On 24 Jun 2016, at 21:47, John Clark wrote:

On Fri, Jun 24, 2016 at 12:04 PM, Bruno Marchal <marc...@ulb.ac.be> wrote:

​> ​Read the definition in the literature, it does not involve physical assumption.

​A definition will tell you absolutely positively 100% NOTHING about the underlying nature of mathematics or physics, it will just tell you things about human mathematical notation and language. ​ You learn about nature from examples not from definitions, even the writers of dictionaries know that.


You are just delirious or what?

I just meant that if you consult the literature, the notion of partial computable function, or Turing computable function, or Church lambda calculus, and the relative computations, etc. does not involve any physical assumption.

Here you make a "knock on the table argument", but that the ancient already knew that this is invalid.



​>> ​in fact nothing is ​Turing emulable​, not even arithmetic, UNLESS the Turing Machine in question is physical. ​

​> ​The sigma_1 part of arithmetic is Turing emulable,

​Don't tell me show me, don't give me another definition give me an example, calculate 2+2 without using anything physical, ​​or if that's too hard try 1+1. Do that and I'll concede the argument​ ,​​ and immediately after that I'll get on the phone to Silicon Valley. ​

Silicon valley exists thanks to those mathematicians having discovered the universal numbers. Some, like Turing, will indeed participate in the physical implementation. Babbage discovered it, and get the main consequences, I think, when realizing that his description language was as much powerfull than its machine, which is the HaHa of Church's thesis.





​​>> ​If there was only one thing in the physical world mathematicians wouldn't have the slightest intuition about what numbers mean, they'd just be playing with squiggles. Of course if there was only one thing in the physical world mathematicians couldn't even exist, but never mind. ​

​> ​You confuse

​No I don't confuse.​

​> ​the mathematics developed by the humans, which are very plausibly inspired by the observation of nature, and the reality of some mathematical facts.


​You admit that to a mathematician who had no experience with anything physical a equation would just mean a sequence of squiggles that had a "=" ​squiggle somewhere in it, and that's all it would mean. That's it.

A local truth does not make a global truth false. The numbers, as studied today, by mathematicians, does not use physical assumption. They use arithmetical, or set theoretical assumptions.





But if pure mathematics is the most fundamental science and contains profound truths independent of the physical world why does the mathematician need physics to give his equations meaning?


In the big picture, it does not.

It is an an infinity of dream, John, albeit some can be quite persistent one, and apparently sharable.

And it is not math which is the fundamental science, it is more a science of the universal person, the one defined by G and G* and its important intensional variants, in relation with consistency, and truth.




Stephen Hawking​ once asked:​


​"What is it that breathes fire into the equations and makes a universe for them to describe? The usual approach of science of constructing a mathematical model cannot answer the questions of why there should be a universe for the model to describe. Why does the universe go to all the bother of existing?​"​

​Hawking is saying a ​mathematical model ​can't explain why the physical exists,

I guess he means theory. I agree with him. You need at least a theory of the mind and belief, to have at the least a believer in something. But this arithmetic provides amply.



but I think a physical model (like a brain) can explain why mathematics exists.

Also, here, I am afraid we abstract away from the fact that just defining the brain activity involves implicit assumption in numbers and something turing universal.




​Higher levels can not be expected to explain the ​existence of more fundamental levels, but more fundamental levels can explain higher levels, and physics is more fundamental than mathematics.


If you were not stuck in step 3, you would plausibly understood that if we assume Church-Thesis, and "yes doctor", things are no more that simple, and the theoretical computationalist has the task to derive physics from the universal machine mind. But just the genuine intensional restriction on this domain gives basically what we ere searching: an intuitionistic logic for the first person, a quantum logic for the better/observer, and hopefully some day some "Gleason theorem" providing the unique (quantum) measure.

It is more rich than physics in the sense that it gives the quantum logic and the qualia logic, which resemble, yet are different. Note that eventually the quanta themselves are sort of qualia, which makes Everett MWI saving us from solipsism, we do share rich and probably very deep (arithmetical) dreams.

Bruno




John K Clark


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