By completing these activities students should be able to:
·       outline the features of the aether model for the transmission of light

·       describe and evaluate the Michelson-Morley attempt to measure the relative velocity of the Earth through the aether

·       discuss the role of the Michelson-Morley experiments in making determinations about competing theories

·       gather and process information to interpret the results of the Michelson-Morley experiment

The Aether

At the time of Michelson and Morley, that is the late 19th Century, it was unknown for energy to move from one location to another unless it was carried through matter.  For example sound energy moves from one person to another by making the air particles between the two people vibrate, therefore no air will mean no sound.  So the same was assumed of light.  If light energy was to move from the sun and distant stars to be seen on Earth then there must be a form of matter that existed between Earth and the source of light.  This matter, though, must have special properties such as: 
  • filling all of space and be stationary in space
  • be perfectly transparent
  • permeate all matter
  • have a low density
  • have great elasticity in order to propagate the light wave
The last two properties were explained as it was known that the speed of light was approximately 3.0 x 10^8 m/s, significantly faster than sound energy, and that energy travelled faster in more dense materials, therefore particles needed to be able to collide easily, but the aether needed to be low in density so objects, such as planets, could easily move through it.  It was postulated that this aether was stationary and was the universal reference point of all motion including the rotation of the Earth; that is as the Earth moved around the Sun it moved through the aether, a bit like a person swimming in a pool of water.

Such a material was labelled as luminiferous aether and carried light energy from one source to another.  It was hypothesised that if the Earth was moving through this aether then there should be relative distortion of light as a consequence.

The following three videos provide a good introduction to the Michelson Morley experiment and how it relates to the later work of Einstein.

Michelson-Morley Experiment

To begin your investigation of the Michelson and Morley Experiment, firstly read the material located at http://galileo.phys.virginia.edu/classes/109N/lectures/michelson.html and investigate the flashlet linked to on this webpage.

TASK: Write up the experiment using the scientific method; that is what is the hypothesis to be tested, what is the predicted result, how does the experiment work, what was found out, how does this inform the hypothesis?  In your write-up include a diagram of the equipment used by Michelson-Morley.

Question: It is often stated that the Michelson-Morley experiment produced a null hypothesis, undertake a search of this term and discuss whether you think the Michelson-Morley experiment was a failure or success.

Question: Einstein once said "...remember gentlemen, we have not proven that the Aether does not exist, we have merely proven that we do not need it ..." (source: sci.tech-archive.net).  Reflect on your response to the first question and consider the value of the Michelson-Morley experiment to the developing understanding of light and space.