The Lightbenders

Today’s question is probably something we have all been listening to since our childhood. This is one of the myths that I used to have as a child as even the science textbook used to say that light always travels in a straight line. But is it true?

Does Light Always Travel in a Straight Line?

The quick answer: NO. Here’s the slightly longer explanation:

I’ll give two examples of where light bends:

• Refraction
  We have all seen this with out own eyes. As light passes from one medium to another, it slows down, but more importantly, it bends. This is why a pencil dipped inside a beaker looks bent. Here is the explanation for the same. So, I think that should be enough to convince you that light doesn’t really travel in a straight line.

• Gravity
  Einstein in his Theory of Relativity explained that light is made up of particles called photon that have a non-zero mass. The mass is usually very small as they travel at the speed of light. But, the presence of a mass can be thus affected by gravity. Places in space with a very high gravitational pull can bend a ray of light passing nearby. Supermassive blackholes have enough gravitation to even pull light inside of them!

Light does indeed tend to travel in a straight line (as does everything else - says Newton) unless it interacts with an external force or medium. But I think the above two examples (especially the second one) can be considered as light bending and not travelling in a straight line.

For the people who think I tricked you, as there was a change in the medium or a force acted on the light, here is an article (2012) where scientists show that light can travel in a curve without any external influence!