16 ms·

Reversible computing escapes the lab

277 points by jasondavies 2y ago

EncomLab 2y ago
The miniscule amount of energy retained from the "reverse computation" will be absolutely demolished by the first DRAM refresh.
- fintler 2y ago
  I doubt it would use DRAM. Maybe some sort of MRAM/FeRAM would be a better fit. Or maybe a tiny amount of memory (e.g. Josephson junction) in a quantum circuit at some point in the future.
  - colanderman 2y ago
    SRAM is actually very architecturally similar to some adiabatic circuit topologies.
siver_john 2y ago
This is really cool, I never expected to see reversible computation made in electrical systems. I learned about it undergrad taking a course by Bruce MacLennan* though it was more applied to "billiard ball" or quantum computing. It was such a cool class though. *Seems like he finally published the text book he was working on when teaching the class: [https://www.amazon.com/dp/B0BYR86GP7?ref_=pe_3052080_397514860][https://www.amazon.com/dp/B0BYR86GP7?ref_=pe_3052080_397514860] https://www.amazon.com/dp/B0BYR86GP7?ref_=pe_3052080_3975148...
colanderman 2y ago
Nice, these ideas have been around for a long time but never commercialized to my knowledge. I've done some experiments in this area with simulations and am currently designing some test circuitry to be fabbed via Tiny Tapeout. Reversibility isn't actually necessary for most of the energy savings. It saves you an extra maybe 20% beyond what adiabatic techniques can do on their own. Reason being, the energy of the information itself pales in comparison to the resistive losses which dominate the losses in adiabatic circuits, and it's actually a (device-dependent) portion of these resistive losses which the reversible aspect helps to recover, not the energy of information itself. I'm curious why Frank chose to go with a resonance-based power-clock, instead of a switched-capacitor design. In my experience the latter are nearly as efficient (losses are still dominated by resistive losses in the powered circuit itself), and are more flexible as they don't need to be tuned to the resonance of the device. (Not to mention they don't need an inductor.) My guess would be that, despite requiring an on-die inductor, the overall chip area required is much less than that of a switched-capacitor design. (You only need one circuit's worth of capacitance, vs. 3 or more for a switched design, which quadruples your die size....) I'm actually somewhat skeptical of the 4000x claim though. Adiabatic circuits can typically only provide about a single order of magnitude power savings over traditional CMOS -- they still have resistive losses, they just follow a slightly different equation (f²RC²V², vs. fCV²). But RC and C are figures of merit for a given silicon process, and fRC (a dimensionless figure) is constrained by the operational principles of digital logic to the order of 0.1, which in turn constrains the power savings to that order of magnitude regardless of process. Where you can find excess savings though is simply by reducing operating frequency. Adiabatic circuits benefit more from this than traditional CMOS. Which is great if you're building something like a GPU which can trade clock frequency for core count.
- itissid 2y ago
  Can one define the process of an adiabetic circuit goes through like one would do analogusly for the carnot engine? The idea being coming up with a theoretical cieling for the efficiency of such a circuit in terms of circuit parameters?
  - colanderman 2y ago
    Yes a similar analysis is where the above expression f²RC²V² comes from. Essentially -- (and I'm probably missing a factor of 2 or 3 somewhere as I'm on my phone and don't have reference materials) -- in an adiabatic circuit the unavoidable power loss for any individual transistor stems from current (I) flowing through that transistor's channel (a resistor R) on its way to and from another transistor's gate (a capacitor C). So that's I²R unavoidable power dissipation. I must be sufficient to fill and then discharge the capacitor to/from operating voltage (V) in the time of one cycle (1/f). So I=2fCV. Substituting this gives 4f²RC²V². Compare to traditional CMOS, wherein the gate capacitance C is charged through R from a voltage source V. It can be shown that this dissipates ½CV² of energy though the resistor in the process, and the capacitor is filled with an equal amount of energy. Discharging then dissipates this energy through the same resistor. Repeat this every cycle for a total power usage of fCV². Divide these two figures and we find that adiabatic circuits use 4fRC times as much energy as traditional CMOS. However, f must be less than about 1/(5RC) for a CMOS circuit to function at all (else the capacitors don't charge sufficiently during a cycle) so this is always power savings in favor of adiabatics. And notably, decreasing f of an adiabatic circuit from the maximum permissible for CMOS on the same process increases the efficiency gain proportionally. (N.B., I feel like I missed a factor of 2 somewhere as this analysis differs slightly from my memory. I'll return with corrections if I find an error.)
