X-Message-Number: 19226
From: 
Date: Fri, 7 Jun 2002 10:19:15 EDT
Subject: spacetime

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Yvan Bozzonetti says that time is not a dimension in the same sense as the 
dimensions of space, and I agree--it is profoundly different. Yet Einstein's 
theory--supported by countless experiments--showed that space and time are 
intimately related and not independent.

One can use (any) spatial coordinates to designate two locations, and from 
these derive an invariant distance. One can also incorporate time 
coordinates, and using these and the space coordinates together one can 
derive an invariant "interval" between two events. A simple formula gives the 
relationship, using the same "units" of "length" for space and for time.

This is enlightening in some ways and certainly useful, but it is also 
confusing--and I suspect the experts are confused sometimes in some ways. The 
problem is partly analogous to the use of the same "dimensions" for work and 
for torque, or for torque and the work done when a torque acts through an 
angular displacement. We need a better system.

Robert Ettinger 


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