I studied on YouTube that when mass is converted into energy, energy is converted into mass somewhere, but when I searched for this theory, I did not find it. Does anyone know what the name of this theory is, and if it is mentioned in a book, what is the name of that book?

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    $\begingroup$ I don’t know if it has a name, but it is incorrect $\endgroup$
    – Dale
    Jul 6, 2021 at 17:37
  • $\begingroup$ It may be an attempt to simplify special relativity so as to ease comprehension. $\endgroup$
    – Trebor
    Jul 6, 2021 at 17:43
  • $\begingroup$ read about conservation of energy and momentum in special theory of relativity. It's not exactly that the mass is changing, it's the change in momentum which induces change in relativistic energy $\endgroup$
    – KP99
    Jul 6, 2021 at 17:47

1 Answer 1


It is incorrect: mass can be converted into energy without energy being converted into mass somewhere. For example, when a Higgs boson in the LHC decay into two photons ($H \rightarrow \gamma \gamma$), the mass of the Higgs boson ($125 \;\text{GeV}/c^2$) turns into the energy of two massless photons, without any other process converting some energy into mass.


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