when we talk about light, the first thing that comes to our mind is its dual nature. We all know that light is an electromagnetic wave in a visible region from 400nm to 700nm wavelength. We also know that light behaves as packets of energy called photons. But why does it exhibit dual nature? what is it actually made of? And what makes light to move with such an incredible speed which any other object in the world cannot compete with ? These are all the questions that was continuously asked among Scientists throughout many centuries.
I have read in one book about Albert Einstein that as a child he always wondered what is it like to travel on one of the light particle(photon) with a speed of light, how does the world behind him looked like or how does another photon travelling adjacent to him with same speed looked like ? These were the questions that led him to write a paper on special and general theory of relativity. That is a total different story!
For a moment let us think only about light. We know that we can see all the objects because of light , that is when light hits on any object and reflect back to our eyes. But light does not travel instantaneously. It requires some time to travel from one point to another. For example light from our Sun requires 8 minutes to reach us , this means that when we look at our Sun we see it as it was 8 minutes earlier.
Imagine our Sun to disappear suddenly (which is not going to happen but just in case!). We cannot feel any effect as soon as it disappears. It is only after 8 minutes we come to know that there is no Sun anymore! Same is the case of all the stars that we see in our night sky. When we look at stars, we are not seeing as it is right now but we are looking back in time(as stars were many many years ago).Amazing right!
Hence light can be termed as messenger of universe because light from the core of our galaxy or light during big bang explosion has not yet reached us and if we study that light we can know what happened at the beginning of time or how the Universe was many million years ago. That’s the beauty of light!
It is from the study of light (red shift of light) , that we discovered that the universe is expanding . Also from the study of light (spectrum analysis) , the composition of stars , planets etc are known. To understand the nature of universe, duality of light is very important. Even though study of light is done from the time of Issac Newton or even before that , there are still so many unanswered questions and still lot more to learn about it.