
Constraints on the Universe as a Numerical Simulation (2012) - aq3cn
https://arxiv.org/abs/1210.1847
======
jackcosgrove
Even if we live inside a simulation inside a simulation inside a simulation,
ultimately there is a base reality that influences the design of the
simulations contained within it, and can impinge upon the simulations at any
time. Infinite regression doesn't work here - using the term "simulation"
implies some special pleading when moving from the outermost simulation to the
base reality. If you want to regress forever, then there is no qualitative
difference between layers of reality and the word "simulation" is meaningless.

We live in the base reality. All a simulation could do is obscure complexity.

Interestingly this isn't a new idea. The gnostics of the first two centuries
BCE had a theology of this, in which a flawed world, in which humans lived,
was created by an imperfect creator called the demiurge. There was a perfect
realm beyond this world with an intercessor named Sophia (wisdom) who would
rescue us from our flawed world, the simulation created by the demiurge.

~~~
logicallee
I disagree with you that:

>and can impinge upon the simulations at any time

A simulation could just be some states. Consider the rule, double and subtract
one to get to the next world-state, over the integers, and start the world
with the state 1. So the next state is 1. The one after is also 1. The one
after is also 1. The universe is stuck in a static state.

As I, you, or a Python script is modeling this universe, where does the
outside universe "impinge" on it?

Then let's do a different universe, starting at 2. Then the next state is 3,
the state afrer is 5, the state after is 9, and so forth.

As you do this universe in your head, where does the outside universe
"impinge" on it?

There is a problem, however. All future states are well-defined in the
universe I've given even if nobody in our universe or any other is calculating
them.

It is trivially obvious that the human mind is an emergent property of its
neural firings (of the brain), and that replacing some part of it with a black
box that interacted with the rest would leave it with the same emergent
properties, even if this black box were modeling in a different medium.

The question is, if you can model the whole thing over a well-defined program
that did not require non pseudorandom entropy, then it would be similar (just
start with more complex data than 1 or 2, and more complicated rules than
double and subtract one) - so in order for these states to exist, would anyone
have to actually calculate it, or is it enough for these states to be
mathematically defined?

What I am saying is that it is a statistical certainty that within a thousand
years we can create a deterministic model of a brain in a VR, where the brain
reports consciousness. (this is 100.000% absolutely necessarily true and not
open to debate. The brain is a couple of pounds of stufd, with just a few
hundred billion neurons or fewer - I bet we could practically have the
hardware to model one today.)

Does this mean that that model already exists? (before anyone chose to
calculate it)?

This is similar to asking whether the quintillionth prime exists. Yes, of
course it exists.

Really? Even if nobody calculates it? Then what is to say that we might not
exist without anyone calculating us?

Perhaps the states of the universe, like the quintillionth prime, exist
without anyone calculating it. Perhaps there is no underlying reality at all,
just as there is not an underlying reality in which the quintillionth prime is
embedded.

~~~
breatheoften
Reminds me of a short story called Luminous by Greg Egan. In that story the
universe is a declarative system that does have a non-pseudo random component
to it -- with actual reality being an emergent phenomenon between this
declarative model and the entities within exploring that model by causing the
universe to imbue the mathematical objects implied by the universe with
specific reality by actually computing them, in so doing "expanding" the size
of the universe and introducing new effects from this expansion into the
evolution of the system ... in the story it turns out there are multiple
actors active at the edge of defining the universe -- and their actions can
actually influence the ability of other actors to continue in their
participation in the universe creation process ...

Edit: my attempt to elaborate on the idea from the story ... I don't know if I
can summarize the concept that well -- I think the framing within the story
for the plot is something along the lines of: 1\. Mathematical truth exists
2\. There is an existential difference between a mathematical truth and a
specific occurrence of the "pattern" described by that truth within the
physical material of the universe.

I think the eli5 example in the story is based on the integers. You have the
integers which are infinite, and you have an instantiated version of some
number n if you have an occurrence of n things in nature. The reality of n is
fundamentally different if you are in A universe with "n things" vs one with
only m things m<n.

