Natural Science Forum / Physics / Relativity / February 2007

Professor solves Einstein's twin paradox
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Months after having a flash of inspiration under the summer heat,
Subhash Kak has resolved one of physics' most famous puzzles -
Einstein's twin paradox.

The International Journal of Theoretical Physics,
a peer-reviewed journal that focuses on original research
and reviews in theoretical physics and neighboring fields,
published Kak's findings.

The paradox, which is based on a thought experiment,
involves two twins, one of whom sets out on a journey
into space and returns to Earth.

Stanford Encyclopedia of Philosophy defines a thought experiment
as a device of the imagination used to investigate the nature of things.

According to the theory of general relativity,
the twin who leaves Earth will experience a
slowing down of time because of acceleration.
This means the twin on Earth will appear to
have aged a lot more than the one in space.

This phenomenon is considered a paradox because
special relativity theory shows that either
twin could be taken to be at rest with respect
to the other twin.

Kak, distinguished professor of electrical and
computer engineering, in his introduction to the
article, said the diversity and mutual inconsistency
of the offered solutions only reinforces the
reality of the paradox within relativity.

"The time appears to have come to look very hard
at things that have been taken to be settled," Kak said.

The most popular explanations for the paradox include
those based on doppler shifts, spacetime diagrams and
general relativity.

Kak said his solution uses an analysis based on probability
to determine which of the twins is really moving with respect
to the far corners of the universe, that is the distant stars.

Kak said his resolution brings into the problem the idea
that motion cannot be spoken of in isolation.

"This is something called Mach's principle, which makes
the framework much more sound, logically," Kak said.

Paul Davies, an astrophysicist at Arizona State University,
in an article for Guardian online said Mach's principle
requires that acceleration can be defined only relative
to the distant stars.

Bradley Schaefer, associate physics professor,
said there was no paradox in Einstein's special
relativity theory if the mathematics were carefully
followed through.

Schaefer, who had not read the article by the time of
the interview, said experiments using atomic clocks
have consistently proved that special relativity is correct:
basically, from the point of view of someone at rest
moving clocks are slow.

"Suppose a student looked at the time on the Memorial tower clock
and his watch, both would read the same time," Schaefer explained.
"Now suppose, an alien picked up the clock and started
accelerating upward, if the student compared his watch to
the clock, the watch would appear to be faster."

Schaefer said doubts about the theory persist because
the idea is counterintuitive as effects due to relativity
kick in only when an object attains a velocity near the
speed of light - a speed which is not experienced under
normal circumstances.

"There is no viable alternative to special relativity,"
Schaefer said.

David Finkelstein, professor emeritus at the
Georgia Institute of Technology, in an e-mail said
he prefers not to use the term "paradox," but that
new resolutions for the observation were needed.

Click to view David Ritz's Web site.
http://www.physics.gatech.edu/people/faculty/dfinkelstein.html

"Why institutionalize the viewpoint of an inaccurate
theory when the better theory is available?" Finkelstein said.

Kak said his article does not dispute special relativity,
rather that it was interested only in identifying inertial
frames - a frame that moves at constant speed.

Kak's work may impact quantum communications
because atomic clocks on board communication satellites
rotating around the globe move at speeds that
are fast enough so as to have possible effects on their accuracy.

John Stachel, director of Center for Einstein Studies at
Boston University, said it takes time for ideas like Kak's
to be accepted into the scientific canon.

"But I will say that mere publication in a journal -
even a peer-reviewed one - is no guarantee of the
accuracy of the results, nor of their significance,"
Stachel said in an e-mail. "A much longer period of
testing and evaluation after publication is needed until
these things can be settled."