Source: Physics.about.com

Author: Andrew Zimmerman Jones

Emphasis Mine

(N.B.: “Scientists don’t believe, we test hypotheses.” John Gribben)

Science is, at its core, a method of looking at questions about the physical world and reaching conclusions that are as consistent as possible with the physical reality. We reach this end through experimentation and observation, and by being willing to let go of an idea if it doesn’t match with reality.

The scientific method is a set of techniques used by the scientific community to investigate natural phenomena by providing an objective framework in which to make scientific inquiry and analyze the data to reach a conclusion about that inquiry.
Steps of the Scientific Method
The goals of the scientific method are uniform, but the method itself is not necessarily formalized among all branches of science. It is most generally expressed as a series of discrete steps, although the exact number and nature of the steps varies depending upon the source. The scientific method is not a recipe, but rather an ongoing cycle that is meant to be applied with intelligence, imagination, and creativity. Frequently, some of these steps will take place simultaneously, in a different order, or be repeated as the experiment is refined, but this is the most general and intuitive sequence. As expressed by Shawn Lawrence Otto in Fool Me Twice: Fighting the Assault on Science in America:

There is no one “scientific method”; rather, there is a collection of strategies that have proven effective in answering our questions about how things in nature really work.

Depending on the source, the exact steps will be described somewhat differently, but the following are a good general guideline for how the scientific method is often applied.

Ask a question – determine a natural phenomenon (or group of phenomena) that you are curious about and would like to explain or learn more about, then ask a specific question to focus your inquiry.
Research the topic – this step involves learning as much about the phenomenon as you can, including by studying the previous studies of others in the area.

Formulate a hypothesis – using the knowledge you have gained, formulate a hypothesis about a cause or effect of the phenomenon, or the relationship of the phenomenon to some other phenomenon.
Test the hypothesis – plan and carry out a procedure for testing the hypothesis (an experiment) by gathering data.
Analyze the data – use proper mathematical analysis to see if the results of the experiment support or refute the hypothesis.

If the data does not support the hypothesis, it must be rejected or modified (N.B.: that is Reject the hypothesis, NOT the data) and re-tested. Frequently, the results of the experiment are compiled in the form of a lab report (for typical classroom work) or a paper (in the case of publishable academic research).

It is also common for the results of the experiment to provide an opportunity for more questions about the same phenomenon or related phenomena, which begins the process of inquiry over again with a new question.
Key Elements of the Scientific Method
The goal of the scientific method is to get results that accurately represent the physical processes taking place in the phenomenon. To that end, it emphasizes a number of traits to insure that the results it gets are valid to the natural world.

objective – the scientific method intends to remove personal and cultural biases by focusing on objective testing procedures.
consistent – the laws of reasoning should be used to make hypotheses that are consistent with broader, currently known scientific laws; even in rare cases where the hypothesis is that one of the broader laws is incorrect or incomplete, the hypothesis should be composed to challenge only one such law at a time.
observable – the hypothesis presented should allow for experiments with observable and measurable results.
pertinent – all steps of the process should be focused on describing and explaining observed phenomena.
parsimonious – only a limited number of assumptions and hypothetical entities should be proposed in a given theory, as stated in Occam’s Razor.
falsifiable – the hypothesis should be something which can be proven incorrect by observable data within the experiment, or else the experiment is not useful in supporting the hypothesis. (This aspect was most prominently illuminated by the philosopher of science Karl Popper.)
reproducible – the test should be able to be reproduced by other observers with trials that extend indefinitely into the future. It is useful to keep these traits in mind when developing a hypothesis and testing procedure.
Conclusion
Hopefully this introduction to the scientific method has provided you with an idea of the significant effort that scientists go to in order to make sure their work is free from bias, inconsistencies, and unnecessary complications, as well as the paramount feat of creating a theoretical structure that accurately describes the natural world. When doing your own work in physics, it is useful to reflect regularly on the ways in which that work exemplifies the principles of the scientific method.

