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Michelson- Morley's experiment

  1. Sep 22, 2007 #1
    Hi everyone I'm a new member

    Despite I'm not graduated from college of physical science, but I'm super interested in physics. this summer I tried to study relativity theory by my self with some good references, I was very happy when I get to understand the concepts of relativity and I convinced my self that the ultimate relative speed between any two objects is (C) based on the results of Michelson- Morley's experiment.

    but when I investigated more carefully about this experiment I realized that the source of light emission which they used were fixed on the same earth which the mirrors and detector were fixed on, (previously I thought that they were using a fixed star as a source of light or some thing like that) so there was no relative motion between the emitter and the detector how could fringes occur in this state?? What If we assumed that the light composed of particles, the results of this experiment could be easily explained just by Galilean transformations with out using Lorentz transformation.

    I searched the net and I found many other researches proves that of Michelson- Morley's demonstration has many fatal errors could not be trusted to prove any thing, e.g try this research (a pdf document).
    also try this one click here

    And also I found this site:
    the author of this site is a strong supporter of classical physics and he claims that time dilation, length contraction, perihelion of mercury, every thing could be explained by classical physics and even E=MC2 could be derived with out using relativity concepts!!!

    Now, at the end of this summer I'm near a bout to loss my confidence in relativity theory unless someone from this lovely forum save me.

    My question is that does any one has a strong evidence rather than Michelson- Morley's experiment to show me that C is the ultimate relative speed between any two objects even if they approach opposite direction to each other with a velocity more than 200000km/s?

    And thank you
  2. jcsd
  3. Sep 22, 2007 #2
    That's kind of the point. The Michelson-Morley experiment shows the lack of an absolute "aether" through which EM waves propagate. It doesn't show anything else about light. Special relativity has two postulates, the one about the speed of light being c in all frames is partially tested by this experiment.

    Let's look at it this way: for the last hundred years, we've come a remarkably long way, with the help of special relativity, and some very clever people who used it to produce technology and new theories. What's more likely: relativity has such huge, gaping holes that no-one has noticed, or that you've not yet fully grasped the details?

    By the way, don't trust what you read on websites. Look in things which have been reviewed by many people, and which have been used to build on: papers in peer reviewed journals, often used and highly regarded textbooks, etc. Random rantings on a website by semi-insane people are not as reliable.
  4. Sep 22, 2007 #3


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    I am going to let this stand, for now, because there is a need to debunk this thing clearly. However, take note that, per our PF Guidelines, crackpottery, crackpot links, and this-physics-is-wrong type of arguments are not allowed on PF without VALID citation. And valid citation must include peer-reviewed papers, NOT simply someone's pet website.

    If you don't understand something, ASK first. Don't make proclamations based on lack of understanding. If this thread deteriorates into another "Relativity is wrong" argument, it will be locked or completely deleted.

  5. Sep 22, 2007 #4


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    You completely miss the purpose of the experiment. The purpose of the experiment was to find/measure the motion of the aether past the detector and emitter.

    It works similar to having fixed observers on both sides of a river. By sending a boat across the river at a known speed, you can measure the speed of the river based on the time the boat took to get across. The boat has to angle upstream to go straight across and thus travels further than if the river wasn't moving.

    That is all the MM experiment was trying to measure.
    Particle accelerators show that. GPS satellites show the time dilation that accompanies that.

    And please - takea step back and a deep breath. Thousands of physicists use these theories every day and tens (hundreds?) of thousands have worked on the issues and and performed the experiments to back up the theories since they were first proposed. It is pretty arrogant to believe that with no formal education and having never performed an experiment, you know something they don't.
    Last edited: Sep 22, 2007
  6. Sep 22, 2007 #5
    The hole relativity theory is build upon the constancy of the speed of light in vacuum.
    That constancy is assumed to be true, no matter the circumstances : mouvement of the observers or emitters, presence of forces or gravity nearby ...
    Until now, no experiment or observation contradicted that fact, but rather support it.
    So the speed of light in vacuum is a universal constant, at least as far as our current knowledge of the universe and the laws that govern it is involved.
    End of story.

    Correct me if I am wrong.
  7. Sep 22, 2007 #6
    Thank for your advices, it returns some confidence to me. But the above research shows that MM experiment even can not disprove the existence of absolute ether its just like someone tries to measure the speed of his car by using Doppler effect while he puts the sound source and the detector on the same car so there will be no change in frequency.

