Scientific theory - Wikipedia
A scientific theory is based on large amounts of data and observations that have Linnaeus did not explicitly discuss change in organisms or propose a reason for gathering observations of the relationships between different rock formations. The explanation of a phenomenon is called a scientific theory. Laws are generalized observations about a relationship between two or more. A scientific theory is an explanation of an aspect of the natural world that can be repeatedly . From the American Association for the Advancement of Science: . Unlike hypotheses, theories and laws may be simply referred to as scientific fact.
Your friend is highlighting a simple difference in vocabulary. To a chemist, the term organic refers to any compound in which hydrogen is bonded to carbon. Tomatoes like all plants are abundant in organic compounds — thus your friend's laughter. In modern agriculture, however, organic has come to mean food items grown or raised without the use of chemical fertilizers, pesticides, or other additives.
So who is correct? Both uses of the word are correct, though they mean different things in different contexts. There are, of course, lots of words that have more than one meaning like bat, for examplebut multiple meanings can be especially confusing when two meanings convey very different ideas and are specific to one field of study.
Scientific theories The term theory also has two meanings, and this double meaning often leads to confusion. In common language, the term theory generally refers to speculation or a hunch or guess.
- Theories, Hypotheses, and Laws
You might have a theory about why your favorite sports team isn't playing well, or who ate the last cookie from the cookie jar.
But these theories do not fit the scientific use of the term. In science, a theory is a well-substantiated and comprehensive set of ideas that explains a phenomenon in nature. A scientific theory is based on large amounts of data and observations that have been collected over time. Scientific theories can be tested and refined by additional researchand they allow scientists to make predictions. Though you may be correct in your hunch, your cookie jar conjecture doesn't fit this more rigorous definition.
All scientific disciplines have well-established, fundamental theories. For example, atomic theory describes the nature of matter and is supported by multiple lines of evidence from the way substances behave and react in the world around us see our series on Atomic Theory.
Plate tectonic theory describes the large scale movement of the outer layer of the Earth and is supported by evidence from studies about earthquakesmagnetic properties of the rocks that make up the seafloorand the distribution of volcanoes on Earth see our series on Plate Tectonic Theory. The theory of evolution by natural selection, which describes the mechanism by which inherited traits that affect survivability or reproductive success can cause changes in living organisms over generationsis supported by extensive studies of DNAfossilsand other types of scientific evidence see our Charles Darwin series for more information.
Each of these major theories guides and informs modern research in those fields, integrating a broad, comprehensive set of ideas. So how are these fundamental theories developed, and why are they considered so well supported? Let's take a closer look at some of the data and research supporting the theory of natural selection to better see how a theory develops.
Comprehension Checkpoint A theory is simply an educated guess made by a scientist. Evolution and natural selection The theory of evolution by natural selection is sometimes maligned as Charles Darwin 's speculation on the origin of modern life forms.
However, evolutionary theory is not speculation. While Darwin is rightly credited with first articulating the theory of natural selection, his ideas built on more than a century of scientific research that came before him, and are supported by over a century and a half of research since. Cover of the edition of Systema Naturae. Research about the origins and diversity of life proliferated in the 18th and 19th centuries.
Carolus Linnaeusa Swedish botanist and the father of modern taxonomy see our module Taxonomy I for more informationwas a devout Christian who believed in the concept of Fixity of Speciesan idea based on the biblical story of creation.
The Fixity of Species concept said that each species is based on an ideal form that has not changed over time. In the early stages of his career, Linnaeus traveled extensively and collected data on the structural similarities and differences between different species of plants. Noting that some very different plants had similar structures, he began to piece together his landmark work, Systema Naturae, in Figure 1.
In Systema, Linnaeus classified organisms into related groups based on similarities in their physical features. He developed a hierarchical classification systemeven drawing relationships between seemingly disparate species for example, humans, orangutans, and chimpanzees based on the physical similarities that he observed between these organisms. Linnaeus did not explicitly discuss change in organisms or propose a reason for his hierarchy, but by grouping organisms based on physical characteristics, he suggested that species are related, unintentionally challenging the Fixity notion that each species is created in a unique, ideal form.
The age of Earth: At the time, many people thought of the Earth as 6, years old, based on a strict interpretation of the events detailed in the Christian Old Testament by the influential Scottish Archbishop Ussher.
1.3: Hypothesis, Theories, and Laws
By observing other planets and comets in the solar systemLeclerc hypothesized that Earth began as a hot, fiery ball of molten rock, mostly consisting of iron.
Using the cooling rate of iron, Leclerc calculated that Earth must therefore be at least 70, years old in order to have reached its present temperature.
Hutton approached the same topic from a different perspective, gathering observations of the relationships between different rock formations and the rates of modern geological processes near his home in Scotland.
He recognized that the relatively slow processes of erosion and sedimentation could not create all of the exposed rock layers in only a few thousand years see our module The Rock Cycle. Based on his extensive collection of data just one of his many publications ran to 2, pagesHutton suggested that the Earth was far older than human history — hundreds of millions of years old.
