Apparently light can be sent out in very narrow beams. That is easy to understand as particles. However, I don’t know of any way to send waves as a narrow beam. Of course I’m thinking of things like waves in water. Waves in water could be narrow with linear fronts to the waves if it is contained between 2 walls, but as soon as it exits the walls it will spread out in circular form. What’s the deal with light? How can light as waves go in a narrow beam?
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You can have a narrow beam of sound waves. See this link. – Peter Shor May 18 '16 at 19:54
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What is EM radiation, photon, EM wave – HolgerFiedler May 18 '16 at 20:00
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the link for narrow beam of sound waves doesn't work – Huck Rorick May 26 '16 at 14:38
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@HuckRorick: there was an extra 'l' in the URL. Try this revised link. – Peter Shor Jun 03 '16 at 15:23
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If you have a beam of light that is a millimeter wide (1/25th of an inch), then its width is approximately 2000 times the wavelength (since the wavelength of visible light is ~400-700 billionths of a meter, depending on color).
Due to diffraction, that means that the beam will spread out by roughly 1 unit for every 2000 units it travels: send the beam down the length of a football field and it will be narrower than a football.
Water waves typically are much closer to the size of the gap they pass through (say, ocean waves through the mouth of a harbor) and so they spread out a lot more.
DMPalmer
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