In the context of classical physics, the concept of mass can be defined without requiring the existence of multiple material bodies. Mass is an intrinsic property of matter that determines its resistance to acceleration when subjected to a force. It is a fundamental property of an object regardless of its interactions with other objects.
Even if there were only one material body in the universe, it would still possess mass. Mass is not contingent upon the presence or interaction with other bodies. It is an inherent characteristic of matter itself.
In the framework of classical physics, an object's mass can be measured independently of other objects. For instance, the mass of an isolated object can be determined through various methods, such as measuring its gravitational interaction with other objects or applying forces to it and measuring its resulting acceleration.
However, it's worth noting that in the context of modern physics and general relativity, mass is considered to be a property that affects the curvature of spacetime. The presence of mass and energy, whether from a single body or multiple bodies, influences the geometry of the surrounding spacetime. This curvature then affects the motion of objects, including the paths they follow in the presence of gravitational forces.
In summary, according to classical physics, the concept of mass exists regardless of the presence of other material bodies. However, in the realm of modern physics, the interaction of mass with spacetime and the resulting gravitational effects depend on the distribution and arrangement of mass-energy in the universe.