On 30/09/2011 07:32 PM, Darren New wrote:
> On 9/30/2011 10:04, Orchid XP v8 wrote:
>> Small difference: ALUs require energy. A storage medium typically
>> doesn't.
>
> ALUs don't require much energy. Look up "reversible computing" some
> time. That's what it's all about. And yes, people have actually built
> computers that take no energy to run, using quantum effects.

I thought the problem with reversible computing is that it's just as 
likely to run backwards (which is no use at all) as to run forwards?

>> If you're saying "you could make an analogue computer that was
>> Turing-complete" then, yes, of course you could. If you're saying "the
>> analogue computers what people actually built were Turing-complete" then,
>> no, not really...
>
> Well, sure, and neither are the real digital ones. That's kind of my point.

By that definition, nothing that can exist in the physical universe will 
ever by Turing-complete. That's not a useful definition.

>> Exhibit A: Totallistic cellular automaton number #110.
>
> Exactly.

You said "it's always absurdly easy to prove that something is 
Turing-complete". I hold up an example of something that took ages to 
prove, and even now some people argue the proof isn't very sound.

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