I think that's the motivation for the concept -- and in the story a researcher
sets off to find scenarios where the universe had not yet "instantiated" one
of the "laws" that could be derived from mathematical reality -- and ends up
finding out that there is more than one possible way for the laws of "reality"
to expand ... -- with different implications on what laws might be discovered
in the future ...

~~~
logicallee
This is really, really interesting. As I don't have access to the book just
now, could you expand (by editing) your comment a little, your summary is very
dense. I realize you might not remember it all exactly but it's really
interesting to me.

EDIT: Thanks for the expansion! Fascinating and really interesting idea. The
idea, "There is an existential difference between a mathematical truth and a
specific occurrence of the 'pattern' described by that truth within the
physical material of the universe" is a fascinating one.

------
lossolo
I would be surprised if we are not living in simulation. Look at superposition
and function collapse in quantum physics, it's equivalent to what we are doing
in games today = do not render if player is not watching, save resources.
Think about it, look for example at GTA V, what we can achieve today and think
about how world looked like 100 years ago.

I imagine that in 1000 years from now, simulating world similar to ours will
not be a problem at all. Maybe not as complex because every level you go
deeper you have less resources at your disposal. Who knows which level deep we
are? Maybe we are simulation in simulation in simulation...

~~~
comicjk
This is a common misconception, but superposition has nothing to do with "do
not render if the player is not watching." As far as we know, every particle
in the universe is interacting with every other (with a light speed delay) and
thus "measuring" it (modifying and responding to its wavefunction) at all
times. In the two-slit experiment, for example, the wavefunction of a particle
moving through a slit interacts with the wavefunction of the particle used to
detect it, causing both wavefunctions to be more narrowly distributed in the
space around the slit. But before or after this interaction, the whole
wavefunction still needs to be simulated to produce the effects we see
experimentally. The wavefunction itself is the real thing being simulated, and
it's always "running."

You may be right that it will become easier to simulate worlds like ours, but
it will require innovations that make a quantum computer look like an etch-a-
sketch. The universe is really big and really detailed.

~~~
Vraxx
I see the distinction you're making (I think), but I still don't see how that
invalidates GP's analogy. Surely "running" a wavefunction is computationally
cheaper than re-evaluating the particle's characteristics at every universal
frame. Perhaps it's not so much about our own "watching" but rather "do not
calculate when irrelevant". My own analogy might be an online map frame like
google maps, where tiles outside the viewing box are not loaded. This is
because we can tell what needs to be calculated by the bounding box of the
viewer without needing all the other finer details. I see it more as a lazy
eval.

~~~
comicjk
The particle's characteristics ARE the wavefunction - or to say it another
way, the wavefunction is the only real characteristic a particle has.

When I run a quantum mechanics simulation at work, I might afterwards
calculate the particle positions or some other classical characteristic of the
system. But I need those characteristics only because I'm trying to get a
classical model of the system. The system itself, when it's running, doesn't
do any of that. It interacts wavefunction-to-wavefunction. As far as we know,
that's how the universe works.

~~~
wolfgke
> The particle's characteristics ARE the wavefunction - or to say it another
> way, the wavefunction is the only real characteristic a particle has.

As far as I know not in the De-Broglie-Bohm theory (but I'm not a physicist,
so correct me if I'm wrong):

>
> [https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory](https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory)

> [http://plato.stanford.edu/entries/qm-
> bohm/](http://plato.stanford.edu/entries/qm-bohm/)

> [http://plato.stanford.edu/entries/qm-
> decoherence/#PilWavThe](http://plato.stanford.edu/entries/qm-
> decoherence/#PilWavThe)

~~~
davorak
> As far as I know not in the De-Broglie-Bohm theory

As a physicist I am telling you should not conclude that the De-Broglie-Bohm
theory is tell you anything different than what comicjk said.

> The particle's characteristics ARE the wavefunction

This kind of statement is normally said to stress the fact that the best
evidence and experiments indicate quantum mechanics accurately describe the
physical world and even parts like superposition(single particle double slit
experiment, tunneling etc) that defy more classical intuitions.

De-Broglie-Bohm theory includes the same set of non-intuitive behaviors that
all valid interpretations of quantum mechanics have, in other words it is not
testable different from other interpretations.

~~~
wolfgke
> De-Broglie-Bohm theory includes the same set of non-intuitive behaviors that
> all valid interpretations of quantum mechanics have, in other words it is
> not testable different from other interpretations.

There exist opinions that disagree:

>
> [https://en.wikipedia.org/w/index.php?title=De_Broglie%E2%80%...](https://en.wikipedia.org/w/index.php?title=De_Broglie%E2%80%93Bohm_theory&oldid=740277352#Non-
> equivalence)

"In 2016, Pisin Chen and Hagen Kleinert argued that the Copenhagen
interpretation and the De Broglie–Bohm theory yield different results for the
ratio of peak intensities in the double-slit experiment. They concluded that
they are thus not mathematically equivalent."

>
> [http://www.ejtp.com/articles/ejtpv13i35p1.pdf](http://www.ejtp.com/articles/ejtpv13i35p1.pdf)

~~~
davorak
Thanks for the citation, I had not seen that recent paper(2016).

