Illustration by Matt Murphy
Posted on 09/20/2015 1:35:08 PM PDT by SunkenCiv
If you visit the Paris Observatory on the left bank of the Seine, you'll see a plaque on its wall announcing that the speed of light was first measured there in 1676. The odd thing is, this result came about unintentionally. Ole Romer, a Dane who was working as an assistant to the Italian astronomer Giovanni Domenico Cassini, was trying to account for certain discrepancies in eclipses of one of the moons of Jupiter. Romer and Cassini discussed the possibility that light has a finite speed (it had typically been thought to move instantaneously). Eventually, following some rough calculations, Romer concluded that light rays must take 10 or 11 minutes to cross a distance 'equal to the half-diameter of the terrestrial orbit'.
Cassini himself had had second thoughts about the whole idea. He argued that if finite speed was the problem, and light really did take time to get around, the same delay ought to be visible in measurements of Jupiter's other moons -- and it wasn't. The ensuing controversy came to an end only in 1728, when the English astronomer James Bradley found an alternative way to take the measurement. And as many subsequent experiments have confirmed, the estimate that came out of Romer's original observations was about 25 per cent off. We have now fixed the speed of light in a vacuum at exactly 299,792.458 kilometres per second...
The Scottish physicist James Clerk Maxwell showed that when electric and magnetic fields change in time, they interact to produce a travelling electromagnetic wave. Maxwell calculated the speed of the wave from his equations and found it to be exactly the known speed of light. This strongly suggested that light was an electromagnetic wave -- as was soon definitively confirmed.
(Excerpt) Read more at aeon.co ...
Illustration by Matt Murphy
Whoops! [blush] Thanks Avoiding_Sulla.
We all know that the speed of light is faster than the speed of sound. That must be why some people appear to be bright, until they speak.
LOL!!
I loved seeing that for the first time, in the Charles Cinema, West End, Boston, in 1977.
Before CGI...(sigh) The Good Old days.
Divide the electric force constant (K sub e) by the magnetic force constant (K sub m),...
...and you get the square of a speed (m=meters, s=seconds). ...but what speed?
...taking the square root, we get...
The speed of light! This I believe was Maxwell's first clue that light was somehow related to electricty and magnetism.
The speed of dark must be at least a little faster than the speed of light, because the dark can never been seen leaving the room when I switch on the lights.
It made the Kessel Run in less than 12 parsecs.
One of these days I’m going to finish the late Milton Monson’s book. Gotta find it, and the time.
It must be true that the higher you are the faster
the speed of sound, cause when I’m high every thing
sounds funny, Heheheheeeeeeee.
You’re in luck! (anyone who is interested in this stuff)
I found the Mechanical Universe and Beyond episode on Maxwell! (28min)
39. Maxwell’s Equations:
Maxwell discovers that displacement current produces electromagnetic waves or light.
http://www.dailymotion.com/video/x2z2gf0
...it’s where I got those equations.
Related episodes of the series here:
39. Maxwell’s Equations
Maxwell discovers that displacement current produces electromagnetic waves or light.
41. The Michelson-Morley Experiment
In 1887, an exquisitely designed measurement of the earth’s motion through the ether results in the most brilliant failure in scientific history.
VOD42. The Lorentz Transformation
If the speed of light is to be the same for all observers, then the length of a meter stick, or the rate of a ticking clock, depends on who measures it.
VOD43. Velocity and Time
Einstein is motivated to perfect the central ideas of physics, resulting in a new understanding of the meaning of space and time.
VOD44. Mass, Momentum, Energy
The new meaning of space and time make it necessary to formulate a new mechanics.
The Mechanical Universe and Beyond (52 half-hour episodes)
http://www.learner.org/resources/series42.html
Is the amount of potential energy in the zero point field increasing?
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