Due to the nature of another book I am writing, this time of a more scientific nature, I have been discussing science more and more often with people, and have been absolutely astounded as to how many people misunderstand the scientific method and the terminology associated with it.

So here is a pop-quiz for you to see if you yourself are completely free of any misunderstanding surrounding theories, facts, laws, hypotheses, etc.


Check all that apply.
Gravity is:

• A fact.
• A theory.
• A law.
• A hypothesis.

Many of you will be saying, “I see the catch. I know the difference between a fact and a theory. Easy question.”
But that isn’t the catch.

Let’s cover the basics.


The scientific method begins with empirical observation. You observe something and then ask (postulate), “How does that work?”.
Then you make a best guess based on whatever information you can gather (a hypothesis) and test it. You observe the results and compare/contrast them with the observed phenomena. After many tests and perhaps many revisions to the hypothesis, a conclusion might be drawn and a scientific theory formed.
A scientific theory is never considered a fact within the scientific community—it simply best-explains the observed phenomena but could later be proven false.


Most likely all of you knew that, right? No one here mistakes a theory for fact, right? So the answer must be #2, right?


But I said that wasn’t the catch. The astute reader may have noticed that we haven’t discussed laws yet.

A scientific law is a statement based on repeated experimental observations that describes some aspects of the universe. A scientific law always applies under the same conditions, and implies that there is a causal relationship involving its elements.

http://en.wikipedia.org/wiki/Scientific_law
In other words, a scientific law provides a prediction of “what will happen under these circumstances”.
Generally speak, the law of gravity suggests that if you let go of a standard ball from the roof of a building, it will fall towards the earth. For the sake of brevity we are not going to explain that the building does not reach into space, nothing is attached to the ball to make it float, etc. Just keep it simple.


So is the answer #3? Or is it #2 and #3?


If you think it is either of these suggestions, you are not paying close-enough attention. Consider the implications if the answer is “#2 and #3” or “#2”. If the theory (#2) changes, does that change how we are attracted to the earth or how the moon orbits Earth?

At the very beginning of the explanation of the scientific method I mentioned very important key words: Empirical observation.
When you make an observation, the thing you are observing does exist, or the phenomena you are observing is actually happening (not delving into discussions related to trusting your senses etc.—that is for another day).
In other words, you might say that thing factually exists, or that phenomena factually occurs.


The correct answer is “#1, #2, and #3”. All theories originate from empirically observed phenomena, which by definition themselves must actually exist—a non-factual phenomena can’t be factually observed; it exists within the realm of imagination and in that case can at-best be only a theorem (if anything).
The reason people get confused is because theories and laws have the same name as their observed phenomenon. To make the distinctions clearer, I have color-coded facts, theories, and laws below.


Laws, theories, and facts are not mutually exclusive—that is the catch. Gravity is a fact that we observe. Because of its predictable behavior we also made the Law of Gravity, which doesn’t explain anything about how gravity works, but predicts that a ball dropped from a building will fall, and equations can even determine how fast it will fall. The Theory of Gravity attempts to explain how gravity works. The key point here is that theories provide explanatory purposes.


To deny that gravity is a fact is to deny that the moon orbits Earth and the earth orbits the sun.
Gravity is an observable fact, with an associated theory (gravitational theory) which tries to explain why bodies of mass attract (and indeed there have been many attempts to explain how gravity (the attraction of 2 bodies of mass, regardless of how that attraction takes place) works).

And while working on the theory, the nature of gravity is predictable enough that there is also the law of gravity, which explains what happens between 2 bodies of mass in regards to attraction.

Appendix:

Scientific Theory: http://en.wikipedia.org/wiki/Scientific_theory

“A scientific theory is a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method and repeatedly tested and confirmed through observation and experimentation.”

Scientific Method: http://en.wikipedia.org/wiki/Scientific_method

“The scientific method is a body of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. To be termed scientific, a method of inquiry must be based on empirical and measurable evidence subject to specific principles of reasoning.”

- Evidence must factually exist or factually occur to be empirically observed or measured.

Scientific Law: http://en.wikipedia.org/wiki/Scientific_law

“A scientific law is a statement based on repeated experimental observations that describes some aspects of the universe. A scientific law always applies under the same conditions, and implies that there is a causal relationship involving its elements.”

I hope this has been useful. Surprisingly many people are confused by the fact that events/phenomena, theories, and laws all have the same name, and it makes it hard to make the distinction between them. If you say gravity is a fact, you will likely get a reply along the lines of, “No, it’s just a theory,” followed by an explanation of the differences between facts and scientific theories and how a theory is never considered a fact.

This is true, but the person replying has misunderstood the founding principles of the scientific method—all theories begin as factually observed phenomenon. In other words, you could say, all theories are facts before they are theories—scientific theories can’t exist unless there is something already there to explain.

Now you can explain to anyone the real difference between facts and theories.

L. Spiro

I would say that objects falling to Earth and the orbits of planets, among others, are the observations / facts. I have never observed gravity directly, only these consequences of it.

It’s just semantics at this point. The observed phenomena is bodies of mass being attracted to each other. We call this phenomena “gravity”. When you say you can’t “observe” gravity, you’re applying more to it than just that, as if you need to see some form of physical particle or something to call it “gravity”.

Gravity itself is just the attraction between 2 bodies of mass, so when you see orbits, you are seeing gravity, and also the consequences of gravity.

Semantics may make it confusing but think of it this way. As I said above, things are not mutually exclusive. Effectively, you are seeing both gravity and the law of gravity.

