momentum 4-vector energy–momentum relation energy momentum
The invariant magnitude of the momentum 4-vector generates the energy–momentum relation:






P


2


=

η

μ
ν



P

μ



P

ν


=
−


(


E
c


)


2


+

p

2


.


{\displaystyle \mathbf {P} ^{2}=\eta ^{\mu \nu }P_{\mu }P_{\nu }=-\left({\frac {E}{c}}\right)^{2}+p^{2}.}


