This article is concerned primarily with the natural sciences such as physics, chemistry, biology, earth sciences, and their various branches (some of which are summarised later). The word "science" may also be used to refer to "an organized body of knowledge on any subject", e.g. social sciences, though this meaning is not considered here.
Much work in the natural sciences is concerned with formulating a hypothesis which agrees with (almost) all relevant and available data. A hypothesis is particularly useful if it can be used to make testable predictions; a hypothesis expressed as one or more mathematical equations lends itself well to this approach. Any hypothesis must be thoroughly tested by further experiments and/or observations.
- Note that the above paragraphs are only an approximate definition of science. For more details see the sections below: Terminology and Scientific method.
There are many misunderstandings about the nature of science. In relation to proof: "science is based on the principle that any idea, no matter how widely accepted today, could be overturned tomorrow if the evidence warranted it. Science accepts or rejects ideas based on the evidence; it does not prove or disprove them."
Science was originally a branch of philosophy, and although not generally recognised as such now, is still dependent on its philosophical underpinnings.
"Science uses specialized terms that have different meanings than everyday usage. These definitions correspond to the way scientists typically use these terms in the context of their work. Note, especially, that the meaning of “theory” in science is different than the meaning of “theory” in everyday conversation." 
A scientific fact is an observation or measurement which other scientists accept as correct.  Note that scientific facts must be replicable, i.e. other scientists using sufficiently similar equipment under sufficiently similar circumstances must be able to make the same observations or measurements.
"Science is how we describe the natural world, and if you search the web for “what is science,” three words tend to come up more often than others: observation, experiment, and evidence. Observations and experiments may not be perfect, even at the limits of our technologies, and interpretations may be flawed, but it’s the evidence that supports, or doesn’t, an argument that is the most important. And we choose to either accept it, or not."
A scientific law expresses an observed relationship between facts. Note that such a law is merely a concise description of what happens under certain circumstances; no causality is implied; it is not an explanation of why something happens. 
Some laws are thought to be exact, e.g. Ohm's Law expresses a relationship between voltage, current, and resistance in a electrical circuit.
Some laws have been known to be approximate from when they were first formulated, e.g. Zipf's Law which gives the probability of encountering a common word. Surprisingly, the law also provides probabilities for the sizes of cities in a given country.
Some laws were originally thought to be exact, but have since been discovered to be approximate, e.g. Newton's Laws of Motion  have been refined by Einstein's Theory of Relativity. In practice, Newton's laws are still used for calculations where speeds are small compared with the speed of light, since they give sufficiently accurate results under such circumstances and are much simpler to use than relativity.
A hypothesis is essentially an educated guess, based on facts, and may represent an attempt to provide an explanation for facts and/or laws. In many cases, a hypothesis is a suggested solution for an unexplained occurrence that does not fit into current accepted scientific theory.
An important attribute of any scientific hypothesis is that it be testable and falsifiable, i.e. futher observations and/or experiments can be used to test if the hypothesis is false. Note that it is not possible to test if a hypothesis is true; the best that done can do is to say that it has not yet been proven false.
"To scientists, a theory is a coherent explanation for a large number of facts and observations about the natural world.
A theory is:
- Internally consistent and compatible with the evidence
- Firmly grounded in and based upon evidence
- Tested against a wide range of phenomena
- Demonstrably effective in problem-solving
In popular use, a theory is often assumed to imply mere speculation, but in science, something is not called a theory until it has been confirmed over many independent experiments. Theories are more certain than hypotheses, but less certain than laws. The procedures and processes for testing a theory are well-defined within each scientific discipline."
To "do" science, what is known as the "scientific method" has been developed. The scientific method can be described in four steps:
- Observation and description of a phenomenon.
- Formation of an explanation for the observed phenomenon.
- Use of the explanation to predict other phenomena, or to predict the results of new observations.
- Independent testing of the predictions by properly performed experiments.
It is by this scientific method that science has renewed its views, even when such a renewal means the abandonment of a long and widely held belief; for instance, the Michelson–Morley experiment in 1887 was an attempt to determine the nature of the luminiferous aether (the supposed medium through which light travels). The result was practically impossible to reconcile with other experiments by any theory that was not complex and contrived. This discovery ultimately opened the way for the revolutionary new theories in physics in the twentieth century, in particular Einstein's special theory of relativity, which had no need for an aether.
