What to Remember from Lesson 16

16.10. What to Remember from Lesson 16#

16.10.1. The Postulates of Relativity#

Simple, but profound. Einstein postulated that:

  1. Not only are mechanical “laws” of nature invariant when compared from one inertial frame to another, but also the “laws” of electromagnetism are invariant as well. At that time, it looked like the former was the case and that the latter was not.

  2. The speed of light is the same value for any inertial observer. This one was shocking.

16.10.2. Simultaneity#

There is no measurement that can be made between inertially moving frames of reference in which two events which are simultaneous in one will also be simultaneous in the other. Simultaneity is a barren concept.

16.10.3. Consequences of the Second Postulate#

Time intervals between co-moving inertial frames of reference are not the same when measured by observers in those frames: $\( T_H = \gamma T_A. \nonumber \)$

Likewise, lengths are similarly different between co-moving inertial rest frames:

\[ L_H=\frac{L_A}{\gamma} \nonumber \]

Many measurements have confirmed these consequences.

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