Re: beginner thought experiments


Ning Hu wrote:
Hi I have a few thought experiments I like to see how other peoples
opinions are on the results,

Experiment 1:

A space ship travelling at close to the speed of light shoots a
constant stream of Laser beam out of it's back end. To a stationary
observer away from the space ship, Does the beam travel at speed of
light or does it travel at the speed of light minus the speed of the
space ship?. What does the people on the space ship see?

Space ships melt long before they achieve relativistic speeds.


Experiment 2:

point A, B and C lay on a straight line with B being the midpoint of A
& C. Assuming B to be a stationary point in space. 2 friends depart
from point B in similar space ships, 1 heading for point A and the
other heading for point C at same speed/accelleration, When they reach
their destination, they will both turn back and head back towards B.
Have they aged the same amount when they finally unite?

They will share birthday cake equally.


Thanks,
Ning

A 'thought experiment, in physics should represent something
that is physically possible. For example:
"Retarded potential"
http://farside.ph.utexas.edu/teaching/em/lectures/node50.html



Abstract
Einstein addressed the twin paradox in special relativity
in a relatively unknown, unusual and rarely cited paper
written in 1918, in the form of a dialogue between a
critic and a relativist. Contrary to most textbook versions
of the resolution, Einstein admitted that the special
relativistic time dilation was symmetric for the twins,
and he had to invoke, asymmetrically, the general relativistic
gravitational time dilation during the brief periods
of acceleration to justify the asymmetrical aging.
Notably, Einstein did not use any argument related to
simultaneity or Doppler shift in his analysis. I discuss
Einstein's resolution and several conceptual issues
that arise. It is concluded that Einstein's resolution using
gravitational time dilation suffers from logical and
physical flaws, and gives incorrect answers in a general
setting. The counter examples imply the need to reconsider
many issues related to the comparison of transported
clocks. The failure of the accepted views and
resolutions is traced to the fact that the special relativity
principle formulated originally for physics in empty
space is not valid in the matter-filled universe.

C. S. Unnikrishnan
Gravitation Group,
Tata Institute of Fundamental Research,
Homi Bhabha Road, Mumbai 400 005, India
http://www.iisc.ernet.in/currsci/dec252005/2009.pdf
-----


Sue...

.

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