- #1
ScienceNerd36
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How can a photon exist if it has no mass? I've always found this concept hard to grasp. (Rhyming not intended)
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SUMMARY
The discussion centers on the existence of photons despite their lack of rest mass. It highlights the principles of relativity and quantum mechanics, specifically referencing the energy-momentum relation E² = (mc²)² + (pc)². Participants emphasize that photons possess energy and momentum, which allows them to exist without mass. The conversation also touches on classical electrodynamics, where electromagnetic waves carry energy and momentum independently of mass.
PREREQUISITES- Understanding of Einstein's theory of relativity
- Familiarity with quantum mechanics concepts
- Knowledge of classical electrodynamics
- Basic grasp of energy-momentum relations
- Study Einstein's energy-momentum relation in detail
- Explore the implications of massless particles in quantum field theory
- Research classical electrodynamics and its relation to modern physics
- Investigate the concept of rest mass versus relativistic mass
Students of physics, educators in relativity and quantum mechanics, and anyone interested in the fundamental nature of light and energy.
- #2
jtbell
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We're not in classical physics any more. Photons are quintessentially relativistic and quantum-mechanical. The general relation for energy, mass and momentum is
E^2 = (mc^2)^2 + (pc)^2
(This uses what is often called "rest mass", not "relativistic mass".) An object can have zero mass but still have nonzero energy and momentum.
Note that even in classical electrodynamics, electromagnetic waves carry energy and momentum without having mass.
- #3
malawi_glenn
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Why does everything that exists have to have mass? Is there an a priori reason??
- #4
tiny-tim
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Hi ScienceNerd36! 
(erm
… rhyming not achieved)
mass is energy, energy is mass
a photon does have mass
(it has no rest-mass, but why should that matter when a photon is never at rest?
)
(erm
… rhyming not achieved)mass is energy, energy is mass
a photon does have mass
(it has no rest-mass, but why should that matter when a photon is never at rest?
)- #5
malawi_glenn
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tiny-tim said:Hi ScienceNerd36!
(erm
mass is energy, energy is mass
a photon does have mass
(it has no rest-mass, but why should that matter when a photon is never at rest?
oohh now you have started this war again Timmy, prepare for battle
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