Pisin Chen and Hagen Kleinert say that De-Broglie-Bohm theory does not agree
with experimental results or the rest of quantum mechanics.

This is surprising since there evidence of this is from a 1979 paper, their
citation [15]

[15] C. Philippidis, C. Dewdney and B. J. Hiley, Il Nuovo Cimento 52B, 15
(1979)

can be found online(republished) at: [http://www.pbx-
brasil.com/FisQuan/Notas/Area01/semana041/pap...](http://www.pbx-
brasil.com/FisQuan/Notas/Area01/semana041/papers/QuantumInterferenceAndTheQuantumPotential.pdf)

I would want to do some additional research before agreeing with Pisin Chen
and Hagen Kleinert that the De-Broglie-Bohm theory has been experimentally
disproven.

Other then combining the existing research double checking the numerical
simulation and algorithms in [15] would be my approach.

Pisin Chen and Hagen Kleinert paper seems to lack such an examination which
would have made for a more conclusive argument.

------
astrodust
Keep in mind that if you wanted to create a simulated universe you can ensure
nobody ever finds out.

If someone does find out, you can simply fix the problem and revert to a point
in time just before the data leading to the discovery was captured.

Speaking academically, you might be playing with fire if you probe the outer
limits of the universe _and_ we are in a simulation run by some entity
concerned with keeping that a secret.

~~~
4ad
> you can simply fix the problem and revert to a point in time just before the
> data leading to the discovery was captured.

Only with classical computers, not quantum computers.

~~~
aswanson
Who's to say "real" computing, or "reality" at all, has to adhere to the laws
we observe within the simulation? That's like Luigi in Super Mario Brothers
saying you can't kick a turtle into a brick in the our world and not expect a
gold coin to pop up in front of our faces.

~~~
jblow
I wish most of the people who talk about the Simulation Argument understood
this.

There is not even a reason to believe that the "outer universe" has such
things as _space_ and _time_ or _information as we know it_ , and no way to
know what a "computation" might comprise in such a situation.

Maybe the situation is not that pessimal, and an outer universe is much like
ours, but to prefer that believe one would need evidence, of which we have
none.

~~~
monktastic1
Various eastern philosophies have a somewhat different solution to this whole
problem.

Consciousness -- as in the sheer fact of experience -- is itself the base
"reality," out of which everything is made. If you examine everything you're
calling "the universe," all you will ever discover is sights, sounds, thoughts
about sights and sounds, belief (or certainty) that those sights and sounds
are caused by something external, etc. What are all of those made of?
Consciousness, of course.

In this reality, "brains" are the entities that consciousness has dreamed up
to demonstrate correlations with conscious properties. In our reality, we
therefore say that "the brain causes consciousness."

If you investigate your experience closely, you'll discover that the
epiphanies "I exist," "I am conscious," "I am alive", "a world exists" all
point to the same ineffable "miracle" of existence, the one "substance" of
which all realities are made.

Upon hearing this, perhaps the mind thinks "just as there are realities that
exist without time and space, why can't there be some without consciousness?"
There's a very interesting answer to that question, but it won't come in the
form of thoughts.

Of course, there's no reason to believe any of that. On the other hand, as the
Buddha said, don't believe me....

------
mkstowegnv
IMHO as a biologist infused with awe of the natural world from observation and
reading, it is laughable that gods or computers could design or simulate the
infinite levels of mind numbing complexity and unimaginable patterns that
evolution has produced. But most people who are more focused on, and hungry
for, the order created by technology and society in general, find it easy -
with occasional cognitive dissonance, my favorite expression of which is the
poem "Design" by Robert Frost:

I found a dimpled spider, fat and white,

On a white heal-all, holding up a moth

Like a white piece of rigid satin cloth-

Assorted characters of death and blight

Mixed ready to begin the morning right,

Like the ingredients of a witches’ broth--

A snow-drop spider, a flower like a froth,

And dead wings carried like a paper kite.

