Relativity: A Very Short Introduction
Russell Stannard
Language: English
Pages: 128
ISBN: 0199236224
Format: PDF / Kindle (mobi) / ePub
If you move at high speed, time slows down, space squashes up and you get heavier. Travel fast enough and you could weigh as much as a jumbo jet, be flattened thinner than a CD without feeling a thing-and live forever! As for the angles of a triangle, they do not always have to add up to 180 degrees. And then, of course, there are black holes. These are but a few of the extraordinary consequences of Einstein's theory of relativity. It is now over a hundred years since he made these discoveries, and yet the general public is still largely unaware of them. Filled with illuminating anecdotes and fascinating accounts of experiments, this book aims to introduce the interested lay person to the subject of relativity in a way which is accessible and engaging and at the same time scientifically rigorous. With relatively few mathematical equations--nothing more complicated than the Pythagoras's Theorem--this VSI packs a lot time into very little space, and for anyone who has felt intimidated by Einstein's groundbreaking theory, it offers the perfect place to start.
About the Series: Combining authority with wit, accessibility, and style, Very Short Introductions offer an introduction to some of life's most interesting topics. Written by experts for the newcomer, they demonstrate the finest contemporary thinking about the central problems and issues in hundreds of key topics, from philosophy to Freud, quantum theory to Islam.
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room full of people, everyone would see something different. Some would see a short-looking pencil, others a long one. The appearance of the pencil depends on one’s viewpoint – whether one is looking at it end-on or broadside-on. Do these differing perceptions worry us? Do we find them disconcerting? No. This is because we are all familiar with the idea that what we see is merely a two-dimensional projection of the pencil at right angles to our line of sight (see Figure 11). What one sees
finished, that time ‘flows’. All these conspire against acceptance of the idea that the past still exists and the future also exists and is merely waiting for us to come across it. Some leading physicists, while accepting that all 30 observers are indeed agreed on the value of the mathematical quantity we are calling ‘the distance, or interval, between two events in four-dimensional spacetime’, nevertheless deny that we must go that extra step and conclude that spacetime is the true
two effects leads to an overall reduction in curvature such that by the time one has reached the centre of the sun, the curve has flattened out. This is what one would expect as the sun exerts no gravity force at its central point. And what is true for the sun, is true of the other stars, and the planets; they create curvatures rather like Figure 27. But again let me emphasize that, although such diagrams might be helpful in visualizing what is going on, in practice we do not see
the universe. Here we recall the insight offered by the special theory of relativity that mass and energy are equivalent through the equation E = mc 2. An object can be considered to have energy in the locked-up form of rest mass, plus kinetic energy by virtue of its motion. But it is not just matter that has energy. Electromagnetic radiation has energy, as do gravitational fields. So in this context we have to take note of the different kinds of energy there might be. So energy density is
rotating black energy density of 104–8 hole) 89 expansion of 101–9 strangeness 41 supernova explosion 84–5 synchroton radiation 95 W weightlessness 45–6 T Wheeler, John 85 white dwarf 84 tachyons 35 white holes 92–3 Taylor and Hulse experiment 76, world line 24, 73 96 worm hole 92–3 Relativity 114
