Dear Bruno,
it is so fascinating to read about "universal machines".
Is there a place where I could learn in short, understandable terms what
they may be? Then again the difference between a 'Turing machine' and a
'physical computer' (what I usually call our embryonic Kraxlwerk).
I grew up into my science without computers, got my doctorates in 1948 and
1967 and faced a computer first on a different continent (USA) in 1980. At
that time I had already ~30 patents and a reputation of a practical
scientist.
So I need more than the 'difference' into the universal.

Descriptions I saw turned me off. My chemistry-based polymer science does
not give me the base for most (and mostly theoretical!) descriptions.
How'bout common sense base?
John M

On Thu, Mar 21, 2013 at 2:02 PM, Bruno Marchal <marc...@ulb.ac.be> wrote:

>
> On 21 Mar 2013, at 02:32, Stephen P. King wrote:
>
> Are physical computers truly "universal Turing Machines"? No! They do not
> have infinite tape, not precise read/write heads. They are subject to noise
> and error.
>
>
>
> The infinite tape is not part of the universal machine. A universal
> machine is a number u such that phi_u(x, y) = phi_x(y).
>
> Please concentrate to the thought experiments, the sum will be taken on
> the memories of those who get the continuations, and the extensions.
>
> When a löbian universal number run out of memory, he asks for more memory
> space or write on the wall of the cave, soon or later. And if it does not
> get it it dies, but from the 1p, it will find itself in a situation
> extending the memory (by just 1p indeterminacy).
>
>
> Universal machines are finite entities. Physical Computer are particular
> case of Turing machine, and can emulate all other possible universal
> number, and the same is true for each of them. All universal machine can
> imitate all universal machines.
> But no universal machines can be universal for the notion of a belief,
> knowledge, observation, feeling, etc. In those matter, they can differ a
> lot.
>
> But they are all finite, and their ability is measured by abstracting from
> the time and space (in the number theoretical or computer theoretical
> sense) needed to accomplish the task.
>
> That they have no precise read/write components, makes them harder to
> recognize among the phi_i, but this is not a problem, given that we know
> that we already cannot know which machine we are, and form the first person
> point of view, we are supported by all the relevant machines and
> computations.
>
> And they are all subject to noise and error, (that follows from
> arithmetic).  Those noise and errors are their best allies to build more
> stable realities, I guess.
>
> Bruno
>
>
>
>
> http://iridia.ulb.ac.be/~marchal/
>
>
>
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