On 3/17/2021 2:42 AM, Bruno Marchal wrote:
On 16 Mar 2021, at 19:53, 'Brent Meeker' via Everything List
<[email protected]
<mailto:[email protected]>> wrote:
On 3/16/2021 2:27 AM, Bruno Marchal wrote:
On 15 Mar 2021, at 10:23, smitra <[email protected]
<mailto:[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.
You seem to be assuming I'm not a realist because I think we invent the
laws of physics. I assume there is some reality and the laws of physics
we write down are our attempts to describe it. But they are almost
certainly not the real laws, only approximation that are accurate on
limited domains. This is easily seen, not only from the history of
physics in which one "law" after another has been replaced with a
different, more accurate, more comprehensive "law", but also from the
fact that our most accurate and comprehensive laws, quantum field theory
and general relativity, are incompatible.
Brent
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