🚀 go-pugleaf

Always said so !!

MA

"Pentcho Valev" <pvalev@yahoo.com> a �crit dans le message de news: 
1186812840.164678.38300@k79g2000hse.googlegroups.com...
> On 10 Aug, 17:52, Tom Roberts <tjroberts...@sbcglobal.net> wrote:
>> qbit wrote:
>> > To see the steps how Einstein theorized that the speed of light in a
>> > gravitational field is actually not a constant, but rather a variable
>> > depending upon the reference frame of the observer:
>> > 'On the Influence of Gravitation on the Propagation of Light',
>> > Annalen der Physik, 35, 1911. Einstein wrote this paper in 1911 in 
>> > German
>> http://www.physik.uni-augsburg.de/annalen/history/papers/1911_35_898-908.pdf
>> > It predated the full formal development of general relativity by 
>> > about four years.
>> > You can find an English translation of this paper in the Dover book
>> > 'The Principle of Relativity' beginning on page 99; you will find in
>> > section 3 of that paper Einstein's derivation of the variable speed 
>> > of light
>> > in a gravitational potential, eqn (3). The result is:
>> >   c' = c * (1 + phi / c^2)
>> > Where phi is the gravitational potential relative to the point where
>> > the speed of light c is measured. Simply put:
>> > Light appears to travel slower  in stronger gravitational fields 
>> > (near bigger mass).
>> > [...]
>>
>>         [Beware: Pentcho Valev obsesses about that equation, and
>>          posts endless articles about it around here, ALL WRONG.]
>>
>> That 1911 article was documenting a portion of Einstein's arduous trek
>> from SR to GR. The above formula does not hold in GR, except in certain
>> approximations for specific physical situations; it is not a general
>> formula at all. In GR, the speed of light (in vacuum) is c in EVERY
>> locally inertial frame (when measured with standard clocks and rulers).
>> But due to the curvature of spacetime, when measured over a non-local
>> distance one can obtain other values. The above formula purports to
>> describe the speed of light "there" when measured by an observer "here"
>> -- in GR that in general makes no sense; in the small-field
>> APPROXIMATION to GR it does make sense, and that formula holds
>> APPROXIMATELY for certain specific measurements (even in the 
>> small-field
>> approximation it is not a general formula).
>>
>> So yes, there are cases where the speed of light is not c (in vacuum).
>> But it is considerably more subtle than you seem to think.
>>
>> Tom Roberts
>
> Bravo Roberts bravo Tom bravo Albert Einstein of our generation
> (Hawking is no longer the Albert Einstein of our generation etc.).
>>From now on your zombies will know everything about Einstein's 1911
> formula
>
> c' = c * (1 + phi / c^2)
>
> and what is even more important Roberts Roberts, your explanation is
> so clear and unambiguous that even other hypnotists' zombies will be
> able to learn something from it (you used to say Einstein's formula
> was wrong but now you do not wish to be so rude). Yet there is a small
> detail you forgot to explain clearly and unambiguously: there is an
> equivalent formula proved experimentally by Pound and Rebka and
> showing how the frequency varies with the gravitational potential:
>
> f' = f * (1 + phi / c^2)
>
> I say the two formulas are "equivalent" because they are related by
> the textbook equation
>
> frequency = (speed of light)/(wavelength)
>
> So Roberts Roberts the danger is not over: unless you offer more clear
> and unambiguous explanations, even your zombies will find that the two
> formulas are JUST TRUE, confirmed by experiment, and will also find,
> by applying Einstein's equivalence principle, that
>
> c' = c * (1 + phi / c^2)
>
> is equivalent to
>
> c' = c + v
>
> where c is the initial speed of photons relative to the light source
> and v is the relative speed of the light source and the observer, in
> the absence of a gravitational field.
>
> Pentcho Valev
>