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Paradoxes in Classical Physics
Table of Contents :
There are a least three paradoxes in classical physics that have slipped past the experimental physicists. Before discussing these paradoxes, I would like to mention the "big mistake."
The 'Big Mistake'
Remember Ben Franklin? His inquiries into the nature of static electricity led to the invention of lightning rods. His apparatus was a Leyden jar and batteries, and he wondered about the flow of the electric fluid, and it direction. He surmised that it was ionic in nature and labeled the battery terminal that was the ion emitter 'positive' , and the receiving terminal 'negative'. This polarity convention ('the big mistake') was carried on through the 19th century by chemists working on battery improvements for the wired telegraphy industry.
By this time, physics had developed an experimental device for investigating electron emission, now called the cathode ray tube (CRT), and it was then realized that the battery convention of polarity was wrong. It was obvious that the cathode (-) was the emitter, and by convention should have been labeled positive (+). Academia was in a quandary. What to do! All those text books! The answer was "nothing".
Imagine two young physicists sent to a seminar in Elbonia. They were assured that the seminar would be presented in perfect English. They didn't know the Elbonians mean "up" when they say "down", and "in" when they say "out." The physicists were named Abbott and Costello. Inverted language can cause great harm to conceptualization, or cause a chuckle.
What is a paradox ?
Webster's dictionary says: "A tenet contradictory to received opinion (dogma)"
Paradox #1 - Light
Early in the 19th Century, there was much discussion between Thomas Young (English physicist) and Fresnel (French engineer) on the nature of light. One proposal was that light waves behaved like sound waves, namely; energy was transported, only longitudinally in a fluid medium (bulk modulus of elasticity) and both longitudinally & transversely in elastic solids. The counter proposal went thus; "No, the polarized light, being a transverse wave, could not develop from a longitudinal wave". Natural light must be a random bundle of transverse waves. I believe it was Young who won the day.
Two experimenters "Airey" and "Dove" felt that this question could be settled if they produced monochromatic light. They knew that a single frequency light wave, being a randomly oriented bundle of transverse waves, would self destruct due to interference. They arranged slits and prisms in series to achieve monochromicity. Diffraction limits defeated this idea, so they abandoned the effort.
In 1960 the ruby rod laser was invented. It produced non-polarized monochromatic red light. Not only that, but it was coherent (in phase.) The science community never noticed that this was a paradox! If randomly oriented transverse waves didn't interfere, why not? (Exception, circular polarization is two orthogonal plane waves 90 degrees out of phase.) The only possible answer to this is that natural light is longitudinal. - One up for Fresnel!
There is a parallel to this in ultrasonics. In a sandwich of epoxy and aluminum Brewster's' polarizing angle for sound is about 46 degrees. Using a longitudinal transducer set at 46 degrees from the vertical, and scanning with a transverse (shear wave) transducer, one can see that conversion takes place.
Due to the nature of solids, the output is more complex. Also, there may be a clue as to why polarization occurs. A Raleigh wave emanates along the interface and is probably involved in the process.
Finally, if natural light is a longitudinal wave, the mechanism of production is simple - quantized mass defect at the atomic level, ergo, natural light is a gravity wave! This includes the entire non-polarized spectrum.
Paradox #2 - FARADAY DISC
Michael Faraday, in the early 19th century, was a noted experimenter in electric and magnetic phenomena. His work led to the conclusion that electric flow in a conductor made magnetic fields, which reacted to do mechanical work. His apparatus was two draped wires, a battery and an electrolyte cell as a flow detector. His inspired idea was to investigate what happened in an unbounded conductor. For this experiment, he crafted a copper disc, free to rotate with sliding contacts at the hub and rim. A stationary magnet was located between the contacts. The magnetic field was perpendicular to the disc. When energized, the disc would rotate. When manually rotated he would detect electric flow, thus was born the homopolar motor/generator; an important contributor to our hydrogen powered future!
But, something seems wrong. Free electrons should simply have moved sideways in a spiral path (the Hall effect), as they do in a magnetron or cyclotron, which have vacuum spaces, rather than copper. Copper must do something more than simply act as a "pipe" for electrons. My guess is that the free electrons put a drag on the bound electrons, which are displaced slightly from their proton nuclei. The resulting mutual spin gives rise to magnetic effects. To actually do mechanical work, a proton/electron dipole must be created. This would remove the paradox. Also, it would really upset the applecart! So many text books!
Paradox #3 - MAXWELL
Casting doubt on Maxwell's theory is not what anyone should do casually. His grand synthesis of electro-magnetism and light has stood the test of time quite well. However, once one challenges the concepts of light, one must follow the consequences. The paradox is in the details.
Envision a quarter wave dipole - two rods each ¼ wave length long, fed at the center with a resonant frequency. Resonance means the voltage phase precedes the current phase by 90 degrees. When the opposite electric charges peak at rod ends, an electric dipole field also peaks, and has a field strength that varies as 1/R squared, except where the field forms a waist at the center, where field strength varies as 1/R cubed.
Meanwhile, 90 degrees later, a magnetic loop (doughnut shaped) forms at the waist, and its field strength varies as 1/R. Notice the huge change in strength of the electric and magnetic field waists as distance R increases.
So what's the paradox? Maxwell introduced a new electric field associated with the magnetic field, justified by a displacement current. The literature now avoids any reference to this virtual current.
Dipoles inductively couple best when parallel, suggesting that the magnetic loop is really doing the whole job. The electric fields must be responsible only for the 'near field phenomenon.' Finally, radio waves are always polarized. For a good review of Maxwell's theory, "Feynman's Lectures on Physics Volume II" is a good start. Remember, when confronted with a paradox, the entire edifice of a theory is put in question, and alternatives should be looked at.
MICHELSON/MORLEY - EPILOGUE
In the 1880's Albert Michelson developed the interferometer. It can measure a change in the distance between two mirrors by ¼ wave of light. With laser light the measurement is crisp and certain. It was expected that, even with the light in 1880's, they should detect the earth's motion through space, and every one bought the idea. However, consider the ratio between the speed of light, 300,000,000 meters/sec and one meter between mirrors. Any phase shift would be buried by observational limits. No paradox here, just an understandable mistake.
Retired, Lawrence Livermore National Laboratory