Question for the physics gurus

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Ken g6

Programming Moderator, Elite Member
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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.
 

jagec

Lifer
Apr 30, 2004
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Yahoo answers is wrong 99% of the time.

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

Here is the real equation:
latex.php


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

Lifer
Oct 3, 2003
12,221
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Yahoo answers is wrong 99% of the time.

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

Here is the real equation:
latex.php


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

Administrator Elite Member Goat Whisperer
Mar 5, 2001
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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.
 
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