Corpuscular theory
Encyclopedia
In optics
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...

, corpuscular theory of light, set forward by Sir Isaac Newton, states that light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

 is made up of small discrete particles called "corpuscles
Corpuscularianism
Corpuscularianism is a physical theory that supposed all matter to be composed of minute particles, which became important in the Seventeenth century. Among the leading corpuscularians were Rene Descartes, Robert Boyle, and John Locke....

" (little particles) which travel in a straight line with a finite velocity
Speed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...

 and possess kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...

.

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
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...

, interference and polarization of light it was abandoned in favour of Huygen's wave theory.

Newton's corpuscular theory was an elaboration of his view of reality as interactions of material points through forces. Note Albert Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...

's description of Newton's conception of physical reality:


[Newton's] physical reality is characterised by concepts of space, time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

, the material point
Point particle
A point particle is an idealization of particles heavily used in physics. Its defining feature is that it lacks spatial extension: being zero-dimensional, it does not take up space...

 and force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...

 (interaction between material points
Point particle
A point particle is an idealization of particles heavily used in physics. Its defining feature is that it lacks spatial extension: being zero-dimensional, it does not take up space...

). Physical events are to be thought of as movements according to law of material points
Point particle
A point particle is an idealization of particles heavily used in physics. Its defining feature is that it lacks spatial extension: being zero-dimensional, it does not take up space...

 in space. The material point
Point particle
A point particle is an idealization of particles heavily used in physics. Its defining feature is that it lacks spatial extension: being zero-dimensional, it does not take up space...

 is the only representative of reality in so far as it is subject to change. The concept of the material point
Point particle
A point particle is an idealization of particles heavily used in physics. Its defining feature is that it lacks spatial extension: being zero-dimensional, it does not take up space...

 is obviously due to observable bodies
Physical body
In physics, a physical body or physical object is a collection of masses, taken to be one...

; one conceived of the material point on the analogy of movable bodies by omitting characteristics of extension
Extension (metaphysics)
In metaphysics, extension is, roughly speaking, the property of "taking up space". René Descartes defines extension as the property of existing in more than one dimension. For Descartes, the primary characteristic of matter is extension, just as the primary characteristic of mind is consciousness...

, form
Substantial form
A theory of substantial forms asserts that forms organize matter and make it intelligible. Substantial forms are the source of properties, order, unity, identity, and information about objects....

, spatial locality, and all their 'inner' qualities, retaining only inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...

, translation
Translation (physics)
In physics, translation is movement that changes the position of an object, as opposed to rotation. For example, according to Whittaker:...

, and the additional concept of force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...

.

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