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EtherPhysicists have tried for hundreds of years to determine whether light is a stream of particles or a set of waves.

In the 1860s and 1870s Scottish physicist James Clerk Maxwell formulated a theory that linked electricity and magnetism, and light, to waves of electromagnetic energy. His theory predicted that waves of varying electric and magnetic fields travel through space in the form of electromagnetic waves. These waves carry energy from place to place. Maxwell showed that these electromagnetic waves travelled at 300,000 km/s (190,000 mi/s) - the same speed that earlier scientists had measured to be the speed of light. His theory was thus strong evidence that light is carried by

Before Maxwell's theory was established, all of the types of waves that scientists knew of needed a medium - a substance through which to travel.

For example, waves on a rope travel along the rope, and sound waves travel through air or some other substance. Scientists deduced that light waves must also travel through a medium. Scientists knew that light waves reached the earth from distant stars, and so they knew that light could travel through outer space. Physicists reasoned that outer space must be filled with an invisible medium, which they called the luminiferous ether, or just the ether.

The function of the ether was to allow light waves to travel through space. The ether was assumed to be weightless, transparent, frictionless, undetectable chemically or physically, and literally permeating all matter and space.

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