
I don't know, Timmy, being God is a big responsibility - negativity
http://qntm.org/responsibility
======
pserwylo
This was a very well written discourse on the existence of different
universes, and a bit of an intuition about how to think about them.

It reminds me a lot (though it is quite different) of "Flatland: A Romance of
Many Dimensions" [0]. This book gave me the best intuition yet about what it
would be like to experience a fourth spatial dimension.

Having said that, I still don't quite know what to think about it. I
definitely don't have a mental picture of what it would be like. All I know is
that when I was reading the book, I had a part of my brain clicking along,
which _felt_ like it understood what it is to experience an additional spatial
dimension. Yet there is still very little actual comprehension going on in
there.

[A bit of a spoiler alert follows]

It starts by explaining in meticulous detail what it is like to live in and
experience fictional 2D world instead of the 3D one we are used to.

Then, the main character transcends into a 1D world. The book explains to the
2D inhabitant what it is like to live in a 1D world. Explaining this to the 2D
inhabitant is the same as explaining the 2D world to us (and our 3D world).

Finally, the character moves up to a 3D world, which they cannot comprehend.
However the explanations which are given to the character are quite intuitive
and satisfying, and help to explain what it might be like for us to move up
one dimension and experience it.

[0] -
[https://en.wikipedia.org/wiki/Flatland](https://en.wikipedia.org/wiki/Flatland)

p.s. The book is also a hilarious parody on victorian era attitudes towards
women.

~~~
afatc
There's a 5min video on youtube by TED-Ed that sums up the Flatland topic. Is
really good.

[https://www.youtube.com/watch?v=C6kn6nXMWF0](https://www.youtube.com/watch?v=C6kn6nXMWF0)

------
achille
Read this in the past and there's a few things that bother me

* It's impossible to simulate a universe of our current resolution, because it would take more matter than the original universe.

* You can't just simulate 'observable areas'. Everything needs to be simulated.

* An infinite loop does not end, even in an infinitely powerful computer

* A fun calculation from the ZFS folks: To fully populate a 128bit filesystem (ie permute all combinations) you a lot of energy. So much energy you could boil the world's oceans, See:

* [1] Physical Limits of Computation: [http://arxiv.org/pdf/quant-ph/9908043.pdf](http://arxiv.org/pdf/quant-ph/9908043.pdf)

* [2] [https://blogs.oracle.com/dcb/entry/zfs_boils_the_ocean_consu...](https://blogs.oracle.com/dcb/entry/zfs_boils_the_ocean_consumes)

~~~
wreegab
> You can't just simulate 'observable areas'. Everything needs to be
> simulated.

I can't make sense of this. Whatever is outside the causality sphere is by
definition irrelevant.

~~~
chiph
At what point do objects & events outside the causality sphere stop
influencing things inside it?

~~~
delluminatus
Immediately, by definition. By causality sphere he means light cone [0]. If
you want to simulate an entity, you only need to simulate the entity and the
contents of its light cone. Anything outside the cone could not have a causal
impact on the entity without FTL travel.

Of course, an entity's light cone is still likely to be quite large,
especially if your simulated universe is old.

[0]:
[https://en.wikipedia.org/wiki/Light_cone](https://en.wikipedia.org/wiki/Light_cone)

~~~
haldean
Except you have to have been simulating outside the light cone so that, once
the light cone expands to include that space you know its state. So in
reality, if you're interested in location V at time t, you have to simulate
everything that will end up within the sphere centered at V at time t, not
just whatever is in the sphere instantaneously.

~~~
delluminatus
Yes, which is why the light cone is actually described as a 4D object that
exists in spacetime, not a 3D sphere.

Some back of the envelope calculation indicates that the spacetime "volume" of
the light cone of an object is 1/8th of the spacetime volume of the universe
up to that point. So using the light cone would net you an 8x speedup over a
brute-force Universe render. Nothing to write home about if you have infinite
computing power.

