What was the motive of michelson morley experiment

[abhi-iitb]

what was the real motive of MM experiment
to measure the speed of light or to measure the orbital speed (or speed of ether) of Earth with respect to stationary ether?

plss anyone reply

 

[JustinLevy]

The MM experiment could not measure a value for the speed of light, due to the way it was setup.
It used an interferometer, so only could measure a relative change in either the speed of light or length along one arm of the interferometer compared to the other.

If it wasn't for length contraction in SR, maxwell's equations predicted we should be able to detect the Earth's speed through the aether as it orbits the sun. They of course didn't detect anything. It is one of the most celebrated "null results" ever measured.

 

[bcrowell]

what was the real motive of MM experiment
to measure the speed of light or to measure the orbital speed (or speed of ether) of Earth with respect to stationary ether?

They expected to measure the speed of the Earth relative to the aether. When it didn't work, they were very disappointed, and they tried very hard to "fix" their experiment. As late as the 1930's, people were still trying to do experiments that would succeed in detecting the aether wind. For instance, they repeated the MM experiment in a tent on top of a mountain, hoping to get rid of problems with the Earth dragging the aether along with it.

 

[D H]

If it wasn't for length contraction in SR, maxwell's equations predicted we should be able to detect the Earth's speed through the aether as it orbits the sun. They of course didn't detect anything. It is one of the most celebrated "null results" ever measured.

The inherent irreconcilability between Maxwell's equations and Newtonian physics at the end of the 19th century was much, much deeper than the conundrum of today, reconciling general relativity with quantum mechanics. Newtonian physics assumes Galilean relativity. Velocities are of course additive in Galilean relativity, and this does not jibe well with Maxwell's equations, which say that electromagnetic radiation travels at c in vacuum.

The purpose of the Michelson Morley experiment was to reconcile Maxwell's equations with Newtonian physics. The two could be reconciled if the one true inertial frame in which the speed of light truly is c could be found. This is the frame in which the luminiferous aether (the medium through which EM waves propagated) is at rest. Many physicists, including some great ones, clung to the concept of a luminiferous aether and the concept of one true inertial frame long after the Michelson Morley experiment failed to show the existence of either.

There has long been some debate over whether Einstein deserves full credit for special relativity. The work of Poincaré, Lorentz, and Fitzgerald in particular are often raised as objections to granting Einstein sole credit. Lorentz and Poincaré developed the Lorentz Ether Theory, which is mathematically indistinguishable from special relativity. The two theories (LET and special relativity) differ in their axioms but not in their predictions. LET, as the name implies, maintained the concepts of an ether and one true inertial frame -- except now the ether was completely unobservable and the one true inertial frame completely unknowable. The Lorentz contraction (axiomatic in LET) hid the ether and the one true inertial frame from view.

Einstein instead took Maxwell's equations at their face value. There is nothing in Maxwell's equations that says a luminiferous aether has to exist, or that the speed of light in vacuum is c (but only if observed from a frame at rest with respect to luminiferous aether). Maxwell's equations quite clearly say that the speed of light is the same to all observers, period. Einstein threw out all that non-essential stuff and started with the speed of light being constant (period) as axiomatic. That move was a huge game changer compared to the LET patchover. In my mind Einstein does indeed deserve full and sole credit for special relativity.

 

[abhi-iitb]

den that means Maxwell's equations came later than relativity

 

[D H]

No. How did you read that into what I wrote?

 

[abhi-iitb]

i thot sinc conceptt of aethr exists and at that time it was thought dat even electromagnetic waves require medium 2 travel n maxwel proposd oposite of that so i gues maxwel came later