## Category Archives: Physics

### Euclidean and Non-Euclidean Continuum

##### Reference: Einstein’s 1920 Book

This paper presents Part II, Chapter 7 from the book RELATIVITY: THE SPECIAL AND GENERAL THEORY by A. EINSTEIN. The contents are from the original publication of this book by Henry Holt and Company, New York (1920).

The paragraphs of the original material (in black) are accompanied by brief comments (in color) based on the present understanding.  Feedback on these comments is appreciated.

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## Euclidean and Non-Euclidean Continuum

The surface of a marble table is spread out in front of me. I can get from any one point on this table to any other point by passing continuously from one point to a “neighbouring” one, and repeating this process a (large) number of times, or, in other words, by going from point to point without executing jumps.” I am sure the reader will appreciate with sufficient clearness, what I mean here by “neighbouring” and by “jumps” (if he is not too pedantic). We express this property of the surface by describing the latter as a continuum.

Space is basically a continuum. Every dimension varies continuously in it.

Let us now imagine that a large number of little rods of equal length have been made, their lengths being small compared with the dimensions of the marble slab. When I say they are of equal length, I mean that one can be laid on any other without the ends overlapping. We next lay four of these little rods on the marble slab so that they constitute a quadrilateral figure (a square), the diagonals of which are equally long. To ensure the equality of the diagonals, we make use of a little testing-rod. To this square we add similar ones, each of which has one rod in common with the first. We proceed in like manner with each of these squares until finally the whole marble slab is laid out with squares. The arrangement is such that each side of a square belongs to two squares and each corner to four squares.

The surface of the table may be divided into rows and columns of unit squares.

It is a veritable wonder that we can carry out this business without getting into the greatest difficulties. We only need to think of the following. If at any moment three squares meet at a corner, then two sides of the fourth square are already laid, and as a consequence, the arrangement of the remaining two sides of the square is already completely determined. But I am now no longer able to adjust the quadrilateral so that its diagonals may be equal. If they are equal of their own accord, then this is an especial favour of the marble slab and of the little rods about which I can only be thankfully surprised. We must needs experience many such surprises if the construction is to be successful.

The Euclidean continuum assumes certain conditions for the above to happen.

If everything has really gone smoothly, then I say that the points of the marble slab constitute a Euclidean continuum with respect to the little rod, which has been used as a “distance” (line-interval). By choosing one corner of a square as “origin,” I can characterize every other corner of a square with reference to this origin by means of two numbers. I only need state how many rods I must pass over when, starting from the origin, I proceed towards the “right” and then “upwards,” in order to arrive at the corner of the square under consideration. These two numbers are then the “Cartesian co-ordinates” of this corner with reference to the “Cartesian co-ordinate system” which is determined by the arrangement of little rods.

The Cartesian coordinate system is based on the assumptions of the Euclidean continuum.

By making use of the following modification of this abstract experiment, we recognise that there must also be cases in which the experiment would be unsuccessful. We shall suppose that the rods “expand” by an amount proportional to the increase of temperature. We heat the central part of the marble slab, but not the periphery, in which case two of our little rods can still be brought into coincidence at every position on the table. But our construction of squares must necessarily come into disorder during the heating, because the little rods on the central region of the table expand, whereas those on the outer part do not.

Such squares shall distort if the units of length change, as they do in a field. So we shall not be able to use the Cartesian coordinate system.

With reference to our little rods—defined as unit lengths—the marble slab is no longer a Euclidean continuum, and we are also no longer in the position of defining Cartesian co-ordinates directly with their aid, since the above construction can no longer be carried out. But since there are other things which are not influenced in a similar manner to the little rods (or perhaps not at all) by the temperature of the table, it is possible quite naturally to maintain the point of view that the marble slab is a “Euclidean continuum.” This can be done in a satisfactory manner by making a more subtle stipulation about the measurement or the comparison of lengths.

We may be able to use the math based on Euclidean system, if we add the dimension of inertia. Changes in length and time units can be adjusted by changes in inertia.

But if rods of every kind (i.e. of every material) were to behave in the same way as regards the influence of temperature when they are on the variably heated marble slab, and if we had no other means of detecting the effect of temperature than the geometrical behaviour of our rods in experiments analogous to the one described above, then our best plan would be to assign the distance one to two points on the slab, provided that the ends of one of our rods could be made to coincide with these two points; for how else should we define the distance without our proceeding being in the highest measure grossly arbitrary? The method of Cartesian co-ordinates must then be discarded, and replaced by another which does not assume the validity of Euclidean geometry for rigid bodies. [Mathematicians have been confronted with our problem in the following form. If we are given a surface (e.g. an ellipsoid) in Euclidean three-dimensional space, then there exists for this surface a two-dimensional geometry, just as much as for a plane surface.] The reader will notice that the situation depicted here corresponds to the one brought about by the general postulate of relativity (Section XXIII).

Einstein is exploring the math that will geometrically take care of the field problem.

NOTE:—Gauss undertook the task of treating this two-dimensional geometry from first principles, without making use of the fact that the surface belongs to a Euclidean continuum of three dimensions. If we imagine constructions to be made with rigid rods in the surface (similar to that above with the marble slab), we should find that different laws hold for these from those resulting on the basis of Euclidean plane geometry. The surface is not a Euclidean continuum with respect to the rods, and we cannot define Cartesian co-ordinates in the surface. Gauss indicated the principles according to which we can treat the geometrical relationships in the surface, and thus pointed out the way to the method of Riemann of treating multi-dimensional, non-Euclidean continua. Thus it is that mathematicians long ago solved the formal problems to which we are led by the general postulate of relativity.

Einstein’s approach is that of using the math which applies to non-Euclidean geometry. But there is another approach possible that uses the dimension of inertia. This approach requires a definition of inertia as a form of density of substance that is tied to duration.

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The problem of field presents the problem of varying space and time characteristics. Einstein had to figure out how to approach it mathematically. That math appears to be quite complex.

Another mathematical approach is possible by associating the changes in space and time characteristics to changes in inertia of substance. Inertia may be defined as the density of force as a substance. As the density of force increases, the length contracts and time gains endurance. This increasing endurance can be seen as decreasing velocity.

By working out a relationship between inertia and velocity, the problem of field may be solved more simply.

