How does einstein's equation change the law of conservation of energy?

Einstein said (among many other things) that:

##E = mc^(2)##

The consequence of this is that and mass can, theoretically, be interconverted. As a result, it's possible for mass to be converted to energy - something that violates the law of conservation of mass, but is observed in . Likewise, if energy can be converted into mass during a process, the amount of energy will be different after the change.

As a result, there's no law of or law of conservation of mass anymore. Instead, we get the law of conservation of mass/energy which states that: For any change, the amount of mass and energy present in the beginning will be equivalent to that present when the process has ended (though one may have converted to the other).

OK.