robphy's latest activity
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No. Light does not experience time. There is no valid frame of reference for a photon. This is a direct result of the postulates of... -
robphy replied to the thread Graduate Can a causal or time-like structure emerge without assuming a metric?.Did you look at the Szekeres "Signal Space" reference? His S relation is reflexive, but not symmetric.
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robphy replied to the thread Graduate Can a causal or time-like structure emerge without assuming a metric?.This might be of interest: E. H. Kronheimer & R. Penrose (1967) "On the structure of causal spaces" Mathematical Proceedings of the...
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robphy replied to the thread Graduate Can a causal or time-like structure emerge without assuming a metric?.Along these lines (assuming (3+1)-spacetime): "The causal order C determines the conformal structure of space-time, or nine of the ten...
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robphy reacted to renormalize's post in the thread Graduate Can a causal or time-like structure emerge without assuming a metric? with
Like.
Take a look at https://en.wikipedia.org/wiki/Causal_sets: "The causal sets program is an approach to quantum gravity. Its founding... -
robphy replied to the thread Graduate Can a causal or time-like structure emerge without assuming a metric?.You might be interested in David Malament’s dissertation: “Does the Causal Structure of Space-Time Determine its Geometry”...
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robphy replied to the thread Graduate Can a causal or time-like structure emerge without assuming a metric?.I think that’s a fair statement.
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robphy replied to the thread Graduate Can a causal or time-like structure emerge without assuming a metric?.AA Robb studied the “conical order” in terms of “before” and “after”.
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robphy replied to the thread Graduate Dirac's 1958 lecture on spinors.From https://www.nobelprize.org/uploads/2024/02/penrose-lecture.pdf You can read this 1936 Dirac reference here...
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robphy replied to the thread Graduate Dirac's 1958 lecture on spinors.You could try to browse Dirac's collected papers Cambridge U. - https://archivesearch.lib.cam.ac.uk/repositories/9/resources/1531...
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robphy replied to the thread Undergrad Gravitational analog of electromagnetic force.This reminds me of a very old post of mine (reconstructed here because the old-style LaTeX on PF appears broken): It might be...
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robphy replied to the thread Undergrad Gravitational analog of electromagnetic force.Is this the paper you seek? From the WIkipedia article.... Bel, L. (1958), "Définition d'une densité d'énergie et d'un état de radiation...
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robphy replied to the thread History Biographies, History, Philosophy of Physics.Here's a 2025 interview with Abhay Ashtekar (Penn State), split into parts. (I was especially interested in his stories with Robert...
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So are we! :welcome:
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robphy reacted to jedishrfu's post in the thread High School True static equilibrium and effects on time with Like.
MENTOR NOTE: This thread has been split into two parts. This part discusses the Static Equilibrium and is now closed, while the...