How sunlight crosses space
Inside the Sun, nuclear reactions release energy that eventually escapes from its surface as light. Light is electromagnetic radiation: changing electric and magnetic fields that can travel through a vacuum, unlike sound, whose vibrations need matter such as air. In quantum terms, light’s energy comes in packets called photons.
A photon does not need to shove its way through space or ride on a stream of material. It carries energy from where it is emitted until it is absorbed or scattered. When sunlight reaches Earth, its photons are absorbed by soil, water, buildings, and living things; their energy becomes heat or helps drive processes such as photosynthesis.
Light can push, too
Photons also carry momentum. When light is absorbed by an object, it gives that object a tiny push; when light reflects, the change in direction transfers momentum as well. The force from ordinary sunlight is very small, but it is real.
That push is the principle behind a solar sail. Instead of burning fuel to propel a spacecraft, a sail uses reflective material to catch sunlight’s momentum. The acceleration is slight, so it builds over time—but the spacecraft needs no propellant for that push. The same light that warms a planet can therefore also serve as a form of transport through the vacuum between worlds.
