''Science'' (from ''scientia,'' Latin for ''knowledge'') refers to the systematic acquisition of new knowledge about nature and the body of already existing knowledge so gained. The Scientific Method is based on careful observation and the testing of theories by experiment. Science does not claim to make any statements about how nature actually ''is'', for the scientist should know that we can only make conclusions about our ''observations'' of nature. The development of Quantum Mechanics in the early 20th century showed us that our observations equate to interactions, and the incredible implications of wave-particle duality made ''objectivity'' in Science practically impossible.
Implicit in classical Science's devotion to acquiring knowledge about the Universe is an assumption that atoms, animals, gravity, stars, wind, microbes, etc. all exist independently of our observations of them. This essentially metaphysical view is termed Realism. The opposed view of modern Science parallels a metaphysical position, that of Idealism which in varying forms denies the existence of matter independent of mind. The two views are metaphysical because although both are consistent with our experience there appears to be no way to get outside of that experience in order to see which (if either) is true.
Some of the findings of Science can be very counter-intuitive. Atomic theory, for example, implies that a granite boulder which appears as heavy, hard, solid, grey, etc. is actually a combination of subatomic particles with none of these properties, moving very rapidly in an area consisting mostly of empty space. Many of humanity's preconceived notions about the workings of the universe have been challenged by new scientific discoveries.
Perhaps surprisingly, realism is not necessary to Science. Instrumentalism, for example, posits that while entities, such as atoms, help explain and predict data from experiments, these entities do not necessarily exist. This approach is favored by some when it comes to committing to the ontological status of a scientific entity which may seem unobservables in principle.
Philosophers sometimes distinguish between the actual reality of things within the universe, which may or may not be fully perceivable by humans, and our perception of things within the universe. Immanuel Kant coined the phrases Phenomena (the universe as humans experience it) and Noumena (things-in-themselves).
In contrast to Kant's views (and despite wide acceptance that human perception of phenomena is not necessarily an accurate reflection of the universe as it really is), most scientists assert that it is possible to understand and accurately explain (at least somewhat if not fully) the universe using the scientific method to hone accurate scientific theories and laws. Scientists to not claim to ''prove'' anything in the sense that it is absolute, unquestionable proof, but with a good degree of certainty based on experiments and current observations and data.
Scientists point out that while some people criticise the basic ideas of Science, it is Science alone that has provided information on the mysteries of the atom, the cell, the solar system, and the observable universe. It is Science alone that has provided knowledge to develop tens of thousands of technological advances in medicine, engineering, communications and beyond. No other system which claims to compete with Science has ever actually succeeded in actually producing useful information about the physical world in which we live. One criticism, commonly made by paranormalists, is that scientists can be closed-minded towards new ''discoveries''; although discoveries and theories such as Relativity and Quantum Mechanics have broadly changed the way scientists view the universe.
__Previous definitions of the term__
Until The Enlightenment, the word ''Science'' (or its Latin cognate) meant any systematic or exact, recorded knowledge. ''Science'' therefore had the same sort of very broad meaning that ''Philosophy'' had at that time.
There was a distinction between, for example, ''natural Science'' and ''moral Science,'' which latter included what we now call philosophy, and this mirrored a distinction between ''natural philosophy'' and ''moral philosophy.'' More recently, ''Science'' has come to be restricted to what used to be called ''Natural Science'' or ''natural philosophy.'' Natural Science can be further broken down into Physical Science and Biological Science. Social Science is often included in the field of Science as well.
Fields of study are often distinguished in terms of ''hard Sciences'' and ''soft Sciences,'' and these terms (at times considered derogatory) are often synonymous with the terms natural and social Science (respectively). Physics, Chemistry, Biology and Geology are all forms of ''hard Sciences''. Studies of Anthropology, history, Psychology, and Sociology are sometimes called ''soft Sciences.'' Proponents of this division use the arguments that the ''soft Sciences'' do not use the Scientific Method, admit anecdotal evidence, or are not mathematical, all adding up to a ''lack of rigor'' in their methods. Opponents of the division in the Sciences counter that the ''social Sciences'' often make systematic statistical studies in strictly controlled environments, or that these conditions are not adhered to by the natural Sciences either (for example, Behavioral Biology relies upon fieldwork in uncontrolled environments, Astronomy cannot design experiments, only observe limited conditions).
Mathematics is widely believed to be a Science, but it is not. It is more closely related to Logic; it is not a Science because it makes no attempt to gain Empirical Knowledge. However, mathematics is the universal language of all Sciences.
The term ''Science'' is sometimes pressed into service for new and interdisciplinarity fields that make use of scientific methods at least in part, and which in any case aspire to be systematic and careful explorations of their subjects, including Computer Science, library and information Science, and Environmental Science. Mathematics and Computer Science reside under ''Q'' in the Library of Congress classification, along with all else we now call Science.
__Scientific models, theories and laws__
''Main article:'' Scientific Method
The terms ''hypothesis'', ''model'', ''theory'' and, ''law'' have a different use in Science to colloquial speech. Scientists use the term ''model'' to mean a description of something, specifically one which can be used to make predictions which can be tested by experiment or observation. A ''hypothesis'' is a contention that has not (yet) been well supported nor ruled out by experiment. A ''physical law'' or a ''law of nature'' is a scientific generalization based on empirical observations.
Most non-scientists are unaware that what scientists call ''theories'' are what most people call ''facts''. The general public uses the word ''theory'' to refer to ideas that have no firm proof or support; in contrast, scientists usually use this word to refer only to ideas that have repeatedly withstood test. Thus, when scientists refer to the theories of biological evolution, Electromagnetism, and Relativity, they are referring to ideas that have survived considerable experimental testing. But there are exceptions, such as String Theory, which seems to be a promising model but as yet has no empirical evidence to give it precedence over competing models.
