Tuesday, March 25, 2008

The Difference Between a Law and a Theory

The difference between a law and a theory in science really needs to be cleared up. Its causing, as my Thomas the Tank Engine-obsessed son would say, confusion and delay in my blog comments. Let's explore.

I found this very nice entry at the MadSci Network in which Dan Berger offers this:

The current consensus among philosophers of science seems to be this:

Laws are generalizations about what has happened, from which we can generalize about what we expect to happen. They pertain to observational data. The ability of the ancients to predict eclipses had nothing to do with whether they knew just how they happened; they had a law but not a theory.

Theories are explanations of observations (or of laws). The fact that we have a pretty good understanding of how stars explode doesn't necessarily mean we could predict the next supernova; we have a theory but not a law.

This is not, "a simplistic, hierarchical view of the relationship between theories and laws whereby theories become laws depending on the availibility of supporting evidence." (from the same site)

If you're an auditory learner and need a nice, simple explanation try this page, scroll to the bottom and click on, "To hear this program click here." From the transcript:

D: Well, the definition of a law is easy. It's a description--usually mathematical--of some aspect of the natural world.

Y: Like gravity.

D: Exactly. The law of gravity describes and quantifies the attraction between two objects. But the law of gravity doesn't explain what gravity is or why it might work in this way. That's because that kind of explanation falls into the realm of theory. And the theory that explains gravity is the theory of general relativity.

Y: Right. According to the National Academy of Sciences, a scientific theory is a "well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses." In other words, all scientific theories are supported by evidence, and you can test them, and--most importantly--you can use them to make predictions.

D: So based on that definition, theories never change into laws, no matter how much evidence out there supports them. Formulating theories, in fact, is the end goal of science.

Y: So to say evolution is just a theory is actually an argument for it and not against it. You can't do any better in science than to be a theory.


Here's a fun page from high school chemistry teacher, David Dice - Proof and Science. This page isn't simply valuable for the person who doesn't understand the difference between theory and law but also for those of us who tend to talk of evolution being 'true'.

No scientist will ever claim that a theory is true. What they will do is state that the evidence agrees with the theory.

Maybe those of us who accept the theory of evolution need to tidy up our terms too. The site is an excellent read, generally agrees with the definitions from the MadSci Network and has a quiz. Kudos Mr. Dice!

Let's hear from Ronald Matson, Professor of Biology at Kennesaw State University but instead of his definition of laws and theories (you can guess by now what at least one of his definitions will be), let's hear what he has to stay about what laws and theories most definitely are not:

Regardless of which definitions one uses to distinguish between a law and a theory, scientists would agree that a theory is NOT a "transitory law, a law in waiting". There is NO hierarchy being implied by scientists who use these words. That is, a law is neither "better than" nor "above" a theory.

I hope this clears the matter up somewhat. A theory is not a baby law. A law is not a theory that's been proven. Next time you're discussing the matter with someone defending the theory of evolution you will know that you simply can't, with any honesty, claim evolution is a theory because it's unproven. Next time you're discussing the matter with a creationist you will know that when you insist evolution is the truth, you're using inexcusably sloppy language.


Doc said...

From Doc:
Creation is not a valid scientific theory. Scientific theory is not an “unproven assumption”. A scientific theory is a logical, systematic set of principles or explanation that has been verified and has stood up against attempts to prove it false. A scientific theory must make testable predictions. Simply stated, scientific theory starts with a hypothesis and works through to a conclusion. Creation, begins with the conclusion - God as creator - and works backward to the hypothesis, and as a theory, can not be modified by fact or observation. This is not scientific method.

You know, it's like trying to nail jello to a tree. They're at it again, with the grasshopper story (which has nothing to do with evolutionary theory). No matter how you put it to a creationist, they come back with the same responses, over and over and over, like a dog returning to its vomit, and then they wonder why an educated person gets frustrated with them.

Anonymous said...

Great post Dawn. Sloppy use of these words irritates me to no end.

A law is a single statement about the world, usually with a few blanks we get to fill in so that we can apply to an arbitrary number of similar situations.

Laws are usually the result of direct experimental observation, but indirect observation works too: Newton didn't go out into space and measure the force of gravity to see it vary inversely with the square of the distance from the source. He just observed that the planets move as though this is the case.

His law of gravitation was still pretty good.

A theory is a very different sort of thing. A theory starts with a few laws or hypotheses and uses logic to generate an infinite set of statements about our world. Theories let us hold vast amounts of knowledge in our heads, and to understand all sorts of unexpected phenomena.

This is really cool, but it leads to a couple of problems:

[1] It's easy to come up with theories that explain everything. Karl Popper picked on Marxism and Psychology for this, but I bet you can think of a more modern example ;)
[2] Since a theory let's you deduce an infinite number of statements from a few simple laws, and since a good theory should forbid a lot of things from happening, it's almost certain to produce some statements that are false. Think about Newton's gravity again. It's not quite right, and as the masses get big and distances small, we start to see the errors.

