A Few Words on Gravity

March 12th, 2010

One regularly used and specious counterargument to the objection that a scientific theory is “just a theory” is to point out that gravity is also “just a theory.”. The implication (sometimes explicitly stated) is that since no one would doubt that gravity exists, no one should doubt whatever other theory is being considered.

I say the counterargument is specious for good reason. Gravity is a fact. There is a phenomenon we call “gravity.” The “Theory of Gravity” however is science’s attempt to describe the phenomenon in a quantifiable manner, ie with a model. Over the course of history, science has developed many models for gravity. Each one has in time been proven to be either wrong, or incomplete. The current Theory of Gravity describes gravity accurately so far as we can tell, but one would be foolish to rule out a future advancement that might revolutionize our understanding of gravity.

For example, we observe strange and unexpected gravitation in the universe at large. We don’t have a good explanation for this behavior as of yet, but many have posited “dark matter” or “dark energy” is involved, to make the current gravity models fit.

Meanwhile, we have a good working model for gravity. A large body of experimental data has been shown to agree with predictions the current gravity model makes. In particular, ie. there was a bunch of data that the model had to describe/fit initially, and the model has since accurately predicted future data. For example, if you drop any weight of any shape in a vacuum, shoot a satellite into space, or anything else where gravity is concerned, the model predicts the outcome with a high degree of accuracy. Any lack of accuracy we might observe between the prediction of the model and the outcome of events is generally from other forces involved, such as air resistance.

So, we see that while “gravity is just a theory” it is a pretty good one. The model fits past data very well, one might say perfectly within margins of measurement errors. But more importantly, it accurately predicts future data, such as outcomes of experiments done by physics students do an equal degree of accuracy.

This is vastly different from most of the theories that gravity is compared to in argument. Climate change/global warming for example has no model that is able to make such accurate predictions. It does have a model that fits existing/old data to a degree of accuracy (not as good as the gravity model). But so do many competing climate models. In fact, other models are better able to predict future data. The model itself doesn’t prove or disprove the theory behind it, but the lack of a good, reliable model does place the theory on a completely different plane from that of gravity. One that is much lower and subject to skepticism.

So, please. Stop comparing things to gravity just because both are called “theories.” There is no relation between them beside the fact that the models for each of them might be wrong. It just turns thinking individuals off from your argument. Instead, if the “theory” has merits, discuss them.

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