> [...] after the renowned physicist Juan Maldacena discovered that the bendy space-time fabric in its interior is “holographically dual” to a quantum theory of particles living on the lower-dimensional, gravity-free boundary.
What does "holographically dual" mean?
What boundary are we talking about here?
> The bendy fabric of space-time in the interior of the universe is a projection that emerges from entangled quantum particles living on its outer boundary
What is the "interior" of the universe? What is the "outer boundary"?
anti-de Sitter universes are bounded by a horizon. The example given in the article is an Escher print with an infinite number of tiles bounded by a circle. They get smaller as they get closer to the edge, but there's an infinitude of them, so you have a universe that is infinite from "inside", but "from the outside", there's an outer boundary. As far as occupants of a hyperbolic universe go, they can't see the horizon directly because there's an infinite number of tiles between them and the edge.
That boundary has lower dimensionality than the universe itself (the Escher universe boundary is 1D and the interior is 2D).
Holographic duality is where you can describe the entire interior of the universe by characterizing "stuff happening" on the boundary- that the stuff happening inside the universe looks 2D, but is fundamentally one dimensional. Real-world holograms work like this- they encode a 3D scene onto a 2D substrate.
Our universe is not anti-de Sitter- it appears to be flat and does not pack away nicely into a bounded area like the Escher universe does, so it's as yet unclear how to apply the stuff they've found in their model universe to our own.
There isn’t an exterior in this model, just a boundary you can’t get “outside of” because everything including space and time are part of the universe. What this is all based on is the observation that the information required to describe the volume of (for example) a black hole, can be encoded on its event horizon. The theory says that the universe and it’s horizon(s) can be similarly modeled. In essence that we live not in the volume of a soap bubble but in the fluctuations of the skin of the bubble. It’s only to us, at our energy level and scale that a higher dimensional volume appears to emerge.
It’s important to say that this is all entirely speculative, based on the physical possibility which allows for the resolution of some outstanding problems in physics. That doesn’t mean it is in any way real, it is just another possible model, and one without observation to support it as the way our universe actually works.
It states that if you have a volume of space - say, a cube 1 meter side - containing some electric charges, and you calculate the total flux of the electric field across the boundary of that volume - that is, across the surface of that cube - then you'll find that total charge Q and total flux FF are proportional, FF = Q / epsilon_0 , where epsilon_0 is a fundamental constant. And that ratio doesn't in fact depend on shape or size of that volume of space.
That means Gauss law allows you to go along the boundary surface, calculate total electric flux and calculate the total charge inside the volume within that surface.
Similarly here, "holographically dual" means that you can derive important properties of matter inside some volume from properties which are observable on the boundary surface of that volume. What are those properties is another matter - but this duality principle says that there is a certain relation between them.
So, let's imagine you have a function that takes a phase space (ie, the positions, momentum, etc of a bunch of particles in normal 3+1 space time) as an argument and produces an evolution of that phase space in time. It's got a bunch of rules in the function regarding gravity.
Now imagine you've new function, which also takes a phase space as an argument, but instead of operating in 3 spacial dimensions, it has five. And that it doesn't have any rules regarding gravity.
Now imagine, you have a one to one mapping between states in those functions. So you can take a state in 3d space, translate it to 4d space -- run both functions for the same amount of time, and they both should produce states which you can still map to each other.
To my computer scientist mind this can easily be a parallel to checksum and hashing. Quantum error correction is analogous to using checksum to validate file integrity. Memory chips use similar schemes (ie parity bits) to correct errors. The same is being applied to quantum computing, ie. a sort of quantum hashing scheme based on (spacial) logic gates.
Now new research is being conducted where this quantum hashing scheme could be used to solve some of physics hardest problems. One of them could be Hawkins paradox, where "data" gets corrupted while being "processed" by a black hole. Maybe, scientists argue, error correcting data is stored at the black hole entrance so that it can be somehow applied as correcting code at the exit, ie when Hawkins radiation is released.
Or maybe the entire universe has gone through a hashing function and now there's error correcting code keeping information error-free using the "hash value". That's what the boundary stores that describes the bulk in certain theoretical universes.
