
Simulations back up theory that Universe is a hologram - ForHackernews
http://www.nature.com/news/simulations-back-up-theory-that-universe-is-a-hologram-1.14328
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crazygringo
1) What the heck do they mean by a hologram? The analogy here baffles me. Is
this just a layman's analogy, or does this actually mean something scientific?

2) Anybody have any suggestions on a high-quality layman's explanation? I
finished reading Feynman's QED the other week, and loved it, and was wondering
what the closest might be for string theory.

~~~
jasonwatkinspdx
From Wikipedia
([https://en.wikipedia.org/wiki/Holographic_principle](https://en.wikipedia.org/wiki/Holographic_principle)):

"The holographic principle is a property of quantum gravity and string
theories that states that the description of a volume of space can be thought
of as encoded on a boundary to the region—preferably a light-like boundary
like a gravitational horizon. First proposed by Gerard 't Hooft, it was given
a precise string-theory interpretation by Leonard Susskind[1] who combined his
ideas with previous ones of 't Hooft and Charles Thorn.[1][2] As pointed out
by Raphael Bousso,[3] Thorn observed in 1978 that string theory admits a
lower-dimensional description in which gravity emerges from it in what would
now be called a holographic way. In a larger sense, the theory suggests that
the entire universe can be seen as a two-dimensional information structure
"painted" on the cosmological horizon, such that the three dimensions we
observe are only an effective description at macroscopic scales and at low
energies."

So the analogy is that the field inside the volume can be completely described
by some function over the bounding surface of the volume, similar to how the
light field captured by a hologram is projected and recorded on a flat glass
or film plane. I can visualize that pretty easily, but I don't know enough to
tie that to some concrete relationship to the fundamental physical forces of
the universe.

~~~
jjjeffrey
After reading this, it reminded me of Cauchy's integral formula. From
Wikipedia
([https://en.wikipedia.org/wiki/Cauchy%27s_integral_formula](https://en.wikipedia.org/wiki/Cauchy%27s_integral_formula)):

"In mathematics, Cauchy's integral formula, named after Augustin-Louis Cauchy,
is a central statement in complex analysis. It expresses the fact that a
holomorphic function defined on a disk is completely determined by its values
on the boundary of the disk, and it provides integral formulas for all
derivatives of a holomorphic function. Cauchy's formula shows that, in complex
analysis, "differentiation is equivalent to integration": complex
differentiation, like integration, behaves well under uniform limits – a
result denied in real analysis."

Does anyone who knows this stuff better than me know if there's any meaningful
connection?

~~~
zvrba
Oh, thanks for reminding me of complex analysis. For me it was the most
beautiful math course I had at the uni.

~~~
eru
It's the one part of analysis that looks like linear algebra.

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Sakes
They took two different universe models, neither of which match the one we
live in, and mathematically produced the same black holes. The key
differentiators being that one universe has gravity and multiple dimensions
while the other has no gravity and 1 single dimension.

While the article likes to take a logical leap and assume this supports the
theory that our universe is a hologram, what was actually proved by this
numerical experiment is eloquently explained in the article's quoting of
theoretical physicist Leonard Susskind.

"They have numerically confirmed, perhaps for the first time, something we
were fairly sure had to be true, but was still a conjecture — namely that the
thermodynamics of certain black holes can be reproduced from a lower-
dimensional universe"

\- Leonard Susskind

~~~
proofofconcept
When I see "experiment X backs up/supports/proves conclusion Y" in a headline
I always mentally correct it to "experiment X does not definitively disprove
conclusion Y" where X and Y are random variables operating on whatever the
actual scientific experiment and conclusion respectively are.

~~~
gjm11
In fairness, the way even the most firmly established scientific theories get
firmly established is precisely by having a lot of experiments done that fail
to disprove them.

(Disclaimer: That's a bit of a simplification. In practice the acceptance of a
theory also has something to do with how explanatory the theory _feels_ , how
elegant it is, what prejudices the highest-status experts have, etc.)

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tlarkworthy
I have lead loads of these physics theory of universe things and I am none the
wiser about anything in the field. Might as well say "Physics have shown we
are an electronc's imagination in 7.5D space like a windy coral on an orange
Tuesday"

~~~
jmpe
This is pretty much one of the Ultima Thules of Mathematics. Reading about it
won't make you understand it, the metaphors used in popular science are just
that: simple analogies that fool the reader. If you want to understand it I'd
suggest allocating 6 years of your life to be thought the foundations and move
on from there.

Edited to remove a shitty snark re fractional dimensions, hence the replies.

~~~
jaibot
Fractional dimensions are a thing (for certain values of "dimension").

