The following is a Letter to the Editor of the IEE journal 'Electronics and Power' published in the July, 1966 issue at p. 236.


Dear Sir - I read with interest P. Knight's letter on the radiation-pressure discrepancy.

The fallacy in the discrepancy may lie in the assumption used in deriving the Poynting vector itself. This is that the field energy in an electromagnetic wave actually moves with the wave. The quantum theory and experiment have shown that an energy quantum can be received at a region remote from a wave source long before enough energy to sustain the quantum has, using the Poynting vector, been intercepted by that region. The Poynting vector may really have no significance in electromagnetic energy transfer. An electromagnetic wave is a disturbance of the medium which propagates it, and may well be sustained by energy deployed from that medium. The process of electromagnetic energy transfer may be a lot more complicated than we presently believe.

Furthermore, the normal source of electromagnetic radiation, the accelerated electron, does not really radiate electromagnetic wave energy - though it can be calculated that it does if we ignore the presence of the electric field which causes the acceleration. This was pointed out in a discussion [1] of Prof. Hammond's paper [2] about the Poynting vector. It may also be shown [3] that the familiar formula E=Mc2 is an essential requirement for non-radiation of energy by the accelerated electron, and it is not surprising that, as Mr. Knight has found, the formula and the Poynting vector lead to a discrepancy if used together.

Yours faithfully,
IBM United Kingdom Laboratories Ltd.,
Hursley Park, Winchester, Hants.,
3rd May 1966.

1 ASPDEN, H.: Discussion contribution, Proc. IEE, 1958, 1O5C, p. 359 [See [1958a]
2 HAMMOND, P.: 'Electromagnetic energy transfer', ibid., 1958, 105C, p. 352
3 ASPDEN, H.: 'The theory of gravitation' (Sabberton Publications, Southampton, 1966). See [1966a]