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Does Gravity Travel at the Speed of Light? (1998)
Updated 2011 by Steve Carlip, and 1998 by Steve Carlip, Matthew Wiener and Geoffrey Landis. Original by Steve Carlip.
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Can a Human See a Single Photon? (1996)
The human eye is very sensitive; but can we see a single photon? The answer is yes: sensors in the retina can respond to a single photon. But neural filters only allow a signal to pass to the brain to trigger a conscious response when at least about five to nine arrive within less than 100 ms. If we could consciously…
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Why is C the symbol for the speed of light? (2004)
"As for c , that is the speed of light in vacuum, and if you ask why c , the answer is that it is the initial letter of celeritas , the Latin word meaning speed." Isaac Asimov in "C for Celeritas (1959)" [1]
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Noether's Theorem in a Nutshell (2020)
Noether's theorem is an amazing result which lets physicists get conserved quantities from symmetries of the laws of nature. Time translation symmetry gives conservation of energy; space translation symmetry gives conservation of momentum; rotation symmetry gives conservation of angular momentum, and so on.
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Is Faster-Than-Light Travel or Communication Possible? (1997)
It might be thought that special relativity provides a short negative answer to this question. In actual fact, there are many trivial ways in which things can be going faster than light (FTL) in a sense, and there may be other more genuine possibilities. On the other hand, there are also good reasons to believe that…
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500 Exabytes per Raindrop
People like to say this is the "information age". But just how much information are we talking about? I recently found a nice source of... umm... information about this question:
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The Relativistic Rocket
Thanks to Alan R. Wilson for correcting a two-word typo involving GPS satellites. Thanks to Aron Yoffe for suggesting the newtonian comparison. Thanks to Tom Fuchs for suggesting the analogy to the stone thrown upwards. Fuel numbers added by Don Koks, 2004. Updated by Phil Gibbs, 1998. Thanks to Bill Woods for…