Is gravity a theory or a law?

Jan 10, 2019 14 comments
Is gravity a theory or a law?

Why is it called Newton's law of universal gravitation and not Newton's theory? Is Einstein's theory of general relativity inferior to Newton's law of gravitation since in our day-to-day usage law is a "more intense" word than theory?

If these questions have haunted you before, it is time to understand scientific terminology. Because before studying science, you must know the meanings of axiom, hypothesis, experiment, model, law and theory.

It so happens that all of these scientific terms are incorporated in a method of science. So, let us first understand the scientific method with an example and then we will see whether gravity is a theory or a law. Ready?

It is observed that bees are attracted to flowers. This statement is taken to be true to serve as a premise or starting point for further reasoning and arguments. This is called an axiom.


Then, a natural question arises. Why are bees attracted to flowers? This is our first step of the scientific method. An observation is followed up by a question. Remember, on a summer day, Isaac Newton had questioned the fall of an apple.

One may guess that bees are attracted by the color of flowers. Another person may say that bees are attracted by the nectar in the flowers, the more reasonable guess. A third individual may offer another point of view that bees are attracted by both.

All guesses are hypotheses.

A scientific hypothesis can be tested in laboratory with the help of an experimentFirst, bees are let inside a glass chamber containing artificial flowers. Second, bees are let inside another glass chamber containing real flowers. Further observations are noted down.

example of scientific method

It is observed that bees are attracted to artificial flowers, sit on them briefly, then fly away. The first hypothesis turns out to be true because bees are indeed attracted by the color. In the second set-up, bees sit on real flowers and remain there for long. Thus, the second hypothesis is also true.

After our hypotheses have been tested, it is time to formulate laws. theories or conclusions on the basis of result of the experiment. In our simple example, "bees are attracted to flowers due to both color and nectar."

A law is a formula which describes the physical situation. Thus, Newton's law of universal gravitation is used only to calculate the "magnitude" of the gravitational force between two objects of mass separated by a given distance.

Is gravity a theory or a law?
Newton's law

Newton's law of universal gravitation can also used in a model so as to represent any local physical phenomena, such as falling of an apple or sky-diving. Thus, a model is generally a simulation. But Newton's law does not attempt to explain how or why gravity works.

In science, a theory is a well-substantiated explanation of the natural world that can incorporate all facts, laws, inferences, and tested hypotheses. So, Einstein's theory of general relativity explains correctly "why" things fall.

While laws rarely change, theories get modified frequently as new evidence is discovered. Einstein published his version of the theory of general relativity in 1915 and since then the theory has adapted as new technologies and new evidence have expanded our view of the universe.

Is gravity a theory or a law?
Is gravity a theory or a law?

So, when we are discussing about gravity, are we referring to it as a theory or a law? Well, we can talk about it as both. The law calculates the amount of attraction while the theory describes why the objects attract each other in the first place.

You have now an understanding of terms such as axiom, hypothesis, experiment, law, model and theory, in this particular order, through our use of the scientific method. Whenever you encounter a phrase such as "just a theory" you will know how to respond.

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