Evolution of Physics by Einstein

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e-book: The Evolution of Physics

I am currently studying this book by Einstein to get an insight into his thinking. This book was originally published in 1938 by Cambridge University Press. It was a popular success, and was featured in a Time magazine cover story.

Here is some information on this book from Wikipedia:

Background of collaboration

Einstein agreed to write the book partly as a way to help Infeld financially. Infeld collaborated briefly in Cambridge with Max Born, before moving to Princeton, where he worked with Einstein at the Institute for Advanced Study. Einstein tried to get Infeld a permanent position there, but failed. Infeld came up with a plan to write a history of physics with Einstein, which was sure to be successful, and split the royalties. When he went to Einstein to pitch the idea, Infeld became incredibly tongue-tied, but he was finally able to stammer out his proposal. “This is not at all a stupid idea,” Einstein said. “Not stupid at all. We shall do it.”

Book’s point of view

In the book, Einstein pushed his realist approach to physics in defiance of much of quantum mechanics. Belief in an “objective reality,” the book argued, had led to great scientific advances throughout the ages, thus proving that it was a useful concept even if not provable. “Without the belief that it is possible to grasp reality with our theoretical constructions, without the belief in the inner harmony of our world, there could be no science,” the book declared. “This belief is and always will remain the fundamental motive for all scientific creation.”

In addition, Einstein used the text to defend the utility of field theories amid the advances of quantum mechanics. The best way to do that was to view particles not as independent objects but as a special manifestation of the field itself: “Could we not reject the concept of matter and build a pure field physics? We could regard matter as the regions in space where the field is extremely strong. A thrown stone is, from this point of view, a changing field in which the states of the greatest field intensity travel through space with the velocity of the stone.”

Contents

Preface

I. THE RISE OF THE MECHANICAL VIEW

  1. The great mystery story
  2. The first clue
  3. Vectors
  4. The riddle of motion
  5. One clue remains
  6. Is heat a substance?
  7. The switchback (roller-coaster)
  8. The rate of exchange
  9. The philosophical background
  10. The kinetic theory of matter

II. THE DECLINE OF THE MECHANICAL VIEW

  1. The two electric fluids
  2. The magnetic fluids
  3. The first serious difficulty
  4. The velocity of light
  5. Light as substance
  6. The riddle of colour
  7. What is a wave?
  8. The wave theory of light
  9. Longitudinal or transverse light waves?
  10. Ether and the mechanical view

III. FIELD, RELATIVITY

  1. The field as representation
  2. The two pillars of the field theory
  3. The reality of the field
  4. Field and ether
  5. The mechanical scaffold
  6. Ether and motion
  7. Time, distance, relativity
  8. Relativity and mechanics
  9. The time-space continuum
  10. General relativity
  11. Outside and inside the lift
  12. Geometry and experiment
  13. General relativity and its verification
  14. Field and matter

IV. QUANTA

  1. Continuity—Discontinuity
  2. Elementary quanta of matter and electricity
  3. The quanta of light
  4. Light spectra
  5. The waves of matter
  6. Probability waves
  7. Physics and reality

The third chapter (Field, Relativity) examines lines of force starting with gravitational fields (i.e., a physical collection of forces), moving on to descriptions of electric and magnetic fields. The authors explain that they are attempting to “translate familiar facts from the language of fluids…into the new language of fields.” They state that the Faraday, Maxwell, and Hertz experiments led to modern physics. They describe how “The change of an electric field produced by the motion of a charge is always accompanied by a magnetic field.”

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Comments

  • vinaire  On March 10, 2014 at 12:32 PM

    A magnet behaves like an electric dipole (two oppositely charged spheres separated by an insulator)… But the magnet consists of very small elementary magnetic dipoles which cannot be broken into separate poles… Order reigns in the magnet as a whole, for all the elementary dipoles are directed in the same way… The dependence of magnetic attraction or repulsion on distance is the same as in Newton’s law of gravitation and Coulomb’s law of electrostatics… We see again in this theory the application of a general point of view: the tendency to describe all phenomena by means of attractive and repulsive forces depending only on distance and acting between unchangeable particles.
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  • vinaire  On March 10, 2014 at 12:33 PM

    Then came the breakdown of the belief that all phenomena can be explained mechanically… In a Voltaic battery a higher potential in copper relative to zinc is maintained even when the two plates are connected… There seems to be an unlimited supply of an endless current of “electrical fluid”… This is similar to unlimited supply of “heat fluid” when boring the cannons… In an attempt to save the fluid theory, we may assume that some constant force acts to regenerate the potential difference and cause a flow of electric fluid… from the standpoint of energy, a noticeable quantity of heat is generated in the wire carrying the current… this is the chain of transformations which are taking place: chemical energy -> energy of the flowing electric fluid, i.e., the current -> heat.
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  • vinaire  On March 10, 2014 at 12:34 PM

    The experiment which actually revealed the great difficulties in applying the mechanical ideas is as follows… When a circuit is closed initiating a surge of current in a ring of wire, it generates a force perpendicular to the plane of wire. This force is observed in the movement of a magnetic needle… This experiment shows a relation between two apparently quite different phenomena, magnetism and electric current. It also shows that the force between the magnetic pole and the small portions of the wire through which the current flows does not lie along lines connecting the wire and needle, or the particles of flowing electric fluid and the elementary magnetic dipoles.

