Gravity is not a "force"

Today I received my copy of the American Journal of Physics. I have been assimilating my first year teaching high school physics. What I write here has to be taken as very preliminary thoughts. I want to separate ideas on how to teach at this level, from how I personally "feel" about the experience; the first topic is more objective, and the second less. When I feel more settled about the second I can do it more justice.

I have considered for a long time how to teach modern physics at earlier stages of students academic life. There is a conceptual core related to the human experience with the Microworld and the Universe at large through particle accelerators, and different types of telescopes. As a species we know more about these realms than our predecessors just fifty or so years ago. The issue is then how do we communicate this knowledge to our children.

I start with a direct quote from Robert M. Wald's Resource Letter TMGR-1: Teaching the mathematics of general relativity. This letter appears in The American Journal of Physics, Volume 74, No. 6, June 2006.

"Gravity is not a "force" at all, but rather a change in space-time structure that allows inertial observers to accelerate relative to each other."

How does one go about "translating" that to a high school student?

The way I taught physics this year emphasizes that there are four known fundamental forces. Some students can repeat what I said, others cannot. I have not looked carefully at what they mean when they tell me that there are four fundamental forces, when they do tell me that. Right off, to use Prof. Ward's definition quoted above I have to change my introduction. I am afraid that there are many elementary school teachers that have to change even more what they say.

This note is just a first try on presenting that idea to young ones.

To begin with I have to state as clear as I can, what do I understand by that description. I believe Prof. Ward wants to separate gravity from the other three known forces; namely Electromagnetic, Nuclear Weak, and Nuclear Strong. In my mind I am tempting to paraphrase Ward in saying that neither of those other three are "forces" at all, but rather a change in internal space-time structure that allows inertial observers to accelerate relative to each other."

I am expressing here an speculation that is not only mine. There may be more dimensions to the Universe than the four we are used to; and there are mathematical ways to relate those extra dimensions with the internal symmetry groups associated with electric charge, nuclear strong charge, and nuclear weak charge. Even though this is speculation, it is not inconceivable that in the future humanity knows better the origin of all the "forces" of the Universe. Then what?, do they stop being forces, and turn into curvatures of ever more abstract spaces?

I do not know, but I agree with Ward that we should start talking to students more and more about what we do know about this Universe of ours. Unfortunately or fortunately we have to wait unitl ALL TEACHERS join the conversation. They cannot talk about what they don't know.

Education is our way to bring young ones into our conversations. I for one intend to keep the conversation alive.