In the post, What is Time, if not relative? , I wrote about slowing down of time at high speeds or Special Relativity and how Einstein discovered it in an attempt to reconcile Newton’s laws of motion with Maxwell’s theory of electromagnetism. Einstein’s discovery was a huge revelation and changed forever our perception of time. The story though does not end here. Einstein spent next ten years of his life investigating how to encompass gravity into relativity and was born the theory of General Relativity. According to the General Relativity, perceived time or the elapsed duration observed between any two events depends upon the gravity of the objects surrounding the observer in addition to the speed of the observer. In simple words, time slows down near a massive object (due to its gravitational pull). Going back to the example of the readers of this blog, a reader reading this blog on earth will observe a gap of 9 days between this post and the previous post on this topic, however a reader in the outer space near a massive star or a black-hole (provided he is not already sucked into it) is still on the first line of the previous post. This is already looking quite complex and interesting, isn’t it?
Time that we observe is not an absolute but relative to our speed and position in the universe. Our high school Newtonian Physics meticulously trained us to observe the position of an object in 3-dimensional spatial co-ordinates (the way we visually observe objects in space) and how this position changes with time defines its trajectory through space. With General relativity, time is no longer a book-keeping unit for the trajectory of the objects in space but a co-ordinate of the space itself. This is how Einstein’s theory of general relativity is sometimes interpreted, that everything is happening in a 4-dimension space with time being the fourth dimension.
Let me leave you with this thought that your brain is a clever virtual machine and you are navigating through this universe in a virtual world.