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You probably know that light and all electromagnetic radiation is a type of energy wave, but how does light travel especially when all other waves like sound need a medium to pass through? This is one of the great mysteries of physics. However, we do have some ideas about why light is able to travel through both vacuums and air with no problem. It all has to do with the dual nature of light.
Thanks to Einstein and Bose we know that light is both a wave we know as electromagnetic radiation and a particle called a photon. The photon because of its weird nature as a force carrier called a boson has no mass. However it can still be absorbed, reflected, or refracted if it come in contact with a medium. That is why like sound the speed of light slightly varies between when it is in our atmosphere and when it is in space.
When in the medium of air how it travel makes sense as waves travel by vibrating through a medium. In space the particle does not need to interact with a medium in fact its speed improves in a vacuum. The main thing that can stop or slow down light in space is gravity. One reason proposed for this strange phenomenon once again comes from Einstein and quantum physics. It is proposed and proven in general relativity that space and time is one entity and that gravity is a curve in space-time. In quantum physics particles operate on a flat plane. So if a photon is moving on the plane of space time near a massive object like a black hole it would act like a penny in a cyclone machine. The curve would change the direction of the photon catching it in its funnel.
In the end despite the big things we know about what light is and how it works we still have many questions that are not answered. For example why is light massless but still acts like a particle. Also if light is a manifestation of a fundamental particle does it mean a force like gravity might also have a corresponding article. These are questions left for future scientists to discover.
If you’d like more info on light, check out these articles from The Physics Hypertextbook and Physics Post.
We’ve also recorded an entire episode of Astronomy Cast all about Interstellar Travel. Listen here, Episode 145: Interstellar Travel.