Introduction

From the time that we are infants, our senses and understanding of what we see and hear lead us to make basic assumptions and reasonable conclusions about the makeup of our world and how it operates. But science is slowly but surely unveiling a picture of the world that differs greatly from how things would seem to work.

For example, consider the computer that you are using to read this article. From a practical standpoint it is a solid object, made of plastic, metal, and other substances that you can feel and touch. But in reality it's substances are made up of tiny molecules that are moving around. In turn, these molecules are made up of atoms, which in turn are made up of different arrangements of subatomic particles which give them their differing properties. Some of these particles are constantly whirling around the central nucleus of the atom at fantastic speeds.

This is just one basic example of how science reveals an entirely different picture of the universe then that which we can see and sense. What was once a solid, stationary object is now a jumble of particles, constantly moving in intricate patterns and arrangements that keep them linked together as a static mass that we can feel and move.

As science explores the extremes of physics at the fastest speeds, coldest temperatures, and smallest scales it is gradually changing our understanding of how the world works. Currently one of the most baffling and seemingly impossible of these fields is that of quantum mechanics.

The Basics of Quantum Mechanics

Simply defined, quantum mechanics is the application of the uncertainty principle to our interpretation of real life. The uncertainty principle basically states that certain pairs of related properties can not both be measured accurately. Attempting to measure one property always disturbs the measurement of the other property. This has been proven to be the case with subatomic particles, in which it is impossible to measure both the velocity and the position of a particle.


This mathematical principle has broad applications which explain some of the most baffling problems across an immense field of sciences, including nuclear, particle, atomic, and light physics.

The Double Slit Experiment

One of the fundamental experiments used to prove quantum mechanics is the double slit light experiment. In this experiment a thin plate with two narrow slits is placed in the path of a bright laser. The laser is aimed at the solid area between the two slits.

Even with a laser, in which the light is concentrated in a very narrow beam, it is to be expected that there will always be some light spillage and stray photons that will go through the two slits. Therefore, it is to be expected that the experiment will yield two narrow bands of light.

Researches were baffled, though, when they discovered that the result was a wave pattern, with the majority of the photons hitting the area directly behind the solid portion between the slits. This lead scientists to change their theory or light to consider light to be either a wave, or else made up of particles that traveled in waves.

In time scientists developed a way of creating a light source that emitted photons one at a time. Over time these photons still created an interference wave pattern, rather than two parallel beams. This would seem to be impossible, for a single particle can not interfere with itself.

So researchers decided to put a sensor on one of the slits to detect whether the particle was passing through the slit. In this way they could see if the photon was indeed going through one slit or the other. But when the detection mechanism was added the interference pattern disappeared, and the device began behaving as would be expected, yielding two individual bands of light.

Again and again over the decades experimenters repeated the double slit experiment, using electrons, photons, and other particles. The results were always the same. Contrary to reason, single particles produced interference patterns. When measurement devices were added the interference patterns disappeared and the experiment began behaving as expected.

The Theories of Quantum Mechanics

Quantum mechanics attempts to explain the double slit experiment using the uncertainty principle. Mathematical formulas and experiments would seem to indicate that as long as no measurement mechanism is in use a single, physical particle goes through both slits at once. In fact, at any given point the position of the particle is never in one certain space.

One of the more bizarre applications of quantum theory is Schrödinger's cat. This strange thought experiment links the life of a cat to the state of a subatomic particle. Why Schrödinger choose to use a cat for the experiment no one will ever know, but one thing is certain, the experiment links the cat to a "diabolical mechanism," as Schrödinger put it in his own words.


A cat is placed in a box sealed against any outside influence that could measure what was happening inside the box. Also present inside the box are an extremely small piece of radioactive material that decays at a slow rate. A Geiger counter is also present to detect radiation emitted by decay of the material. It may be hours before an atom decays and releases radiation, but if the Geiger counter detects it then it triggers a mechanism that shatters a vial of lethal airborne poison that kills the cat.

According to the laws of quantum physics, and the mathematics used to approximate it, then as long as the box is kept sealed the cat is both dead and alive. This superposition of states simply doesn't make sense.

However there are far too many experiments and mathematical proofs to throw quantum theory out completely. That is why ever since quantum theory was discovered philosophers, mathematicians, and physicists have been trying to find a rational explanation or reasonable theory to link it to our observable world and way of thinking.

In 1972 Hugh Everett released a paper theorizing that quantum physics was simply a case of parallel worlds. If there are no observers then the cat is neither dead nor alive. When the box is opened, however, the universe splits apart into two parallel tracks, one in which the cat is still alive, the other in which it is dead.

Why Quantum Theory Matters

The truth of the matter is that no one knows why mathematics and experimentation seems to prove such a bizarre theory as quantum mechanics. To be truthful, the theory is hotly contested by many people, with arguments to disprove it or argue that the experiments behind it are meaningless.

One thing is certain: if quantum mechanics could be applied to computing it would completely change the face of world forever. With quantum mechanics there is theoretically no limit to how fast a computer can be. Because a quantum photon or electron exists in all states at once you could theoretically design a device that ran all possible cases of an iteration in the time that it takes to do one iteration.

Programmatic loops would work totally differently than they do now. The loop's counter would simultaneously take all possible values that could be assigned to it, and calculate all possible results in the time required to run one iteration of the loop. For example, if the quantum program entered a loop of one million iterations it would be as if the computer split apart into one million computers (each in its own parallel universe, according to Everett).

This would completely destroy all computer security because it would make brute force attacks against encrypted files a trivial thing. The encryption key would simply be made a quantum variable and the code would decrypt all possible key or password cases in the time required to decrypt the code once.

There is only one small problem.

Attempting to measure the results or determine the answer should force the quantum system out of its superpositional state into a single deterministic value, just as in the two slits experiment where adding a measuring device destroyed the wave pattern and forced the photons to go through one slit or another.

For this reason quantum computing will probably never happen. But who knows? The field of quantum research has already turned up many strange and apparently inexplicable possibilities. There is no telling what is around the corner.

For more information see:

The Big View

A very professional and full featured site that covers not only quantum theory, but also relativity, time dilation, and space time.

Srikant.org

A very scholarly site with a lot more of the mathematics and intermediate research that I didn't cover in this simplified coverage of quantum mechanics and quantum theory.

Quantum Computers

More detailed information about quantum computers, from Wikipedia. One of the most interesting sentences: "Both practical and theoretical research continues with interest, and many national government and military funding agencies support quantum computing research to develop quantum computers for both civilian and national security purposes, such as cryptanalysis." You know that governments and the military would love to be able to decrypt any message nearly instantaneously.