# Pierre-Simon de Laplace

## Early Life

Pierre was born on March 28, 1749 in Beaumont-en-Auge in Normandy, France. His father, Pierre Laplace senor, was in the cider trade, and his mother, Marie-Ann Sochon, came from a prosperous farming family. He attended a Benedictine priory school between 7 and 16 years old. He attended because his father wanted him to pursue a career in church, and later, when he attended Caen University to study theology, Pierre still had that goal. This was until he discovered his love and talent for mathematics.

## Interests Grow

He had first realized his talent to mathematics thanks two of the teachers at his college named Christophe Gadbled and Pierre Le Canu. After graduating from Caen in the Faculty of Arts with a Master's Degree, at age 19, he left for Paris to pursue his mathematics. He sent a letter to a famous French mathematician named Jean le Rond d'Alembert (on the right). he had first, rejected Pierre, but was impressed with his next letter about the principles of mechanics, and got him into a position in the Military School of Paris as a prof. of mathematics.

## Contributions to Science: The Black Hole

Pierre was the first person to theorize the exsistance of black holes. This occured in 1796 when he was studying escape velocity. while doing so, he had found out a relationship between the size of an object and its mass, saying that if the object got smaller, but kept the same mass, then the escape velocity would increase. He used this relationship with Earth and calculated the escape velocity if you made it half as small. He went further to find out if you kept making hit smaller and smaller, that the escape velocity would be the same as the speed of light, and by that time, the Earth would only be 1.8 mm across. From this, the idea of blacks holes was born.

## The Nebular Hypothesis

Pierre had spent a lot of his time dedicated to astronomy. He had seemed to be most interested in the natural order of the solar system, like how all the planets exsisted on the same plane, and the path they followed. This interest sparked him to study their motions and how the solar system remained so stable, and even later led him to speculate the origin of the solar system. The Nebular Hypothesis had appeared in his book Exposition of a World System, gave the reason for the stability of the solar system is the evolution from chaos. He suggested that:

1. The sun was originally a giant cloud of gas or nebulae that rotated evenly.
2. The gas contracted due to cooling and gravity.
3. This forced the gas to rotate faster, just as an ice skater rotates faster when his extended arms are drawn onto his chest.
4. This faster rotation would throw off a rim of gas, which following cooling, would condense into a planet.
5. This process would he repeated several times to produce all the planets.
6. The asteroids between Mars and Jupiter were caused by rings which failed to condense properly.
7. The remaining gas ball left in the center became the sun.

## Bayes' Theorum

Laplace became interested in resolving conflicting data given known events. He wanted to use probability to work from known events back to the most likely causes. He referred to his version of Bayes' Theorem as the probability of causes. His version said in words rather than an equation, and said that the probability of a cause given an event is proportional to the probability of the event given its cause. Pierre's 1774 version didn't include prior probability. He helped spread Bayseain's ideas about the justification of flat priors or better know as the principle of indifference.
53 How the Earth Was Formed - Pierre Simon de Laplace