L. Spiro

Whatever you do, don't base your understanding of gravity on the recent "Interstellar" :)

Understanding something is not a prerequisite for its existence - as it is, Newton postulated his Law of Gravity without having the first clue as to what it is or how it works. Just the same, gravity's existence here and now does not necessarily make it a universal fact (this is a supposition), although our universe seems to be deeply dependent on the existence and very particular strength of gravity (most profoundly in the sense that it would otherwise simply, for lack of a better word, disintegrate due to other, far more exotic theoretical things like dark energy). The truth is that, on a fundamental level, even String Theory doesn't fully explain "what gravity is", while Einstein's Theory Of General Relativity goes into great detail in describing "how it works".

Notably, gravity is an elusive little bugger since there is no straightforward explanation to its basic properties (like its strength), which forces us to hypothesize what other forms gravitons may take - for instance outside of our four-dimensional spacetime. Yet, at the same time it is one of the four fundamental forces that make our universe possible. The latter, to me, sounds very much like fact.

In this respect:

#1 gravity is a law, which is has been accepted by the scientific community and has been around for 350 years

#2 gravity is a fact, since it is crucial to our existence, it's tangible and has been empirically tested over and over again. We know the speed at which gravity travels, we can accurately calculate its strength and so forth.

#3 gravity is a theory, because despite all this we lack a complete understanding of its underlying mechanism and possible hidden form(s)

#4 gravity is not a hypothesis, but it is subject to other hypotheses

Hence, unless you define a context or choose your definition based on your particular needs, mutual exclusivity goes out of the window. If I had to choose one, then for the sake of clarity I would go with law since it's the most widely accepted of the four, even though deep inside I consider gravity a constant and hence a fact (albeit one that we do not yet fully understand).

Here are some common misconceptions that I will post as I encounter them.

1. After a theory is completely tested and proved and fully understood, it becomes a law.
   1. No. A law is completely separate from a theory. A theory is the highest level an explanation can have in science. There is no promotion above a scientific theory. A law is completely separate, and as mentioned above serves a separate purpose: Predictions. Theory: Why/how something happens. Law: What happens if…

And while we are in the swing of correcting misconceptions, someone posted this interesting link:

L. Spiro

A theory is an explanation for a fact. To call a theory a fact is only ever a rhetorical device, a kind of puffery. The theory of gravity is a good explanation of the observation (fact) that objects seem to be attracted to one another proportional to their mass and relative distance.

A hypothesis is a falsifiable statement about a fact. They connect theories to facts. Most theories will produce hypotheses about facts, and if those hypotheses can be falsified (shown to be inconsistent with observation), it generally means the theory is either incorrect or incomplete.

A scientific law is a statement that provides reliable and useful predictions consistent with observed facts. Inversely, a law is a terse way of generalizing an observed phenomenon (a fact).A law can usually be expressed in strict and rigorous terms (the pressure of a gas is proportional to its volume and temperature, PV = nRT, or a body in orbit follows an elliptical path with its orbital primary at one focus of the ellipse). Often one or more theories offer an explanation for a law.

The law of gravity is g = m1m2r-2 and the theory of gravity says that this is due to a mysterious and invisible but very weak force that operates over long distances. An alternative theory is that angels push things around. The fact is that if I hold an apple in my hand and let it go, it falls toward the ground, and repeated observation reveal the fact that it accelerates toward the ground at a rate of 9.8 m/s2. I hypothesize that the next time I have an apple in my hand and let it go, it will fly into the sky (sadly, I recently disproved this hypothesis, and now I have a soft brown spot on my apple).

So, there is a law of gravity, and there is a theory of gravity -- they're two different things with confusingly similar names. Gravity is not a fact. That things fall is a fact, the law of gravity describes that fact and the theory of gravity explains it.

And yes, it's all semantics. That's what semantics is.

Whatever you do, don't base your understanding of gravity on the recent "Interstellar"

To be fair, you really shouldn't base your understanding of gravity on any depiction of it in any movie. Most falls from tall heights that action heroes survive would kill a person in the real world.

L. Spiro, you have confused the observable phenomena (facts) with the explanation.

Things fall down. We don't call that gravity, we call it "things falling down". Now, if you ask any vaguely educated person *why* things fall down, they'd say gravity. But that's only a few hundred years old. Until Newton, we didn't really have a concept of gravity, but things still fell down.

To take a more controversial example, consider evolution. Even Dawkins wouldn't say evolution is a fact. Diversity of species is a fact, and the theory of evolution explains that.

A scientific law always applies under the same conditions

I think that's the most misunderstood or just forgotten aspect of scientific laws.

The law of gravity applies under all observed conditions. As long as the conditions are met, the law applies.

Of course, astronomical observations have found that, under extreme conditions, the law fails to represent what's being observed, but that does not invalidate the law under 'normal' conditions. It simply indicates that a new theory needs to be developed that accurately explains both normal and extreme behavior. That, or some theory that explains why things work differently under normal vs extreme conditions.

L. Spiro, you have confused the observable phenomena (facts) with the explanation.

Things fall down. We don't call that gravity, we call it "things falling down".

You have confused some terms. I was very specific with the definitions of things in my post. I never defined gravity as “things fall down”. That is a result of gravity as viewed from our typical vantage point on Earth.
Gravitation or gravity is a natural phenomenon by which all physical bodies attract each other.

Even Dawkins wouldn't say evolution is a fact.

Evolution is a fact.

http://en.wikipedia.org/wiki/Evolution_as_fact_and_theory
Richard Dawkins tends to say evolution is a fact by taking it to the semantic levels described in the 2nd paragraph of that page, but one needn’t involve semantics at all, as the first paragraph explains correctly what I have already explained here.
All scientific theories are also facts. It is impossible to formulate a scientific theory (an explanation for something) without there already existing a thing or event that needs to be explained. The scientific process begins with observation.
Evolution is indeed a fact, which we try to explain via the theory of evolution.


L. Spiro