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### Einstein 1920: Heuristic Value of Relativity

##### Reference: Einstein’s 1920 Book

This paper presents Part 1, Chapter 14 from the book RELATIVITY: THE SPECIAL AND GENERAL THEORY by A. EINSTEIN. The contents are from the original publication of this book by Henry Holt and Company, New York (1920).

The paragraphs of the original material (in black) are accompanied by brief comments (in color) based on the present understanding.  Feedback on these comments is appreciated.

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## The Heuristic Value of the Theory of Relativity

Our train of thought in the foregoing pages can be epitomised in the following manner. Experience has led to the conviction that, on the one hand, the principle of relativity holds true, and that on the other hand the velocity of transmission of light in vacuo has to be considered equal to a constant c. By uniting these two postulates we obtained the law of transformation for the rectangular co-ordinates x, y, z and the time t of the events which constitute the processes of nature. In this connection we did not obtain the Galilei transformation, but, differing from classical mechanics, the Lorentz transformation.

The Principle of Relativity works in conjunction with the velocity of light simply because light is serving as a “point of zero inertia” for all inertial systems in the material domain, which is characterized by the rigidity of the rectangular co-ordinates x, y, z and t. The point of zero inertia makes it possible to account for subtle change in inertia in the material domain, and their effect on velocity. This effect was not accounted for by the Galileian transformation.

The law of transmission of light, the acceptance of which is justified by our actual knowledge, played an important part in this process of thought. Once in possession of the Lorentz transformation, however, we can combine this with the principle of relativity, and sum up the theory thus:

Every general law of nature must be so constituted that it is transformed into a law of exactly the same form when, instead of the space- time variables x, y, z, t of the original co-ordinate system K, we introduce new space-time variables x’, y’, z’, t’ of a co-ordinate system K’. In this connection the relation between the ordinary and the accented magnitudes is given by the Lorentz transformation. Or, in brief: General laws of nature are co-variant with respect to Lorentz transformations.

The x, y, z, t co-ordinates are a function of inertia. The Lorentz transformations provide this function for the material domain only in an approximate but fairly accurate manner. In other words, general laws of nature are co-variant with respect to Lorentz transformations in the material dimension only.

The law of transmission of light is incomplete until a relationship is found between light’s velocity and its inertia (quantization).

This is a definite mathematical condition that the theory of relativity demands of a natural law, and in virtue of this, the theory becomes a valuable heuristic aid in the search for general laws of nature. If a general law of nature were to be found which did not satisfy this condition, then at least one of the two fundamental assumptions of the theory would have been disproved. Let us now examine what general results the latter theory has hitherto evinced.

Inertia may be defined by finding the relationship of the x, y, z, t co-ordinates with mass.

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Lorentz transformation is more accurate than the Galileian transformation because it takes into account the changes in velocity due to subtle changes in inertia in the material domain. These changes are accounted for because taking the large velocity of light as constant is equivalent to treating light as a point of zero inertia. This allows subtle changes in inertia to be converted into equivalent changes in velocity.

The Principle of Relativity is simply accounting the variation in inertia through the rectangular co-ordinates x, y, z and t. This relationship needs to be understood better and related with mass.

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### Einstein 1920: Experiment of Fizeau

##### Reference: Einstein’s 1920 Book

This paper presents Part 1, Chapter 13 from the book RELATIVITY: THE SPECIAL AND GENERAL THEORY by A. EINSTEIN. The contents are from the original publication of this book by Henry Holt and Company, New York (1920).

The paragraphs of the original material (in black) are accompanied by brief comments (in color) based on the present understanding.  Feedback on these comments is appreciated.

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## Theorem of the Addition of Velocities. The Experiment of Fizeau

Now in practice we can move clocks and measuring-rods only with velocities that are small compared with the velocity of light; hence we shall hardly be able to compare the results of the previous section directly with the reality. But, on the other hand, these results must strike you as being very singular, and for that reason I shall now draw another conclusion from the theory, one which can easily be derived from the foregoing considerations, and which has been most elegantly confirmed by experiment.

Velocities in the material domain are small compared with the velocity of light because of high inertia. High velocities exist in the radiation domain only where the inertia is much lower. Velocities closer to the velocity of light cannot be expected in the material domain.

In Section 6 we derived the theorem of the addition of velocities in one direction in the form which also results from the hypotheses of classical mechanics. This theorem can also be deduced readily from the Galilei transformation (Section 11). In place of the man walking inside the carriage, we introduce a point moving relatively to the co-ordinate system K’in accordance with the equation

x’ = wt’.

By means of the first and fourth equations of the Galilei transformation we can express x’and t’in terms of xand t, and we then obtain

x = (v + w)t.

This equation expresses nothing else than the law of motion of the point with reference to the system K (of the man with reference to the embankment). We denote this velocity by the symbol W, and we then obtain, as in Section 6,

W = v + w…………………………………. (A)

But we can carry out this consideration just as well on the basis of the theory of relativity. In the equation

x’ = wt’

we must then express x’ and t’ in terms of xand t, making use of the first and fourth equations of the Lorentz transformation. Instead of the equation (A) we then obtain the equation

Equation (B) is valid only when c is infinite or very large compared to the material velocity v that is being added to a radiation velocity w.

which corresponds to the theorem of addition for velocities in one direction according to the theory of relativity. The question now arises as to which of these two theorems is the better in accord with experience. On this point we are enlightened by a most important experiment which the brilliant physicist Fizeau performed more than half a century ago, and which has been repeated since then by some of the best experimental physicists, so that there can be no doubt about its result. The experiment is concerned with the following question. Light travels in a motionless liquid with a particular velocity w. How quickly does it travel in the direction of the arrow in the tube T (see the accompanying diagram, Fig. 3) when the liquid above mentioned is flowing through the tube with a velocity v?

In accordance with the principle of relativity we shall certainly have to take for granted that the propagation of light always takes place with the same velocity w with respect to the liquid, whether the latter is in motion with reference to other bodies or not. The velocity of light relative to the liquid and the velocity of the latter relative to the tube are thus known, and we require the velocity of light relative to the tube.

It is clear that we have the problem of Section 6 again before us. The tube plays the part of the railway embankment or of the co-ordinate system K, the liquid plays the part of the carriage or of the co-ordinate system K’, and finally, the light plays the part of the man walking along the carriage, or of the moving point in the present section. If we denote the velocity of the light relative to the tube by W, then this is given by the equation (A) or (B), according as the Galilei transformation or the Lorentz transformation corresponds to the facts. Experiment 1 decides in favour of equation (B) derived from the theory of relativity, and the agreement is, indeed, very exact. According to recent and most excellent measurements by Zeeman, the influence of the velocity of flow v on the propagation of light is represented by formula (B) to within one per cent.

