The energy is not Lorentz invariant quantity since energy depends on the state of motion. Then how come the physics is the same in every inertial reference frame when every inertial frame measures different energy?

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    $\begingroup$ Energy isn’t invariant under Galilean boosts either, so you could ask the same question about Newtonian physics. $\endgroup$
    – Ghoster
    Commented Nov 10, 2023 at 22:49
  • $\begingroup$ Okay thanks for the additional information, but why are these things okay? Isn't it absurd to think that in one frame the energy measure 300 MeV and in other frame it measure 200 GeV ? $\endgroup$ Commented Nov 10, 2023 at 22:54
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    $\begingroup$ No, it is not absurd. It’s a new concept to you and so it’s surprising, that’s all. It’s unfortunate that you didn’t get used to this idea in your Newtonian mechanics course. $\endgroup$
    – Ghoster
    Commented Nov 10, 2023 at 23:01
  • $\begingroup$ Okay, thanks for your time. $\endgroup$ Commented Nov 10, 2023 at 23:07
  • $\begingroup$ @Ghoster by the way, is the center-of-mass energy in collider experiment Lorentz invariant ? $\endgroup$ Commented Nov 10, 2023 at 23:21

1 Answer 1


The key point is that energy is still conserved within each frame. As long as all of our physical laws are the same (e.g. conservation of energy), then the lack of Lorentz invariance is not a problem. There are lots of things that are not agreed upon among change of coordinates, but as long as they facilitate the same physical processes, it's fine. It just means that there are different ways to describe the same physical process. This is a concept we are introduced to as early as kinematics in choosing convenient bases to decompose our force vectors.


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