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Re: [Phys-l] three central misconceptions about relativity



One more thing about contracted rulers and dilated clocks:

Nobody here as actually said that's sufficient ... but some
remarks (including mine) could be open to misinterpretation,
and there are in fact widespread misconceptions about this.

A spacetime rotation (like any other rotation) necessarily
has *four* elements:
a) One element is correctly interpreted as distance = rate * time.
b) Another is sometimes "interpreted" as length contraction.
c) Another is sometimes "interpreted" as time dilation.
d) Another is correctly interpreted as the breakdown of
simultaneity at a distance.

Let's be clear: Even if you think (a) goes without saying, and
even if you thing (b) and (c) are "interpretations" rather than
misinterpretations, that's still not enough. If you leave out (d),
the theory is so incomplete and inconsistent as to be totally wrong.

We are getting into Pentcho Valev territory here. PV is fond
of pointing out that a theory based on dilated clocks and
contracted rulers makes no sense. He thereby scores a victory
against the straw man.

This is yet another argument in favor of the spacetime approach:
By unifying space and time, it unifies the four elements itemized
above, making it much less likely that students will overlook or
forget one of them. That is, the boost matrix
cosh sinh
sinh cosh
contains all four elements, and is well-nigh unforgettable, in
analogy to the more-familiar spacelike rotation matrix.