What Is Relativity? by Jeffrey Bennett

What Is Relativity? by Jeffrey Bennett

Author:Jeffrey Bennett [Bennett, Jeffrey]
Language: eng
Format: epub, mobi
Tags: -
Publisher: Columbia University Press
Published: 2014-01-20T05:00:00+00:00


EINSTEIN’S HAPPIEST THOUGHT

In 1907, just two years after finishing special relativity, Einstein hit upon what he later called “the happiest thought of my life.” To understand his happy thought, put yourself back in your accelerating spaceship. As it accelerates through space at 1g, you will be able to sit down, get up, or walk around on the floor with your normal Earth weight. If you toss a ball in the air, from your point of view it will fall back down just as it would on Earth. In fact, if you close all the window shades, everything inside your spaceship will seem to behave just as it would at home in your room on Earth (figure 5.4).

If you were a physicist living at the time, your first reaction to Einstein’s happy thought might have been “Well, duh.” Since the time of Newton, it had been well known that the effects of gravity and the effects of acceleration would feel the same. But to those scientists who thought more deeply about it (and they were many), this seemed to be a rather astonishing coincidence. Consider Galileo’s famous discovery that all objects fall with the same acceleration on Earth (disregarding air resistance). If you apply any other type of force to objects of different masses, such as the force you apply when trying to throw them, it’s more difficult to accelerate a larger mass than a smaller mass; that is why it’s harder to throw the metal ball used in shot put than a baseball. Yet when we deal with gravity, the acceleration comes out exactly the same, regardless of the mass.2



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