This is a problem science just has to live with. We're always approximating the truth, but never quite there. Good theories will always have problems. When this happens we don't throw the theory away, we refine it.

So there's nothing wrong with theories -- they are wonderful things. A theory that has stood up to an onslaught of falsification attempts is even better.

When a problem is found with a good theory -- and this almost always happens -- it doesn't mean the theory is bad, it just means that it can be better. You can't nitpick evolution or any other theory out of existence, even if you find valid nits to pick.

If you want to get scientists to discard a theory, you have to come up with a better theory. And that better theory is going to have to explain why the old one worked so well.

I haven't seen a single step in this direction from the "scientific creationists".

Brian said...

First of all, "A hypothesis is an idea or proposition that can be tested by observations or experiments, about the natural world". http://sci.waikato.ac.nz/evolution/Theories.shtml

"To scientists, a theory is a coherent explanation for a large number of facts and observations about the natural world. Theories are more certain than hypotheses, but less certain than laws."(same ref.)

"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". (same).

And notice I'm using information from a page entitled "Evolution For Teaching".

I agree, this is somewhat of a tricky issue, but I think the main difference between theory and law in a practical sense is that a law has observable and measurable effects, even if we don't fully understand how it operates.

For example, you can see the effect of gravity by watching me hurtle over the edge of a cliff (hold the applause, please), and we can measure its effects by stepping on a scale and screaming.

Newton's Law of Gravity states that "Each object in the universe attracts each other body". and is expressed by the following:
"If object A has mass Ma and object B has mass Mb,
then the force F on object A is directed toward object B
and has magnitude F = G Ma Mb / r2"(r squared, with r the distance between the objects-my note) http://zebu.uoregon.edu/~soper/Orbits/newtongrav.html

"So, considering the force between the Sun and the Earth:

-The force exerted on the Earth by the Sun is equal and opposite to the force exerted on the Sun by the Earth.
-If the mass of the Earth were doubled, the force on the Earth would double.
-If the mass of the Sun were doubled, the force on the Earth would double.
-If the Earth were twice as far away from the Sun, the force on the Earth would be a factor four smaller". (same ref.)

So a law in this case can be expressed by an equation and its effects quantified, even if we can't fully explain how it operates.

The theory of relativity (there are actually 2, general and special), states: "For objects traveling near light speed, however, objects will move slower and shorten in length from the point of view of an observer on Earth" and Einstein also derived the equation E = mc2(Energy=Mass x Speed of Light squared) http://www.allaboutscience.org/theory-of-relativity.htm

Though we have an equation, it cannot be quantified in the same way since there is no way known to accelerate an object to those kinds of speeds. In fact, there is some question as to whether the speed of light is even a constant, but that's too far afield to discuss.

Here is another quote on this matter of theories: "Regardless, as with any other scientific theory, it is not the absolute, entire and final description of the universe. Because it is a scientific theory, it contains certain assumptions and approximations of nature and ultimately, fails to describe several phenomena altogether (i.e. electromagnetism). Unfortunately, Einstein's Theory of Relativity, much like Darwin's Theory of Evolution, has become popularized as a "scientific truth" because it offers a simplified explanation to the complexity observed in the natural universe." http://www.allaboutscience.org/theory-of-relativity.htm

So to summarize, there appears to be a range of definitions for Law and Theory, depending on the source, so it is somewhat of a gray area.

But again, it appears that the main difference is that laws, like the Laws of Motion, can be observed and tested, have never been shown to be false, but exactly how they operate may not be fully understood.

A theory is an explanation for a large number of facts and observations about the natural world. If a theory is not able to be proven incorrect, than it's not a good scientific theory.

For example, the existence of God is not a valid scientific theory, because it can't be disproven by ordinary means. It doesn't rule out that it may be true, it simply means it cannot be disproven.

Dawn said...

Brian - Your key quote leads to a site with no references or no clue as to who the author might be. It's worthless.

Rolfe - Thanks for that. I think sloppy language in science education and in how science is covered in the media probably adds to the problem as much as any creationist. They come to science with basic misunderstandings and then see those misunderstandings reinforced in classrooms and on TV screens.

Anonymous said...

Brian: I agree that the language is fuzzy. But if you want to attack something because someone else calls it a theory, you need to use their definition of theory, not your own.

A theory consists of:
(1) a set of assumptions about the world. These may be "laws", they may not. They may be backed up by experiment, they may not.
(2) Some rules of inference that let you deduce new statements about the world from ones you already know.
(3) All of the statements that we can deduce from our assumptions using our rules of inference.

So if you have some "laws" and add in logic and mathematics, presto, you get a theory.