------
wfn
* simulation, consciousness, cellular automata, artificial life: [https://en.wikipedia.org/wiki/Permutation_City](https://en.wikipedia.org/wiki/Permutation_City) (check [http://libgen.org/](http://libgen.org/) for preview/pdf)

* more of sam's great stuff: [http://qntm.org/structure](http://qntm.org/structure) and [http://qntm.org/ra](http://qntm.org/ra) (ongoing)

~~~
andrewflnr
I just want to second the recommendations for Ra and Fine Structure. Fine
Structure is older and not as polished, but still a lot of fun and fairly well
executed. Ra is better. I enjoyed mood of the authors other stories too.

I first found this site when someone linked to Fine Structure here on HN. And
so it goes...

~~~
bashinator
It's funny, I first found that site many many years ago, when I did a web
search (might not even have been Google) for "how to destroy the Earth".

~~~
wfn
His Earth Destruction article[1] is pretty well known indeed!

iirc I first found the site via Everything2[2], a curious place where people
do writeups about pretty much everything (from short technical articles to
poetry.) I stumbled upon what looked like one of those diary entries (didn't
see the 'fiction' label) by some 'sam512'[3], and was confused when giant
robots and aliens suddenly appeared.

[1]: [http://qntm.org/destroy](http://qntm.org/destroy)

[2]: [http://everything2.com/](http://everything2.com/)

[3]:
[http://everything2.com/user/sam512/writeups/March+9%252C+200...](http://everything2.com/user/sam512/writeups/March+9%252C+2003)

------
nullc
It bothers me that this uses "quantum computing" since it plays into common,
frustrating, misapprehensions of what quantum computing is even theorized to
do.

They could at least call it a hyper-computer or acausual timeloop processor or
something.

~~~
justinpombrio
I know. I loved the story, but twitched every time it said "quantum".

~~~
lazugod
Even the domain is qntm.

------
geuis
Yes, I'm late. So what. People miss the fundamental point.

The characters clearly state that since their level of emulation is
approaching infinity, anything they do to their child universes will simply be
reflections of the parent simulations.

Look at it this way. You rewind to 1942. You're going to kill Hitler. But your
universe simulation is so in tune to the parent universe they're already doing
the same thing. What you interprets as free will is the averaged responses of
all parent universes. At some point in the simulation universe 2 billion plus
above you someone actually has an original though to kill Hitler. This is
simply re-emulated endless times.

There are no original thoughts in this view of the universe.

~~~
ordinary
_But your universe simulation is so in tune to the parent universe they 're
already doing the same thing. What you interprets as free will is the averaged
responses of all parent universes._

Not averaged.

For example, the chain of universes may follow an alternating sequence: Mary
in universe N kills Hitler in universe N-1 (one layer down). Suppose that this
murder has the unfortunate side effect of preventing the birth of the Mary in
that universe. The Hitler in universe N-2 therefore survives until 1945,
allowing the Mary in that universe to kill Hitler in universe N-3. Ad
infinitum.

What we're dealing with here is stability. The average Hitler is half-dead and
the average Mary half-born. The stable Hitler is dead half the time (in all
odd universes); the stable Mary alive half the time (in all even universes).

In fact, even stability is probably not the correct term. Let's broaden our
scope. The Hitler example is just one cycle, of length 2. But there may be
many cycles, of arbitrary length, from 2 to 3 or 10 or a million universes
long. These cycles that interact will almost certainly do so chaotically. The
odds that stability will occur is remote.

------
simias
It's very cool, I'm only a bit disappointed that the author did not consider
what would happen if they tried to run the simulation ahead of them to see the
future. What would happen then? All kinds of paradoxes arise.

~~~
ambrop7
Assuming that Timmy and Diane are simulating a universe identical to their
own, they will not succeed at changing their future relative to their
simulation (almost by definition).

One solution to this is that they never have the idea to try that in the first
place. So one could argue the author _has_ considered it ;)

------
TrainedMonkey
I would post obligatory link of someone calculating expected number of
universes on top of ours based on planks distance and something else, but I
can't find it.

Instead have this simulation argument here: [http://www.simulation-
argument.com/](http://www.simulation-argument.com/)

~~~
negativity
Are you referring to the SMBC comic?

[http://www.smbc-comics.com/?id=2535](http://www.smbc-comics.com/?id=2535)

~~~
shurcooL
"Like maybe a minimum temperature or a maximum speed..."

Max speed, sure. But minimum temperature? It's zero (Kelvin). Of course
there's gonna be a minimum, this doesn't belong here.

