Saturday, September 5, 2009

Quantum Mechanical Way of Thinking

Atanasoff-Berry Computer
(Wikipedia, 2009)

I’m asking you to read this whole blog without skipping any details. I know that is a lot to ask of my readers but this is a topic that few people understand. I will try to make it clear as possible.
Why should you read it? Do you own a cellphone? Do you have a computer at home? Do you use a DVD player? All these devices need quantum mechanics in order to operate. We are indebted to the brilliant people that discovered quantum mechanics.
What is quantum mechanics? It is the study of matter at the molecular, atomic, or microscopic level which doesn’t follow Classical or Newtonian Physics. Scientists found during the early 20th century that they couldn’t use Newton’s laws to describe electromagnetic radiation or light emitted from a black body. A blackbody is a perfect vessel that absorbs but doesn’t reflect light. It will emit radiation like infrared, visible or ultraviolet light according to its increasing temperature.

Scientists had to come up with a different way of thinking to solve the problem with electromagnetic radiation. They realized that light didn’t contain an infinite amount of energy. Max Planck was the first person to suggest that photons (or particles of light) were quantized. This means that each photon of ultraviolet or infrared light contains a specific amount of energy.
Planck suggested using a constant, h (which is a specific number) to figure out how much energy was contained in that photon of light. Albert Einstein came up with an explanation for the photoelectric effect. If ultraviolet light is absorbed by a metal plate, electrons are ejected from the plate. He used Planck’s idea the blackbody behavior to describe the photoelectric phenomenon. Einstein suggested that each photon or particle of light contained a specific energy which was proportional to the light’s wavelength multiplied by Planck’s constant (E = h x v). Einstein later won the Nobel Prize for this in 1921.
This opened the door to quantum mechanics. Scientists began asking themselves if electrons could be particles or waves. Niels Bohr postulated that electrons were quantized into different energy levels. He tried to explain the wavelengths of light that were emitted from excited hydrogen gas (see picture below). Bohr incorrectly described the electrons as orbiting particles around a nucleus.
Louis de Broglie suggested that electrons and other matter under certain conditions would behave as a particle or wave. When light is passed through two narrow slits, an interference pattern. This is evidence of wave properties. Clinton Davisson and Lester Germer demonstrated an interference pattern with an electron beam and a crystal of nickel. The wave properties of electrons were then described mathematically by Erwin Schrodinger. His wave equation helped predict the probability of locating an electron in a certain position. Schrodinger later won the Nobel Prize for his work with electron wave equations in 1933.
With Schrodinger’s equation (which is considered quantum mechanics) the electron configurations were described for hydrogen. Heisenberg, Dirac, and Pauli added more mathematical descriptors that helped identify the shape of atoms larger than hydrogen. Scientists learned how to predict the behavior of atoms once they understood their structure.
With the advent of atomic structure, the information age had begun. The first computer was made in 1939 by Dr. John Atanasoff and graduate student Clifford Berry. The Atansoff-Berry Computer (ABC) was a simple machine that used the binary system and electricity. It used Boolean algebra which is the basis for “on” or “off” (also known as 0 or 1). The second and more well known computer was Electronic Numerical Integrator and Computer ENIAC in 1945. It was the size of a suburban house and was originally designed to calculate artillery firing tables for the Army. Since it was completed after the war, the military used ENIAC for its nascent nuclear weapons program.
In 1947 at Bell laboratories, the first transistor was made of gold contacts and germanium. This early semiconductor couldn’t have been created without quantum mechanics and the understanding of how atoms behave. Present day microprocessors are multicore silicon chips with halfnium-infused circuitry. These microprocessors run at 3.2 GHz (gigaHertz) speed.

Lasers wouldn't have been created without Einstein's theory about photons. Electrons can absorb and emit photons so a laser is a light emitter at a specific frequency like infrared. Lasers are used for CD-ROMs and DVD players. We wouldn't be in this information age without quantum mechanics.

I hope this essay has helped you understand quantum mechanics a little better. It's a fascinating topic that has many applications. Who knew that Planck, Einstein and Schrodinger (to name a few would) leave behind a useful legacy. Here's to quantum mechanics and the information age.

Astronomy Podcast (Quantum Mechanics) 

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