Nevertheless we must now draw attention to the fact that a theory of this phenomenon was given by H. A. Lorentz long before the statement of the theory of relativity. This theory was of a purely electrodynamical nature, and was obtained by the use of particular hypotheses as to the electromagnetic structure of matter. This circumstance, however, does not in the least diminish the conclusiveness of the experiment as a crucial test in favour of the theory of relativity, for the electrodynamics of Maxwell-Lorentz, on which the original theory was based, in no way opposes the theory of relativity. Rather has the latter been developed from electrodynamics as an astoundingly simple combination and generalisation of the hypotheses, formerly independent of each other, on which electrodynamics was built.

According to the principle of relativity the general laws are consistent with changes in uniform motion and inertia. This applies to the laws of electrodynamics too. Addition of velocities is valid when the inertia of the systems is of the same order of magnitude (both in the material domain). Lorentz transformation is valid when the inertia of the systems is many orders of magnitude apart (as in material and field domains).

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According to the principle of relativity the general laws are consistent with changes in uniform motion and inertia. This applies to the laws of electrodynamics too.

Addition of velocities is valid when the inertia of the two systems is of the same order of magnitude (both in the material domain). Lorentz transformation is valid when the inertia of the systems is many orders of magnitude apart (as in material and field domains). Neither of the equations may apply when the inertia of both systems is in the field domain. This is because the inertia associated with the velocity of light is not exactly zero.

For equations to work flawlessly a relationship between velocity and inertia needs to be derived for material domain as well as for field domain.

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### Maxwell and Gravity

##### Reference:Disturbance Theory

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Here are my comments (in bold colored italics) on the following article by Kevin Brown.

## Why Maxwell Couldn’t Explain Gravity

##### Einstein to M. Besso, August 1918

In other words, if the gravitational field is there, then the energy in that field has to be in a state of stress. That is the basis of Newtonian forces. The energy represents physical substance that is in motion. This property is defined by the energy-momentum conservation concept.

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From the earliest recorded thoughts about physics and philosophy, beginning in ancient times, theories about the constitution of nature have been divided into two opposing conceptual frameworks, one based on the idea of a continuum of substance permeating all space, and the other based on the idea of isolated entities moving through a void of empty space. (See Continuity and the Void).

The void of empty space is difficult to conceive because space, by definition, represents the extents of substance. Empty space, therefore, must consist of invisible substance that has little consistency. This substance is energy of very low quantization. I, therefore, subscribe to the first conceptual framework.

From matter to space, energy is continually diminishing in its consistency. Faraday described it as “lines of force” that were concentrated in atoms, and which spread out in space. Matter does not end abruptly and space starts. However, Newton’s mechanics uses this latter framework from which comes the idea of action at a distance.

Although one view or the other has sometimes been predominant, neither view has ever won unanimous assent, and the “mainstream” view has alternated back and forth between the two frameworks many times throughout the history of science. At the beginning of the scientific revolution, Descartes adopted the philosophy of the continuum, insisting that space and matter are co-extant (indeed, that they are the same thing), so there is no such thing as empty space, and he asserted that objects affect each other only by direct contact. However, the swirling vortices of Descartes were soon discredited by Newton’s theories of dynamics and gravitation. Newton himself was equivocal, but his theories strongly tended to support the idea of isolated particles of matter moving in an empty void, capable of interacting with each other, via the force of gravity, over great distances.

The “continuum of substance” framework gives us a spectrum of a physical substance of varying consistency from space to matter. Matter is the most condensed form of this substance, and space is the least condensed form. We may call this substance energy. The primary characteristic of this substance is force. This was Faraday’s view. The swirling vortices of Descartes may be used as a model for an atom with energy condensing towards the center.

The framework of “isolated entities moving through a void of empty space” is used in Newtonian mechanics. It is a very simplified binary view of the former framework, consisting only of matter and space. Here space is seen as a void (absence of matter). This simplification then provides us with the various concepts of distance, velocity, acceleration, mass, force, and energy of Newtonian mechanics. It defines the force of gravity as action at a distance.

The early theories of electricity and magnetism developed by Coulomb, Ampere, and Oersted, were based on the Newtonian model of gravity, which is to say, they were based on the premise that isolated objects moving in the void of empty space exert forces on each other even when separated by some distance (rather than just when they are in direct contact). This theoretical approach proved very successful, and was developed to a high level, culminating in the work of Weber, Neumann, and others by around 1849. However, simultaneously with those developments, Faraday was investigating the same phenomena of electromagnetism from a completely different perspective, reverting to the idea of contact forces exerted through some kind of substance permeating all of space.

On a macroscopic scale, the Newtonian mechanics, with its theory of “action at a distance” has been rather successful. It has been able to explain the motion of the planets. This theory of force is used successfully even in the explanation of electromagnetic phenomenon. Faraday, however, used the continuum of substance perspective in investigating the electromagnetic phenomenon. His experiments led him to the concept of field consisting of lines of forces. Faraday’s approach takes Newton’s concept of inertia to the level of “innate force of substance” pervading all space.

This approach was taken up by Maxwell, who in 1855 published a paper, “On Faraday’s Lines of Force”, in which he sought to express Faraday’s ideas in mathematical form. Maxwell continued his investigations in a paper entitled “On Physical Lines of Force”, published in 1861, and then another, entitled “A Dynamical Theory of the Electrodynamic Field” in 1864. This work ultimately led to his great and highly influential “Treatise on Electricity and Magnetism”, published in 1875, which is the basis for most treatments of the classical theory of electromagnetism to this day.

Maxwell sought to express Faraday’s ideas of lines of force in mathematical form. But the mathematics used by Maxwell maintained the identity of substance rigidly separate from space as per Newtonian mechanics. Maxwell’s mathematical lines of force did spread out and came together in space, but they did so as an incompressible fluid, and not as a substance thinning out or thickening up on a gradient. The Maxwell’s field is, therefore, based on the “action at a distance” theory of Newton, and not on Faraday’s “continuum of substance” approach.

