Iago: "By Janus, I think no."

----Shakespeare, Othello

The old familiar question still remains: What is Light? The basic two-slit experiment proves that light is a wave. The photoelectric effect proves that light is a quantified particle. Both of these experiments are repeatable and they both yield conflicting answers.

So what does all this mean? It can mean one of two things. Since common sense tells us that a particle is the opposite of a wave, one possibility is that we are misinterpreting the results of one of these experiments and that light is definitely a wave or a particle, but not both. The other option is that our current model of the subatomic realm must be drastically changed to account for particles behaving like waves and visa versa. It is the second option that QMs decided to take, because for all their genius they couldn't find anything wrong with the interpretation of the experiments' data and it seemed more likely that scientists a century before might have made a mistake in their model of the light and other subatomic interactions, after all they are only human. So with this in mind they went on to try to make a model that explains light's dual nature. Little did they know that they were about to make the strangest and most creative leap of human imagination in history. Even worse they were going to call it a science.

All the real trouble started with Einstein. He had just shown that waves of light come in discreet bundles called quanta. The photoelectric effect had just proven that light was indeed a particle and not a wave as the two-slit experiment shows. This seems weird enough by itself, but Einstein took it one step further. Einstein said that energy has mass and mass has energy in his famous equation E=mc2. To put it another way, a wave (Energy) is the same as (equal) a particle (mass) times the speed of light squared (c2). Energy is equivalent to mass and a wave is equivalent to a particle. To put it even another way, mass has energy and energy has mass. Einstein showed that light bends around stars and is effected by gravity. Gravity is a force that effects mass and therefore light has a mass. Einstein also showed that in order for something to travel at the speed of light it can't have a mass. In order to remedy this, Einstein said that light wouldn't have mass if it was at rest, but since light is moving it has the energy of motion and this energy has mass that can be effected by gravity.

If Einstein began to put cracks in the classical model of the universe, then Louis De Brogue demolished it with a wrecking ball. Louis came up with the concept of mater waves. Using the equations of Einstein and Planck he developed his own equation, (=h/mv. This equation gave the wavelength of matter depending on its momentum. The equation basically says that the more momentum an object has the smaller it's wavelength. When numbers are put into the equation it shows that any object in the real world would have a wave length so small relative to its size that waves would be unnoticed. This explains why matter and energy are considered two separate entities in our commonsense or macroscopic world. The equation also shows that waves would be detected in the subatomic world because they are large when compared with the particle's mass. This demonstrated that not only were waves a particle, but particles were also waves. This had some interesting repercussions. If all matter were waves then not only should light go through two holes at once, but so should electrons, atoms, and even pieces of furniture. All of these have been done experimentally, except the furniture.

If you are like me, this is about the time my head feels like someone smashed with a large brick. This feeling lets you know that you have run into duality. Light is a trickster and two faced. Light is both a wave and a particle; it just manifests itself as one or the other depending on the experiment. Light has duality. Thanks to the great literary creativity of physicists the English language has names for these two new phenomena: mass-energy and wave-particles. These concepts are difficult to grasp because they stretch commonsense to the breaking point and then gives it a swift kung-fu chop. It may make you think that the universe is just one elaborate practical joke. Fortunately there are a couple ways out of this trap. The best way to escape the prison and headaches of commonsense is to abandon it all together and embrace the imagination. This is what being a good QM is all about. This forced use of the imagination also makes quantum mechanics intrinsically valuable because it forces us to think in different ways than we are use to and hopeful they may not seem so strange, but instead just another different perspective. For example, try to imagine that mass is a representation a very condensed amount of energy needed to exist in the macroscopic world. Mass is the energy of existence. Since mass is an amount of energy, then energy itself must have mass.

Another way to get around the paradoxical trap of wave-particles and mass-energy is not to take it to seriously. Remember that it is just a model that humans make so that they can try to understand it by comparing it to something familiar. This is one of scientists favored tricks. They simple make mathematical model and leave it as that. If the math works why should we wonder what the math means. That's a philosopher's job. Although, this is one way to side step paradoxical pitfalls it is certainly not the best because it stifles progress. It impedes progress because it limits our perspective to purely a mathematical view and in order to use math practically you need to know what it means.

The invention of the wave-particle was all fine and good, except it threw a rather large monkey wrench into the fundamental clockwork of the current model of the universe. Now instead of an electron particle orbiting around the nucleus at specific levels there is a two faced wave-particle that doesn't become one or they other until it is measured. It was time for a new model; a quantum model. Armed with imagination the early QMs went out to defeat the evil wave-particle. The stage was set for the emergence of the probability wave.