[ExI] More Fermi Paradox

[Eugen Leitl]

On Wed, May 15, 2013 at 11:52:28AM +0100, Anders Sandberg wrote:

> You misunderstood me. I was just talking about the total amount of
> stuff to colonize and whether it could form cohesive computational

The total colonizable area is limited by how soon you start and
how hard you travel. For us that would be something like
16+ GYrs, which is not too bad.

> structures, not the refresh rate. Either of the above approaches

Cohesiveness would be relativistically limited, and not contraining
the underlying processes. So you'd have a hierarchy, which can
be arbitrarily (within pingpong latencies across the traversable
universe) slow at the top, and as fast as it's possible at the bottom.
(i.e. these theoretical 100 PHz refresh rates for classical computers).

> benefit from high refresh rates, although the vast mind will likely
> have at least some serial components causing an Amdahl's law
> slowdown.

I disagree. There are no serial sections in biology, everything
is asynchronous at the bottom. The top processes may appear
serial (just as we're communicatinig now by a serial stream
of ASCII), but that does not translate down weell.
 
> On the big scales the constraints are (1) if you can accept parts of
> your domain losing contact forever (due to accelerating expansion

You're shedding skin cells, and not noticing it much, so
I don't see how shedding periphery (which is very slow initially,
and only picks up in earnest in the last years and months
of the universe) is going to be a problem.

> 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.

Yep.
 
> 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

Yeah, these 100 PHz refresh rate are indeed quite far removed from
what you could operate in a classical computation. I also don't
have the impression that spintronics is particularly fast, rather
the opposite.

> 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

Reversible computation should be slow, and might be too slow for
practical purposes.

> 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.

I'm not counting on nonclassical computation. I expect there won't
be a free lunch anywhere.
 
> 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.

I wonder where the 4 PByte @ >EPflops realtime human equivalent is
coming from. I expect some severe number creep there.