While we now know that both Leclerc and Hutton significantly underestimated the age of the Earth by about 4 billion yearstheir work shattered long-held beliefs and opened a window into research on how life can change over these very long timescales.
Fossil studies lead to the development of a theory of evolution: Illustration of an Indian elephant jaw and a mammoth jaw from Cuvier's paper. With the age of Earth now extended by Leclerc and Hutton, more researchers began to turn their attention to studying past life. Fossils are the main way to study past life forms, and several key studies on fossils helped in the development of a theory of evolution.
Through his work, Cuvier became interested in fossils found near Paris, which some claimed were the remains of the elephants that Hannibal rode over the Alps when he invaded Rome in BCE. In studying both the fossils and living speciesCuvier documented different patterns in the dental structure and number of teeth between the fossils and modern elephants Figure 2 Horner, Based on these dataCuvier hypothesized that the fossil remains were not left by Hannibal, but were from a distinct species of animal that once roamed through Europe and had gone extinct thousands of years earlier: The concept of species extinction had been discussed by a few individuals before Cuvier, but it was in direct opposition to the Fixity of Species concept — if every organism were based on a perfectly adapted, ideal form, how could any cease to exist?
That would suggest it was no longer ideal. While his work provided critical evidence of extinctiona key component of evolutionCuvier was highly critical of the idea that species could change over time. As a result of his extensive studies of animal anatomy, Cuvier had developed a holistic view of organismsstating that the number, direction, and shape of the bones that compose each part of an animal's body are always in a necessary relation to all the other parts, in such a way that In other words, Cuvier viewed each part of an organism as a unique, essential component of the whole organism.
If one part were to change, he believed, the organism could not survive. His skepticism about the ability of organisms to change led him to criticize the whole idea of evolutionand his prominence in France as a scientist played a large role in discouraging the acceptance of the idea in the scientific community. Studies of invertebrates support a theory of change in species: Lamarck Jean Baptiste Lamarck, a contemporary of Cuvier's at the National Museum in Paris, studied invertebrates like insects and worms.
As Lamarck worked through the museum's large collection of invertebrates, he was impressed by the number and variety of organisms. All facts are true under the specific conditions of the observation. What is a Hypothesis? One of the most common terms used in science classes is a "hypothesis". The word can have many different definitions, depending on the context in which it is being used: Tentative or Proposed explanation - hypotheses can be suggestions about why something is observed, but in order for it to be scientific, we must be able to test the explanation to see if it works, if it is able to correctly predict what will happen in a situation, such as: A hypothesis is very tentative; it can be easily changed.
What is a Theory? The explanation becomes a scientific theory. In everyday language a theory means a hunch or speculation. Not so in science. Theories also allow scientists to make predictions about as yet unobserved phenomena. Such fact-supported theories are not "guesses" but reliable accounts of the real world. The theory of biological evolution is more than "just a theory.
Our understanding of gravity is still a work in progress. But the phenomenon of gravity, like evolution, is an accepted fact. Theories are explanations of natural phenomenon.
They aren't predictions although we may use theories to make predictions. They are explanations why we observe something.
Theories aren't likely to change. The phrase " the received view of theories " is used to describe this approach. Terms commonly associated with it are " linguistic " because theories are components of a language and " syntactic " because a language has rules about how symbols can be strung together. Problems in defining this kind of language precisely, e. Theories as models[ edit ] Main article: Scientific model The semantic view of theorieswhich identifies scientific theories with models rather than propositionshas replaced the received view as the dominant position in theory formulation in the philosophy of science.
One can use language to describe a model; however, the theory is the model or a collection of similar modelsand not the description of the model.
A model of the solar system, for example, might consist of abstract objects that represent the sun and the planets. These objects have associated properties, e. The model parameters, e. This model can then be tested to see whether it accurately predicts future observations; astronomers can verify that the positions of the model's objects over time match the actual positions of the planets.
For most planets, the Newtonian model's predictions are accurate; for Mercuryit is slightly inaccurate and the model of general relativity must be used instead. The word " semantic " refers to the way that a model represents the real world. The representation literally, "re-presentation" describes particular aspects of a phenomenon or the manner of interaction among a set of phenomena. For instance, a scale model of a house or of a solar system is clearly not an actual house or an actual solar system; the aspects of an actual house or an actual solar system represented in a scale model are, only in certain limited ways, representative of the actual entity.
A scale model of a house is not a house; but to someone who wants to learn about houses, analogous to a scientist who wants to understand reality, a sufficiently detailed scale model may suffice.
Differences between theory and model[ edit ] Main article: Conceptual model Several commentators  have stated that the distinguishing characteristic of theories is that they are explanatory as well as descriptive, while models are only descriptive although still predictive in a more limited sense.
