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Newton to Einstein: The Trail of Light Published online by Cambridge University Press: 05 June 2012
Time is that great gift of nature which keeps everything from happening at once.
C.J. OverbeckChapter 9 began with the assertion, “Space and time are different from what you thought they were like.” By now, probably you agree. This brief chapter draws together verbally the remarkable properties of the space and time in which we live.
The interconnection of space and time
Space and time are intrinsically different from each other. We determine locations in space by laying off a wooden meter stick or by stretching a metal tape, but we determine “locations in time” by reading a clock, be it a pendulum clock or a digital watch or a cesium beam atomic clock. Such an intrinsic difference was appreciated before Einstein's 1905 relativity paper, and it persists to this day. Nonetheless, relativity theory showed space and time to be more closely linked than people had thought. Let us review the connections.
The linkage of space and time shows up most clearly when Alice and Bob – in motion relative to each other – compare the locations in space and time that they assign to the same events. Our investigation of the relativity of simultaneity provides an excellent context. Look again at figures 9.6 and 9.7. Focus first on the event of light's reaching marker (a), fixed in Alice's frame. For Bob, the location in space of that event depends on both the distance of marker (a) from the origin of Alice's frame and on how long she has been moving since the origins of the two frames passed each other.
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