What had that flower to do with being white,

The wayside blue and innocent heal-all?

What brought the kindred spider to that height,

Then steered the white moth thither in the night?

What but design of darkness to appall?--

If design govern in a thing so small.

~~~
smrtinsert
As a BS in bio as well I learned everything in biology arises from chemistry
which arises from physics which can be explained (mostly?) with math. If that
isn't abundantly clear on graduation your teachers did you a disservice.

You don't have to design anything, it should just show up if its an accurate
enough simulation.

~~~
mkstowegnv
You are assuming unlimited computational resources. At some point the computer
required is bigger than the universe and exceeds the limits of what our
current knowledge of physics and cosmology allows us to speculate about in any
kind of meaningful way. I actually believe that a computer with human level
intelligence and consciousness will be possible - but only because it won't
need to be as messy as real human minds. To paraphrase Hitchhikers Guide,
biology is messy. Really messy. You just won't believe how vastly, hugely,
mind-bogglingly messy it is.

~~~
notduncansmith
If the idea is that our universe is a simulation then its state is, by
definition, represented by a finite subset of the state of the simulating
universe. In other words, yes, it would be a computer bigger than our
universe, in the same way we simulate a universe smaller than ours on one of
our computers today.

~~~
mkstowegnv
It's turtles all the way up. Or in this case It's Turing Machines all the way
up.

------
aq3cn
For those, who want to read it in lay man's language, they can go through
following articles:

[https://www.technologyreview.com/s/429561/the-measurement-
th...](https://www.technologyreview.com/s/429561/the-measurement-that-would-
reveal-the-universe-as-a-computer-simulation/)

[http://www.huffingtonpost.in/entry/physicists-may-have-
evide...](http://www.huffingtonpost.in/entry/physicists-may-have-
evide_n_1957777)

~~~
yodon
The tech review summary seems to be saying this super intelligent universe-
simulating computer builder doesn't know about Bresenham's line drawing
algorithm [0] and as a result it can only walk high energy particles along a
limited number of paths.

[0]
[https://en.m.wikipedia.org/wiki/Bresenham%27s_line_algorithm](https://en.m.wikipedia.org/wiki/Bresenham%27s_line_algorithm)

~~~
komali2
Possibly? I can see why one would want to assume that an entity that can
simulate a universe would be able to know more than the collective ability of
that simulation, but on the other hand, we simulate things and learn
unexpected results from our simulations. I think it's entirely feasible that a
simulation can generate _more_ knowledge, or _different_ knowledge, than
exists outside the simulation.

~~~
yodon
Certainly, but the idea that some hyper intelligent entity would develop the
tech to build a universe-scale finite element simulator without groking anti-
aliasing along the way is simply absurd. Bresenham's algorithm is a big deal
because it's essentially the first thing everyone needs to invent when they
start trying to render continuous processes on a discrete grid.

~~~
to3m
Bresenham's algorithm draws aliased lines.

------
AnimalMuppet
So we stopped believing that God created the universe, and us as part of it.
We believed only in science and natural processes. Following that through, we
started believing that we live in a computer simulation with, presumably, some
kind of programmer. That's pretty ironic.

~~~
code_sardaukar
The root distinction seems to be whether you prioritize reality or
abstractions.

If reality comes first, you might not even believe that there is a set of
universal mathematical laws governing nature (Feynman expresses this
viewpoint, and raises the possibility that no such laws exist here[0]). Edward
Nelson came up with similar ideas on the limits of abstractions in
mathematics, based on Christian philosophy [1].

[0]
[https://www.youtube.com/watch?v=QkhBcLk_8f0](https://www.youtube.com/watch?v=QkhBcLk_8f0)

[1]
[https://web.math.princeton.edu/~nelson/papers/warn.pdf](https://web.math.princeton.edu/~nelson/papers/warn.pdf)

------
CuriouslyC
It kind of irks me that they basically assume a cubic lattice. Nature does not
form cubic lattices, when nature forms a lattice (for example, in a foam) it
tends to form roughly dodecahedral cells (with coordination number 12). Given
this property, a space-time lattice would be very nearly isotropic.

