Yes, according to the principles of relativity in physics, both energy and momentum are also relative to the observer's frame of reference. This is a fundamental concept in the theory of special relativity, which was developed by Albert Einstein.
In classical physics, energy and momentum were considered to be absolute quantities. However, in special relativity, it was realized that the laws of physics should be consistent for all observers, regardless of their relative motion. As a result, the concepts of energy and momentum had to be redefined.
According to special relativity, the energy of an object is not solely determined by its mass and velocity but also includes a contribution from its rest mass (mc²), where m is the mass of the object and c is the speed of light. This means that different observers, moving relative to each other, will measure different values of energy for the same object.
Similarly, momentum is also relative in special relativity. The classical definition of momentum (mass times velocity) is modified in relativity to include a factor of γ (the Lorentz factor), which depends on the relative velocity between the object and the observer. As a result, observers in different frames of reference will measure different values of momentum for the same object.
It's important to note that while energy and momentum are relative, their differences are still related through the principle of conservation. The total energy and momentum of a system, including all its objects and particles, are conserved in all inertial frames of reference. This conservation principle ensures that energy and momentum remain meaningful and consistent even though their values may differ between observers.