Without any doubt, the regularity which astronomy shows us in the movements of the comets takes place in all phenomena. The trajectory of a simple molecule of air or vapour is regulated in a manner as certain as that of the planetary orbits; the only difference between them is that which is contributed by our ignorance. Probability is relative in part to this ignorance, and in part to our knowledge.
Interpretation
This quote highlights the deterministic nature of the universe, suggesting that all phenomena follow predictable patterns, much like the orbits of celestial bodies.
In this quote, Pierre-Simon Laplace emphasizes that the certainty observed in astronomical movements extends to all aspects of nature, including the behavior of molecules. He suggests that the only true distinction between the predictable trajectories of comets and those of smaller particles lies in human ignorance, meaning that greater knowledge can lead to a clearer understanding of these phenomena. Thus, probability itself is influenced by both what we know and what we do not know.
In practice
During a lecture on the predictability of physical laws.
It is interesting thus to follow the intellectual truths of analysis in the phenomena of nature. This correspondence, of which the system of the world will offer us numerous examples, makes one of the greatest charms attached to mathematical speculations.
All the effects of Nature are only the mathematical consequences of a small number of immutable laws.
The word 'chance' then expresses only our ignorance of the causes of the phenomena that we observe to occur and to succeed one another in no apparent order. Probability is relative in part to this ignorance, and in part to our knowledge.
Given for one instant an intelligence which could comprehend all the forces by which nature is animated and the respective positions of the beings which compose it, if moreover this intelligence were vast enough to submit these data to analysis, it would embrace in the same formula both the movements of the largest bodies in the universe and those of the lightest atom; to it nothing would be uncertain, and the future as the past would be present to its eye.
The weight of evidence for an extraordinary claim must be proportioned to its strangeness.
Probability theory is nothing but common sense reduced to calculation.
If you represent the Earth's lifetime by a single year, say from January when it was made to December, the 21st-century would be a quarter of a second in June - a tiny fraction of the year. But even in this concertinaed cosmic perspective, our century is very, very special: the first when humans can change themselves and their home planet.
Every great advance in natural knowledge has involved the absolute rejection of authority.
Mitt Romney's energy policy is a relic of the 19th century. We need a 21st century plan. The fate of the planet is at stake.
The tool that's most associated with the recent progress against malaria is the long-lasting bed net. Bed nets are a fantastic innovation. But we can do even better. We can invent new ways to control the mosquitoes that carry the malaria parasite.
Ninety-nine percent of all species that ever lived are now extinct.
Extinguished theologians lie about the cradle of every science as the strangled snakes beside that of Hercules; and history records that whenever science and orthodoxy have been fairly opposed, the latter has been forced to retire from the lists, bleeding and crushed if not annihilated; scotched, if not slain.
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