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- Newsgroups: sci.physics
- Subject: Re: Magnetic lenses
- Message-ID: <mcirvin.712367862@husc8>
- From: mcirvin@husc8.harvard.edu (Mcirvin)
- Date: 28 Jul 92 23:57:42 GMT
- References: <ceRLP2O00WB78ZLEYJ@andrew.cmu.edu>
- Nntp-Posting-Host: husc8.harvard.edu
- Lines: 38
-
- gr1c+@andrew.cmu.edu (Greg Howard Rhodes) writes:
-
- >Would it be possible to use a strong stationary E and/or M field to bend
- >light in such a way to mimic an eyeglass? And if it would be possible, how
- >strong would the field have to be? (and, from a consumer standpoint, how
- >small could it be made?
-
- No, not at any human-feasible scale, because electromagnetic
- fields carry no electric charge or magnetic moment, and therefore
- do not interact with themselves (see qualifications below!) Therefore
- you can superpose electromagnetic fields linearly in classical E&M;
- light beams do not scatter off of each other; and light beams are
- not bent by electromagnetic fields.
-
- Qualification 1: Electromagnetic fields *DO* self-interact
- quantum-mechanically, by the exchange of charged particle-
- antiparticle pairs. However, this effect is extremely feeble,
- since the leading term in the coupling is proportional to the
- square of the fine structure constant 1/137, and scattering
- probabilities for photons would be proportional to the square
- of *that*. I don't know if the effect has even been observed
- experimentally.
-
- Qualification 2: Electromagnetic fields also self-interact
- gravitationally, but this effect is much tinier: for rough
- order-of-magnitude calculations you can replace the energy in
- the field with mass E/c^2 and consider the resultant
- gravitational lensing. (Though, to avoid rehashing arguments
- we've been having for weeks, I must stress that this will
- *only* give you order-of-magnitude estimates.)
-
- To a very good approximation, then, light is
- not bent by electric or magnetic fields. It's the same
- approximation you're doing when you use Maxwell's equations
- classically, so that fields superimpose linearly.
-
- --
- Matt McIrvin mcirvin@husc.harvard.edu
-