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How to correctly measure an unknown length with a clock.


by Ka-In Yen,
Chungli city, Taiwan
yenkain@yahoo.com.tw

1. Example 1: Tom sits in a train which moves at a constant 
velocity. Tom need to measure the distance from city A to
city B. Obviously, He can not use a ruler to do this. Fortunately,
Tom has a clock, and he cleverly figures out a method which
allows him to measure the distance with a clock. Tom has no idea
about the speed of the train, but he knows that a railroad bridge's
length is L. When the train passes the bridge, Tom records the time
difference, t0, of two ends of the bridge; Next, he records the
time difference, t1, between city A and city B. Finally, Tom does 
his calculation. 

      distance AB = L * t1 / t0.

Surprisingly, Tom finds the negative of the length contraction.

  |     Tom, clock
  |     Train 
  |     -->
  |         ----         --------------------
  |         bridge(L)    city A             city B
  +----------------------------------------
  Frame S(ground)   
               Fig. 1

2. Discussion:  The most primitive way to measure a length is
a ruler. But in many situation, a ruler is fail to measure;
for example, a tall tree, or a long distance. A lot of alternate 
methods are invented for measuring length, and most of them need a
known length as reference. In example 1, a measuring method is 
proposed: a clock can be used to correctly measure an unknown length 
without contraction. 
   
3. Conclusion: Example 1 shows: to an intelligent life form, the
length contraction is a result of wrong measuring method.

P.S. This paper originally was posted on internet:
http://groups.google.com/groups?group=sci.physics.relativity&selm=9f181401.0306182257.3e846f2f%40posting.google.com&rnum=1