
The Measurement That Would Reveal The Universe As A Computer Simulation - iProject
http://www.technologyreview.com/view/429561/the-measurement-that-would-reveal-the-universe-as/
======
nkoren
While I wouldn't entirely discount the notion that we're living in a
simulation, I suspect that this measurement is probably quite problematic, for
various reasons other people have addressed. Nevertheless, this article got me
thinking:

 _Really?_ Can we actually simulate _any_ part of the universe with 100%
quantum accuracy? I hadn't heard about that, and it seems a bit implausible to
me. But okay, fine, let's take it as a given that we can in fact simulate a
volume a few femtometres in diameter, as the article says. Furthermore, let's
say that our universe-simulating capability increases in line with Moore's
Law, doubling every 18 months without regards for the limits of silicon or
anything else.

The question is: how long would it take _us_ to become those universe-
simulating gods?

This is not a serious question, just a fun little exercise. If all of the
above are true, then what will we be able to simulate, and when?:

2019: The nucleus of a single gold atom (8.45 femtometres)

2077: An entire helium atom (62 picometres)

2090: A cesium atom (423 picometres)

2115: A ribosome (20 nanometres)

2152: A red blood cell (7 micrometres)

2192: The smallest vertibrate, Paedophryne amauensis (7.7 millimetres)

2217: A human brain (150 millimetres)

2245: A small apartment and its occupants (10 metres)

2274: A small town (1 kilometre)

2335: Planet Earth (12,742 kilometres)

2407: The earth-moon system (812,000 kilometres)

2454: The inner solar system, inclusive of the asteroid belt (6.6 AU)

2475: The entire solar system, to the extremities of the Kuiper built (200 AU)

2516: Sol's sphere of influence, to the edges of the Oort cloud (100,000 AU)

2589: The Milky Way galaxy (120,000 light years)

2617: The Local Group of galaxies (10,000,000 light years)

2670: The observable universe (29,400,000,000 light years)

...But seeing as none of the initial assumptions are likely to be true, alas
for all that. Would be kind of cool, though! (also, a femtometre is _really_
bloody small)

[Edit: mixed up radius & diameter for the size of the observable universe.
_Hate_ it when that happens!]

~~~
thedufer
Its definitely not 100% accurate. We can calculate observables like mass from
basic principles to +/- 2-3%. However, there are a few things they didn't
mention.

First, these things are not simulated at anything approaching realtime. Things
are simulated on timescales almost as vanishingly small as the space-scales,
and even this takes hours on some of the largest research clusters.

Second, these aren't simulations in the sense that you're used to. They
involve taking a volume in 4-space (3x space and 1x time) and using Monte
Carlo techniques to approximate what happens in that space-time. It is non-
trivial to pick up where (in time) one calculation left off and start a new
one, and would introduce a lot of error.

Third, the calculation time doesn't scale with the volume (or even the 4-space
volume). Naively, it scales with volume squared.* We actually do somewhat
better than this right now, but again, approximations are required to get
there.

*Its actually the number of points in the lattice squared, so increasing accuracy by decreasing the space between sites scales as you'd expect.

Source: I spent more time than I care to admit writing a very simple version
of these simulators as an undergrad.

~~~
guylhem
Why should we have to make it 100% accurate ?

I mean, just like with videogames emulators, it can be good to simplify some
things. That's how most supernes emulators were made until very recently IIRC.

I'm not a physicist, but for exemple if the subatomic particles can't be
accurately modeled, couldn't they just be replaced by atomic particles and
special case handling?

~~~
nkoren
(Standard disclaimer: IANAQP, but...)

I think you're on to something. Rather than model each quark and gluon
explicitly, you could just model probabilistic interactions at much larger
scales. Maybe put in some special case handling so that if an observer within
our simulated universe were to go looking for quarks and gluons, they'd find
them. If they looked hard enough, some gaps might show: since subatomic
particles are not actually being simulated in a continuously deterministic
fashion, it would never be possible to observe both position and velocity
simultaneously. An observer looking at an electron shell in two discrete
moments would not be able to track a continuous orbit between them, since
they'd actually just be seeing two separate expansions of what is effectively
a lossy compression algorithm.

Also, it ought to be possible to model only the macroscopic dimensions
explicitly, replacing the other seven microscopically enfolded dimensions with
a bunch of arbitrary constants that accomplish more or less the same thing.
Might drive our observers a bit batty, because those constants would _appear_
to refer to a bunch of microscopic enfolded dimensions, which they'd never
actually be able to detect.

Right, now I'm starting to freak myself out...

