EINSTEINs GENERAL THEORY OF RELATIVITY.

 

Till Einstein arrived on the scene Newton’s theory of gravitation has been taken as Gospel truth. But Einstein had this habit of shocking us humans by propounding theories that went right over our heads. They cannot be rejected because he had provided mathematical proof for them but to accept them, our mind rebels. Yet, science that provides mathematical proof had to be accepted and we have no choice on that.

I have already written 3 short notes on Einstein’s Special Theory of Relativity propounded by him in 1905; the General Theory of Relativity is a later development that came about in 1915.

His General theory said there is no such thing as gravity and in the presence of bodies light curves itself. He said that this curvature of light appears to us as Gravity. He called that area where light curves in space as Space Time Continuum.

Okay, Einstein had his mathematical proof for the theory but there are not many who could understand his mathematical deduction at his time. So Einstein tried to explain this theory by giving real life examples, so that ordinary people could understand it.

Einstein said supposing you are sitting in a room all of whose doors are tightly closed. Suddenly the room is taken into space far from the earth and from any other body and then left there. Your room would then be falling (or better say moving) at a uniform speed. Suppose you leave an object in your hand, it merely stays there without hitting the ground because that too is travelling at the same speed. Then if you jump, you would find yourself floating in the air. That means there is nothing called up or down in that room now.

Now suppose the room had a rocket engine and you start the engine and accelerate the room, then the so called gravitational attraction comes back. Whichever side the engine is there, that side becomes the floor for all the objects in the room. The opposite side of the room that has the engine becomes the ceiling. If you then give the room the same acceleration as we have on earth due to gravity, then you would feel perfectly the same as on earth.

Now, the room does not have any gravity, yet by merely accelerating it equivalent to earth’s acceleration, we feel the same way as we feel on earth and have the same weight.

Now let us take the path of light in your travelling room. Suppose the room is dark and a small ray of light entered into the room from one side window. As the room is travelling, by the time the light reaches the opposite wall, the light also has to traverse some distance which would take some time. During that time, the room would have moved at least a fraction if it is travelling with ordinary speeds or much more if it is traveling near to the speed of light. That means, the ray of light that entered the room would not hit the opposite side of the room in a straight-line. But light always travels in a straight line, therefore in that room the curved line is the straight line.

In that room, the space has become curved, not just space but the space time continuum got curved. In the entire Universe the space time continuum is curved. In large bodies like the Sun and stars this curving of light can be clearly seen from the light received from other stars. Not only did Einstein merely state that, he calculated the curvature of light near the Sun and stated it is 1.75 seconds of arc. He challenged the scientists to measure and check his deduction.

But how to measure the curvature of light from the stars when the stars themselves are invisible when the sun shines? The Sun becomes dark during a solar eclipse and that is the time to measure the curvature. The scientists then waited for a full solar eclipse to occur and it finally came about in 1919. Scientists then travelled to West Africa and Brazil where there was a complete solar eclipse and indeed found that light curved as Einstein has propounded and has curved 1.63 seconds which is slightly less than Einstein’s mathematical deduction. Thus Einstein has become a mathematical prophet.

From this curvature, it automatically follows that around every large object light curves. This happens in the case of all the stars in the Universe. Collectively the enormous number of stars is making the space curve on itself. That is why the Universe is finite but boundless.

Okay thought some scientists, from this can we deduct the extent of the Universe? They thought light curves around every large body, so if they can calculate the mass of the Universe then they would know the extent of curvature.

The Astronomer Edwin Hubble of Mount Wilson laboratory observed the Heavens for some time and calculated the density of the universe to be 10^-30 gms/cc. Using this value he calculated the radius of the Universe to be 3500 crore light years. Many scientists, however, expressed skepticism about the validity of this calculation on the extent of the Universe.

But nothing is final in science. Newton talked about Gravity but Einstein came in and made it redundant. That is why in science and specifically in Astronomy where there are too many imponderables, there is always scope for improvement, and new discoveries may displace the old ones again.

At the time Einstein propounded his theories we did not know that Universe is expanding and that came about later. Einstein made his calculations assuming a static universe and his deduction supported that.

When it was discovered that the Universe is expanding, some scientists have checked Einstein’s mathematical model and found a minor mistake that made him believe in a static universe. In turn after rectifying that mistake they found that the Universe can in fact never be static and has to go on expanding.

Again it was Edwin Hubble himself scanning the Universe through the Mt Wilson 100 inch telescope who discovered that the Universe is expanding. Galaxies are running away from each other. The farther the galaxy, the faster it would run away from us. Hubble analyzed through spectroscope the radiation from the galaxies and arrived at this result. 

Hubble then discovered a law for the proportionate recession of galaxies. This is called the “Hubble’s Law” and as per that if a galaxy “B” is twice as farther away from us than galaxy “A” then “B” would run away twice as faster from us than “A”. If it is 3 times as far then it would recede at 3 times the velocity.

But in this law comes a paradox. Suppose a galaxy that is 400 crore light years away is moving away from us at a speed of 110,000 Km/Sec, then as per Hubbles law as galaxy 1200 crore light years from us should recede at a speed of 3,30,000 Km/Sec or over the speed of light. Now as per our laws, no object can travel faster than light, so where lay the problem? The only answer we can currently give to that is we do not know.