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Michelson-Morley Experiment

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The Michelson-Morley experiment was aimed at determining the presence of the luminiferous aether, a fictitious material that pervades space and is assumed to carry light waves. The experiment is also known as the "most famous failed experiment", but in order to understand how the experiment was a failure and famous at the same time, the process and outcome of the experiment should be studied in depth.

What is the Michelson-Morley experiment?

The Michelson-Morley experiment is an experiment that took place in an effort to understand the relative motion of matter through the stationary luminiferous aether. To achieve this, researchers examined the speed of light in perpendicular directions.

Michelson and Morley observed no substantial difference between the speed of light in the direction of flow through the supposed aether and the speed at right angles, which suggested that there was no such thing as aether. This conclusion is widely regarded as the first substantial evidence against the then-popular aether hypothesis. It also started a line of inquiry that ultimately led to the theory of special relativity, which eliminates the possibility of the existence of aether.

The purpose of the experiment

Theories in physics in the 19th century assumed that, just as sound and water waves require a medium to transmit their wave motions, light also needs a medium to transmit its wave motions, luminiferous aether. It was even thought that a vacuum also has to be filled with aether, since the light can travel through it.

The purpose of the Michelson-Morley experiment was to prove the existence of luminiferous aether, which was based on the following statement: "depending on your relative position in space, the light should pass through the aether at varying speeds." If the existence of aether had been confirmed, the goal then would have been to determine the Earth's velocity in relation to this hypothetical medium.

The process of the experiment

Before the experiment took place in 1887, in 1886 Michelson and Morley were successful in confirming Fresnel's drag coefficient. This coefficient was seen as proof of the stationary aether theory since it measured the effect a moving medium had on light.

It was seen as proof of the theory to say that the aether is dragged by a moving body or moves with the moving body. This outcome boosted their confidence in detecting the aether wind. For the procedure, a Michelson interferometer was used.

An interferometer is a sensitive optical device that compares the optical path length of light in two mutually vertical directions.

Michelson suggested that by comparing the speed of light in the direction of the Earth's movement and the speed of light when seen at a certain angle with respect to the Earth's rotational direction, they could detect a difference. This difference would prove that the speed of light is constant with respect to the proposed aether through which the Earth would be moving. But there were no differences to be found from the results of the experiment.

The outcome of the experiment

Since the outcome was negative, they disproved their theories and the aether theories which came before them. Instead, the results of the experiment proved that there is no difference between the speed of light while traveling in different directions.

Michelson and Morley's results, Camacho - StudySmarter Originals

In the figure above are the results of the experiment, where the top solid line represents the midday observations and the bottom solid line represents nighttime observations. The theoretical and actual curves are not presented at the same scale; in fact, the dotted curves represent just one-eighth of the theoretical displacements.

Why is it known as “the most famous failed experiment”?

The experiment is known as “the most famous failed experiment” because while the results of the experiment were negative and they couldn't prove what they had wanted to prove, it has allowed physicists to prove that the speed of light is constant in any situation, while also being a foundation for the theory of special relativity.

Impact on the theory of special relativity

Albert Einstein released a paper in 1905, over two decades after the Michelson-Morley experiment, explaining its perplexing findings. He claimed that there is no aether, since light is a specific kind of wave that does not need a medium to transmit it. There is no specific frame of reference showing different measurements of the speed of light without the concept of aether.

While I had these ideas in mind as a student, I came to know the strange result of the Michelson experiment. Then I came to realize intuitively that, if we admit this as a fact, it must be our mistake to think of the movement of the Earth against the aether. That was the first route that led me to what we now call the principle of special relativity. -Albert Einstein

Michelson-Morley Experiment - Key takeaways

• The Michelson - Morley experiment was designed to determine the presence of the luminiferous aether, a fictitious substance that pervades space and is assumed to carry light waves.
• Michelson and Morley found no significant difference in the speed of light in the direction of flow through the theorized aether and the speed at perpendicular angles, which was a result contradicting the initial predictions.
• The result of the experiment is widely regarded as the first substantial evidence against the then-popular aether hypothesis.
• The experiment is known as the “most famous failed experiment” because, even though it was a failure in its own terms, it was a big step in physics as the aether hypothesis was disproved.
• The Michelson-Morley experiment has played a big role in the development of the theory of special relativity.

The experiment took place in 1887.

The purpose of the Michelson-Morley experiment was to prove the existence of luminiferous aether.

The inevitable conclusion was that, after all, there was no aether. Einstein's theory about the speed of light being a universal constant to which no motion could be added was backed up by this conclusion.

Final Michelson-Morley Experiment Quiz

Question

When they examined the speed of light in perpendicular directions, what kind of differences do Michelson and Morley observe?

No substantial difference.

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Question

Which of the following was the first substantial evidence against the aether hypothesis?

Michelson-Morley experiment.

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Question

Which of the following eliminated the possibility of a stationary aether?

Michelson-Morley experiment.

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Question

Which device was the main component of the Michelson-Morley experiment?

Michelson interferometer.

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Question

Which of the following did the Michelson-Morley experiment prove?

There is no aether.

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Question

Did Einstein know about the Michelson-Morley experiment?

Yes he did.

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Question

Does light need a medium to transmit it?

No it doesn't.

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Question

What was the given name for light's required medium at the time it was accepted?

Luminiferous aether

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Question

The purpose of the Michelson-Morley experiment was to prove the existence of luminiferous aether. True or false?

True.

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Question

When did the Michelson-Morley experiment take place?

1887.

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Question

An interferometer is a sensitive optical device that compares the light's two mutually vertical directions' optical path lengths. True or false?

True.

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What did the Michelson-Morley experiment disprove?

Aether hypothesis.

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Question

What is a hypothetical medium for transmitting light and heat (radiation)?

The Aether.

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Question

Before their experiment, Michelson and Morley were successful in confirming Fresnel's drag coefficient, which was also seen as proof of what?

The theory of existence of aether.

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Question

When did Michelson and Morley confirm Fresnel's drag coefficient?

In 1886, 1 year before their experiment.

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