Scientists have debated for centuries whether light is a wave or a particle. Isaac Newton (1642–1727) was one of the early proponents of the particulate (or corpuscular) theory of light. According to this theory, light travels as a stream of particles that come from a source, such as the sun, travel to an object and are then reflected to an observer. One of the early proponents of the wave theory of light was Dutch physicist Christiaan Huygens (1629–1695). According to the wave theory of light, light travels through space in the form of a wave, similar to water waves. Albert Einstein’s work in 1905 showed that light is a bundle of tiny particles, called photons. Scientists now believe that light has properties of both waves and particles, explained as wave-particle duality.