Nevertheless, the tradition of Weber, et al, has continued, notably with the work of Lorenz, the retarded potentials of Lenard and Weichert, and the absorber theory of Wheeler and Feynman. It is generally conceded today that electrodynamics can be formulated either as a field theory or as a distant-action theory, although one may be more convenient than the other in any given circumstance. This ambiguity arises because, even in field theories, we never actually observe a field, we only observe the behavior of material entities. Based on this behavior, we find it convenient to hypothesize the existence of certain fields, partly as a computational aid, i.e., a simple way of encoding the rules that evidently govern the behavior of material entities. But it is also possible to formulate those laws without reference to any hypothetical fields in empty space, by allowing for distant action, provided we allow the forces to be retarded functions of the relative motions of particles (not just their relative positions).

The current field concepts of Electrodynamics in quantum mechanics, and of the Standard model in particle physics are based on distant-action theory.

Maxwell was well aware of the viability of this “fieldless” approach, but was not satisfied with it. He wrote in his 1864 paper

##### This theory, as developed by W. Weber and C. Neumann, is exceedingly ingenious, and wonderfully comprehensive in its application to the phenomena … The mechanical difficulties, however, which are involved in the assumption of particles acting at a distance with forces which depend on their velocities are such as to prevent me from considering this theory as an ultimate one…

Ironically, the reason given here by Maxwell for being dissatisfied with the distant-action approach to electromagnetism was actually based on a misunderstanding, as Maxwell later acknowledged. He originally thought a velocity-dependent force law must automatically violate the conservation of energy. Indeed, the first such law to be proposed (by Gauss) was subject to this objection. However, the force law of Weber fully satisfies the conservation of energy, so Maxwell’s original stated motivation was unfounded. After realizing this, he amended his reasons for opposing distant action theories. In later treatments he emphasized the requirement (as he saw it) for the electromagnetic energy (and momentum) emitted by one body and absorbed some time later by another body to have some mode of existence between the emission and absorption events. Thus, his mature rationale for fields was that they provide the vehicle for spatially and temporally continuous conservation of energy and momentum during the intervals of communication–which he showed were non-zero, because of the finite speed of propagation of electromagnetic disturbances. Others have considered the sheer simplicity and clarity of the field formulation to be the strongest evidence for the “reality” of the fields. For example, this seems to have been Einstein’s view.

Maxwell viewed the field to exist separate from space same as matter. The field was not integrated with space the way Faraday’s lines of force were. Thus, the field is treated in the mechanical sense given by Newton in terms of momentum and energy.

In any case, Maxwell’s understanding of the electrical force that exists between charged particles was based on the idea that even the “empty space” of the vacuum is actually permeated with some kind of substance, called the ether, which consists of individual parts that can act as dielectrics.

##### The theory I propose may therefore be called a theory of the Electromagnetic Field, because it has to do with the space in the neighbourhood of the electric or magnetic bodies, and it may be called a Dynamical Theory, because it assumes that in that space there is matter in motion, by which the observed electromagnetic phenomena are produced.

Maxwell used the idea of “aether filling the space,” which is not the same as “space is a substance with inherent characteristic of force,” as visualized by Faraday.

The simplest component of this theory was the electrostatic field, which Maxwell envisaged as a displacement of the dielectric components at each point in the medium. In simple terms, he pictured ordinary empty space, when devoid of any electric field, as consisting of many small pairs of positive and negative charge elements, and in the absence of an electric field the two opposite charges in each pair are essentially co-located, so there is no net change or electric potential observable at any point. If an electric potential is established across some region of this medium (e.g., empty space), it tends to pull the components of each pair apart slightly. Maxwell termed this an electric displacement in the medium. Of course, the constituent parts of the dielectric pairs attract each other, so the electric displacement is somewhat like stretching a little spring at each point in space.

As an aside, it’s interesting that this theory, which supposedly denies the intelligibility of distant action, nevertheless ends up invoking (albeit on a very small scale) what appears to be elementary attraction between distinct and separate entities. It’s clear that Maxwell recognized this aspect of his theory when he wrote

##### I have therefore preferred to seek an explanation of the facts … without assuming the existence of forces capable of acting directly at sensible distances.

The qualifier “sensible” is obviously intended to side-step the fact that his “explanation of the facts” does still assume the existence of forces capable of acting at a distance, but he excuses this on the grounds that it is not a “sensible” distance. This can certainly be criticized, since if the objection to action at a distance is based on principle, then it isn’t clear why it should be considered more acceptable over short distances than over long distances. Ironically, Maxwell himself even commented on this critically in an article on Attraction written for the 9th edition of the Encyclopedia Britannica in 1875.

##### If, in order to get rid of the idea of action at a distance, we imagine a material medium through which the action is transmitted, all that we have done is to substitute for a single action at a great distance a series of actions at smaller distances between the parts of the medium, so that we cannot even thus get rid of action at a distance.

and elsewhere he said even more pointedly

##### …it is in questionable scientific taste, after using atoms so freely to get rid of forces acting at sensible distances, to make the whole function of the atoms an action at insensible distances.

Maxwell didn’t have the right mathematical model to represent Faraday’s ideas correctly. He simply dispersed the Newtonian “matter” over larger space without using the insight of Faraday that force means the presence of substance, and space simply represents the extents of this substance.

Despite these scruples, Maxwell’s theory of electrodynamics, based on forces acting over insensible distances, proved to be tremendously successful. The elaborate and complicated material mechanisms that Maxwell originally conceived to embody the mathematical relations of the field eventually receded in his thinking, as he came to focus more and more on purely abstract energy-based considerations.

Energy-based considerations mean that the total force (substance) of a system must be conserved.

##### We may express the fact that there is attraction between the two bodies by saying that the energy of the system consisting of the two bodies increases when their distance increases. The question, therefore, Why do the two bodies attract each other? may be expressed in a different form. Why does the energy of the system increase when the distance increases?

Increase of distance represents thinning of substance (force). Change in velocity represents change in consistency of energy as substance.

