Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Special Relativity



From the point of view of a beginning student as I already pointed out, I
would not use diagrams.

However there is a reasonable explanation for the twin problem from the
point of view of the traveling twin if one ignores the details of the
acceleration just as JD did. I also think that this is a much more concrete
explanation that may be easier.

Now let us assume that both twins are in contact every hour, or that each
one sends a contact pulse every hour.
The traveling twin judges that the stationary twin has been slowed down
according to the time dilation.
The traveling twin also can cross the distance in a short time because of
the length contraction.
If the traveling twin slows down in between hourly contacts, they receive
the next message from the stationary twin just as expected. They notice
that the time dilation has now gone away. However another important change
has occurred. During the slowdown they observe that the length contraction
has also gone away so now the traveling twin "observes" that his stationary
counterpart must have suddenly aged a great deal.

As for my assertion that special relativity is necessary for "full"
understanding, I would like to point out that in an accelerated reference
frame you experience a force which is indistinguishable from a gravitational
field on the surface of a planet. At this point one must invoke some of the
machinery of special relativity. While the corrections are small they are
nonetheless there.

I believe that the original idea of invoking special relativity may come
from a commonly cited textbook example. One way of reversing the traveling
twin's motion is to do a slingshot around a massive body. At that point it
is obvious that you are dealing with GR.

John M. Clement
Houston, TX

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