A theory "explains" a law when you can deduce the law using the theory.

A good theory should produce a lot of "surprising" statements. Or at least statements that are easily tested and falsifiable. And it should pass those tests. I've never seen any falsifiable statements coming from scientific creationism.

A law is no more certain than a theory. Newton's law of gravitation is wrong. It's still a law, and it still tells us an awful lot about the truth of our universe.

Einstein's theory of relativity does not explain electromagnetism. It still explains an awful lot more than Newton's theory did.

Yes, theories are approximations of reality. So are laws. But we have some really good approximations. If you demand absolute correctness, you'll get nothing.

Elisheva Hannah Levin said...

Good post, Dawn. It clears up a lot of the language issues.

Before I continue my comment, I do want to give my credentials. I am an evolutionary biologist and neuroscientist. I have taught biology at several levels, including the university level. Just so you know I am not pulling what I say out of my a_ er,...hat.

To broaden this discussion a bit more, so-called scientific creationism is not a scientific theory for reasons stated by your astute readers, and it is also not science. For a field of study to be science requires that evidence be confined to what can be observed in the natural world using senses or extensions thereof, and it requires the use of the scientific method.

So for example, when Van Gogh painted his sunflowers, he was certainly observing the natural world with his sense, but he was not deriving evidence from it, nor was he using the scientific method. He was doing art--another human endeavor, but not science. (And I am sure he would have been insulted if we tried to make it into science).

Creationism is not science because it apriori posits that the mechanism for the origin of species is supernatural. It cannot be observed, but only taken on faith. That is why one came claim to 'believe' in creationism. (OTOH it is silly to say that one 'believes' in evolution. Such a faith statement only confuses the issue. Rather, one should state that there is evidence for the evolution by natural selection of species).

Creationism's pedigree is from theology and religion, still another realm of human endeavor.
And that would be all well and good, except that the advocates of creationism claim a false scientific pedigree for a theological search for truth. This makes it pseudo-science. Psuedo-science is a false claim for the scientific origins of an idea that has no such origins.

I have no problem with people who wish to claim a belief that a supernatural being created the world and all that is in it. I have no problem with people who chose to believe that the world was created according to the Priestly story in Genesis (B'reshit 1:1-2:1a). That is their perogative. And if they want to teach their kids this, that is fine.

But I do have a problem and an argument with people who want to then go on and claim a scientific pedigree for an idea that is clearly not science. Such a claim is false, and more so, it is dishonest.

Brian said...

When I follow the link through that you have given, and then follow the link referenced there,it ends up on a university website (curiously, mine went to a university website too, which you apparently didn't like, but let's follow this through).

I read there: "...theories and laws are different kinds of knowledge and one can not develop or be transformed into the other. Laws are statements or descriptions of the relationships among observable phenomena". http://www.chem.vt.edu/confchem/1998/lederman/lederman.html (I know, it's not formatted for easy reading-it's under "What is the NOS?", 3rd paragraph)

I agree. Laws tell us, for example, that there is a measurable, predictable gravitational effect between two bodies.

The ref. continues: "Boyle's law, which relates the pressure of a gas to its volume at a constant temperature, is a case in point".

"Theories, by contrast, are inferred explanations for observable phenomena. The kinetic molecular theory, which explains Boyle's law, is one example. Moreover, theories are as legitimate a product of science as laws. Scientists do not usually formulate theories in the hope that one day they will acquire the status of "law." Scientific theories, in their own right, serve important roles, such as guiding investigations and generating new research problems in addition to explaining relatively huge sets of seemingly unrelated observations in more than one field of investigation".

So to summarize, a law is a statement or description of the relationships among observable phenomena.

We see a parked car, and we know that it is not going to move unless someone pushes it or starts the engine, or some other outside force acts upon it, because of the law of inertia (objects at rest tend to remain at rest, objects in motion tend to remain in motion).

A theory, by contrast, is an attempt to explain observable phenomena. Notice in the example above that the theory EXPLAINED Boyle's LAW.

So a law states or describes a relationship among things we can observe, and a theory is an attempt to explain things we observe.

On this, using your source, I agree. And I agree that "theories and laws are different kinds of knowledge and one can not develop or be transformed into the other", because of the differences between the two noted above.

Whether a particular theory is TRUE or not, though, doesn't enter into this definition. It's only an attempt to explain ("inferred explanations", above, using your source).

So to claim evolution is true simply because it may be considered a theory does not follow. This definition gives us no clue as to whether ANY theory is true or not.

We would have to look at how reliable the evidence presented is, where it came from, and other factors. Is it really based on factual evidence, or something else?

But then, I noticed the following on the same page:

"Third, even though scientific knowledge is, at least partially, based on and/or derived from observations of the natural world (i.e., empirical), it nevertheless involves human imagination and creativity. Science, contrary to common belief, is not a totally lifeless, rational, and orderly activity. Science involves the invention of explanations and this requires a great deal of creativity by scientists."