Characteristics of a science
For a subject to qualify as a science, it is expected to have most, if not all, of the following characteristics:
- Consistent (internally and externally)
- Parsimonious (sparing in proposed entities or explanations; see Occam's Razor)
- Useful (describes and explains observed phenomena, and can perhaps be used in a predictive manner)
- Empirically testable and falsifiable (potentially disprovable by experiment or observation)
- Based on multiple observations (often in the form of controlled, repeated experiments)
- Correctable & dynamic (modified in the light of observations that do not support it)
- Progressive (achieves all that previous theories have and more)
- Tentative (admits that it might not be correct rather than asserting certainty)
Subjects which only have a few of these characteristics are unlikely to be scientific, regardless of what they claim.
Boundaries of science
While science is an extremely powerful tool, it is also very limited in scope. Specifically, the scientific method can only be applied in the repeatable testing of falsifiable hypotheses. If a question is not falsifiable, science is powerless to test it, and the question (and all opinions on the question) are outside the scope of science. For instance, science can say nothing about of the beginning of the universe, because hypotheses about those events cannot be repeatedly tested. Similarly, the origin of life is outside the scope of science, because hypotheses about that event or events cannot be repeatedly tested.
However, just because something is outside the scope of science does not make belief illegitimate. For example, we cannot scientifically test the hypothesis that the ancient Aztecs practiced human sacrifice, because there is no possible experiment to test that hypothesis. We can only rely on historical accounts, and interpretations of evidence, which are not themselves falsifiable. Nevertheless, one can reasonably believe that the events occurred as reported in history texts, not based on "science," but based on "history."
Those holding a materialist philosophy often argue that assertions about things beyond the scope of science (such as creation) are "unscientific" because they cannot be tested. In making this argument, however, they are applying a double standard, because their own views on the same topics are also impossible to test. Thus, they argue that an unrepeatable, unfalsifiable hypothesis that life arose spontaneously is "science," while an unrepeatable, unfalsifiable hypothesis that life was designed is "not science."
In making this argument, they are conflating science and materialism. In other words, they are claiming that "science" proves a thing (like the non-existence of God, or the absence of free will) which science cannot prove, because the question itself is not capable of being repeatedly tested in a lab.
... the view that prevailed among scientists of the late 19th century was to look for the causes of our behaviour in the brain alone.
Some psychologists[Who?] disagree with this viewpoint, asserting the existence of an eternal soul which transcends the physical world. Yet they still seek to apply to the study of the human mind the same principles which astronomers and geologists apply to their study of the heavens and the earth.
There is an ongoing debate whether Science is limited to physical science[Citation Needed], or whether it can study things that cannot be directly observed (such as the functioning of the human mind) and things that are not even physical.
Some philosophers, such as René Descartes (1641), suggest there are two kinds of substance: matter and mind. This leads to a division between the study of deterministic matter -- "natural philosophy", later called "natural science" -- and the study of volitional mind -- which falls outside the domain of "natural science", into the domain of "social sciences" and the humanities and theology -- and the "formal sciences" of mathematics and logic. The techniques used and the amount of certainty in the results obtained vary widely from one field of knowledge to another.
Branches of science
- Study of the material remains of cultures.
- Study of the universe beyond the Earth's atmosphere.
- Study of living organisms.
- Study of plants.
- Study of matter and its physical and chemical properties.
- How organisms interact with each other and their environment.
- Study of the Earth, its structure, and history.
- Study of the atmosphere and its phenomena, such as weather and climate.
- The exploration and study of the ocean.
- Studying fossils and the forms of life that existed in the past.
- Study of matter and energy and their interactions.
- Study of animals.
For more information, see Philosophy of science.
Science has a philosophical basis, without which it wouldn't be possible. The philosophical basis has a number of components, and it was the Christian worldview that gave rise to science. More recently, atheistic thought, opposed to the Christian worldview, threatens to undermine the basis for science even though it espouses the importance of science, and attempts to use it to justify atheism.
