How Newton found this formula? Nobody said to us, i suppose is from experimental values and from that values the best formula which descripes the values is F=GMm/r^2 but this does not mean that is right because theoretically we can find unlimited approximated formulas which descripe our values. Also there is a book about this, "What is this thing we call science" which says the weakness which science has to find the equation of truth. In physics we have many formulas which in reality are approximations ex F=ma (in lab is the equation of truth and 100% right) and when a factor changes (u starts to be very great) then the Newton formula is wrong and general relativity is right Frel=F(newton).γ (for example) but even general relativity starts to be wrong when other factors change e.t.c SO what is this thing we call science? We can make science and find the formulas of truth just from experimental values? If i am wrong then why every time a theory collapse and starts something new? Is because we are more near to truth or because the methods we use to make science are just wrong or just approximations. Is not so easy to answer as you think.