electron), instead of keeping them separate.
May
19
comment What is negative about negative energy states in the Dirac equation?
"Holes in the sea are positive-energy positrons, equivalent to the action of the positron creation operator on the vacuum." pretty much, just make sure the two pictures (negative/positive energy electrons aka. holes/electrons and positrons/electrons) are kept very separate in your mind.
Jul
6
comment Why aren't there compression waves in electromagnetic fields?
Something to keep in mind is that longitudinal waves are actually possible in EM, however they require a medium in which to propagate (you can't do this in a vacuum). Typically they show up in waveguides in a dielectric.