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:
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.
These days, physicists rarely apply the word "law" to their ideas. In part, this is because so many of the previous "laws of nature" were found to be not so much laws as guidelines, that work well within certain parameters but not within others.
The word "law" is often invoked in reference to a specific mathematical equation that relates the different elements within a theory. Pascal's Law refers an equation that describes differences in pressure based on height. In the overall theory of universal gravitation developed by , the key equation that describes the gravitational attraction between two objects is called the .
Laws are typically part of a specific theory, though this may not always be obvious. For example, the conservation of matter is part of the Newtonian world view that things can't just appear from nowhere. In quantum physics they can, so this law has to be modified.
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.
For example in the 1820s astronomers noticed that the planet Uranus didn't move in the way it should have done if they used Newton's theories to do the calculations. Several astronomers independently came up with the hypothesis that there was another planet outside Uranus. The hypothesis was mathematical and predicted where in the sky to look for this planet.
The major difference between a scientific law and a scientific theory is that theories are huge, complex structures with raggedy edges that would take a book to describe. A law can be written in a single sentence.
When you make a prediction about an experiment at school you should really say that 'My hypothesis is that...' rather than 'My theory is that...'
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 theory is an explanation for a set of related phenomena, like the theory of evolution or the .
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.
Sometimes a hypothesis is developed that must wait for new knowledge or technology to be testable. The concept of atoms was proposed by the , who had no means of testing it. Centuries later, when more knowledge became available, the hypothesis gained support and was eventually accepted by the scientific community, though it has had to be amended many times over the year. Atoms are not indivisible, as the Greeks supposed.
A hypothesis is normally based on fairly well accepted grounds (e.g. Uranus isn't following the orbit predicted by Newton's theories) and can be fairly easily tested (let's see if this new planet is where we say it is).
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.