#### Erland

Science Advisor

- 734

- 134

Anyway, is it correct that in defining the Lorentz group, one assumes that the spacetime distance dx

^{2}+dy

^{2}+dz

^{2}-c

^{2}dt

^{2}is preserved by the Lorentz transformations?

I am not willing to take this as an axiom (for physics), except when this distance is 0, since this is just another way of stating the invariance of the light speed. Otherwise, it seems in no way obvious and no

*simple*consequence of Einstein's postulates.