Reference: Am J. Sci. 3rd Series
Vol. XXXIV #203 Nov. 1887
Michelson & Morley
"On the Relative Motion of the Earth and the Lumeniferous Ether"

In their experiment they used mirrors to extend the light path.
Thus the light travelled half the time in the OPPOSITE direction.
Would this not vitiate the experiment?

sanfran: "Thus the light travelled half the time in the OPPOSITE direction."

- As it turned out, that's right - but it's not what they expected. They expected the time spent travelling in each direction to be different, owing to the effect of 'ether wind'.

sanfran: "Would this not vitiate the experiment?'

- It should not have, had there in fact been an 'ether'; but their negative result was convincing evidence that there isn't.

See (scroll down to 'Detecting the Aether Wind: the Michelson-Morley Experiment'):

http://galileoandeinstein.physics.virginia.edu/lectures/michelson.html

Thank you for taking the time. I've got to spend a bit of time chewing on the material in your referenced website.
sanfran

Here's an interactive animation (Adobe Flash Player) of the apparatus:

http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/mmexpt6.htm

It works well if you set the 'light speed' slider somewhere from 2 to 4, and set the 'aether speed' to maximum.

Neat and interesting.

But..... what if aether exists and is all-pervasive like gravity?

sanfran: "But..... what if aether exists and is all-pervasive like gravity?"

Ether was, in fact, believed to pervade all space.

Many more experimenters have since tried to detect ether, and all have concluded, with increasing certainty, that it doesn't exist. There are no indications that the current understanding of light is incomplete, and no observations to suggest that an 'ether' is required to account for any phenomena.

There were unexplained observations regarding gravity, such as the characteristics of galaxy rotation, but these are currently attributed to dark matter for which there is very strong evidence (some say 'proof'). Dark matter, having mass, does affect light, but it's quite different from the concept of ether; and it seems that if any other new 'all-pervasive' energy or matter were discovered (currently, we have the dark energy hypothesis), it wouldn't qualify, by definition, as ether.

Thank you again, but I want to get back to the original question.

Please refer to illustration #4 on page 338 of the original article.
Note that 8 mirrors were used for each direction.
Using your analogy of a person swimming upstream and then downstream, consider what happens to the swimmer reversing his direction for an equal time period.
Whatever gain he derives from supplementation by the river current while going downstream is wiped out by an equal loss
going upstream. This bothers me.
The experimenters noted no change and that is what I would expect
with regard to a swimmer.

The misconception is in: "equal time period".

The time taken to swim a given distance upstream is greater than (not equal to) the time taken to swim the same distance downstream.
That's the point: the distance is the same, but the time is different. The time would be the same only if there were no river current (no 'ether wind').

Example:

Distance to swim, d, = 15 metres
Swimmer speed, v, = 1 metre per second
Stream flow rate, r, = 0.5 metres per second

Upstream time = d/(v - r), Downstream time = d/(v + r)

Upstream: 15/(1 - 0.5) = 30. Downstream: 15/(1 + 0.5) = 10

So, after 40 seconds, the swimmer returns to his starting point.

That's 10 seconds longer than it would have taken with a stream flow rate = 0.
______________

If the swimming time were the same in each direction, e.g. 30 seconds:

Distance to swim = t*(v - r) + t*(v + r) = 30*(1 - 0.5) + 30*(1 + 0.5) = 45

That takes the swimmer 15 metres downstream from their starting point!

You are absolutely right. Thank you. Now I can sleep.

You are quite right. Thank you. Now I can sleep.

Just found this in Wiki:

"Some adherents of modern geocentrism claim that the Michelson-Morley experiment proves that the Earth is stationary...Many of these ideas are related to fundamentalist interpretations of Christianity." !!! Arrggh ...OK, I feel better now

Hi All,

Been busy for a while.

Ok. Last time I looked at this thread it was about the Michelson-Morley experiment. I only scanned through this, but it looks as though there are some misconceptions about this experiment.

I will read this through again and get back to you after I've slept on it. I might be able to contribute something.

Dr. R.

Dr. R.: "I only scanned through this, but it looks as though there are some misconceptions about this experiment."

Any update, doc?