How Can Photons Have Energy Without Mass?

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Discussion Overview

The discussion revolves around the nature of photons, specifically addressing how they can possess energy despite having no rest mass. Participants explore various properties of photons, including energy, momentum, and the implications of mass in these contexts.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants question the assertion that mass is the only property of photons, noting that photons also have energy, travel at the speed of light, and possess spin.
  • One participant argues that if mass is zero, then energy and momentum must also be zero, suggesting a misunderstanding of the relationship between mass, energy, and momentum.
  • Another participant clarifies that for massless particles like photons, energy is related to momentum rather than mass, emphasizing the need to think relativistically.
  • There is a suggestion that if photons must have mass, then energy itself must also have mass, prompting further examination of the equations governing these relationships.
  • One participant challenges the idea that photons have mass, reiterating that momentum is what relates to energy for massless particles.

Areas of Agreement / Disagreement

Participants express differing views on whether photons can be said to have mass and how energy relates to mass and momentum. The discussion remains unresolved, with multiple competing perspectives presented.

Contextual Notes

Participants reference equations and concepts from relativity, but there are indications of misunderstandings regarding the implications of mass being zero and its effect on energy and momentum. The discussion reflects a range of interpretations of these relationships.

ddr
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!
----------------------------------------------------------------
ha, ha, ha...ain't it funny?
 
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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.
 
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...).
 


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!
 
Last edited by a moderator:


Originally posted by neutroncount
If mass is 0, than energy is equal to momentum times c.
Ok, how much is the momentum then?
 
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 ?
 
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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