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# Why does light move? Answered

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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## 14 Replies

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.

frollard (author)2010-06-09

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.

nickodemus (author)2010-06-08

Whoa. You just melted my face.

frollard (author)2010-06-09

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.

kelseymh (author)2010-06-08

No, that was the laser.

kelseymh (author)2010-06-08

:-D Check my profile. I don't just play one on TV ;->

orksecurity (author)2010-06-08

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 (author)2010-06-08

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 (author)2010-06-08

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 (author)2010-06-08

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 (author)2010-06-08

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 (author)2010-06-08

Oh, my head hurts.

caarntedd (author)2010-06-08

Light moves because it got in Chuck Norris' way.

That is also why it moves so fast.

Jack A Lopez (author)2010-06-08

All matter and energy in the universe, including stars in distant galaxies, is/are trying to get away from Chuck Norris.  Astronomers call this phenomenon Hubble's Law, even though the underlying cause is Chuck Norris.