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PHYSICS 002C Lecture 18

# PHYSICS 002C Lecture 18 - PHYSICS 002C Lecture 18 Serway...

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PHYSICS 002C Lecture 18 May 11, 2009 Serway and Jewett Chapter 9 – Relativity Chap 9 Prelude – What is time? What is space? We think of space as a possible place to put something, where separations are vectors, and where the laws of Euclidian geometry hold. Time seems to be separate from space and unlike it totally. Time seems to be a scalar parameter (a number) that can be defined everywhere and agreed upon by all observers. While we can move about in space, there is apparently nothing we can do to slow the ineluctable passage of time, nor to revisit the past or see the future. Since light does not travel instantaneously, which means it is not merely a conveyor of information but has an existence of its own much as the human runner bring the news from the Battle of Marathon, it is not so unreasonable that there should be funny effects when you look at something going by at high speed. Because the back of the object is farther away then the front, we might expect its image to be delayed, giving the appearance of a shear. In fact it looks instead like the object has been rotated! OK, you may think, these are just appearances, caused by us observing using light. Now watch a clock go by in the distance. It is easy to see that a light clock (Fig 9.5) might appear to run slower as it whizzes past, but we would expect if time is Newtonian, i.e. separate from space and simply an absolute parameter, that there would be no real effect on the clock. In fact clocks are slowed when they move, and rapid muons live much longer than stationary ones. In our imagination there is a reality beyond our perceptions. Like a blind person with a stick, we make a map of our world, and having used it to get around sucessfully, we think the territory in our head to be real.

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PHYSICS 002C Lecture 18 - PHYSICS 002C Lecture 18 Serway...

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