Christianity teaches that God created everything, so the principles such as motion that were studied on Earth would also apply to objects in the heavens. It also teaches that God is a rational, law-giving God, so it is to be expected that He created a rational universe with laws of nature for His creation to follow. Unlike some religions that teach that nature to be God or manifestations of the gods, and therefore improper to study, Christianity taught that creation was distinct from God and proper to study, and that man's God-given dominion over nature also gave us the right to study it.
This Christian basis of science has been acknowledged by numerous historians and other scholars. For example, Loren Eisely wrote:
The philosophy of experimental science … began its discoveries and made use of its methods in the faith, not the knowledge, that it was dealing with a rational universe controlled by a creator who did not act upon whim nor interfere with the forces He had set in operation … . It is surely one of the curious paradoxes of history that science, which professionally has little to do with faith, owes its origins to an act of faith that the universe can be rationally interpreted, and that science today is sustained by that assumption.
Atheists and other non-Christians have brought their own philosophies to science. James Hutton, for example, decided that geology should work on the principle that "the present is the key to the past", and thereby ignore the historical account in the Bible that talks about unique past events such as the Global flood. More recently, they have argued that science must adopt naturalistic explanations, even though that means ruling out supernatural explanations even if they make more sense. Dr. Scott Todd wrote: "Even if all the data point to an intelligent designer, such an hypothesis is excluded from science because it is not naturalistic".
For more information, see Pseudoscience.
Pseudoscience is something that claims or appears to be or has some similarity to science, but which is not science. However, in many cases whether or not something is science or pseudoscience is disputed. For example, astronomy is accepted as a science, but astrology is generally viewed as a pseudoscience, although why this is the case is not so clear.
Also, the label is often applied to topics that one group doesn't accept even though another group does. Therefore biblical creation is labelled pseudoscience by anti-creationists, although it is no less scientific than evolution.
For more information, see Scientism.
Scientism is treating science as religion or as the only valid source of information. Many people who regard science highly will fall into the trap of making claims that if something has not been shown to be true by science, it should be disregarded.
Most scientists will overtly reject the validity of scientism, even though in some cases they show evidence of thinking that way. Since the scientific method cannot rationally justify scientism, scientism itself is self-defeating.
Bertrand Russell put it this way: Science is all there is to know. There is nothing beyond science as far as knowledge goes. It's only beliefs that are supported by science that are respectable, or worth holding. But the irony is, that belief itself is not supported by science. You can't give empirical evidence for that belief; that belief is a piece of philosophy. Or it might even be a kind of a piece of theology, but it's not a piece of science.
- Bumbulis, Michael, Christianity and the Birth of Science, 24 November 1996
- Hannam, James, Christianity and the Rise of Science, 3 February 2009.
- "What is Science?" by Richard Feynman
- "So what, exactly, is science?" – "A science checklist", part of "Understanding Science: how science really works" at UC Berkeley.
- Community wiki: What is science?
- Meatball wiki: What is science?
- The original wiki: What is science?
- ↑ 1.0 1.1 Compact Oxford English Dictionary, third edition, 2008
- ↑ Open University degree in Natural sciences
- ↑ Define hypothesis
- ↑ What is a testable prediction?
- ↑ Misconceptions about science
- ↑ Definitions of Fact, Theory, and Law in Scientific Work
- ↑ Facts, Hypotheses, Theories, and all that stuff
- ↑ Scientific fact 1
- ↑ Scientific fact 2
- ↑ Why I don’t believe in science…and students shouldn’t either
- ↑ Scientific Hypothesis, Theory, Law Definitions
- ↑ Scientific law
- ↑ Ohm's Law
- ↑ Zipf's Law for words
- ↑ Zipf's Law for city sizes
- ↑ Newton's laws of motion 1
- ↑ Newton's Laws of motion 2
- ↑ What is a scientific hypothesis?
- ↑ What is a Scientific Hypothesis?
- ↑ hypothesis and scientific method
- ↑ Scientific Hypothesis, Theories and Laws
- ↑ Is astrology a pseudoscience
- ↑ The Mind-Brain Problem
- ↑ "Fields arranged by purity"
- ↑ The branches of science
- ↑ Fast facts: branches of science
- ↑ Paul R. Thagard, Why Astrology Is A Pseudoscience, PSA, 1978 Volume 1, 1978.