~~~
guylhem
I got the same feeling when I was studying physics and saw those constants!
And now I still get it when I see the normal distribution. (e phreak me out
more than pi)

------
SideburnsOfDoom
"the lattice spacing imposes some additional features on the spectrum. The
most striking feature... the cosmic rays would travel preferentially along the
axes of the lattice, so we wouldn't see them equally in all directions. "

That assumes an awful lot about a simulation which by definition is not even
in this universe. Maybe they would detect a simulation which has those
features, but the assumption that it would work like that, because that's how
we'd do it here and now in this 3-d space is I think a very tenuous one.

~~~
Cushman
That's pretty much the claim, right? Not that this will determine whether or
not the universe is a simulation, but that it may determine that it is-- or at
least probably is. Simulationism is predicated on the hypothesis that we could
construct a completely accurate simulation of our universe _in_ our universe,
as if recursively-simulated universes are possible it becomes vanishingly
unlikely that we do not live in one, so demonstrating that that's possible
would be pretty important.

Personally, my money's on the universe is a simulation of itself.

~~~
jemfinch
It's not actually a true statement to say that "if recursively-simulated
universes are possible it becomes vanishingly unlikely that we do not live in
one."

Yes, I've read Bostrom's paper[0], but he misses a key point: the number of
rational beings in each simulated universe may decrease exponentially. If, on
average over all universes, each rational being simulates only 0.5 rational
beings during his or her lifetime, the total number of simulated rational
beings would be exactly equal to the total number of unsimulated rational
beings, making it equally plausible that we are in the root universe or one of
the simulations.

The possibility that rational beings diminish in number exponentially as
universes are simulated seems not only plausible, but _likely_ given the
nature of the simulations necessary to replicate our universe in all its
detail.

[0] <http://www.simulation-argument.com/simulation.html>

~~~
Cushman
I think it might be heading down the wrong path to talk in terms of "rational
beings" as atomic units rather than in terms of energy (or rather information)
balance.

Remember that you _do_ live in a simulation of the universe so compressed it
fits between your ears, and it _does_ contain many simulations of other
rational actors. They're nowhere near as complex as your whole universe, but I
bet they're complex enough to know that they're complex enough.

~~~
voodoomagicman
Are you implying that concepts of people in your mind are themselves self
aware?

~~~
bduerst
Do you think that I am self aware?

Can you predict where I am going with this line of questioning?

------
jeremyswank
fundamentally, how do we distinguish between 'simulation' and 'reality'? if a
simulation (of any sort) exists, it is therefore real. how would a
hypothetically 'simulated' universe be any different from a 'real' one?

further, proposed research that seeks to 'reveal' the universe as a 'computer
simulation' suggests a limited vision. why must it be a 'computer' doing the
simulating? maybe the universe (in some sense) 'computes' itself in coming
into existence (think cellular automata or things of the like). if so, then it
is not a 'simulation' coming into being, but 'reality' itself.

i will simply state that it is not surprising to me that 'simulations' and
'realities' have much in common -- so it is not surprising that might be
mistaken for the other.

in any event, these ideas are off the top my head, i don't know how seriously
to take them.

~~~
tylerneylon
My impression is that anything you can simulate via a program could just as
well be the fundamental laws of physics -- and vice versa.