It’s easy to see that Maxwell’s conception of the electric field is quite consistent with this energy-based approach. First, recall that, according to standard electromagnetic theory, the energy density of an electric field in vacuum is (1/2)ε0E2, where E is the magnitude of the electric field at the given point and ε0 is the permittivity of the vacuum. (For the spherical field around a stationary mass point, E drops off as the square of the distance, so the energy density drops off as the fourth power, so the total integrated energy is finite.) Now consider two particles with equal and opposite electric charges, and suppose they are initially co-located at a single position. Their electric fields cancel out, because the union of these oppositely charged particles is an electrically neutral particle. As a result, the dielectric medium surrounding these two particles is “un-stressed”, i.e., none of the tiny springs are displaced at all, so no energy is stored in those springs. Now suppose we separate the two oppositely charged particles by some distance. This displacement results in a net electric field in the surrounding medium. Much of the two fields still cancel out, but not all, so the dielectric elements are displaced, the “springs” are stretched slightly, and the medium now holds some energy. The energy came from the work done to separate the particles, so we see that these two oppositely charged particles exert a force of attraction on each other (through the intermediary of the dielectric medium). The further we separate the particles, the more energy we put into the field, and we approach the energy of two complete isolated fields when the particles are infinitely far apart.

The universal substance is energy that determines the activity which follows. An electric field is energy in a certain state. The magnitude of energy (E) is measured by its inherent force. Energy density is the consistency of energy, which is proportional to the square of its inherent force. The constant of proportionality is the “permittivity of the vacuum.”

Electric charge is distortion at a location. Positive distortion is balanced by negative distortion elsewhere. Therefore, the net distortion is always zero. A single isolated charge has a spherical field  around it. The inherent force and consistency of this field drops off rapidly with distance, so the total energy associated with that charge is finite.

For two equal and opposite charges, all lines of force start from one charge and terminate into the other. The lines do not exist when the charges are co-located. There is no charge, field or space. We are not considering the mass and material space in this situation. Separating of these two charges would mean supplying additional force (energy-substance) to create the two charges and the distance between them. Ultimately, we approach the force that forms two isolated charges infinitely far apart. This force must have come from a virtual dimension.

The other case to consider is two particles with the same electric charges, both positive or both negative. Again we start with the two particles co-located, but in this case the fields do not cancel each other, they combine to produce a spherical field of twice the strength (and hence four times the energy) of a single charged particle. Thus the surrounding dielectric medium is already significantly “displaced”, and it contains energy in all those stretched “springs”. If we now separate the two particles by some distance, some cancellation of the fields is introduced (most notably in the region between them, where the fields point in opposite directions), and the fields are less additive in other regions. As a result, the stress and displacement of the dielectric medium is reduced, as is the amount of energy stored in the field. The released energy as the particles move further apart corresponds to a force of repulsion between the two positively (or two negatively) charged particles. The further apart we move the particles, the more energy is removed from the field, and we again approach the energy of the fields of two individual isolated particles. (This is less than the energy of the original single field with twice the strength, because the energy is proportional to the square of the field strength.)

A double charge at a single location would naturally try to spread out to attain equilibrium, and that is why two similar charges repel each other. A single charge cannot spread out further because of its quantum nature (possibly being an energy vortex).

Two equal and opposite charges separated by a distance, and maintained as an isolated system, will not annihilate each other as long as the total force of that isolated system is conserved. Instead, they will start circling around each other. This is the situation within an atom. The force must leak back to the virtual dimension for opposite charges to come together and annihilate each other.

Toward the end of his 1964 paper, Maxwell inserted a brief note regarding the force of gravitation. He had commented previously on the formal similarities between the electric, magnetic, and gravitational fields, but now, after describing his energy-based model for the electric (and magnetic) forces between charges, he faced an obvious difficulty when trying to account for the force of gravity in a similar way.

##### Gravitation differs from magnetism and electricity in this; that the bodies concerned are all of the same kind, instead of being of opposite signs, like magnetic poles and electrified bodies, and that the force between these bodies is an attraction and not a repulsion, as is the case between like electric and magnetic bodies.

To be more explicit, suppose we regard the force of gravitation as arising from the actions of a field, and suppose the presence of a gravitational field represents a certain energy content. The stronger the field, the more energy it contains. Now if analyze a pair of massive particles, we find that when they are initially co-located, we have a field with twice the intensity of the field of either particle individually, and as we move the particles apart, the integral of the squared field strength (i.e., the total energy content of the field) drops, just as in the case of the electric field of two positively charged particles. Since the energy of the combined gravitational field drops as the particles are moved apart, it follows (by Maxwell’s reasoning) that there is a force of repulsion, not attraction, between the particles. The force of gravity predicted by this simple energy-based reasoning is in the wrong direction. Indeed this reasoning implies that it is impossible for “like” charges to attract each other – at least if their interaction can be represented as a continuous field.

It appears that charge is the distortion of basic substance. This distortion was created from the force from virtual dimension. When all the distortion is evened out there is no more charge and no electromagnetic field.

But there is still the basic substance, and that may be responsible for the gravitational field. The gravitational field may have been created also from the force that came from virtual dimension. This force expanded out from a point in the real dimension creating space. The opposite charge of gravitation is not in the real dimension; it is in the virtual dimension. Gravitation is, therefore, an attractive force only in the real dimension as it is trying to contract back to the virtual dimension. The virtual dimension is the dimension of the anti-matter.

The only possibility that Maxwell could see for salvaging the field-based approach to gravity was if we suppose that a massive body contributes negatively to the energy of the gravitational field in its vicinity. It would then be the most negative when the two particles are co-located, and become somewhat less negative as they are moved apart. Since the change in energy as the particles are moved apart would be positive, so this would represent a force of attraction. However, Maxwell was not prepared to contemplate negative energy (notice that, since energy is proportional to the square of the field strength, a negative energy would imply an imaginary field strength), so he suggested that we could postulate a huge positive background energy content for empty space, and then we could suppose that the presence of matter somehow diminishes the energy of this background field in its vicinity. To ensure that the total energy density of the field at any point is never negative, he said the background field stress would need to be at least as great as that of the strongest gravitational field anywhere in the universe. (He apparently ruled out the possibility of point-like masses, which would require the background stress to be infinite.)

##### The assumption, therefore, that gravitation arises from the action of the surrounding medium in the way pointed out, leads to the conclusion that every part of this medium possesses, when undisturbed, an enormous intrinsic energy, and that the presence of dense bodies influences the medium so as to diminish this energy wherever there is a resultant attraction. As I am unable to understand in what way a medium can possess such properties, I cannot go any further in this direction in searching for the cause of gravitation.

Maxwell’s energy-based model failed to apply to gravitation because the concept of charge cannot be applied to mass in the real dimension alone.

