[ExI] QT and SR

[Jeff Davis]

On Wed, Aug 20, 2008 at 12:33 PM, Damien Broderick <thespike at satx.rr.com> wrote:

>... I think the explanation is best displayed on a Minkowski diagram, with x and y rotated to x' and y', as shown in at least one of the sites referenced  early in this discussion.

Earlier in the discussion I googled up "Bell's spaceship paradox" and
went to this site:

http://grenouille-bouillie.blogspot.com/2007/10/how-to-teach-special-relativity.html

where I encountered the work of Mr. Minkowski.

I studied the diagram briefly, having never before seen such, but was
unable to "use" it.  I don't doubt for a minute that, as with Mr.
Bell, Mr. Minkowski is a heavyweight in such matters, yet an argument
from authority is unpersuasive, so the question remains.

Regarding the Minkowski diagram then,...  logic requires (If logic
itself remains unassailable) that either the string breaks or it
doesn't.  If the string breaks, the application of the Minkowski
diagrams would appear to be validated.  Conversely, if it does not
break, then some aspect of the "Minkowski evidence" is in error.  Are
we any further along in settling this issue?  I think not.

My utter lack of familiarity with Minkowski spacetime diagrams means I
cannot **directly** challenge their application to this problem.
Someone else will have to do that.  But I maintain my indirect
challenge.

> But intuitively, I try to consider what happens to the two craft if they  accelerate using the Nearly Magical Drive to the merest smidgen below light velocity. To an earth-based observer, they each shrink to a terrifying flatness in the direction of motion, and their clocks all but stop. What happens to the gap between these fast flat plates?

That's the crux.  That space between the ships.

> (Btw, do they shrink from either end toward the middle of the craft, or backward from the bow to the propulsive units at the stern?

Or from either end toward the middle of the string?

>  Are we having fun yet?)

Oh, yes.  Much fun.  But little progress.

 > If the string shrinks as well, as surely it must, won't it snap?

Shrinkage (and consequences) can only occur in a frame of reference
different from that of the ships.  Agreed?  What happens to the string
must be consistent in all reference frames, ie it breaks or it
doesn't, to all observers. Agreed?  Then, with sincerity and respect,
please, falsify the following if you can find a way.

>From aboard the ships, shrinkage cannot be observed.  Without
shrinkage, the string cannot break.  Therefore, the string does not
break.  Therefore, the **gap** between the ships must shrink along
with the ships.

I use the term "gap" here to distinguish it from "space", because it
seems that we're talking about the "space" between without giving much
(certainly not enough) thought to what exactly it is and does, when in
fact this is the very central feature/question at the heart of this
so-called paradox.  For the record: Nature doesn't "do" paradoxes.
Humans do insufficient understanding.

Also, re the shrinkage of the gap (and of space), a question:   On any
ship heading in any direction at relativistic velocities, will the
entire universe ahead and behind exhibit a Lorentz contraction?
Similarly, will two stars ahead of you be closer to one another than
before you set out?  Or will they be at the same distance

> Powered by nothing better than intuition here, Goff, but still barely in the game.

Me, too. (Eyes closed, pawing around in the dark).

                            ***********************

One little quibble.

Am I the only one who gets irritated when someone says something like
"...the merest smidgen below light velocity".  I mean how can you get
"close" to something you can never get to no matter how "fast" you go?
  As with the horizon no matter how close you get, you're still the
same distance away.  I know it's just an old Newtonian habit, but
still, if one is dealing with relativity issues shouldn't one be more
careful?

Best, Jeff Davis

   "Everything's hard till you know how to do it."
                           Ray Charles