What is meant by Dual nature of matter as well as energy?

 

What is meant by Dual nature of matter as well as energy?

      Hindi movies like Seeta Aur Geeta, Chalbaz, Judwa, Tanu weds Manu was well known for Double roles played by one actor or actress. Generally, one role is mild character and another role is dashing nature. Our entire life is based on matter and energy. Matter as well as energy play double roles.   I think this double role idea may be the outcome of this. Hence let us discuss the Dual nature ( Double role ) of matter and energy.

 Historical Developments of theories of light:

     Nature ( the Universe ) is constituted by Matter and Energy. 

  Matter and Energy

 To explain how and why matter and energy behave, observations were made. This leads to some conclusions about the properties of matter and energy. Theories were formulated to explain these properties. If both theory and observation were matched then that theory was accepted, otherwise,  it is rejected.

    Newtonian mechanics along with Maxwell’s electromagnetic wave theory and thermodynamics guided the development of science and engineering during the 17^th to 19^th centuries. All the scientific results were explained successfully with these theories.  These developments are termed classical physics or classical mechanics or Newtonian mechanics.

    The properties of light such as reflection, refraction, polarization, diffraction, and interference are satisfactorily explained by classical physics, which stresses on wave nature of light.  Up to the end of the 19^th century, it was settled that light has a wave nature.  New properties invented during the first quarter of the 20^th century challenged the wave nature of light.

    One of the first excellent results about the black body radiation indicated that wave theory was not sufficient to explain it. In 1896, Wien attempted to explain the spectrum of black body radiation only for lower wavelengths.  In 1900, Rayleigh and Jeans attempted to explain radiation for longer wavelengths.  Then, in 1900, Max Planck,  a German physicist proposed his quantum theory to explain the experimental result of black body radiation and succeeded in it.  But his idea was against classical physics.  He proposed that light has a particle nature.  This quantum theory is further supported by an experimental result in later years, such as photoelectric effect, Compton effect,  line spectrum, etc.

      In 1887 Heinrich Hertz first proposed the photoelectric effect and details were studied by Philipp Lenard.  The photoelectric effect could not be explained by classical physics.  Albert Einstein, in 1985, with the help of  Planck’s quantum theory, successfully explained the photoelectric effect by his photoelectric equation.  Einstein was awarded Nobel Prize in 1921 for this result, not for the theory of relativity which brought him much richer laurels.

     Latter an American physicist A.H.  Compton, in 1926, discovered that the scattered X-rays were associated with increasing wavelength. This effect is called the Compton effect, which was satisfactorily explained based on  Planck’s quantum theory. Gilbert Lewis, an American physicist, termed the quantum of a wave of light as a 'Photon'  in 1926. Neil Bohr Denmark physicist, in 1913, using Planck’s quantum theory, accounted for spectral lines of a hydrogen atom.

Dual nature of light ( Energy ):

    All these developments in physics from 1900 to 1930 led to a conflict that whether light behaves as a wave or a particle. On one hand properties like reflection, refraction, interference, diffraction, and polarization, which are propagation properties of light, can be explained by considering the wave nature of light.  On the other hand, black body radiation, the Photoelectric effect, Compton effect emission of a spectral line, which is interaction properties of light with matter,  can be explained by considering the particle nature of light.

          The wave and particle nature are contradictory to each other. But it is seen that both natures, wave or particle,  are not observed simultaneously in anyone property of light.  All properties of light indicate that light behaves as a wave or a particle one at a  time. This led to the idea to consider by a physicist that light has dual nature, the wave as well as the particle. These aspects of light are a compliment to each other.

 To understand more clearly about dual nature, let us consider everyday life examples. Consider a tank full of water. Near the tank, there is a channel to take away water from a tank when poured through the bucket. If water is lifted from the tank by the bucket by bucket and thrown in the channel speedily, then it is seen that water appears to flow in the channel continuously after some distance. Even though water is taken discontinuously from the tank, water is flowing continuously in the channel. 

