Re: michelson morley experiment questions


"gamma" <darkknight.21@xxxxxxxxx> wrote in message news:e42f687d-d27e-423b-a4fa-1990a842f1bd@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hi

I have some questions about the michelson morley experiment that tried
to detect ether.

That is inaccurate: it tried to detect the absolute speed of the Earth to test the stationary ether theory of that time. Here is the original paper:
http://www.aip.org/history/exhibits/gap/PDF/michelson.pdf

Among others, the paper is based on a hypothesis that it fails to mention but which turned out to be wrong: that L'=L (Galilean transformation).

On this web page http://galileoandeinstein.physics.virginia.edu/lectures/michelson.html
it shows some of the mathematics involved in calculating the
difference in the length/time of the two paths of the light beam. The
article says that the apparatus was built to be rotated so that as it
is rotated, the interference pattern should change. The article says
that after 90 degree rotation, the two path lengths have "changed
places" so the interference pattern should change e.g. a 20 degree
phase difference would become a 70 degree phase difference I guess.
As far as I can tell, the article doesn't give the mathematics of how
the two path lengths vary when the apparatus is rotated by say, five
degrees and why the interference pattern would be expected to change.

Here are my questions.

1. Is it true that after a 90 degree rotation, the interference
pattern should change (assuming the ether theory is correct) - e.g.
would a 70 degree phase difference have a different interference
pattern to a 20 degree phase difference?

The theory assumed that L=L', in which case the interfernce pattern should change indeed. It is explained in detail in the original paper.

2. (this question has a yes or no answer) - is it possible to show
mathematically that as the apparatus is rotated, the interference
pattern and the phase difference should change (assuming the ether
theory is correct).

Yes, as shown.

3. Was the "null result" of the experiment the fact that the
interference pattern didn't change when the apparatus was rotated?

A "null result" means that the predicted value has not been measured. In this case, the minimally predicted fringe shift was not detected.

4. Did the experiment at the time, depend on the path lengths of the
two paths being exactly equal and was any effort made to make them
equal or was this completely unnecessary?

That was unnecessary; however the arms had to be made "approximately equal" because white light was used. Later a similar test (as part of a different test) was done with one short and one long arm by Kennedy and Thorndike with the same result.

5. I've heard that the error/noise/inaccuracy of the original
experiment was too great for its result to be meaningful.

Yes, the original experiment was done in 1881. The one we talk about is the more accurate one of 1887.

If the
experiment depended only on observing the change in interference
pattern, what kind of error could invalidate this result?

Many kinds of errors are possible, but only their interpretation of the result has been seriously put in doubt. The experiment has been repeated and is still being repeated in many ways, always disproving the classical theory of that time.

Regards,
Harald

.

Quantcast