Nebular Hypothesis Of Laplace

 French Mathematician Laplace propounded his Nebular Hypothesis in the year 1796. Laplace’s hypothesis is just the modified version of Kant’s hypothesis. Laplace propounded his hypothesis without mathematical formulation. In fact, Laplace postulated his hypothesis after removing the inherent weak points and erroneous concepts of Kant’s hypothesis which suffered from three basic defects e.g.

 1. large amount of heat can not be generated due to collision of cold particles of primordial matter;
 2. Mutual collision of particles can not generate motion in the primordial matter and the random in the primordial matter;
 3. The angular velocity of rotatory speed of the Nebula can not increase due to increase in the size of Nebula.

Assumptions of Laplace’s Hypothesis:

 In order to remove the defects of Kant’s hypothesis, Laplace assumed certain axioms for the postulation of his Nebular Hypothesis to solve the riddle of the origin of the earth.
1. He assumed that there was a huge and hot gaseous Nebula in the space. Thus, he solved the  problem of heat of the Nebula through the assumption.
2. From the very beginning huge and hot Nebula was rotating on its axis.
3. The Nebula was continuously cooling due to loss of heat from its outer surface through the process    of  radiation and thus it was continuously reducing in size due to contraction of cooling.

The Origin Of The Earth According To Laplace:

   Based on aforesaid assumptions Laplace maintained that there was a hot and rotating huge gaseous Nebula in the space.There was gradual loss of heat from the outer surface of the Nebula through radiation due to circular motion or rotation of the Nebula. Thus, gradual loss of heat resulted into the cooling caused gradual concentration in the size of the Nebula. Thus, reduction in the size and volume of the Nebula increased the circular velocity of the Nebula. As the size of the Nebula continued to decrease, the velocity of rotatory motion continued to increase. Thus, the Nebula started spinning at very fast speed and consequently the centrifugal force became so great that it exceeded the centripetal force. When this stage was reached the materials at the equator of the   Nebula became weightless. Consequently, the outer layer was condensed due to excessive cooling and so it could not rotate with the still cooling and contracting central nucleus of the Nebula and thus the outer ring was separated from the Nebula and it started moving around the Nebula. This original ring was divided into nine rings and each ring moved away from the other ring. All the materials of each ring condensed at a point or knot in the form of  ‘hot gaseous agglomeration’. Each such agglomeration was later on cooled and condensed to form planet. Thus, nine planets were formed from nine rings and the remaining central nucleus of  the Nebula became the sun. Satellites were formed from the planets due to repetition of the aforesaid mechanism and processes.

Evaluation:

   The Nebular hypothesis began to fade away due to severe criticisms of the hypothesis by the scientists on various grounds. The demerits of Nebular hypothesis is given below.
1. Laplace assumed that initially there was a hot and rotating Nebula but he did not describe the    source of the origin of the Nebula. He also unable to describe the source of heat and motion of  Nebula.
2. He could not explain the formation of only a rings come out from the irregular ring detached from    the Nebula, why not more or less rings? It is quite unreasonable to imagine the situation that all  matter of one ring could condense into one incandescent gaseous mass to form one planet.
3. If the sun is the remaining nucleus of the Nebula as claimed by Laplace. It should have a small bulge around its middle part which would point out the probable separation of irregular ring from the sun but there is no such bulge in the middle part of the sun.
4. If we accept tenet of Laplace that the planets were formed from the Nebula, then the planets must  have been in liquid state cannot rotate and revolve around the sun properly because the rotatory  motion of different layers of the liquid is not equal. Only the solid mass of matter has the property to  perform rotatory and revolutionary motions along a near circular path without losing its original  shape.
5. According to the Nebular hypothesis all the satellites should revolve in the direction of their father   planets but contrary to this a few satellites of Saturn and Jupiter revolve in the opposite direction of    their father planets.
Based on above arguments Nebular hypothesis of Laplace is rendered untenable.

References:

  • K.Siddhartha – “The Earth’s Dynamic Surface”
  • S.Singh – Geomorphology
  • https://en.wikipedia.org
  • Strahler & Strahler – Physical Geography
  • M.J.Shelby – Earth’s Changing Surface

Read about Knat’s Hypothesis,
https://smoothknowledge.com/2017/08/24/the-hypothesis-of-the-origin-of-the-earth-by-kant/

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2 Responses

  1. nick says:

    The slide attachment added to the page clearly has the wrong year. it was proposed in 1796, not 1976….

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