The principles and theories of science have been established through repeated experimentation and observation and have been refereed through peer review before general acceptance by the scientific community. Acceptance does not imply rigidity or constraint, or denote . Instead, as new data become available, previous scientific explanations are revised and improved, or rejected and replaced. Science is a way of making sense of the world, with internally-consistent methods and principles that are well described. There is a progression from a hypothesis to a theory using testable, scientific laws. Only a few scientific facts are natural laws and many hypotheses are tested to generate a theory. Find out how scientific hypotheses, theories and laws describe the natural world.
A hypothesis is an idea or proposition that can be tested by observations or experiments, about the natural world. In order to be considered scientific, hypotheses are subject to scientific evaluation and must be falsifiable, which means that they are worded in such a way that they can be proven to be incorrect.
Example: When Gregor Mendel in 1865 studied the pattern of single trait inheritance of garden peas he formed a hypothesis on the manner of how these traits were inherited. The hypothesis he formed based on his observations included the following:
- In the organism there is a pair of factors that controls the appearance of a given characteristic.
- The organism inherits these factors from its parents, one from each.
- Each is transmitted from generation to generation as a discrete, unchanging unit.
- When the gametes are formed, the factors separate and are distributed as units to each gamete. (This statement is also known as Mendel's rule of segregation.)
- If an organism has two unlike factors for a characteristic, one may be expressed to the total exclusion of the other.
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.
Example: Between 1856 and 1863 Mendel cultivated and tested some 28, 000 pea plants which brought forth two theories of how character traits are inherited. Ironically, when Mendel's paper was published on 1866, it had little impact. It wasn't until the early 20th century that the enormity of his ideas was realized.
A scientific law is a description of a natural phenomenon or principle that invariably holds true under specific conditions and will occur under certain circumstances.
Example: In the early 20th century, after repeated tests and rejection of all competing theories Mendel's Laws of Heredity were accepted by the general scientific community.
- The law of segregation, which states that the alleles governing a trait are separated during the creation of gametes (meiosis).
- The law of independent assortment, which states that the genes controlling different traits are distributed separately from each other during meiosis.
Example 2: In the late 17th Century, Nicholas Steno established some natural laws relating to geology.
- The law of original horizontality - this states that when sediments are deposited in water, they will sink through it and deposit as horizontal layers as the result of gravity (unless acted on by other forces).
- The law of stratigraphic succession - this states that in a given sequence of sediments, the oldest will be at the bottom and the youngest at the top. It does not provide ages for those sediments, simply the sequence of their deposition.
Why are theories and laws not absolute.
Because they may not apply in all situations.
The first law of thermodynamics is true everywhere.
The second law of thermodynamics isn't true inside the event horizon of a black hole
The third law of thermodynamics isn't a law but merely a point of reference to make measurements from.
Newtonian laws of motion are not absolutely true but are only approximately true but valid for things that travel at less than 1/2 the speed of light.