Recent content by deSitter

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    Hard evidence for quasar lensing

    Hello, could someone point out to me 1) Ironclad evidence of correlated light curves - and I mean a correlation that is beyond doubt - among lensed quasars 2) Morphological correspondence - e.g. corresponding jets - in images of lensed quasars. I can find sketchy cases which may be...
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    Is the speed of light actually constant or just always measured to be the same?

    This is simply false, it's physics-false, and math-false. As I pointed out above, the speed of light is 1 in natural units. It will always be 1, until the photon becomes massive. The parameter C does not represent something about light so much as it represents the pseudo-Euclidean nature of the...
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    How to obtain Kerr Metric via Spinors (N-P Formalism)

    A null tetrad is something of a ruse. Two of its legs are real null vectors whose inner product is 1, while the other two are formed by the introduction of a spurious "i" and have components that are real, orthogonal spacelike vectors: (s1 + i s2)^2 = (s1^2 - s2^2) + 2i (s1.s2) = 0 ..so you...
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    Is the speed of light actually constant or just always measured to be the same?

    Yes, it is constant-constant. The speed of light is 1, and 1 is always 1. In a sense, the speed of light plays the same role in pseudo-Euclidean (Minkowski) geometry, that infinity does in Euclidean geometry. I mean that in the sense of projective geometry - that is, in Minkowskian affine...
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    On the Physical Separation of Time

    Anamitra, how do you interpret this? https://www.physicsforums.com/showthread.php?t=172288 Here we have an example of something is both moving and stationary, depending on how you interpret it. So time means something different with distant objects. Cooperstock was at pains to explain this in...
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    How can I Bel-decompose the Riemann tensor over SO(3,3)?

    Good points, thanks for the grist :) -drl
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    How can I Bel-decompose the Riemann tensor over SO(3,3)?

    Not really - there is a definite procedure here for carving up the Riemann tensor, sort of like the Ricci decomposition, but I'll be damned if I can remember the details. You need a time-like congruence, which should still exist for SO(3,3) because there is still a light cone. Well I can't...
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    How can I Bel-decompose the Riemann tensor over SO(3,3)?

    Hello, I need to Bel-decompose the Riemann tensor built over SO(3,3). Does anyone have a decent reference? Funny how this topic is elusive. Is this in Wald? Thanks in advance. -drl
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    Why is the speed of light limited in physics?

    Yes this is an excellent point - one could go so far as to say "c" should be banned from equations! There is another way of looking at this that goes very deep into the heart of the geometry. In relativity, propagation is elevated to a primitive fact by welding space and time into a geometric...
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    Why is the speed of light limited in physics?

    Actually the entire point is that, yes, there is a physical limit with dimensions of a velocity, and light happens to go at that speed because it is mediated by a field with no mass. See this for an explanation requiring nothing more than algebra to understand - no mirrors, no trains, no barns...
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