Re: Afshar and ...the idea of a photon is dead

2004-08-02 Thread Saibal Mitra 
Questioning whether the speed of light has changed within a certain class of
theories is nonsense and this is not an opinion but an elementary
mathematical fact. Of course, one may e.g. question whether photons are
massive and whether this mass has changed, leading to a (wavelength
dependent) change of speed of light.

The recently proposed variable speed of light theories are legitimate
theories. However, they don't imply a changing speed of light. That's just
the name given to the theory, not its content.

The speed of light depends on the way you choose your units and is thus
completely arbitrary. It is not possible to measure the speed of light
before you define your units of space and time. If you use the speed of
light to relate your units of time to that of space, you find that the speed
of light is constant, regardless of your theory.

If a ''variable speed of light theory'' is confirmed by experiment, it is
still a matter of convention to say that the light speed has changed and not
some other dimensional constant. Only dimensionless combinations of
constants can be said to have changed independent of conventions.

This is the point that Duff made.


CMR wrote:


 With respect, I think it was Dawkins in the Blind watchmaker who quipped
 your incredulity alone is no measure of reality (I paraphrase..)

 You may well be correct that the speed of light is and has always been
 constant, but this remains a point of some controversy that only continued
 scientific research will settle (and never finally, at least according to
 Popper). Your opinion that questioning the fact of the SOL's constancy
is
 nonsense, is just that (an opinion not nonsense, that is). And such an
 opinion is less in the spirit of good science and more that of dogma, in
my
 own humble opinion. I submit that just because a position is held by a
 minority and is not yet well supported by empirical data does not
 automatically disqualify it or justify ridicule. Indeed, all currently
 favored theories, including Einstein's, were once so.

Re: Afshar and ...the idea of a photon is dead

2004-08-02 Thread Saibal Mitra 
I agree. If the photon did behave in an erratic way you would be able to say
that the photon is behaving erratic and not the laws of physics that make
your instruments work. But in this hypothetical case you would use some
other way to relate time to space. This relation also has to involve a
constant with the dimensions of a speed. We could call it c. And then
someone else could claim that this c is changing as well!

Ultimately c is a conversion factor to convert meters into seconds. The TOE
doesn't have separate units to measure space, time mass, etc. These are all
human constructs. Because we measure time and space in our own units, it is
inevitable that dimensional conversion factors will appear in our formulas!






- Oorspronkelijk bericht -
Van: Henry Sturman [EMAIL PROTECTED]
Aan: [EMAIL PROTECTED]
Verzonden: Sunday, August 01, 2004 07:18 PM
Onderwerp: Re: Afshar and ...the idea of a photon is dead


 You are right that there are no fundamental dimensional constants, i.e.
 those constants are determined by our choice of units. But that doesn't in
 itself imply that the speed of light can't change, although the speed of
 light might be unchangeable for other reasons. The fact that a pint is an
 arbitraty unit does not mean that a package of milk in the super market
 can't contain less milk today than yesterday. If the speed of light were
 something totally arbitrary, then there would be no point in ever
measuring
 it. If today I measure a speed of light x in whatever units and tomorrow I
 measure 0.5 x, then the speed of light has changed. Put in a constant-free
 wording: if today light travels x times the diameter of earth during one
 earth revolution, and tomorrow it travels 0.5 x times that distance during
 the same time, then the speed of light has changed. Well, at least
 something has changed, and if not the speed of light, then either time,
the
 diameter of the earth, or the rotational speed of the earth has changed.
 And Occam's razor implies we should assume the thing that has changed is
 that which we can change with the fewest number of associated changes
 required in our model of the universe and that would typically be the
speed
 of light.

 At 14:02 1-8-2004 +0200, you wrote:
 Unfortunately, sensationalists articles that are completely baloney
appear
 in most scientific journals from time to time.
 
 Nature published an article claiming that if the fine structure conswtant
is
 changing, as suggested by some astronomical observations, then this
change
 must be due to a change in the speed of light. Now, this must be
nonsense,
 because the value of the speed of light, being a dimensional constant,
is
 determined by our choice of units. In fact, that there are dimensional
 constants at all, is an artefact of  using inconsistent units at the same
 time.
 
 
 Michael Duff has explained this in the articles:
 
 http://arxiv.org/abs/hep-th/0208093
 
 and:
 
 http://arxiv.org/abs/physics/0110060
 
 
 - Oorspronkelijk bericht -
 Van: Nicole Barberis [EMAIL PROTECTED]
 Aan: [EMAIL PROTECTED]
 Verzonden: Friday, July 30, 2004 06:15 PM
 Onderwerp: Afshar and ...the idea of a photon is dead
 
 
   I was stunned to read Quantum Rebel in July 24th's
   New Scientist.  Shahriar Afshar, an American, comes to
   the conclusion that we have no other choice but to
   declare the idea of Einstein's photon dead (page 35).
His work has been tested and is now being peer
   reviewed.   How trustworthy is New Scientist as a news
   source?  Is it prone to sensationalists articles.  I'm
   a fairly new reader of this magazine, but it seemed to
   me to be a good source of science news until last
   week's rushed Hawking article and this week's
   no-such-thing-as-a-photon showcase article.  Of
   course, if it is repeatedly proved true than I would
   welcome the new finding but for now I'm just a bit
   stunned by the news.
  
   -Nicole
  
  
  
  
  
  
  
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