One of the most important theories in the history of Astrophysics which has changed our views to see the universe entirely. One of the most brilliant minds the world has ever seen, Albert Einstein has proposed this theory of general relativity. The General theory of relativity and Time Dilation go hand in hand. This theory further expands the views of time dilation and combines it with space expansion. Let’s get into it. Again, this might shatter some of our preoccupied notions and might be thought as sci-fi but, it has been accepted by many scientists and its time we do too.
Let’s again start with a hypothetical experiment. We are sitting in the car which is at rest and the headlights are blinked. The speed of light emitted from headlights is measured and is recorded accurately as speed of light. Now, if the car is moved at a speed of say 80 and the headlights are again blinked, and the speed is recorded, the speed remains constant. Yes, as the speed of car is negligible as compared to that of light but still there is not even negligible increase in the speed of light when measured accurately enough. The reason for this as we know now is Time Dilation. The time moves slowly so as to keep the speed of light constant. But, Einstein says that it’s not only time that moves slowly but, the space (or in case of car ‘Distance’) expands. So, basically, we know Speed= distance(Space)/Time. Einstein says not only time slows down but also the space expands and both of them thus keep resultant speed of light constant. This led to a new revolutionary theory that space and time are not different entities at all. They are related and linked to each other. This new entity, Einstein called it as Spacetime.