|MadSci Network: Physics|
Hello: I wish you great success in your work on K-12 science curriculum, It is a great challenge and a most important effort. Please pardon my long answer to your brief question. However, I would like to make several important points (to me at least) about the wave - particle issue. To answer your question let me start by saying that the speed of light in the vacuum of space is one of the fundamental constants of the universe as we currently understand it. As Einstein predicted early in this century, even time must be changed to explain the constant speed of light in space-time coordinates. Today we have navigation satellites that must set the clocks in orbit ahead in time so that their time signals received on earth are corrected for retavistic time shift. When light encounters matter it rattles through the atoms and molecules delaying the passage through the material. The light does not slow down in the matter, it is detoured in a zig zag path so that it takes longer to pass through the matter. We call the delay the index of refraction of the material. If the light takes twice as long to pass through the matter than it would through an equal (straight line) distance in a vacuum, the refractive index is 2. Three times longer gives an index of 3 etc. The index is related to how dense the matter is along with other factors in the chemical structure of the material. It was also demonstrated about the turn of the century by Maxwell, Hertz and others that all electromagnetic energy including radio, infrared, visible light, ultraviolet x-rays and cosmic rays also travel at the speed of light in a vacuum. Consequently all electromagnetic energy can be described in terms of particles (photons) or as waves (electromagnetic waves). As formulated by Max Planck, the energy of a photon is equal to Planck's constant times the frequency of the oscillation. Thus there are photons in radio signals, television signals , radar, light etc. A recent example of research with radio frequency photons is the work of Professor Daniel Kleppner and his associates at the Massachusetts Institute of Technology using masers operating in the microwave spectrum where today's cellular telephones operate (Kleppner et al,Physics Today, 42, 24, 1989). This work, which has not been reported in the popular press, has also uncovered many strange effects at photon levels of energy which raise interesting questions similar to those published in the popular press about optical photons. However, an important point to make is that explaining signals, such as used in cellular telephony, using a few photon levels of energy, at any frequency in the electromagnetic spectrum, would be unfathomable to anyone except experts in quantum electrodynamics. However; for completeness, if we did discuss optical photons in our science texts (as your question suggests) should we not also discuss Kleppner's work with microwave photons? I believe that emphasis on photons (particles) would confuse the student, the teacher and for that matter many scientists including myself. The problem is that we are discussing esoteric phenomena at the leading edge of scientific thought which may or may not be explainable in a systematic way for decades, just as the search still continues for the gravity waves predicted by Einstein in his famous papers on general relativity. The same argument holds true for the strange behavior of photons in optical region of the spectrum. In the 21st century the new photonic devices now emerging from the laboratory to replace and /or augment electronic devices will generate ,transmit, store, manipulate and display information at incredible rates. Today's fiber optic links can transmit the contents of a 30 volume encyclopedia in 1/10 of a second. However, these systems operate by using many millions of photons per second. Signals at these levels, , measured in microwatts and milliwatts, completely overwhelm the few photon effects being studied at the leading edge of physics. In Industry today we are having to retrain optical physicists in the complex wave theory used in microwave research to enable them to understand the design and operation of the new generation of photonic devices. In my opinion, for completeness, the particle/wave duality issue should be mentioned in science curriculum (just as relativistic time shift effects and gravity waves are). However, any attempt to present the behavior of small numbers of photons while explaining the revolutionary new applications of photonics in information technology would best be delayed until students thoroughly understand the wave like nature of electromagnetic energy. In the U.S. today this generally occurs in university level education. This understanding is well beyond the scope of a K-12 science curriculum.
Return to MadSci Network