# Michelson-Morely Experiment

What was the objective of the MME?
Did the Lorentz contraction actually explain the null result of the MME?

NateTG
Homework Helper
HannonRJ said:
What was the objective of the MME?
Did the Lorentz contraction actually explain the null result of the MME?
The Michelson-Morely experiment was set up to test the (at the time) rather unexpected prediction of Maxwell's equations that the speed of light in vacuum is constant and independant of the frame of reference.

Alternatively, it could be looked at as an attempt to measure the speed of the 'luminus ether wind'.

HannonRJ said:
What was the objective of the MME?
The original objective was to show that the speed of light was different moving in the direction of the hypothetical ether wind than it would be moving across at a right angle to the ether wind. If ether really existed, it would be unreasonable to believe that it travels along with the earth at all times of the year. You would expect the planet to be moving through it at some time of the year, if not all the time.

Did the Lorentz contraction actually explain the null result of the MME?
Since the observers were moving along with the apparatus, I don't think so.

What explains the null result of the MME is that there really is no ether that is the medium of which light travels. If one could set up an MME but with sound waves, it would show a positive result if the air was moving passed and through the apparatus. That's because air is the medium in which sound propagates. There is no such medium for electromagnetic waves.

r b-j

According to M+M, the purpose of their experiment was to test the validity of Fresnel's hypothesis that "the ether is supposed to be at rest except in the interior of transparent media." M+M concluded that their experiment indicated that, "...the relative velocity of the earth and the ether is probably less than one sixth of the eatth's orbital velocity, and certainly less than one-fourth".[The American Journal of Science, No. 203, Nov. 1887, p333.]

If one applies the Lorentz contraction to M+M's math (in the cited article), it does not explain the results of the experiment.

Why did the MME produce the result that it did?

HannonRJ said:
According to M+M, the purpose of their experiment was to test the validity of Fresnel's hypothesis that "the ether is supposed to be at rest except in the interior of transparent media." M+M concluded that their experiment indicated that, "...the relative velocity of the earth and the ether is probably less than one sixth of the earth's orbital velocity, and certainly less than one-fourth".[The American Journal of Science, No. 203, Nov. 1887, p333.]
the only curiosity to me is why they would expect the "the relative velocity of the earth and the ether [to be] certainly less than one-fourth" earth's orbital velocity at all times of the year. if the earth happened to be moving along with the ether wind in spring, it should be moving rapidly through it in the fall. the only reason to suspect not would be some wild theory that the ether wind moves along side of the earth wherever it is, as if the earth is the center of all things.

If one applies the Lorentz contraction to M+M's math (in the cited article), it does not explain the results of the experiment.
i have absolutely no idea why anyone would be applying any Lorentz transformation to the experiment at all. is the observer moving relative to the apparatus?

Why did the MME produce the result that it did?
isn't the ostensible answer obvious? you need to read what responses given you previously.

when an experiment turns out different than the expectation, the first thing to do is double and triple check the procedure to make sure you did it right. and then rerun it to see if the previous result was spurious. i think that "M+M" did that multiple times. if you've conceived the experiment properly and carried out carefully and without error, and it turns out opposite of theory, it's time to recheck the theory and the underlying assumptions of it.

r b-j

russ_watters
Mentor

"i have absolutely no idea why anyone would be applying any Lorentz transformation to the experiment (Michelson-Morley) at all. is the observer moving relative to the apparatus?"

Your comment implies that you accept the tenets of relativity. If that is the case, then you would expect a null result from the experiment, knowing that the velocity with which your frame is moving has no effect on observations within your frame. However, if you believe that Galilean transformations apply, then you would expect a non-null result as Michelson did.

Andrew Mason