An electron is a particle having mass. It is also a quantum excitation in the “electron-positron quantum field”. All fundamental particles are quantum field excitations. It is a particle with a certain amount energy.
The generator of time translation is energy – having energy is a kind of entity’s “gate pass”. Since persistence through time is what exists, it is possible to have more or less energy. It is possible to generate spatial translation using momentum, but not necessarily needing it.
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