Question for the physics gurus

[Juddog]

If a photon has an actual weight, then wouldn't particles that had less mass than a photon be able to move faster than the speed of light?

I was looking here:
http://wiki.answers.com/Q/How_much_does_a_quantum_of_light_weigh

It states that the photon does have mass, although that mass is incredibly small.

 

[Ken g6]

Technically, I've heard that a photon has no rest mass. I don't think photons are ever at rest. Relative to anyone or anything.

Though there was some speculation that neutrinos might move faster than photons, I think that's generally been disproved.

 

[Murloc]

I knew that it has no rest mass. Wikipedia agrees.

that wiki answers thing is sketchy.

Maybe this:
https://en.wikipedia.org/wiki/Mass_in_special_relativity
makes more sense?

Also I don't know if the notion that particles with less mass move faster still applies in more advanced physics than the ones I saw.

 

[jagec]

Yahoo answers is wrong 99% of the time.

Photons have no rest mass, but they do have momentum.

Here is the real equation:

Note that if you're stationary, the equation simplifies to the well-known E=mc^2. If you're massless, then THAT side of the equation cancels and energy is proportional to momentum. Also note that E=hf, so energy is also proportional to frequency. Which is why UV photons are more energetic (and therefore carry more momentum) than IR photons.

 

[Krazy4Real]

Yahoo answers is wrong 99% of the time.

Photons have no rest mass, but they do have momentum.

Here is the real equation:

Note that if you're stationary, the equation simplifies to the well-known E=mc^2. If you're massless, then THAT side of the equation cancels and energy is proportional to momentum. Also note that E=hf, so energy is also proportional to frequency. Which is why UV photons are more energetic (and therefore carry more momentum) than IR photons.

*nods head*

 

[DrPizza]

Photons don't have mass, moving or "at rest." They do have momentum. Having momentum does NOT mean they have mass. See this:

http://www.youtube.com/watch?v=IM630Z8lho8


edit: yeah, what jagec said. 🙂

 

[Juddog]

Yahoo answers is wrong 99% of the time.

Good thing nobody mentioned yahoo answers in the thread.

 

[DrPizza]

Technically, I've heard that a photon has no rest mass. I don't think photons are ever at rest. Relative to anyone or anything.

Though there was some speculation that neutrinos might move faster than photons, I think that's generally been disproved.

Speculation isn't quite the right term. Data results: over a few hundred or thousand miles, whatever it was, the neutrinos were about 60 feet ahead of where they would be if they traveled at exactly the speed of light. The researchers did all they could to find where they had made an error, suspecting their results were wrong, since they flew in the face of what we know. After they couldn't find an error, they are ethically obligated to publish those results, so that others can either confirm, or find the fault. That's what peer review does. And, eventually, the error was found.

Fortunately, from what I could see, the researchers went about it the right way - it was, "gee, these results don't really seem right, but this is what we got, and this is what it implies. We can't find an error." Had neutrinos actually gone faster than the speed of light, a bit of math, explanation later, and they very well could have had a Nobel prize in physics. BUT, by not announcing it to the world like this: "OMG! Cold Fusion! We're teh awesome!", they saved their careers.