This problem helps to explain why it took longer to devise a viable field theory for gravitation than it did for electromagnetism. Of course, in a sense, a field theory for gravity already existed in the form of the classical scalar potential, which satisfies the (Poisson) field equation

in suitable units, where φ is the potential energy and ρ is the mass density. This equation is identically satisfied by setting φ (r) = k/r + C for any constants k and C, positive or negative, but in order for the φ field to give an attractive force, we must set k to a negative value. This is entirely consistent with Maxwell’s comments, i.e., the potential gravitational energy associated with a configuration of mass particles must decrease as the particles are brought closer together. The only way in this classical context to avoid actual negative energy (which Maxwell deemed necessary) is to set the “background” constant C to a value greater than the largest magnitude of k/r anywhere in the universe. In pre-relativistic physics, people worked with Poisson’s equation without worrying about the meaning of negative energy, they simply set C = 0, accepting the (apparent) fact that gravitational potential energy is negative. This “works” fine for most applications, but it doesn’t satisfy Maxwell’s desire to form an intelligible conception of the gravitational field in terms of ordinary classical dynamics.

In classical dynamics inertia is limited to matter only, and it does not extend to space. Therefore it requires the unusual assumption of the “background void” having an enormous intrinsic energy in order to avoid negative energy. This shows the weakness of distant-action theory of Newtonian mechanics.

Remarkably, the expression corresponding to the “potential” in the weak field limit of general relativity actually does correspond to something like what Maxwell suggested. The effective classical “potential” for a spherically symmetrical field surrounding a mass M in the weak field limit is (half of) the time-time component of the metric tensor

where G is Newton’s gravitational constant and c is the speed of light. The classical pre-relativistic expression for gravitational potential energy per unit mass is -GM/r, so a test particle of mass m is assigned the potential energy -GMm/r. Re-writing gtt in a form that isolates this expression, we have

Thus when Maxwell said that the gravitational medium must possess enormous intrinsic energy, and the leading constant term must (to avoid negative energy) equal “the greatest possible value of the intensity of gravitating force in any part of the universe”, he could have been (as we see in retrospect) referring to the field intensity at the Schwarzschild radius of a black hole, where the gravitational “potential” is comparable to the intrinsic “rest” energy of a test particle. In a sense, the enormous background energy corresponds to the “rest” energy E = mc2 of the test particle, which in turn corresponds to the ratio of proper time to some suitable coordinate time at any location in the field. Of course, there need not always be a “suitable” coordinate time, and hence energy cannot always be unambiguously localized in general relativity. However, in special circumstances such as a spherically symmetric field going to flat Minkowski spacetime at infinity, we have a fairly unambiguous definition of energy.

This unusual assumption, “the gravitational medium must possess enormous intrinsic energy to avoid negative energy”, also appears in the general theory of relativity. This could be the energy in the virtual dimension referred to above.

As an aside, the attractive nature of gravity is sometimes said to be closely related to (if not a direct consequence of) the equivalence principle, according to which the gravitational “charge” m of a given body is identical to the inertia of that body. In the case of electricity, reversing the sign of a particle’s electrical charge will reverse the direction of the applied force, but not of its inertia, so the resulting acceleration is reversed. In contrast, reversing the sign of the mass of a body would not only reverse the direction of the force, it would also reverse the direction of the resulting acceleration relative to the force, so the acceleration would be in the same direction, regardless of the sign of the mass. On the other hand, it could be argued that the gravitational interaction between two “like” particles involves three applications of the sign of mass: The mass producing the field (active charge), the mass responding to the field (passive charge), and the inertial mass of the responding particle. On this basis, reversing the sign of mass would reverse the direction of acceleration. This kind of superficial algebraic conundrum highlights the importance of energy-based reasoning.

The equivalence principle is a basic postulate of general relativity, stating that at any point of space-time the effects of a gravitational field cannot be experimentally distinguished from those due to an accelerated frame of reference. This principle is consistent with Faraday’s conceptualization of force (substance or inertia) and its gradient. The electromagnetic spectrum demonstrates this gradient of force of which neither Newton nor Maxwell was aware. Though Einstein came up with the equivalence principle, he also ignored the gradient of force as gradient of inertia or substance.

The error comes from Newton’s treatment of substance as either there (matter) or not there (space), and no gradient in between. This black and white assumption appears in the consideration of inertia (force) with respect to mass only and not with respect to the electromagnetic substance. From this assumption comes the energy-based approach. The moment we expand this “black and white” mathematical approach of Newton by the “gradient of force-substance” approach of Faraday, we see a host of new solutions to appear.

In his encyclopedia article on “Attraction” Maxwell did suggest one possible representation of the gravitational force in terms of a dynamical field that he hadn’t mentioned in 1864. After explaining how forces (such as electricity and magnetism) that are repulsive between “like” bodies may be represented in terms of a medium in a state of stress “consisting of tension along the lines of force and pressure in all directions at right angles to the lines of force”, he turns again to the vexing problem of gravity.

##### To account for such a force [of attraction between like bodies] by means of stress in an intervening medium, on the plan adopted for electric and magnetic forces, we must assume a stress of an opposite kind from that already mentioned. We must suppose that there is a pressure in the direction of the lines of force, combined with a tension in all directions at right angles to the lines of force. Such a state of stress would, no doubt, account for the observed effects of gravitation. We have not, however, been able hitherto to imagine any physical cause for such a state of stress.

In electricity and magnetism the forces of attraction and repulsion are there to bring the local gradients of force into equilibrium. If there is a gap in the gradient then the force is one of attraction. If there is overlapping gradient, the force is one of repulsion. Once the gradient is established, there are no electric and magnetic forces. These are local forces only in the gamma range.

When the local gradient of forces is established, the wider equilibrium of gradient (in terms of inertial force over the whole electromagnetic spectrum) still needs to be established among mass objects. The gravitational force of attraction exists because there are gaps in gradients of inertial force between two mass objects.

This is interesting because his theory of electromagnetism is normally regarded as a vector field (corresponding to a spin-1 mediated force), and all such fields are known to yield repulsion for “like” charges, and yet Maxwell seems to be saying that he can conceive of an attractive force “on the [same] plan”, merely by exchanging tension and compression. On the other hand, his specification of both tension and compression in various directions at each point within the medium is more suggestive of a tensor field (i.e., a spin-2 mediated force) rather than a vector field. The usual textbook explanation is that even-order fields (e.g., scalars and tensors) are attractive for like particles, whereas odd-order field (e.g., vectors) are repulsive for like particles, all under the assumption of strict positivity of energy. This shows how prescient was Maxwell in imposing this requirement on his field theories.

