[ExI] Lethal future was Watson on NOVA

Kelly Anderson kellycoinguy at gmail.com
Tue Feb 22 21:01:36 UTC 2011

On Tue, Feb 22, 2011 at 7:20 AM, Anders Sandberg <anders at aleph.se> wrote:
> Kelly Anderson wrote:
> The real issue is how much computation you need to replace brains and how
> much this has to dissipate. I have made some estimates that the likely range
> for brain emulation is 10^22 to 10^25 flops.

I suspect that in the very long term, some super intelligence will
figure out how to optimize the computational activity of the brain.
Nature has done a good job of it, but I suspect it can be improved
upon. So brain emulation may not be the ultimate goal, but rather
advanced computation that doesn't tax the brain so much. For example,
for many purposes, you might not need a visual cortex at all, or at
least not a fully functional one. Vision processing is a huge
proportion of the brain's capacity, is it not?

> Right now the Roadrunner does
> 376 Mflops/W, so we are *far* away. But the Darpa exascale study suggests we
> can do 10^12 flops per watt using extrapolated but not blue sky technology -
> a lot of current computation is very wasteful, and it is just recently heat
> dissipation has become a towering problem. Quantum dot cellular automata
> could give 10^19 flops per watt, putting the energy needs at 200-2000 watts
> per brain.
> http://netalive.startlogic.com/debenedictis.org/erik/Publications-2005/Reversible-logic-for-supercomputing-p391-debenedictis.pdf
> As I noted in my essay on this,
> http://www.aleph.se/andart/archives/2009/03/a_really_green_and_sustainable_humanity.html
> while this energy demand is higher than the biological brain it can be
> supplied more efficiently than growing organisms, harvesting them, possibly
> passing them through other animals, and then digesting them. Even this kind
> of not-Drexlerian nanotech computing would be very green.

Very interesting paper. Thank you for sharing those thoughts.

> Estimating the ultimate limits is hard, since we do not know how many
> dissipative calculations we need. Assuming one irreversible operation every
> millisecond at every synapse leads to 10^17 dissipating operations per
> second and an energy dissipation of 3*10^-6 watts per degree (colder
> computers are more efficient). So even here nanowatts is going to be tough
> (cooling below a few Kelvin is expensive), but less than a milliwatt per
> brain seems entirely feasible using LN- if we have reversible computers with
> little need for error correction.
>>> Reversible logic is slow, and it's not perfectly reversible.
> Not necessarily, just a lot of the current proof-of-concept designs. I
> expect that once we actually start working on it seriously we are going to
> optimize it quite a lot, including how to get the error correction (which
> dissipates) done in a clean fashion. It wouldn't surprise me if there was a
> practical tradeoff between speed and dissipation, though (all those quantum
> limits to computation involve energy, and fast changes do involve high
> wattages that are hard to keep dissipationless).
>> An interesting question to be answered is what is the most limiting
>> factor? Is it matter out of which to build intelligence? Is it energy
>> to power it? Time to run it? Or space to house it? Or is there some
>> other limiting factor? I think it will take a while for the
>> exponential growth to stop, but it must eventually stop. I'm just not
>> sure which of the above is the most limiting factor. Only time and
>> technology will tell. I'm not sure we can even guess at this point
>> what the most limiting factor will be.
> In the really long run you cannot get more mass than around 10^52 kg, due to
> the accelerated expansion of the universe. And there are time limits due to
> proton decay and quantum noise. But long before that lightspeed lags will
> make it hard to maintain cohesive thinking systems when the communications
> delays become much longer than the local processing cycles.

Even light speed may prove not to be a barrier in the sense that some
of the small loop time travel of information may make some of that go
away. The future isn't limitless, but it is WAY out there by any

> A lot of the limits depend on what you *want* minds to do. Experiencing
> pleasure doesn't require long-range communications or even much storage
> space, while having the smartest possible mind requires a lot of
> communications and resources.

What I would like to do is have a conversation with every other living
human being all at the same time, perhaps more than one conversation
with very interesting people... :-)

Thank goodness that we'll eventually figure out fusion. :-)


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