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? In my view they refer to a model (in the
physics sense) in which the equation expresses a relation between
elements of the model. That the model is a useful approximation does
happen to depend on our circumstances. 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".
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? 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.
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.
Most people can't do even simple addition beyond one digit without using
symbols at least mentally.
Brent
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