🚀 go-pugleaf

Hypnotists in Einstein criminal cult often hint that, by using
Einstein's 1905 false light postulate, they can trap a long train
inside a short tunnel:

http://www.youtube.com/watch?v=VSRIyDfo_mY&mode=related&search

and also a 80m long pole inside a 40m long barn:

http://www.math.ucr.edu/home/baez/physics/Relativity/SR/barn_pole.html
"These are the props. You own a barn, 40m long, with automatic doors
at either end, that can be opened and closed simultaneously by a
switch. You also have a pole, 80m long, which of course won't fit in
the barn....So, as the pole passes through the barn, there is an
instant when it is completely within the barn. At that instant, you
close both doors simultaneously, with your switch. Of course, you open
them again pretty quickly, but at least momentarily you had the
contracted pole shut up in your barn."

However in the end hypnotists always confuse the breathtaking news as
in the above case where it is not at all clear why the doors should be
reopened "pretty quickly" once the 80m long pole is safely trapped
inside the 40m long barn. Only an extremely silly zombie can explain
the miracle without any confusion:

http://groups.google.com/group/sci.physics.relativity/browse_frm/thread/cac579628f39e93d?
Tom Roberts, Mar 5, 2008:
Dono wrote:
> I am not denying length contraction,

So take it one step at a time:

Since you accept length contraction, in the barn frame the pole will
be measured to be shorter than its proper length.

In the barn frame, that measurement must be made simultaneously at the
two ends of the pole (because the pole is moving relative to the barn
frame).

In the barn frame, at the instant when the two ends of the pole are
measured, we know that the pole is located entirely between its two
endpoints.

Therefore, at the instant the measurement is made in the barn frame,
there could be two closed doors at rest in the barn frame and outside
the region between the pole's endpoints -- these doors would not
intersect the pole at this instant.

Since you accept length contraction, for a large enough speed of the
pole relative to the barn frame, at the instant of measurement it is
possible for the two endpoints plus the two closed doors to all be
closer together than the proper length of the pole.

Here is a drawing at the instant of measurement in the barn frame
(note the pole is not at rest in this frame, so its proper length is
for reference only):

         proper length of pole (for reference only)
  -------------------------------------------------------

           |   -------------------------   |
         Door1  measured length of pole  Door2

Now it's just engineering to make the doors open and close fast enough
to "trap" the pole in between the two closed doors, as in my earlier
scenario. As this is a gedanken, we simply accept such engineering as
possible and move on.

Tom Roberts
__________________________________
[end of Tom Roberts' explanation]

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