this system there is no actual matter, there are only holes in the aether." Finally he repeats this exact problem of "Newton's principle" from 1904 again in 1908 publication in his section on "the principle of reaction" he notes that the actions of radiation pressure cannot be tied solely to matter in light of Fizeau's proof that the Hertz notion of total ether drag is untenable. This, he clarifies in the next section in his own explanation of Mass–energy equivalence: Thus Poincaré's mass of a fictitious fluid led him to, instead, later find that the mass of matter itself was "fictitious." Einstein's own 1906 publication grants credit to Poincare for previously exploring the mass-energy equivalence and it is from these comments that it is commonly reported that Lorentz ether theory is "mathematically equivalent." Momentum and cavity radiation However, Poincaré's idea of momentum and mass associated with radiation proved to be fruitful, when in 1903 Max Abraham introduced the term „electromagnetic momentum“, having a field density of per cm3 and per cm2. Contrary to Lorentz and Poincaré, who considered momentum as a fictitious force, he argued that it is a real physical entity, and therefore conservation of momentum is guaranteed. In 1904, Friedrich Hasenöhrl specifically associated inertia with radiation by studying the dynamics of a moving cavity. Hasenöhrl suggested that part of the mass of a body (which he called apparent mass) can be thought of as radiation bouncing around a cavity. The apparent mass of radiation depends on the temperature (because every heated body emits radiation) and is proportional to its energy, and he first concluded that . However, in 1905 Hasenöhrl published a summary of a letter, which was written by Abraham to him. Abraham concluded that Hasenöhrl's formula of the apparent mass of radiation is not correct, and on the basis of his definition of electromagnetic momentum and longitudinal electromagnetic mass Abraham changed it to , the same value for the electromagnetic mass for a body at rest. Hasenöhrl recalculated his own derivation and verified Abraham's result. He also noticed the similarity between the apparent mass and the electromagnetic mass that Poincaré would comment on in 1906. However, Hasenöhrl stated that this energy-apparent-mass relation only holds as long a body radiates, i.e. if the temperature of a body is greater than 0 K. Modern view Mass–energy equivalence The idea that the principal relations between mass, energy, momentum and