How is that possible – And how can we take advantage?
We know that light has no mass. And, according to classical mechanics, momentum is given by 1/2mv^2; in other words, according to classical mechanics, light cannot have momentum. But, as we know, light is different — and oh so interesting! By virtue of energy transfer, light creates the phenomenon of radiation pressure, which results in momentum being exerted on objects which are struck by the photons. The upshot of all of this is, that with clever engineering, and a massive surface for which the photons to strike, we can actually propel a spacecraft using only light! A square sail with sides 800m long can result in a force of 5N. This might seem incredibly small, but over time, a force as tiny as this can result in sufficiently accumulated acceleration to reach, surprisingly, incredible speeds. We will need to get creative to explore the universe. Solar sails might be the beginning of something truly incredible.
Solar Expedition 
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