No, it isn't. It is convention which defines reference frames. You can take the same material objects making the same measurements and adopt a convention assigning any coordinates you like. As usual, one good example is the GPS Earth centered inertial frame in which none of the material measurement devices are at rest.vanhees71 said:As usual at this point I disagree. A reference frame is something real. You can take the corner of your lab and the clock on the wall as a reference frame as the most simple example. Physics is after all an empirical science and deals with the quantified description of real things you can measure with the adequate measurement devices. That can be a simple yard stick to measure distances up to a ultraprecise interferometer like LIGO to measure tiny distortions of its arms by hitting gravitational waves, but it's a material things that defines reference frames.
The material objects alone certainly don't define the frame, it clearly also requires a convention in addition to the material objects.vanhees71 said:to fix a frame to begin with you need material objects to define one frame.
You can use one set of objects to define a coordinate system and relabel it with other coordinates to define a different coordinate system. But the coordinate system is the frame, not the objects. If the objects were the frame you couldn't use the same objects to define two different frames.vanhees71 said:Sure you can use one frame and relabel it witah other coordinates, but to fix a frame to begin with you need material objects to define one frame.