Re: starship-design: Fwd: The Speed of Light - A Limit on Principle ?

[kuo@bit.csc.lsu.edu (Isaac Kuo)]

L. Parker wrote:

>The Speed of Light - A Limit on Principle ?
>A physicist's view on an old controversy
>by Laro Schatzer <schatzer@ubaclu.unibas.ch>

"Physicist"?  Based on what he writes in this essay...maybe not.

>In Galilean Space-Time the physical existence of an absolute time is 
>assumed. The pioneer of physics Isaac Newton defined it in the following 
>way [1]:

"Galilean Space-Time"?  There was indeed a physics model which
Galileo developed based on his scientific experiments, but it
erroneously included a factor which caused objects to follow the
curve of the Earth's rotation.  This unnecessary (and incorrect)
extra factor was eliminated by Newton, who used his mathematics
of calculus to really turn it into the first physics model.

>Minkowski Space-Time

>Minkowski Space-Time does not know any absolute time. It was Albert 
>Einstein who gave it a physical definition of simultaneity. Especially, 
>because all experimental tests to determine the motion of an observer 
>relative to some absolute space-time frame had failed, he decided to 
>abandon the notion of absolute time at all. In his famous theory of 
>relativity he postulated two principles which should hold for all physics:

>1) All physical laws appear according to the same laws in all reference 
>frames.
>2) The speed of light is constant in all reference frames.

>While the first postulate seems well established by observation and 
>experiments, the second one is simply an assumption.

I don't think any "physicist" who knew his stuff would call the
second principle "simply an assumption".

It is one of the most heavily tested and controversial phenomenon
ever experimentally discovered and verified.  Ever since the
electromagnetic nature of light was revealed, all scientists
believed light travelled at a constant speed along a medium (which
fit the models and was experimentally verified), and simply
assumed that if you were travelling w.r.t. this medium, the
speed of light would be different in different directions (because
of how classical mechanics and adding velocities works).

The discovery that the speed of light was actually the same in
every direction, no matter what, came as quite a shock, and
since then it's been experimentally verified innumerable times
and many theories to explain this phenomenon have been proposed
and disproven.  Einstein's theory of general relativity, by
far the most elegant of those theories, is also the one which
has stood the test of time and skeptical experimental verification.

To say the constant speed of light is "simply an assumption" is
almost insulting.

>Remark: It has to be emphasized that H. A. Lorentz version of the ether 
>theory (which is set in such a Newtonian framework), ie. Lorentz 
>relativity, is still a valid alternative to special relativity.

Remark: it has to be emphasized that Lorentz's version of the theory
is mathematically identical to special relativity, it's just that
he didn't realize the implications it had to simultanaity and
apparent time the way Einstein did.  There's a reason we still
call it a Lorentz transformation.

Remark: Special relativity is wrong.  It's a special case of General
relativity where space is flat.  However, space is (in our immediate
viscinity at least) slightly convex due to the effects of gravity.

>Thus, there exists no 
>covariant 4-position operator in quantum mechanics. This is one of the main 
>reasons why it has not yet been possible to construct a reasonable quantum 
>field theory of gravitation. Thus, the usual theory of relativity and 
>quantum mechanics appear to be incompatible.

This is indeed a serious limitation to our current understanding of
physics, as mysterious to us as wave-particle duality was to physicists
before quantum mechanics.  The fact is that general relativity and
quantum mechanics have both been experimentally verified to work
for everything we've tested them against so far (and this includes
skeptical experimentation).  Our inability to link the two
theoretically doesn't change that.  We can't do it either with or
without any "absolute time" yet, so it isn't any argument in favor
of "absolute time".

>[tenuous heuristic arguments in favor of "absolute time" snipped]

Guys, beware of stuff you read, especially stuff drawing
conclusions from "recent discoveries" that "seem to indicate"
something or other.

>Incidentally, there are active research groups trying to experimentally 
>detect the existence of a preferred reference frame in this context.

Look at that "evidence".  Active research has been trying to detect
the existence of a preferred reference frame since the Michelson-Morley
experiment showed the constant speed of light.  At the time, _every_
scientist who performed such experiments believed there must be a
special frame of reference, and some continue to believe it.  None
has ever been found.

Maybe one will be found someday.  But don't be on it.
-- 
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
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/___________\ "Mari-san...  Yokatta...
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