[samloveshummus]

Who cares if there's no gravity? Gravity wasn't sent down to us from heaven on a stone tablet, it's just a concept that lets us make predictions. At school I was taught it was a force and at university I was taught it was a pseudoforce resulting from fixing a non-inertial frame. Both approaches give correct answers, even though they're conceptually very different. There's no objective way to say which is right; they're just different approaches to modelling.

And maybe the 4.7 is actually more correct? The 4-parameter model is an approximation that neglects friction and air resistance. Moreover the double pendulum is a chaotic system and chaotic systems sometimes have dynamics described by laws with non-integer exponents such as Lyapunov dimension. I'm just spitballing, but the point is that it's not a priori ridiculous.

It's definitely possible to estimate mass from images. How do you think we know the masses of asteroids and planets? No-one put them on a scale, we just record their motion and work out which value fits best.

[goatlover]

> Who cares if there's no gravity? Gravity wasn't sent down to us from heaven on a stone tablet, it's just a concept that lets us make predictions.

A concept that says gravity is the result of bending spacetime, with the speed of light being constant. It's not just a model, it's saying the universe is 4D spacetime, which explains why GR is so predictive.

[samloveshummus]

It is just a model though! Everything in science is just a model. We better hope it's just a model, because it's incompatible with quantum field theory, which is another very accurate model. The only consistent model that bridges the two, superstring theory, says that spacetime and gravity could fundamentally be many things, from closed strings travelling between D3-branes to the holographic projection of a conformal theory - and you still get the same predictions.