Limitless-X's video: Mass energy equivalence E mc2 briefed

Einstein correctly described the equivalence of mass and energy as “the most important upshot of the special theory of relativity” (Einstein 1919), for this result lies at the core of modern physics. Many commentators have observed that in Einstein’s first derivation of this famous result, he did not express it with the equation E=mc2. Instead, Einstein concluded that if an object, which is at rest relative to an inertial frame, either absorbs or emits an amount of energy L, its inertial mass will correspondingly either increase or decrease by an amount L/c2. In Newtonian physics, inertial mass is construed as an intrinsic property of an object that measures the extent to which an object resists changes to its state of motion. So, Einstein’s conclusion that the inertial mass of an object changes if the object absorbs or emits energy was revolutionary and transformative. For as Einstein concluded “If the theory agrees with the facts, then radiation transmits inertia between emitting and absorbing bodies” (Einstein, 1905b). Yet, in Newtonian physics, inertia is not the kind of thing that can be transmitted between bodies. Over a century after Einstein’s first derivation of mass-energy equivalence, as his famous result is called because one can select units in which one can express it with an equation of the form E=m, the result continues to receive outstanding empirical support. Furthermore, as the physicist Wolfgang Rindler has pointed out, the result “has been found applicable and valid in many branches of physics, from electromagnetism to general relativity” (Rindler 1991, p. 74). Thus, from Rindler’s perspective, which is shared by many physicists, mass-energy equivalence “… is truly a new fundamental principle of physics” (Rindler 1991, p. 74). The two main philosophical questions surrounding Einstein’s equation, which are the focus of this entry, concern how we ought to understand the assertion that mass and energy are in some sense equivalent and how we ought to understand assertions concerning the convertibility of mass into energy (or vice versa). The equation E=mc2 is, arguably, the most famous equation in 20th century physics. To appreciate what Einstein’s famous result is about, and what it is not about, we begin in Section 1 with a description of the physics of mass-energy equivalence. In Section 2, we survey six distinct, though related, philosophical interpretations of mass-energy equivalence. We then discuss, in Section 3, the history of derivations of mass-energy equivalence and its philosophical importance. Section 4 is a brief and selective account of empirical confirmation of Einstein’s result that focuses on Cockcroft and Walton’s (1932) first confirmation of mass-energy equivalence and a more recent, and very accurate, confirmation by Rainville et al. (2005).