The First Postulate (1)

Here is the first postulate:

The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems of co-ordinates in uniform translatory motion.

How do we know the first postulate is right?

To make sure the first postulate is a reasonable assumption, we have to:

1. Find a physical law, in which the reference frame plays a role
2. Prove that this physical law behaves the same in all reference frames
3. There exists no physical law, which contradicts the first postulate

There is also a hidden assumption here. The physical law we choose must have a mathematical representation, so that:

1. Using it as a base, we can build Special Relativity from it.
2. Using it as a test case, we can validate Special Relativity against the first postulate.