While it was once believed that all waves must travel through a medium, it is now known that this is not always the case. Light is an example of an electromagnetic wave, which is a type of wave that can travel through a vacuum or empty space without the need for a medium. Unlike mechanical waves, such as sound waves, which require a material medium to propagate, electromagnetic waves consist of oscillating electric and magnetic fields that can travel through empty space at the speed of light. Therefore, light does not require a medium to travel and can travel through a vacuum, as well as through other materials, such as air, water, and glass.
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If the answer requires a medium, the medium through which light travels is called the electromagnetic field. The electromagnetic field is a physical field that is created by the presence of electrically charged particles, such as electrons, and is responsible for the behavior of electromagnetic waves, including light. In a medium such as air or water, the electromagnetic field interacts with the atoms and molecules of the medium, causing the light to slow down and change direction. This effect is known as refraction and is responsible for many of the optical phenomena that we observe in our everyday lives, such as the bending of light as it passes through a prism or a lens.