From Newsgroup: sci.physics.relativity

Reviving this old thread in the hope that Mr. P. B. Andersen might find
it useful.

FLP-II-27: MOMENTUM IN THE ELECTROMAGNETIC FIELD (A.K.A AETHER)

https://www.feynmanlectures.caltech.edu/II_27.html#Ch27-S6

"FLP-II:27-6: We pointed out in Section 26rCo2 THE FAILURE OF THE LAW OF
ACTION AND REACTION WHEN TWO CHARGED PARTICLES WERE MOVING ON ORTHOGONAL TRAJECTORIES. The forces on the two particles donrCOt balance out, so the action and reaction are not equal; therefore the net momentum of the
matter must be changing. It is not conserved. But the momentum in the
field is also changing in such a situation. If you work out the amount
of momentum given by the Poynting vector, it is not constant. HOWEVER,
THE CHANGE OF THE PARTICLE MOMENTA IS JUST MADE UP BY THE FIELD
MOMENTUM, SO THE TOTAL MOMENTUM OF PARTICLES PLUS FIELD IS CONSERVED."

https://www.feynmanlectures.caltech.edu/img/FLP_II/f27-07/f27-07_tc_big.svgz

The EM field momentum is usually very small (= U/c), and Arindam's
appratus most likely does not have the sensitivity to measure this. But,
still just pointing this out, as the EM field (or aether) is yet another
place that missing momentum can go into.

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