Timon and Pumba on photons

  • Thread starter ddr
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  • #1
ddr

Main Question or Discussion Point

Timon, Timon, I wonder howcome photons have no mass at rest and yet mass is their only property?
Pumba, Pumba, you wonder - I know. There are no photons at rest!
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ha, ha, ha...ain't it funny?
 

Answers and Replies

  • #2
mathman
Science Advisor
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mass is their only property?
What do mean by that? Photons have energy, travel at the speed of light, have spin 1, and other properties.
 
  • #3
ddr
it is because...

the energy of the photon is E=mcc
the momentum p=mc
...
---------------------------
if m=0 (there is no m) then
E=0;p=0... too(there is no E,p...).
 
  • #4
neutroncount


Originally posted by ddr
the energy of the photon is E=mcc
the momentum p=mc
...
---------------------------
if m=0 (there is no m) then
E=0;p=0... too(there is no E,p...).
Doesn't work that way.

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/relmom.html

If mass is 0, than energy is equal to momentum times c.

Think relativistically!
 
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  • #5
ddr


Originally posted by neutroncount
If mass is 0, than energy is equal to momentum times c.
Ok, how much is the momentum then?
 
  • #6
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Obviously then the photon must have mass ,right ? And if we follow this statement through to its conclusion it means that energy must have mass ?
 
  • #7
neutroncount
Originally posted by McQueen
Obviously then the photon must have mass ,right ? And if we follow this statement through to its conclusion it means that energy must have mass ?
Why must a photon has mass? Look at the equations again. Energy approximately equates to momentum with a zero rest mass particle (mass disappears at c/c in the equation). So its MOMENTUM that relates to energy with the photon, not mass.
 
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