Re: Proof by construction, again (was Re: [sl4] prove your source code)

From: Nick Tarleton (
Date: Sun Jul 20 2008 - 14:11:43 MDT

On Sun, Jul 20, 2008 at 1:02 PM, Matt Mahoney <> wrote:

> --- On Sun, 7/20/08, Tim Freeman <> wrote:
> > So you stand by your bold assertion that backing up computers is
> > impossible. The backup media are defined to be part of the computer
> > that's being backed up, so the loss of previous contents of the backup
> > media is a failure of the backup. Odd.
> No. I stand by my assertion that backing up a computer does not disprove
> that an agent cannot know its own source code. How do you know the backup is
> correct? You could make a second backup and compare the results, but that
> doesn't prove the process is correct. You could reload your computer from
> the backup, but then how do you know nothing is changed?
> An agent making a copy of itself would have the same problem. It could not
> verify that the copy is exact. It has to trust the copy process.

Isn't this just fully general skepticism?

Being a bit more specific: If we define "source code" to mean the entire
system state, the mind can be very confident (based on examining the copy
process) that "this hard drive [connected to, but defined to be outside, the
system] contains what my state was at time t". This isn't common usage of
"source code", though; it would be considered very odd to say that two text
editors with different documents open have different source code simply by
virtue of that. Under the more common definition, a mind can be very
confident under some circumstances that some external hard drive contains
its current source.

But this has little to do with Tim's original thought experiment, which is
more about making goals transparent and actions predictable than proving
specific code.

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