Scientists stop light

[Az]

what mass of a photon?

[Japher]

ref.

"A particle like a photon is never at rest and always moves at the speed of light; thus it is massless," says Dr. Michael S. Turner, chair of the Department of Astrophysics at the University of Chicago.
What about experimental evidence? Experiments don't determine exact quantities because of small errors inherent in making measurements. We have, however, put an upper limit on the photon rest mass. In 1994, the Charge Composition Explorer spacecraft measured the Earth's magnetic field and physicists used this data to define an upper limit of 0.0000000000000006 electron volts for the mass of photons, with a high certainty in the results.
This number is close to zero; it is equivalent to 0.00000000000000000000039 times the mass of an electron (the lightest particle), says Turner.

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It has to have mass...

[Az]

Ok, so far you've presented me with evidence that no such mass have been found.

am I supposed to take your word for it?

[Japher]

"am I supposed to take your word for it? "

I said I could be wrong.

Have you taken Classical Chemistry/Quantum Mechanics yet? Everything is based on assumptions, denying those assumptions everything falls apart. Including that in order for something to contain energy it must also have a mass. If you want to refute that light does not have energy than you can say it does not have a mass, but I don't think you want to say that. Do you?

[Az]

are you referring to the Hamiltionian operator?

[Az]

I still don't understand where do you see that Photons must have a mass.

[Japher]

This helped me

Though it still doesn't make a whole lot of sense in that all equations for energy require a mass, and that "rest masses" have been calculated for a photon, yet they still say it is zero.

[Az]

I think you've misunderstood.

for the standard definition this applies:

E=mc^2/sqrt(1-v^2/c^2)

if you enter v=c, you get E-->infinity, that's, obviously, incorrect.

[Japher]

yup.

[Boris Godunov]

Most gracious Apolyton concession ever.

Dammit, don't you know how to go out kicking and screaming, man?

[Az]

That's why the mass in that one should be also zero.

[Japher]

Most gracious Apolyton concession ever.

yup

It's still conceptually wrong. I think the last link addresses that point but makes not attempt to address that fact besides saying 'if we change it now than we have to change a theory which we have no way of testing anyway'... rather bogus if you ask me.

Anywho, has no practical implications for me, only that maybe that theory is wrong, but then I'm not going to do anything about it.

THIS SUCKS!!!

Dammit, don't you know how to go out kicking and screaming, man?

Was that better?

[Boris Godunov]

No, I was hoping for a joke based on the penis receptical idea.

[Rogan Josh]

OK kiddies, time for a physics lesson.

Light has no mass. period. The masslessness of light is one of the best measured quantities we have, so if you want to believe anything a scientist tells you, believe this.

Secondly, your (Japher's, Azazel's) equation E=mc^2 is wrong. This is only true for a particle at rest, which a photon can never be (despite what CNN tells you). The real equation (applicable to everything) is:

E^2 = m^2 c^4 +p^2 c^2

where p is momentum. Since an object at rest has p=0, this gives E=mc^2 at rest. But for a photon, m=0, so the equation becomes a relation between energy and momentum:

E=p c

So Kramerman is completely correct. If they had actually 'stopped' light it would have amazing consequences. It would break the U(1) symmetry of electromagnetism and for a start.

But they didn't really stop light - this is just a journalist's take. They absorbed the light and emitted it again with no energy loss. This is perfectly ok, and violates no physics laws. In fact, it is well known that light travels more slowly through water for example - experiments to detect neutrinos use the 'warp boom' of the netrino passing through water to detect it - because the neutrino passes through the water faster then light, it gives off a lot of light in analogy to the sonic boom of an aircraft travelling faster than sound.

The fact that they can do it with no energy loss is quite cool, but certainly has no consequences for fundamental physics.

[Az]

Most gracious Apolyton concession ever.

That's real honor.

GR is right. nothing to do about it.