[ExI] QT and SR

[Lee Corbin]

Jeff writes

> Will someone help out with a clarification?   From
> my limited understanding of SR, in a strictly inertial
> frame of reference -- i.e. no acceleration -- two
> observers in motion relative to one another will
> each observe the other's clock to be running
> slower than their own.
> 
> Under what conditions will one
> observe another's clock to be running faster?

Under the conditions that you have stated, namely
no accelerating reference frames or forces of any
kind, no one will ever measure another's clock
to be running faster than his own.

John Clark writes

> It occurs to me that this entire spaceship and string deal
> would make an absolutely first rate MythBusters episode.

I assume that you read Stuart's excellent analysis. So
you must be suggesting that even with a current 
expenditure running into the billions, it is *John Bell's*
and *Special Relativity's* so-called "myths" that
would be busted.

However, Stuart or someone could certainly have the
absolutely last word on this paradox by calculating a set
of (acceleration, mass, string-length, time) quadruples under
which the string does break, as theoretically but correctly noticed by
John Bell, by the first two pages of the Matsuda and Kinoshita article
http://www.aapps.org/archive/bulletin/vol14/14_1/14_1_p03p07.pdf .
(which unfortunately, after the first two pages, for the beginning reader
no longer supplies any intuitive backdrop for what is being said
mathematically), or as I myself explained from a 17th century
viewpoint in Part Four of a dialog with Galileo that I posted yesterday
in "Intuitive Solution to Bell's Spaceship Paradox".

As for Stefano's remark 

  > So, should we eventually conclude that it is not a good thing for
  > near-c flying spaceships to have parts independently accelerated,

Yes

  > or for that matter more than one motor (as it would amount to the
  > same, at the end of the day), as otherwise they would break?

No, if they're mounted in parallel no problems arise.

  > But I am again confused. Shouldn't the engine itself, which has an
  > extension in space along the movement directions, and molecules that
  > individually react to the forces applied to them, break at some point?

It ought to depend on engine architecture. The simplest case of
reaction mass---particles are somehow ejected with tremendous
force from the back end of the spaceship---does not pose any
problem because the counter-force accelerating the spaceship
would apply at just one point, or over a very small area. Then
the inter-molecular forces between *those* atoms and the rest
of the spaceship would gradually be spread throughout the 
length and breadth of the vessel.

(However, if we were to take unrealistically extreme views of
the forces able to be exerted on a single point, then indeed the
force on such a reactive point might damage any known substance
so severely that the body of the spaceship would not able to
contain the force.)

Lee