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Constraints on physical computers in holographic spacetimes
- hurryer 3y agoThey seem to be saying that to do a quantum computation there is a minimum volume of space required in which to perform it which grows in relation to the number of qubits.
- WJW 3y agoThat makes sense. The whole point of the theory about holographic spacetime is that the 3d universe is completely described by the information densities on its edge. This implies that if you need to contain a computation involving a certain amount of information, then you need to have at least that amount of information on the edge. Since the amount of information anywhere is not infinite, this also implies that you need a non-zero amount of edge surface for that computation and thus a non-zero volume. TL;DR: If the volume is too small, you just cannot fit enough information inside and so you cannot do computations which require more information than that.
- PaulHoule 3y agoBut what is the point of computing inside a black hole? You’re not going to get the answer out.
- hoseja 3y agoYou're currently possibly living inside one. Big Bang? - The initial collapse. Universe expansion? - Matter falling in. It may be unfalsifiable from inside though.
- WJW 3y agoFrom the article: While we are ultimately interested in the physical limits of computers in our universe, working within the context of the AdS/CFT correspondence gives us a precise framework for quantum gravity. As well, a fundamental observation in computer science is that the power of computers is robust to “reasonable” changes in the details of the computing model: classical computers can be described in terms of Turing machines, uniform circuits, etc. and the resources needed to solve a given computational problem will change only polynomially. Quantum computers are similarly robust. This robustness suggests understanding the power of computers in AdS is likely to yield insights that apply more broadly. I'm decidedly not an expert in this field but as I understand it there are two points to doing the math in this way: - We know how to describe the inside of a black hole mathematically from an AdS perspective. - IF the AdS/CFT correspondence is true (likely but unproven), then you can generalize from "works inside black hole" to "works inside the normal universe". It's more an exploratory step towards getting a better understanding of complexity theory for quantum computers than it is a practical result intended for doing computations inside black holes.
- tsimionescu 3y agoIt's important to remember that we know very well that we don't live in an AdS space. It's actually not all that likely that many of these theories apply to a de Sitter space-time like our universe, though it remains to be seen. That is, even if the AdS/CFT correspondence is true, it may still turn out that the dS/CFT correspondence is not, and so the results are not applicable to the physical universe.
- bee_rider 3y agoIt turns out it is pointless, we just work in a very fad-driven industry. Once Google started computing in a black hole, it just automatically became popular, and eventually it became common knowledge. “Can’t get fired for computing in a black hole” they’d say. Then the Hackernews guys put their server in a black hole that turned out to be a wormhole, one thing lead to another, and posts were getting sprayed across the timeline. What a mess.
- Nevermark 3y agoGreater understanding is never pointless. Throwing around general accusations of fads doesn’t reduce a paper to part of a fad. Papers stand on their own merits, based on their reasoning, independent if any associations with fads. I expect the properties of a black hole are simply a convenient context to talk about the holographic principle. If the holographic principle holds true, it is true across any border separating one space from another. Likewise, mathematicians prove things about infinities, which we will never encounter directly, but which have useful implications for things in math that can relate to things we might create or encounter.
- thomashop 3y agoI think the comment you are responding to was a joke
- bee_rider 3y agoThe time police insist that I inform everyone that my post about accidentally posting across timelines is, in fact, just a joke, nothing serious, haha.
- KineticLensman 3y agoThis is how you lose the time war...
- 3y ago
- spacecadet 3y agoMaybe.
- Tagbert 3y agoIt's possible that our universe is inside a black hole or a black hole analog.
- nabla9 3y agoThey describe computations that are forbidden despite the inputs to these computations being small, and the description of the computation being easily fit inside the black hole.
- WJW 3y agoSure? That doesn't even matter for normal computers though. Busy beaver algorithms can be described in very few lines of code but can generate incredible complexity. It's not super difficult to devise an algorithm that would need many more bits of information than just its description+inputs to accurately describe all the state required, and that is in fact exactly what the authors of this paper did.
- Nevermark 3y agoLimits on all computational complexity in a given regime are a quite different result from noting particular algorithms have high computational complexity. And if these results and the holographic principle holds, then these limits would apply to all computers. Even “normal” ones.
- goldenkey 3y agoThis makes a lot of sense. Laundauer's principle shows that the amount of energy to store a bit is directly proportional to temperature, thus, energy loop size/travel time at the speed of light. The lower the temperature, the smaller the loop radius, the lower the energy requirement. There is no primitive of storage in our universe, it's all delay line memory. https://en.wikipedia.org/wiki/Delay-line_memory https://en.wikipedia.org/wiki/Delay-line_memory
- alecst 3y agoLandauer's principle is about memory erasure, not storage. Charles Bennett talks about this in one of his papers.
