On 29 Oct 2012, at 17:03, John Clark wrote:

On Mon, Oct 29, 2012  Bruno Marchal <marc...@ulb.ac.be> wrote:

>> We now know that computing or thinking is physical,

> We don't know that.

We know that as well as we know anything about physics.

This is not valid. A priori we can be dreaming in some world based on a different physics. Or, as with comp we might belong only to sophisticated computations, which are entirely emulated already by degree four diophantine polynomials.

And computation is a the start a purely mathematical, indeed arithmetical, concept. All physical computations are defined by the physical incarnation of the corresponding mathematical computation.

> We deduce that in the Aristotelian's theories.

I have no idea what if anything that means.

There are two main rational conception of reality.

1) the Aristotelian one, in which the ultimate reality is a physical world, and the erst emerges from it.

2) the Platonist one, in which the physical reality is the border, or the shadow of a vaster invisible reality.

The idea that today science has solved the question of deciding between those two conception is a crackpot idea of sunday type philosophers.

The UDA illustrates this, by showing that if we take computationalism seriously enough, the Platonist conception of reality is about unavoidable, and that the physical reality is no more a primitive notion, but a derivative of an ability owned by complex relation between some numbers. This makes also comp testable, as the derivation is constructive (albeit technically difficult).

>> it takes energy to do it and it gives off heat;

> Actually computation can be made reversibly, without dissipation of energy.

With reversible computing you can make the amount of energy used for a calculation arbitrarily small and thus the heat emitted arbitrarily close to zero BUT, as I said before, only at the price of slowing down the computation;

I give a good energy at the start, and I can sped the non dissipating process at the speed limited by light.

we were talking about the theoretical feasibility of making a prediction and making a forecast of yesterday's weather is not of much use.

No. We were talking on something else.



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