Michelson-Morley Experiment in testing Special Relativity

As we learned in class, the predictions made by the Special Relativity theory are made from the assumptions that nature is the same for everybody, and that the speed of light is always constant.

In 1887, A. A. Michelson and E.W. Morley tested the fundamental premise of Special Relativity, which claims that the speed of light is always absolute. In a nutshell, the Michelson-Morley experiment showed that even though Earth moves around the Sun, the speed of light is unaffected. The experiment actually aimed to test if light waves require a medium, called a “luminous ether”, to move across. It turns out that no luminous ether is needed, and that the speed of light is always constant.

Basically, the Michelson-Morley experiment uses a device called an interferometer as shown below.

An interferometer model that was used in the Michelson-Morley Experiment

<http://scienceworld.wolfram.com/physics/Michelson-MorleyExperiment.html>

The idea of the experiment is to basically measure the speed of light from different directions in order to measure the speed of the “luminous ether” relative to Earth, in order to establish the ether’s existence. However, the results of the experiment indicated no shift in interference patterns, implying that there is no ether, and that the speed of light is always constant.

Personally, I feel that testing the speed of light is difficult, and would require complex experiments such as the one above. I think this is because everyday, we are not exposed and are not interacting at such extreme high speeds, and therefore this concept of light speed is difficult to conceptualize, and hard to demonstrate. We even had to do thought experiments like we did in class in order to understand the speed of light – this demonstrates the difficulty of demonstrating and testing special relativity.

Additionally, I feel that these types of complex experiments that test relativity are based on so many assumptions (e.g. the Michelson-Morley experiment assumes that Earth orbits the Sun at 30km/s), thus making them fragile. However, because these assumptions have been tested and verified many times, I am quite confident that they represent reality well, and that we should keep testing past theories to improve their accuracy.

Sources:

• The Cosmic Perspective: Stars, Galaxies & Cosmology, Page 411 by Bennet, Donahue, Schneider and Voit.
• http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/mmhist.html
• http://www.aps.org/programs/outreach/history/historicsites/michelson-morley.cfm
• http://scienceworld.wolfram.com/physics/Michelson-MorleyExperiment.html
• http://en.wikipedia.org/wiki/Michelson–Morley_experiment