- goldenkey 3y agoFrom what I understand, the cost of "erasure" is really just the cost of replacement. True erasure can't exist in a unitary universe. In the same way, the cost of "allocation" is effectively the cost of replacement too, since our universe is unitary and no information can actually be lost at the fundamental level. Think virtual memory vs actual memory, forks, copy-on-write mechanics, etc. Are we juggling/managing memory or actually creating any? As far as we know, the universe itself is a reversible quantum supercomputer. There are no erasures and a reversible computer is 100% efficient. If the formula is correct at all, it should apply to the reverse process of setting bits, not just deletion.
- alecst 3y agoIf you're talking about Landauer's principle, you're talking about a universe where entropy increases, which means some information is lost. By the way, here's the paper I was talking about. I feel like you might enjoy reading it: https://sites.cc.gatech.edu/computing/nano/documents/Bennett%20-%20The%20Thermodynamics%20Of%20Computation.pdf https://sites.cc.gatech.edu/computing/nano/documents/Bennett...
- goldenkey 3y ago
- ko27 3y agoThere is one important thing everybody seems to be missing here. This applies to the theoretical AdS universe, NOT to our universe as far as we know.
- 3cats-in-a-coat 3y agoBut our universe adheres to AdS constraints. As far as we know. When you reach the information density limit in AdS, in our universe you get a black hole.
- undersuit 3y agoA theory used to establish the scene in https://en.wikipedia.org/wiki/Vacuum_Diagrams https://en.wikipedia.org/wiki/Vacuum_Diagrams
- snarkconjecture 3y agoThe AdS/CFT correspondence was published slightly after that collection. Are you saying Baxter scooped Maldacena?
- queuebert 3y agoWhile that correspondence proof is relatively new, AdS as a theory is quite old.
- snarkconjecture 3y agoThe great-grandparent comment was talking about an "information density limit" and black holes in our universe, so I assumed the referenced sci-fi collection had something to do with holography. I don't know of any particular emphasis on AdS in that context before 1997. Elaborate? Obviously you can stick GR in AdS, but AFAIK nothing about that would've seemed interesting with regards to holography before Maldacena, let alone plausibly providing inspiration to a fiction author. To be less roundabout than my previous comment: I think Baxter may have been inspired by the holographic principle in general, but I doubt AdS crossed his mind at all when he was writing these stories in the 80s and early 90s. (EDIT: or maybe Baxter was thinking about AdS but not about holography. I haven't read his work.)
- lanstin 3y agoNot minimum volume but volume with a minimal boundary area proportional to the size of the states your computation explores. The weird thing about these holographic mappings is that stuff you would expect to be limited by volume is limited by surface area of which there is rather a lot less of. The cool thing is that there are few independent such results, starting with the entropy of a black hole, so if you like to speculate on possible physics beyond QFT it gives you some material.
- konstantinua00 3y ago...so just do a zigzag to fit more in same space?
- cvoss 3y agoEven if you can imagine a baroque and spacious boundary that is to your liking, it remains the case that the simpler, economical boundary still exists, and you have to reckon with that one.
- narinxas 3y ago> They seem to be saying that to do a quantum computation there is a minimum volume of space required in which to perform it which grows in relation to the number of qubits. they say information uses up space. got it...
- Woshiwuja 3y agoELI5? am dummy
- block_dagger 3y agoTo compute, a minimum physical space is required. Mostly impossible inside black holes.
- Woshiwuja 3y agoThank you my brother, my physics lingo for this was kinda lacking
- Nevermark 3y agoCorrection: a volume with a minimal surface area is required. Surface area goes up slower than volume, if a volume shape simply scales up. That is the interesting result, if it holds up. My conjecture: An increasingly fractal surface whose area increases as fast or faster than an increasing volume would get around this limit.
- Suppafly 3y agoI assumed it was going to be something about how we live in a holographic simulation or something.
- bobsmooth 3y agoThis will be useful when humanity needs to retreat into black holes to (subjectively) extend the heat death of the universe.
- nielsbot 3y agoSounds like a Three Body Problem
- kridsdale3 3y agoMaybe that already happened 14 gigayears ago.
- deleted 3y ago[deleted]
- onetimeuse92304 3y agoMy first glitch happens when trying to parse "computations (...) which cannot be implemented inside of black holes". My assumption is that whatever computer is used it is falling between the event horizon and the singularity. The masses involved are the mass of black hole before the object falling into it and the mass of the object. The amount of computation that can be done is dependant on the mass of the object and the time available. The time available is some kind of product of the mass of the object and the mass of the black hole. As the object is reaching the event horizon, the event horizon expands to accommodate the object, but this expansion isn't super simple as my understanding the expansion itself progresses at a speed of light (the other side of the black hole takes time to be affected by the object falling).
- user8501 3y agoAw crap! What are we gonna do now?