Special Relativity Year 3

Why is Special Relativity… Special?

Because it is specific to flat space-times

Restate the first postulate of SR in terms of invariance

The laws of physics are co variant, frame invariant, and form invariant in flat space-times

Define an invariant

If an equation is invariant, it means it is completely general– you do not need to change the form of the equation, or the constants, to apply the equation to another relevant problem

Define form invariant

If an equation is form invariant, it means that the equation will retain the same form when applied to another relevant problem. For instance an inverse-square law would remain an inverse-square law

Define frame invariant

If an equation is frame invariant, it means that the equation does not change provided that the relative frame of the observer has been accounted for.

If an equation is not completely frame invariant then we might add some specificity to this description… For instance we might say that the equation is frame invariant if we consider only inertial frames.

Define Co-variant

This has a more mathematical meaning; in terms of relativity it means that the system of equations will adapt to the shape of the underlying space-time (so the “co” here means “with” as in “co-operate”), this is one of the properties of general laws of physics that enables them to comply with other forms of invariance.