Hashes have always fascinated me. The fact that a relatively short binary sequence can uniquely describe all of Shakespeare's works. What if we could completely reverse hashes, creating the most powerful compression ever? Well quantum physicists just might do that at cosmic scales!
"Boundary" refers to the boundary of Anti-de Sitter (AdS) space. The model that is typically studied is that of five-dimensional AdS space for which the boundary is four-dimensional. One can now formulate a quantum field theory on this boundary that is "dual" to the theory in the interior in the sense that there is precise dictionary between quantities living on the boundary and quantities in the interior ("the bulk"). "Holographically" refers to the difference in dimensions of the theory living on the boundary and the one living in the bulk.
Its cod profundity which the author shouldn't have attempted to popularize. People haven't even demonstrated quantum error correction in a single qubit in an actual quantum computer, and suddenly it's the source of space and time. Chyeah, dude; whaddevah.
The model universes they're talking about, FWIIW, are all just models, with very little relationship to the world of matter we all live in.
In our universe, construct an object that is perfectly spherical, and perfectly reflective. Now glue it to a table somewhere. Put another 3D object on the table. It has mass and volume, and felt real when you held it. Now look at the sphere. The 3D object is mapped onto the 2D surface of the sphere.
Now turn reality inside out. Because of various symmetries, it looks pretty much the same as it did before. Mathematically, it isn't all that important whether the signs of various things are positive or negative.
Instead of placing a 3D object on the table, draw a 2D shape on the surface of the sphere. Because you everted reality, this causes a 3D object to be reflected onto the table. The math can't really tell whether the object causes the reflection on the sphere, or the pattern on the sphere causes the object to exist.
Now turn the sphere inside out. Put the entire universe on the inside, and all of the stuff inside it (that you knew nothing about anyway, because it's perfectly reflective) on the outside. Now that your sphere encloses the entire universe, you can draw a 2D shapes on the outer boundary and reflect them as 3D shapes somewhere in the interior.
I don't know much about it but from what I've read imagine that we are inside a black hole. Every black hole is a universe of its own. The boundary of the black hole is the outer boundary if we are inside it. From the outside it would be just the surface of the black hole. Something like that perhaps
Sounds like if you imagine the universe as a sphere, like we (me?) "normally" do (3 dimensions), you use volume to describe its contents. Well... I think what they're saying is that the outside of the sphere, in this case the universe, just its surface, describes everything (all the information) inside of it... because in fact the volumetric area we know as the universe is a projection of a "flat" surface.
And... like I'm not very smart, but this is probably a bit like the non-euclidean space demo from yesterday's front page, where the geometry is doing really weird things... perhaps someone smart will come along and give a proper explanation.
I feel I don't have enough background information to understand this article.
>...space-time in the interior of the [anti-de Sitter] universe is a projection that emerges from entangled quantum particles living on its outer boundary
A projection? How would this differ if the quantum particles on the outside were not entangled?
>holographic “emergence” of space-time works like a quantum error-correcting code.
holographic in what way? and how is this similar to error correcting code?
>quantum error correction explains how space-time achieves its “intrinsic robustness,”
what is an example of this robustness in space-time?
>...error-correcting codes can recover the information from slightly more than half of your physical qubits, even if the rest are corrupted. This fact that hinted quantum error correction might be related to the way anti-de Sitter space-time arises from quantum entanglement.
how does the effectiveness of error correcting codes, being able to recover information despite 50% corruption, explain space-time?
if anyone could point me in the right direction, I'd really appreciate it. I find this interesting and important but am not smart enough to comprehend it.
Here's a talk given by Patrick Hayden, one of the guys quoted in the article, about related topics. It was to an IEEE Information Theory chapter, so may use a bit more information theoretic terminology than you're used to. Even so, I think it is very accessible.
In quantum physics and cosmology, "holographic" (and "projection", in this context) are related to the holographic principle, which is kind of like a Stokes' theorem for information-- it says that specifying the state of the universe on the boundary of a manifold is sufficient to completely specify the state inside.
If someone's read the full paper, maybe they can explain the other things-- this article is a bit too vague.
