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Re: [Phys-l] Why question(s), again?



At 12:09 -0800 01/11/2011, Bernard Cleyet wrote:

A teacher member of the PTSOS** list posted:
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We're discussing Special Relativity in my conceptual physics class,
and a student asked WHY light goes at 300,000 km/s, and what limits it.

Have you any recommendations for a response?
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Does one answer such questions by: physics deals w/ how and what, not why (that's meta-physics), or delve into Maxwell -- which leads to why is mu 4Pi E-7 and e 8.85 etc.

bc stumped, after cursorily searching JD's site.

p.s. is the answer a just-so story?

Is the question why does the SOL happen to be 300,000 km/s, or is it why does it have a finite speed at all? If it is the first question the answer may be a just-so story. After all, it has to go at some speed. On the other hand, if it is the second question, the answer may go much deeper. At this level of instruction, it probably is best to limit the answer to a just-so story. Delving into Maxwell's theory seem inappropriate for beginning non-mathematical students, and dealing with some philosophical questions about the nature of photons is probably giving the wrong impression to the students.

It might be reasonable to say that the speed of light depends on the value of certain universal constants (epsilon-nought & mu-nought) and so whatever those values turn out to be will determine th speed of light, but that is pretty circular, since the value of mu-nought has been set at exactly 4*pi x E-7 in order to keep the current value for the speed of light, and now that SOL is a defined constant the whole thing gets pretty confusing.

The more I think about it, just-so seems like the best answer.

Hugh
--

Hugh Haskell
mailto:hugh@ieer.org
mailto:haskellh@verizon.net

It isn't easy being green.

--Kermit Lagrenouille