# Revisiting the Michelson-Morley experiment

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If we assume that:
• the earth has an atmosphere
• the Michelson-Morley experiment measured an isotropic speed of light inside the atmosphere
We can conclude that the speed of light inside the atmosphere remains isotropic while the earth is moving through space.

But if we assume that:
• the earth does not have an atmosphere
• the Michelson-Morley experiment measured an isotropic speed of light in space (from the surface of the earth)
We can conclude that the speed of light is constant/isotropic for all observers, irrespective of their motion.

The fact of the matter is, the earth does have an atmosphere.
Do you see where this is going?

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No.

russ_watters and Michael Price
Ibix
Do you see where this is going?
Given the number of experiments with light in a vacuum (edit: and Fizeau's experiments which measure the "drag" effect of a medium) of which you are apparently ignorant, towards a thread lock I suspect.

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Michael Price and weirdoguy
edit: and Fizeau's experiments which measure the "drag" effect of a medium
Aha. Have you considered that the Fizeau and the Michelson-Morley experiments are actually equivalent?
Both measured the speed of light in a moving optical medium but did it differently:
• Fizeau measured the speed of light as light passes through the moving medium (water)
• Michelson-Morley measured the speed of light inside the moving medium (the atmosphere)
Fizeau measured a partial "drag" effect, whereas Michelson-Morley measured a full "drag".
The accuracy of the Michelson-Morley was vastly superior (1200+ times better).

The point is, you can't really conclude that the speed of light is constant for all observers if you are aware that the MM experiment measured the speed of light inside the atmosphere.

Not looking to pick a fight here. Just pointing out the obvious.
Best regards

If we assume that:
• the earth has an atmosphere
• the Michelson-Morley experiment measured an isotropic speed of light inside the atmosphere
We can conclude that the speed of light inside the atmosphere remains isotropic while the earth is moving through space.

But if we assume that:
• the earth does not have an atmosphere
• the Michelson-Morley experiment measured an isotropic speed of light in space (from the surface of the earth)
We can conclude that the speed of light is constant/isotropic for all observers, irrespective of their motion.

The fact of the matter is, the earth does have an atmosphere.
Do you see where this is going?
You can do the experiment in a vacuum chamber.

Ibix
Just pointing out the obvious.
Meta-question: if it's obvious to you, do you really think it would have been missed by the entire physics community for more than a century? You are talking about an ether-dragging model, effectively. Between stellar aberration experiments, Michelson-Morley and Fizeau (not to mention interferometry done in a vacuum), all such models (partial and complete dragging) were ruled out decades ago.
Fizeau measured a partial "drag" effect, whereas Michelson-Morley measured a full "drag".
Evidence for this claim...?

russ_watters
Meta-question: if it's obvious to you, do you really think it would have been missed by the entire physics community for more than a century?
Yup. That's exactly what I'm thinking ;).

weirdoguy
Ibix
Yup. That's exactly what I'm thinking ;).
And that you wish to continue to think this is why you don't acknowledge the point about people repeating the experiment in vacuum, and why you offer no evidence for your partial/full dragging claim about the Fizeau experiment.

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2019 Award
IBTL

people repeating the experiment in vacuum
Georg Joos, in the 1920's.

Ibix
russ_watters
Mentor
Yup. That's exactly what I'm thinking ;).
Suffice to say, that's an unreasonable thing to think. There's ample documentation of light speed experiments (MM and other) conducted in a vacuum if you choose to look at them.