One of the reasons I like that series is they seem intent to do some justice to competing theories and the fact that we still don't really have a working model of the universe, or know answers as to why theories work the way they do.
Anyways this article was a really hard read for me. It's like the relatively-readable paragraphs are laughing at me--written like I should be understanding them, but I don't, ie:
>The best error-correcting codes can typically recover all of the encoded information from slightly more than half of your physical qubits, even if the rest are corrupted. This fact is what hinted to Almheiri, Dong and Harlow in 2014 that quantum error correction might be related to the way anti-de Sitter space-time arises from quantum entanglement.
I'd also like to recommend the semi-technical talks by Nima Arkani-Hamed and Leonard Susskind. They are the only reason I have the faintest hint of what is going on in theoretical physics and cosmology.
Space Time is fantastic. Upon watching the entire series (catching up to present time, to be more exact, since new episodes are still being released weekly), I went on a graph traversal spree of related YouTube videos. Another great series I loved was from Fermilabs, with Dr. Don Lincoln.
How I understand it: The world around us is some sort of "projection" of stuff at the very edges of our universe, and that stuff is inherently fragile and unstable. Yet our world/reality/spacetime is not fragile and unstable - quite the opposite, despite being dependent on that fragile stuff in the first place.
Thus it must somehow be "correcting" for the intrinsic instability of the stuff on the outer edges that gives rise to our reality. Therefore it is in some sense an error correcting code.
Happy to be corrected by those with a deeper understanding!
Just came to say it makes me happy to see the term "discovered" used in a what is essentially an engineering/software context, instead of the term "invented." The more that people in our industry speak clearly about that fact that many of the constraints in our problem space are universal, and thus much of our solution space is discovered, not invented, the more we shift the culture to understand e.g. the absurdity of software patents, etc.
Do they use a similar terminology in mathematics when talking about proofs? Software solutions don't seem that much different in regards to solving specific problems.
The study of Black Holes with the lens of Quantum information has been an exciting sub-field of Physics for the past couple of years. If you are curious about it, I recommend Patrick Hayden's "The Quantum Computational Universe" lectures [0][1]. The first one is an introduction to Quantum computation and the second one is more in line with what this Quantamagazine article is about.
It reminds me of old quote "Time is what keeps everything from happening at once" [1] and similar "Space is what keeps everything from happening in the same place".
Could someone explain to me why we should look into this, because we do not live in an anti-deSitter universe. So what is the relevance (beyond the obvious mathematical curiosity and elegance)?.
It's a toy model, but the hope is that the insights gained by playing with it will apply to ours: "On the physics side, it remains to be seen whether de Sitter universes like ours can be described holographically, in terms of qubits and codes. “The whole connection is known for a world that is manifestly not our world,” Aaronson said. In a paper last summer, Dong, who is now at the University of California, Santa Barbara, and his co-authors Eva Silverstein and Gonzalo Torroba took a step in the de Sitter direction, with an attempt at a primitive holographic description. Researchers are still studying that particular proposal, but Preskill thinks the language of quantum error correction will ultimately carry over to actual space-time."
Also, black holes at least superficially have a spatial boundary (the event horizon) so perhaps you can model what happens inside using the holographic principle.
My understanding (from Patrick Hayden) is that in the center of AdS space, things look very much like normal space. Physicists are working in AdS space because they can actually do some analysis there, even though they would very much like to work in de Sitter space.
Because string theory gave us AdS/CFT correspondence, and maybe if we try harder than we tried for the past 20 years, something similar will pop out that works for our universe.
My personal belief is that it's very much a case of looking for the keys where the light is.
For the same reason as why biologist spend a lot of time studying E. Coli, fruit flies and mice (besides being interested in them in themselves). It's because those organisms are similar enough to humans, but still a lot simpler to study. In this way we get important clues and ideas of how stuff might work for human cells, which is still very hard to work out and prove, but is a lot easier than just starting in the dark with human cells.
Awesome idea, but is there any way to test the hypothesis? Or will it be forever locked in the box of "extremely elegant but untestable" along with string theory?
Well, I think a lot of folks here find the description strange and opaque - I studied a bit differential geometry for my math degree and this seems way up there.
