In scientific research, we often come across the terms fact, law, hypothesis, and theory that may be confusing for a new researcher. This blog provides a brief description that may help develop an appropriate research framework with appropriately used terms. Firstly, a distinction between fact, law, hypothesis, and theory is made through defining each term. It is followed by a description linking the terms into a simple framework.
In most simplistic way, these terms can be viewed as follows. A fact is an observation e.g., "Apple fell down". A law is a fact that is accepted universally e.g., "Gravitation pulls objects together". A theory is an accepted explanation of facts and laws e.g., "Gravitation comes from the masses of the objects". A hypothesis is a tentative explanation of facts and laws that is to be tested, e.g., "Gravitation comes from the energies of the objects". In the following text, these views are further elaborated.
Fact: A fact is an observation that is accepted to be true and is undisputed. For example, it is a fact that sun rose this morning and right now it has a certain ascension in the sky. It is also a fact that the sun rose yesterday from the east, ascended in the sky, then descended towards the west resulting in sunset. Facts can be thought of as observations in an experiment. The observation of an apple falling from a tree that was made by Isaac Newton is a fact. Obviously, many before must have observed zillions of other objects falling down through out the history. And all of these observations are facts. Facts are produced from some underlaying phenomenon, which may or may not be known. We don't know how many may have wondered and couldn't come up with any explanation. Someone may have compared a falling feather or leaf with falling apple and come up with an explanation that weight of an object causes it to fall down. This explanation was an acceptable explanation for a long period and also lead further elaboration that heavier objects fall faster than lighter objects. This Aristotelian view was challenged by Galileo by dropping two different weights from the tower of Pisa. Galileo found new observations (facts) that challenged the existing belief and proposed new explanation of phenomenon. Hence, facts are observations that are used to explain an underlaying phenomenon and may lead to confirming or disproving an existing explanation.
Law: A law states a fact or phenomenon that is accepted to be universally true. Scientific laws are also often called physical laws of nature that have been discovered from hundreds of years of constantly repeated observations. It is not necessary to have an underlaying explanation of the law. The only necessary condition for a law is that it should hold. For example, wether it be Galilean, Aristotelian, or pre-Aristotelian era, the law of gravitation has prevailed. Someone letting go of an object mid air can confidently predict the outcome that the law of gravitation will hold itself making the object fall down. Wether the explanation of the phenomenon is correct or even exists is not necessary. Actually, the explanation of gravitation has changed over time and still remains a mystery and an area of active research. Some other examples of historical physical laws include Archimedes principle, Kepler's laws, law of reflection, and law of refraction (Snell's law). In classical physics, we come across with Newton's laws of motion, principle of least action, Ohm's law, Faraday's law, Gas law, and laws of thermodynamics. The modern physics has introduced, Planck's radiation law, Pauli exclusion principle, and Heisenberg uncertainty principle. Most scientific laws are expressed in the form of mathematical relationship. For example, Heisenberg uncertainty principle is an inequality that sets a lower bound for the product of uncertainty in position and uncertainty in momentum. Similarly, Newton's law of gravitation equates a force as a function of masses and distance between the masses. Thus, law is a statement or a mathematical description of a fact that is universally accepted based on constantly repeated observations.
Facts and laws often lead to questions or predictions with possible answers and explanations. These are hypotheses (questions or predictions) and theories (answers and explanations).
Theory: A theory is an explanation of the phenomenon describing the facts and laws. Having a theory doesn't imply correctness. Throughout the history of humans, many theories were proposed and accepted for centuries until new facts lead to the replacement of old with new theories. For example, geocentrism was an accepted model of the universe in which objects in the sky, including the sun, orbited around the earth. This theory flourished for centuries and was used to explain many facts such as sunrise, seasonal variability of sunrise, eclipses, etc. Later observations showed that this theory didn't explain everything, leading to a new heliocentric theory. This theory provided a better match with the historical observations and also better predicted the future motion of planets. All theories can also be used to predict what's going to happen next. The ability of a theory to explain historical facts and predict the future reinforces its validity. Any failure limits the validity and scope of a theory.
Hypothesis: A hypothesis is a statement that can be tested to be true or false by experimentation. Wether it be theory or facts, both lead to hypotheses which are questions or predictions. For example, the hypothesis "the sun always rises from the east" can be tested by looking towards the east in the morning. What is needed to accept or reject this hypothesis? In order to accept it, we have to observe every morning from the beginning to the end of earth. If all mornings confirm this hypothesis, we accept the hypothesis and it becomes a law of nature. Realistically, we cannot do such an experiment. Instead, we do what we can: observe the next morning. If that next morning agrees with the hypothesis, instead of accepting the hypothesis, we fail to reject the hypothesis. Failure to reject a hypothesis doesn't imply acceptance. It only means that the underlaying geocentric or heliocentric theory are still explaining the facts. All we need is one fine morning of a non-east sunrise to reject our hypothesis and thus challenge the underlaying theory. For example, if due to some strange celestial phenomenon, the earth spin wobbles and results in a new sunrise location, the old theories will need revision to explain it. <strong>In other words, it is not possible to "prove" a hypothesis, though such is a commonly used phrase. Instead, we disprove or fail to disprove.</strong>
With all four terms defined, how do we use them? Generally, we take laws and facts and try to explain the underlaying phenomenon. In some cases, we may also have a theory available in a different setting or discipline that can be tested to explain our facts. In other cases, we may have to come up with our own theory. In either case, we develop hypotheses and perform validation tests. The outcomes of the tests either reinforce the theory (fail to disprove) or disprove the theory. In either case, we learn from it and repeat the process.
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