What does the principle of relativity state regarding observers?

The principle of relativity asserts that the laws of physics are the same for all observers, irrespective of their relative motion. This means that if two observers are moving relative to one another, they will still observe the same physical laws governing motion, energy, and other phenomena. This principle emphasizes that physics is not dependent on the specific frame of reference of the observer; rather, the laws themselves are constant regardless of the observer's state of motion.

This particular aspect underpins much of modern physics, particularly in the theory of relativity proposed by Albert Einstein, which revolutionized the understanding of space and time. Thus, the assertion that all physical laws appear constant regardless of the observer aligns perfectly with the principle of relativity.