This document contains comments about the document "Principle of relativity" in Wikipedia
• The text in italics is copied from that url
• Immediate followed by some comments
In the last paragraph I explain my own opinion.

### Introduction

The article starts with the following sentence.
In physics, the principle of relativity is the requirement that the equations describing the laws of physics have the same form in all admissible frames of reference.
It is very important to know:
• Which laws of physics are meant
• What means all admissible frames, with the emphasis of laws.
• That physical processes have nothing to do with reference frames. They are a usefull tool to describe the evolution of physical processes i.e. experiments.
For example, in the framework of special relativity the Maxwell equations have the same form in all inertial frames of reference.
In the framework of general relativity the Maxwell equations or the Einstein field equations have the same form in arbitrary frames of reference.
That maybe true (and most probably is) but that is not a guarantee that these equations describe the underlying physical processes correctly.

### 2. Basic relativity principles

Certain principles of relativity have been widely assumed in most scientific disciplines.
Relativity principles should be beyound the basic scientific disciplines.
One of the most widespread is the belief that any law of nature should be the same at all times; and scientific investigations generally assume that laws of nature are the same regardless of the person measuring them.
The processes that are involved in the evolution of the universe do not have to be the same all the time. As such the laws or equations that describe these processes can be a function of the age of the universe. Friedman's equation is one example. Other examples are the shape of galaxies.
Any principle of relativity prescribes a symmetry in natural law: that is, the laws must look the same to one observer as they do to another.
This sentence is not clear. Different observers can observe and perform the same experiments. The descriptions and results normally are the same but it is not a must.
For example to drop a ball in a train at rest versus a moving train is not the same experiment. The laws that describe these experiments should be different (i.e. take the speed into account)
For example, if two observers at different times see the same laws, then a quantity called energy will be conserved.
Observers do not see laws. Observers observe experiments.
In this light, relativity principles make testable predictions about how nature behaves, and are not just statements about how scientists should write laws.