THEORY OF RELATIVITY IN SIMPLE TERMS-II

This is the second note in the series of 3 notes made for my daughter to explain the Theory of Relativity. 

Imagine that 2 trains were standing side by side in a station. If our train starts, we feel that the other train is moving. If the other train moves, we feel that our train is moving. If you really want to know which train is moving, then you have to look to the other side say at the station or a telegraph pole to find out which train is moving.

If two trains cross each other, then to the observer in the train it appears that the other train is passing very rapidly. If two trains are traveling in the same direction at the same speed, then both the trains appear stationery unless we look to the other side.

If we are traveling in a train with all the shutters closed and if we are traveling in a straight-line, and the train has perfect shock absorbers and does not accelerate or decelerate, then we would not be able to figure out whether the train is moving or not. Whatever scientific experiments we may conduct on the train we would not be able to find out whether the train is moving or not.

This indicates that movement is relative. There is no absolute motion in the Universe. If you want to find out the velocity of one object, then you have to compulsorily compare it with another object. Suppose there is nothing else in the Universe except the train in which we are traveling, then we cannot even figure out whether the train is moving or not. In such an instance, the difference between movement and inertia ceases.

Relativity of motion is known even before Einstein to Newton as well.  

Earth is like the train we mentioned. If we take the earth alone, then no experiment would be able to tell us whether the earth is moving or not. Only by comparing the position of the earth with other bodies like the Sun, Moon and the stars, we can find the motion of the earth.   

The earth is rotating on its axis at a speed of 1600 Km per hour and it is also revolving around the Sun at a speed of 32 Km per sec. Not just the earth alone, the Sun, the planets and the stars are moving. The solar system is moving compared to our star cluster. The star cluster is moving compared to the Milky Way galaxy. The Milky Way galaxy is moving compared to the other galaxies. This means there is nothing in the Universe that is stationery and every object is moving compared to another. All these are relative motions.

Does that mean, there is no absolute motion in the Universe? Newton felt there is. He assumed that the space surrounding us is not moving and at absolute rest. He felt that by comparing the speeds of the objects with space one can find out the absolute speeds at which they are moving. There is no proof for this concept, yet all the scientists after Newton took it to be true. Not only that, they even postulated that absolute space had certain characteristics and the space is permeated with a substance called Ether.  

Subsequently scientists discovered that light traveled in waves. They then believed a medium is required to transmit the waves and Ether is the medium that transmits light. This concept has brought in many inconsistencies which the scientists were unable to answer and a doubt arose as to whether Ether existed or not.

This doubt was taken up as a challenge by an American scientist named Michelson. There is no other experimental scientist in the nineteenth century who is better than Michelson.  He developed an instrument called interferometer in the year 1887 and along with Edward William Morley he conducted an experiment to establish the presence of Ether. This is known as the Michelson Morley experiment.

If a ship is traveling on a calm sea, the sea recedes back as fast as the ship is traveling forward. Similarly when a ship called earth is traveling in a sea called Ether, Ether has to recede as fast as the earth is traveling forward.

When a ship is traveling we can see the flag on the ship fluttering even when there is no breeze when stationery. If we stand on top of the ship we can feel the wind blowing against us.  

Similarly when the ship called earth is speeding through the sea called Ether, then we have to feel the flowing of Ether. But scientists believed that Ether is so minute that it can even pass through atoms and therefore we do not feel its presence but they assumed that it will certainly bring about changes in the speed of light waves.

In the case of sound waves, their intensity decreases in upwind and increases in downwind. Similarly light waves would have to travel faster in the direction of Ether breeze and slower against the Ether breeze.

Michelson and Morley experimented to find out as to much the speed of light decreases when it is going against Ether and how much it decreases when it is going with the Ether. Scientists knew that light travels approximately at a speed of 300,000 KM per second (298,051 KM/Sec to be exact).  They also knew that earth is revolving around the sun with a speed of 32 Km/Sec.

Therefore if a light wave is sent in the direction of the earth’s revolution around the sun, then its speed has to increase by 32 Km/Sec and if the light wave is sent against the earth’s revolution its speed has to decrease by 32 Km/Sec.  To find this out Michelson used the interferometer which had the capacity to measure changes in the speed of light with an accuracy of 0.4 Km/sec.

