
Bremermann's limit - monort
https://en.wikipedia.org/wiki/Bremermann%27s_limit
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sevenless
This is an entertaining read:

Ultimate Limits to Computation [http://arxiv.org/abs/quant-
ph/9908043](http://arxiv.org/abs/quant-ph/9908043)

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danieltillett
It is always worth keeping Bremermann's limit in mind when anyone talks about
general AI being impossible. We are so far from it (as humans) that to even
have an opinion about what is possible seems silly.

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ci5er
Intelligence and Bremermann's limit are pretty unrelated. Most people have
what they consider to be intelligence and self-awareness with a system that
uses a lot fewer atoms than are contained in this universe. The worry, with
non-human intelligences, maybe trying to bootstrap themselves to be able to
take advantage of this universe's computational capacity, is with what a
person once apocryphally said: "The machine does not love or hate you, but you
are made of atoms it can use for other things.”

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gjm11
It's not apocryphal; you can find the original on page 27 of this:
[https://intelligence.org/files/AIPosNegFactor.pdf](https://intelligence.org/files/AIPosNegFactor.pdf)

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ak39
This sort of thing fascinates me.

If the universe is a simulation, is this not to be understood as the processor
clock speed?

(I've not read much of Nick Bostrom's work nor do I claim to know much about
reasoning that the universe is in fact a computer simulation.)

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joshmarlow
I don't think so; the passage of 'time' measured in the simulation could be
quite a bit faster/slower than on the hardware underlying the simulation (I
would assume quite a bit 'slower').

So if we were in a simulation, I'm skeptical that we could guess much about
the properties of the 'host' system.

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ak39
But we can determine the maximum speed of causality, can't we?

I was watching a (Bostrom, I think ?) presentation where the vocabulary used
to explain Einstein's "c" (the speed of light) included words like "maximum
speed of causality". That blew my mind. Because light moves as fast as it
theoretically can (many Newtonians believed there was no ubound to the speed
of light), light speed still cannot breach the absolute limit of 299 792 458
m/s. That speed limit is embedded directly into the action-reaction
architecture of our universe.

(Anyway, didn't mean to hijack)

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joshmarlow
That's a super interesting point actually. I'd never thought of the "maxium
speed of causality". Thanks for sharing!

We could determine the maximum speed within our terms, but again that doesn't
necessarily translate to how things happen in the underlying substrate.

Thought experiment: let's imagine we create our own simulated environment and
put a sentient AI into it (which is implemented in the physics of that
environment). The AI gets curious and does some experiments and figures out
the maximum speed that causality can propagate in it's environment. Suppose
the speed of light in the simulation is as fast as the speed of light in our
environment. So something takes 1 in the simulation and 1 second in ours.
Cool. Now, suppose you and I as the developers put in a 'sleep' call into the
event loop or whatever so that the simulation runs at 1/10 the speed of real
time. Light in the simulation is now 10 times slower than it was by our clock
time. Now the code operates _considerably_ slower - but any entity in the code
wouldn't perceive the slowdown because it has slowed down too in the same way.

Same thing - any slowdown in the simulation would not be noticeable to us
because it's also a slowdown in _us_.

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jere
I've always found the idea of the universe being a simulation rather silly.
There are estimated to be 10^80 particles in the observable universe.

Assuming our universe is being simulated on an earth sized computer (this is
mind bogglingly ridiculous to me) _and_ that the simulation meets Bremermann's
limit (also ridiculous, since we're 40 orders of magnitude away according to
this [http://arxiv.org/pdf/quant-ph/9908043v3.pdf](http://arxiv.org/pdf/quant-
ph/9908043v3.pdf)), then it would take on the order of _a whole earth day_ to
simulate a single time step.

Of course, perhaps the host universe doesn't have the same limitations. Such
speculation seems pointless. Maybe solipsism is true. Maybe the simulation
runs on magical fairy dust.

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sevenless
[https://xkcd.com/505/](https://xkcd.com/505/)

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voidlogic
Does Bremermann's limit account for quantum computers?

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Pitarou
No, it doesn't. A quantum computer would make very short work of a 512 bit
key.

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toth
That is kind of misleading statement. What quantum computers change is not how
many operations per second you could do, but how many operations you need to
factor large numbers.

I believe that Bremermann's limit should also apply to quantum computers, but
you are right in that example given for breaking cryptography is way off if
you allow quantum computers.

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NegativeK
We're veering off topic, but quantum computing algorithms extend beyond just
Shor's algorithm.

