When Does a Theory Become a Law?

When Does a Theory Become a Law?

This is something that comes up quite frequently in discussions between scientists and the general public. How much proof does it take for a theory to graduate to being a law?




Because the words theory and law have such different meanings in the language of science, it is often a difficult question to answer, so instead, I'll start by giving you a few similar questions to answer.

  1. How perfectly do you have to build a house so that it will become a single brick?
  2. How well do you have to write to change an entire dictionary into a single word?
  3. What would you have to do to change an entire symphony into a single note?

If you are thinking that those questions don't make much sense, then you are feeling very much like a scientist who has been asked "How much proof does it take for a theory to graduate to being a law?" A house is made up of many bricks, boards, nails, windows, doors, concrete, etc. A dictionary is made up of thousands of different words, and a symphony can easily have thousands of notes that all fit together in just the right way to produce pleasing music. In the same way, theories are based on a variety of scientific laws, facts, testing, and other evidence, all fit together in a way that offers an explanation of how some part of the universe works.


Ohm's Law

In science, laws are simple facts and formulas that are so basic that they apply universally. For example, Ohm's Law has the formula I=V/R, which tells us that in an electrical circuit, the amperage is equal to the voltage divided by the resistance. That is it. All of it. It is an important law if you are working with electricity because it applies to any electrical circuit, but it tells us nothing about what amperage is, why it equals voltage divided by resistance, or what we can do with the information. It is simply one of the "notes" in the symphony of Electromagnetic Theory, which explains why light bulbs light, why electric heaters heat, and why computers compute.

So just as houses don't become bricks, theories don't become laws. Both are important, but they tell us very different things.

Laws tell us what happens.
Theories examine what happens and tell us how and why it happens.

But what if a theory turns out to be wrong? What if it has a flaw? Well, lets go back to the earlier questions. What if you build a house, and then realize that there is a room with no door, no way to get in or out. Clearly, something is wrong. Do you walk away, and start all over from scratch? Or do you look to see if there is a way to install a door to make the room useable? Or maybe you decide that the room is not necessary, and remove that part of the building. The same is true for scientific theories. Finding one flaw in the theory of gravity would probably not send everyone back to construct an entirely new theory. Instead, scientists would examine the new evidence, and see if there was a way to adjust the theory so that the new evidence fit. That happens quite frequently. As we learn more and more about the universe, we expand and refine our theories about how the universe works.

Occasionally discoveries are made that are so profound that they do require that we discard the old theory, and start from scratch to develop a new one that fits the new evidence as well as the old. Then the testing begins, with everyone looking for evidence that the new theory is wrong. Wrong? Isn't it mean to try and prove that it is wrong? No. It is the way of science. In the words of a famous scientist:

"No amount of experimentation can ever prove me right;
a single experiment can prove me wrong."

Albert Einstein

Even after all those years, scientists are still performing tests to see if there are flaws in Einstein's Theories of General and Special Relativity. Neither has been shown to be wrong, so they are still accepted and highly respected scientific theories.

The same is true for new explanations of how and why things work. After a great deal of testing, and with enough solid evidence, often with much modification as more evidence is gathered, a new explanation may eventually be accepted for the exalted title of Theory.

Home - Process of Science - What is Science?
Hypotheses, Laws, and Theories - What Do Scientists Do?

Anonymous wrote on Wed, 04/17/2013 - 20:41:

Your explanation is very clear and simple but only after making the untrue statement that laws are simple and basic facts. That is like saying that the earth revolving around the sun is a simple and basic fact. Something that seems simple and true today until one considers that this concept was rejected for the better part of mankind's existance and people risked their lives to even express it as possible.
When Ohm began experimenting with electricity, E=IR was not a simple and basicly known fact. Through observation he arrived at the hypotheis that there was a relationship between voltage, amperage, and resistance. Through additional experimentation he devised experiments to prove the relationship as E=IR. This hypotheis and his clearly defined experimental parameters were reproduced by others thereby transitioning from a hypotheis into a theory. At some undefined point, this theory was generally accepted as a Law. The term hypothesis and theory are clearly defined terms. Laws are theorys that prove valid under continous experimentation, the amount and detail of which are not defined. It would be interesting to point out the exact date and time when any theory was documentated as being declared a Law. The reason this question continues to come up is because there is no clear answer. Simple theories generally become more widely accepted as Laws more quickly than complex ones.
But in all cases Hypothesis > Theory > Law.

rkrampf wrote on Wed, 04/17/2013 - 22:10:

The problem you are running into is with the scientific definition of the terms. That causes confusion in many areas of science where the scientific term means something different from the way it is used in everyday language. In the language of science, laws and theories are very different things. A theory is causal, it explains why something happens, but it is never "proved". As Einstein said about his theory of special relativity, "No amount of experimentation can ever prove me right; a single experiment can prove me wrong."

On the other hand, laws are facts. E=IR tells you what happens, but does not tell you why. There was a time when E=IR was unconfirmed, but that does not make it a scientific theory. There is nothing in the equation that tells WHY there is a relationship between voltage, amperage, and resistance. That, along with Faraday's Law, Lenz's Law, and many other facts are explained by the Electromagnetic Theory.

Anonymous wrote on Tue, 11/08/2011 - 09:27:

I actually stumbled across this blog looking for when legal 'theory' becomes law but it was a very interesting read and actually very relevant... the question of when a a presumption (or conclusions - logical or otherwise) becomes gospel. We see it at lot in precedents and how they are used to establish legislation going forward; someone makes a decision that pushing it over the edge and from then on it exists with its own authority.

Making a difference in the established legislation will always be difficult without young blood entering the industry to challenge attitudes no longer deemed relevant to society. It's vital that universities and other colleges provide opportunities for legal practice courses to allow new barristers, solicitors and other legal professionals a chance to make a difference.

Anonymous wrote on Thu, 11/03/2011 - 22:33:

Thanks for setting me straight in simply written post. I always suffered from the misconception you addressed here. And the analogies you used at the start are so good, I think I might borrow them to explain it to others!

Anonymous wrote on Thu, 09/22/2011 - 11:47:

I love this post. My daughter is taking Physics in high school and this kind of question comes up often at our dinner table.