    But the accuracy of a theory is not measured by the time which it has survived for e.g Newton's lows lasts for 300 years without any one notice an error and also Aristotle's lows of motion lasts for about more than 1000 years before Newton find the errors. this dose not mean that the previous human beings were less intelligent than the current (the theory is a theory every time its liable to change)

    I'm so sorry I did not read the lows of this forum, so forgive me this time. I'm just wanted to seek help to return my confidence in this theory because I loved this theory and seeking for stronger evidences to increase my faith in this theory.

    There is a science dealing with reflections of light on moving mirror and it states that reflection of light on moving mirrors will differ from that of fixed mirrors and they said that MM experiment were over simplified because its ignored the effect of moving mirrors, we know that in 1887 the scientists were so confident about the existence of ether even after MM experiment they tried to explain the results without rejecting the existence of ether even Lorentz him self derived his equation on length contraction to save the postulate of absolute ether as he explained by his equation that moving objects in ether contracts at direction of its motion, later Einstein removed that part of lorentz equation which describe ether, so this means that there is a fixed style of thinking dominated in brains of scientist at that time, they did not consider particle property of light and many other properties which discovered later. At last lets know that lorentz transformation born to save ether theory on bases of MM experiment.

    I'm very sorry if I behave arrogantly so forgive me I'm just like a child interested in some thing, so please do not reject me.

    Thank for everyone replies and sorry for any misunderstanding, I believe in relativity theory I just want to increase my confidence in it by empting any question in my mind bothers me.
  8. Sep 22, 2007 #7


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    What you don't seem to understand is that waves in a medium will always travel at the same speed relative to the rest frame of the medium, not relative to the rest frame of the emitter. So if I'm in an open-topped car and I clap my hands in the middle of the car, someone at the back of the car will hear the sound before someone at the front of the car, since the car is moving forward in the air's rest frame, and sound waves from the clap travel at the same speed of sound in both directions in the air's rest frame (not the car's).
  9. Sep 22, 2007 #8


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    The MM experiment measures time delay, not doppler shift. And as Jesse said, you can indeed measure the speed of a car via the time delay of a sound traveling from the back to the front of the car, outside the car.
  10. Sep 23, 2007 #9
    The MMx experiment showed that the over and back average would always be c. It did not disprove the existence of a medium, a medium is as Einstein put it, superfluous to SR since one cannot find a meaningful reference frame in featureless space.
  11. Sep 23, 2007 #10


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    The following is for your interest only (I do not otherwise endorse or rebuke it for I have not spent time studying their theories). Just to show that there exists academics from a "reputable" university (well, at least field medalist Prof. Terence Tao used to go there as an ugrad) who dismisses the MM experiment and probably Einstein's theory as a whole...

    more at
  12. Sep 23, 2007 #11
    It seems that I have failed to give a good example. You are right about that if we consider wave property of sound but light has dual property wave and particle (you can describe light as a wave to describe one phenomenon and as a particle to describe another phenomenon)

    till now no body seems to understood me I wanted to draw a scheme to show my Idea but the PF guidelines did not permit image links so for the last time I will repeat if we consider particle property of light, Einstein described photoelectric effect by considering light as packets of energy and later Compton described light particles as billiard balls to describe Compton effect)
    So… what is the problem if we describe light particles as a gunshots and the light source as a Gun it is very very very very easy & simple to describe the results of MM experiment by using Galilean transformation only.

    Suppose that you have a gun and you are inside a moving room and you stand midway between back wall and the front wall what makes you think that the gunshots which directed toward the front wall will reaches the wall before those gunshots that directed towards the back wall ??? Does the speed of gunshots differ according to direction (in relation to someone in the same room)?????????? of course you can not use this gun to measure the speed of this room you can not even know that the room are moving because you & your system are isolated its just like MM experiment when they used a light source (a gun), fixed one the same earth (moving room) and mirrors (walls), fixed on the same earth then they expected that light beams (gunshots) will reach the mirrors (walls) at different speeds. how could this be???