This tells me that explanations such as evolution are NOT based entirely on empirical, rational, purely 'scientific' facts, but rather on "human imagination and creativity", "the invention of explanations" and "a great deal of creativity by scientists".

Probably not what you're used to hearing from your average college prof, I'll wager.

Dawn said...

It was this link I did not like...


Maintained by AllAboutGOD.com

//So to claim evolution is true simply because it may be considered a theory does not follow.//

Yes. You'll notice the quote from David Dice in my post:

"No scientist will ever claim that a theory is true. What they will do is state that the evidence agrees with the theory."

You'll also notice I took people to task in my last sentence for saying evolution is truth.

As for:

"Probably not what you're used to hearing from your average college prof, I'll wager."

Didn't you get that quote from an average college professor? :D Regardless, the fact that imagination and creativity are put to use in creating theories in no way negates the evidence that also needs to be there.

But hey, what about addressing Elisheva's most excellent points?

Brian said...

It's been really cool debating with you all, and some excellent points have been made, but I've posted some really looooong comments and I hadn't planned on spending anywhere near this amount of time on the subject.

I've got a lot else going on both online and offline (a whole 'nother story altogether), but I'll throw my two nickles in here once more.

We've been debating the meaning of what constitutes a theory vs. a law, and I think we've pretty much agreed that they are two different animals.

For the sake of argument, I'll assume we agree that a Law states or describes a relationship among things we can observe, and a Theory is an attempt to explain things we observe.

We can observe objects in motion, so we have the 3 Laws of Motion that describe the relationships between the forces acting on a body and the motion of the body (Wikipedia).

A theory is a little harder to pin down. The short answer is that they are an attempt to explain phenomena we can observe. Here is the most concise overview of the criteria for a theory that I could find: http://atheism.about.com/library/FAQs/evo/blfaq_sci_theory.htm

Note the URL (atheism.about.com) for those who may be concerned about creationist bias. I'm trying to avoid that argument for now.

And I think we can agree that a theory is not necessarily true (or false, either) simply because it IS a theory.

Where we probably run into the most issues is on these points, particularly the two I've bolded (same ref.):

"A scientific theory must:
1. be empirically testable or lead to predictions or retrodictions that are testable
2. actually make verified predictions and/or retrodictions
3. involve reproducible results
4. provide criteria for the interpretation of data as factual, artifactual, anomalous or irrelevant


A scientific theory must be:
1. a simple unifying idea that postulates nothing unnecessary ("Occam's Razor")
2. logically consistent
3. logically falsifiable (i.e., cases must exist in which the theory can be imagined to be invalid)
4. clearly limited by explicit boundary conditions so that it is clear whether or not particular data are or are not relevant to verification or falsification

According to these definitions, I would agree in principle with Elisheva that creationism does not meet the qualifications for a "scientific theory" mainly because it is not testable nor reproduceable since it was a supernatural event that occurred in the past.

However, evolution also does not qualify under these definitions either, as it is something that supposedly happened in the past and is not occurring today. It also is not testable nor reproduceable.

I know, we could get into a whole discussion about Natural Selection and mutations we see occurring today, and I agree these are indeed happening.

But without opening that can of worms, I'll say this: If evolution were an entirely natural process, as claimed, then it should be occurring today as well, and evolutionists should be able to produce some verifiable specimens of animals that have evolved into an entirely new form.

This does not include cells developing a resistance to some substance, which is the usual example that is put forth as proof. This only constitutes a change within that organism, not a step up the evolutionary ladder.

Surely there should be at least one outstanding example of this by now considering the billions of different life forms and the number of years this has been studied.

Scientists have been studying fruit flies, which mutate frequently, for over 80 years (billions of generations, as they produce a new one every 11 days and there are numerous ongoing studies).

Yet nothing resembling evolution has been observed: “It is a striking, but not much mentioned fact that, though geneticists have been breeding fruit flies for sixty years or more in labs all round the world—flies which produce a new generation every eleven days—they have never yet seen the emergence of a new species or even a new enzyme.”—*Gordon R. Taylor, The Great Evolution Mystery (1983), p. 48.

So until evolutionists can meet the criteria required for a theory, and produce some concrete examples of 'evolved' animals, then it is just as much faith-based as creation is.

Come to think of it, once you dig into the evidence that supports the creation model and exposes the flaws in the evolutionary model, evolution is FAR more faith-based than creation. There's that can of worms again.

On that note, I simply must get back to my other obligations. I doubt I'll change anyone's mind here, but I hope I've given you some food for thought.

I kind of got thrown into this role of 'antagonist/apologist' by default, and it's been interesting, but I do have to give it a rest for now. Only so many hours in a week..