The force of repulsion between “like charges” is due to overlapping gradient of force. The repulsion is there to realign two similar gradients that belong to different sections on the overall gradient. See Comments on Electric Charge.

Maxwell ignores the gradient characteristic of energy-substance, and assumes that energy-substance has same characteristic throughout. This ignorance is then justified through complex mathematics.

However, there is one other important premise underlying the modern textbook answer, namely, that we are working in a relativistic context. We’ve already seen that the classical non-relativistic scalar field representation of gravity implies an attractive force only if we assume that the field energy is reduced when masses are brought together, and yet the magnitude of the field strength clearly increases in such circumstances, just as when two identical electric charges are brought together. So, the modern textbook explanation today is that the total mass-energy of a system is indeed reduced when the matter components are in closer proximity, just as Maxwell surmised. Furthermore, the total overall mass-energy of any system, including the “negative” contribution of gravitational potential energy, is always positive, which again is just as Maxwell surmised, when he suggested the existence of a very large “background” energy that is diminished when objects are close together. Of course, this is the very thing that Maxwell said he could not understand. It is perhaps slightly misleading to say the gravitational potential energy is negative. It might be better to say the absence of gravitational potential represents positive energy, except that even in the case of gravitation the energy of the field is said to be proportional to the square of the field strength, which (as noted above) would seem to imply imaginary field strength in order to give negative energy. In view of all this, is it fair to say that we’ve satisfactorily answered the question Maxwell was unable to answer – or have we simply decided to disregard it? Are we any more able than Maxwell to conceive of how bringing two objects together, increasing the magnitude of the field strength, whose square corresponds to field energy, results in a decrease of energy? Are there any alternative conceptual frameworks within which Maxwell’s question could be answered in a more satisfactory way? Part of his difficulty may be attributed to the fact that he didn’t have a unified concept of energy-momentum, but more fundamentally it could be argued that Maxwell couldn’t explain gravity because he didn’t know that the signature of the spacetime metric is negative.

The relativistic context seems to approach the continuum of substance framework rather than the distant-action framework of Newtonian mechanics. Time and distance, hence velocity, seems to relate directly to the consistency of energy-substance. This consistency is increasing on a continuous gradient from space to matter. This gradient is increasing relatively slowly up to the visible spectrum of light, but then it really accelerates beyond X-rays into the quantum area. When two masses are brought together the consistency of energy-substance increases at a high gradient. If the gradient continues to increase we approach the black hole phenomenon.

When two identical electric charges are brought together, we have increase not in the consistency of energy-substance, but in the distortion imposed on that energy-substance. The distortion attempts to reverse itself in the real dimension to attain equilibrium. But the consistency of energy-substance seems to reverse itself in some virtual dimension. The energy-based system confined to the real dimension cannot address this.

The effect of the negative signature of the spacetime metric is discussed in the note on Path Lengths and Coordinates, and more specifically as it relates to the attractiveness of gravity in the note entitled Accelerating in Place. The latter note explains in detail why, if the signature of the spacetime metric was positive, we would indeed expect gravity (for positive mass-energy) to be a repulsive force. The negative signature implies that geodesic worldlines of material particles actually maximize (rather than minimize) its absolute path length. The sign of the accelerations in the geodesic equations depends on the sign of the metric signature, i.e., on whether the time coefficient has the same or opposite sign as the space coefficients. An even more explicit demonstration of this is presented in the discussion of the Newtonian limit of general relativity in Scholium. There it is shown that the direction of gravitational acceleration is determined by the sign of M/k where M is the mass of the gravitating body and k is the signature of the spacetime metric. If we assume a Euclidean, positive definite, spacetime metric, then k = 1 and the only way for gravity to be attractive is with negative mass-energy. Conversely, with a Minkowski metric we have k = -1, so attractive gravity corresponds to strictly positive mass-energy. (See also the note on Potential Energy, Inertia, and Quantum Coherence for thoughts on the energy implications of falling objects in different contexts, and how the energy is transported away.)

We have lot of mathematics here.

It would be interesting to know if Maxwell’s reversal of stresses can be seen as corresponding to a negation of the signature of spacetime. Related to this is the question of how he derived the value of 37,000 tons per square inch for the pressure (and perpendicular tension) that would be required at the Earth’s surface to reproduce the effects of gravity.

It seems that we require out of the box thinking to explain gravity; and that would involve moving away from distant-action framework and toward the continuum of substance framework.

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### Einstein’s 1905 Paper on Relativity ##### Reference:Disturbance Theory

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Einstein’s theory of relativity works for cosmological dimensions, but not when it comes to atomic dimensions. Einstein was critical of the quantum mechanics having no coherent theory, while he could not come up with a physical theory to explain quantum effects. This bothered him for the rest of his life.

An examination of Einstein’s postulates follows that led to his original paper on relativity. This 1905 paper of Einstein is available at the following link.

On the Electrodynamics of Moving Bodies

Parts of this paper are quoted below that show Einstein’s non-mathematical reasoning. Einstein’s statements are in black italics. My understanding follows in bold color italics.

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## Basic Postulates

It is known that Maxwell’s electrodynamics—as usually understood at the present time—when applied to moving bodies, leads to asymmetries which do not appear to be inherent in the phenomena. Take, for example, the reciprocal electrodynamic action of a magnet and a conductor. The observable phenomenon here depends only on the relative motion of the conductor and the magnet, whereas the customary view draws a sharp distinction between the two cases in which either the one or the other of these bodies is in motion. For if the magnet is in motion and the conductor at rest, there arises in the neighbourhood of the magnet an electric field with a certain definite energy, producing a current at the places where parts of the conductor are situated. But if the magnet is stationary and the conductor in motion, no electric field arises in the neighbourhood of the magnet. In the conductor, however, we find an electromotive force, to which in itself there is no corresponding energy, but which gives rise—assuming equality of relative motion in the two cases discussed—to electric currents of the same path and intensity as those produced by the electric forces in the former case.

#### This “asymmetry” disappears when we use the magnetic lines of force, which are attached to the magnet, as the frame of reference. The conductor moves relative to these lines of force the same way in either case producing the same result. So, the problem has to do with how the frame of reference is selected.

