if you see an object approaching you, there are three basic possibilities.
first, you are stationary and the object is moving towards you.
second, the object is stationary and you are moving towards it.
third, you are both moving towards each other.
who is still and who is moving can only be decided with regard to a fixed reference frame, for example a lamp post at the side of the road. if the lamp post is stationary relative to you, then you know that you must be stationary, and the object is approaching you.
it could be argued that the lamp post is moving with the earth's rotation and therefore not suitable as a fixed reference point, as you are also moving together with the earth.
the consequence means that it cannot be decided who or what is moving
first, you are stationary and the object is moving towards you.
second, the object is stationary and you are moving towards it.
third, you are both moving towards each other.
who is still and who is moving can only be decided with regard to a fixed reference frame, for example a lamp post at the side of the road. if the lamp post is stationary relative to you, then you know that you must be stationary, and the object is approaching you.
it could be argued that the lamp post is moving with the earth's rotation and therefore not suitable as a fixed reference point, as you are also moving together with the earth.
the consequence means that it cannot be decided who or what is moving