On 3/20/2013 6:32 PM, Stephen P. King wrote:


On 3/20/2013 6:37 PM, meekerdb wrote:
On 3/20/2013 2:21 PM, Stephen P. King wrote:

On 3/20/2013 4:07 PM, meekerdb wrote:
On 3/20/2013 11:16 AM, Craig Weinberg wrote:
http://www.sciencedaily.com/releases/2013/03/130320115111.htm

"We are examining the activity in the cerebral cortex /as a whole/. The brain is a non-stop, always-active system. When we perceive something, the information does not end up in a specific /part/ of our brain. Rather, it is added to the brain's existing activity. If we measure the electrochemical activity of the whole cortex, we find wave-like patterns. This shows that brain activity is not local but rather that activity constantly moves from one part of the brain to another."

Not looking very charitable to the bottom-up, neuron machine view.

The same description would apply to a computer. Information moves around and it is distributed over many transistors and magnetic domains.

Brent
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Hi,

Let me bounce an idea of your statement here. Is there a constraint on the software that can run on a computer related to the functions that those transistors and magnetic domains can implement? Is this not a form of interaction between hardware and software?

Sure, a program to calculate f(x) has to be compiled differently depending on the computer. Some early computers even used trinary instead of binary. But assuming it's general purpose computer then it is always possible to translate a program from one computer to another so that they calculate the same function (except for possible space limits).

Brent

OK, but let's zoom in a bit more on this. How much can the translation (from one program to another so that they can calculate the same (identity is assumed here!) function) exactly cancel out the constraint that one physical machine places on logical functions that could run on it? Surely we can see that is we consider an infinite number of physical machines to cover the variation of physical systems we can show that the computation of the function becomes "independent of physics", but that is an 'in principle' proof of the Universality of computations. Bruno rightly points out that this Universality can be used to argue that computer programs have nothing at all to do with the physical world and he uses that argument to good effect. I don't wish to cancell out the physical worlds. I am asking a different question. How much does a given physical computer constrain the class of all possible computer programs? 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.

I agree, but the same constraints would also apply to brains.

Brent

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