Michelson–Morley experiment facts for kids

The Michelson–Morley experiment was a famous science experiment done to find out if a special substance called aether existed. Scientists at the time believed this aether filled all of space and allowed light to travel. The experiment was carried out by two scientists, Albert Michelson and Edward Morley, in 1887.

Think about how waves in water need water to move through, and sound waves need air. In the same way, scientists in the 18th century thought light waves also needed something to travel through. They called this invisible substance "aether," named after the Greek god of light. They believed aether was everywhere, even in the vacuum of space. Michelson and Morley designed their experiment to try and prove that this aether really existed. They used a special tool called an interferometer for this.

The Michelson–Morley Experiment

A Michelson interferometer uses the same basic idea as the original experiment. But it uses a laser for a light source.

The Earth moves very, very fast around the Sun, about 100,000 kilometers per hour. If aether existed, the Earth moving through it would create an "aether wind". This is similar to how you feel wind outside a moving car. To someone inside the car, the air outside seems to be moving past them. In the same way, aether should have seemed like it was moving past things on Earth.

The interferometer was built to measure the speed and direction of this "aether wind." It did this by checking for tiny differences in the speed of light traveling in different directions. The device worked by splitting a beam of light into two parts using a mirror that was only partly covered in silver. One part of the light beam would go one way, and the other part would go a different way.

Both parts of the light beam would then bounce off other mirrors and come back together. When they recombined, they would create interference patterns. By carefully looking at these patterns, Michelson and Morley hoped to see any changes in the light's speed caused by the supposed aether wind.

However, when they did the experiment, they found almost no difference in the measurements. This was very confusing for scientists at the time. Their discovery suggested that the aether might not exist at all. This surprising result led to many new ideas and theories. The most important one was Albert Einstein's special theory of relativity, which changed how we understand space and time.

Images for kids

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  Figure 1. Michelson and Morley's interferometric setup. It was placed on a stone slab that floated in a ring-shaped pool of mercury.

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  Michelson's 1881 interferometer. This early version helped them learn important lessons for the 1887 experiment.

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  Figure 5. This picture shows the folded path light took in the Michelson–Morley interferometer. This made the light travel a total of 11 meters.

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  Figure 6. The fringe pattern created by a Michelson interferometer using white light.

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  Figure 7. Michelson and Morley's results from 1887. The lines show their observations at noon and in the evening.

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  Figure 8. A simulation of a later, more precise version of the Michelson–Morley experiment.

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  Figure 10. A NMR spectrum of LiCl. This shows that mass and space are the same in all directions.

See also

In Spanish: Experimento de Michelson y Morley para niños