[ExI] More Fermi Paradox
Anders Sandberg
anders at aleph.se
Wed May 15 10:52:28 UTC 2013
On 2013-05-15 10:19, Eugen Leitl wrote:
> On Wed, May 15, 2013 at 10:12:36AM +0100, Anders Sandberg wrote:
>
>> It all depends on what the ultimate goal is. If it is
>> experience-moments or pleasure, then spread far and wide and convert
>> everything to computronium or hedonium. If the goal requires a
>> cohesive big mind for a long time, then you only need a supercluster
> I don't see why you can't have GYr scale coherent plans with
> ~ps..~fs local refresh rates.
You misunderstood me. I was just talking about the total amount of stuff
to colonize and whether it could form cohesive computational structures,
not the refresh rate. Either of the above approaches benefit from high
refresh rates, although the vast mind will likely have at least some
serial components causing an Amdahl's law slowdown.
On the big scales the constraints are (1) if you can accept parts of
your domain losing contact forever (due to accelerating expansion moving
non-bound systems beyond the horizon), (2) how much stuff you can reach
(depends on speed and start time), (3) your trade-off between update
speed, memory storage and energy usage.
If you have M units of mass divided into memory cells of mass m, the
minimal energy dissipation per second due to error correction scales as
kTln(2)(M/m)exp(-qm), where q is some constant linked to the
tunneling/error probability. For fast dissipation getting rid of the
heat is a big problem and likely limiting things; using Wei Dai-style
black hole cooling or radiating it towards the cosmological horizon has
a limited thermal emission ability. For slow dissipation your overall
mass M will decline as an exponential with constant kTln(2)exp(-qm)/mc^2
- big m allows you to last long, but you get few bits. T also declines
towards an asymptote due to horizon radiation, so waiting is rational
only up to some time.
Note that this assumes all computations to be reversible. I recently
checked quantum computation and error correction, and it is pretty
awesome... but you still need to erase ancilla bits once they have
become error tainted. Using quantum computation allows you to get a lot
of computation done in few steps, but m will be very low so you will
have to pay a lot for it.
In a universe where little but your activities are going on external
time does not matter much. So running things slowly is OK if you get
more ops. But before that a spoiler civilization might want to do their
short-term projects that use "hot" low-m, high T very wasteful
computation; there is some interesting game theory here about how
different goals might try to pre-empt each other.
> Speaking about clusters:
> https://docs.google.com/file/d/0B83UyWf1s-CdZnFoS2RiU2lJbEU/edit?usp=drive_web
> Pony: not yours. At least not by 2020. Little novelty there for anyone
> who's been paying attention, but this is mainstream now.
In fact, for being a pessimistic lecture it is pretty optimistic. Maybe
we won't get ponies, but cats.
--
Dr Anders Sandberg
Future of Humanity Institute
Oxford Martin School
Oxford University
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