Book contents
- Frontmatter
- Contents
- Preface
- Introduction
- 1 Getting started
- 2 Rough and ready Relativity
- 3 The dilation of time
- 4 Three clocks and a pair of twins
- 5 Starting again
- 6 Space–time diagrams
- 7 Time and distance ‘over there’
- 8 Co-ordinate systems
- 9 Combining speeds
- 10 Causality and the speed of light
- 11 The nature of spacetime
- 12 Interval
- 13 Old friends revisited
- 14 The scales of the spacetime diagram
- 15 The radar point of view
- 16 Relations between the radar and time–distance systems
- 17 Constant acceleration
- 18 Dynamics–mass, momentum, force
- 19 The mass–energy relation
- 20 The effect of acceleration on time measurement
- 21 Time as experienced by a constant acceleration traveller
- 22 Time and distance measurements of a constant acceleration observer
- 23 The Principle of Equivalence
- 24 The metric
- 25 Introducing geodesies
- 26 How to find ordinary geodesies
- 27 Inverse square law gravity
- 28 Curved spacetime
- 29 The metric around the Sun
- 30 Light and gravity
- 31 The scandal about Mercury
- 32 How Einstein did it
- 33 A few conclusions
- Index
- Frontmatter
- Contents
- Preface
- Introduction
- 1 Getting started
- 2 Rough and ready Relativity
- 3 The dilation of time
- 4 Three clocks and a pair of twins
- 5 Starting again
- 6 Space–time diagrams
- 7 Time and distance ‘over there’
- 8 Co-ordinate systems
- 9 Combining speeds
- 10 Causality and the speed of light
- 11 The nature of spacetime
- 12 Interval
- 13 Old friends revisited
- 14 The scales of the spacetime diagram
- 15 The radar point of view
- 16 Relations between the radar and time–distance systems
- 17 Constant acceleration
- 18 Dynamics–mass, momentum, force
- 19 The mass–energy relation
- 20 The effect of acceleration on time measurement
- 21 Time as experienced by a constant acceleration traveller
- 22 Time and distance measurements of a constant acceleration observer
- 23 The Principle of Equivalence
- 24 The metric
- 25 Introducing geodesies
- 26 How to find ordinary geodesies
- 27 Inverse square law gravity
- 28 Curved spacetime
- 29 The metric around the Sun
- 30 Light and gravity
- 31 The scandal about Mercury
- 32 How Einstein did it
- 33 A few conclusions
- Index
Summary
It's time to attempt some sort of summing up. We've left the Special Theory so far behind that I'm not going to return to it now. Anyhow, since it's so generally acknowledged as a well-established theory that lies at the roots of so much of today's scientific thought, what is there to discuss? The General Theory is a more interesting topic–still subject to active controversy.
Let's begin with a limitation. It never lived up to its title, with the suggestion of a great all-round generalisation of the Special Theory. It turns out, as I said in the Introduction, to be only a theory of gravitation, and as such we must judge it. So let's start by comparing Einstein's theory of gravitation with Newton's at a philosophical level. You'll know by this time where my preference lies.
Please reread §§26.46–7. There we have one reason for preferring Einstein's outlook: at the most basic level it involves one assumption fewer than Newton's. And so (although technically more complicated) it is simpler in principle. And most of us would agree (though it's hard to say precisely why) that simple explanations are philosophically preferable to complicated ones.
We can't, of course, blame Newton for being more complicated–the Einstein approach was inconceivable in his time. But we can note what caused him to be so. And that is simply that his theory begins by saying, in essence, ‘If there were no gravity’, things would behave in such and such a way. That's unsatisfactory, because you can never find true no-gravity conditions in which to test its truth.
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- Discovering Relativity for Yourself , pp. 406 - 418Publisher: Cambridge University PressPrint publication year: 1981