THEORY BALLS A theory ball is a collection of observations, explanations, and predictions. A complete theory ball is considered to be perfectly round, and indicates that every observation is explained, and every prediction is observed. Where the theory ball is not round, then some observations are not explained, or some predictions are not yet observed. The scientific method consists of the following sequence: Observation -> explanation -> prediction -> observation. Notice it is a circle. For example, light was observed to have different colors. This was explained by theorizing that light was a wave with frequency, speed and wavelength, each color being a different frequency. People were already very familiar with wave mechanics through their study of air and water. From this idea that light was a wave it was predicted that light should show defraction (spreading) when sent through one slit and interference patterns when sent through two slits. These predictions were then observed and thus became part of the complete theory ball of light. Notice the above does not PROVE in any sense of the word that light is in fact a wave, only that by assuming that light is a wave (the explanation), one could make workable predictions that always turned out true. This is called the 'test of time'. However from the assumption that light was a wave, it was also predicted that the wave must be a wave IN some medium, just as air waves are waves in air, and water waves are waves in water. Both air and water waves exhibit diffraction and interference just as light does, so it made sense to think that light might also travel in a medium. Both air and water also have fixed speeds relative to the medium they are traveling in, and so it was also predicted that light had a fixed speed relative to the medium it traveled in. Both air and water also displayed Doppler shifts in speed. When a car is moving towards the source of a sound wave, not only is the frequency perceived to be higher, but the speed of the sound wave passing by the car is higher by the speed of the car. And when the car is moving away from the sound wave, the frequency is perceived to be lower, and the speed of the wave passing by the car is slower again by the speed of the car. It was therefore predicted that light should show the same behavior. The medium that light traveled in was called the aether and was futher predicted to be the background fabric of space and time itself. Further since the Earth was moving like the car through that background fabric, the measured speed of light should change depending on how fast the Earth was moving through the medium. Since the Earth moves around the sun in a circle through out the year, it should be found to be moving through the aether during most of that time, except during a possibly very short moment when its speed matched the aether, if it ever did. Remember the Earth is moving around the Sun, but the Sun isn't still in any sense of the word, it is moving around the galaxy which itself is moving at humongous speeds away from everything else. So frankly it was predicted that the Earth would never be found to be moving at the same speed as the aether. It was easy enough to find out the speed of light but the problem was that the measured speed was the same no matter what direction it was measured in, and no matter what time of year it was. Since the earth was moving at a significant speed through the medium itself, then the speed of light should have reflected the speed of the Earth, depending on the time of the year, as the Earth went around the sun and completely changed directions. At first they theorized this observation was caused by the Earth dragging the aether along with it, so that at all times the speed of the Earth relative to the aether was zero. But then they repeated the experiment with light coming in from the moons of Jupiter as they orbited around the giant planet. Light leaving the moon as it moved away from Earth should be traveling slower than the light leaving the same moon as it was approaching Earth on the other side of Jupiter. But they got the same answer, the speed of light was constant no matter how fast the source or observer were moving, or in what direction. This could not be reconciled by the existing explanation that light was a wave like air or sound. In fact it couldn't be reconciled by any existing theory of the time at all, it was so impossible that most dismissed the observations as false and badly done experiments. Eventually Einstein came to the rescue with a 'new' explanation of why the speed of light was constant, called the special theory of relativity. Things haven't been the same since. Light was a wave, but there was no medium, no aether, and space and time were relative to the speed observers had with each other. Space and time obligingly 'adjusted' themselves to make sure that the speed of light was always the same no matter the speed of the observer or source. It was almost as if every observer/source pair lived in a universe of its own. But people no longer worried about the physical significance of theories any more, physics was very happy and great things came of special relativity over time. So the theory ball of light was round and complete again, all observations were explained, and all predictions were observed. However a few years later another observation was made about light that once again threw the whole world into chaos. This was the photo electric effect. When light is shined on a metallic surface electrons are freed from the surface with an energy equal to the energy of the light shining on the metal minus the energy it took to escape the metal's hold. The problem was, with a wave, the 'energy' of the wave is usually considered to be the sum total energy of the whole wave. Thus the prediction was that by shining a brighter light of the same frequency on the metal, more energy was hitting it, and more electrons should come off. What they found instead was that below a certain frequency electrons did not come off the metal at all, no matter how bright the light was. And yet above a certain frequency electrons started coming off the metal no matter how dim the light was. This was definitely not wave like behavior. But then light was already pretty weird so people set about trying to explain these observations, as clearly the predictions were wrong. Einstein again came to the rescue by suggesting that light was not a wave but a particle called a photon, and each particle had an energy