~~~
aminorex
It kind of irks me that they basically assume 3+1- space-time.

~~~
raattgift
That's pretty natural since it is extremely hard to recover the inverse square
law (for gravitation and electromagnetism) from any configuration of
spacetime, assuming large dimensions (large compared to the Planck length).

Ehrenfest and Weyl showed this as early as 1920 and 1922, respectively.

3+1 is also baked into the Minkowski metric by the latter's definition, which
leads to the Poincaré group being the isometry group on local patches of
spacetime; the Poincaré group is a subgroup of the Standard Model, and is
extremely well tested in controlled, laboratory settings (and supported by an
abundance of observational evidence too).

Extra dimensions of spacetime have to be small compared to the Planck length
in order not to be obvious today. For all practical purposes, if such tiny
dimensions exist, we can safely omit them from effective theoretical
descriptions of everyday physics, just like we can ignore things like very
large extra dimensions where the smallest step one can take is much bigger
than the Hubble diameter.

------
zizzles
Should we perhaps hypothesize the motive of this simulation, if any? Death
seems to be a very important focal point: All living organisms are condemned
to their aging bodies, eventually begin decaying, then die. Death of the
universe is also inevitable, "Heat Death". Then there are other existential
issues our feeble brains have to deal with. Then of course, our Earth is
replete with suffering around every corner. Perhaps other terrestrial planets
operate differently, for better or worse. You would think our maker(s) should
have known the possible outcomes and scenarios before hitting the "start
existence now" button, or perhaps it is just part of the grand plan.

You have to wonder: Are these entity/entities sadistic pranksters of some
sort?

~~~
3chelon
A cursory reading of most religious texts would certainly indicate a degree of
sadism and lack of empathy with our human feelings. Human sacrifice? Plagues?
Genocide? As an experiment, they would make sense. Virtual vivisection.

The old God-as-a-Programmer argument certainly has its appeal :)

------
kornork
If we're living in a simulation, the question of whether AIs can have
consciousness is solved.

~~~
astrodust
What if the simulation is actually being "run" inside an entity or organism
that was the natural product of its environment?

~~~
GavinMcG
Still, human intelligence would be simulated within that, presumably. So the
platform might not be the obvious one, but the software would still be
theoretically possible.

That, or there's some interface to that platform that provides a source of
intelligence. Maybe we're nothing more than Docker containers running on God's
hardware.

------
mentos
What is interesting is if we are the result of an unfathomable number of
transistor gates, the consciousness that arises from it would never be able to
understand the 'platform' (hardware) that it sits on.. would it? The idea
being that you are creating a new dimension that cannot see the dimension that
gave rise to it.

I feel like no matter what we are in a 'simulation' where another dimension
gave rise to ours whether it was intentional or not.

What dimension is thought in?

~~~
tonmoy
Nobody said the simulation is being done with transistors. Even if it was why
wouldn't it be possible? I don't see any constraints. One day humans will
fully understand neurons. One day we will make an AI using transistors who
will be able to "understand" transistors

~~~
mentos
I meant it more in an abstract sense. They don't have to be silicon they could
be enormous metal planets and moons..

------
3chelon
On a semi-serious note, I've always had this nagging feeling ever since I
first heard of Planck time and Planck length. Why would there be a lower limit
to the resolution of the universe, unless there was something spooky going on?

(I know they're just theoretical, but...)

~~~
niftich
I'm not a physicist, so I'm speaking as 100% layman, but I can better accept a
fixed-resolution universe, where forces have a certain magnitude and beyond
them (in either direction, smaller or larger) matter doesn't behave in
productive ways.

For a long time, we thought atoms were these building blocks; now we think
it's quarks; the Standard Model does a pretty good job at relating all
observed phenomena to each other, except for, you know, gravitation, and that
pesky observed-but-unaccounted-for thing we deemed 'dark matter'.

A few things about the Standard Model make my head hurt, but the idea of a
fractal universe that is infinitely scalable up and down and assumptions about
spacetime and forces still hold the same way is truly mindbending that I don't
know how to reason around it. So perhaps conversely, can we flip the question
and ask, why wouldn't the universe have a finite resolution in terms of matter
actually existing and behaving like we know and love?

~~~
raattgift
That's a good question you asked.

The Standard Model has as a subgroup the Poincaré group, which is the isometry
group of flat spacetime, which is both the (global) spacetime of Special
Relativity and is the local spacetime of General Relativity for a pretty
narrow definition of local, although we regularly construct Local Inertial
Frames which are regions of spacetime that are so approximately flat that the
difference is negligible.

The Poincaré group has as a subgroup the Lorentz group, and its generators
include rotations about the three spacelike axes of Minkowski (i.e., flat)
spacetime.