Philosopher Stephen Pepper also distinguished between theories and models, and said in that general models and theories are predicated on a "root" metaphor that constrains how scientists theorize and model a phenomenon and thus arrive at testable hypotheses. Engineering practice makes a distinction between "mathematical models" and "physical models"; the cost of fabricating a physical model can be minimized by first creating a mathematical model using a computer software package, such as a computer aided design tool.
The component parts are each themselves modelled, and the fabrication tolerances are specified.
An exploded view drawing is used to lay out the fabrication sequence. Simulation packages for displaying each of the subassemblies allow the parts to be rotated, magnified, in realistic detail. Software packages for creating the bill of materials for construction allows subcontractors to specialize in assembly processes, which spreads the cost of manufacturing machinery among multiple customers.
Computer-aided engineeringComputer-aided manufacturingand 3D printing Assumptions in formulating theories[ edit ] An assumption or axiom is a statement that is accepted without evidence. For example, assumptions can be used as premises in a logical argument.
Isaac Asimov described assumptions as follows: It is better to consider assumptions as either useful or useless, depending on whether deductions made from them corresponded to reality Since we must start somewhere, we must have assumptions, but at least let us have as few assumptions as possible.
However, theories do not generally make assumptions in the conventional sense statements accepted without evidence. While assumptions are often incorporated during the formation of new theories, these are either supported by evidence such as from previously existing theories or the evidence is produced in the course of validating the theory.
The Relationship Between Hypothesis, Theory, Law and Facts by Joselin Alfaro on Prezi
This may be as simple as observing that the theory makes accurate predictions, which is evidence that any assumptions made at the outset are correct or approximately correct under the conditions tested. Conventional assumptions, without evidence, may be used if the theory is only intended to apply when the assumption is valid or approximately valid.
For example, the special theory of relativity assumes an inertial frame of reference. The theory makes accurate predictions when the assumption is valid, and does not make accurate predictions when the assumption is not valid.
Such assumptions are often the point with which older theories are succeeded by new ones the general theory of relativity works in non-inertial reference frames as well. The term "assumption" is actually broader than its standard use, etymologically speaking. The Oxford English Dictionary OED and online Wiktionary indicate its Latin source as assumere "accept, to take to oneself, adopt, usurp"which is a conjunction of ad- "to, towards, at" and sumere to take.
The root survives, with shifted meanings, in the Italian assumere and Spanish sumir. The first sense of "assume" in the OED is "to take unto oneselfreceive, accept, adopt". The term was originally employed in religious contexts as in "to receive up into heaven", especially "the reception of the Virgin Mary into heaven, with body preserved from corruption", CE but it was also simply used to refer to "receive into association" or "adopt into partnership".
Moreover, other senses of assumere included i "investing oneself with an attribute ", ii "to undertake" especially in Lawiii "to take to oneself in appearance only, to pretend to possess", and iv "to suppose a thing to be" all senses from OED entry on "assume"; the OED entry for "assumption" is almost perfectly symmetrical in senses. Thus, "assumption" connotes other associations than the contemporary standard sense of "that which is assumed or taken for granted; a supposition, postulate" only the 11th of 12 senses of "assumption", and the 10th of 11 senses of "assume".
From philosophers of science[ edit ] Karl Popper described the characteristics of a scientific theory as follows: Confirmations should count only if they are the result of risky predictions; that is to say, if, unenlightened by the theory in question, we should have expected an event which was incompatible with the theory—an event which would have refuted the theory.
Every "good" scientific theory is a prohibition: The more a theory forbids, the better it is. A theory which is not refutable by any conceivable event is non-scientific.
Irrefutability is not a virtue of a theory as people often think but a vice. Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability; but there are degrees of testability: Confirming evidence should not count except when it is the result of a genuine test of the theory; and this means that it can be presented as a serious but unsuccessful attempt to falsify the theory.
I now speak in such cases of "corroborating evidence". Some genuinely testable theories, when found to be false, might still be upheld by their admirers—for example by introducing post hoc after the fact some auxiliary hypothesis or assumption, or by reinterpreting the theory post hoc in such a way that it escapes refutation.
Such a procedure is always possible, but it rescues the theory from refutation only at the price of destroying, or at least lowering, its scientific status, by tampering with evidence. The temptation to tamper can be minimized by first taking the time to write down the testing protocol before embarking on the scientific work. Popper summarized these statements by saying that the central criterion of the scientific status of a theory is its "falsifiability, or refutability, or testability".
It must accurately describe a large class of observations on the basis of a model that contains only a few arbitrary elements, and it must make definite predictions about the results of future observations. Rather, people suggested that another planet influenced Uranus' orbit—and this prediction was indeed eventually confirmed. Kitcher agrees with Popper that "There is surely something right in the idea that a science can succeed only if it can fail.
He insists we view scientific theories as an "elaborate collection of statements", some of which are not falsifiable, while others—those he calls "auxiliary hypotheses", are.