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GR time question
On Jan 1, 7:02*pm, Tom Roberts wrote:
wrote in sci.physics.relativity: On 1 jan, 08:06, Tom Roberts wrote: The signals coming up from the clock at the center will tick slower than the clock at the surface. I agree, but could you justify your answer? Sure! This is what GR predicts. Moreover, we have literally zillions of experiments and observations that confirm this sort of redshift for EM signals propagating from lower to higher gravitational potential. Tom Roberts Isn't this redshift due to the fact that the speed of light "varies with position" in a gravitational field, Honest Roberts, in accordance with the formula: frequency = (speed of light)/(wavelength) Divine Albert and many of your brothers would confirm this variability of the speed of light (and you know that if the speed of light "varies with position", there is NO GRAVITATIONAL TIME DILATION, don't you Honest Roberts): http://math.ucr.edu/home/baez/physic..._of_light.html Steve Carlip: "Einstein went on to discover a more general theory of relativity which explained gravity in terms of curved spacetime, and he talked about the speed of light changing in this new theory. In the 1920 book "Relativity: the special and general theory" he wrote: ". . . according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity [. . .] cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position." Since Einstein talks of velocity (a vector quantity: speed with direction) rather than speed alone, it is not clear that he meant the speed will change, but the reference to special relativity suggests that he did mean so. THIS INTERPRETATION IS PERFECTLY VALID AND MAKES GOOD PHYSICAL SENSE..." http://www.physlink.com/Education/AskExperts/ae13.cfm "So, it is absolutely true that the speed of light is not constant in a gravitational field [which, by the equivalence principle, applies as well to accelerating (non-inertial) frames of reference]. If this were not so, there would be no bending of light by the gravitational field of stars....Indeed, this is exactly how Einstein did the calculation in: 'On the Influence of Gravitation on the Propagation of Light,' Annalen der Physik, 35, 1911. which predated the full formal development of general relativity by about four years. This paper is widely available in English. You can find a copy beginning on page 99 of the Dover book 'The Principle of Relativity.' 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' = c0 ( 1 + V / c^2 ) where V is the gravitational potential relative to the point where the speed of light c0 is measured." http://www.blazelabs.com/f-g-gcont.asp "So, faced with this evidence most readers must be wondering why we learn about the importance of the constancy of speed of light. Did Einstein miss this? Sometimes I find out that what's written in our textbooks is just a biased version taken from the original work, so after searching within the original text of the theory of GR by Einstein, I found this quote: "In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust. But in reality this is not the case. We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity ; its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (e.g. of light)." - Albert Einstein (1879-1955) - The General Theory of Relativity: Chapter 22 - A Few Inferences from the General Principle of Relativity-. Today we find that since the Special Theory of Relativity unfortunately became part of the so called mainstream science, it is considered a sacrilege to even suggest that the speed of light be anything other than a constant. This is somewhat surprising since even Einstein himself suggested in a paper "On the Influence of Gravitation on the Propagation of Light," Annalen der Physik, 35, 1911, that the speed of light might vary with the gravitational potential. Indeed, the variation of the speed of light in a vacuum or space is explicitly shown in Einstein's calculation for the angle at which light should bend upon the influence of gravity. One can find his calculation in his paper. The result is c'=c(1+V/c^2) where V is the gravitational potential relative to the point where the measurement is taken. 1+V/c^2 is also known as the GRAVITATIONAL REDSHIFT FACTOR." http://www.mathpages.com/rr/s6-01/6-01.htm "In geometrical units we define c_0 = 1, so Einstein's 1911 formula can be written simply as c=1+phi. However, this formula for the speed of light (not to mention this whole approach to gravity) turned out to be incorrect, as Einstein realized during the years leading up to 1915 and the completion of the general theory. In fact, the general theory of relativity doesn't give any equation for the speed of light at a particular location, because the effect of gravity cannot be represented by a simple scalar field of c values. Instead, the "speed of light" at a each point depends on the direction of the light ray through that point, as well as on the choice of coordinate systems, so we can't generally talk about the value of c at a given point in a non- vanishing gravitational field. However, if we consider just radial light rays near a spherically symmetrical (and non- rotating) mass, and if we agree to use a specific set of coordinates, namely those in which the metric coefficients are independent of t, then we can read a formula analogous to Einstein's 1911 formula directly from the Schwarzschild metric. (...) In the Newtonian limit the classical gravitational potential at a distance r from mass m is phi=-m/r, so if we let c_r = dr/dt denote the radial speed of light in Schwarzschild coordinates, we have c_r =1+2phi, which corresponds to Einstein's 1911 equation, except that we have a factor of 2 instead of 1 on the potential term." Pentcho Valev |
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