- #36

strangerep

Science Advisor

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The "invariant speed" in Galilean relativity turns out to be ##\infty##.Galilean relativity doesn't have an invariant speed and it has spatial isotropy and homogenity. Galilean boosts in one axis are also a 1-parameter Liegroup (don't they?). So I don't see how only using the postulates you mention you get an invariatn speed, since those postulates are also in the galilean relativity.

In the more general derivation, one actually derives a constant with dimensions of inverse speed squared. SR corresponds to the choice of ##1/c^2## for this constant. Galilean relativity corresponds to the choice ##0##, which is equivalent to letting ##c\to\infty##.