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. They suggest rather that, as has already been shown to the first order of small quantities, 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 inasmuch 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 “luminiferous ether” was assumed to be a material-like medium of light waves. The inertial frame with the above two postulates then replaces the idea of “luminiferous ether”.

The theory to be developed 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.

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## § 1. Definition of Simultaneity

Let us take a system of co-ordinates in which the equations of Newtonian mechanics hold good. In order to render our presentation more precise and to distinguish this system of co-ordinates verbally from others which will be introduced hereafter, we call it the “stationary system.”

If a material point is at rest relatively to this system of co-ordinates, its position can be defined relatively thereto by the employment of rigid standards of measurement and the methods of Euclidean geometry, and can be expressed in Cartesian co-ordinates.

#### Einstein defines a “stationary system” in which the equations of Newtonian mechanics hold good. The space-time coordinates of this system have the rigid characteristics of the inertia applied to matter.

If we wish to describe the motion of a material point, we give the values of its co-ordinates as functions of the time. Now we must bear carefully in mind that a mathematical description of this kind has no physical meaning unless we are quite clear as to what we understand by “time.” We have to take into account that all our judgments in which time plays a part are always judgments of simultaneous events. If, for instance, I say, “That train arrives here at 7 o’clock,” I mean something like this: “The pointing of the small hand of my watch to 7 and the arrival of the train are simultaneous events”.

#### To describe the motion of a material point we give the values of its coordinates as functions of “time”. To represent this motion mathematically, we must define “time” with the understanding of simultaneity of events.

It might appear possible to overcome all the difficulties attending the definition of “time” by substituting “the position of the small hand of my watch” for “time.” And in fact such a definition is satisfactory when we are concerned with defining a time exclusively for the place where the watch is located; but it is no longer satisfactory when we have to connect in time series of events occurring at different places, or—what comes to the same thing—to evaluate the times of events occurring at places remote from the watch.

#### The judgment of simultaneous events is possible only at the location of the event. Additional considerations are required to define simultaneity of events at different locations.

We might, of course, content ourselves with time values determined by an observer stationed together with the watch at the origin of the co-ordinates, and co-ordinating the corresponding positions of the hands with light signals, given out by every event to be timed, and reaching him through empty space. But this co-ordination has the disadvantage that it is not independent of the standpoint of the observer with the watch or clock, as we know from experience. We arrive at a much more practical determination along the following line of thought.

#### The “time-value” comes from the position of the hand of the watch that is moving at a constant rate. The position of hands of watches at two different locations would have to be coordinated to achieve simultaneity. The communication between the two locations can be made through light signals.

If at the point A of space there is a clock, an observer at A can determine the time values of events in the immediate proximity of A by finding the positions of the hands which are simultaneous with these events. If there is at the point B of space another clock in all respects resembling the one at A, it is possible for an observer at B to determine the time values of events in the immediate neighbourhood of B. But it is not possible without further assumption to compare, in respect of time, an event at A with an event at B. We have so far defined only an “A time” and a “B time.” We have not defined a common “time” for A and B, for the latter cannot be defined at all unless we establish by definition that the “time” required by light to travel from A to B equals the “time” it requires to travel from B to A. Let a ray of light start at the “A time” tA from A towards B, let it at the “B time” tB. be reflected at B in the direction of A, and arrive again at A at the “A time” t’A.

In accordance with definition the two clocks synchronize if tB – tA = t’A – tB.

#### Simultaneity of clocks between two locations requires that light takes the same “time” of travel between the two locations in either direction.

We assume that this definition of synchronism is free from contradictions, and possible for any number of points; and that the following relations are universally valid:—

1. If the clock at B synchronizes with the clock at A, the clock at A synchronizes with the clock at B.
2. If the clock at A synchronizes with the clock at B and also with the clock at C, the clocks at B and C also synchronize with each other.

Thus with the help of certain imaginary physical experiments we have settled what is to be understood by synchronous stationary clocks located at different places, and have evidently obtained a definition of “simultaneous,” or “synchronous,” and of “time.” The “time” of an event is that which is given simultaneously with the event by a stationary clock located at the place of the event, this clock being synchronous, and indeed synchronous for all time determinations, with a specified stationary clock.

In agreement with experience we further assume the quantity 2AB/( t’A – tA) = c to be a universal constant—the velocity of light in empty space.

#### But for reasonable synchronization of clocks only a synchronization of tempo is needed. The rest is taken care of by the knowledge of distance between the two locations and the speed of light.

It is essential to have time defined by means of stationary clocks in the stationary system, and the time now defined being appropriate to the stationary system we call it “the time of the stationary system.”

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## § 2. On the Relativity of Lengths and Times

[Please refer this section in the original paper. I am only writing my comments on the contents of this section here.]

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## § 3. Theory of the Transformation of Co-ordinates and Times from a Stationary System to another System in Uniform Motion of Translation Relatively to the Former

[Please refer this section in the original paper. I am only writing my comments on the contents of this section here.]

#### Einstein then comes up with the same relationship that Lorentz had come up earlier. .

## § 4. Physical Meaning of the Equations Obtained in Respect to Moving Rigid Bodies and Moving Clocks

[Please refer this section in the original paper. I am only writing my comments on the contents of this section here.]

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## § 5. The Composition of Velocities

[Please refer this section in the original paper. I am only writing my comments on the contents of this section here.]

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## § 6. Transformation of the Maxwell-Hertz Equations for Empty Space. On the Nature of the Electromotive Forces Occurring in a Magnetic Field During Motion

[Please refer this section in the original paper. I am only writing my comments on the contents of this section here.]

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## § 7. Theory of Doppler’s Principle and of Aberration

[Please refer this section in the original paper. I am only writing my comments on the contents of this section here.]

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## § 8. Transformation of the Energy of Light Rays. Theory of the Pressure of Radiation Exerted on Perfect Reflectors

[Please refer this section in the original paper. I am only writing my comments on the contents of this section here.]

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## § 9. Transformation of the Maxwell-Hertz Equations when Convection-Currents are Taken into Account

[Please refer this section in the original paper. I am only writing my comments on the contents of this section here.]

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## § 10. Dynamics of the Slowly Accelerated Electron

[Please refer this section in the original paper. I am only writing my comments on the contents of this section here.]

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