5 Falsifiability

You may have learned in a previous science class that scientific hypotheses must make testable predictions. A less simplified statement is that scientific hypotheses must be falsifiable.

Falsifiability is a cornerstone of science.  Start by reading the entry on the Criterion of falsifiability from Encyclopedia Britannica.

I like to simplify the definition of falsifiable by saying A hypothesis is falsifiable if I can imagine an observation that, if I made it, would cause me to discard my hypothesis. Note that I only have to be able to imagine the observation, I don’t have to actually make it.  After all, the hypothesis might not be false.

We do not have to be able to prove a hypothesis true. In contrast, we CANNOT prove that a hypothesis is true. There’s a strange circular logic here….  If we declare that hypothesis is incontrovertible, then there is no imaginable observation that would force us to discard it, and the hypothesis is no longer falsifiable.  Declaring a hypothesis to be true removes it from the realm of scientific knowledge.

The misconception that scientists prove things is extremely common.  Once you start to look for it, you’ll see it everywhere. Hopefully, some of our hypotheses are true, but we’ll never know for sure.

Another common misconception is that scientists don’t know anything.  After all, if you can’t prove anything, then how can you know anything? This question is addressed on the next page, but the short answer is that we can gain confidence in our hypotheses. For example, we don’t know for sure that our theories of gravity are correct, but we had enough confidence in them to spend billions of dollars designing and launching a system of satellites that form the backbone of the GPS system, which millions of people a day use to navigate.

Here are few example hypotheses, some of which are falsifiable.

Near the surface of the Earth, gravity does not affect pens.

This hypothesis is both falsifiable and false.  I can imagine releasing a pen and seeing it drop to the ground.  I’m imagining an observation that would prove the hypothesis false.  Then I can drop my pen, thus proving that the hypothesis is false. Note that we can prove that a hypothesis is false, but we can’t prove that one is true.

In Mesa, Arizona, everyday is sunny.

In August, this seems like a pretty good hypothesis. It is falsifiable, I can imagine looking out the window and seeing a cloudy or rainy day.  By imagining these scenarios, I demonstrate that this hypothesis is falsifiable. In fact, despite a long string of sunny days, I can remember days that weren’t sunny and expect that (someday) I will look out the window to see a cloudy day.

In Mesa, Arizona, it never snows

This hypothesis seems even better than the last.  It is falsifiable, I can imagine looking out the window and seeing a dark, snowy day. If it ever did snow in Mesa, then I would have to discard this hypothesis.

Near the surface of the Earth, gravity does affect pens.

This hypothesis is falsifiable, but to the best of our knowledge it isn’t false. I can imaging releasing a pen and seeing it float still in the air, unaffected by the downward pull of gravity. I do not have to actually see this happen.  By imagining this observation, and admitting that it would cause us to abandon (or at least modify) this hypothesis, we show that it is falsifiable.

The Universe is filled with billions upon billions of undetectable particles.

This hypothesis almost sounds scientific.  It uses science words like Universe, billions, and particles. Unfortunately, these billions of particles are undetectable.  When I try to imagine an observation that would force me to abandon this hypothesis, I can’t.  Imagining not detecting them doesn’t work; they aren’t detectable.  Imagining detecting them doesn’t work…. if I detect them, they aren’t these particles.  I’m stumped.  My brain hurts just trying to think about it.  This hypothesis is not falsifiable.

Somewhere out there in the great unknown there is a flying purple unicorn.

My daughters went through a My Little Pony phase that I never quite grew out of.  I hold this hypothesis close to my heart.  She is magical, she can teleport, and she does not want us to find her.  Nothing anyone sees or hears will force me to abandon this hypothesis.  Alas, it is not falsifiable.

The Earth is flat

I’ll hop up on my science soapbox for a moment to say that sometimes falsifiability is personal.  For example, the Earth is flat sounds like a falsifiable statement.  I can imaging riding into space and seeing the blue curve of the round Earth against the dark sky. To me, the Earth is flat is falsifiable. But there are people out there who will not discard this hypothesis no matter what they see or hear.  For them, the question of whether the Earth is flat or round has ceased to be a scientific one.

Chocolate is good for you.

Try to get me to abandon this hypothesis…. just try it.