Formal-ity and the Church-Turing thesis

[Chris Angelico]

On Wed, Oct 9, 2013 at 12:11 AM, Steven D'Aprano
<steve+comp.lang.python at pearwood.info> wrote:
> On Tue, 08 Oct 2013 18:16:01 +0530, Ravi Sahni wrote:
>
>>> So in that sense, computers are Turing Machines. Anything a physical
>>> computing device can compute, a Turing Machine could too. The converse
>>> is not true though: a Turing Machine with infinite tape can compute
>>> things where a real physical device would run out of memory, although
>>> it might take longer than anyone is willing to wait.
>>
>> Thanks Sir the detailed explanation. You are offering me many thoughts
>> inside few words so I will need some time to meditate upon the same.
>>
>> Presently Sir, I wish to ask single question: What you mean "wave our
>> hands"??
>
> It is an idiom very common in Australia. (It may not be well known in the
> rest of the English-speaking world.) It means to figuratively flap one's
> hands around in the air while skipping over technical details or
> complications. For example, we often talk about "hand-wavy estimates" for
> how long a job will take: "my hand-wavy estimate is it will take two
> days" is little better than a guess.

A derivative of the term has gone mainstream, too:

http://tvtropes.org/pmwiki/pmwiki.php/Main/HandWave

The term is commonly used when moving to a higher level of abstraction
- we all know a computer doesn't have a soul, can't "feel", and is
ultimately just executing code and crunching numbers, but we handwave
that (eg) the computer "thought" that this program was a risk, and
that's why it quarantined it. When you're trying to explain to some
user that he can't email .EXE files around, it's easier to take the
slightly-inaccurate but simple explanation, hence the handwaves.

ChrisA