Critique of the Concept of Inertia

There are two forces associated with mass: static and dynamic force, or, by other names, the weight and inertial force. The mass, the source of these forces, is defined once by Newton’s law of gravitation for static force and a second time by the equation of motion F = ma for dynamic force. It is assumed that the masses in these two cases are equivalent. Einstein extended this equivalence and assumed that the gravitational field and acceleration are equivalent. I will argue that the gravitational field and acceleration are not equivalent. The force caused by the gravitational field has a reaction force on another mass, satisfying the principle of action and reaction. Assigning an inertial property to the mass and explaining inertial force by inertial mass that resists acceleration in space violates the principle of action and reaction. The principle of action and reaction is satisfied in every experiment with mass dynamics on the Earth. All our experience with mass dynamics is based on observations and experiments on or near the Earth. Discussed is the explanation of the inertial force by the field theory that satisfies the principle of action and reaction. According to this concept, every mass that accelerates relative to the centre of masses creates a dynamic gravitational field in the space around it, and this field creates inertial force. In the field concept of inertial force, the mass of the Earth plays a fundamental role in creating an inertial force. The most serious criticism of the field concept of inertial force is that such a field may not exist, as no one has detected it. A laboratory experiment that can detect a dynamic gravitational field or invalidate the force field concept of inertial force is proposed to address that criticism. The experiment is designed to test if the principle of action and reaction is valid for mass dynamics or if acceleration and gravitational field are equivalent. Mentioned are some observations in nature, and it is shown that the field theory of inertial force agrees with those observations. It is pointed out that astronomical observations of the velocity of the stars in the galaxy suggest that a dynamic gravitational field could exist.