By A. EINSTEIN. June 30, It is known that Maxwell's electrodynamics—as usually understood at the present time—when applied to moving bodies, leads. ELECTRODYNAMICS OF MOVING BODIES Doc. ON THE ELECTRODYNAMICS OF MOVING BODIES by. A. Einstein [Annalen der. Physik 17 (). On the Electrodynamics of Moving Bodies ( edition) The Principle of Relativity: Original Papers by A. Einstein and H. Minkowski.

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phenomena in a system moving with any velocity less than that of light / by H.A. Lorentz -- On the electrodynamics of moving bodies / by A. Einstein -- Does the. physics students we studied the Special Theory of Relativity. Yet Albert Einstein's original paper that started it all, “On the. Electrodynamics of Moving Bodies,”[1]. ELECTRODYNAMICS. OF MOVING BODIES. By A. Einstein. June 30, It is known that Maxwell's electrodynamics--as usually understood.

If this were the case scientific theories would face the serious problem of underdetermination. That is, there would always be a number of theories, which are able to explain the empirical evidence, although they fundamentally disagree about their theoretical structure.

For instance the Copernican model of the solar system explains the same observational evidence as the Ptolemaic account although the Copernican model is based on the principle of heliocentrism, while the Ptolemaic account embraces the principle of geocentrism. In this situation Einstein recommends pragmatically to distinguish a logical from a practical point of view.

From the logical point of view, Einstein grants that there are always numerous theoretical accounts, which could in principle account for the available evidence. For there seems to be no limit to the number of competing constructions, which, at least in principle, could claim to give a coherent and simple account of the available phenomena. This is due to the fact that theories are the result of human ingenuity. Yet in practice, the number of available theories is always limited.


Einstein did not believe that many competing representations of the empirical world could be sustained. He goes even further: he believes that there is one correct theory. The structure of the external world has the power to eliminate many rival accounts. The surviving theory displays such a degree of rigidity that any modification in it will lead to its falsehood. Although we are free to insert any word into the columns and rows of a word puzzle, this freedom is very restricted.

They pose no problem in terms of underdetermination. Rival accounts therefore pose a problem from the point of view of underdetermination.

In the practice of science, however, there is little underdetermination. How can this be explained? Einstein locality, logical simplicity and unification are methodological constraints, since they are principles of the methods of science. Compatibility with available and new evidence is an empirical constraint. In the present context the methodological constraints are of lesser importance than some of the other constraints, which are associated with the theory of relativity.

In particular, as we shall see, the light postulate, relativity principles, covariance and invariance principles. We can characterize constraints as restrictive conditions of an empirical or theoretical kind, which descriptive and explanatory accounts must satisfy to count as viable candidates for the scientific description and explanation of the natural world.

With respect to the theory of relativity, Einstein holds that the interplay of specific constraints—like covariance, invariance, relativity—creates a fit of the theory or model with the evidence extracted from the external world.

Any modification, he holds, would destroy the coherence of the theory of relativity. The representation is illustrated in terms of fit, as in the analogy of the crossword puzzle.

The structure of the systems is the work of reason; the empirical contents and their mutual relations must find their representation in the conclusions of the theory.

In the possibility of such a representation lies the sole value and justification of the whole system, and especially of the concepts and fundamental principles which underlie it.

In the simplest case, a model represents the topologic structure of a system; e. The models used in the theory of relativity are more sophisticated structural models, which combine a topologic with an algebraic structure. The algebraic structure of the model expresses the mathematical relations between the components of the model.

This is its topologic aspect. But the main interest lies in the algebraic structure, e. To carry out the measurements, measuring rods are placed along the radius and tangentially to the edge of the disc. Due to length contraction of the tangential rods the circumference will appear greater on B than on A.

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Now place two similar clocks on B, one at the centre, C1 and one at the periphery, C2. Judged from A, C2 will go slower than C1. We may assume that no faulty instruments are involved. These respective measurements are objective.

Observers on the respective discs will regard their respective measurements as accurate. Mathematically, the thought experiment stresses the effect of motion on the measurement of the parameters. Note that the algebraic structure implied by Euclidean geometry fails and must be replaced by a structure provided by Riemannian geometry. The theory of relativity satisfies a number of empirical and theoretical constraints, which improve its fit to the external world.

The empirical facts comprise Einstein famous predictions: the red shift of light as a function of gravitational field strengths and the bending of light rays in the vicinity of strong gravitational fields. He also explains the perihelion advance of Mercury and other planets. Einstein turned this value into a theoretical postulate such that the speed of light becomes the limit velocity, which no material particle can reach.

In the language of the Minkowski representation of space-time this means that from any event, E, light signals converge from the past and diverge into the future at a constant speed, forming past and future cones. The light cones do not tilt. And all observers measure the same velocity for c, irrespective of the direction and their state of motion with respect to the light source.

He complained that according to the then current view an asymmetry of explanation for an observationally indistinguishable phenomenon occurred. If the coil is in motion with respect to the magnet at rest in the ether , the charges in the coil experience a magnetic force, which pushes the electrons around the coil, inducing a current. If the magnet is in motion with respect to a coil at rest, the magnetic force is no longer the cause of the current, for no magnetic force applies to charges at rest.

