When a Theory is not a Theory

I was reading an article online from the Express when I read the following: “Black holes are often found at the hearts of galaxies and up until April this year have been purely theoretical.“ The statement threw me for a bit of a loop, mostly because black holes have been an active part of astrophysics since the discovery of Cygnus X-1 in 1971. Using the day to day word theoretical misleads the general public into thinking that black holes were not confirmed in science until this past April with the discovery of M87*’s shadow. This is a dangerous statement to make.

In day to day language, theory is used to mean a hunch or an educated guess. However, in the sphere of science, a theory is an explanation of what something is or how it works. Theories are often large bodies of work and research and are quite detailed.

Take gravity for example. Newton’s law of universal gravitation does not explain what gravity is, it only shows mathematically how two bodies affect each other through gravitational attraction. It is the theory of general relativity that explains how gravity works and what it is (a result of mass curving space-time). Black holes are part of the general theory of relativity. To start they were a mathematical quirk of Einstein’s field equations, but the discovery of Cygnus X-1 showed that black holes were not a mathematical quirk.

Further observations about black holes have been made over time adding to the theory and supporting the existence of these massive objects. Accretion disks, relativistic jets, active galactic nuclei, gravitational waves and other observations were all documented well before the Event Horizon Telescope document M87*’s shadow.

None of these observations, including the observation of a shadow, have moved black holes out of the realm of scientific theory. Instead, they help keep black holes as active parts of the general theory of relativity.

Science writers and communicators need to take extra caution when using terms like theory, theoretical, law, fact, hypothesis or conjecture. They have different meanings inside and outside of the sphere of science and using them inappropriately can build a false impression of what science does; that in turn can cause misunderstandings and mistrust of science as a whole.

I am not without fault and am often rereading and refamiliarizing myself with the different terms. It is part and parcel of the job as a science communicator. One of my go-to’s is this article from liveScience.com. Writer or reader, it is probably worth a second look and remember to give critical consideration when you see those terms in an article.

– KMSB