Michelson Morely Experiement And Inertial Frames Of Reference Flashcards
What is the Luminiferous Aether
All other known waves at the time (sound and water) travelled through a medium, so physicists assumed light did too
Huygens called this medium for light waves the “luminiferous aether” (or just aether) and physicists wanted to study its properties
What was the aim of the Michelson Morley experiment?
In 1849, Hippolyte Fizeau measured the speed of light in moving water
One beam of light travelled with the current and the other travelled against the current of the water
Through the interference between the two beams, he found that light moving in the same direction as the medium travelled faster than light in a direction opposing the motion of the medium
Interestingly, the speed decrease when travelling against the medium was greater than the speed increase when travelling with the medium
-In the 1880s, Michelson and Morley wished to use a similar method to prove the existence of the aether
If the aether existed, then the Earth was travelling through it
Light travelling in the direction of the Earth’s motion would be travelling against the aether
The motion of the aether against the light was called the aether wind
Like with water, if light was travelling into the aether wind, it would be travelling more slowly than light travelling perpendicular to the aether wind
What travels faster, Light travelling in the motion of the earth against the ether or light travelling perpendicular to the ether?
LIGHT perpendicular!
Light travelling into the aether wind was predicted to travel a small fraction slower than light travelling perpendicular to the aether wind
How could Michelson Morley experiment show absolute motion of the earth relative to the Ether?
-Absolute motion : motion of all bodies in the universe can be measured relative to the ether
-phase difference between the 2 beams of light can determine the earths motion relative to the ether
What was the Michelson-Morley Interferometer?
Two arms of identical lengths at right angles to each other, with mirrors at each end and a beam splitter (a semi-silvered mirror which allows some light to pass through and reflects some light) at their intersection
Why did the light reflected by the beam splitter go through another plane of glass
ensure both beams travel through the same amount of air and the same amount of glass
Both beams are reflected by mirrors at B and C and meet at an eyepiece
Why was the Michelson Morley interferometer made to float on a bath of mercury ?
The Michelson-Morley interferometer was set up to float on a bath of mercury
This allowed it to be rotated with minimal friction
What would turning the interferometer do to the interference pattern?
-Rotating the interferometer would affect the phase difference of the beams differently, causing a phase shift in the interference pattern
What was the result of the experiment ?
-Michelson and Morley performed the experiment at different angles and at different times of the day (so the Earth had also rotated relative to the aether)
However, their results only ever showed displacements of the interference project around 0.02 fringe widths and not even in the expected orientations
These values were far too small to be significant and most likely experimental noise
What did the lack of displacement of interference lead to the conclustion to
This null result led scientists to the following conclusions:
The aether does not exist and therefore light is a wave able to travel without a medium
The speed of light is unchanged by the Earth’s motion - it is invariant
If there is no medium from which to measure the motion of the Earth, there is no absolute motion - everything is moving with respect to everything else
Why is it phase shift not phase difference
-the beams travel the same distance so there’s no difference in path taken.. speeds are different
The invariance of speed of light
-whether your running or not, speed travels at the same speed for every observer… so if you are running away from the light, the light is practically faster than C relative to you which is impossible
Inertial frames of reference
-reference frame that’s non-accelerating so are much at constant velocity relative to each other
Why is there no such thing as absolute reference fram?
-no place in the universe that’s completely stationary
-everything is moving relative to something else
