MadSci Network: Physics

Re: How is light propagated through a vacuum?

Area: Physics
Posted By: David Barlow, Private individual, Grad education in Physics/Astrophysics and Comp. Support
Date: Mon Mar 24 10:22:36 1997
Message ID: 856562982.Ph

Dear Yugal

Light is not a disturbance in the electromagnetic (EM) field. It is the electromagnetic field. That is, a light ray is an EM wave travelling through space. Ever since Newton determined that light behaved as a wave it was thought that the wave must travel in some medium, like sound through air. This medium was called the Superluminous (sometimes Lumiferous) Aether. In order for light to travel in the Aether, the Aether must exist at all points in space. This implies that it should be detectable by some means. As the Aether was never detected by anyone it was thought to have zero density yet would have to be infinitely elastic. Properties that are mutually exclusive.

By the late 1800's it was discovered that moving magnets induced electricity and alternating electric currents created magnets. In a famous experiment by Michelson and Morley, it was also discovered that the Aether did not exist as well. So, James Clerk Maxwell set out to tie these properties together. He proposed that Electricity and Magnetism where special cases of another force, Electromagnetism. The Maxwell Equations describe how this force works and how EM waves move.

These directly describe the motion and propeties of light as a Wave travelling through a vacuum as a combined magnetic and electric field changing with time. One of the most difficult concepts that these equations throw up is that light is self-propagating and `self powering', it is simply energy travelling without any resistance, and needs no medium to travel in. Another strange idea is that of the vacuum having electromagnetic properties called Permittivity and Permeability. The value for these quantities are what determines the speed of light in a vacuum. A full analysis of the Maxwell Equations can be found in any book on electromagnetism and only requires knowledge of vector analysis and vector fields. As you are in a University I suggest visiting a Library or your Physics Department.

As an aside here. The Maxwell Equations where found to be incomaptible with Newtonian Physics and ultimately led to the Special and General theories of Relativity being discovered. Once light was better understood it was realised the Universe was stranger than was ever imagined before. I think most physicists will, very relunctantly, admit that we still do not really understnd what light is even today. Even though light is wave it behaves as a particle sometimes. These different properties are what Quantum Mechanics (QM) is concerned with. QM though interprets waves as the probability of where the particle exists.

Current Queue | Current Queue for Physics | Physics archives

Return to the MadSci Network

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network
© 1997, Washington University Medical School