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I know light and sound travel along wavelengths and in all diagrams I have seen the pictures of photons travelling up and down and forward. How does something travelling so fast stay within the confines of the wave please ? I am new to this site but intelligent enough to understand complex answers.

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It would be easier if you could include an example of the kind of image you mean, but I can guess that you're thinking of those drawings where there's a sine wave drawn in space and suggesting that that's what a wave "looks like".

enter image description here

This plot from EMS 2- Wave Properties of Light shows "crest", "trough" and "rest position" when explaining light waves, and this might be a good example of the problem. All three imply that there is some up-and-down-ness and that's not what a light wave is.

I've seen much worse, floating sine waves with arrows at one end, or hitting people or plants, and those drawings are crazy-wrong! ;-) When we draw those sine waves, it's on a graph or a plot of something versus time or versus space on the x-axis, and the y-axis axis on the plot is pressure for sound or usually electric field for light or electromagnetic radiation.

Light or photons, or sound waves for that matter don't physically go up-and-down like that.

The plot below is somewhat better. The arrows are the amplitudes of the electric and magnetic fields. There's nothing that is actually moving up and down, it's just a mathematical plot.

Electromagneticwave3D.gif Source

English: Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This diagram shows a plane linearly polarized wave propagating from left to right. The electric field is in a vertical plane and the magnetic field in a horizontal plane.

Found in Transverse wave

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    $\begingroup$ Wow perfect thank you, now I know. $\endgroup$
    – John
    Commented Feb 25, 2020 at 15:08
  • $\begingroup$ Fun thing -- it is the extent of the EM wave (amplitude) which leads to the situation where the evanescent wave allows light to "jump" a gap where classical theory predicts total internal reflection. $\endgroup$ Commented Feb 25, 2020 at 20:20

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