Lecture 14 - Special Theory of Relativity

The one-sided relativistic jets of radio galaxies, as seen in Cygnus-A, was predicted through the application of relativistic Doppler boosting. Interestingly, the `Principle of Relativity' was first considered by Newton. However, the world had to wait for more than two centuries for Einstein to generalise this principle and give us the modern `Theory of Relativity'.

In 1687, Newton published his Principle, considered the greatest intellectual achievement by mankind. In that, he stated his Laws of Motion. He also stated a Principle of Relativity. More than two centuries later, Einstein felt that this principle needed to be ‘generalized’ to include all laws of physics, and not just the laws of motion. But he faced a serious difficulty in accommodating the great discovery by Maxwell that the velocity of light is absolute. In order to accommodate this, he had to abandon two key assumptions of classical physics, namely, the absoluteness of space and time. And when he abandoned the concept of the absoluteness of space and time, several consequences emerged which were truly revolutionary. After a brief introduction, this lecture explains a few dramatic consequences of Einstein’s Special Theory of Relativity in astronomical contexts.