    For the first time there appears a force quite different from that to which, according to our mechanical point of view, we intended to reduce all actions in the external world.
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  • vinaire  On March 10, 2014 at 2:56 PM

    From The Evolution of Physics:

    This difficulty was stressed even more by an experiment performed with great skill by Rowland nearly sixty years ago. Leaving out technical details, this experiment could be described as follows. Imagine a small charged sphere. Imagine further that this sphere moves very fast in a circle at the centre of which is a magnetic needle. This is, in principle, the same experiment as Oersted’s, the only difference being that instead of an ordinary current we have a mechanically effected motion of the electric charge. Rowland found that the result is indeed similar to that observed when a current flows in a circular wire. The magnet is deflected by a perpendicular force.

    Let us now move the charge faster. The force acting on the magnetic pole is, as a result, increased; the deflection from its initial position becomes more distinct. This observation presents another grave complication. Not only does the force fail to lie on the line connecting charge and magnet, but the intensity of the force depends on the velocity of the charge. The whole mechanical point of view was based on the belief that all phenomena can be explained in terms of forces depending only on the distance and not on the velocity. The result of Rowland’s experiment certainly shakes this belief. Yet we may choose to be conservative and seek a solution within the frame of old ideas.

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  • vinaire  On March 12, 2014 at 8:16 AM

    From The Evolution of Physics:

    In the old theories of electric fluids, in the corpuscular and wave theories of light, we witness the further attempts to apply the mechanical view. But in the realm of electric and optical phenomena we meet grave difficulties in this application.

    A moving charge acts upon a magnetic needle. But the force, instead of depending only upon distance, depends also upon the velocity of the charge. The force neither repels not attracts but acts perpendicular to the line connecting the needle and the charge.

    In optics we have to decide in favour of the wave theory against the corpuscular theory of light. Waves spreading in a medium consisting of particles, with mechanical forces acting between them, are certainly a mechanical concept. But what is the medium through which light spreads and what are its mechanical properties? There is no hope of reducing the optical phenomena to the mechanical ones before this question is answered. But the difficulties in solving this problem are so great that we have to give it up and thus give up the mechanical views as well.

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  • vinaire  On March 12, 2014 at 4:21 PM

    From The Evolution of Physics – III. FIELD, RELATIVITY – The field as representation

    > We know from mechanical view that two particles attract each other and that this force of attraction decreases with the square of the distance.
    > Imagine a 3D space with sun at the center. Any test body brought somewhere within the vicinity of the sun will be attracted along the line connecting the centres of the two bodies.
    > We can imagine such lines directed toward the sun from all around the sun for different positions of the test body.
    > We may view these as lines of force of the gravitational field of the sun that are constructed in space, where no matter is present.
    > These lines only indicate how a test body would behave if brought into the vicinity of the sphere for which the field is constructed.
    > The lines in our space model are always perpendicular to the surface of the sphere.
    > Since they diverge from one point, they are dense near the sphere and become less and less so farther away.
    > If we increase the distance from the sphere twice or three times, then the density of the lines will be four or nine times less.
    > Thus, the density of the lines of force in space shows how the force varies with the distance.
    > The lines of force help explain the force generated by a circulating charge that is perpendicular to its plane, which cannot be explained by the traditional mechanical view.
    > This is “lines of force” or “field” model. The mechanical model was two-dimensional. This model is three-dimensional.
    > The properties of the field alone appear to be essential for the description of phenomena; the differences in source do not matter.
    > The concept of field reveals its importance by leading to new experimental facts.
    > The field translates the laws into a simple, clear language, easily understood.
    > an electrostatic field does not influence a magnetostatic one and vice versa. The words “static field” mean a field that does not change with time.
    > Electrostatic, magnetostatic and gravitational fields are all of different character. They do not mix; each preserves its individuality regardless of the others.
    > As long as a charge is at rest there is only an electro static field. But a magnetic field appears as soon as the charge begins to move.
    > the faster the electric field changes, the stronger the accompanying magnetic field.

    We have tried here to translate familiar facts from the language of fluids, constructed according to the old mechanical view, into the new language of fields. We shall see later how clear, instructive, and far
    reaching our new language is.