- pfdietz 2y ago
  Maybe this would work better with superconducting electronics?
  - colanderman 2y ago
    Possibly, that's an interesting thought. The main benefit of adiabatics as I see them is that, all else being equal, a process improvement of the RC figure can be used to enable either an increase in operating frequency or a decrease in power usage (this is reflected as the additional factor of fRC in the power equation). With traditional CMOS, this only can benefit operating frequency -- power usage is independent of the RC product per se. Supercondition (or near-superconduction) is essentially a huge improvement in RC which wouldn't be able to be realized as an increase in operating frequency due to speed of light limitations, so adiabatics would see an outsize benefit in that case.
EncomLab 2y ago
Calling the addition of an energy storage device into a transistor "reverse computing" is like calling a hybrid car using regenerative braking "reverse driving". It's a very interesting concept - best discussed over pints at the pub on a Sunday afternoon along with over unity devices and the sad lack of adoption of bubble memory.
- perching_aix 2y ago
  Sounds like a good time :)
- colanderman 2y ago
  The reverse computing is independent of the energy storage mechanism. It's used to "remember" how to route the energy for recovery.
- IIAOPSW 2y ago
  Well actually, "reversible driving" is perfectly apt in the sense of acceleration being a reversible process. It means that in theory the net energy needed to drive anywhere is zero because all the energy spent on acceleration is gained back on braking. Yes I know in practice there's always friction loss, but the point is there isn't a theoretical minimum amount of friction that has to be there. In principle a car with reversible driving can get anywhere with asymptotically close to zero energy spent. Put another way, there is no way around the fact that a "non-reversible car" has to have friction loss because the brakes work on friction. But there is no theoretical limit to how far you can reduce friction in reversible driving.
  - immibis 2y ago
    Actually, a non-reversible car also has no lower energy limit, as long as you drive on a flat surface (same for a reversible one) and can get to the answer arbitrarily slowly. An ideal reversible computer also works arbitrarily slowly. To make it go faster, you need to put energy in. You can make it go arbitrarily slowly with arbitrarily little energy, just like a non-reversible car.
  - EncomLab 2y ago
PaulHoule 2y ago
Notably the physical limit is https://en.wikipedia.org/wiki/Landauer%27s_principle https://en.wikipedia.org/wiki/Landauer%27s_principle it doesn't necessarily take any energy at all to process information, but it does take roughly kT work of energy to erase a bit of information. It's related to https://en.wikipedia.org/wiki/Maxwell%27s_demon https://en.wikipedia.org/wiki/Maxwell%27s_demon as, to complete cycles, the demon has to clear its memory.
- Y_Y 2y ago
  Does it not take energy to process information? Can any computable function be computed with arbitrarily low energy input/entropy increase?
  - colanderman 2y ago
    No, and yes, so long as you don't delete information. Think of a marble-based computer, whose inner workings are frictionless and massless. The marbles roll freely without losing energy unless they are forced to stop somehow, but computation is nonetheless performed.
    - Y_Y 2y ago
      I don't know how to compute with marbles without mass and stopping. Marble computers I've seen rely on gravity and friction, though I'd love to see one that didn't.
pama 2y ago
The ideas are neat and both Landauer and Bennet did some great work and left a powerful legacy. The energetic limits we are talking about are not yet relevant in modern computers. The amount of excess thermal energy for performing 10^26 erasures associated to some computation (of say an LLM that would be too powerful for the current presidential orders) would only be about 0.1kWh, so 10 minutes of a single modern GPU. There are other advantages to reversibility, of course, and maybe one day even that tiny amount of energy savings will matter.
leoc 2y ago
Also an Edward Fredkin https://en.wikipedia.org/wiki/Edward_Fredkin https://en.wikipedia.org/wiki/Edward_Fredkin interest https://en.wikipedia.org/wiki/Fredkin_gate https://en.wikipedia.org/wiki/Fredkin_gate .