I'd love to hear why a physicist would roll their eyes at this.
>So, how do quantum error-correcting codes work? The trick to protecting information in jittery qubits is to store it not in individual qubits, but in patterns of entanglement among many.
So are quantum encoding patterns the Proof Of Work of multidimensional holgraphic blockchains?
> But a fundamental problem stood in the way of actually building quantum computers: the innate frailty of their physical components.
It's entirely possible that there is some sort of physically limiting factor that makes it nearly impossible to entangle more than X qbits. Something akin to Amdahl's law for quantum computing. It wouldn't be a very sexy result.
I'm thinking of the infeasibility of building a rocket to get off a large planet (compared to earth).
The intuition of a layperson is a bad guide, but I've always had the gut feeling that quantum error correction would prove to be exponentially difficult to scale. If smart people think otherwise, I can hope they're right, but I wouldn't bet money on it until I find an explanation I can grasp. It just sounds like a free lunch, or cold fusion.
> Ahmed Almheiri, Xi Dong and Daniel Harlow did calculations ...
It's pretty cool to see a Westerner, Middle Easterner and an East Asian dude (at least based on names ...) collaborate to push the frontiers of science like this!
> Westerner, Middle Easterner and an East Asian [...] based on names
This international variety of names is common outside the English-speaking world, e.g. the 3 biggest internet companies in China (Alibaba, Tencent, Baidu).
This makes error-correcting the foundation of the universe, but I would prefer to have causality be fundamental, such as with the causal sets program. This is interesting though, especially for quantum computing.
> The bendy fabric of space-time in the interior of the universe is a projection that emerges from entangled quantum particles living on its outer boundary.
Guess we are living in a simulation, after all. A quantum one, to be precise.
[+] [-] kamac|7 years ago|reply
> [...] after the renowned physicist Juan Maldacena discovered that the bendy space-time fabric in its interior is “holographically dual” to a quantum theory of particles living on the lower-dimensional, gravity-free boundary.
What does "holographically dual" mean?
What boundary are we talking about here?
> The bendy fabric of space-time in the interior of the universe is a projection that emerges from entangled quantum particles living on its outer boundary
What is the "interior" of the universe? What is the "outer boundary"?
[+] [-] roywiggins|7 years ago|reply
That boundary has lower dimensionality than the universe itself (the Escher universe boundary is 1D and the interior is 2D).
Holographic duality is where you can describe the entire interior of the universe by characterizing "stuff happening" on the boundary- that the stuff happening inside the universe looks 2D, but is fundamentally one dimensional. Real-world holograms work like this- they encode a 3D scene onto a 2D substrate.
Our universe is not anti-de Sitter- it appears to be flat and does not pack away nicely into a bounded area like the Escher universe does, so it's as yet unclear how to apply the stuff they've found in their model universe to our own.
[+] [-] toufiqbarhamov|7 years ago|reply
It’s important to say that this is all entirely speculative, based on the physical possibility which allows for the resolution of some outstanding problems in physics. That doesn’t mean it is in any way real, it is just another possible model, and one without observation to support it as the way our universe actually works.
[+] [-] avmich|7 years ago|reply
It states that if you have a volume of space - say, a cube 1 meter side - containing some electric charges, and you calculate the total flux of the electric field across the boundary of that volume - that is, across the surface of that cube - then you'll find that total charge Q and total flux FF are proportional, FF = Q / epsilon_0 , where epsilon_0 is a fundamental constant. And that ratio doesn't in fact depend on shape or size of that volume of space.
That means Gauss law allows you to go along the boundary surface, calculate total electric flux and calculate the total charge inside the volume within that surface.
Similarly here, "holographically dual" means that you can derive important properties of matter inside some volume from properties which are observable on the boundary surface of that volume. What are those properties is another matter - but this duality principle says that there is a certain relation between them.
[+] [-] jahnu|7 years ago|reply
https://www.youtube.com/watch?v=2DIl3Hfh9tY
[+] [-] psychometry|7 years ago|reply
[+] [-] empath75|7 years ago|reply
Now imagine you've new function, which also takes a phase space as an argument, but instead of operating in 3 spacial dimensions, it has five. And that it doesn't have any rules regarding gravity.
