When Einstein in early 1917 published a paper entitled 'Cosmological Considerations on the Genaral Theory of Relativity', there were only a few people in the world who could comprehend his theory which was based on the mass-energy equivalence formula E=mc2 (E=energy/m=mass/c= the speed of light in a vacuuma).
In essence what relativity says is that space and time are not absolute both to the observer and to the thing being observed, and the faster one moves the more pronounced these effects become.

One of the best attempts to explain what Einstein meant by his Relativity theory, was made by the mathematician and philosopher Bertrand Russel.

Einstein's Theory of Relativity Explained for Non-Scientists.

He asked the reader to envision1 a train 100 yards long moving at 60 per cent of the speed of light. To someone standing on a platform watching it pass, the train would appear to be only 80 yards long and everything on it would be similarly compressed. lf we could hear the passengers on the train speak, their voices would sound slurred and sluggish, like a record played at too slow a speed, and their movements would appear similarly ponderous. Even the clocks on the train would seem to be running at only fourfifths of their normal speed.

However - and here's the thing - people on the train would have no sense of these distortions. To them, everything on the train would seem quite normal. It would be us on the platform who looked weirdly compressed and slowed down. It is all to do, you see, with your position relative to the moving object.

This effect actually happens every time you move. Fly across the United States and you will step from the plane a quinzillionth2 of a second, or something, younger than those you left behind. Even in walking across the room you will very slightly alter your own experience of time and space. It has been calculated that a baseball thrown at 160 kilometres an hour will pick up 0.000000000002 grams of mass on its way to home plate. So the effects of relativity are real and have been measured. The problem is that such changes are much too small to make the tiniest detectable difference to us. But for other things in the universe - light, gravity, the universe itself - these are matters of consequence.

So if the ideas of relativity seem weird, it is only because we don't experience these sorts of interactions in normal life. However, ... we all commonly encounter other kinds of relativity - for instance, with regard to sound. If you are in a park and someone is playing annoying music, you know that if you move to a more distant spot the music will seem quieter. That's not because the music is quieter, of course, but simply that your position relative to it has changed. To something too small or sluggish3 to duplicate this experience - a snail, say - the idea that a boom box4 could seem to two observers to produce two different volumes of music simultaneously might seem incredible.

The most challenging and non-intuitive5 of all the concepts in the General Theory of Relativity is the idea that time is part of space. Our instinct is to regard time as eternal, absolute, immutable; to believe that nothing can disturb its steady tick. In fact, according to Einstein, time is variable and ever-changing. It even has shape. It is bound up - 'inextricably6 interconnected', in Stephen Hawking's expression - with the three dimensions of space in a curious dimension known as spacetime.

Spacetime is usually explained by asking you to imagine something flat but pliant (=biegsam, weich) - a mattress, say, or a sheet of stretched rubber - on which is resting a heavy round object, such as an iron ball. The weight of the iron ball causes the material on which it is sitting to stretch and sag7 slightly. This is roughly analogous to the effect that a massive object such as the Sun (the iron ball) has on spacetime (the material): it stretches and curves and warps (=verziehen, verzerren) it. Now, if you roll a smaller ball across the sheet, it tries to go in a straight line as required by Newton's laws of motion, but as it nears the massive object and the slope of the sagging fabric, it rolls downwards, ineluctably8 drawn to the more massive object. This is gravity - a product of the bending of spacetime.

Every object that has mass creates a little depression in the fabric of the cosmos. Thus the universe, as Dennis Overbye has put it, is 'the ultimate sagging mattress'. Gravity on this view is no longer so much a thing as an outcome - 'not a "force" but a byproduct of the warping of spacetime', in the words of the physicist Michio Kaku, who goes on: 'In some sense, gravity does not exist; what moves the planets and stars is the distortion of space and time.'

Of course, the sagging mattress analogy can take us only so far, because it doesn't incorporate the effect of time. But then, our brains can take us only so far, because it is so nearly impossible to envision a dimension comprising three parts space to one part time, all interwoven like the threads in a plaid (=kariert) fabric. At all events, I think we can agree that this was an awfully big thought for a young man (=Einstein) staring out of the window of a patent office in the capital of Switzerland.
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Source: A Short History of Nearly Everything by Bill Bryson, Black Swan paperback 2004, GB, pp. 163/65

a. speed 'c' = 'c' is not just the velocity of a certain phenomenon, namely the propagation of electromagnetic radiation (light)—but rather a fundamental feature of the way space and time are unified as 'spacetime'
1. to envision - sich vorstellen
2. quinzillion/quintillion - eine Trillion
3. sluggish - träge, schwerfällig
4. boom box - Ghettoblaster
5. non-intuitive - nicht gefühlsmäßig
6. inextricable - unentwirrbar
7. to sag - absacken, absinken
8. ineluctable - unvermeidlich

1. Why is it so hard to comprehend Einstein's Theory of Relativity?
2. What's the reason for the passengers on the train thinking that people outside are 'slowed down' and look distorted?
3. Explain in your own words the relationship between the Sun and spacetime in comparison to the mattress and the heavy iron ball. What have forces exerted in these two analogies to do with the movement of planets and stars?
4. This text type is obviously not written in a style that a purely scientific essay would be. What would be different in a genuinely scientific text concerning language and style?

amazon.de A Short History of Nearly Everything
Bill Bryson

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