In optics, the corpuscular theory of light, set forward by Sir Isaac Newton, says that light is made up of small discrete particles called "corpuscles" (little particles)which travel in straight line with a finite velocity and possess kinetic energy.This theory also rules out the presence of any medium for propagation of light. In its contemporary incarnation, the theory of photons, this idea explains many properties of light, in particular the photoelectric effect. However, it fails to explain other effects, such as interference and diffraction. It was therefore superseded by the wave theory of light, later understood as part of electromagnetism, and eventually supplanted by modern quantum mechanics and the wave–particle duality.

Newton's theory remained in force for more than 100 years and took precedence over Huygens' wave front theory, partly because of Newton’s great prestige. However when the corpuscular theory failed to adequately explain the diffraction, interference and polarization of light it was abandoned in favour of Huygen's wave theory.^[1]

Newton had no problem in explaning rectilinear propagation with his theory. In fact, this property of light provided the supporters of his theory with one of their strongest arguments against the wave. How could waves travels in straight lines? A sound could be easily heard around a corner, but light can't be seen from behind a wall. The former observation is unquestionably a wave phenomenon. How can the latter be, too? The simple and direct explanation of rectilinear propagation provided by the particle of light model, along with the prestige of Newton, were largely responsible for the preference of the particle theory in the 17th and 18th centuries.

1. Reflection.

(the return of a wave from the boundary of a medium) When light hits a smooth surface, like the back of a CD, it's reflected. How do particles behave under the same circumstances? Steel ball bearings thrown at a smooth steel plate rebound just like light reflects. Perfectly elastic particles bouncing off a rebounding surface could provide a good model for the reflection of light.

2 Refraction. (the bending of a wave as it moves from one medium to another causing the wave to have different velocity)

Newton was able to demonstrate the nature of refraction with his particle model. We can duplicate this experiment. First we need two level surfaces, one higher than another, with their neighboring edges connected by a slope. If you roll a ball along the higher surface, down the slope and across the lower surface, the ball will have sped up. This added speed is, of course, due to gravity.

Newton's corpuscular theory was an elaboration of his view of reality as interactions of material points through forces. Note Albert Einstein's description of Newton's conception of physical reality:

[Newton's] physical reality is characterised by concepts of space, time, the material point and force (interaction between material points). Physical events are to be thought of as movements according to law of material points in space. The material point is the only representative of reality in so far as it is subject to change. The concept of the material point is obviously due to observable bodies; one conceived of the material point on the analogy of movable bodies by omitting characteristics of extension, form, spatial locality, and all their 'inner' qualities, retaining only inertia, translation, and the additional concept of force. ^{[2] [3]}

[edit] References

RutuparnDalvis_Encyclopedia.com

[edit] External links

• Observing the quantum behavior of light in an undergraduate laboratory JJ Thorn et al.: Am. J. Phys. 72, 1210-1219 (2004)

[edit] See also

• Corpuscularianism
• Speed of gravity

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