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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 Sklivvz, David Z Dec 23 '12 at 7:04

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

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
Clarify "manitested"? If typo, please fix. –  Jen May 25 '11 at 19:27
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
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? –  AlanSE 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
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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