Every major science, including physics, biology, and chemistry, are disciplines that were once considered as philosophy. Medicine was always considered a practical art, however. As facts about nature became more understood, these subjects branched away. Psychology only split a century and a half ago. In our own time, subjects such as consciousness studies, decision theory, and applied ethics have increasingly found independence from philosophy as a whole. Because of this, philosophy seems useful because it spins off new kinds of science.
Philosophers ask questions about ideas (concepts). They try to find answers to those questions. Some thinkers find it very hard to find those words that best describe the ideas they have. When they find answers to some of these questions philosophers often have the same problem, that is how to best tell the answers they found to other people. Depending on the meaning of the words they use, the answers change.
Some philosophers are full-time thinkers (called academics), who work for universities or colleges. These philosophers write books and articles about philosophy and teach classes about philosophy to university or college students.
Other philosophers are just "hobby" thinkers who think about philosophy during their free time. A small number of hobby thinkers have thought so much about philosophy that they are able to write articles for philosophy magazines. Other people approach philosophy from another job. For example, monks, artists, and scientists may think about philosophical ideas and questions.
Most philosophers work by asking questions and looking for good definitions (meanings) of words to help them understand what a question means.
Some philosophers say the only thing needed to answer a question is to find out what it means. The only thing that makes philosophical questions (such as those above) difficult is that people do not really know what they mean. Ludwig Wittgenstein believed this.
Philosophers often use both real and imaginary examples to make a point. For example, they may write about a real or fictional person in order to show what they think a good person or a bad person is like.
Some philosophers look for the simplest way to answer a question and say that is probably the right answer. This is a process called Occam's razor. Others believe that complicated answers to questions can also be right. For an example of a philosophical problem, see the God paradox.
Philosophers use logic to solve problems and answer questions. Logical consistency is a cornerstone of any acceptable theory. Philosophers who disagree with a theory will often try to find a logical contradiction in a theory. If they find a contradiction, this gives them a reason to reject that theory. If they do not find an inconsistency, the philosopher might show that the theory leads to a conclusion which is either unacceptable or ridiculous. This second approach is usually called reductio ad absurdum.
People listed here should be genuine philosophers, rather than social or political campaigners. The lists are not meant to be complete.
Physics
Physics is a branch of science. It is one of the most fundamental scientific disciplines. The main goal of physics is to explain how things move in space and time and understand how the universe behaves. It studies matter, forces and their effects.
The word "physics" comes from the Greek word ἡ φύσις, meaning "nature". Physics can also be defined as "that department of knowledge which relates to the order of nature, or, in other words, to the regular succession of events".
Astronomy, a part of physics, is the oldest natural science. In the past it was a part of 'natural philosophy' with other fields of science, such as chemistry and biology. During the scientific revolution, these fields became separate, and physics became a distinct field of knowledge.
Physics is very important in the development of new technologies, such as airplanes, televisions, computers and nuclear weapons. Mechanics, a branch of physics, helped develop the mathematical field of calculus.
Modern physics connects ideas about the four laws of symmetry and conservation of energy, momentum, charge, and parity.
Astronomy is the oldest natural science. The Sumerians, and Ancient Egyptians studied the stars, mostly with a view to prediction and religion. The first Babylonian star maps date from about 1200 BC. That astronomical events are periodic also dates back to the Babylonians. Their understanding was not scientific, but their observations influenced later astronomy. Much astronomy came from Mesopotamia, Babylonia, Ancient Egypt, and Ancient Greece. Astronomers from Egypt built monuments that showed how objects in the sky moved, and most of the names for the constellations in the Northern hemisphere came from Greek astronomers.
Natural philosophy started in Greece around 650 BC when a movement of philosophers replaced superstition with naturalism, which refuted the spiritual. Leucippus and his student Democritus suggested the idea of the atom around this period.
Islamic scholars continued to study Aristotelian physics during the Islamic Golden Age. One main contribution was to observational astronomy. Some, like Ibn Sahl, Al-Kindi, Ibn al-Haytham, Al-Farisi and Avicenna, worked on optics and vision. In "The Book of Optics", Ibn al-Haytham rejected previous Greek ideas concerning vision and proposed a new theory. He studied how light enters the eye, and developed the camera obscura. European scientists later built eyeglasses, magnifying glasses, telescopes, and cameras from this book.
Physics became a separate field of study after the scientific revolution. Galileo's experiments helped to create classical physics. Although he did not invent the telescope, he used it when he looked into the night sky. He supported Copernicus' idea that the Earth moved around the Sun (heliocentrism). He also investigated gravity. Isaac Newton used Galileo's ideas to create his three laws of motion and his law of universal gravitation. Together these laws explained the motion of falling bodies near the earth and the motion of earth and planets around the sun.
In a couple centuries, the Industrial Revolution was in full swing and many more discoveries were made in many fields of science. The laws of classical physics are good enough to study objects that move much slower than the speed of light, and are not microscopic. When scientists first studied quantum mechanics, they had to create a new set of laws, which was the start of modern physics.
As scientists researched particles, they discovered what classical mechanics could not explain. Classical mechanics predicted that the speed of light varied, but experiments showed the speed of light stayed the same. This was predicted by Albert Einstein's theory of special relativity. Einstein predicted that the speed of electromagnetic radiation through empty space would always be the same. His view of space-time replaced the ancient idea that space and time were quite separate things.
Max Planck came up with quantum mechanics to explain why metal releases electrons when you shine a light at it, and why matter emits radiation. Quantum mechanics applies for very small things like the electrons, protons, and neutrons that make up an atom. People like Werner Heisenberg, Erwin Schrödinger, and Paul Dirac continued to work on quantum mechanics and eventually we got the Standard Model.