Space-Time, if you ever watched “Interstellar”, I’m sure this space-time concept stroked your mind and heart. That movie triggered the entire science community, where they even virtualized the 5D world. But 5D is far to understand and it’s kinda far for human capabilities right now but thanks to all those great legends who worked in this field, we can clearly understand “The four dimensions”. Well, we all know the basic definition of four dimension manifolds; a fusion of three dimensions of space and one dimension of time. But this is just a mere statement and this concept is beyond this and deep.

So if you are physics lover, I bet you gonna love this article as I will try to make it simple and fun as much as possible. The article is inspired by Stephan Hawking and Einstein’s work. As I myself ain’t any science scholar or some professional in this field but like every other person I crave for cosmos and I always try to find out the new ways to explore the cosmos.

So the story started with Aristotle ( yeah you have read many quotes of this guy ), so he used to believe that the natural state of any body is at rest and without applying any impulse it won’t move, well seems logical for now. He also added that heavy body will fall faster compare to lighter one as of the greater pull towards the Earth. (Note: during Aristotle time, Gravitational concept didn’t come into the picture but he does believe in the greater pull which is part of “ARISTOTELIAN PHYSICS”). But like every other theory, someone came with the better explanation and that’s the beauty of science, the different possibilities.

Galileo came with some explanation which showed that Aristotle’s belief was false. He used the assumption of “dropping weights from the leaning tower of Pisa”. Well the main motive of this assumption is to show that when we drop the bodies from some surface, each body increase its speed at the same rate irrespective to their weights. Imagine a stone and a feather, obviously the lead/heavy weight would fall faster but their increase in speed rate would be same but the feather will be slowed down due to “air resistance”. If we somehow manage to cancel the air resistance or take two bodies that don’t have much air resistance, they will fall at the same time.

So further these assumptions and measurements were used by Newton and Newton gave those famous laws which we still follow. Now the question is that why I’m telling you these two stories and how it is related to Space-Time, because of the assumption Newton and Aristotle made about the time ; that is the Time is absolute i.e. Absolute Time. Because they both took the time absolute while their assumptions.

Let’s take some simple example,

Imagine you are standing at the station and there is a train where a person just dropped the ping pong ball, now for you (the person standing in the station) the ping pong ball took two bounces but each bounce was made further meter apart as you are stationary and the train is moving but for the person inside the train, he is experiencing the two bounces in the same frame.  So that’s why we can’t give absolute position of the ping pong ball bounces, because for you it is something different and for the guy inside the train is different.

Newton was too very worried about this lack of absolute position because it counters his idea of absolute God. According to Newton, absolute time and space respectively are independent aspects of reality. (One can read his explanation about this idea in “Philosophiæ Naturalis Principia Mathematica” by Sir Issac Newton).

Now let’s talk about Albert Einstein (yeah that “I don’t comb my hair “guy ). For many long and still it is a hot topic in this world “NEWTON VS EINSTEIN”. As they both were great personalities but let’s face it their ideas and assumptions were completely different. Well whom I’m kidding here, my article’s topic is giving the clear cut idea that here I’m gonna take Einstein side. But it is not about who is right and who is wrong. Its science actually which has to be right always and for that we have to consider the different possibilities.

So our beloved “I don’t comb my hair “ guy came with the “Theory of Relativity” which by the way solved many problems, before that Ole Christensen Roemer (1676) already came with the speed of light being finite but yeah very high speed. But the problem was only one “that is speed of light same for all medium and observer?” which was proven by “Michelson-Morley Experiment (1887)” to detect the aether, a supposed medium that is the carrier of light waves, which by the way can prove that the speed of light could be taken same.

After that Einstein discarded the idea of aether by explaining the famous equation (energy of an object has due to its motion will be added to its mass, so the only light and other waves that has no intrinsic mass, can move at the speed of the light and nothing can move more than that as the weight increase and the energy will be infinite)

And the theory of relativity put an end to Absolute Time as well.

“The time taken is the distance the light has travelled (which the observers don’t agree on) divided by the light’s speed (which they agree on).” In Relativity all observer must agree on the speed of light.

Therefore when the time is not any longer absolute, according to the relativity; the time is not completely separated from space creating Space-Time.

The above explanation was to have an idea about space and time that they can work together. And obviously one can study it more deeply too and this era of internet we all have this opportunity and internet is filled with wonders.

But why Space-Time, wasn’t the three dimension system enough?

Well NO! See if we want to locate something in Earth we can use the latitude, longitude and the certain height above sea level. But when it comes to position the planets, the stars and galaxy it became difficult. I mean we can use some references like distance from sun, moon and Alpha Centauri but that’s not enough for some stars and galaxy.

The whole universe is collection of patches and each patch can use different 3D coordinate system to specify the position. So how can we determine one fix system?

We know an event is something which is described by particular position in space and the time of occurrence, without referring the time of an event we can’t describe it. Like one can specify it by any three coordinates and any measure of time.

Similarly in Relativity,

There is no real distinction between the space and time.

Imagine throwing a stone in lake, you can see ripple generating and with time there will be more ripples. Therefore we can generalized that the light spreading out from an event forms a 3-D cone in 4-D space time called Future light cone of the event. Similarly there would be a Past light cone too as shown in above figures. Absolute future of the event is the region with all events that can possibly be affected by an event in present. Similarly past cone represents the past events. And event outside the cone “elsewhere” is not part of the cone and doesn’t affect the event as nothing travel faster than light and the cone is representation of light.

By these two figures it is clear that we can show any event in the space-time. And in the theory of relativity there is no unique absolute time and instead each individual have its own personal time that depends on the person movements. When body moves, it affects the curvature of space and time and it turns the structure of space and time and that also affects the way body moves. This can be easily understood by TWIN PARADOX as an example.

Space and time not only affect but also are affected by everything that happens in the universe.

This shows that universe must have a beginning and possibly, an end.

(By Roger Penrose and Stephan Hawking’s work on Einstein’s general theory of Relativity)

This was some brief history and explanation of the four dimensions and yeah one can always dig it more.

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