Saturday, 21 April 2018

electromagnetism - Will a change in reference frame produce light?



Let's say I have a charged particle in front of me. If I start spinning in place, the charged particle will appear accelerated to me from my reference frame. If the laws of physics pertaining to this scenario are valid in all reference frames, if I spin with with an appropriate angular velocity to bring the emitted waves into the visible light spectrum, will I see light? If there are many such particles, will the entire room light up for me and remain dark for a stationary observer next to me?



Answer




The acceleration that you plug into the Larmor formula to calculate the radiation is the proper acceleration.


It is certainly true that if you start spinning then in your frame the charge is circling you and therefore it is accelerating towards you. However this is what we call a coordinate acceleration i.e. the velocity changes in time when measured using your coordinates. The acceleration you measure is not because the particle is accelerating, it is because your coordinates are accelerating. If you calculate the proper acceleration of the charge, using your rotating coordinates, then you'll find the proper acceleration comes out zero and hence the charge won't radiate.


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