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Notes on Relativity and Cosmology - Physics Department, UCSB

Notes on Relativity and Cosmology - Physics Department, UCSB

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Chapter 8<br />

General <strong>Relativity</strong> <strong>and</strong><br />

Curved Spacetime<br />

Read Einstein, ch. 23-29, Appendices 3-5<br />

In chapter 7 we saw that we could use the equivalence principle to calculate<br />

the effects of a gravitati<strong>on</strong>al field over a finite distance by carefully patching<br />

together local inertial frames. If we are very, very careful, we can calculate the<br />

effects of any gravitati<strong>on</strong>al field in this way. However, this approach turns out<br />

to be a real mess.<br />

C<strong>on</strong>sider for example the case where the gravitati<strong>on</strong>al field changes with time.<br />

Then, it is not enough just to patch together local inertial frames at different<br />

positi<strong>on</strong>s. One must make a quilt of them at different places as well as at<br />

different times!<br />

y<br />

ff31 ff32 ff33<br />

ff21 ff22 ff23<br />

ff11 ff12 ff13<br />

As you might guess, this process becomes even more complicated if we c<strong>on</strong>sider<br />

all 3+1 dimensi<strong>on</strong>s. One then finds that clocks at different locati<strong>on</strong>s in the<br />

gravitati<strong>on</strong>al field may not agree about simultaneity even if the gravitati<strong>on</strong>al<br />

193<br />

x

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