The mystery of waves in nothing

Waves transmit energy and information from place to place; light certainly does just that. Energy is transferred from the sun to the earth in the form of light, and information about everything we see is transmitted to our eyes by light. Of course, carrying energy and information is not a feature of waves alone. Particles also carry energy and could be used to transmit information!

There is a strong argument that light could not possibly be a wave. Light can travel through empty space. Sunlight travels across 100 million miles in which there are virtually no particles of matter, no atoms and no molecules. Sound waves and other waves in gases, liquids and solids require a medium, as vibrations are transmitted from one particle to another. If there is no medium, how can vibrations be transmitted when there is nothing to vibrate?

The protagonists of the wave theory attempted to resolve this paradox in a simple, but not very satisfactory, way by proposing the existence of an invisible medium which permeates the universe. This hypothetical medium, with no known properties other than the ability to carry light waves, was given the name 'ether'. No theory is satisfactory if it applies to one phenomenon and that phenomenon only. To give the ether hypothesis credibility, one must have independent evidence, and many clever experiments were devised to try to observe some sign of the ether.

A series of such experiments was carried out by Albert Michelson and Edward Morley in Los Angeles in the 1880s. Their idea was to attempt to detect an 'ether wind' blowing past the surface of the earth as it rotates and travels in its orbit around the sun. (We will look at their experiment in greater detail in Chapter 15.) Despite the best efforts of Michelson and Morley, no evidence was found for an ether wind and they were forced to conclude that either the ether does not exist or, if it does exist, it is invisible and undetectable! We must leave it to the philosophers to decide whether something invisible and undetectable can be said to exist.*

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