In the experiment Michelson sent the light ray against the earth’s revolution, in the direction of the earth’s revolution and also to all other sides but found that the speed of light did not change an iota irrespective of the direction of the wave. With this experiment all the scientists in the world were shocked and assumed that some error has crept into their experiment. Many scientists therefore repeated the experiment but again with the same result.

Now, what are they to assume? Ether existed or not? They believed that it existed for 200 years and could not easily give up the concept and it put them in a quandary and confused them.  

In 1905 Einstein unraveled this mystery when he published his special theory of relativity. He said that Ether does not exist. He also said in his theory that the speed of light is a Universal constant and irrespective of what speed an object is moving and a ray of light emanating from that object is always the same at 300,000 Km/Sec. Nothing in the Universe as per his theory can surpass the speed of light. There is no absolute motion in the Universe and all motion is only relative. There is no absolute space either. Because there are objects we perceive the distance between them is space. If there are no objects, then there is no space either.   

THEORY OF RELATIVITY IN SIMPLE TERMS-I

My daughter asked me about the Theory of Relativity which can be easily understood because she felt confused by the abundance of matter she found on the net about the theory...I wrote this small intro for her with the help of a wonderful Telugu book I have on the subject.......I wrote two more notes to her explaining it a bit more which I would post later sometime......

The Universe is finite but boundless. This sentence appears paradoxical and contradictory, but if we investigate further on the meaning, then the mystery reveals itself.

For example, take the earth. The surface of the earth is finite, yet it is boundless. One may walk or ride miles and miles on the earth but the earth never ends and there is no board saying that this is the end of the earth. But does that mean earth has infinite dimensions? No but it is a sphere and curves in on itself and closes so that we can never reach its end by going on it. 

Einstein says that the Universe is also like this and curves in and closes on itself. This means that the Universe is not infinite but yet it is boundless. But one caution here, one can compare the surface of the earth with that of the Universe but not its volume.

Einstein postulated that like the earth, the Universe curves on itself and closes. The Universe we see is of 3 dimensions (as per our perception) Length, breadth and height. Now Einstein postulates that our Universe has not 3 but for dimensions and the fourth is time.

What is time? It is duration between 2 events. The same way as we measure length in meters and Kilometers, similarly we are measuring time in seconds, minutes and hours. Therefore time is also a dimension. Without specifying the time an event becomes meaningless. For example “Buddha is born”. But when was he born? Until the time frame is supplied it does not become specific to us and complete.

Because of this, time and space cannot be separated and the both have a relationship. This concept was used in science by Einstein. He named it “Space time continuum”. Therefore for Einstein, Universe consists of both space and time and they are interlinked. This discovery was done by Einstein with the Theory of Relativity. As per him there is nothing absolute in the Universe and everything is relative.

For example we can give many examples for relativity in life. Can you call a person only a Father? He is a father only to his children, but to another he is a husband, to another he is a son and to yet another he is a friend.

Big and small are also relative. A mouse is big to an insect but small to a cat. Here we can remember the riddle of the line where a bigger line drawn before it makes it small.  

Similarly left and right are also relative. In a street, if you enter from one side if it is left, then if you enter from another side it would be right. Newton’s theory of gravitation was ruling by Einstein’s time but inconsistencies in the theory started emerging slowly and scientists found them very hard to reconcile.

Then in 1905 Einstein published his special theory of relativity and his General Theory of Relativity in 1915 which satisfactorily answered those inconsistencies that could not be reconciled by Newton’s theory. Einstein’s theory is full of mathematical deductions and it is said that initially very few scientists in the world could understand it. Einstein never entered a laboratory and brought out all his deductions purely with the help of mathematics.  

Einstein is like a prophet. After Einstein postulated, scientists have carried out various tests that proved him to be correct. His mathematical deductions are beyond our comprehension but his theory can be revealed in everyday terms. It seems a student asked his professor as to what is the theory of relativity. The professor said “ If you lover is with you, then an hour seems a second to you, and if she is not there then one second seems like one hour”. So time is but relative.

When Einstein died, he was working on a “Unified Field Theory” that proposed to combine the Theory of Relativity with Electromagnetism. One wonders what mysteries he would have unraveled if he stayed alive. Einstein died in 1955 and unfortunately to this day the Unified Field Theory is incomplete.