proportional to its frequency. Only one photon was involved in the release of one electron from the surface of the metal, and if the photon's collision with the metal did not have the required energy, no electrons would be freed no matter how many photons were hitting that electron at once. This is counter intuitive. Consider being hit by a one pound ball of lead, that would hurt, right? Now consider being hit by a ping pong ball. That wouldn't bother you, right? But now consider being hit by a million ping pong balls all at once. That would bother you right? But not so the electron, the electron didn't care how many half pint photons hit it, but all it took was one full pint photon and out of orbit the electron went. In other words photons were not additive the way waves and ping pong balls are. So if the photons did have a higher freqency and thus a higher energy, then each photon would release one electron from the metal surface. This indicated that whatever light was, it could only transfer energy to electrons in finite quanta of energy, which was the energy of the photon. With this understanding that light was a wave when looked at on a macro scale, but a particle when looked at on a micro scale, the theory ball again became round and complete. All observations explained, and all predictions observed. But then someone chimed up and destroyed the happiness. He said remember that waves show diffraction and interference patterns when sent through two slits but particles don't. This is because waves interfere, crests add with troughs to cancel out, particles don't have this so they don't. So now we know that light is a particle at the micro scale, how come it produces diffraction and interference patterns when sent through two slits? Worse one day, someone got real ornery and decided to really bring the point home. He built a long pipe with two slits at the far end. He made sure that the source of the light was so dim that only one photon could be in the pipe at any one time, and thus there was no possibility that any photon going through the right slit would ever meet up with another photon going through the left slit and thus cancel producing an interference pattern. He thus predicted that since light is a particle at the micro scale, and surely one photon is micro scale, that it ought to act as a particle and go through either the right or the left hand slit and not produce an interference pattern on the other side. Interference patterns are only produced when TWO waves go through TWO slits AT THE SAME TIME and thus cancel AT THE SAME TIME at the phosphor screen at the far end. So he did the experiment predicting no interference patterns, but lo and behold there it was, an interference pattern. If God was wise, he was also obviously a jerk. Was the photon going through BOTH slits at once? How could it go through both slits, if it were a particle? It could only go through both slits at once if it were a wave, then it could interfere with itself. Well it took a while, but eventually they came up with a final theory which is of course quantum mechanics. Quantum mechanics has been hailed as the most universally workable theory human kind has every devised to explain anything, the products of its genius are all around us, cell phones, TV's, computers, you name it. But any quantum physicist will tell you that quantum mechanics is also the first theory that no one on Earth has a clue what it saying. Well its actually the second, special relativity was the first. Roughly what quantum mechanics is saying about light, is that light is neither wave nor particle, but a probability which is spread out over space and time, concentrated and high at some points, and defuse and low at others. Thus as the light wave approaches the two slits, it has a probability of going through either slit that is non zero. The probabilty wave will probably be higher for one slit than the other, but will always have some finite probability at both, even if the photon is aimed way off course from both slits. The probability wave thus does go through both slits and thus interfers with itself, thus producing interference patterns. The photon only stops being a probability and becomes an actual photon when it needs to, namely when it finally hits the phosphor screen on the other side and has to make it glow. So that made everyone happy and they chattered about it on their cell phones and video cameras, until one day someone thought to carry the experiment further. They put a sensor on each side of the two slits which would detect the photon passing through the slit and thus report if it was in fact going through both, or just one. They had to know, it was driving them crazy. So they set up the same experiment with the sensors in place but turned off, and there was the interference pattern indicating that the single photons were going through both slits at the same time. Remember there was only one photon in the tube at a time. Then they turned the sensors on, and suddenly the interference pattern vanished and started to look like a simple spread as if light really was a particle going through one slit or the other but not both. The sensors reported this very same fact and for every photon that went through the slits, the sensors could tell exactly which slit the photon went through. They were not going through both. But turn the sensors off, and the interference pattern came back. It seemed like trying to detect which slit the photon went through forced its proabability wave to decide before it entered the slit that it was going to be left or right. But turn the sensors off and the decision was never made until it hit the phosphor screens where it was too late to avoid self interference. They still haven't explained this one to this day, oh yeah there are lots of theories to explain it, each one more incomprehensible than the one before it, and the real sign of how bad it is, is that the various camps holding each theory aren't even on talking terms with the other. "Yours is more incomprehensible than mine!" You will find most of them playing Jacob's Ladder with string theory. Such is the state of knowledge today about the nature of light, the theory ball isn't quite round yet. Homer ------------------------------------------------------------------------ Homer Wilson Smith The Paths of Lovers Art Matrix - Lightlink (607) 277-0959 KC2ITF Cross Internet Access, Ithaca NY homer@lightlink.com In the Line of Duty http://www.lightlink.com Mon Feb 26 22:54:31 EST 2007