Now imagine, you have a one to one mapping between states in those functions. So you can take a state in 3d space, translate it to 4d space -- run both functions for the same amount of time, and they both should produce states which you can still map to each other.
[+] [-] ojosilva|7 years ago|reply
Now new research is being conducted where this quantum hashing scheme could be used to solve some of physics hardest problems. One of them could be Hawkins paradox, where "data" gets corrupted while being "processed" by a black hole. Maybe, scientists argue, error correcting data is stored at the black hole entrance so that it can be somehow applied as correcting code at the exit, ie when Hawkins radiation is released.
Or maybe the entire universe has gone through a hashing function and now there's error correcting code keeping information error-free using the "hash value". That's what the boundary stores that describes the bulk in certain theoretical universes.
Hashes have always fascinated me. The fact that a relatively short binary sequence can uniquely describe all of Shakespeare's works. What if we could completely reverse hashes, creating the most powerful compression ever? Well quantum physicists just might do that at cosmic scales!
[+] [-] irrep|7 years ago|reply
> What boundary are we talking about here?
"Boundary" refers to the boundary of Anti-de Sitter (AdS) space. The model that is typically studied is that of five-dimensional AdS space for which the boundary is four-dimensional. One can now formulate a quantum field theory on this boundary that is "dual" to the theory in the interior in the sense that there is precise dictionary between quantities living on the boundary and quantities in the interior ("the bulk"). "Holographically" refers to the difference in dimensions of the theory living on the boundary and the one living in the bulk.
[+] [-] scottlocklin|7 years ago|reply
The model universes they're talking about, FWIIW, are all just models, with very little relationship to the world of matter we all live in.
[+] [-] logfromblammo|7 years ago|reply
Now turn reality inside out. Because of various symmetries, it looks pretty much the same as it did before. Mathematically, it isn't all that important whether the signs of various things are positive or negative.
Instead of placing a 3D object on the table, draw a 2D shape on the surface of the sphere. Because you everted reality, this causes a 3D object to be reflected onto the table. The math can't really tell whether the object causes the reflection on the sphere, or the pattern on the sphere causes the object to exist.
Now turn the sphere inside out. Put the entire universe on the inside, and all of the stuff inside it (that you knew nothing about anyway, because it's perfectly reflective) on the outside. Now that your sphere encloses the entire universe, you can draw a 2D shapes on the outer boundary and reflect them as 3D shapes somewhere in the interior.
[+] [-] galaxyLogic|7 years ago|reply
[+] [-] rubyn00bie|7 years ago|reply
And... like I'm not very smart, but this is probably a bit like the non-euclidean space demo from yesterday's front page, where the geometry is doing really weird things... perhaps someone smart will come along and give a proper explanation.
[+] [-] kerenua|7 years ago|reply
>...space-time in the interior of the [anti-de Sitter] universe is a projection that emerges from entangled quantum particles living on its outer boundary
A projection? How would this differ if the quantum particles on the outside were not entangled?
>holographic “emergence” of space-time works like a quantum error-correcting code.
holographic in what way? and how is this similar to error correcting code?
>quantum error correction explains how space-time achieves its “intrinsic robustness,”
what is an example of this robustness in space-time?
>...error-correcting codes can recover the information from slightly more than half of your physical qubits, even if the rest are corrupted. This fact that hinted quantum error correction might be related to the way anti-de Sitter space-time arises from quantum entanglement.
how does the effectiveness of error correcting codes, being able to recover information despite 50% corruption, explain space-time?
if anyone could point me in the right direction, I'd really appreciate it. I find this interesting and important but am not smart enough to comprehend it.
[+] [-] chrispeel|7 years ago|reply
https://www.youtube.com/watch?reload=9&v=v5UbN0xx4X0
[+] [-] tbabb|7 years ago|reply
If someone's read the full paper, maybe they can explain the other things-- this article is a bit too vague.