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  • vinaire  On March 12, 2014 at 9:27 PM

    From The Evolution of Physics – III. FIELD, RELATIVITY – The two pillars of the field theory

    > “The change of an electric field is accompanied by a magnetic field.”
    > “The change of a magnetic field is accompanied by an electric field.”
    > New facts suggested by the field theory are confirmed by experiment!
    > To use the field concept and its language consistently, we must regard the magnetic field as a store of energy. Only in this way shall we be able to describe the electric and magnetic phenomena in accordance with the law of conservation of energy.

    Starting as a helpful model, the field became more and more real. It helped us to understand old facts and led us to new ones. The attribution of energy to the field is one step farther in the development in which the field concept was stressed more and more, and the concepts of substances, so essential to the mechanical point of view, were more and more suppressed.

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  • vinaire  On March 13, 2014 at 7:00 AM

    From The Evolution of Physics – III. FIELD, RELATIVITY – The reality of the field

    > The quantitative, mathematical description of the laws of the field is summed up in what are called Maxwell’s equations.
    > These equations form a pattern for a new type of law.
    > Maxwell’s equations are laws representing the structure of the field.
    > One of the principal steps leading to Maxwell’s equations is an idealized experiment performed in imagination by repeating Faraday’s experiment with a circuit shrinking to a point. We may imagine the same with Oersted’s experiment.
    > the whole step yields a connection between the changes of the magnetic and electric fields at an arbitrary point in space and at an arbitrary instant.
    > the electromagnetic field is, in Maxwell’s theory, something real. The electric field is produced by a changing magnetic field, quite independently, whether or not there is a wire to test its existence; a magnetic field is produced by a changing electric field, whether or not there is a magnetic pole to test its existence.
    > the electromagnetic field once created exists, acts, and changes according to Maxwell’s laws.
    > Maxwell’s equations describe the structure of the electromagnetic field. All space is the scene of these laws and not, as for mechanical laws, only points in which matter or charges are present.
    > In Newton’s theory only big steps connecting distant events are permissible. In Maxwell’s theory there are no material actors. The equations allow us to predict what will happen a little farther in space and a little later in time, if we know what happens here and now. They allow us to increase our knowledge of the field by small steps.
    > the study of Maxwell’s equations gives a much deeper insight into the problem of the oscillating electric charge. It predicts the electromagnetic wave. Energy radiates from the oscillating charge travelling with a definite speed through space.
    > As field represents energy, all these changes spreading out in space, with a definite velocity, produce a wave.
    > The electromagnetic wave spreads in empty space. This, again, is a consequence of the theory.
    > (Vinaire) An electromagnetic wave travels in space. But what is that space? Is that space a distant harmonic?
    > From Maxwell’s equations: the velocity of an electromagnetic wave is equal to the velocity of light.
    > The theoretical discovery of an electromagnetic wave spreading with the speed of light is one of the greatest achievements in the history of science.
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  • vinaire  On March 13, 2014 at 11:27 AM

    For the first time I have understood the deep revolutionary aspect of the Maxwell’s Equations..

    The idea of FIELD started with Faraday. It was put forth as a theory by Maxwell. This provided a new reality that was firmly put in place by Einstein’s Theory of Relativity.

  • vinaire  On March 13, 2014 at 2:31 PM

    From “The Evolution of Physics”:

    To use a comparison, we could say that creating a new theory is not like destroying an old barn and erecting a skyscraper in its place. lt is rather like climbing a mountain, gaining new and wider views, discovering unexpected connections between our starting point and its rich environment. But the point from which we started out still exists and can be seen, although it appears smaller and forms a tiny part of our broad view gained by the mastery of the obstacles on our adventurous way up.

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  • vinaire  On March 13, 2014 at 2:38 PM

    From “The Evolution of Physics” – III. FIELD, RELATIVITY – Field and Ether

    > The electromagnetic wave is a transverse one and is propagated with the velocity of light in empty space.
    > The fact that their velocities are the same suggests a close relationship between optical and electromagnetic phenomena.
    > The same Maxwell’s equations describe both electric induction and optical refraction.
    > From the physical point of view, the only difference between an ordinary electromagnetic wave and a light wave is the wave-length: this is very small for light waves, detected by the human eye, and great for ordinary electromagnetic waves, detected by a radio receiver.
    > The physicist of the early years tried to describe the action of two electric charges only by concepts referring directly to the two charges. The field did not exist for him. The electromagnetic field is, for the modern physicist, as real as the chair on which he sits.
    > The new theory shows the merits as well as the limitations of the old theory and allows us to regain our old concepts from a higher level.
    > Our only way out seems to be to take for granted the fact that space has the physical property of transmitting electromagnetic waves, and not to bother too much about the meaning of this statement.
    > We may still use the word ether, but only to express some physical property of space.
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    • Chris Thompson  On March 13, 2014 at 6:04 PM

      We may call it either or we may call it a field, but it looks like we may be talking about the raw properties of space.

