Turning Points - Special Relativity Flashcards
What is an ether ?
The ether was thought to be an invisible medium, through which all objects moved through. It was used to explain the speed of light. As light was a wave scientist thought that it needed a medium to travel through, and they thought that light travelled through the ether.
What did Michelson-Morley try to show in their experiment?
It was assumed that the Earth travelled through the ether, and therefore there is an ether wind. They thought that this ether wind would affect the speed of light, depending on whether the light was travelling parallel to the earths motion, or perpendicular. The aim of the experiment was to observe a difference in speeds of parallel and perpendicular beams of light, and therefore determine the speed of light relative to the ether.
They expected to see a shift in the interference pattern when they shift their interferometer as this would show that the speed of light is different depending on their direction relative to the ether.
What was the set up of the Michelson-Morley experiment?
Monochromatic light was used and was directed at a beam splitter. The beam splitter would transmit half of the light, and reflect half of the light. The 2 reflected light beams would travel perpendicular to each other towards a plane mirror, each plane mirror placed perpendicular to each other.
When the beam of light hit the plane mirrors, they are reflected back towards the beam splitter, where they superpose and cause an interference pattern of bright and dark fringes depending on their phase difference.
The interferometer was rotated, to swap the perpendicular beam and the parallel beam, in order to observe a shift in the interference pattern.
What did Michelson and Morley find?
No matter how much they shifter the interferometer, they found that there was no shift in the interference pattern, and this showed that there was no change in the speed of light, whether the observer was moving relative to the source or not.
