What is Rest Mass? Explaining Photon Mass Zero

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Rest mass refers to the mass an object possesses when measured in its own frame of reference, meaning it is stationary relative to the observer. Photons, which are particles of light, have a rest mass of zero because they do not possess mass in any frame of reference. This characteristic allows photons to travel at the speed of light. Understanding rest mass is crucial in the context of physics, particularly in relation to the behavior of particles like photons. The concept highlights the fundamental differences between massless particles and those with mass.
imran
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what is rest mass? why does a photon have rest mass zero? :rolleyes:
 
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Rest mass is the mass an object has when you are in its frame of refrence (IE its stationary to you). Photons have rest mass zero because they dont have any mass :)
 
thank q for ur ans
 

Thread 'Two equivalent statements of time reversal symmetric Hamiltonian'

Time reversal invariant Hamiltonians must satisfy ##[H,\Theta]=0## where ##\Theta## is time reversal operator. However, in some texts (for example see Many-body Quantum Theory in Condensed Matter Physics an introduction, HENRIK BRUUS and KARSTEN FLENSBERG, Corrected version: 14 January 2016, section 7.1.4) the time reversal invariant condition is introduced as ##H=H^*##. How these two conditions are identical?
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