    • vinaire  On March 13, 2014 at 7:20 PM

      As a scientist, Einstein is very careful in what he writes. You’ll get a better idea by reading this section.

  • vinaire  On March 14, 2014 at 9:34 AM

    From “The Evolution of Physics” – III. FIELD, RELATIVITY – The mechanical scaffold

    > The earth is our co-ordinate system and it is rotaing.
    > The observation of the law of inertia on earth deviates slighly from a simple statement of it, because of its rotation.
    > We use a mechanical scaffold, called the frame of reference, or coordinate system, to measure any location in space and time.
    > If two coordinate systems rotate with respect to each other, then the laws of mechanics cannot be valid in both.
    > Galilean relativity principle: if the laws of mechanics are valid in one c.s., then they are valid in any other c.s. moving uniformly relative to the first.
    > Inertial systems are those for which the laws of mechanics are valid. The question as to whether an inertial system exists at all is still unsettled.
    > We can always transform not only positions, but also velocities from one c.s. to another if we know the relative velocities of the two c.s.
    > The distance of two points is, however, invariant, that is, independent of the choice of the c.s. Similarly, another quantity independent of the c.s. is the change of velocity.

    Our conclusions can be summarized as follows :

    (1) We know of no rule for finding an inertial system. Given one, however, we can find an infinite number, since all c.s. moving uniformly, relative to each other, are inertial systems if one of them is.

    (2) The time corresponding to an event is the same in all c.s. But the co-ordinates and velocities are different, and change according to the transformation laws.

    (3) Although the co-ordinates and velocity change when passing from one c.s. to another, the force and change of velocity, and therefore the laws of mechanics are invariant with respect to the transformation laws.

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  • vinaire  On March 15, 2014 at 5:20 AM

    From “The Evolution of Physics” – III. FIELD, RELATIVITY – Ether and motion

    > The Galilean relativity principle is valid for mechanical phenomena. The same laws of mechanics apply to all inertial systems moving relative to each other. Is this principle also valid for non-mechanical phenomena?
    > All problems concentrated around this question immediately bring us to the starting-point of the relativity theory.
    > In case of sound the medium also moves with the source of sound (or the c.s.) and the classical transformation applies.
    > In the case of light, there is no mechanical medium that moves with the c.s. or with the source of light.
    > Indirect experimentation shows that the velocity of light is always the same in all c.s. independent of whether or not the emitting source moves, or how it moves.
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  • vinaire  On March 15, 2014 at 5:29 AM

    (Vinaire) The medium that helps sound propagate is at the same disturbance level as the source of sound. But the medium of light (field) that helps light propagate is at a very different disturbance level as the source of light. The mechanical c.s. is tied to the mechanical source.

    In case of sound the source as well as the medium of sound is rigidly connected to the c.s. (coordinate system) because they belong to the same disturbance level (DL100).

    In case of light, the source of light is considered to be mechanical (DL100), but the medium of light is considered to be a field, which is at the disturbance level of DL50.

    How can a DL100 be the source of DL50?
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  • vinaire  On March 15, 2014 at 5:33 AM

    How do we consider the motion in DL100 relative to the motion in DL50?

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    • vinaire  On March 15, 2014 at 5:37 AM

      The classical transformations apply only when both c.s. are at DL100.
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    • vinaire  On March 15, 2014 at 5:45 AM

      DL50 seems to make the background for motion at DL100. Here we have two very different relative motions. There is relative motion at DL100. Then there is relativity of DL100 with respect to DL50.

      This is similar to the time dimension where motion is occurring in the present. But the whole “plane of present” can be looked upon in some historical perspective in a much larger sense of time.

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    • vinaire  On March 15, 2014 at 5:54 AM

      In case of sound, the vibration of the object creates displacement in the medium. Both the vibrating object and the displaced medium are at the same macro level.

      In case of light, the “vibration” is occurring at a subatomic level, and so is the displacement of “media”. It is a whole different level.

      Motion at macro level may be compared to another motion at macro level. Similarly, motion at subatomic level may be compared to another motion at subatomic level.

      How can the motion at subatomic level be compared to the motion at macro level in any significant manner?
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  • vinaire  On March 15, 2014 at 5:56 AM

    This seems to be a problem of scales in the realm of relativity.
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    • vinaire  On March 15, 2014 at 6:16 AM

      It is also a problem of levels. A macro level cannot “operate” at subatomic level. A macro object is inherently incapbale of motion at subatomic level.

      It is ludicrous to think of a macro object moving at the speed of light. It would be like thinking of a stone shrinking to the size of an electron.

    • vinaire  On March 15, 2014 at 6:18 AM

      All the ridiculous projections from Einsteins Theory of Relativity are simply that – ridiculous projections.
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