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I made a commitment to understand special relativity. Right now I'd like to understand Electro-Magnetic Radiation. What would it "look like"if I could see it emanate. From a book (Simply Einstein) I'm told any movement of an electric charge (e.g. an electron) can start an electromagnetic wave. Now that is cool. So, finally, my question - once a wave is started does it emanate in all directions (a rock thrown in a lake goes in all directions in 2 dimensional lake surface, so would shaking an election start an emf wave that expands as an ever-growing surface of a sphere. That is, a sphere whose radius is growing at the speed of light? If so, where is the photon on this sphere?

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  • $\begingroup$ Yes light radiates in all directions but it’s best to think of it in terms of photons. Billions and billions of individual photons Radiate outward in every direction from the source. $\endgroup$ – Bill Alsept May 3 '18 at 4:51
  • $\begingroup$ Electromagnetism is based on special relativity. You should understand special relativity first before moving to electromagnetism. $\endgroup$ – safesphere May 3 '18 at 6:08
  • $\begingroup$ To safesphere: Linear learning may work for some, but not for all. There are many ways to learn. Linear learning can sometimes make it harder to see the big picture or concept. $\endgroup$ – Lambda May 3 '18 at 16:11
  • $\begingroup$ @Lambda OK, fine. May he learn electromagnetism first. I don't mind. I'm not sure what sense he'd make of 4-tensor Maxwell equations, but it's none of my business. $\endgroup$ – safesphere May 4 '18 at 5:42
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You are right; when an electric charge is forced to vibrate in all directions, it gives off electromagnetic radiation in all directions. You can think of this as consisting of a large number of photons being sprayed in all directions. That radiation then moves away through space as an expanding spherical wavefront, traveling at the speed of light.

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  • $\begingroup$ A single photon can have a spherically expanding wave function and an equal probability to be registered anywhere on the sphere. $\endgroup$ – safesphere May 3 '18 at 6:05
  • $\begingroup$ For my information, how is the propagation of the wave function in space identified with the propagation of the electromagnetic wave? and in the case of a single photon, does this mean that the wave packet associated with it expands in a spherically symmetric manner, or does it propagate as a wave packet? $\endgroup$ – niels nielsen May 3 '18 at 6:10
  • $\begingroup$ @safesphere How many photons are emitted in the direction of the acceleration vector? $\endgroup$ – Rob Jeffries May 3 '18 at 10:10
  • $\begingroup$ @RobJeffries I didn't say the spherical wave function was a result of a charge acceleration. It could be a result of a spontaneous emission of on excited atom or of something else. My point is that the answer is wrong in stating that a spherical wave requires a large number of photons and cannot be associated with a single photon. It can. The answer also mixes quantum and classical concepts that is a dangerous approach for electromagnetism. $\endgroup$ – safesphere May 3 '18 at 12:24

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