Last night I was driving home from a long field job. I was exhausted and it was showing in my driving quality. I needed help staying awake, so I called my Dad. I had nothing to talk about, but just needed to keep talking to help me stay awake. My Dad was kind enough to go over some things he had been thinking about. And in the midst of this groggy conversation I had a new insight into light. It may not seem like much, but here it is:
If light were a wave like sound waves or water waves that traveled on some medium (water or air), we wouldn't be able to see the stars. The energy would diffuse over so much distance. But because light is made up of discrete packets of energy, photons, that exist independent of everything else around them we get to see the stars at night. There is an underlying assumption here that the medium is fundamentally granular. Air and water are both made up of lots of little atoms. Even sound traveling through a more rigid material like steel is made up of lots of little atoms. This granular nature is what causes the wave energy to disperse over a distance. But light being made up of its own little particles can only disperse down to single photons. After that it cannot get more dispersed.
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