The other symmetries of the Standard Model are invariant under these
rotations.

A distant observer moving transversely relative to a particle observes a tiny
rotation of the particle. The particle's fundamental properties do not change
under that rotation, which can be arbitarily small.

Rather than descending into group theory to reason about a minimum translation
or boost, we can look to the energy-mass-momentum equivalence E_r^2 = (m_0
c^2)^2 + (pc)^2 and focus in on photons so we can ignore the m_0 term. Here we
have E = E_r = (pc) = \hbar\omega = hc/\lambda = hf. Photons come at arbitrary
frequencies, and we have good blackbody radiators all across our sky. If there
were a minimal length scale, we would expect that derivatives of position
would incorporate that minimal length, and so we would impose observables on
things like the doppler shift, for example if we accelerate in a straight line
towards a radiator emitting extremely high energy photons.

So it's not so much "why wouldn't it have" but rather, "Q: does observation or
experiment support a minimum scale that is large compared to the Planck scale
for spacetime intervals in our universe? A: no"

The answers for minimum length et al. scales that are small compared to the
Planck scale are subtler (essentially by definition of the Planck scale, at
those scales quantum corrections to account for gravitation become
significant, spoiling the observability of short spacetime intervals) but so
far still 'no'. For every particle in the universe there can be an
(ultrarelativistic) observer who sees the particle wavelength shrink below the
Planck length; there is nothing special about this observer -- there is
likewise a possible observer who sees the particle at some much longer
wavelength -- and the point of relativity is that neither observer is more
correct than the other. Furthermore, if the former type of observer manages to
see a star ultra-blueshifted and extremely Lorentz-FitzGerald-contracted, that
observer does not create a black hole; no event horizon forms (event horizons
are a _global_ feature of the causal structure of spacetime[0]), and so we can
turn an argument about Planck length into an argument about localized Planck
energy: there is nothing obviously special in _spacetime_ about the Planck
scale. However, our ultrarelativistic observer will certainly see some very
strange stuff courtesy of the Unruh effect: different observers observe
different particle counts, and one would expect our observer would see an
explosion in the number of particles compared to a more typical observer, and
those particles -- like all others -- will also interact gravitationally, and
we don't know yet how to decomplicate the picture enough to do useful
calculations on them.

[0] different observers may disagree on precisely where the event horizon is,
what its shape is, and even the count and energy of the particles just outside
the event horizon. but they will all agree that there is an event horizon.

------
danbruc
In my opinion this seems all pretty pointless. To be able to differentiate
between a simulation and reality you have to know at least how one of those
works in quite some detail. What if we discover floating point rounding errors
in the laws of physics we observe? Who is to say that this is not a feature of
reality? What if it is the other way round, what if we live in a simulation
with laws of physics made out of real real or complex numbers but the reality
outside of our simulation has laws of physics behaving like floating point
numbers? It seems pretty impossible to ever figure out what reality or a
simulation must look like so that we can determine what surrounds us. Maybe
there is some incredible self-consistency law at the bottom of reality,
forcing reality to be what it is because there is one and only one way reality
can be. But besides something like that?

~~~
pmontra
Not so pointless. Think that one of the NPC in a computer game gets
intelligent. It could learn how to trigger bugs or cheats in the game or
features thought only for the player. Examples: crash the game, which
hopefully restarts from the last save. Get where no NPC was supposed to be,
only players, and get teleported somewhere else. Trigger a stack overflow and
perform actions in the host, maybe changing the programming of the game or the
data in the save files.

In our case it could be the way to FTL. Did any Sci-fi author considered that
yet?

~~~
danbruc
But how would that NPC know that it is in a game? What if we figured out how
to do teleportation or time travel? How would you determine whether that is a
feature of reality or whether we discovered a bug in a simulation?

~~~
pmontra
Gut feeling: it can't know. But the simulation in some way is part of reality
and maybe that's why it couldn't be known.

I guess there has been plenty of philosophical research on this subject.

~~~
danbruc
But exactly that was my point - unless you know what either reality or a
simulation really looks like, you can not look around and draw conclusions
whether we live in reality or a simulation. People trying to do this make the
assumptions that a simulation would have properties similar to simulations we
perform and that reality would have properties similar to the laws of physics
as we know them, but neither assumption seems really justified.