The idea behind this line of inquiry - which I hope is continued - seems to be
assuming that, if we are simulated, then we are simulated using a similar
computation model to our own, and using data structures that we would have
come up with ourselves. I don't have better suggestions for which model to
use, but it's good to keep in mind that even if one model of a simulation
fails to match our physics, then there may just as well be another that does
match it.

~~~
electrograv
It looks like for a long time we've suspected this strange relationship
between our own mathematical inventions (a computer simulation is just a
machine that applies a discrete mathematical model), and the universe itself:

[http://en.wikipedia.org/wiki/The_Unreasonable_Effectiveness_...](http://en.wikipedia.org/wiki/The_Unreasonable_Effectiveness_of_Mathematics_in_the_Natural_Sciences)

It certainly is a mystery. I persnally believe this mystery is logically
equivalent to the question "what is existence?" Whether this question is
answerable or not, I can't say.

------
nagrom
This is interesting. If you could map out preferred directions in the universe
(even if those directions changed across space), you would be able to
establish an absolute, universal reference frame. That would be...incredible.

------
narrator
If the universe is a "computer simulation" running on the computer called the
universe then a computer is a "computer simulation" running on a computer and
we all are human simulations running on the computer called the human body.

Occam's razor would say that the simplest explanation is the best. Since this
"simulation" works exactly the same as the known universe and we don't know
about anything that is outside the universe, we can safely ignore this theory
and not lose any information about how the universe works.

~~~
run4yourlives
Apart from the fact that a simulation isn't initiated all by itself, and
points to a purpose important to something outside of the simulation.

~~~
bduerst
"Initiation" is a four dimensional word.

As our existence is on a four dimensional level, so naturally we see
everything as having a start and a finish, i.e. a line on a two dimensional
surface.

But there exists situations where there is no start or finish, i.e. a line on
a mobius strip. Since we hypothesize that our universe exists on 10
dimensions, we shouldn't assume that our universe's existence has a set start
and finish, even though we can only measure back to the big bang.

~~~
run4yourlives
Fair point, but you can take initiation with regards to a simulation as being
whatever confluence of events is triggered by something external to the
universe to cause the universe/simulation to exist.

Point being is that by definition, a simulation has to simulate something, and
therefore needs to exist sometime _after_ the thing it is simulating.

~~~
bduerst
Within the constraints of a four dimensions simulation as we know it, of
course.

But when you start stretching to simulations on the Nth dimension, you are
back to the mobius strip.

------
Eliezer
Everyone knows how software works. You have a program, and you give it to a
computer, and the computer conforms itself to the program and instantiates all
the rules and carries out the program's instructions. The universe works just
the same way, only without the computer. -- the negation of the Simulation
Hypothesis

~~~
zerostar07
Actually there are cannot be variables determining some phenomena
<http://en.wikipedia.org/wiki/bell_theorem>

~~~
jimrandomh
Bell's Theorem says there cannot be _local_ variables determining some
phenomena. That raises the computational cost of simulating the universe, and
shrinks the set of possible universes that could simulate ours, but does not
preclude the universe being a simulation.

~~~
zerostar07
Good point, thanks for correcting me. Can you give a hint how this would raise
the computational cost?

------
bediger4000
I (tried to) read the Beane/Davoudi/Savage paper. I am not a theoretical
physicist, but I only vaguely got the feeling that this paper is one of those
Markov-Chaining-bot-written papers. I would like to note that it's true:
advanced math now looks exactly like the ravings of a madman.

~~~
sillysaurus
Hmm, which paper? Would you link to the PDF?

~~~
iamalexalright
<http://arxiv.org/pdf/1210.1847v1.pdf>

------
joezydeco
I just better not end up being flushed out of a sewer pipe when this is all
over. I hate swimming naked.

~~~
ctdonath
Naw. You're just on the Thirteenth Floor.

------
ynniv
Are we really suggesting that people studying cosmic rays would not have
already noticed a geometric pattern in their observations? If I were studying
cosmic rays, and noticed what appeared to be pixelation in the universe, _you
would have heard about it by now_.

~~~
nagrom
Not necessarily (if the data exists then this paper would already have
referenced it, surely? These are serious scientists at very respectable
institutes - the INT at Seattle is highly prestigious). Firstly, you would
need to select rays that are very close to the cutoff...the further your
distribution slides down the energy axis, the less noticeable your deviation
will be. Secondly, you need to orient your distribution geo-spatially, i.e.
take into account the Earth's position throughout the measurement. Thirdly,
you need to find a way of correcting for all known sources of very high energy
cosmic ray background.

