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If energy can be converted into mass then why isn't photon's energy being converted into mass?

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  • $\begingroup$ It's called an intrinsic property of photons. If they had finite rest mass, they wouldn't be able to travel at c and as and at the same time follow Maxwell's equations. They would be a different kind of particles $\endgroup$ – rnels12 Jan 30 at 11:30
  • $\begingroup$ Where did you find that photon's energy isn't converted into mass. as far as I know,photons itself is energy $\endgroup$ – user212727 Jan 30 at 11:39
  • $\begingroup$ It has to do with closed vs. open systems. A photon in a closed system gives that system rest mass. $\endgroup$ – Digiproc Jan 30 at 11:57
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You probably mean something different than you ask: a photon is influenced by gravity and it behaves as it had a mass when traveling through the space. When it is said that photon is a massless particle, it is in a context that it has no rest mass $m_0$ i.e. $E^2=m^2c^4=p^2c^2 + m_0^2c^4$ turns into $p^2c^2$ ($p$ is momentum), but $mc^2$ still speaks about the amount of its gravitational interaction.

I have also a funny answer (slightly less correct) - based on recent Ethan Siegel's popular article: photon is converted into mass (or something) instantaneously. Since the photon travels by velocity $c$, it itself (because of special relativity) doesnt experience the time flow and its birth and death are (from his own point of view) instantaneous.

Maybe you mean what you really tell, but then it is a discussion about interactions and/or allowed final states. Since the photon is the lowest energy state (of a photon?) it cannot decay into something. And while it doesnt meet any interacting (virtual or other) particle, there is no reason for any transformation.

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