To Frame My Frame And Hold it True (Frame I : Newton) – 1.Intro

December 6, 2005

In my attempt to understand General Relativity better, I am trying to write an article at a semi-popular science level. I had completed the first part sometime before and gave it to the editors of our physics Wall-magazine Eigenspace. Since almost nobody seems to have read it, I am putting it up here. So here we go.

Now to consult the rules of composition before making a picture is a little like consulting the law of gravitation before going for a walk. Such rules and laws are deduced from the accomplished fact; they are the products of reflection…
EDWARD WESTON

Hi,

First If you don’t have the slightest idea of who Edward Weston (the author of the above quote) was, don’t worry. I don’t either.

Okay, now that I’ve told you that, let’s come to the business.

Well, We owe to Einstein a lot of things. But, in my opinion the most beautiful of them all is the theory of General Relativity, which I shall refer by the acronym GR henceforth.

Okay, so what is GR ? Well, there are two main defining characteristics of GR. One is that it is a theory of gravitation. Hmm, let me put it like this -if we go out into the world and see it, we observe that matter talks to matter. The earth on which we stand is affected by the sun, for example.

To start with, there are the beautiful rays of dawn that sweep through the land waking up the sleeping electrons. To which, electrons respond in the form of blooming flowers and the multitude of life forms that wake up to welcome the wonderful morning sun. This is the elegant hand of electromagnetism that ties electrons to atoms and stitches atoms into molecules of nature and technology and from them builds most of the structure we see in this world.

This is the light which like a fairy jumps out of the distant stars racing out in all directions reaching us, the electricity that flows in the metal veins that her human son had carefully laid, the signals that run through our spine and heart – just to mention a few of electromagnetism’s “magic?. But, this slightly overromanticised anthropomorphisms not withstanding, GR does NOT talk about electricity and magnetism.:-)

What GR talks about is an apparently more down to earth stuff … Well, atleast in the literal sense of the word. It supposedly talks of some other force altogether – the force of gravitation, that which pulls a mango(why should it always be an apple ?) towards the earth. The force which holds our solar system together. The claims of gravity do seem much more humble, don’t they ?

In school, for example, gravitation is a much more simple subject than electromagnetism. One formula$F=-\frac{GMm}{r^2}$ is enough to sail you through ! Compare it with the laws of Coulomb and Biot-Savart,Gauss and Ampere, Faraday and Maxwell not to talk of Kirchoff and Ohm and it’s obvious which is simpler, right ?

Well, you know physicists always like to unify things, they believe in equality you see. So they saw this, and wanted to make things equal. Since they couldn’t make electromagnetism any more simple, they went on to make gravitation complicated ! And, so they came up with GR ! In fact, they were so successful that GR is arguably among the most complicated theories that physicists have ever come up with. Hey! I was just joking.

But, GR is much more than a theory of gravitation. It makes a grandiose claim of being a theory of spacetime itself, whatever that word means. In fact, the very word General Relativity betrays no relation to gravity ! Rather it seems (rightly) related to the subject of relativity that talks of space,time,lorentz contraction,time dilation blah blah. This relation in fact is the second defining characteristic of GR.

Now, it is fair to ask, what is it that allows GR to have such a double existence – as a theory of both spacetime and gravity. What justifies clubbing together such unrelated subjects and talking about them in one breadth ? In fact, it is simply not clear what do we mean by a theory of spacetime. And, what the heck is spacetime anyway ?

(continued here)

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