I'm not sure whether anyone has ever done all that at once. I'm not saying
that they haven't; I'm just not familiar with any measurement that meets all
those criteria. I'm not a cosmic physicist though, so it's entirely possible
the measurement has been done.

~~~
juiceandjuice
I'm sure it's been done. Anisotropic studies of UHECRs is a very popular thing
to do for UHECR experiments, almost as popular as looking for neutrinos.

I worked at such an experiment for 4 years.

------
dfan
If you want to read more about the simulation argument, the place to start is
Nick Bostrom's page on it: <http://www.simulation-argument.com/>

------
torstein
If the universe is a (deterministic?) simulation, would it matter to us if it
were actually computed?

And if no, does anyone (or thing) need to come up with the rules for the
simulation for us to experience it?

~~~
stephengillie
No, but knowing the rules would help if we're trying to break them (hack the
universe).

------
codex
It's fun to speculate about this (heck, I may even found a religion around it)
but there's no way to prove that one is in a simulation.

It's possible that the creators of the simulation do not wish to let the cat
out of the bag. Any test which aims to probe the limits of the simulation can,
itself, be simulated at higher accuracy with only a slight loss of real-time
speed. In fact, it's highly likely that different parts of the universe are
simulated with varying amounts of precision.

Heck, even if the simulators goofed, they can always fix the simulation,
rewind the universe back to a prior checkpoint, and begin anew.

------
Aardwolf
If the universe would be a simulation, then what about the universe in which
ours is being simulated? Can we measure that too?

What if the creator of the simulation thought of this and programmed his
simulation such that this measurement will not work by making it give fake
values for non lattice directions? :p

If the measurement says it's a simulation, who says it really is a simulation?
It could just be that physics actually is like that, without any "computer"
running it being involved.

~~~
mingmecca
"You're very clever, young man, very clever, but it's turtles all the way
down!"

------
wes-exp
The argument seems to be that if the smallest workings of space/time exist in
discrete points rather than being continuous, then we must be in a simulation,
if I understand correctly. Personally I find discrete math much more natural
and it's the continuous math that seems imaginary to me. So a discretized
universe seems perfectly natural to me, and hardly evidence that it is being
simulated.

~~~
bdr
I agree with you about preferring a discrete model of the universe. This may
be a common affliction among programmers. For some apparently good theoretical
reasons, though, it's a minority opinion among physicists.

There is at least one notable figure who explores the idea: Nobel laureate
Gerard 't Hooft. Here's a recent starting point:
<http://www.math.columbia.edu/~woit/wordpress/?p=5022>

------
thestu
I had a professor pose a similar idea to a class I was in, the idea being that
if a perfectly simulated universe is a technological possibility at some point
in the future, and that more than one simulation could be created, and that
simulations could be created inside of simulations, and so on for simulations
within simulations, then odds are we are in a simulation.

~~~
crpatino
Seems your professor never heard of the Halting Problem.

~~~
thestu
It was a political science class, so you're probably right; but how exactly
does it apply?

~~~
ajuc
It doesn't.

------
RivieraKid
Claiming that we're in a simulation because our universe is discrete is wrong
on 2 levels.

1\. The discreteness of our universe doesn't say anything about whether we're
in a simulation or not. What if the "higher level" universe has indiscrete
computers? If our universe is discrete, it can be simulated on a Von Neumann
model computer - that's all we can say.

2\. And more importatnly: saying that we're in a simulation actually doesn't
mean anything. It is 0 bits of information. Adding this statement to our model
of the world is like adding comments to source code or defining a function
that is not used. It's like saying that gravity is caused by tiny invisible
dwarfs pushing elementary particles.

------
michaelfeathers
It's amazing what simulated physicists are up to these days.

------
aprescott
I find it interesting that, at the the end of the article, the point is made
that failing to find evidence in the relevant measurement doesn't necessarily
indicate that we're _not_ in a simulation, followed straight after by the
remark that it is worth making so as to rule out that we're living in one.
Isn't that a lot like giving a null hypothesis and suggesting we go out and
_prove_ it?

------
ajuc
Reminds me of "Permutation City" by Greg Egan.

------
csense
If we actually do live in a computer simulation, and scientists carry out
research to systematically find and test all the corner cases, we'd better
hope they don't trigger a segfault and accidentally destroy the universe :)

------
james4k
So, wait. What if our universe is being simulated with 'different' laws of
physics? I guess we would never be able to find that out, even if we could
somehow conclude it is in fact simulated.

------
hcarvalhoalves
Looking for hints of discrete patterns in our universe? Awesome, go ahead.

If you want to make a case of wheter we are in a simulation or not though, you
are not in the domains of science anymore.

------
OldSchool
How much of this speculated artifact wouldn't be there if The Great Computer
was for example analog, and used polar coordinates to simulate our universe?

------
ktizo
I like Ian Banks take on this from his book "The Algebraist".

 _“Any theory which causes solipsism to seem just as likely an explanation for
the phenomena it seeks to describe ought to be held in the utmost suspicion.”_