The magnet now produces an electric field in the coil, resulting in the current. To avoid this asymmetry of explanation—an asymmetry not present in the phenomena—Einstein postulated the physical equivalence of reference frames. In its general form the principle of relativity states that all coordinate systems, which represent physical systems in uniform or non-uniform motion with respect to each other, must be equivalent from the physical point of view.

So it is not admissible that an induced current is explained differently, depending on whether the magnet or the coil is in motion. They are subject to various symmetry operations, like rotation or translation in space and time. The Special theory obeys the Lorentz-transformations, because the Galilean transformations fail as we approach the speed of light.

The Galilean transformations, for instance, result in different values for the speed of light, if we change from a stationary to a moving reference frame. The Lorentz-transformations deal with space-time transformations of a global kind; that is, they are constant throughout the space-time region. They form a symmetry group. The General theory requires a larger symmetry group. Symmetry constraints emphasize physical aspects: the symmetry operations return some values of parameters as invariant like the space-time interval and leave others as variant like the clock readings in different reference frames, in constant motion with respect to each other.

Symmetries result from transformations that leave all relevant structure intact. We are familiar with such symmetry transformations in daily life. We easily change the clock as we travel between different time zones. But the tennis games we play at home and abroad are the same as far as the physical parameters are concerned. The modern use is quite different from the way Einstein uses the notion of covariance. Einstein associates covariance with the transformation rules of the theory of relativity.

This leads to the characterization of covariance as form invariance. For Einstein a fit must exist between the theory of relativity and the material world. We explicated fit in terms of the satisfaction of constraints, associated with the theory of relativity. If their amount and their interconnections can be increased, then many scientific theories will fail to satisfy the constraints.

It will usually leave us with only one plausible survivor. For instance, after the development of the Special theory, Einstein increased the constraints on an admissible relativity theory. Inertial reference frames should not be privileged over non-inertial frames. This extension of the relativity principle and the demand of covariance lead to the General theory of relativity.

This theory was able to explain the perihelion advance of Mercury, where Newtonian mechanics had failed. It would be exaggerated to claim that there is such a tight fit between the theory and the world, that there is a one-to-one mapping of the theoretical with the empirical elements.

For instance, the evidence does not tell us whether space-time exists, devoid of all matter. But Einstein holds that one theory always satisfies the constraints better than its rivals.


It does not follow from this argument that the survivor—let us say the theory of relativity—will be true. It does follow that the process of elimination will leave us with the most adequate theoretical account presently available.

New experimental or observational evidence may force us to abandon this survivor.

The desire for unification and logical simplicity may persuade us to develop alternative theoretical accounts. Although Einstein does claim that there is one correct theory, he cannot mean this in an absolute sense. His insistence on the eternal revisability of scientific theories, including constraints, speaks against this interpretation.

What he must mean is that there is always one theory, at any one point, which best fits the available evidence. This one theory copes best with all the constraints, which logic and evidence erect; but there is nothing final about such a theory; it will always remain falsifiable. Each camp can claim textual evidence for its preferred interpretation [Frank ] [Holton ; ] [Howard, ; ; ]. According to this interpretation there exist logically incompatible theories, which nevertheless are equally compatible with the evidence.

Einstein actually employs these constraints, as we have seen, to argue in favour of the relativity theory. Discussions of holism usually highlight the radical underdetermination of an entire theory by empirical evidence. According to this aspect, theories are structured conceptual systems, which entertain many mathematical and conceptual interrelations between them.

This aspect makes the deducibility of empirical laws from more fundamental laws possible.

Duhem, for instance, appeals to an analogy of science with an organism, in which one part cannot be made to function except when the parts that are most remote from it are called into play, some more than others, but all to some degree. Einstein is fond of the view that theoretical constructions are not inductive generalizations from experience but free inventions of the human mind.

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This fit is achieved in the theory of relativity, we suggested, through the introduction of constraints. The increase in constraints—extension of the relativity principle to non-inertial motion, the introduction of the principle of equivalence and the form-invariance of laws covariance principle —takes Einstein from the STR to the GTR.

Einstein reflected on the status of geometry in the light of the GTR. But Einstein sees an important difference between an axiomatic and a practical geometry: the former makes no reference to the world of experience, whilst the latter does.

The question whether the practical geometry of the universe is Euclidean or not, has a clear meaning, and its answer can only be furnished by experience. Einstein certainly approved of this way, in which Lenzen and Northrop characterized his epistemological position See [Lenzen ] [Northrop ] [Einstein b, ]. It simply regards scientific theories as hypothetical constructs, free inventions of the human mind.

But there is also an external world, irrespective of human awareness. To be scientific, theories are required to represent reality. They represent reality by satisfying both empirical and theoretical constraints. A theory is not a mirror image of the world. It is a mathematical representation, which provides coherence of the empirical data and shows their interconnections.

Theories are hypothetical, approximate constructions, which in a process of fitting and refitting, deliver a coherent picture of the external world.

