SPACE-TIME: UNDERSTANDING THE TRUE NATURE OF TIME

space-time: understanding the true nature of time

In my previous blog I discussed about how Einstein’s theory of relativity changed the perspective of space and time and discussed about how space and time are not independent but they are combined as space-time continuum. It was just an introduction to the space-time concept, in this blog I will discuss about how this unification helped us in understanding the true nature of time and another mind-blowing concept called time dilation.

Time as I described in my previous blog is very confusing, each and every person has their own measure of time which we don’t observe due to the speed with which we are moving is less. What is nature of time then, how can we describe past, present and future in space-time? is there any difference between these three or is it just a persistent illusion? let us find out answers for these questions.

Visualizing a 4-dimensional structure of space-time is very difficult, so most of the time to understand the space-time, it is converted to 2-dimensional structure. Before understanding the graph, knowing what an event is important. An event is something which happens at a particular place in space and at a particular time, one can specify it by using four numbers or coordinates.

Maxwell’s equation says that speed of the light should be constant irrespective of the source. Whenever a pulse of light is emitted from a point in space at a particular time, it is observed that as time goes on, the pulse becomes sphere of light spreading across the space. For ex: when ripples are formed when you throw a rock in the pond. If we take the snaps of this event at different time periods and kept above each other we would notice that it forms the shape of a cone. Tip of the cone would be the place at which pulse of light was emitted and then slowly spreading as sphere of light just as ripples of water.

The light which is spreading in the space forms a 3-dimensonal cone in the 4-dimensional space-time structure or graph. This cone is what we call future cone of the event, similarly we can also draw another cone called past cone below the future cone.

Now, we can divide the given event into three classes or three types. The events which can be reached from point P (P is the point where event takes place) by a particle or wave traveling at or below the speed of light is said to be in the future of P. whatever takes place at P has an effect on the future of P. similarly past of P can be defined as set of all events which leads us to reach the event P traveling at or below the speed of light. The below diagram shows the light cone in space-time graph

Some of the events neither lie in the future cone nor in the past cone, these events are said to be in the elsewhere section of P. whatever happens in this neither affects or gets affected by P. To understand this let’s take an example which happens daily. when the rays of sun start its journey at this very moment, it would not affect the things on earth at this moment, because it would be in the elsewhere event. We can only observe its affect after 8 minutes, as the light from the sun takes this much time to reach the earth. Only then we will be in the future light cone of the event that took place. In the same way the light which we see from the distant galaxies and stars are actually of past and our earth has now entered the future cone of the event. This tells us that what we are seeing is actually a past, a kind of time traveling.

Now, we saw the representation of past, present and future in the space-time but the real shocking revelation done by Einstein in his theory of relativity is that, there is no difference between past, present and future. All of this is just a persistent illusion which in turn says that time what we see is just an illusion. when I got to know about this, I was like Archimedes yelling in the streets “Eureka, Eureka”, but I was doing it inside my mind. Now, you might be thinking how’s it possible. Let me explain this in a simple way.

Consider all the things happening at right now moment, for ex: right now, I’m in front of my laptop writing my blog, my roommate is sleeping, flight is taking off from an airport, a star exploding somewhere in the universe. These are some of the events which are taking place at the very moment, in the common-sense point of view we all agree that these are happening right now. But when motion comes into play this common-sense view of time goes out of window. Imagine space-time as a loaf of bread. There are different ways to cut this loaf into slices, in the same way space-time can be cut into different ‘now’ slices. As motion affects the time and we all are moving with a particular speed, we cut the space-time loaf in a particular ‘now’ slice. But the person who is far away from us and has his own motion will have his own perception of ‘now’ slice. Which tells us that his ‘now’ is different and my ‘now’ is different. Let me give you an example to understand this confusing thing.

Imagine an alien sitting still some billion light years from earth. And here on earth I’m sitting on the bench reading a book. Since we both are still and our clocks are ticking at the same rate, we both share same ‘now’ time on slice.

Now, imagine alien sitting on bike and moving away from earth, this makes our clocks ticking at different rates and we no more share same ‘now’ slice. Alien’s ‘now’ slice will be cut into a different angle. Even if the angle is small, due to vast distance it creates such a large difference that Alien will be seeing 200 years past of earth. What’s even stranger is direction makes the difference too. Imagine alien moving towards the earth now, this makes alien’s ‘now’ slice cutting into the future. His ‘now’ would be seeing the future of earth. I would no longer be sitting on the bench there and the alien would be seeing my great, great, great grand daughter or son time traveling or teleporting.

This says that your ‘now’ can be my past, your ‘now’ can be my future and we both are at our own ‘now’ time, then the past is real and the future is also real. Which concludes that past, present and future all exist at the same time. there is no difference between these three and it’s just an illusion. everything that has ever happened or will happen all exists in this big loaf of space-time bread.

The universe in which we are living is lot stranger than what we thought, its beyond of our thoughts and imagination. As my favourite astrophysicist Neil deGrasse Tyson says “we are stardust brought to life, then empowered by the universe to figure itself out and we have only just begun”.