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Light traveles a straight line write down the principle in which this is manifested.

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closed as not a real question by Ebenezer Sklivvze, David Z Dec 23 '12 at 7:04

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Concerning v2, I would say that the tags 'light', 'optics', and 'variational-principle' are more appropriate than 'homework'. –  Qmechanic May 25 '11 at 16:39
    
is this a homework question? –  David Z May 25 '11 at 18:27
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Clarify "manitested"? If typo, please fix. –  Jen May 25 '11 at 19:27
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It's also nice to show what you've tried, what did or didn't work with your approach, and a 'please' at the end also help in posing a question. –  yatima2975 May 25 '11 at 20:34
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Should "manitested" be "manifested"? –  Henry May 26 '11 at 6:55

1 Answer 1

Principle of least action; or more specifically Fermat's principle of least time. The least time traveled at a constant speed (first postulate of special relativity) between two points in a flat geometry is a straight line as can be simply shown with variational calculus.

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To be clear, doesn't this only require a local minimum? After all, light can loop fully around a black hole before making it to its target. Is this correct? –  Alan Rominger May 25 '11 at 15:04
    
@Zassounotsukushi: Yes. The principle of least action/least time are more accurately called stationary action/time with the classic example of light going from A into a mirror and reflecting to point B, being more time then light going straight from A to B. See Feynman chapter vol 1-26 or 2-19. But they are still commonly known as 'least' even though its a bit of a misnomer. –  dr jimbob May 25 '11 at 15:08
    
@Jimbob, it's spelled "principle" - "principal" is a director of the high school. ;-) –  Luboš Motl May 25 '11 at 15:16
    
@Lubos: Silly typo from quickness (I know the distinction; as evidenced by the 5 other times principle was spelled correctly before you mentioned this). While we are pointing out typos, we should we fix: Nuradeen's two spelling mistakes of "traveles" to "travels" and "manitested" to "manifested" and poor overall grammar. –  dr jimbob May 25 '11 at 16:11
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Not sure what the downvote is for. In case anybody is confused, this is a correct answer. –  Colin K May 26 '11 at 0:05

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