A scientific law is a statement or mathematical equation that describes or predicts a natural phenomenon. It does not explain why or how a phenomenon occurs. Another name for a scientific law is a law of nature or law of science. All scientific laws are based on empirical evidence and the scientific method. In science, an assertion can be disproven, but never proven, so it’s possible for a scientific law to be revised or disproven by future experiments. In contrast, a mathematical theorem or identity is proven to be true.
Key Takeaways: Scientific Law
- A scientific law describes a consistent and universal natural phenomenon but does not explain why it happens.
- Scientific laws are often expressed as mathematical equations.
- Laws differ from theories and hypotheses, though all are part of the scientific method.
- Scientific laws are based on empirical evidence and are falsifiable.
- A theory does not become a law, and a law does not become a theory. They serve different purposes.
What Is a Scientific Law?
A scientific law, sometimes called a law of nature or law of science, is a statement that summarizes a pattern observed in the natural world. These patterns occur repeatedly across time and space, regardless of location, and can be expressed qualitatively or quantitatively.
Scientific laws:
- Derive from repeated observations and experiments.
- Often use equations to describe physical relationships.
- Do not provide underlying mechanisms (that’s the role of theories).
For example, Newton’s law of universal gravitation quantifies the gravitational force between two masses but does not explain the nature of gravity itself.
Examples of Scientific Laws
There are laws in all scientific disciplines, although primarily they are physical laws. Here are some examples:
- Beer’s law– Relates absorbance of light to concentration of a solution.
- Dalton’s law of partial pressures– States that the total pressure of a gas mixture equals the sum of the partial pressures of individual gases.
- Ideal gas law– Describes the relationship among pressure, volume, temperature, and number of moles of a gas (PV = nRT).
- Kepler’s laws of planetary motion– Describe how planets orbit the Sun.
- Law of conservation of mass– States that mass is neither created nor destroyed in a chemical reaction.
- Law of conservation of energy– States that energy cannot be created or destroyed, only transformed.
- Law of conservation of momentum– Momentum of a closed system remains constant.
- Law of reflection– Angle of incidence equals angle of reflection.
- Laws of thermodynamics– Fundamental principles governing heat, energy, and work.
- Newton’s law of universal gravitation– Describe how forces affect the motion of objects.
- Newton’s laws of motion– Describes gravitational attraction between masses.
Difference Between a Scientific Law and Scientific Theory
Both scientific laws and scientific theories are based in the scientific method and are falsifiable. However, the two terms have very different meanings. A law describes what happens, but does not explain it. A theory explains how or why something works.
For example, Newton’s law of universal gravitation describes what happens when two masses are a given distance apart. The law can be written as a mathematical equation [F = G(m1m2/r2)] and used to make predictions and calculations. However, the law does not explain how gravity works or why two masses are attracted to one another. Scientists didn’t really have an explanation for gravity until Einstein’s theory of general relativity, which continues to be revised as we understand more about the nature of spacetime.
As another example, Hubble’s law of Cosmic Expansion (velocity = Hubble constant x distance) describes the movement of galaxies away from each other. It does explain why this occurs. The Big Bang Theory is one of the theories that explains why galaxies move apart, but the theory does not offer a formula for calculating this motion.
| Feature | Scientific Law | Scientific Theory |
|---|---|---|
| What it does | Describes what happens | Explains why or how it happens |
| Based on | Observations and experiments | Observations, experiments, and synthesis |
| Format | Often a mathematical equation | Conceptual framework with evidence |
| Example | Newton’s law of gravity | Einstein’s theory of general relativity |
| Status | Falsifiable, subject to revision | Falsifiable, may be modified over time |
Can a Hypothesis or Theory Become a Law?
A hypothesis, theory, and law are all parts of scientific inquiry, but one never becomes another. They are different things. A hypothesis never becomes a theory, no matter how many experiments support it, because a hypothesis is simply a prediction about how one variable responds when another is changed. A theory takes into account the results of many experiments, testing different hypotheses. A theory explains how something works. Like a theory, a law draws on the results of repeated observations and experiments. But, a law states in words or mathematical equations what happens. Laws don’t explain why.
Why Scientific Laws Can Change
While scientific laws appear absolute, they depend on current knowledge and are always subject to falsification or refinement. Sometimes:
- A law is limited in scope and replaced with a broader or more general version.
- New evidence modifies or redefines a law.
- Advances in theory prompt re-examination of what was thought to be immutable.
For example, Newton’s laws are still useful for most engineering calculations, but they are incomplete at relativistic speeds or quantum scales.
FAQs About Scientific Laws
Q: Can a theory become a law?
A: No. Theories and laws serve different roles in science. Theories explain phenomena, while laws describe consistent patterns.
Q: Are scientific laws always true?
A: They are true within the limits of current experimental evidence but can be revised or disproven with new data.
Q: Are scientific laws proven?
A: In science, nothing is ever truly “proven.” Laws are strongly supported by evidence, but always remain open to falsification.
Q: What’s the difference between a law and a formula?
A: A formula is a mathematical expression. A scientific law may include a formula, but also includes the conceptual summary of natural behavior.
Q: Do all scientific laws have equations?
A: Many do (especially in physics and chemistry), but some laws are qualitative and stated verbally.
References
- Barrow, John (1991). Theories of Everything: The Quest for Ultimate Explanations. ISBN 0-449-90738-4.
- Feynman, Richard (1994). The Character of Physical Law (Modern Library ed.). New York: Modern Library. ISBN 978-0-679-60127-2.
- Gould, Stephen Jay (1981). “Evolution as Fact and Theory“. Discover. 2 (5): 34–37.
- McComas, William F. (2013). The Language of Science Education: An Expanded Glossary of Key Terms and Concepts in Science Teaching and Learning. Springer Science & Business Media. ISBN 978-94-6209-497-0.