SPACE-TIME CONTINUUM

Space-time continuum: An introduction to the baffling concept of

Albert Einstein

  

On 25^th November 1915 a theory was released by a scientist which shook the whole world of classical mechanics, ‘The theory of relativity’ by Albert Einstein. Until this date we had heard of space and time as independent things but in this theory, Einstein unified the space and time as one i.e. space-time continuum.

Before moving towards the concept of space-time continuum, let us study space and time independently and a brief touch upon history of classical mechanics or as it is said Newtonian physics.

So, what is space?

When I say space most of us picture the outer space which is far away from earth, but space can be found everywhere. Atoms which are the basic ingredients of everything we see, actually contains 99.99% of space. So, the chair you are sitting on, the computer you are using is nothing but empty space. We understand what space is but we don’t know what exactly space is. Mathematically space is 3-dimensional with the co-ordinates x, y, z. Now, you must be thinking how can empty space be 3-dimensional. Empty space is not really empty it has lot going inside. In simple words we can say space is real i.e. it contains something which we can’t see. space can bend, it can twist and it can ripple. Space is still a mysterious book with lots of hidden stories which are yet to be told.

We know what space is now but the most confusing and unanswerable question is what is time?

We encounter time every day in our life, we can tell what time it is now but we can’t tell what time itself is. What if I say “we don’t have time we have time’s”, that’s a bit difficult sentence to grasp so let’s put it in simple words. Each individual or each one of us have different measures of time and it is affected by our motion i.e. how we move. but why don’t we see the difference? Why our clocks are ticking at the same rate?

Its because the speed with which we move is so tiny that we don’t see any difference.

 So, how was time born?

Time is said to be born at the very moment of big bang. There was no time before this, that’s the reason we can’t imagine what was before big bang. We still find it difficult to answer what exactly time is but all we can say is time is just an illusion.

So, now we have idea of what space and time are, but to understand space-time continuum we must know what was Newton’s view on space and time which we call as classical mechanics or Newtonian physics.

Aristotle and Newton both believed that time is absolute i.e. time would be same whoever measures it but the difference between both is Aristotle had a preferred state of rest or we can say absolute space, he thought earth is at rest but according to newton’s laws earth was rotating this, led to lack of absolute rest or space in his laws. Lack of absolute space means that one could not determine whether two events that took place at different times occurred at the same position in space. Newton refused to accept the lack of absolute space and continued his work. Time is separate form and is independent of space. it holds good for apples, planets which move slowly but we have to change our ideas on space and time when things are moving at or near the speed of light.

 The first attempt to tell that light had definite speed was done by Danish astronomer Christensen Roemer in 1676 but his answer was not accurate but it was near to it. later James clerk Maxwell gave us the exact speed of light which is 186,000 miles or 3*10^8 m/s. Newton had got ridden of the idea of lack of absolute space which was implied by his own laws to which he got lots of criticism. So, if light is moving with a definite speed then it must be moving with relative to something which is at rest. So, they came up with the idea that light moved relative to ‘ether’ which is present all over the space. When we measure the speed of light relative to ether it would be same but different observers moving relative to ether would measure different.

But in 1887 Michelson and Morley showed that speed of light measured along with the rotation of earth and right angle to the rotation of earth were same, which meant speed of light is exactly same whoever measures it, which questioned the newton’s and Maxwell’s work. This what we saw is a brief history of classical mechanics where Newton says time is absolute and there is no absolute space.

Now, we will see what is space-time continuum and how it destroyed the Newtonian physics.

In 1905, Albert Einstein said that time is not absolute, everyone has their own measure of time which is affected by the motion in space. For ex: imagine I’m moving at the speed of light and I have clock with me, you are standing with another clock in your hand observing me. When I move, you would see that my clock is ticking slower than yours and for me your clock would be ticking faster than mine. He also noticed that space would adjust itself according to the speed of the object. This made him realize that space and time are not independent, they are actually one and called it space-time continuum. 

Space-time continuum is like a fabric or rubber sheet which is spread all over the space. All the planets, stars are actually rotating on the space-time fabric creating a bend in the fabric. Einstein said that gravitational force is not produced by “two bodies having masses m1 and m2 separated by some distance r” [which was said by the newton in his law of gravitational force F=Gm1m2/r^2] but instead it is produced by the bend in the space-time which is made by heavier objects like planets and stars. To make you people understand this, I have an example. Imagine a stretched rubber sheet or fabric. when you put a heavy ball on it, it creates a bend on the fabric. Now, put a smaller and lighter ball inside that bend, what happens is the smaller ball rotates around the heavy ball with a constant velocity. It neither falls in the bend nor moves away from it, the ball just keeps rotating around the heavier ball in a certain position with constant velocity. This is exactly how planets rotate around the sun and moon’s around planets. The heavier the object is, larger the bend in the space-time fabric. Black holes are so heavy that they actually wrap the space-time around them. That’s why gravity is more and time stops around them. This discovery from Einstein destroyed the entire classical mechanics created by Newton. Yet today we still study the law of gravitational force created by Newton, it’s because we are comfortable with it and easy to understand and also it holds good in common sense point of view. Mathematically space-time is 4-dimensional with 3-dimensions of space and 1-dimension of time, therefore it is very difficult to imagine a 4-dimensional structure.

 After this there were many tests conducted to check whether Einstein’s theory was correct. One such test was conducted by NASA in 2004 which tested whether space-time fabric produced gravity. The mission was called gravity probe-B. NASA sent a satellite called gp-B which had 4 gyroscopes attached to it and gyroscopes were aligned in such a way that their tip pointed straight at the nearest star. If gravity is produced due to the bend in space-time fabric then due to it, gyroscopes would change the angle. And after continuously observing them they found out that the tip which was pointing straight at the nearest star was actually tilted at some angle. This proved that Einstein’s theory was right.

What we have studied until now is just an introduction to the space-time continuum of theory of relativity. In my next blog I will be telling how space-time continuum gave us the true nature of time, difference between past, present and future and time dilation. So, be ready for more mind boggling theories in my next blog.