  Fig A

  From Fig A same effect is seen while raining. The rain is by drop by drop, but flow is continuous.

   Likewise, light from a bulb is produced by the jumping of the electron from the higher orbit to the lower orbit in the atom and emits the photon discontinuously, but we see that light is coming from a bulb continuously.

 Thus light behaves as the particle during production from the source, while behaves as a wave when propagating.  Both these are independent processes indicating light shows one nature at one time and simultaneously.

  Dual nature of Matter :

     The wave-particle dualism was extended to matter by Louis de  Broglie, in 1924. In 1927, Davisson and Germer gave experimental proof for matter waves. Prince Louis de  Broglie was awarded by Nobel Prize in 1929.

He proposed this because of the following points:

 1  Nature is symmetrical in many ways.

 2 The observable universe is composed of light and matter.

 3  Successful explanation of Bohr's theory of atomic structure.

     The suggestion of the de  Broglie that like radiation, matter also has dual nature,  particle as well as wave.  According to de  Broglie's hypothesis, " the matter in motion have wave association with it".

   The wave associated with the matter is called 'matter wave 'or ' de Broglie wave '.  He deduced the expression for matter wavelength based on Planck's expression of the energy of an electromagnetic wave.

    Due to the parallelism between wave and particle, the energy of the photon is nothing but the energy of the wave. Using this equation he deduced the expression for the wavelength of matter-wave. 

λ = h/ mv

Where h is Planck's constant, m is the mass of the body, and v is velocity.

   The wave aspect of the matter, which is spreading whereas a particle aspect of the matter, which is localized in space, leads to the problem of accepting the dual nature of matter.  This was simplified by the German physicist, Werner Heisenberg,  in 1927, who discovered 'the uncertainty principle'.  This principle considered wave packets instead of particles. 

    All these discoveries were related to the micro-world and are explained by Planck's quantum theory.  These developments give birth to 'Quantum mechanics' which is the foundation of modern physics.  Upto  1900 century, Newtonian or Classical mechanics based on Newton's equation governed by the laws of physics.  To govern quantum mechanics the question was proposed by Erwin Schrodinger, an Austrian physicist.  In 1926, the Schrodinger equation includes all the important elements of  Planck,  de  Broglie, and Heisenberg.

     The properties of light such as reflection, refraction, interference, diffraction, and polarization can be explained by considering light behaves as a wave.  These properties are seen when light interacts with itself in propagation. Hence, the radiation interacts with radiation in propagation, then radiation behaves as a wave. These properties could not be described by quantum theory.

    The properties like the Photoelectric effect, Compton effect, emission of the spectral line are clearly understood by considering light behaves as a particle. When light interacts with the matter then these properties are observed.  Hence, radiation when interacts with matter behaves like a particle.  Quantum theory fit for these properties, whereas, a classical theory could not.

    Bohr proposed the principle of complementary which states that " the particle and wave nature of radiation is the complementary description of radiation ". Thus, it is accepted that light has dual nature, a wave as well as a particle. This is labeled as "wave-particle duality". Radiation cannot behave simultaneously as wave and particle.  It shows one nature at a time as seen in these properties of light.

 Thus matter and energy both play double roles, a wave as well as a particle. Round us,  most of the properties of matter are observed with moderate speed showing matter as the particle in the macroscopic world.  In the microscopic world particles like electrons, protons, etc moving with high-speed show wave association with them indicating wave nature of matter.

   Energy particularly light is in the microscopic state showing wave nature due to most of the properties observed by us like reflection, refraction, diffraction on a large scale. But particle nature is observed in a few cases like photo-electric effect, Compton effect due to photon of light. Hence, generally, we look the matter as a particle and propagating energy as a wave. But now we say that Matter and Energy play double roles, WAVE AS WELL AS PARTICLE.