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Weird Physics

Section 6 – How Light Moves – Coupled Oscillators

The historic debate about whether there is such a thing as the “ether” cuts at the question of whether there is a medium through which light travels.  The assumption there is that light, an electromagnetic wave phenomenon, exists independently of the stuff that is being polarized.  This was discussed in the earlier chapter touching on the bogus Michelson-Morley experiments that purported to disprove the existence of an ether wind.

What is being polarized by the moving electric field?  The electromagnetic material that occupies space, of course.  Light travels through populated space where there is polarizable material, NOT through a total vacuum, which has no polarizable material in it.  To polarize material, you must move the positive and negative charges further apart (gage by center-of-mass when you’re talking about waves).  Atomic nuclei are relatively heavy and don’t move much, so really you’re talking about nudging the electron’s wave function away from the nucleus.  This actually changes the shape of the orbital being occupied (which is the same as saying the electron’s wave function is shifted in that way).  If the shift is strong enough, the electron may be twisted into a different orbital from the one originally occupied, which might then be stable.  This would involve absorbing or adding the difference in the energy to the strength of the electric field.

What we are describing here is the absorption of passing light energy in a way that causes the electron to shift into a different state.  These states are at characteristic levels so the possible units or quanta of energy are fixed by the spectrum of the atom.  However, there are other processes, such as were discussed earlier in connection with the Hubble Red Shift, in which smaller amounts of energy could be absorbed or picked up, for instance from the rotation or vibration of a complex molecule, or from the mere translation of the center of mass of the atom.

But all these processes presupposes that there was a stand-alone electric field to start the process.  Now you might say we can create static electric fields by putting charge on parallel plates, for instance – but where did that charge come from?  In charging the plate, you are separating a proton from its associated electron.  I would suggest that all electric fields are in fact generated by distortions in atoms (and molecules).

So, in the general case, a distorted atom distorts the one next to it, and so on to propagate the wave, just like the “swinging-balls” toy.  When it gets to the end, the energy can’t be absorbed so it bounces back and the wave continues.  All this with energy that does not match a particular transition electron orbital transition so there is no significant absorption of light.

A more interesting case is when the wave is started by an electron dropping from a well-defined high energy state to a lower energy state, and an identical atom is near-by.  Now instead of the energy release just distorting the neighboring atom’s orbitals, there is an easy response in the neighboring atom – it simply absorbs the light and does the reverse of the electron transition of the first molecule.  For book-keeping purposes we are taught to think of the first atom emitting a photon, then later the second atom absorbs that photon, but when you do the quantum wave mechanics you find that the transfer of energy from one atom to the other is a continuous rather than digital process.  As the first atom is dropping from 100% to 0% of the energy, the other atom is simultaneously rising from 0% to 100% energy.  Energy is conserved.  The rate that this happens depends on the distance between them and, low and behold, it is this interaction rate that defines what the speed of light is.  As such a packet of excitation energy skips from atom to atom (or molecule to molecule) we see that each interaction slows the wave down a trifle, giving a speed a light slightly reduced due to the presence of matter (ratio is called the index of refraction, and is a function of polarizability.  Delay is due to the time to move around the electrons).  Taken to the extreme of distance, the delays vanish and we get the pure speed of light in a vacuum, except of course with such a weak interaction, no energy moves so no exchange is happening on realistic time frames.  If the local universe is comprised of just two atoms (otherwise described as harmonic oscillators), then the energy just cycles back and forth between them indefinitely.  When you look at a distant star, the atoms in that star are not coupling with your retina – the energy left that star years ago.  The molecules in your retina are interacting with the atoms and molecules that occupy the space in front of your face.

A lot of this was learned by the study of chlorophyl in leaves.  Sunlight excites one chlorophyl molecule.  That energy packet then bounces from molecule to molecule in an array of chlorophyl molecules arranged in the leaf.  Excitons race in lines to the edge of the leaf, then bounce back.  Eventually the exciton is absorbed by a slightly different molecule that dissipates a small part of the energy.  The exciton is now too small to move back to the chlorophyl because the energy doesn’t match any more, so the energy is “trapped” by this second molecule.  This then is the site where the cellular mechanism is located, to convert that energy to ATP bio-energy.  The cellular mechanisms are vastly outnumbered by the chlorophyl mechanisms that are there to absorb sunshine and send it through the leaf to the trap site.

So far we’ve come to the same conclusion as we did in a previous chapter.  Light photons do not exist by themselves, they are simply a book-keeping mechanism for energy moving from one atomic or molecular system to another.  Einstein ran into trouble trying to predict the spontaneous emission of light by an isolated atom because they don’t do that.  If there is no environment to interact with, there is no loss of energy.

So what is the ether?  Still no such thing per se – since there are no photons there is no need for a separate medium to carry light.  What we call light is an energy exchange between atoms (or molecules) and the proper reference frame should be the center of mass of those objects, with the relative velocity between them as a variable that affects the energy exchange in some complicated way.  If the energy being exchanged matches with a shift of the electron from one orbital wave pattern to another, it happens easily and may be lasting, but if the energy absorbed does not match with a stable transition, the electron will doggedly return to a stable state and spit that energy back out again.

A more general case here makes a valuable take-home message.  Any time you have two “harmonic oscillators” with similar energy levels, they will act like they are “coupled” and any excitation energy on one will be shared with the other system.  This is a pervasive concept in quantum mechanics, that coupled systems will blend together and find a replacement set of states (same number of choices as before), one of which is lower energy state than would be the case in the absence of blending, and another of which is the opposite, with higher energy and thus less stable.  Since entropy demands that the extra energy wander away to find the maximum entropy state, the atoms always move to the more stable blended state and release the excess energy.  The more different the oscillators are in energy level, the weaker the coupling, so the less this happens.

In short, our universe is a massive collection of coupled, interacting harmonic oscillators.  Understand this, and you’re on the way to understanding gravity.

[© Copyright 2016 by Gerald Keep.  All Rights Reserved.]



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