Free Space?

One of the basic assumptions in the whole of physics is the concept of motion and forces referenced to free space.

It is a well known principle that a spinning gyroscope always points in the same direction relative to free space. Similarly a planet spinning around the sun always follows an almost constant elliptical orbit relative to free space.

What is meant by spinning or moving in a circular path?

It is all referenced to something, which we call free space.

But what is free space?

In the case of a planet spinning around the sun, or any other lighter object spinning around a "central" large mass, what is it that prevents the two objects from simply moving directly towards each other?

We say it is the combination of velocity and mass (inertia), which the lighter object has relative to free space, and the force of attraction between the two (gravitation), which causes the lighter object to move in a circular (or elliptical) path around the central large mass.

Why does free space have the magical property of preventing two objects from moving towards each other?

In the case of a planet spinning around the sun, one would think that other objects in the universe (except other nearby planets of the solar system) would be so far away that their gravitational influence on the spinning planet would be negligible. In which case, why could not free space be moving with the planet so that the planet moves in a straight line to the sun?

What is free space?

What is free inertia?

Does anyone get what I am trying to say?