> On 16 Mar 2021, at 19:53, 'Brent Meeker' via Everything List > <[email protected]> wrote: > > > > On 3/16/2021 2:27 AM, Bruno Marchal wrote: >>> On 15 Mar 2021, at 10:23, smitra <[email protected]> wrote: >>> >>> On 14-03-2021 20:03, 'Brent Meeker' via Everything List wrote: >>>> On 3/14/2021 3:24 AM, Bruno Marchal wrote: >>>>>> The laws are constructs of the human mind. [Lawrence] >>>>> The expression of the laws are constructs of the human mind, but I >>>>> guess you are OK that F=GmM/r^2 was as much approximately true >>>>> before human life appears on this planet and after. OK? >>>> I think "approximately true" implicitly assumes someone for whom the >>>> approximation is good enough. Someone with values and purpose. >>>> Brent >>> There exists an as of yet unknown exact description of gravity. The leading >>> term of the expansion of that theory for large distances, low energies and >>> velocities will yield the Newtonian theory. >>> >>> It's not much different from saying that sin(x) = x + O(x^3) >> >> I agree. "3,14 is an approximation of PI” is true, independently of any >> observer, even if it is a vague proposition. Its degree of precision are >> themselves independent of us, even if the taste for this or that precision >> might depend on us, and of some context. >> >> I used “approximately true” because it is hard to find a law of physics >> which is not an approximation of such sort, but for the point I was making I >> was alluding to some such laws, and that would make sense for anyone realist >> on some physicai reality (fundamental or not). If not, then “the laws is a >> construct of mind” would be interpreted in an anthropomorphic way, like if >> the humans are at the origin of the physical reality. The fact that F = >> GmM/r^2 does not depend on some human thinking about “F= GmM/r^2. > If it doesn't depend on human thinking, then what does the "=" sign mean? > What does "F" refer to?
It means that IF an observer was there, and want to evaluate the acceleration toward the object of mass M, of an object of mass m, by F=ma, we get ma = GmM/r^2, and thus a = GM/r^2. In passing we see that all objects near M have the same accelaration, and thus we get the usual orbits, etc. So, in absence of any observer, the planet will move around a star in some way, etc… I use Einstein’s principle of Reality here, which is the counterfactual asserting that if we can predict a result with certainty, then, even if we don’t make the measurement, there is an element of reality (fundamental or not). > In my view they refer to a model (in the physics sense) in which the equation > expresses a relation between elements of the model. Which is interesting only if the elements of that model (in a physician sense) correspond to element or reality (which “model” in the logician’s sense, basically). > That the model is a useful approximation does happen to depend on our > circumstances. The usefulness of that approximation depends on the circumstances, and the goal of some observer. Yet, the fact that it is true, or approximately true, should be true independently of any observer. Earth is approximately a sphere, and it makes sense to assume/believe that Earth was approximately a sphere long before life appeared on it. > If we lived a planet closely orbiting a red dwarf/black hole binary it might > not be close enough to be considered useful, much less a "law”. ? You might need better equation, like Einstein GR, if you have the time. The was of physics are not contradicted by a Black Hole, and if that was the case, it means that the law we discovered was false, and would search for a better law. But those laws are supposed to be independent of the observer. Quarks exchanged gluon already two seconds after the big-bang. If a human is needed for having a reality obeying some law, we will need some human to start the physical histories. That become a form of solipsism. We cannot prove the existence of a Reality does not mean that there is no Reality. Indeed, that is the reality that we will confront with our theories. > >> Brent might have confuse a law and a human (correct or incorrect) >> description of that law. > > And what would an "incorrect description of a law" be? F = mv (like Aristotle did, which still makes sense due to friction, but it is Newton who got the correct (or better) insight, and then Einstein get even more correct on this. > One can say describing a cow as a bird is an incorrect description of a cow, > because you can point to the cow and say "That is not a bird". But you can't > point to a law, you can only point to a better approximation. The theory which classify a cow as a bird can be considered as a better approximation than the theory classifying the cow as a star, which is better that the theory according to which the cow is a number. > >> >> This difficulty appears also in arithmetic. The fact that the arithmetical >> reality run all computations must not be confuse with that fact that we can >> describe the computations in arithmetic, as a computation is not the same as >> a description of a computation, even if to prove that Arithmetic is Turing >> universal imposed *us* to go through those description. There is a complex >> pedagogical problem here. It is like the difference between the number 1 and >> the symbol “1”, those are extremely different entities. Nobody knows what >> the number 1 is, but everybody can handle it very easily, and the symbol “1” >> is anything you want, even the Mount Everest if you want, although that >> would not be a practical symbol, for sure. > > But they handle it easily because they learn the rules for handling the > symbol and the semantics for translating from symbols to the meaning. OK. They got the semantics and the use, in this case, rather together. > Most people can't do even simple addition beyond one digit without using > symbols at least mentally. But they don’t doubt that the results are well definite, even if they can’t do the calculation, which is the point of being realist on such relations and laws, both in mathematics and physics. But to get the mind-body relation right, we need to be correct at a deeper level, and be precise on what we assume at the start, and what we derive from what we assume. Bruno > > Brent > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/everything-list/ae99fbf8-0dde-7a30-97db-b2b5df2d4b75%40verizon.net. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/B66A55C1-B6CA-4880-8BB3-36408C3E9D2A%40ulb.ac.be.
