The discussion centers around the apparent contradiction of how photons can be massless yet possess energy, as described by Einstein's equations. Participants explore the implications of mass in relation to energy for both massive and massless particles, examining the equations that govern these relationships.
Participants express differing views on the applicability of Einstein's equations to massless particles, with some emphasizing the need for momentum in the energy calculation while others focus on the implications of rest energy. The discussion remains unresolved regarding the interpretation of these equations in the context of massless photons.
Some participants note the limitations of applying E = mc² to massless particles and the need to consider momentum in energy calculations. There is also a distinction made between rest energy and total energy, which may affect interpretations.
This discussion may be of interest to those studying physics, particularly in understanding the relationship between mass and energy, as well as the implications of Einstein's equations for different types of particles.
That formula is only correct for stationary massive objects. The general formula is ##m^2c^4=E^2-p^2c^2##, from which you can see that you can have zero mass objects with non-zero energy as long as their momentum, ##p##, satisfies ##E=|p|c##.ginevradabenci said:Since E = mc^2, how can photons be massless?
The equation ##E = mc^2## only applies to a particle with mass. And, indeed, that's its energy only when it is at rest. The full equation is:ginevradabenci said:TL;DR Summary: How can photons be massless if they have energy?
Since E = mc^2, how can photons be massless? If a photon has no mass, then, according to Einstein's formula, its energy is given by E = 0 x c^2, which is 0. Yet, photons do have energy. This seems to be a complete contradiction. Please explain! Thank you.
Because the correct equation is ##E_o=mc^2## where ##E_o## is the so-called rest energy. Rest energy is one of Einstein's greatest discoveries.ginevradabenci said:Since E = mc^2, how can photons be massless?