🚀 go-pugleaf

"Pentcho Valev" <pvalev@yahoo.com> wrote in message 
news:e1543361-e7e1-4970-a884-4251f0a3a364@t66g2000hsf.googlegroups.com...
>I am shocked by the idiocies Tom Roberts has written below. It turns
> out Roberts is sillier than his zombies, much sillier than Dono in
> particular. I should not have paid so much attention to zombie
> Roberts' writings.
>
> Pentcho Valev
> pvalev@yahoo.com
>
> Dono wrote in sci.physics.relativity: There is a large class of
> thought experiments (the pole in the barn being one of them) that rely
> on the misguided idea that length contraction allows larger objects
> (like the pole) to fit inside smaller enclosures (like the barn) as a
> byproduct ofrapid relative motion. This is not the case.
>
> Tom Roberts wrote: I assume you intend "smaller" and "larger" to refer
> to objects' PROPER length, along the axis of their relative motion.
> Then you are wrong. The "pole and barn" gedanken is valid. Let me
> phrase it without any accelerations -- a pole of length 2L can fit
> inside a barn of length L, if it is moving faster than 0.866 c
> relative to the barn, in this way: With pre-arranged timing in the
> barn frame, one could start with the front door closed and the rear
> door open, and then close the rear door before opening the front door
> -- so in the barn frame both doors can be closed with the pole inside
> (opening and closing must be VERY fast (:-)). In the pole frame, the
> front door opens before the rear door closes, and the pole is never
> wholly inside the barn (which appears to be shorter than the pole to
> the pole observer). This example is every bit as much a demonstration
> of the relativity of simultaneity as it is of length contraction.
>
> Dono also said: if you close both doors simultaneously in the barn
> frame, you have trapped the pole inside the barn. This can only happen
> if the pole has become physically shorter than the barn.
>
> Tom Roberts: This is confusing, if not wrong -- you are using a PUN on
> "physically". Yes, the pole itself is unchanged by measurements
> performed in the barn frame, or doors closing, etc. But the PHYSICAL
> relationship between front end of pole and front door, and the
> PHYSICAL relationship between rear end of pole and rear door, can be
> such that in the barn frame the pole fits in between the two closed
> doors for a (very) brief interval of time. At least in a gedanken.
> Consider these two spatially-separated events: A) front door opens
> with front end of pole still inside barn B) rear door closes with rear
> end of pole already inside barn It is possible, given the conditions
> of the gedanken, for B to precede A in the barn frame; in the pole
> frame A precedes B.
>
> Dono also said: the only way the pole would fit inside the barn is if
> the pole got compressed.
>
> Tom Roberts: This is not true. The way the pole can fit into the barn
> when moving rapidly is that the time-ordering of spatially-separated
> events is frame dependent: in the barn frame B precedes A, but in the
> pole frame A precedes B. There's no need for the pole to be
> "compressed". As I have often said around here, attempting to argue
> via exhaustive enumeration nearly always fails. It did for you in this
> case. TomRoberts

  The pole would not be compressed:

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The pole's velocity, though, might just be a value negative to (apparent) 
zero rather than positive.

GLB