Special Theory of Relativity
58Lorentz, Poincare and Einstein are considered to be the 3 codiscovers of Special Relativity Theory
The most amazing article relating to special relativity to be published before 1900 was a paper of Henri Poincaré La mesure du temps which appeared in 1898. In this paper Poincaré says
... we have no direct intuition about the equality of two time intervals.
The simultaneity of two events or the order of their succession, as well as the equality of two time intervals, must be defined in such a way that the statements of the natural laws be as simple as possible.
By 1900 the concept of the ether as a material substance was being questioned. Paul Drude wrote
The conception of an ether absolutely at rest is the most simple and the most natural - at least if the ether is conceived to be not a substance but merely space endowed with certain physical properties.
Henri Poincaré, in his opening address to the Paris Congress in 1900, asked Does the ether really exist? In 1904 Poincaré came very close to the theory of special relativity in an address to the International Congress of Arts and Science in St Louis. He pointed out that observers in different frames will have clocks which will
... mark what on may call the local time. ... as demanded by the relativity principle the observer cannot know whether he is at rest or in absolute motion.
The year that special relativity finally came into existence was 1905. June of 1905 was a good month for papers on relativity, on the 5th June Poincaré communicated an important work Sur la dynamique de l'electron while Einstein's first paper on relativity was received on 30th June. Poincaré stated that It seems that this impossibility of demonstrating absolute motion is a general law of nature. After naming the Lorentz transformations after Lorentz, Poincaré shows that these transformations, together with the rotations, form a group.
Einstein's paper is remarkable for the different approach it takes. It is not presented as an attempt to explain experimental results, it is presented because of its beauty and simplicity. In the introduction Einstein says
... the introduction of a light-ether will prove to be superfluous since, according to the view to be developed here, neither will a space in absolute rest endowed with special properties be introduced nor will a velocity vector be associated with a point of empty space in which electromagnetic processes take place.
Inertial frames are introduced which, by definition, are in uniform motion with respect to each other. The whole theory is based on two postulates:-
1. The laws of physics take the same form in all inertial frames.
2. In any inertial frame, the velocity of light c is the same whether the light is emitted by a body at rest or by a body in uniform motion.
Einstein now deduced the Lorentz transformations from his two postulates and, like Poincaré proves the group property. Then the FitzGerald-Lorentz contraction is deduced. Also in the paper Einstein mentions the clock paradox. Einstein called it a theorem that if two synchronous clocks C1 and C2 start at a point A and C2 leaves A moving along a closed curve to return to A then C2 will run slow compared with C1. He notes that no paradox results since C2 experiences acceleration while C1 does not.
shaq5150 14 months ago
Of course, although the question as to whether, and to what extent, the thinking of either Lorentz or Poincare comprise some form of precursor to Einstein's presentation of the theory of relativity has been much debated, I have personally never encountered the relationship stated as that "Lorentz, Poincare and Einstein are considered to be the 3 codiscover[er]s of Special Relativity Theory." In the first instance, the bringing together of the terms 'theory' and 'discovery' appears to go against the role of theory in scientific description. 'Facts' (to use a loose term) are discovered; theory is 'developed', and may be so developed either from such experimentally-verified facts, or else on the basis of a small number of postulates which are deemed to be capable of leading to a theory which will only be subject to experimental verification upon development. Einstein's theory of relativity may be considered, in my view, to be of the latter form.
That Poincare may have made some or other statements that offer resemblances to conclusions that may be drawn from the theory of relativity - such as that "we have no direct intuition about the equality of two time intervals" - does not amount to theory. Indeed, although Poincare did indeed appear to recognise the validity of applying the restricted principle of relativity (as it later came to be known), he never proceeded to build any complete theory around it. Nor did he permit himself to accept, or even fully acknowledge, Einstein's theory once developed. As such, in my view, it is wholly untenable that he could be thus be regarded as a co-founder of any such theory as that of relativity. Poincare did pursue the implications of Lorentz's 'local time' for systems in motion with respect to a stationary ether but, like Lorentz himself, he never identified this with the actual time as experienced, and thus measurable, within the moving frame. For Poincare, as for Lorentz, it remained a "mathematical convenience," and nothing more.
With this limitation, neither Lorentz nor Poincare could be regarded as having contributed to the development of the 'theory' of relativity, in the sense that entire basis of this theory could be said to lie in Einstein's bold readiness to give up the one-for-all nature of time.
Lorentz, at least, did present a theory, but one that remained fixed in its conception of an absolute ether at rest, and which thereby required the addition of a number of arbitrary hypotheses, such as the FitzGerald contraction. (Note that, in Einstein's theory, this is not a contraction at all, in the sense that Lorentz interpreted the effect, and thus it is preferable to avoid such statements as that, in Einstein's 1905 paper, "Then the FitzGerald-Lorentz contraction is deduced.")
The precise relationship between the ideas of Lorentz, Poincare and Einstein is a complex one. Yet to say that the first two were 'co-developers' of a theory that at least Poincare could never bring himself to ultimately accept, is in my view to misunderstand what exactly it is that this theory actually expresses (as different from what is contained in Lorentz's theory) and what actually constitutes a 'theory' (the development of which Poincare avoided altogether).