Re: Einstein's math and physical objects

dseppala_at_austin.rr.com
Date: 01/08/05 

Date: Sat, 08 Jan 2005 23:59:57 GMT

On Thu, 06 Jan 2005 02:55:59 GMT, "Todd" <nope@nospam.com> wrote:

>
>"Todd" <nope@nospam.com> wrote in message
>news:j3WCd.282655$5K2.75608@attbi_s03...
>>
>> Now imagine that somehow the cylinder is accelerated along the x-axis such
>> that each point of the cylinder has identical acceleration relative to the
>> earth frame for the same amount of time (relative to the earth frame).
>> This will cause tensile stress to build up in the cylinder, .....
>
>Not just tensile stress, but also *torsional* stress. After all, the
>cylinder will now be 'twisted' (as well as stretched) in its own rest frame.
>
>That's kind of neat - a twisted version of the Bell spaceship 'paradox'!
>
>Todd
>
If we are in a frame that has zero velocity wrt to the disks and the
wires are attached and stretched as described in my original post ,
you must agree if the disks aren't rotating that the wires will cross
(touch) if the relative rotation angle of the two disks is 180
degrees. Its real easy to do this experiment with short wires or
rubber bands. Furthermore, if the disks are rotating, and the disks
develop a relative rotation angle of 180 degrees or more, the two
wires will cross just as they did in the case where the disks are not
rotating. This too can be confirmed by experiment. The wires cross
because if they are stretched, they try to follow the shortest
connection path between the two disks. This steady-state condition
may take awhile to achieve if the wires are long, but each wire will
eventually take the shortest path connecting its two attachment
points. When this occurs the wires will cross. And for each 180
degrees of relative rotation angle between the disks, the wires will
wrap around each other.

In the problem I posted, the situation that I just described in the
previous paragraph is the situation that occurs when the acceleration
of the disks has stopped. The two disks have a relative rotation
angle greater than 180 degrees, and the wires are stretched between
the two disks. Therefore, as we know from experiments, the two wires
must cross when a steady-state condition is achieved. But observers
in the original reference frame never observe these wires crossing
each other and wrapping around each other as they must do in the final
reference frame. The only way the wires get "braided" is by having
the relative rotation angle 180 degrees or greater. This never occurs
in the original reference frame. Einstein's notions of space and time
seem to lead to a physically impossible situation.

Several people who posted a response think that the wires remain as if
they were on the surface of a cylinder before, during and after the
acceleration as viewed by observers in the final reference frame.
This cannot be because Einstein's theory actually requires a physical
stretching of the wires during the acceleration because the two disks
are accelerated in an identical fashion as measured in the original
reference frame.
David

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