To what? If you are referring to relation of MASS and energy (special relativity, initially proposed by Einstein), energy is relative to mass because the more mass an (arbitrary) object the more energy it contains. That is the very simplest explanation of it. Although the theory of relativity encompasses a lot more, complex ideas, such as time dilution. Google it (the theory of special relativity) to find out more.
Einstein developed the theory of mass-energy equivalence, which is famously expressed as E=mc^2. This breakthrough was part of his theory of relativity and fundamentally changed our understanding of the relationship between mass and energy.
E=mc^2
Einstein's theory of relativity states that mass and energy are inter convertible. The theory can be numerically verified by the mass energy equation i.e. E=mc2 (where E is energy, m is mass and c is the velocity of light).
Einstein's theory of relativity consists of two theories: Special Relativity and General Relativity. In Special Relativity, the letter "E" stands for energy, and the letter "m" stands for mass. The famous equation E=mc^2 shows the equivalence of energy and mass. In General Relativity, the letter "G" stands for gravity, and the theory describes gravity as a curvature of spacetime caused by mass and energy.
Einstein discovered mass and energy relation (e=mc2)
According to the principle of mass-energy equivalence (E=mc^2), energy and mass are interchangeable. In theory, energy can be created without mass, such as in the case of virtual particles popping in and out of existence in quantum mechanics. These particles have energy but no permanent mass.
Mass-energy equivalence
...and Mass
The famous equation is E = m c squared. c is the speed of light- a constant. m is mass. Mass is the answer to your question. Mass can be converted to a lot of energy, but not easily, unfortunately.
his theory of relativity. E=mc2 saying mass is energy energy is mass. and comparing space and time the same way .
Einstein - E=MC2E = EnergyM = MassC = speed of lightBasically mass and energy are interchangeable