# Why does light move?

From the theory of relativity, we learn that time is relative to the observer. And that time starts going slower and slower as the observer (reference point) moves faster and faster. And if the reference point reaches the speed of light (c), time stops, and if it theoretically surpasses it, time would go backwards.
Now, light travels at the speed of light, so if we consider a photon as the reference point, isn't time still for it? And if time is stopped, how does the photon ever get anywhere?

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kelseymh says: Jun 8, 2010. 1:39 PM
Time is stopped within the photons frame of reference. In that same frame of reference, everything and everywhere is all at the same place. So the photon doesn't have to go anywhere, it already is there.

Of course, this whole argument is just juvenile sophistry.

Light moves because a time varying electric field induces a time varying magnetic field, which induces an electric field, and so on.  The wave equation you can derive from Maxwell's equations includes a numerical constant which specifics the speed of the wave.  Having such a numerical constant is inconsistent with Newtonian mechanics (technically, it is inconsistent with the Galilean rules for velocity transformation).

Einstein's insight was that Maxwell's equations are right, and the Galilean transforms are wrong.  He showed that using the Lorentz transformations for velocity yields Maxwell's equations for light, and in the limit of low velocities, reduces to the familiar Galilean result.  It is only in the intermediate regime (velocities high compared with normal experience, fractions of c) that the Lorentz transformations give unexpected results.
nickodemus in reply to kelseymhJun 8, 2010. 4:57 PM
Whoa. You just melted my face.
kelseymh in reply to nickodemusJun 8, 2010. 5:35 PM
:-D Check my profile. I don't just play one on TV ;->
kelseymh in reply to nickodemusJun 8, 2010. 10:55 PM
No, that was the laser.
frollard in reply to nickodemusJun 9, 2010. 12:00 AM
Top notch answer - tonnes of info and not too impossible to reference definitions for each component of the argument to further understand whats going on.
frollard in reply to kelseymhJun 9, 2010. 12:01 AM
Addendum: May I suggest the OP read the book "a brief history of time" by Stephen Hawking. The later chapters may or may not melt your brain, but the earlier stuff explains relativity in the simplest possible terms.
orksecurity says: Jun 8, 2010. 6:17 PM
It sounds like you're basically expressing a relativistic version of Zeno's Paradox (which, by ignoring the fact that integrating an infinite series can yield a definite finite value, attempts to prove that nothing can ever reach its destination).
kelseymh in reply to orksecurityJun 8, 2010. 9:11 PM
Sort of, although he's premising it on a deliberate arithmetic fallacy, whereas the original version was arithmetically correct, but relied on a misinterpretation of convergent series.
lemonie says: Jun 8, 2010. 2:14 PM
You've pegged this to a photon.
Remember that a photon is an abstract-concept that is useful for some situations (when you're digesting Kelsey's excellent answer)

L
orksecurity in reply to lemonieJun 8, 2010. 6:19 PM
Agreed -- Kelsey, you may want to refactor your response as a separate Answer so it can be directly voted as Best. (I figured I'd pass the suggestion along since people keep giving it to me...)
kelseymh in reply to orksecurityJun 8, 2010. 9:10 PM
It is a top-level answer, and started out that way. You might be getting fooled by yet another annoying I'bles bug :-)
Re-design says: Jun 8, 2010. 1:57 PM