# [ExI] QT and SR

John K Clark jonkc at bellsouth.net
Sun Aug 10 05:43:20 UTC 2008

```"Jeff Davis" <jrd1415 at gmail.com>

>Such an observer would see the entire assembly shrink
>proportionately along its length.  No breakage.

I am absolutely positively 100% certain the string will
break, I might even be correct; at least that's what my
intuition insists is true.

Look at it from the point of view of an observer at one end
of the string. Suppose a fellow at the far end of the string
has a clock and sends a pulse of LASER light to you every
10 seconds and suppose you also have a clock and it's
synchronized with his, so you know how long it took the
light to reach you, hence you know how far away the other
end of the string is. The other fellow also reports from
time to time on how fast he is moving relative to some
fixed point that both of you can both see.

An instant after you start moving you receive a report from
the fellow at the other end of the string saying he hasn't
started moving yet. Because of this you predict that when
you make the next distance measurement you will find that
the distance has decreased, but when the next LASER
pulse arrives you find that the distance is just the same.
You can only conclude that sometime after the last report
the other fellow started to accelerate and did so faster
than you did.

When he sends his next report you find he has indeed
started to move but he still isn't moving as fast as you
are, and yet the distance is the same as before.
The fellow at the other end of the string must still be
accelerating faster than you and in fact he always will be.

Of course an observer at the other end of the string could
make similar observations and conclude that you are
accelerating faster than he is. The two observers disagree
on who started moving first, but both agree that the other
end of the string is accelerating faster than their end;
and that pulls the string apart.

John K Clark

```