In classical mechanics, the first law of motion states that an object at rest will remain at rest, and an object in motion will continue moving at a constant velocity unless acted upon by an external force. This concept is closely related to the concept of inertia. However, when it comes to quantum particles, the situation is fundamentally different due to the principles of quantum mechanics.
In quantum mechanics, particles do not have definite positions and velocities in the same way as classical objects. Instead, their behavior is described by wave functions, which provide probabilities for the different outcomes of measurements. Quantum particles can exhibit wave-like properties such as superposition and entanglement, which are not present in classical objects.
Regarding your question, two quantum particles cannot be considered as comoving with respect to each other in the same sense as classical objects. The concept of constant speed and parallel motion does not directly apply to quantum particles. In quantum mechanics, the behavior of particles is described by wave functions that evolve over time according to the Schrödinger equation, which determines the probabilities of different measurement outcomes.
However, it is worth noting that quantum particles can be entangled, which means their wave functions can become correlated in such a way that the state of one particle is directly related to the state of the other, regardless of the distance between them. This correlation allows for instantaneous changes in the state of one particle when the state of the other particle is measured.
In summary, the classical concept of inertia and the first law of motion do not directly apply to quantum particles. Quantum mechanics introduces a new set of principles and behaviors that govern the behavior of particles at the microscopic scale, and concepts such as constant velocity and parallel motion need to be interpreted in the context of quantum mechanics and its mathematical framework.