[http://en.wikipedia.org/wiki/How_Long_Is_the_Coast_of_Britai...](http://en.wikipedia.org/wiki/How_Long_Is_the_Coast_of_Britain%3F_Statistical_Self-
Similarity_and_Fractional_Dimension)

~~~
bad_alloc
See also this list:

[http://en.wikipedia.org/wiki/List_of_fractals_by_Hausdorff_d...](http://en.wikipedia.org/wiki/List_of_fractals_by_Hausdorff_dimension)

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derefr
So, the naive way I'm reading this might reduce to this lie-to-children
analogy:

"You have a 2D layout of memory cells on a RAM chip (strings), which store the
representation of a 3D universe. From within our 3D universe, we can tell that
we're actually stored on a 2D medium by the way we see the effects of
interactions between things in our 3D world that are distant in 3D, but stored
on 'neighboring' memory-cells."

Anyone who knows enough about this to tell me how far off-base I am?

~~~
astrodust
It's going to be a real downer when we find out the universe is actually one
gigantic one-dimensional Turing machine.

~~~
redthrowaway
Why? It'd prove Hard AI. That'd be nifty.

~~~
eli_gottlieb
The universe already contains human-level intelligent agents. They're called
humans.

~~~
ngoldbaum
But humans aren't necessarily Turing machines.

~~~
deletes
How so?, if a human isn't a Turing machine the you can learn him the rules and
give him the instruction tape and he will perform the same as Tm.

~~~
redthrowaway
Humans can certainly replicate TMs. It's uncertain whether a TM can replicate
a human. If the Universe is a simulation running on a TM, then humans are
replicable and therefore Hard AI is possible on a Von Neumann architecture,
which would be an exciting discovery.

~~~
nardi
From the perspective of computing things, humans are Turing Machines, because
a Turing Machine can compute anything that is computable.

~~~
redthrowaway
That's like saying from the perspective of arithmetic we're abaci because we
can both do sums. Again, whether or not human beings can model a TM is a
boring and silly question. The interesting question, and one that remains not
just unsolved but stubbornly resistant to progress towards a solution, is
whether a TM can model a human. It's far from certain that conscious is
computable, and it's getting further with each plate of spaghetti we throw at
the teflon wall that is Hard AI.

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damon_c
I have found this Leonard Susskind lecture to come closest to answering the
question of "why would anyone even suggest such a thing?" about this subject:

[http://www.youtube.com/watch?v=2DIl3Hfh9tY](http://www.youtube.com/watch?v=2DIl3Hfh9tY)

~~~
Kronopath
That's an excellent lecture, and explains a lot of these things in
understandable terms. Thanks.

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ck2
So basically they are saying we are a 3D projection (extrapolation) of a 2D
source?

Can we do anything useful with that like FTL space folding?

~~~
GeneralMayhem
Basically, but the numbers are higher than 2 and 3. String theory represents
the universe (the projection) as 10-dimensional, for instance.

~~~
X4
Yes, but this theory is simpler compared to the 10+ dimensions of string
theory and m-theory.

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richardjordan
Of course this isn't helpful to the layman who thinks of holograms as things
they get on a card in a cereal box.

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herbig
But not in the Matrix sense, as I was lead to believe from the title.

~~~
at-fates-hands
I had the same reaction.

So they did some calculations on a black hole with and without gravity and
their calculations match and now the entire universe is a hologram?

~~~
dllthomas
"Hologram" in the sense of "it looks like it has a different number of
dimensions than it does", not in the sense of "rendering of something that
isn't real".

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anentropic
I don't see explained anywhere what causes them to make the leap that, because
the math of holographic theory works, the universe 'is' a hologram. Doesn't it
just mean that they've found a way to convert between two abstractions?

~~~
tinco
Well the important thing is that they found a way to abstract it with less
dimensions than they previously did. This means that the previous theory had
unnecessary redundancy, so the new theory has less cruft.

The hologram is their way of describing how they changed their way of thinking
to land on this new theory. So they looked at the problem with the idea that
the interactions in our universe could be a projection of the interactions in
some other universe.

The breakthrough is that they found such a universe ours could be a projection
of, and that universe can be described with less parameters than the previous
leading theory.

The smaller a theory is, the more clear its foundational relationships will
be, so the closer we are to actually understanding why things are like they
are.

So previously we had a big question, why does our theory of everything require
18 (or more?) dimensions to describe the universe?

And now we have a slightly smaller question: Why does our theory of everything
require 10 dimensions to describe the universe?

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diminoten
Wait, I don't understand.

So there's the "flatland" where strings "live" and interact without gravity,
and when these strings interact in this flatland the side-effects of those
interactions are the 10-dimensional space we observe?

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david_otoole
Really a better title for this article would be "Simulation backs up theory
that universe is a simulation".

I find them very curious, the "TheUniverseIsAComputer" people.

Suppose there is an experiment proving that the Universe is indeed a particle
simulation whose discoverable elements are being actuated by unspecified
interactions of presumably very different elements in some other, underlying
"universe", say a substrate of Rule 110, and consciousness can be marked out
as a computable pattern in such, and that the simulation process works well
enough for a group of researchers (presumably "us") to feel as if "we" are
really here. Okay great.

But for this to qualify as a simulation, surely the experiment (and the
conscious experimenters) would have to be reproduced exactly, right down to
the consciousnesses apprehending the results that establish scientific
consensus that the UniverseIsAComputer, in precisely the consciousness-
simulating way that these people fantasize about?

We are to understand that the scientists in the "real" universe presumably
would not reach the same consensus, because theirs is the actually Real
Universe, not the simulated one, and so the Reality Detection Experiment fails
in some way.

So if this alleged difference appears---then why does the "simulation" even
qualify as a simulation? For that matter, why does the author's own computer
simulation qualify as having something to say about the real Universe?

I suppose the simulation is "good enough" for consciousness to be reproduced
more or less exactly, except for just recently the aspect of scientists
becoming conscious of the fact that TheUniverseIsASimulation.

I guess I could accept that everything is perfectly simulated except for...
the evidence for the simulation?

Meh.

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garraeth
I'm a huge Susskind fan. One of the coolest books I've read was his "The Black
Hole War". And he's got tons of his lectures (full lectures from Stanford) on
YouTube -- so if you're curious you can hear it straight from him.

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simonh
Has this got anything to do with the fact that, given relativistic length
contraction, from the pov of a photon the universe is two dimensional?

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analog31
Something puzzles me about the hologram analogy.

A hologram seems totally garbled, and is "played" by projecting it in a
particular way so that we see an image of the original object.

In contrast, our 4-d world doesn't seem garbled to us at all, and there is no
way to "play" it and see an image of a higher dimensional world.

