On 3/21/2013 4:40 PM, John Mikes wrote:
> 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).

Hi John,

    When Bruno discusses Machines, they are never something that might
inhabit your lab. It is the computer program X that generates an exact
simulation of a physical system that has exactly the functional space
required to run X. A logical loop of sorts. It does *not* run on just
any one or finite subset of the hardware box that is a physical system.
Do you see why?


> 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.

    You have a difficulty with Bruno because he lives in an abstract
universe where he does not have to work within the constraints of the
physical world. The computers I know of do constrain and thus influence
the programs that can run on it!

>
> 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
> <mailto: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/
>     <http://iridia.ulb.ac.be/%7Emarchal/>
>
>
>
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-- 
Onward!

Stephen

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