How do solar sails work if photons don’t have mass?
In: Physics
Has anyone proposed sending a million solar sailed miniature vessels out to explore the universe and report back? Be cool if they did.
Imagine you’re in a small boat with a big, light sail. When the wind blows, it pushes against the sail and moves the boat. Now, think about the Sun as a big lamp that shines light instead of wind.
Light is made of tiny particles called photons. Even though photons don’t have weight like you and I, they still have energy and can give a tiny push when they hit something. So, when these photons from the Sun hit the solar sail, they push it gently, just like the wind pushes a sail on a boat. This gentle push makes the solar sail move through space.
Mass is generally defined as “at rest”. Photons can’t be “at rest” because they’re always moving at the speed of light, so mass doesn’t even make sense as a concept for photons.
So with Newton, light has no momentum because he defined momentum as mass times velocity. But photons DO have momentum even if talking about their mass doesn’t make sense. For light with all the cool Einstein relativity stuff, a photon’s momentum is Planck’s constant divided by wavelength of the photon (higher energy, shorter wavelength photons have more momentum). So that means light can also transfer that momentum to things that DO have mass, like a solar sail, just like if you were to smash particles with mass into a solar sail.
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