~~~
aaren
Consider the Anthropic principle: _observations of the physical Universe must
be compatible with the conscious life that observes it_ [1].

We don't think things are garbled because we have evolved to make 'sense' of
the chaos. Perhaps everything _is_ a garbled mess that we think we can
understand.

“I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth.” ― Umberto Eco, Foucault's Pendulum

[1]:
[http://en.wikipedia.org/wiki/Anthropic_principle](http://en.wikipedia.org/wiki/Anthropic_principle)

edit: I think I went off on a tangent. The answer to your original question is
that our observable universe _is_ the thing that is being played - it is the
stuff on the boundary that might be garbled.

We are the projection.

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davidbielen
there are much simpler theories that unite gravity and quantum physics,
without going into 'matrix-mode':
[http://www.sciencedaily.com/releases/2013/12/131205142218.ht...](http://www.sciencedaily.com/releases/2013/12/131205142218.htm)

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apalmer
So basically they are showing that a simple model exists that gives the same
results as a more complex model? I mean the article seems clear that neither
universes they modeled was actually the same as ours... so i dont get the
significance.

~~~
aaren
If it turns out that the universe that we observe is just a projection from a
lower dimensional space then this could radically alter the way in which we
interact with that universe.

Things that seem to be coherent in our space (the things we observe -
electrons, people, solar systems) may not look at all coherent in the source.

Similarly, coherent structures in the source may not be at all coherent in our
space.

It might be that, by fiddling around with this theory, we could work out the
mapping from the source to our space. If we could do this we could conceivably
interact with this space in completely unimaginable ways.

Imagine superconducting levitation as perceived by someone from the stone age
and then go up another few levels...

n.b. by 'our space' I mean the higher dimensional universe, the hologram. By
'the source' I mean the lower dimensional space that the hologram is projected
from.

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easy_rider
I swear I've read this somewhere else before..
[http://en.wikipedia.org/wiki/Holographic_principle](http://en.wikipedia.org/wiki/Holographic_principle)

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mVChr
Excitement builds as more of the article is read until near the end...

> Neither of the model universes explored by the Japanese team resembles our
> own, Maldacena notes.

...way to hide the disclaimer guys.

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mtdewcmu
This sounds like it could have been an Onion headline, e.g. "Simulations back
up theory that Universe is a simulation"

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0xdeadbeefbabe
I was confused till I read the comment by uncle Al, and that didn't help
either. He's talking some science pidgin.

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glifchits
Hmm, now wasn't there a commentary article on HN earlier today about how
papers in Nature (et al.) are sensationalized?

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jasonlfunk
What would it even mean that the universe is a hologram? Wouldn't it imply
some sort of holographic projector?

~~~
DanBC
Strings are the projector. Except, uh, ...

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marsay
Does it mean our dimension is projected to a higher dimension also? Wonder how
this world would look like.

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Demiurge
I wonder if I would age faster or slower in the universe rewritten in Go?

~~~
optymizer
Your cells would age concurrently, depending on the value of GOMAXPROCS.

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tomrod
Could we use these observations to increase storage density of data?

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mabbo
"In two papers posted on the arXiv repository"

aaand I'm out.

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islon
"Breaking news: we live in the matrix!"

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auggierose
It means we are all Flatlanders.

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avaku
I knew it!

------
ygmelnikova
..who (God) stretchest out the heavens like a curtain. - Psalms 104:2 (pre 537
B.C)