In human efforts to understand the world, experience and reason go hand in hand. Such coordinate systems are well-suited to represent physical systems, since they can be regarded as structural models of the target systems. Physical systems typically display structures, consisting of relata and relations. As the models of the relativity theories are able to represent both the topologic and algebraic aspects inherent in physical systems, they can be said to represent the structure of physical systems.

Howard, , ] These representational claims cover both the relata fields, material particles, reference frames and the relations the mathematical relations between the relata. Given that scientific theories manage to represent aspects of the external world, what picture of reality does the relativity theory espouse? What is Reality? Such views have changed with the progression of physical theories. There was a time when physicists liked to think of the world as a massive clockwork.

Particles populated the universe.

Only their primary qualities mattered. They were at rest or in constant regular motion. Einstein suspected that this classical picture was mistaken. Einstein regarded the theory of relativity as a field theory, which dispenses with action at a distance.

But Einstein was never able to overcome the fundamental dualism in the physical worldview between particles and fields. In his relativistic thinking about the nature of reality, Einstein became one of the first physicists to realize the significance of symmetries and invariance in science as a new criterion of what the physicist should regard as objective and physically real.

In the STR it states that all reference systems, which represent physical systems in motion with respect to each other, must be equivalent from the physical point of view. Einstein may not have known about that experiment, but states, Examples of this sort , together with the unsuccessful attempts to discover any motion of the earth relatively to the " light medium ", suggest that the phenomena of electrodynamics as well as of mechanics possess no properties corresponding to the idea of absolute rest.

The speed of light is fixed, and thus not relative to the movement of the observer.

This was impossible under Newtonian classical mechanics. Einstein argues, the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good.

We will raise this conjecture the purport of which will hereafter be called the "Principle of Relativity" to the status of a postulate , and also introduce another postulate, which is only apparently irreconcilable with the former, namely, that light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body.

These two postulates suffice for the attainment of a simple and consistent theory of the electrodynamics of moving bodies based on Maxwell's theory for stationary bodies. The introduction of a " luminiferous ether " will prove to be superfluous in as much as the view here to be developed will not require an "absolutely stationary space" provided with special properties, nor assign a velocity-vector to a point of the empty space in which electromagnetic processes take place.

The theory […] is based—like all electrodynamics—on the kinematics of the rigid body , since the assertions of any such theory have to do with the relationships between rigid bodies systems of co-ordinates , clocks , and electromagnetic processes.

Insufficient consideration of this circumstance lies at the root of the difficulties which the electrodynamics of moving bodies at present encounters.

It had previously been proposed, by George FitzGerald in and by Lorentz in , independently of each other, that the Michelson—Morley result could be accounted for if moving bodies were contracted in the direction of their motion. His explanation arises from two axioms. First, Galileo's idea that the laws of nature should be the same for all observers that move with constant speed relative to each other.

Einstein writes, The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems of co-ordinates in uniform translatory motion.

The second is the rule that the speed of light is the same for every observer. Any ray of light moves in the "stationary" system of co-ordinates with the determined velocity c, whether the ray be emitted by a stationary or by a moving body. The theory, now called the special theory of relativity , distinguishes it from his later general theory of relativity , which considers all observers to be equivalent.

Special relativity gained widespread acceptance remarkably quickly, confirming Einstein's comment that it had been "ripe for discovery" in Acknowledging the role of Max Planck in the early dissemination of his ideas, Einstein wrote in "The attention that this theory so quickly received from colleagues is surely to be ascribed in large part to the resoluteness and warmth with which he [Planck] intervened for this theory".

But the definition is not sufficient when it is required to connect by time events taking place at different stations, —or what amounts to the same thing,— to estimate by means of time zeitlich werten the occurrence of events, which take place at stations distant from the clock.

Suppose an observer —who is stationed at the origin of coordinates with the clock— associates a ray of light which comes to him through space, and gives testimony to the event of which the time is to be estimated, — with the corresponding position of the hands of the clock.

But such an association has this defect, —it depends on the position of the observer provided with the clock, as we know by experience.

We can attain to a more practicable result by the following treatment. If an observer be stationed at A with a clock, he can estimate the time of events occurring in the immediate neighbourhood of A, by looking for the position of the hands of the clock, which are synchronous with the event.

If an observer be stationed at B with a clock, —we should add that the clock is of the same nature as the one at A,— he can estimate the time of events occurring about B. But without further premises, it is not possible to compare, as far as time is concerned, the events at B with the events at A.

We have hitherto an A-time, and a B-time, but no time common to A and B.He required that the notions of space and time, for use in mechanics, must be freed from all reference to material motions.

In order to appreciate what is meant by philosophical consequences, we should distinguish them from the deductive consequences of physical theories. This explains why nuclear weapons and nuclear reactors produce such phenomenal amounts of energy, as they release binding energy during nuclear fission and nuclear fusion , and convert a portion of subatomic mass to energy. According to the definition, both clocks are synchronous, if t.

The Galilean transformations, for instance, result in different values for the speed of light, if we change from a stationary to a moving reference frame.

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