Final answer:
A perpetuum mobile cannot work in a vacuum or any other environment because it would violate the law of conservation of energy.
Step-by-step explanation:
A perpetuum mobile, also known as a perpetual-motion machine, is a hypothetical machine that is designed to operate or produce useful work indefinitely without an input of energy. However, according to the first law of thermodynamics, which is the law of conservation of energy, energy cannot be created or destroyed, only converted from one form to another. Therefore, it is not possible to create a perpetuum mobile that works in a vacuum or any other environment. The machine would need an external energy source to operate continuously.