Re: [Phys-L] another DIY relativity experiment

["Donald Polvani" <dgpolvani@verizon.net>]

On Tuesday, May 17, 2016 9:51 PM, Tom Van Baak wrote:

 
> Wednesday night (May 18) look for a TV show on National Geographic or PBS
> called "Genius by Stephen Hawking". Episode 1: Can We Time Travel?

I did watch the show with interest and also was interested in the URLS Tom
supplied.  I do have a question.  Hawking made a big point of how time
travel back to the past is impossible because we would see a copy of
ourselves moving backwards and how could there be a copy of us apparently
made from nothing.  However, the time dilation experiment purported to show
that time travel to the future was possible by having one person with a
precise pre-synchronized clock stay some time at the bottom of a mountain
and then (in the show after one day to reduce experimental error) bring his
clock to the previously synchronized clock at the top of the mountain. Due
to gravity induced time dilation, the clock at the top was 20 nanoseconds
ahead of the clock which had spent the day at the bottom of the mountain and
so the person previously at the bottom (and his clock) had traveled to the
"future".  If you accept this (and I believe the time dilation result, but
I'm not sure about the traveling to the future interpretation), why couldn't
the people at the top carry their clock down the mountain, again find that
it is 20 nanoseconds ahead of the clock at the bottom and so claim that they
had traveled back in time?