Light has weight. How horrible.

Stephen King’s IT is one of my favorite books of all times.  At one point Ben Hanscomb remembers how awful he felt when he learned in school that light has weight.  That was one of those things that struck me, how very human a reaction that is, to learn that something you take for granted, like light, is actually pushing down on you.  We accept air, of course, because we can feel it, but light?  How horrible.

Many of you are probably ready to throttle me for saying “weight” instead of “mass”.  It’s true, it’s not actually weight.  Weight is a measure of how much gravity is affecting an object.  But mass is just as incorrect.  Mass is a measurement of how much matter makes up an object.  Light does not have mass per se, as it’s energy, not matter.  But it does push against you.  This is the principle behind the idea of solar sails, for example.  Photons push against the sail, moving the vessel attached.

Truly, Tron was ahead of its time.

So it’s not really correct to say that light has weight or mass, but rather “push”.  But how much push?  A new article at explains just how much, though they approach it from the negative state: How much does a shadow weigh?  The great thing is that this is a Vsauce video, and Vsauce is awesome.

Yes, Ben, light does have “weight”.  How horrible.  How horrible.


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