At 10:30 AM 4/15/01 -0400, Robert B Zannelli wrote:
identification between inertia and radiation resistance is erroneous.
Right.
Feynman volume II chapter 28 is particularly clear about this, specifically
pages 28-6 and 28-7. In equations 28.9 and 28.11, the mass is the first
term, and the radiation resistance is the second term. They are quite
different.
Even if you think the mass term is in need of alteration, the radiation
resistance term is pretty much unalterable. It's too easily observable,
and not easily disguised as anything else.
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From time to time on this list there is a discussion of what it means "to
generalize".
For this reason among others, it is edificational to reflect on the
un-numbered expression below eq. 28.11.
People tend to remember the second term in this expression, i.e. the power
radiated by a source in periodic motion (depending on acceleration
squared). So... does this term generalize to aperiodic motion in the
obvious way? No! In general (Bremsstrahlung for example), we need to
include another term (depending on d/dt of velocity times acceleration)...
or better yet, we could forget about acceleration and just remember the
form given in eq. 28.11 (first and third derivatives).
(This has something interesting to say about the physics of radiation from
a charged mass on a spring: Do you think the radiation comes from the ends
of the travel, where there is maximum acceleration, or do you think it
comes from the midpoint-crossings, where there is maximum velocity and
maximum jerk? The distinction might be hard to measure, but it's
interesting in principle.)
In the real world, we are often called upon to start from what we know
about a familiar case and generalize to a less-familiar case. There are
always, in principle, an infinitude of possible generalizations. To make
progress,
-- one always needs theoretical guidance to exclude most of
the possible generalizations,
-- one often needs experimental guidance to distinguish among
whatever possibilities remain, and
-- one sometimes must face a situation where the correct generalization
cannot be confidently determined from the available facts.