Quantum Physics Essay, Research Paper

While researching quantum physics, I realized that I had just finished a book that was based on quantum theory. At the time, I didn t quite realize that quantum theory and quantum physics were related except in name. Niels Bohr once said, Anyone who is not shocked by quantum theory has not understood it. He believed this because quantum physics makes the common laws of classical physics false on small scales.

First, quantum physics is the physics of the incredibly small. It tries to explain the behavior of even smaller particles such as protons, neutrons, electrons, and even the particles that make up those particles. Would you believe that the model of an atom taught to us in chemistry is about 70 years out of date? If you understood calculus in 11th grade then the teachers probably would have taught us this new concept.

In fact, now that you know an atom isn t just a nucleus with electrons looping around it, I guess you re wondering what it looks like. Instead of having a fixed place for the electrons to be, quantum physics gives us a statistical probability of the electron s location at any one moment.

So, how was quantum physics developed? In the early 20th century some experiments produced results that could not be explained by classical physics. For instance, it was well known that electrons orbited the nucleus of an atom. However, if they did this in the manner that resembled the planets orbiting the sun, classical physics predicted that the electrons would spiral in and crash into the nucleus within a fraction of a second. Obviously that doesn’t happen, or life as we know it would not exist. That incorrect prediction, along with some other experiments that classical physics could not explain, showed scientists that something new was needed to explain science at the atomic level. This lead to Quantum Physics, Quantum Mechanics, and the Quantum Theory.

What exactly is the quantum theory? The quantum theory is as follows:

1. Energy is not continuous, but comes in small but discrete units.

2. The elementary particles behave both like particles and like waves.

3. The movement of these particles is inherently random.

4. It is physically impossible to know both the position and the

momentum of a particle at the same time. The more precisely one is

known, the less precise the measurement of the other is.

5. The atomic world is nothing like the world we live in.

This sounds exactly like any other strange theory except it is more important than most in the grand scheme of things. But, if this is right and classic physics is wrong, why do we continue to use it? Classic physics is flawed, but it is only dramatically flawed when dealing with the very small or the very fast. For everyday things, which are much larger than atoms and much slower than the speed of light, classical physics does an excellent job. Plus, it is much easier to use than quantum mechanics although we do need to use quantum mechanics.

For example, quantum mechanics has many great benefits. It can describe things that classic physics cannot, such as: discreteness of energy, the wave-particle duality of light and matter, quantum tunneling, and the Heisenberg uncertainty principle.

First, if you look at the spectrum of light emitted by energetic atoms you will notice that it is composed of individual lines of different colors. These lines represent the discrete energy levels of the electrons in those excited atoms. When an electron in a high energy state jumps down to a lower one, the atom emits a photon of light which corresponds to the exact energy difference of those two levels. The bigger the energy difference, the more energetic the photon will be, and the closer its color will be to the violet end of the spectrum. If electrons were not restricted to discrete energy levels, the spectrum from an excited atom would be a continuous spread of colors from red to violet with no individual lines. It is the fact that electrons can only exist at discrete energy levels which prevents them from spiraling into the nucleus, as classical physics predicts. And it is this quantization of energy, along with some other atomic properties that are quantized, which gives quantum mechanics its name.

Secondly, in 1690 Christiaan Huygens theorized that light was composed of waves, while in 1704 Isaac Newton explained that light was made of tiny particles. Experiments supported both of these theories. However, scientists could not associate light as either being completely wave or particle oriented. So scientists began to think of light as both a particle and a wave. In 1923, Louis de Broglie hypothesized that a material particle could also exhibit wavelike properties, and in 1927, it was shown by Davisson and Germerthat that electrons can indeed behave like waves. I know you are wondering how can something be both a particle and a wave at the same time? For one thing, it is incorrect to think of light as a stream of particles moving up and down in a wavelike manner. Actually, light and matter exist as particles; what behaves like a wave is the probability of where that particle will be. The reason light sometimes appears to act as a wave is because we are noticing the accumulation of many of the light particles distributed over the probabilities of where each particle could be.

Third, is one of the most interesting phenomena to arise from quantum mechanics; without it computer chips would not exist, and a ‘personal’ computer would probably take up an entire room. As stated above, a wave determines the probability of where a particle will be. When that probability wave encounters an energy barrier most of the wave will be reflected back, but a small part of it will ‘leak’ into the barrier. If the barrier is small enough, the wave that leaked through will continue on the other side of it. Even though the particle doesn’t have enough energy to get over the barrier, there is still a small probability that it can ‘tunnel’ through it. On the flip side of tunneling, when a particle encounters a drop in energy there is a small probability that it will be reflected. In other words, if you were rolling a marble off a flat level table, there is a small chance that when the marble reached the edge it would bounce back instead of dropping to the floor. Again, for something as large as a marble you’ll probably never see something like that happen, but for photons (the massless particles of light) it is a very real occurrence. This is exactly the type of behavior that was described in the book, Timeline , which I talked about earlier. It is also the most interesting to me.

Lastly, people are familiar with measuring things in the world around them. You pull out a tape measure and measure the length of a table. A state trooper aims his radar gun at a car and knows what direction the car is traveling, as well as how fast. They get the information they want and don’t worry whether the measurement itself has changed what they were measuring. After all, what would be the sense in determining that a table is 50 cm long if the very act of measuring it changed its length? At the atomic scale of quantum mechanics, however, measurement becomes a very delicate process. Let’s say you want to find out where an electron is and where it is. How would you do it? Get a super high powered magnifier and look for it? The very act of looking depends upon light, which is made of photons, and these photons could have enough momentum that once they hit the electron they would change its course.

Werner Heisenberg was the first to realize that certain pairs of measurements have an intrinsic uncertainty associated with them. For instance, if you have a very good idea of where something is located, then, to a certain degree, you must have a poor idea of how fast it is moving or in what direction. We don’t notice this in everyday life because any uncertainty from Heisenberg’s principle is well within the acceptable accuracy we desire. For example, you may see a parked car and think you know exactly where it is and exactly how fast it is moving. But would you really know those things exactly? If you were to measure the position of the car to an accuracy of a billionth of a billionth of a centimeter, you would be trying to measure the positions of the individual atoms which make up the car, and those atoms would be jiggling around just because the temperature of the car was above absolute zero.

Heisenberg’s uncertainty principle completely flies in the face of classical physics. After all, the very foundation of science is the ability to measure things accurately, and now quantum mechanics is saying that it’s impossible to get those measurements exact. But the Heisenberg uncertainty principle is a fact of nature, and it would be impossible to build a measuring device that could get around it.

In conclusion, quantum physics, mechanics, and theory is extremely confusing to me and I am not sure I understand them although I am shocked by what my research suggests.