# Michelson-Morley experiment proves nothing

1. Aug 16, 2008

### yeti1112007

I believe the experiment proves nothing and the comeout means nothing

the experiment similars to this:

in dashing a car with a velocity V , then Michelson and Morley throw a ball and it rebinds

back(velocity U ). the two great scientists note the time and try to calcuate the

speed of the car V. that is impossible!

2. Aug 16, 2008

### HallsofIvy

Yes, that's the whole point of the Michaelson-Morley experiment!

In Gallilean relativity, Gallileo, long before Einstein or Michaelson and Morley noted that if you were in a carriage moving in a straight line with constant speed, there would be no (mechanical) experiment, such as throwing or dropping a ball that would tell you the speed of the carriage or even if it were moving. In effect that is because "f= ma"- any change in the motion of the ball would be the result of acceleration, not speed.

But I specifically put "mechanical" in parentheses because Gallileo knew nothing about electricity or magnetism and so did not consider such experiments. But Maxwell's equations show that the electric field generated by a charged body depends on its speed not its acceleration. That means that, theoretically, we should be able to do some kind of electro-magnetic to determine "absolute" speed- that an electromagnetic experiment could determine the speed of a carriage from "inside". And, of course, light is an ideal electro-magnetic field.

That was what the Michaelson-Morley experiment was designed to test- and gave a null result. Of course, there were any number of ways of accounting for that. Lorentz came up with a very clever theory in which that very change in magnetic field would be precisely enough to "shrink" the distance between atoms to account for the null result- and developed the "Lorenz transformation". Einstein went even farther and suggested that not only the lengths of material objects but even the space itself between objects was "shrunk". A variation of the Michaelson-Morley experiment, called the "Kennedy experiment" gave results that Einstein's theory predicted and Lorenz's didn't. There was even one theory that accounted for the Michaelson-Morley results by postulating extra dimensions (unfortunately I don't recall the name of the person who came up with it) that Einstein thought was very clever. It wasn't until the famous "eclipse" experiment of the late twenties gave results that matched Einstein but not the other theory that that was settled.

3. Aug 16, 2008

### George Jones

Staff Emeritus
yeti1112007, make sure that you Physics Forums Rules,

In particular,

4. Aug 16, 2008

### rbj

does the windspeed affect the speed of the ball? perhaps a better illustration would be measuring the apparent speed of sound bouncing off a "mirror" in front of the car vs. the speed of sound bouncing off an identical wall to the side of the car. because sound uses this medium we call "air" to propagate in, the two great scientists would measure a speed difference.

if light actually did propagate by use of this hypothetical medium sometimes called "aether", if you believe it is reasonable that, at least at sometime during the year, the Earth in it's orbit around the Sun moves through this aether at a speed that we would expect, around 2$\cdot \pi \cdot$(93000000miles)/(1 year), the difference in speeds of light using the mirrors in "front" vs. the mirrors on the "side" would be measurably different. but since no difference was ever measured, and this experiment was repeated many times and in many different manners, i think the safest thing to conclude is maybe light (and all other E&M radiation) doesn't propagate within any medium. the only other explanation is that this aether somehow sticks to the planet Earth as it revolves around the Sun (therefore we are never moving through the aether). is that reasonable?

Last edited: Aug 16, 2008
5. Aug 16, 2008

### HallsofIvy

No, not if they were in an enclosed car where the air moves at the same speed as the car.

NO, that is not the "only" other explanation. Another possible explanation is that your measuring sticks "contract" in the direction of motion so that you will measure the same speed of light in any direction.

6. Aug 17, 2008

### rbj

well, that would be like the aether that sticks to and travels around with the planet Earth so that we are never moving through it with any appreciable velocity. i think that's a sorta specious exception. of course i meant that the car was moving through the air just as we would expect the Earth to be moving through the aether, if it existed, at least during sometime of the year.

yeah, i guess. they would be sorta intelligent measuring sticks, but that's no farther fetched than an intelligent aether that somehow knows we're moving through it and moves with us.

7. Aug 18, 2008

### yeti1112007

8. Aug 18, 2008

### yeti1112007

I am a Chinese of the mainland, and I am now in China. I am very interested in the theory of

the unchaging velocity of light. But information are poor here because books are copying

each other. So I put what I thought here hoping for more information. I am sorry for

breaking the rules

9. Aug 18, 2008

### rbj

i don't think asking questions or even challenging (as hypothesis) conventional wisdom is breaking the rules. but, yeti, be careful of what you write. you are neither the only nor first person to declare Einstein wrong. and everyone else before ended up eating their words (or stubbornly remained crackpots).

10. Aug 18, 2008

### peter0302

Are you seeking more information? Your first post sounded like you were espousing a (wrong) personal belief.

The speed of light is seen as constant by all observers. Michelson-Morely *disproves* the aether hypothesis that said that light travels in a medium and that there would be a detectable "wake" of the Earth through the aether which would manifest itself by comparing beams of light when the earth was at opposite ends of its orbit. Observing no such wake, the experiment shows there is no aether. It actually proves quite a bit, and while the experimental error may have been quite large at the time, it's since been confirmed to remarkable accuracy.

Moreover, things like nuclear power and nuclear weapons wouldn't work if relativity was wrong.

11. Aug 18, 2008

### Chronos

A helium balloon inside a vehicle travels in the direction of acceleration when the vehicle accelerates.

12. Aug 19, 2008

### yeti1112007

It seems I have a lot to learn before I know the turth.