Think about it more fundamentally. Instead of a person with senses, think of an object experiencing forces. Thats what an inertial reference frame means.
But senses are just ways for an object to experience forces.
I know if I’m hanging upside down because my senses are telling me my body is being pulled down from my head. I’m feeling the gravitational force pulling me down.
An object moving in the universe is indistinguishable to the universe moving around an object. To any observer or to the object itself the forces experienced are the same
Think about it more fundamentally. Instead of a person with senses, think of an object experiencing forces. Thats what an inertial reference frame means.
Exactly. Seeing was just an example. The whole universe moving around an object would cause that object to experience forces.
But senses are just ways for an object to experience forces.
I know if I’m hanging upside down because my senses are telling me my body is being pulled down from my head. I’m feeling the gravitational force pulling me down.
An object moving in the universe is indistinguishable to the universe moving around an object. To any observer or to the object itself the forces experienced are the same