Eliezer’s hard drive comparison is actually wrong. As I commented on Timeless Identity, Peter Gutmann, who wrote the original list of steps to securely erase a disk, is particularly annoyed that it has taken on the status of a voodoo ritual. “For any modern PRML/EPRML drive, a few passes of random scrubbing is the best you can do. As the paper says, “A good scrubbing with random data will do about as well as can be expected”. This was true in 1996, and is still true now.”
This isn’t directly relevant to the question of memory in a brain—but it wasn’t then either, because it just isn’t a very apposite analogy to use in thinking about this question.
I’ve also commented (not in the original thread, can’t remember where) that the hard drive is a very much cherry picked analogy. Substitute it with DRAM and you get the opposite result: information-theoretic “death” within minutes of power loss at room temperature, a few weeks or months at most at liquid nitrogen temperature.
Of course the human brain is neither a DRAM nor a hard drive. Rather than arguing from analogies I think it’s better to listen to actual domain experts: neurobiologists and cryobiologists.
Yep. I put up this hypothetical before: Drop an iPhone into liquid nitrogen, slice it up very thin. Now recover the icons for the first three entries in the address book.
At least in this case we would expect it to be possible for someone with enough money and time, with today’s technology. You should be able to recover the contents of the hard drive.
The domain-expert (Gutmann) says otherwise. At this stage, it’d really take an example of data recovery in practice, not just in “you can’t prove I’m wrong!” hypothetical.
(I’m assuming you don’t have an example to hand of having recovered data yourself in this manner.)
I read Gutmann as talking about what you should expect, security for the real world. I don’t see where they talk about someone willing to put in an unrealistically huge amount of effort. But maybe I missed that? Could you point me that way?
It is true that I can’t philosophically prove that arbitrary hypothetical technology that would achieve something currently nigh-equivalent to magic cannot possibly exist, nor can I philosophically prove the data isn’t there any more, yes. I can say there is no evidence for either, and expertise and evidence against both, and that “but you can’t prove it isn’t true!” isn’t a very good argument.
“For any modern PRML/EPRML drive, a few passes of random scrubbing is the best you can do … A good scrubbing with random data will do about as well as can be expected”
But what does that mean? Can someone with an STM and lots of patience still get the data back? Or is it just “gone for our purposes, with today’s technology”?
What you need to realize is that for 2 states to be distinguishable ever in principle, the states must be separated by an energy barrier taller than thermal fluctuations. Else the thermal noise is going to overwrite it randomly a zillion times a second.
The other issue is that the closer are the states the less metabolic energy you’ll need to switch between them. Which makes something like neurons (evolved over a very long time) settle on an optimum where there’s no room for some weak residuals recoverable with some future technology that got more sensitive probes.
I.e. if the cryo-protectants happen to reset some bits, that information is gone. You have to hope that cryo-protectants do not actually reset anything, i.e. that nothing is forced from multiple states to one state.
edit: another issue. Individual ion channels, gap junctions, etc etc. combine more-or-less additively into final electrical properties of the neuron. When you need to know the value of a sum a+b+c+d+e , losing even a single variable of the sum introduces massive uncertainty in the result. It would’ve been a lot easier if those properties mirrored each other, like a=b=c=d=e , then we’d only need to preserve at least one, but as they combine additively, we need to not lose a single one.
As I note below, if you really want to hold on to this particular example for analogical purposes, it’s at a stage where “you can’t prove it’s false!” isn’t really adequate and you’d need to produce an example of recovering data in practice, not just hypothetically.
Eliezer’s hard drive comparison is actually wrong. As I commented on Timeless Identity, Peter Gutmann, who wrote the original list of steps to securely erase a disk, is particularly annoyed that it has taken on the status of a voodoo ritual. “For any modern PRML/EPRML drive, a few passes of random scrubbing is the best you can do. As the paper says, “A good scrubbing with random data will do about as well as can be expected”. This was true in 1996, and is still true now.”
This isn’t directly relevant to the question of memory in a brain—but it wasn’t then either, because it just isn’t a very apposite analogy to use in thinking about this question.
I’ve also commented (not in the original thread, can’t remember where) that the hard drive is a very much cherry picked analogy. Substitute it with DRAM and you get the opposite result: information-theoretic “death” within minutes of power loss at room temperature, a few weeks or months at most at liquid nitrogen temperature.
Of course the human brain is neither a DRAM nor a hard drive. Rather than arguing from analogies I think it’s better to listen to actual domain experts: neurobiologists and cryobiologists.
Yep. I put up this hypothetical before: Drop an iPhone into liquid nitrogen, slice it up very thin. Now recover the icons for the first three entries in the address book.
At least in this case we would expect it to be possible for someone with enough money and time, with today’s technology. You should be able to recover the contents of the hard drive.
The domain-expert (Gutmann) says otherwise. At this stage, it’d really take an example of data recovery in practice, not just in “you can’t prove I’m wrong!” hypothetical.
(I’m assuming you don’t have an example to hand of having recovered data yourself in this manner.)
I read Gutmann as talking about what you should expect, security for the real world. I don’t see where they talk about someone willing to put in an unrealistically huge amount of effort. But maybe I missed that? Could you point me that way?
It is true that I can’t philosophically prove that arbitrary hypothetical technology that would achieve something currently nigh-equivalent to magic cannot possibly exist, nor can I philosophically prove the data isn’t there any more, yes. I can say there is no evidence for either, and expertise and evidence against both, and that “but you can’t prove it isn’t true!” isn’t a very good argument.
“For any modern PRML/EPRML drive, a few passes of random scrubbing is the best you can do … A good scrubbing with random data will do about as well as can be expected”
But what does that mean? Can someone with an STM and lots of patience still get the data back? Or is it just “gone for our purposes, with today’s technology”?
What you need to realize is that for 2 states to be distinguishable ever in principle, the states must be separated by an energy barrier taller than thermal fluctuations. Else the thermal noise is going to overwrite it randomly a zillion times a second.
The other issue is that the closer are the states the less metabolic energy you’ll need to switch between them. Which makes something like neurons (evolved over a very long time) settle on an optimum where there’s no room for some weak residuals recoverable with some future technology that got more sensitive probes.
I.e. if the cryo-protectants happen to reset some bits, that information is gone. You have to hope that cryo-protectants do not actually reset anything, i.e. that nothing is forced from multiple states to one state.
edit: another issue. Individual ion channels, gap junctions, etc etc. combine more-or-less additively into final electrical properties of the neuron. When you need to know the value of a sum a+b+c+d+e , losing even a single variable of the sum introduces massive uncertainty in the result. It would’ve been a lot easier if those properties mirrored each other, like a=b=c=d=e , then we’d only need to preserve at least one, but as they combine additively, we need to not lose a single one.
As I note below, if you really want to hold on to this particular example for analogical purposes, it’s at a stage where “you can’t prove it’s false!” isn’t really adequate and you’d need to produce an example of recovering data in practice, not just hypothetically.