Final answer:
The second postulate of relativity, concerning the constant speed of light, follows from the first, which states that the laws of physics are constant in all inertial frames because both postulates ensure a consistent universe where the speed of light remains invariant across different frames of reference.
Step-by-step explanation:
The question is addressing the relationship between Einstein's first postulate of relativity and the second postulate. The first postulate states that the laws of physics are identical in all inertial frames, which implies that the outcomes of physical processes are consistent regardless of the inertial frame of reference. This sets the stage for the second postulate about the constant speed of light, which is often seen as following the first postulate because, for both observers in inertial frames (as described in the first postulate), the speed of light must be measured to be the same.
Hence, while the first postulate ensures uniformity in physical laws across inertial frames, the second introduces a constant - the speed of light - that remains invariant across these frames, reinforcing the initial postulate's claim.
Redefinitions of concepts like energy and momentum to satisfy the first postulate then lead to the same prediction by the second postulate concerning the speed of light. These redefined concepts support the famous equation E = mc2, which correlates energy to mass, showing logical consistency between the postulates.