Please, tell! :)
I know I have posted this before, but thought here would be a good place again since there seems to be lots of new folks on the thread and some slight misunderstandings:
Let me post my own example of gravity:
A little history here:
Newtons Law of Universal Gravitation
Every object in the universe attracts every other object with a force directed along the line of centers for the two objects that is proportional to the product of their masses and inversely proportional to the square of the separation between the two objects.
F equals the gravitational force between two objects
m1 equals the mass of the first object
m2 equals the mass of the second object
R equals the distance between the objects
G equals the universal constant of gravitation = (6.6726 )* 10-11 N*m2/kg2 (which is still being refined and tested today)
(BTW this is a simple form of the equation and is only applied to point sources. Usually it is expressed as a vector equation)
Even though it works well for most practical purposes, this formulation has problems.
A few of the problems are:
It shows the change is gravitational force is transmitted instantaneously (Violates C), assumes an absolute space and time (this contradicts Special Relativity), etc.
Enter Einsteins General Theory of Relativity
In 1915 Einstein developed a new theory of gravity called General Relativity.
A number of experiments showed this theory explained some of the problems with the classical Newtonian model. However, this theory like all others is still being explored and tested.
From an NSF abstract:
As with all scientific knowledge, a theory can be refined or even replaced by an alternative theory in light of new and compelling evidence. The geocentric theory that the sun revolves around the earth was replaced by the heliocentric theory of the earth's rotation on its axis and revolution around the sun. However, ideas are not referred to as "theories" in science unless they are supported by bodies of evidence that make their subsequent abandonment very unlikely. When a theory is supported by as much evidence as evolution, it is held with a very high degree of confidence.
In science, the word "hypothesis" conveys the tentativeness inherent in the common use of the word "theory.' A hypothesis is a testable statement about the natural world. Through experiment and observation, hypotheses can be supported or rejected. At the earliest level of understanding, hypotheses can be used to construct more complex inferences and explanations. Like "theory," the word "fact" has a different meaning in science than it does in common usage. A scientific fact is an observation that has been confirmed over and over. However, observations are gathered by our senses, which can never be trusted entirely. Observations also can change with better technologies or with better ways of looking at data. For example, it was held as a scientific fact for many years that human cells have 24 pairs of chromosomes, until improved techniques of microscopy revealed that they actually have 23. Ironically, facts in science often are more susceptible to change than theories, which is one reason why the word "fact" is not much used in science.
Finally, "laws" in science are typically descriptions of how the physical world behaves under certain circumstances. For example, the laws of motion describe how objects move when subjected to certain forces. These laws can be very useful in supporting hypotheses and theories, but like all elements of science they can be altered with new information and observations.
Those who oppose the teaching of evolution often say that evolution should be taught as a "theory, not as a fact." This statement confuses the common use of these words with the scientific use. In science, theories do not turn into facts through the accumulation of evidence. Rather, theories are the end points of science. They are understandings that develop from extensive observation, experimentation, and creative reflection. They incorporate a large body of scientific facts, laws, tested hypotheses, and logical inferences. In this sense, evolution is one of the strongest and most useful scientific theories we have.
Here is another nice page of what a theory is:
"In common usage a theory is often viewed as little more than a guess or a hypothesis. But in science and generally in academic usage, a theory is much more than that. A theory is an established paradigm that explains all or many of the data we have and offers valid predictions that can be tested. In science, a theory can never be proven true, because we can never assume we know all there is to know. Instead, theories remain standing until they are disproven, at which point they are thrown out altogether or modified slightly.
Theories start out with empirical observations such as sometimes water turns into ice. At some point, there is a need or curiosity to find out why this is, which leads to a theoretical/scientific phase. In scientific theories, this then leads to research, in combination with auxiliary and other hypotheses (see scientific method), which may then eventually lead to a theory. Some scientific theories (such as the theory of gravity) are so widely accepted that they are often seen as laws. This, however, rests on a mistaken assumption of what theories and laws are. Theories and laws are not rungs in a ladder of truth, but different sets of data. A law is a general statement based on observations."
"A well-known example is that of Newton's law of gravity: while it describes the world accurately for most pertinent observations, such as of the movements of astronomical objects in the solar system, it was found to be inaccurate when applied to extremely large masses or velocities. Einstein's theory of general relativity, however, accurately handles gravitational interactions at those extreme conditions, in addition to the range covered by Newton's law. Newton's formula for gravity is still used in most circumstances, as an easier-to-calculate approximation of gravitational law. A similar relationship exists between Maxwell's equations and the theory of quantum electrodynamics; there are several such cases. This suggests the (unanswered) question of whether there are any ultimately true physical laws, or whether they are all just cases where our sensory and rational apparatus have generated mathematically simple approximations, valid within the range of normal human experience, to unobtainable true formulas."