~~~
DrStalker
There are temperatures lower than zero kelvin.
[http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/neg...](http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/neg_temperature.html)
for a technical description, [http://www.nature.com/news/quantum-gas-goes-
below-absolute-z...](http://www.nature.com/news/quantum-gas-goes-below-
absolute-zero-1.12146) for a more readable article.

~~~
cperciva
_There are temperatures lower than zero kelvin._

There are negative temperatures, but I wouldn't characterize them as being
"lower than zero kelvin". It would be more accurate to say that negative
temperatures are "higher than $\infty$ kelvin".

~~~
TrainedMonkey
Value that reaches maximum possible energy goes negative? Sounds suspiciously
like integer overflow...

~~~
cperciva
_Value that reaches maximum possible energy goes negative?_

Maximum temperature, not maximum energy. Negative temperatures are even higher
energies.

The real issue here is that T is a dumb unit -- 1/T makes a lot more sense,
and when you look at it that way, the trend is just "higher energies have
lower 1/T" and passing through zero is entirely unremarkable.

------
danielweber
Instead of changing things one universe below, change things 3 universes below
you.

Or change the universe below you to change things 2 universes below it to
change things in the universe 4 layers underneath that.

~~~
Retric
What's more interesting IMO is they assumed there the first and only group to
ever run that simulation for all of time. Realistically your probably running
on someone else simulation which would end up diverging as they pocked at some
other part of reality. In other words you may or may not be a top level
simulation if changes don't get reflected in your world, but if your not a top
level simulation you would want to find out who's simulating you and try
simply to find out what changes to expect in your world.

You can then setup several simulations to try and see if your simulating
yourself just with odd initial starting conditions. Which get's into orders of
infinity and countable numbers as some other groups may have the same idea.

------
bitwize
"What the hell am I looking at?"

"Now, you're looking at now, sir. What's happening now, is happening, now."

"What happened to then?"

"We passed it."

"When?"

"Just now."

"When will then be now?"

"Soon!"

------
bo1024
There's a technical solution concept in game theory that mirrors Diane's
reasoning here. I wish I could remember the name of the solution concept
offhand, but the idea is that, even though your own decision won't affect the
decision anyone else makes, you still make the "altruistic" decision,
reasoning that the other people involved will use the same reasoning and come
to the same conclusion.

The paradox, of course, is that, having come to that conclusion, you could
just choose to make the "non-altruistic" decision. Everyone else has already
decided what they're going to do, so you won't change that. Except the
solution concept stipulates that they reason exactly as you do, so if you make
this decision, so will they.

~~~
arjie
Super rationality is a reasoning approach in game theory. Probably what you're
talking about.

~~~
gwern
[http://gwern.net/docs/1985-hofstadter](http://gwern.net/docs/1985-hofstadter)

------
ck2
So if this is a simulation, is talking to yourself in your head or out loud, a
program being self-reflective? That's quite a program.

~~~
013
[https://en.wikipedia.org/wiki/Self-
awareness](https://en.wikipedia.org/wiki/Self-awareness)

------
mrmaddog
Great story! One thing that stuck out to me—if you had an infinitely powerful
computer, the "coding" aspect of it should take no time at all. All you have
to do is come up with a description language to say what you want•, and b)
seed rules for a genetic programming language, and then throw it at your
infinitely powerful computer. You'll get a working program instantly.

• This might still be significantly difficult. If only you had a simulated
version of yourself that you could use as a control subject so the computer
could test whether or not the generated program met your expectations...

~~~
bad_user
Also, changing outcomes in this simulated universe, as in acts of God that
defy its physical laws, would be extremely difficult without messing it up, so
even if the developer would want to, say, cure all suffering, it would abstain
from doing so. And the developer could save the consciousness of people that
he likes and maybe restore them somewhere else, like in another universe, with
a different set of laws (e.g. heaven).

------
Derpdiherp
This gives me an interesting thought, in the story all lower levels of the
simulation are identical copies from the top level, in every way. The first
time that they create the black ball the top level universe will diverge from
the rest (they will look behind and there will be no ball) at this point there
will be no more perfect copies of the original universe.