[+] [-] joycian|7 years ago|reply
https://youtu.be/2DIl3Hfh9tY
[+] [-] jfhufl|7 years ago|reply
It's an amazing series. Must watch if you want to know how much we humans understand about our universe.
[+] [-] wallace_f|7 years ago|reply
One of the reasons I like that series is they seem intent to do some justice to competing theories and the fact that we still don't really have a working model of the universe, or know answers as to why theories work the way they do.
Anyways this article was a really hard read for me. It's like the relatively-readable paragraphs are laughing at me--written like I should be understanding them, but I don't, ie:
>The best error-correcting codes can typically recover all of the encoded information from slightly more than half of your physical qubits, even if the rest are corrupted. This fact is what hinted to Almheiri, Dong and Harlow in 2014 that quantum error correction might be related to the way anti-de Sitter space-time arises from quantum entanglement.
[+] [-] earthicus|7 years ago|reply
[+] [-] joemag|7 years ago|reply
[+] [-] jgrowl|7 years ago|reply
[+] [-] osrec|7 years ago|reply
Thus it must somehow be "correcting" for the intrinsic instability of the stuff on the outer edges that gives rise to our reality. Therefore it is in some sense an error correcting code.
Happy to be corrected by those with a deeper understanding!
[+] [-] jchrisa|7 years ago|reply
[+] [-] izzydata|7 years ago|reply
[+] [-] vtomole|7 years ago|reply
[0]: https://www.youtube.com/watch?v=AqWuyeh0SxQ
[1]: https://www.youtube.com/watch?v=F6vGAiMz5kQ
[+] [-] yetihehe|7 years ago|reply
[1] https://skeptics.stackexchange.com/a/30402
[+] [-] joycian|7 years ago|reply
[+] [-] roywiggins|7 years ago|reply
Also, black holes at least superficially have a spatial boundary (the event horizon) so perhaps you can model what happens inside using the holographic principle.
[+] [-] chrispeel|7 years ago|reply
[+] [-] jcranmer|7 years ago|reply
My personal belief is that it's very much a case of looking for the keys where the light is.
[+] [-] planck01|7 years ago|reply
[+] [-] unknown|7 years ago|reply
[deleted]
[+] [-] unknown|7 years ago|reply
[deleted]
[+] [-] luc4sdreyer|7 years ago|reply
[+] [-] xchip|7 years ago|reply
edit: I am a physicist.
[+] [-] joe_the_user|7 years ago|reply
I'd love to hear why a physicist would roll their eyes at this.
[+] [-] dsnuh|7 years ago|reply
So are quantum encoding patterns the Proof Of Work of multidimensional holgraphic blockchains?
Edit: accidentally pasted entire article
[+] [-] jcoffland|7 years ago|reply
It's entirely possible that there is some sort of physically limiting factor that makes it nearly impossible to entangle more than X qbits. Something akin to Amdahl's law for quantum computing. It wouldn't be a very sexy result.
[+] [-] perl4ever|7 years ago|reply
The intuition of a layperson is a bad guide, but I've always had the gut feeling that quantum error correction would prove to be exponentially difficult to scale. If smart people think otherwise, I can hope they're right, but I wouldn't bet money on it until I find an explanation I can grasp. It just sounds like a free lunch, or cold fusion.
[+] [-] mkaziz|7 years ago|reply
It's pretty cool to see a Westerner, Middle Easterner and an East Asian dude (at least based on names ...) collaborate to push the frontiers of science like this!
[+] [-] ralusek|7 years ago|reply
[+] [-] vorg|7 years ago|reply
This international variety of names is common outside the English-speaking world, e.g. the 3 biggest internet companies in China (Alibaba, Tencent, Baidu).
[+] [-] jhuni|7 years ago|reply
[+] [-] maggots|7 years ago|reply
You know, math is really great and all, and you can transform a sphere into a torus, but meat doesn't transform into flies.
[+] [-] baron816|7 years ago|reply
[+] [-] dmurthy|7 years ago|reply
[+] [-] airstrike|7 years ago|reply
Guess we are living in a simulation, after all. A quantum one, to be precise.
[+] [-] Bombthecat|7 years ago|reply
[+] [-] ziont|7 years ago|reply