##
Special Relativity in 14 Easy (Hyper)steps

**6.
Time dilation
Lorentz contraction**
Let's look at *Nostromo's* measurement
of *Sulaco's* length from the perspective
of the pancake-loving crew
of *Sulaco*.

Since *Nostromo* makes an indelible
record of the measurement results (permanently stopping the clock or writing
the results in a
logbook),
*Sulaco's*
crew will
be able to learn
what *Nostromo* measured (communicating by radio,
for example). They can compare
the results with the *Sulaco* length they measure in their own (*Sulaco's*)
rest
frame.

Of course, both of *Nostromo's* measurement techniques
are seen by *Sulaco's* crew to yield the same answer.

During the single-clock measurement, *Sulaco's* crew
can measure the *Sulaco's* length by seeing how long it takes the
(**moving**) *Nostromo* clock to coast
past the stationary *Sulaco.* Keep in mind that moving clocks
tick slowly...

I'm only showing *Nostromo's* clock-- not the whole
ship-- in the following diagram.

Less time passes on *Nostromo's* clock than on *Sulaco's*
clocks since moving clocks tick
slowly: *.*

For example, v = 0.8c yields Dt
= 0.6 Dt´.

*Nostromo* measures *Sulaco's* length to be
**shorter**
than *Sulaco* does, by a factor of .

In general, **any/all**
measurements of the length of a moving object
will show it to be **shorter**
by a factor of
than a measurement of the object when it is at rest.

This is called Lorentz
contraction.