Wave Particle Duality

Wave Particle Duality

Joseph Courtney

AP Physics C- Mr. D.A. Young

Updated Friday, May 26, 2006

Wave Particle Duality is just one more phenomenon that shows the non-intuitive-ness of reality.

The entire debate began between Christian Huygens an Isaac Newton. Huygens proposed a wave theory of light which had many problems when attempting to describe many of the often observed properties of light. Isaac Newton then proposed his theory of light explaining that it was composed of corpuscles of light. This allowed him to explain reflection, refraction, and the splitting of light into a rainbow.

As Newton was the god of all that was physics for a long time, his theory was taken as truth and not challenged—until diffraction was discovered. Diffraction is the interference of light waves after passing through a grid or a set of slits. The double slit experiments of Young and Fresnel created interference patterns which could only be described by a wave theory of light. Thus Huygen’s theory gained acceptance.

Then Einstein came along. He studied the Photo-electric effect where the excitation of electrons within a metal by light only occurs when the light’s frequency is above a certain value. This implies that the energy of a photon is related to the frequency of the photon rather than to the amplitude of the “light wave” or to the intensity of the light. Einstein then described this phenomenon by stating that the energy must occur in packets of light, each having a certain frequency. He called these packets of light photons. He also described the energy of a photon by stating that its energy was described by the equation where E is energy, h is Planck’s constant, and is the frequency of the light. This caused an uproar and thoroughly confused people as to whether light occurred in particles or waves.

Then there was de Broglie. He generalized Einstein’s equation for the energy of light by taking the description of the momentum of the photon, p=E/c, and the definition of the wave length of light as λ = c / ν. He combined these to make his own equation λ = h / p. This was generalized for all matter and light. He used this equation to describe the wave length of the electron which he then used to describe the quantized nature of the electron energy levels of the hydrogen atom. He proposed that energy levels only occur when the electrons orbit is a whole number of electron wavelengths which would make the energy of each level also whole number intervals.

This allows me to find my wavelength. If I were driving down college at 20 meters per second and me being roughly 70kg on a good day, I would have a momentum, p, of 1400 kg·m/s. Using the de Broglie equation, my wavelength would be Planck’s Constant devided by my momentum. This would mean that my wavelength at that velocity is about 2.732x10^-37 m.

Since the Particle-Wave, Wave-Particle Duality of matter and light has been accepted, although not intuitively understood, by the majority of physicists. Many experiments have been performed to attempt to diffract larger particles through a double-slit such as neutrons, protons, water, and even Buckminster fullerene. Theoretically a particle such as a bacterium would be impossible to diffract due to its wavelength being smaller than the Planck length, the theoretical quantization of the spatial dimensions. However, work is being done to attempt to diffract virus particles.

Now Wave-Particle Duality has been used to describe many natural phenomena such as the interference caused by the fluctuating densities and thicknesses of soap bubbles which give them their iridescent look, the polarization of light, the reflection of light by Mirrors, classical optics, rainbows, why the sky is blue, the many phenomena in chemistry, and why we can see.

I acquired much of my information from these two websites

http://en.wikipedia.org/wiki/Wave-Particle_duality

http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html

FERROFLUIDS!

Ferrofluids.htm