You probably think like everyone else that light is immaterial, that you can not touch it or use it as you use a jet of water and use it to push objects. But Einstein taught us that it contains energy and that it can exert a force on objects. This force is called the radiation pressure. And it is of course very weak.

Thus in space astronomers can deploy large sails of several kilometers aside and use them to travel, without engine, as does a sailing boat. How?

In fact, sunlight contains photons, kinds of particles or waves, which strike the sail and push it very gently. We can thus use the light to travel between the planets. This mode of propulsion does not work in the atmosphere because the air and the wind blow harder than the pressure of the photons.

Light can also be passed through thin glass (fiber optic) tubes and used to illuminate decorative objects or inaccessible areas. Optical fiber is also used in computing or to communicate between America and Europe by telephone or video as these cables can transmit many more signals, thousands of times more than ordinary copper cable.

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