As we know,
There are known knowns.
There are things we know we know.
We also know
There are known unknowns.
That is to say
We know there are some things
We do not know.
But there are also unknown unknowns,
The ones we don't know
We don't know.
—Donald Rumsfeld Feb. 12, 2002, Department of Defense news briefing
Inspired by the poetry of Donald Rumsfeld and Alexander Hamilton, I will attempt to categorize what scientists can mean when they use the word 'theory' into three categories.
In everyday usage it is often used to portray an idea or opinion like "I theorize that these pretzels are making me thirsty". However, scientists use this word very differently. For them, it is a model that attempts to describe some part of the real world. It is this gap between the public and scientific notions of the word that leads to widespread confusion. Admittedly, even in scientific circles, theories fall somewhere on a spectrum. General Relativity and Evolution on one end and notions about the Flying Spaghetti Monster on the other end.
To prove an idea wrong, scientists hold themselves to the highest of standards. It just takes ONE counterexample to, either, prompt us to make adjustments to the theory to match observation or go back to the drawing board all together.
This, in many ways, is the main difference between the eternal debate between science and religion. In science, counterexamples spell trouble for a theory. In religion, counterexamples are called miracles. Whereas, in science if 1000 identical experiments yield the same result (say, for the value of the mass of the electron) then it is safe to say the 1001st will do the same. But in religion if 1000 children born require a mother and father then 1001st might not. The latter is just one example. Anywho, I digress. Without further ado, here they are:
All theories strive to be in this category.
As mentioned earlier, I would put the theory of Evolution via Natural Selection, General Relativity, Plate Tectonics, and Quantum Electrodynamics (QED) and many others in this category. QED will not make your debts disappear and it will not tell you how to raise your children but that's OK because it doesn't intend to. Likewise, Knot Theory will not teach you how to dance and Plate Tectonics will not tell us anything about sunspots. They are only valid in the regime they claim to be valid in. This might seem obvious but too many it is not. For example, Evolution does not tell us if there is a God or if there is life on other planets. It makes testable assertions. If a baby was ever born with a tattoo that his/her mother received in her college days, our ideas about inheritance and shared traits would be in trouble.
This is not to say that these theories aren't open to further revision or interpretation. Actually, we can always add or take flesh away from the theory but, at the same time, working with the same skeletal structure. The truth takes time to develop but we know a lot more now than we did 400 years ago. In 400 years we will know a lot more assuming the human race is still around.
These theories are much more of a work in progress. I would place String Theory, MOND, or Loop Quantum Gravity here. We currently just don't know if these models work. Still, there is circumstantial evidence that they might one day make it into the first category. In this way, scientists continue to devote their careers to sculpting and refining their ideas until one day they can test them.
This is the where old, perhaps, forgotten theories come to rest. They were bravely attempting to describe the real world but, ultimately failed or something better came along. They might have been competing with another theory to describe a physical phenomenon or attempting to replace that physical theory. In the end, observations ruled them out. Some examples include Alchemy, the theory of the Static Universe, the Ptolemaic View of the Universe, or Lamarckian Evolution. Still, these theories do not get enough credit. True, they were ultimately ruled out but without them we would never get the right answers. Parts of the theory might have been true. In this way, many of the ideas in this category were stepping stones for the more correct theory. Would Sherlock Holmes have always gotten it right if Watson hadn't always gotten it wrong? Or would
Just as importantly, some of these rejected ideas were attempts made using the scientific method to try to explain reality. They were off mark but still much better than just making stuff up and describing how things work based on just one's own personal biases and emotions.
Scientists in all fields need to make a better attempt to qualify what they mean by 'theory' and where on the spectrum a particular theory falls. The lines of evidence for promoting or demoting a theory need tocommunicated more effectively. Easier said then done I know.