robphy's latest activity
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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”. -
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... -
robphy replied to the thread Undergrad Light clock treating horizontal and vertical motion differently?.And so, a model (motivated by physically observed phenomena) and a set of tools to analyze the model lead to testable predictions, which...
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robphy replied to the thread Undergrad Light clock treating horizontal and vertical motion differently?.The Michelson-Morley apparatus is essentially a [typical] transverse light-clock (whose light-signal is perpendicular to the direction...
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robphy reacted to Ibix's post in the thread Undergrad Light clock treating horizontal and vertical motion differently? with Like.
You can't - that would contradict the second postulate.
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robphy replied to the thread Undergrad Light clock treating horizontal and vertical motion differently?.In special relativity, there is no such reference frame (that is equivalent to that of a typical ["timelike"] observer) where light is...
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robphy reacted to Herman Trivilino's post in the thread High School Relativistic simultaneity and effects on time with Like.
My thoughts are just the opposite. I think it's the very first thing that ought to be introduced. Of course only qualitatively at first...
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robphy reacted to Astronuc's post in the thread Tungsten Cubes for STEM Education — Looking for Feedback with Like.
I had the same thoughts. Without other cubes of different metals, e.g., Mo, Fe, Cu, Al, there a limited uses for a single cube. One...
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robphy replied to the thread Tungsten Cubes for STEM Education — Looking for Feedback.Is it just Tungsten, or are there other metals available (in the same size)? These could be useful for measurements of mass and volume...