In my lecture notes on General Relativity, I have the following statements that are said to be wrong in Special Relativity:
- Every physical observer measures a speed of light equal to $c$.
- Every physical observer measures the same speed of light.
- For every physical observer the speed of light is constant.
In a previous course I took, where some Special Relativity was covered, these three statements were assumed to be correct. I'm actually confused right now. Can someone please clarify what's going on?