If light has no mass, why is it affected by gravity?

This is a wonderful question… In the first instance, it’s answered by Einstein’s theory of general relativity. (Spoiler alert, light travels along geodesics, which are approximately straight lines in most circumstances that humans encounter in everyday life, but are curved by gravity). It’s also interesting because there is some sense in which light does have “mass” (and therefore should be influenced by gravity… read on!). In our everyday experience, light seems to travel in straight lines, unaffected by gravity. Of course, light can bend when it passes through the interface between two media — think of light refracting as is passes from air into water, which is the phenomenon that causes a straw in a glass of water to appear kinked at the interface. But that bending is not gravitational; it’s electromagnetic. <a href="https://medium.com/@matthewgeleta/if-light-has-no-mass-why-is-it-affected-by-gravity-b6cc0cbbfec0">Read More</a>