    I hope some one understand what I mean this time
    Thank you.
  13. Sep 23, 2007 #12
    No, we understood perfectly, it's you who's failing to understand. The point of the MM experiment was to find an absolute aether, which supports EM waves, and which is absolute -- so the Earth would be moving through it. The null results shows that no such absolute aether exists. Your example of the room and speed of sound propagation depends on the motion of the air (the medium through which the sound propagates). If the air is moving with the room, then you can't distinguish it. Otherwise, you can. However, we also know that the aether wasn't being "dragged" by the earth, as we do not observe refraction from the boundary where the aether is presumably stationary wrt to some other body. However, none of this suggests that c is a "maximum speed". Indeed, in SR, that's not one of the postulates, but one of the consequences.

    mjsd: it's always possible to change the names that we give things, and arrive at a seemingly different theory. If a theory is self-consistent, and agrees with SR, then it's probably just calling something by a different name. For instance, even in SR, there has been a historical divide reflected in the names "relativistic mass" and "invariant mass".
  14. Sep 23, 2007 #13


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    No it is not. Read the FAQ in the General Physics forum. If you want use this as simply a conversation tool for the general public, then yes, such "duality" is adequate. However, if you want to talk to physicists or formulate a "theory", then such naive and superficial idea is wrong.

    Then would you like to show how you can make Maxwell Equations covariant under galilean transformation?

    Last edited: Sep 23, 2007
  15. Sep 23, 2007 #14
    Treating photons as particles does not validate the emission theory - specifically - the velocity of the light source is not added to the velocity of propagation - there are a number of experiments that have tested for this and they have all proved the emission theory to be incorrect.

    The fact that SR explained the null result of the MMx experiment, however, did not prove the truth of SR. There are other theories that explain the results - in fact any theory that leads to Gamma will work - that is, the experiments all demand a contraction of space and a dilation of time in order to comport with the null result for over and back type measurements. SR offers the simplest solution and is preferred because of its symmetry, but you can still find many who embrace the notion of an ether along the lines originally proposed by Lorentz and Larmore, and while such theories can explain the failure to detect a medium, it will take further experiment to determine if SR needs to be modified. So far SR has weathered all assaults upon its validity
  16. Sep 23, 2007 #15
    "If my theory of relativity proves to be correct, Germany will claim me as one of their own, and France will say I am a citizen of the world. If it proves to be incorrect, France will say I am a German, and Germany will say I am a Jew." Albert Einstein
  17. Sep 23, 2007 #16


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    my point in citing that link was to reply to the subject of this thread
    Michelson- Morley's experiment is wrong!!!!!!!! and perhaps point out to ppl of this forum that SR and GR, in the opinion of some (even academics!), is not the true story.

    again I have to admit I have not studied their theories and not sure how different/inefficient those theories are. :uhh:
  18. Sep 23, 2007 #17
    Then let me take this opportunity to welcome you to the forum! Welcome! :)
    What were these sources? I noted that web page you mentioned above about a guy who believes that Newtonian mechanics can predict things like E = mc^2 etc. If you want to know if this guy is a crackpot or not then read his material. Does it seem reasonable to you? There's a ton of stuff there so it shouild take a very long time to go over it. The important thing is to look for anything he has actually published on what he claims in that web site.
    Many people believe that is how the results should be interpreted. But not everyone. I recommend that you pick up a copy, or get a lend from your library, on a book called Special Relativity, by A.P. French, MIT Press (1968). Turn to page 127-128 and you can read the following
    The author references the physics article in the American Journal of Physics

    Evidence Against Emission Theories, J.G. Fox, Am. J. Phys. 33(1), January 1965

    Unfortunately this is an article I haven't read yet. Perhaps I'll read it this week since I just created a web page on the Michelson-Morely experiment. That web page is located at - http://www.geocities.com/physics_world/sr/mmx.htm

    Since I just made it there may be some errors in it that I have over looked. If anyone can find any errors in it then I would be very appreciative if you can let me know what those errors are.

    If anyone would like to read the Fox article I can make this available online for you to download it at your convinience. Please let me know it this is something you'd like me to do, okay?

    That was the intent of the experiment. It was to detect the motion of light through the ether. If the source is at rest in frame S and emits light in S then the speed of the light will have the value c as measured from the ether frame. If S is not the ether frame then the speed of light will be different for to-and-fro motion along the direction of the ether flow and have different values for to-and-fro motion across the ether wind. This is all shown in the web page I mentioned above.

