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Re: Special Relativity



Robert Cohen wrote:

... I'm confused over what the "paradox" is.

As I said before, so-called "paradoxes" only arise if/when
somebody mis-states the laws of physics.
1) The mis-stated laws of physics are full of paradoxes.
2) The correctly-stated laws of physics are not.
3) There may be some situations where we don't know
the correct laws of physics, but this isn't one
of them. Timekeeping for travelling twins is very
well understood.

... that according to SR one wouldn't be able to tell which twin
was moving and which was stationary

That's a mis-statement. The correct statement is that
any free-falling frame is as good as any other free-falling
frame, and if they are moving relative to each other you
can't say which is moving and which is not.

But SR can certainly tell which twin has a single,
constant velocity and which twin has two velocities
and switches from one to the other.

(i.e., GR was needed to handle the fact
that one twin experienced an acceleration and the other didn't).

That's like using a gold-plated jackhammer to crack
open a pistacio. GR is waaaay more than you need for
this problem.

That one
twin aged and the other didn't implies that motion is not relative, hence
the paradox.

Motion is relative. We can make the frame-independent
statement that one twin has an outbound velocity that
is different from his inbound velocity. That twin's
two velocities are different RELATIVE TO EACH OTHER.
The stay-at-home twin has no such velocity-difference.
That's all that need be said in order to break the
alleged symmetry, and SR has no problem saying that.

http://www.monmouth.com/~jsd/physics/twins.htm

This posting is the position of the writer, not that of Mary Shelley,
Bram Stoker, or William Peter Blatty.

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.