KARL JASPERS FORUM
Commentary 17 (to R6)
( ON SPEED OF LIGHT )
by Varadaraja V Raman
9 April 2008, posted 19 April 2008
[Peter Beamish, C12 :]
velocity of light in empty space is an "absolute constant" of Nature
and is independent of the motion of the emitting body, AND/OR OF ANY SUCH
you support this opinion ?
This is not an <opinion.>
It is a scientific proposition based on fairly sophisticated theoretical and experimental analysis.
As such, its validity will remain for the scientific (physics) establishment for as long as there aren't any significant theoretical or empirical reasons for repudiating it.
People beyond the ivory tower of technical physics, who may have gathered some information on physics from popular expositions and thus only hazy view of what it is all about, can (from their limited understanding) object to it, but the world of physics is not likely to do that on philosophical grounds.
is no reality without subjects; this fiction is only postulated in traditional
don't know what the <this> stands for.
There may or may not be reality without subjects, but such reality is of little interest to those who are limited to describing only the reality that is reflected in subjects.
<There can thus be no such thing as a subject-exclusive speed-(of light or of anything else)-in-itself;>
this perspective there can be no science at all, since all science is knowledge
formulated by (human) subjects.
<nor is this a mathematical constant like pi.>
I don't know what the <this> stands for, but if it is for the velocity of light, then this is a correct statement.
<An operational definition has to specify how the speed of light is determined. The speed of light is a quantifiable aspect, with a magnitude, of a physical event (movement of light).>
This has been done by physicists for centuries, and the speed of light has been determined with every increasing precision over more than three centuries.
<My understanding is that it has been measured and was found to be equal for light coming from a star whether the earth approaches it or recedes from it.>
This is true.
<That result was one of the reasons for Einstein to propose relativity theory.>
Not really. Though Einstein was familiar with the Michelson-Morley negative result, his concern was more with the invariance of Maxwell's equations under appropriate (non-Galilean) transformations. This could be achieved through his two postulates, one of which was the constancy of light.
<But if it is measured by someone (on earth), the speed of the movement is relative to, and not independent of, that 'observer'; s/he can only measure it in distance over time, as seen from where s/he is now.>
All measurements are made by an observer (human or recording device).
<Einstein postulated that the speed is independent of the speed of the emitting source, not that it is independent of the observer.>
No, the postulate of relativity is that the measured value of the speed of light will be independent of the state of motion of the source or the observer or both.
<I would much appreciate a wider debate by physicists, and by others too,>
These matters are not settled by debates, but by experimental results and conceptual consistency. On the basis of scientifically stringent criteria, the special theory of relativity has proved to be one of the most sturdy theories of physics: which is not to say that it can never be replaced by a more satisfactory one to explain all the phenomena that it so elegantly does.
V. V. Raman
e-mail < vvrsps (at) rit.edu>