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The experiment was performed in the days when technology had just become sufficiently advanced to accurately measure the speed of light. At that time it was known that light was behaved like a wave. Scientists believed that light waves (later to be known as consisting of photons) traveled through a medium referred to as the aether (Sometimes spelt ether). The aether was believed to be fixed in space and so was regarded as an absolute frame of reference, relative to which the velocity of any object could (in theory), be measured. The concept of the eather was in some ways similar to the modern concept of "space-time" though some differences exist.Thus the idea was that absolute movement existed.

Scientists at the time believed that if they could accurately measure the relative velocity between the earth and light waves, they would get different results for the speed of the light waves moving in different directions. They believed this would happen because the earth was constantly moving, and the aether was fixed. They believed that by examining the results they could measure the relative velocity between the earth and the aether, and hence determine the absolute velocity of the earth through space. The Michelson-Morley experiment was an attempt to do that.

The experiment gave unexpected results. The velocity speed of light was found to be the same regardless of the direction the light was traveling in. At first it was assumed that the result was due to poor equipment or some other anomaly, but further work ruled that possibility out.

Scientists then faced the dilemma. They believed the earth was moving through space, but the Michelson-Morley experiment and similar experiments indicated that the earth was somehow stationery relative to the aetherat all times.

A number of theories were proposed to explain the paradox, including the idea that the aether might in some way be "dragged along" by the earth. In the end the theory of special relativity (See [[Theory of relativity]]) became the accepted explanation, and the concept of the aether was completely rejected, years later experimental evidence was provided to support the theory of Relativity.

A small number of people feel that the scientific community took a wrong turn when they rejected the concept of the aether. They argue that [[Geocentric theory]] is an alternative explanation of the result. If the earth is in-fact stationary relative to the aether then the result of the Michelson-Morley experiment is easy to understand, this would however make the Earth "special" compared to other celestial objects.