In the third lecture of the series "New Revolutions in
Particle Physics: Basic Concepts" (Fall, 2009) from "The
Theoretical Minimum", Professor Susskind talks about what
a quantum field is and how it is related to particles.
He considers a circle with a coordinate "x" and an amplitude
"exp( i k x )", and says that the momentum "p" is "hbar k".
Then he says (about 8 or 9 minutes into the video):
|"k" is called the "wave number". Uh. It's a wave number.
|And it can be positive or negative? Waves moving to the left,
|moving to the right, corresponding to momenta, going to the
|left or the right.
How can he talk about "waves moving to the left" if his
amplitude "exp( i k x )" does not depend on the time
(contains no "t")?
Do you think that "exp( i k x )" without "t" in his model
means that the amplitudes are constant (not depending on
the time) or is "exp( i k x )" a snapshot of the situation
taken at one instant (but actually depending on the time)?
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