## Pierre Simon LaplaceAstronomer, physicist, mathematician
Date of Birth:
23.03.1749Country: France |

**Content:**

- Biography of Pierre-Simon Laplace
- Scientific Contributions and Professional Achievements
- Contributions to Celestial Mechanics

## Biography of Pierre-Simon Laplace

Pierre-Simon Laplace, an astronomer, physicist, and mathematician, was born on March 23, 1749, in the village of Beaumont-en-Auge in Normandy, France. Coming from a modest peasant family, Laplace attended a Benedictine school and later became a mathematics teacher at a military school in Beaumont. At the age of seventeen, he wrote his first scientific work. In 1766, he moved to Paris and obtained a position as a mathematics professor at the Paris Military School.

## Scientific Contributions and Professional Achievements

In 1773, Laplace became an adjunct member of the Paris Academy, and in 1785, he became a full member. In 1784, Laplace became the examiner of the Royal Artillery Corps. In 1790, the French National Assembly instructed the Academy of Sciences to create a universal system of measures and weights. Laplace was appointed as the president of the Chamber of Measures and Weights.

However, during the Jacobin dictatorship that followed the popular uprising of 1793, the Academy of Sciences, along with other royal institutions, was abolished by a decree of the National Convention. Laplace was dismissed from the Commission of Measures and Weights. In 1795, the Convention replaced the Academy of Sciences with the National Institute of Sciences and Arts. Laplace became a member of the Institute and headed the Bureau of Longitudes, which was responsible for measuring the length of the Earth's meridian.

After the coup of 18 Brumaire, Laplace was appointed Minister of the Interior by Napoleon. In 1803, Napoleon made him the Vice-President of the Senate, and a month later, he became the Chancellor. In 1804, Laplace received the Legion of Honor.

From 1801 to 1809, Laplace was elected a member of the Royal Societies in Turin and Copenhagen, as well as the Academies of Sciences in Göttingen, Berlin, and Holland. On October 13, 1802, Laplace became an honorary member of the St. Petersburg Academy of Sciences. His "Analytical Theory of Probability" was published three times during his lifetime (in 1812, 1814, and 1820). Laplace introduced generating functions to develop his mathematical theory of probability. He organized the results obtained by other scientists into a coherent system, simplified proof methods, and proved the theorem on the discrepancy between the frequency of an event and its probability. Thanks to Laplace, the theory of probability acquired a complete form.

In physics, Laplace derived the formula for the speed of sound in air, created an ice calorimeter, and derived the barometric formula for calculating the change in air density with altitude, taking into account its humidity. He conducted several studies on the theory of capillarity and established a law that allowed the determination of the capillary pressure and thus the mechanical equilibrium conditions for movable (liquid) interfaces.

## Contributions to Celestial Mechanics

Laplace's first work on celestial mechanics, titled "On the Cause of Universal Gravitation and the Century Inequalities of the Planets Dependent on It," was published in 1773. In 1780, Laplace proposed a new method for calculating the orbits of celestial bodies.

Laplace proved the stability of the Solar System. He showed that the average speed of the Moon depended on the eccentricity of the Earth's orbit, which, in turn, varied under the influence of planetary attractions. Using the inequalities of the Moon's motion, he determined the amount of Earth's polar flattening.

Laplace concluded that Saturn's rings could not be solid, as they would be unstable. He predicted the compression of Saturn at its poles and established the laws of motion for Jupiter's satellites. These results were published in his most famous five-volume work, "Celestial Mechanics" (1798-1825).

Laplace's cosmogonic hypothesis, published in 1796 as an appendix to his book "System of the World," proposed that the solar system originated from a nebula composed of hot gas extending beyond the orbit of the farthest planet. The rotational motion of the cooling and contracting nebula caused it to flatten. As a result of this flattening, centrifugal forces caused rings of gaseous matter to break away from the nebula's outer edge, which later aggregated to form planets and their satellites.

After the restoration of the monarchy, Laplace enjoyed the favor of Louis XVIII. The king made him a peer of France and bestowed the title of Marquis. In 1817, Laplace became a member of the newly created French Academy, making him one of the Forty Immortals.

Laplace passed away after a short illness on March 5, 1827. His last words were, "What we know is so little compared to what we do not know."