Talk:Leonard Mlodinow

My question relates to Leonard Mlodinow's book Upright Thinkers in relation to his pointing out (and the first time I realized it) about Newton's theory on gravity  that the gravitational force of a mass is in inverse proportion to the square of the distance from the gravity generating body. I had always presumed Newton had some way of independently measuring the gravitational force, say, from the sun and comparing it to the gravity from some other body that had a known different distance and deriving a measure of the actual gravity of each by comparative method, and using mathematics to postulate the 'inverse square of the distance' formula. In simpler terms, an actual gravitational force was measured in some form, empirically.

However, I am surprised to realize Newton derived his theory based on simple geometry. His example was that a sphere twice the distance from the sun would have an area "four times" the size of the sphere at the shorter "half" distance, that is, postulating the square of the distance for both cases. The logic would, yes, seem to hold that the gravity at the expanded surface would be inversely proportional, because, so to speak, it is more 'spread out' and therefore proportunately weaker at each point on the larger sphere.

Fine, one may say, so what? The so what has to do with the idea of the illusive dark matter, which still unseen at this stage, is presumed necessary to correct the problem of missing matter, as otherwise the universe would not have enough matter for its gravitational force to hold itself together. Quite aside from anything to do with Einstein's theory go general relativity, Newton could have been wrong. Gravitational force may not be proportional at all distances according to a smooth formula.

For all we know it could vary over distances, and also depend on where we are situated in space, as affected by all the matter surrounding ourselves in the universe. There may be no dark matter. Maybe gravitational forces are just not as assumed by Newton. Accumulated gravitational force for all matter in the universe may not be the same as the force that appears to derive between individual bodies. Newton had a great theory about gravity, but I am not sure he really did empirically test it. It is like Darwin's theory on natural selection. It did and does continue to be substantiated over time, by what we can see, and measure. It should be the same for Newton. His theory looks like inverse of the square of the distance, but is it so for everything everywhere.