# Surfing with electromagnetic waves

## Main Question or Discussion Point

Let's say I have some source that generates a spherical wave that propagates outwards at the speed of light, and I have a vehicle that is charged.
The wave will accelerate my vehicle periodically and eventually bring it to great speeds.
Does this work?

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mfb
Mentor
Spherical wave of what?
Electromagnetic waves are transversal - the main acceleration of your charged object would be sidewards, and changing its direction with the frequency of the electromagnetic wave.
The charged object would absorb or reflect some fraction of the wave, which gives an effective acceleration in the direction of the beam - but you do not need to charge the whole object, everything non-transparent will work. Solar sails use this concept.

hmm right.
Actually I'm a bit confused, could someone correct me if I'm wrong.
As i understand it, EM waves are just solutions to maxwells equations and they themselves interact with particles, transferring momentum in the form of a force?
And by the way, why do EM waves reflect off of surfaces? That has always bothered me.Gravity certainly does not reflect off of things, why electromagnetic waves?

mfb
Mentor
As i understand it, EM waves are just solutions to maxwells equations
and they themselves interact with particles, transferring momentum in the form of a force?
They can do that.

And by the way, why do EM waves reflect off of surfaces?
As quantum mechanical description: Electrons (and sometimes other particles) can absorb the energy and re-emit it.
As classical description for metals: EM waves can lead to oscillations of electrons in the surface, those emit electromagnetic waves.

You cannot compare electromagnetic waves to gravity in that way. I think gravitational waves can be scattered in material - but gravity is so weak, we cannot even detect the waves themself with current experiments (might change in 2-3 years), so this is just a theoretic thing.
Gravity (as force between matter) does not reflect, and neither do electrostatic forces (as forces between charges)

I was hoping for a more elegant classical explanation..but I guess that makes sense.
So basically classical Electrodynamics is not enough to explain optics?

mfb
Mentor
It cannot explain atoms or solid objects without effective theories (like a refraction index and so on). As soon as you want to understand that on a microscopic level, you need quantum mechanics.