In common usage, the words hypothesis, model, theory, and law have different interpretations and are at times used without precision, but in science they have very exact meanings.

Hypothesis

Perhaps the most difficult and intriguing step is the development of a specific, testable hypothesis. A useful hypothesis enables predictions by applying deductive reasoning, often in the form of mathematical analysis.

It is a limited statement regarding the cause and effect in a specific situation, which can be tested by experimentation and observation or by statistical analysis of the probabilities from the data obtained. The outcome of the test hypothesis should be currently unknown, so that the results can provide useful data regarding the validity of the hypothesis.

Sometimes a hypothesis is developed that must wait for new knowledge or technology to be testable. The concept of atoms was proposed by the ancient Greeks, who had no means of testing it. Centuries later, when more knowledge became available, the hypothesis gained support and was eventually proven, though it has had to be amended many times over the year. Atoms are not indivisible, as the Greeks supposed.

Model

A model is used for situations when it is known that the hypothesis has a limitation on its validity. The Bohr model of the atom, for example, depicts electrons circling the atomic nucleus in a fashion similar to planets in the solar system. This model is useful in determining the energies of the quantum states of the electron in the simple hydrogen atom, but it is by no means represents the true nature of the atom.

Theory & Law

A scientific theory or law represents a hypothesis (or group of related hypotheses) which has been confirmed through repeated testing, almost always conducted over a span of many years. Generally, a law uses a handful of fundamental concepts and equations to define the rules governing a set of phenomena.

Scientific Paradigms

Once a scientific theory is established, it is very hard to get the scientific community to discard it. In physics, the concept of ether as a medium for light wave transmission ran into serious opposition in the late 1800s, but it was not disregarded until the early 1900s, when Einstein proposed alternate explanations for the wave nature of light that did not rely upon a medium for transmission.

The science philosopher Thomas Kuhn developed the term scientific paradigm to explain the working set of theories under which science operates. He did extensive work on the scientific revolutions that take place when one paradigm is overturned in favor of a new set of theories. His work suggests that the very nature of science changes when these paradigms are significantly different. The nature of physics prior to relativity and quantum mechanics is fundamentally different from that after their discovery, just as biology prior to Darwin’s Theory of Evolution is fundamentally different from the biology that followed it. The very nature of the inquiry changes.

One consequence of the scientific method is to try to maintain consistency in the inquiry when these revolutions occur and to avoid attempts to overthrow existing paradigms on ideological grounds.

Occam’s Razor

One principle of note in regards to the scientific method is Occam’s Razor (alternately spelled Ockham’s Razor), which is named after the 14th century English logician and Franciscan friar William of Ockham. Occam did not create the concept – the work of Thomas Aquinas and even Aristotle referred to some form of it. The name was first attributed to him (to our knowledge) in the 1800s, indicating that he must have espoused the philosophy enough that his name became associated with it.

The Razor is often stated in Latin as:

entia non sunt multiplicanda praeter necessitatemor, translated to English:

entities should not be multiplied beyond necessity

Occam’s Razor indicates that the most simple explanation that fits the available data is the one which is preferable. Assuming that two hypotheses are presented have equal predictive power, the one which makes the fewest assumptions and hypothetical entities takes precedence. This appeal to simplicity has been adopted by most of science, and is invoked in this popular quote by Albert Einstein:

Everything should be made as simple as possible, but not simpler.

It is significant to note that Occam’s Razor does not prove that the simpler hypothesis is, indeed, the true explanation of how nature behaves. Scientific principles should be as simple as possible, but that’s no proof that nature itself is simple.

However, it is generally the case that when a more complex system is at work there is some element of the evidence which doesn’t fit the simpler hypothesis, so Occam’s Razor is rarely wrong as it deals only with hypotheses of purely equal predictive power. The predictive power is more important than the simplicity.