~~~
Symmetry
The sort of simulation they're talking about here doesn't justify solipsism.
Even if it were true, everybody you meet would be just as real as you are.

~~~
ktizo
I think you misunderstand the quote. It is not saying that simulation
justifies solipsism, just that it belongs to the same family of concepts,
along with comedy-gods burying dinosaur bones and stuff like that.

The original context was one character's view of a society in the book that
had elevated the theory of existence being a simulation to the status of
official dogma.

~~~
Symmetry
I'm still confused. Are you saying our society has elevated the theory that
we're a simulation to the status of dogma? That doesn't match with what I
observe. Are you saying it's untestable? That's what the article is about. Are
you saying that we have no _a priori_ reason to believe it might be true? If
you look at the universe as it appears to be, then it's a justifiable surmise
that the majority of humans intelligences that will exist will be in
simulations that we will run. That's why people are interested in figuring out
if we're the people in the simulations in the first place. I really still
don't see why you think the situations are comparable.

~~~
ktizo
No, the society in the book did that, I was giving you the context of the
quote.

Also, I am not sure that a positive result in that experiment would
necessarily prove the hypothesis. The trouble is that if you think you have
evidence for the universe being a simulation, you have actually found evidence
for any number of things from god to solipsism, depending on what hat you are
wearing, but you haven't actually got anywhere and unless you have really
exhausted all possible other explanations for what you have measured, then I
don't think it is a particularly rational position to take, although it is
admittedly quite fun.

Now it could be that we are in a simulation, but if we are, how do you know
that anything you detect wasn't put there on purpose to trick you into
thinking that you are in a different kind of simulation from the one you are
actually in, as a honeypot to fool would be hackers of the simulation? And
suddenly we are back in comedy-god land.

~~~
trhtrsh
You are pushing a bit too far there. It's one (bad) thing to say, "my theory
is X (a miracle), even though Occam's Razor suggests Y (evolution), and both X
and Y explain Z (dino bones), and we agree Z is true".

It is another thing to say, "my theory X (simulation) implies Z (a symmetry-
violation), which has no other proposed explanation, and _we have observed Z_
".

That said, I am more than willing to bet that the lattice will not be
discovered.

~~~
ktizo
If there are no other explanations that fit the data that anyone has come up
with, then fine. But I would not personally be particularly convinced by a
simulationist interpretation until I thought that the evidence had been
repeatedly tested in a fairly wide variety of ways over a long period of time.
For me it is one of the ideas that the phrase "Extraordinary claims must be
backed up with extraordinary evidence." was built for.

------
dmorgan
> _First, some background. The problem with all simulations is that the laws
> of physics, which appear continuous, have to be superimposed onto a discrete
> three dimensional lattice which advances in steps of time._

That's only if we assume a digital simulation.

An "advanced civilization" could also run it in some kind of analog computing
environment, no?

~~~
tadfisher
A digital simulation is exactly what they are trying to detect; a quantized
lattice forming the observable universe would certainly constitute evidence of
such. Not finding such a lattice wouldn't rule out an analog simulation.

