Light's Most Exotic Trick Yet: So Fast it Goes ... Backwards?

University of Rochester ^ | 11 May 2006 | Staff (press release)

[Ichneumon]

I'm not a physicist, but this smells like BS to me.

That's because you're making the mistake of using common sense, and thinking that it has to apply to the quantum level as well. It doesn't. *Lots* of things at the quantum level blatantly violate "common sense" notions of how things "ought" to behave.

[BadAndy]

"That's because you're making the mistake of using common sense, and thinking that it has to apply to the quantum level as well. It doesn't. *Lots* of things at the quantum level blatantly violate "common sense" notions of how things "ought" to behave."

I think I finally understand the behavior of politicians.

[harrowup]

I hope in the paper they managed to use the word "endochronic".

Take this thing down to the Arizona-Mexico border and the President won't have to waste his time Monday night.

[Political Junkie Too]

I can't wait for Sharper Image to sell a mirror that makes me look younger.

-PJ

[Physicist]

First off, light does have mass.

Not that we know of.

[PatrickHenry]

Well, that was provocative. I'll just sit back and wait to see what develops.

[GOPJ]

seY, "sdrawrof"

[Daus]

My '82 Pontiac Bonneville always seemed faster off the line in reverse than in drive. Now I know why. Thanks. :)

[<1/1,000,000th%]

I think I can see myself.

[LuxMaker]

http://math.ucr.edu/home/baez/physics/Relativity/SR/light_mass.html

What is the meaning of the equation E=mc2? You can interpret it to mean that energy is the same thing as mass except for a conversion factor equal to the square of the speed of light. Then wherever there is mass there is energy and wherever there is energy there is mass. In that case photons have mass but we call it relativistic mass. Another way to use Einstein's equation would be to keep mass and energy as separate and use it as an equation which applies when mass is converted in energy or energy is converted to mass as in nuclear reactions. The mass is then independent of velocity and is closer to the old Newtonian concept. In that case only total of energy and mass would be conserved but it seems better to try to keep conservation of energy. The interpretation most widely used is a compromise in which mass is invariant and always has energy so that total energy is conserved but kinetic energy and radiation does not have mass. The distinction is purely a matter of semantic convention.

The above article says light has no mass but with a qualifier that it has "relativistic mass".

More here on relativistic mass:
http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

[LuxMaker]

Also here is the anatomy of an electron described as a photon trapped in a self resonant loop:
http://www.photontheory.com/willis.htm

We know that electrons have rest mass.

[Physicist]

As Baez correctly states:

The interpretation most widely used is a compromise in which mass is invariant and always has energy so that total energy is conserved but kinetic energy and radiation does not have mass. The distinction is purely a matter of semantic convention.

Translation: When physicists say "mass" they mean the observer-invariant quantity, of which light has none. Those who argue with them are playing word games.

To which I can only add: "...or are wrong."

[RightWingAtheist]

Actually, this reminds me of James Blish's classic short story "Bleep".

[freedumb2003]

Hey that's not possible!

The "Theory of Light" is both testable and repeatable. I turn on my flashlight and I see light.

This is complete athiestic, anti-Christian, Commie nonsense.

You evil "lightists." We should be able to discuss in school alterate theories of light. That God created it on the First Day and that is it!

(/best imitation of a CRIDer I could do)

[ ;) ]

[SlowBoat407]

I have a few questions about this:

First, doping usually increases the RI, and is necessary for fiber optics to work. I'm not sure what erbium does as opposed to the more standard doping materials, but the light is still traveling through, basically, glass. What effect does the erbium have?

Second, was the reference shot through a standard glass fiber, or through air?

Third, was Fresnel reflection off the endface of the opposite end of the fiber taken into account? It seems to me that we have a light beam that got to the end faster than the reference, and the Fresnel reflection off the endface had already started on its way back to the origin. Just a thought.

Fourth, was the faster light measured through the core, or through the cladding? In single mode fiber, since the cladding has a lower RI than the core, any light that gets into the cladding (from overfilled launch, for example) will travel faster than that going through the core. From the point of view of the light in the cladding, the light in the core seems to be moving backwards, and if the RI difference between the core and the cladding is great enough, there could be some spectacular chromatic dispersion (waveguide plus material dispersion). That could account for many of the effects described in the article. It all depends on what, exactly, the erbium doping brings to the party.

[PatrickHenry]

/best imitation of a CRIDer I could do)

You're not even trying. Light comes from another dimension, the spiritual plane, where the full glory of light is manifest. It has no mass in this base world of flesh because the light we see isn't at all the full reality of light. You fool! Open your heart. The truth is all around you! It is not yet too late.
</internet idiot mode>