# 2 the time coordinate we imagine that every point of

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Unformatted text preview: of mercury. hDp://e ­duca1on.net/scien1sts/Michelson_Morley_inq.gif Expected diﬀeren1al phase shig between light traveling the longitudinal versus the transverse arms of the Michelson–Morley apparatus: 6 hDp://en.wikipedia.org/wiki/Michelson–Morley_experiment Measuring an Event •  An event is something that happens, and every event can be assigned three space coordinates and one &amp;me coordinate: 1.  The Space Coordinates: We imagine the observer’s coordinate system ﬁDed with a close ­packed, three ­dimensional array of measuring rods, one set of rods parallel to each of the three coordinate axes. 2.  The Time Coordinate: We imagine that every point of intersec1on in the array of measuring rods includes a clock. 3.  The Space ­&amp;me Coordinates: The observer can now assign space ­1me coordinates to an event by simply recording the 1me on the clock nearest the event and the posi1on as measured on the nearest measuring rods. hDp:// www.nyrt.n et/ wordpress/ wp ­content/ ClocksIII.jpg 7 Simultaneity •  If two observers are in rela&amp;ve mo&amp;on, in general, they will not agree as to whether two events are simultaneous. •  If one observer ﬁnds them to be simultaneous, the other generally will not. •  Simultaneity is not an absolute concept but rather a rela&amp;ve one, depending on the mo&amp;on of the observer. 8 Simultaneity Event A: lightning striking tree A. Event B: lightning striking tree B. Observer C: standing s1ll on lawn Observer D: siing s1ll in moving train. 9 Simultaneity hDp://www.youtube.com/watch?v=wteiuxyqtoM 10 Simultaneity: A Closer Look Suppose Sally’s train moves rightward with velocity v. (a) Event Red occurs at posi1ons RR’ and event Blue occurs at posi1ons BB’; each event sends out a wave of light. (b) Sam simultaneously detects the waves from event Red and event Blue. (c) Sally detect...
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## This document was uploaded on 03/22/2014.

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