------
rihegher
13th floor style?
[http://www.imdb.com/title/tt0139809/](http://www.imdb.com/title/tt0139809/)

------
codesnik
I'm really surprised (every time!) when someone talks about conscience or
discoveries or whatever so human-centric and local and unimportant in the
cosmic scale while talking about simulations. If it's simulation, it certainly
isn't made because of us.

~~~
inimino
We are on the only planet we know about with life on it, so it is fairly easy
to assume this is the most interesting place in the universe. Whether that's
rational or not is another question, but it doesn't seem surprising.

------
botw
The other day I saw a post on social media that how he explained spaces from
0-dimension to 10-dimention in simple drawings. At the end, he claims that
10-dimentional space is just a dot, and there is no higher dimensional space
more than 10-dimention any more. And he justifies his claims based on the
string theory. At that time immediately I thought about the billions of
parameter space in deep neural network and fractal spaces such as Mandelbrot
Set. How could one simulate the universe based on only 3D space-time lattice?

------
smrtinsert
What sort of moral issues result from creating a simulation universe that
gives rise to sentient beings? I feel creeped out and reminded of Source Code
with Jake Gyllenhaal for some reason.

~~~
teraflop
Greg Egan has written a (slightly ham-fisted, but still interesting) short
story about that question: [http://ttapress.com/553/crystal-nights-by-greg-
egan/](http://ttapress.com/553/crystal-nights-by-greg-egan/)

The author has commented that he regrets having overlooked the moral
implications of simulated life in his previous works (see e.g.
[http://gregegan.customer.netspace.net.au/PERMUTATION/FAQ/FAQ...](http://gregegan.customer.netspace.net.au/PERMUTATION/FAQ/FAQ.html),
which contains spoilers for _Permutation City_ ) so I wouldn't be surprised if
that was the inspiration for this story.

~~~
pmoriarty
Also highly recommended along these lines is Stanislaw Lem's _Cyberiad_
(published in 1965):

[https://www.amazon.com/Cyberiad-Stanislaw-
Lem/dp/0156027593](https://www.amazon.com/Cyberiad-Stanislaw-
Lem/dp/0156027593)

It touches thoughtfully and humorously on: AI, simulations, robotics, ethical
and moral questions regarding artificial life, among many other interesting
topics. It's one of the funniest and greatest science fiction books I've ever
read.

------
rwallace
> At fixed quark masses, the CRR of a lattice ensemble generation (in units of
> petaFLOP-years) scales roughly as the dimensionless number...

The formula they give, indicates that the largest QCD calculations to date
have taken 7.9e11 petaflop-years; this is consistent with the graph they give,
but not with actual feasibility. What am I missing?

------
alphanumeric0
I'm not sure why people insist on assigning agency to this phenomenon. If you
wanted, couldn't you invoke the 'many worlds' theory and suggest that our
particular universe exhibits the same properties as what you might find in a
simulation? This would do away with the need for an agent who is simulating.

------
xenny
Can someone summarise the paper? Seems to complex for a lay-man. For example,
what is Lattice QCD?

------
45h34jh53k4j
Sigh. Why would you dedicate your life to proving this?

You will either find you cannot prove it, in which case you have wasted your
entire life on falsehood, or you prove it true in which you undo your dilute
your existence and everyone you have ever known and loved.

Kinda like religion I guess...

~~~
Justsignedup
though, if we are a simulation... maybe we can exploit bugs in it and give
ourselves advantages! After all, the only bug-free program is one that was
never started.

~~~
slackware_linux
What are you trying to tell me? That I can dodge bullets?

~~~
Justsignedup
I'm trying to say that when the time comes, you won't have to!

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3chelon
Let's all just think, very hard, of the number 42 and see if the simulation
ends.

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codezero
The title of the arxiv article is: Constraints on the Universe as a Numerical
Simulation

The only time they use the word evidence is in this quote:

__ Therefore, there is a sense in which lattice QCD may be viewed as the
nascent science of universe simulation, and, as will be argued in the next
paragraph, very basic extrapolation of current lattice QCD resource trends
into the future suggest that experimental searches for evidence that our
universe is, in fact, a simulation are both interesting and logical.

~~~
sctb
We've updated the submission title from “Physicists May Have Evidence Universe
Is a Computer Simulation”, which breaks the guidelines by being editorialized.

~~~
codezero
Awesome, thanks!

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AnimalMuppet
Per the arXiv abstract, physicists _may be able to find_ evidence. That's very
different from _may have found_.

------
retox
(2012)

