Published online by Cambridge University Press: 28 February 2022
In 1905 Einstein derived the Lorentz transformations linking inertial coordinate systems. He took as his central principles the relativity principle (RP) and the light postulate (LP), and assumed along the way a symmetry that has become known as ‘spatial isotropy’ (Berzi and Gorini 1969). This symmetry will be defined below but it basically requires that boosting has the same effect whether to the right or left or to the north or south etc. Since it really is a symmetry about boosts I shall call it ‘boost isotropy'.
The purpose of this paper is to explore the relativistic kinematics (both Einsteinian and Galilean) resulting from implementing RP but breaking with the venerable tradition of implementing ‘boost isotropy’.
I wish to thank Jeremy Butterfield for comments on a previous draft, Andrew Hodges for help with the maths and particularly Harvey Brown for lots of help and stimulating discussion. Any errors are my responsibility.