Light through window.
Ether
At the turn of 20th century, physicists wondered if they could use vector addition rules for the motion of light. The first hint that they received about light being different from other phenomena was from Maxwell, who claimed that light was an electromagnetic wave travelling in vacuum at 3.00 x 10^8 m/s.
Until then, physicists believed that waves must have a medium through which they traveled and so if light was a wave, then it must also have an associated medium through which it traveled. Perhaps this medium was the absolute frame of reference of the universe and the frame which Maxwell used for his calculations.
They called this medium ether and believed that it let bodies move through it freely without any resistance. Ether was also thought to have zero density and to permeate all space.
At the turn of 20th century, physicists wondered if they could use vector addition rules for the motion of light. The first hint that they received about light being different from other phenomena was from Maxwell, who claimed that light was an electromagnetic wave travelling in vacuum at 3.00 x 10^8 m/s.
Until then, physicists believed that waves must have a medium through which they traveled and so if light was a wave, then it must also have an associated medium through which it traveled. Perhaps this medium was the absolute frame of reference of the universe and the frame which Maxwell used for his calculations.
They called this medium ether and believed that it let bodies move through it freely without any resistance. Ether was also thought to have zero density and to permeate all space.
The Michelson-Morley Experiment
Figure 3
In order to test whether ether really existed, many scientists began to design a number of ingenious experiments. The most successful and widely regarded of these experiments was conducted by Michelson and Morley in 1887. To summarize, Michelson and Morley essentially compared the relative speeds of light in two perpendicular directions relative to Earth's motion through the ether.
If Earth moved with velocity v, then in a frame on Earth it must be travelling at velocity -v, creating an 'ether wind'. Basically, these experimenters were trying to detect a small difference in the speed of light dependent on the orientation of their apparatus in the ether wind, as shown in the figure to the right. In the end, the Michelson-Morley experiment proved that ether does not exist and many scientists tried to give explanations for this result.
The Special Theory of Relativity
Theory of relativity.
In 1905, Albert Einstein proposed an explanation for the failure of this experiment through his theory of special relativity, which has two postulates:
1.The relativity principle: all the laws of physics are valid in all inertial frames of reference.
2.The constancy of the speed of light: light travels through empty space with a speed of c=3.00 x 10^8 m/s, relative to all inertial frames of reference
References
- Hirsch, A., Stewart, C., Martindale, D, & Barry, M. (2011). Nelson Physics 12. Toronto: Nelson Thomson Learning
- Light through window retrieved from http://udn.epicgames.com/Two/rsrc/Two/ExampleMapsLightBeams/lightbeam.jpg
- Theory of relativity retrieved from http://2.bp.blogspot.com/- fWx3Emp7qm4/ThGlDZOo1CI/AAAAAAAAAto/Rz3PcOg3dQE/s1600/theory-of-relativity.jpg