# Michelson & morley experiment

## Main Question or Discussion Point

Michelson & morley experiment...........

hi there............

We say that the speed of light is constant when seen from any frame of refrence because the ratio of length and time measured from moving and rest frame is same.
Also by Lorentz transformation L= L1 $(L1 and T1 are in the moving frame and$ represents gamma)
And T1 =T $So L/T =(L/$)/T$=L/T ($ 2 )
1 =(1- v2 /c2 )
So v = c…..
This proves that at the speed of light a body, be it any, not necessary a photon, appears constant from any of the frames.

In the Michelson and Morley experiment , if instead of light, electron would have been used what would the results have been ? will the desired shift be observed or not…… would that suggest something about the non existent ether…….??
Let us assume the speed of electron is taken to be on very close to that of light (hence introducing relativistic effect) and the same experiment if repeated with speed of 300 km/s or more…… what would be the result in the two cases?

According to Lorentz transformation I think the result would have been a positive ….. give expected fringe shift because only the velocity of light is constant from any frames. So would that not serve as a positive sign for ether hypothesis……??
Moreover I wish to ask why the experiment was carried out using only light and no other particle like elctron…?

## Answers and Replies

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D H
Staff Emeritus

This proves that at the speed of light a body, be it any, not necessary a photon, appears constant from any of the frames.
This doesn't makes sense. See the FAQ: [thread]511170[/thread].

Moreover I wish to ask why the experiment was carried out using only light and no other particle like elctron…?
The Michelson-Morley experiment was carried out with light because that is the subject of Maxwell's equations. Also note, electrons were not shown to exist until Thomson's 1896 experiment. The MM experiment was performed in 1887.

ZapperZ
Staff Emeritus

It also makes no sense to use electrons, because no one is claiming that the speed of electrons are constant and isotropic! What would we be trying to show here?

Zz.

can you please tell me will the result change if electron beam is used instead of light beam?

This doesn't makes sense. See the FAQ: [thread]511170[/thread]..
how is the speed of light being same seen from any frame, related to rest frame of photn as you have mentioned the link.... please exlpain the relation.?

thanks

D H
Staff Emeritus

This proves that at the speed of light a body, be it any, not necessary a photon, appears constant from any of the frames.
This doesn't makes sense. See the FAQ: [thread]511170[/thread].
how is the speed of light being same seen from any frame, related to rest frame of photn as you have mentioned the link.... please exlpain the relation.?

thanks
Perhaps I misread your initial statement. I read "This proves that at the speed of light a body ..." as meaning from the perspective of something moving at c.

can you please tell me will the result change if electron beam is used instead of light beam?
This makes no sense. Is the speed of a car moving down a highway the same to all observers? (No, isn't.)

what if the car moves at the speed of light.......... (though i know this is not possible due to various reasons)......... will its speed not appear constant from any rest or uniformly moving frame??.......

and this is what that statement was......... but then the connection u gave with photon's rest frame is still not clear.......

Also please explain why won't the speed be of a BODY moving with c same to all observers( ignoring the fact that attaining this speed means having infinite mass but zero length )............
or is it that this limit ensures that only photon appears to move wiht c by all observers................
if true ......i guess i got it...........

Dale
Mentor

Please, stop using so many periods! It makes your posts very annoying to read. One period denotes the end of a sentence. Three may be used to indicate an omitted part of a quote. Any other usage is not helpful in communicating your thought.

Anything which moves at c in one frame will move at c in all frames. Neither electrons nor cars ever move at c, so using them in a variant of the Michelson Morely experiment wouldn't make sense. In principle you could use gluons.

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Sorry. I won't do that again.

how about muons (or so)? will they do?

Dale
Mentor

Muons also have mass, so they travel at v<c.

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Ok.Thanks.