    In the sense stated above, I agree. But this is because the Michelson-Morely experiment was done in open air. Later experimentsm, such as the Kennedy-Thornedyke experiment was done in a hard vacuum. The result of this experiment was a null result meaning that they couldn't measure different speeds along the different arms of the interferometer.
    That is a very honorable request that we will try to help you with. If you have any questions about my comments in this post or in the web page I created yesterday then please let me know. Especially about my web page. All of my web pages I like to have reviewed by others. I usually get that from my friends but I also look at whatever others say too.
    Michelson-Morley experiment seems to be wrong to me in that the presence of an atmosphere will cause the phenomena of extinction to override the speed of light relative to the ether. This is what French's book tells me. And I've met French several times. He's a very sharp educator in physics.

    Best wishes

  19. Sep 23, 2007 #18


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    This is getting frustrating because your previous example was more correct than this one! What you describe is the principle of relativity, but it is not what the MM experiment was trying to measure. Again, the MM experiment was trying to measure the motion of the aether past the detector and emitter. In your example now, you've sealed-off the room, so there isn't any wind to affect the motion of the bullet! Of course it won't be affected by the motion of the room. But aether theory was based on the idea that even if you seal-off the room as best you could, there is still a medium that carries light that would be in motion through the room.

    If what you are saying were correct, we'd measure the speed of light differently inside and outside. We don't.
  20. Sep 25, 2007 #19
    Did you know why I made the title of this thread states that "Michelson- Morley's experiment is wrong"?? Because if I said "can anyone give me an evidence on light speeds constancy" no doubt everyone would gave me Michelson's experiment as an evidence.

    You are right about the original purpose of MM. exp. was to find an absolute aether, which supports EM waves, and which is absolute, but when the experiment failed to do its purpose there was a need to explain this negative result?? What those explanations led to?

    These are some possible explanations to the null results of MM experiment (of course if we ignored technical errors):-

    1) If we supposed that like composed of particles just like bullets their velocity of propagation are added to sources velocity, then its simple to explain the results using Galilean transformation.
    But why nobody thought of this possibility? Because at that time (1887) the corpuscular theory of Newton were dead, as a result of young's experiments and Maxwell's equations, scientists were so confident about the wave nature of light that nobody could mention that light may be composed of particles even if someone did they make fun of him.

    2) If we supposethat aether dragged with moving objects…… (Not succeeded)

    3) If lengths contract in direction of motion, then we can save aether and explain null results of MM, so Lorentz transformation were born to save aether. this will lead us to conclude that if length contraction is correct we ought to believe in existence of absolute ether otherwise the null result of MM couldn't be explained.

    4) Then Einstein came and kicked aether out from equations not on the bases of experimental evidence but he saw that if C is constant, Lorentz transformation will still work well even if there is no aether so he used the principle of cut and economy.

    So ….
    The final consequences based on MM experiment led to the conclusion that C is the absolute relative speed.
    That’s why I can,t take MM experiment as a direct evidence on constant light velocity.

    Well, scientists indeed wanted to modify Maxwell Equations to be covariant under Galilean transformation but after SR appeared they modified Galilean transformation instead and let Maxwell Equations unchanged.
    However nobody know exactly changing which one is better, as you know Max blank modified some concepts of classical EM energy that enable him to explain blackbody's radiation and discovered light quanta

    That’s exactly what I want. Those experiments which you are talking about may greatly satisfy me, if you do not mind; can you give names or links to those experiments? I will be grateful to you

    Thank you for your kindness

    You are right about this guy, he behaves as like Einstein killed his father!!!
    But however we can not say there is no even a single error in SR if it was, then why it can't explain micro-world??

    I read this example from Einstein's book (evolution of physics) however I couldn't understand what it means.

    Why not?? It may be the solving key for my problem I'll be very grateful to you if you do this for me.

    A very very nice page, I saved many pages from it for later reading, however some links in your site led me indirectly to "strong crackpottery" sites. What worried me is their confidence on their claiming even some of them claims that there are mathematical mistakes in Einstein's derivations and they are ready to reveal these mistakes in scientific journals!!!

    Even if the room were opened you will get the same result because the bullet and the observer in the same inertial frame.

    That’s what I search about: an experiment measures velocity of the same light beam in different frames of motion not the same frame as MM experiment.
  21. Sep 25, 2007 #20


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    You have said nothing here. I still want to see how you can make Maxwell Equations covariant under Galilean transformation. Till you can do that, you have shown nothing other than arguing things based on a matter of tastes.

    Oh, and while you're at it, please re-read the PF Guidelines that you have agreed to.

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