Especially fruitful theories that have withstood the test of time are considered to be ''proven'' in the scientific sense-- that it is true and factual but of course can still be falsified. This includes many theories, such as universally accepted onces such as Heliocentric Theory and controversial ones such as evolution, which are backed by many observations and experimental data. Theories are always open to revision if new evidence is provided or directly contradicts predictions or other evidence. As scientists do not claim absolute knowledge, even the most basic and fundamental theories may turn out to be incorrect if new data and observations contradict older ones.
Newton's law of gravitation is a famous example of a law falsified by experiments regarding motions at high speeds and in close proximity to strong gravitational fields. Outside of those conditions, Newton's Laws remain excellent accounts of motion and gravity. Because General Relativity accounts for all of the phenomena that Newton's Laws do, and more, General Relativity is currently regarded as our best account of gravitation.
__Mathematics and the scientific method__
Mathematics is essential to Science. Observing and collecting measurements requires the use of mathematics; hypothesizing and predicting requires extensive use of mathematics. Mathematical branches often used in Science include Calculus and Statistics. A form of systematic reasoning has been applied to mathematics itself at least since the time of Euclid.
Some thinkers see mathematicians as scientists, regarding physical experiments as inessential or that mathematical proofs are equivalent to experiments. Others do not see mathematics as a Science, since it does not require experimental test of its theories and hypotheses. In either case, the fact that mathematics is such a useful tool in describing the universe is a central issue in the Philosophy of Mathematics
R.P. Feynman said ''Mathematics is not real, but it ''feels'' real. Where is this place?''.
__Philosophical foundations of the scientific method__
One school of thought asserts that the scientific method (and Science in general) relies upon basic axioms or ''self-evident truths'' such as internal consistency and Realism. While it is true that many scientists believe these things and do assume them in their everyday work, the method itself does not rely on them: all such assumptions are just part of the hypotheses being tested, and many of them are subject to test as well. For example, one of the ''common sense'' ideas that scientists believed for a long time is that any measurable property of an object is something that exists in the object before it is measured, and our measurements are merely observations of that pre-existing condition; Quantum Mechanics obliges us to question this assumption, because experiments appear to contradict it.
Some believe that scientific principles have been ''solidly'' established, beyond question, and are ''true''. Some scientists themselves may indeed feel that way, having come to rely upon many of the results of Science without having done all the experiments themselves; after all, one cannot expect every individual scientist to repeat hundreds of years' worth of experiments. Most scientists even encourage an attitude of skepticism toward claims that contradict the current state of scientific knowledge or some easy extrapolation from it; but that only means such claims must meet a higher burden before being accepted, not that they can never be accepted. In the extreme, some, including some scientists, may believe in this or that scientific principle, or even ''Science'' itself, as a matter of faith in a manner similar to that of religious believers. However, neither Science nor scientific method itself rely on faith; ''all'' scientific facts (i.e., measurements) and explanations (i.e., hypotheses or theories) are subject to test, and will eventually be rejected as the best available hypothesis when new evidence falsifying them is found.
This is the reason that political, religious, or social enforcement of scientific convictions is inherently pernicious. Examples include the Roman Catholic Church's action against Galileo's non-Aristotelian discoveries about the behavior of the planets (they violated some prestigious, and ancient, philosophical speculation the Church had promoted to dogma), and Stalin's support for Lysenko's biological and genetic beliefs (what was wrong with standard genetics in Stalin's view is not clear; Lysenko was either a deliberate con man or incapable of understanding standard genetics in his day). Such fervor against challenging standard scientific convictions is inherently unscientific.
__Goals of Science__
Despite popular impressions of Science, it is not the goal of Science to answer all questions, only those that pertain to physical reality (measurable empirical experience). Science does not and can not produce absolute and unquestionable truth. Rather, Science consistently tests the currently best hypothesis about some aspect of the physical world, and when necessary revises or replaces it in light of new observations or data.
Science is not a source of subjective value judgements, though it can certainly speak to matters of ethics and public policy by pointing to the likely consequences of actions. However, Science can't tell us which of those consequences to desire or which is 'best'. What one projects from the currently most reasonable scientific hypothesis onto other realms of interest is not a scientific issue, and the scientific method offers no assistance for those who wish to do so. Scientific justification (or refutation) for many things is, nevertheless, often claimed.
__Fields of Science__
__The physical and life Sciences__
** Agricultural Science
** Cell Biology
** Developmental Biology
** evolution (Evolutionary Biology)
** Evolutionary Developmental Biology (''Evo-devo'' or Evolution of Development)
** Freshwater Biology
** Genetics (Population Genetics, Genomics, Proteomics)
** Health Science
*** Veterinary Science
** Marine Biology
** Molecular Biology
** Oncology (the study of cancer)
** Phycology (Algology)
** Structural Biology
* Earth Sciences
** Atomic, Molecular, and Optical physics
** Computational Physics
** Condensed Matter Physics
** Fluid dynamics
** Polymer Physics
** Materials Physics
** Mathematical Physics
** Nuclear Physics
** Plasma Physics
** Particle Physics (or High Energy Physics)
** Vehicle Dynamics
** Analytical Chemistry
** Computational Chemistry
** Inorganic Chemistry
** Materials Science
** Organic Chemistry
** Physical Chemistry
** Quantum Chemistry
__Computer and information Sciences__
* Computer Science
* Cognitive Science
* Cognitive Systems
* Systems Theory