Also I wonder about the ethical connotations of turning off the machine as was
suggested at the end. At what point is life "life". If the simulated beings
are truly perfect, would turning it off be the largest genocide ever
committed?

------
Zikes
If Diane created a complete simulation and then separately created a program
to observe that simulation at certain points in time, then doesn't it follow
that the entire universe from Big Bang to Big Crunch was already calculated
and executed?

In that case, turning the simulation off would do nothing from the perspective
of the people within it, because every simulation has already been played out
to completion. All they would be turning off is the ability to observe what
the simulation looked like at specific points in time.

------
JackFr
The problem I have with this story (and the simulation argument in general)
are the dubious assumptions that simulation within which we exist, 1) is
manifested in a physical reality which is functionally identical our own; and,
2) created by autonomous beings who are fundamentally like us in all important
respects. More likely we would merely be the flashing cells of automata to a
higher order simulation builder.

------
INTPenis
>"Can you wind the clock backwards at all?"

>"Ah, no. Ask me again on Monday."

Really? I'm just a layman but if it's a simulation, like game of life, then
logic tells me that they should also be able to rewind the simulation by
backstepping. Either that, or she just created magic.

~~~
scrumper
It's worth pointing out as an aside that you actually can't rewind the
(Conway) game of life: the current state does not contain enough information
to recreate the previous state. The reason is that many states can arise as a
result of multiple possible precursor states.

Diane's simulation is perhaps similar: a gigantically complex system of
cellular automata.

------
_greim_
So what's the difference between specifying a universe-simulating algorithm,
and specifying its initial conditions, versus actually running it? Since the
entire history is somehow implied in that specification, don't all those
people in some sense exist?

~~~
nitrogen
It's an interesting philosophical question. I would prefer to define existence
as beginning when the computation of those particular molecules first occurs.

~~~
TeMPOraL
> _I would prefer to define existence as beginning when the computation of
> those particular molecules first occurs._

The structure of this argument somehow reminds me of abortion-related
topics...

Anyway, there's a nice article touching this issue:
[http://lesswrong.com/lw/uk/beyond_the_reach_of_god/](http://lesswrong.com/lw/uk/beyond_the_reach_of_god/).

------
zamalek
A question (to which there is an answer), how would you find out how far down
the line you are?

Answer: look behind you, place the value you see plus one into the next
universe.

~~~
TophWells
The residents of the googoolplexth universe would like to know what they're
supposed to do when the number is too big to fit on the screen of the people
below them.

------
etanazir
Auto-cognition occurs in states of coherence; thus as far as we are concerned
the incoherent universe never exists.

------
auggierose
About to hit the mass forward button.

------
teddyh
I dunno about the final twist. _I’d_ turn it off. The top level would still be
fine.

------
jacquesm
Reminds me of 'the Planiverse' by AK Dewdney.

------
twobits
"There is a feedback loop going on. Each universe affects the next one subtly
differently. But somewhere down the line the whole thing simply has to
approach a point of stability"

Why would each universe affect the next one (subtly) differently?

------
hayksaakian
This was highly confusing without context.

------
ben0x539
Oh, and just because you have a infinitely powerful quantum computer
simulating infinitely many recursive universes with their own infinitely
powerful quantum computers, correlation != causation doesn't apply anymore?

~~~
shurcooL
If you have an infinitely powerful computer, does that also imply that you
necessarily have infinite storage?

~~~
JoshTriplett
Infinite CPU capability does not automatically imply infinite storage, but it
_does_ imply that you can compress any storage to an information-theoretic
minimum size, by writing a search for an arbitrary program to generate the
same data.

And that's some absurdly good compression, given the universe simulator
assumed in the story: anything that will ever occur as a state of the universe
can be compressed to a set of space-time coordinates and an extraction
algorithm.

With some additional assumptions about the nature of the pseudo-causal loop
demonstrated in the story, that compression can also include any arbitrary
search parameters you can conceive of, without you having to express them as a
program: just search for the data that will be on your hard drive in the
future after having executed the search you're currently thinking of.

