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Variable Speed of Light
Name: Michael
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
I have heard from what I believe to be a reliable source that
the of light is variable. This person quoted the April issue of the New
Scientist Magazine of 1995 pages 26-29 among others. I have not checked
this, but a similar article can be found here:
http://www.newscientist.com/article/mg17323267.400-the-speed-of-light.html
Is it possible that Einstein was wrong? and why or why not?
Replies:
The speed of light in a perfect vacuum is constant, but not the speed
of light when it interacts with matter. When light interacts with
matter (e.g. it's no longer in a perfect vacuum), the speed of the
light can be affected in lots of ways. Look up "index of refraction"
to learn more.
Hope this helps,
Burr Zimmerman
Michael,
When comparing relativity to quantum mechanics, realize that they do NOT
agree with each other. Relativity is a good model of objects on a large
scale moving extremely fast. Quantum mechanics is a good model of
reality at the scale of individual particles and atoms. Physics has not
yet developed a tested theory that handles both. Superstring theory is
the best we have, but we have not yet figured out how to test it.
On a large scale, where objects are definitely objects and waves are
definitely waves, where every position is well defined and an object can
be at only one position at a time, relativity seems to work. On a tiny
scale, where whether something is a particle or a wave depends on how
you measure it, where nothing has a clearly defined position and
something can reach its destination before it leaves its original
location, relativity does not work. A useful set of three one-hour
videos that discuss this 'problem' and are free to watch can be found on
the PBS Nova site:
http://www.pbs.org/wgbh/nova/elegant/program.html.
Dr. Ken Mellendorf
Physics Instructor
Illinois Central College
Hi Michael,
Einstein did not claim the speed of light was a constant. The claim
is that the speed of light in a vacuum is constant, independent of
the observer's frame of reference.
We have known for a long time that the speed of light can be
changed. For example, the index of refraction of a medium is the
ratio of the speed of light in a vacuum to the speed of light in the medium.
I think it is a good thing that you question the "laws" that we
know. The laws that we have today explain the world as we
understand it. As we learn more about the world the "laws" --
actually theories -- must be modified to fit the new
information. This is a part of the scientific method.
Greg Bradburn
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Update: June 2012
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