- DonHopkins 2y ago
  As well as Tommaso Toffoli, Norman Margolus, Tom Knight, Richard Feynman, and Charles Bennett: Reversible Computing, Tommaso Toffoli: https://publications.csail.mit.edu/lcs/pubs/pdf/MIT-LCS-TM-151.pdf https://publications.csail.mit.edu/lcs/pubs/pdf/MIT-LCS-TM-1... >Abstract. The theory of reversible computing is based on invertible primitives and composition rules that preserve invertibility. With these constraints, one can still satisfactorily deal with both functional and structural aspects of computing processes; at the same time, one attains a closer correspondence between the behavior of abstract computing systems and the microscopic physical laws (which are presumed to be strictly reversible) that underly any concrete implementation of such systems. According to a physical interpretation, the central result of this paper is that it is ideally possible to build sequential circuits with zero internal power dissipation. A Scalable Reversible Computer in Silicon: https://www.researchgate.net/publication/2507539_A_Scalable_Reversible_Computer_in_Silicon https://www.researchgate.net/publication/2507539_A_Scalable_... Reversible computing: https://web.eecs.utk.edu/~bmaclenn/Classes/494-594-UC-F17/handouts/LNUC-II.C.pdf https://web.eecs.utk.edu/~bmaclenn/Classes/494-594-UC-F17/ha... >In 1970s, Ed Fredkin, Tommaso Toffoli, and others at MIT formed the Information Mechanics group to the study the physics of information. As we will see, Fredkin and Toffoli described computation with idealized, perfectly elastic balls reflecting o↵ barriers. The balls have minimum dissipation and are propelled by (conserved) momentum. The model is unrealistic but illustrates many ideas of reversible computing. Later we will look at it briefly (Sec. C.7). >They also suggested a more realistic implementation involving “charge packets bouncing around along inductive paths between capacitors.” Richard Feynman (Caltech) had been interacting with Information Mechanics group, and developed “a full quantum model of a serial reversible computer” (Feynman, 1986). >Charles Bennett (1973) (IBM) first showed how any computation could be embedded in an equivalent reversible computation. Rather than discarding information (and hence dissipating energy), it keeps it around so it can later “decompute” it back to its initial state. This was a theoretical proof based on Turing machines, and did not address the issue of physical implementation. [...] >How universal is the Toffoli gate for classical reversible computing: https://quantumcomputing.stackexchange.com/questions/21064/how-universal-is-the-toffoli-gate-for-classical-reversible-computing https://quantumcomputing.stackexchange.com/questions/21064/h...
entaloneralie 2y ago
Henry G. Baker wrote this paper titled "The Thermodynamics of Garbage Collection" in the 90s about linear logic, stack machines, reversibility and the cost of erasing information: https://wiki.xxiivv.com/docs/baker_thermodynamics.html https://wiki.xxiivv.com/docs/baker_thermodynamics.html A subset of FRACTRAN programs are reversible, and I would love to see rewriting computers as a potential avenue for reversible circuit building(similar to the STARAN cpu): https://wiki.xxiivv.com/site/fractran.html#reversibility https://wiki.xxiivv.com/site/fractran.html#reversibility
jheriko 2y ago
interesting. on a basic level, with the gates, it seems, if you have at most two input amounts of work, and get at most one out, then storing the lost work for later reuse makes sense
iamnotagenius 2y ago
The simplest, dumbest alternative to for reversible computing is to install datacenters in ex-USSR, where there is still (slowly disappearing) rich infrastructure for central hot water. Instead of charging people, utilities can charge both people and datacenters and yet lower the carbon footprint.
- istjohn 2y ago
  I believe it would be more efficient to use a heat pump for the district heating even if the datacenter heat is just dumped. Heat pumps can get up to 400% efficiency.
  - cogman10 2y ago
    What do you mean by efficient? The heat emitted by the electronics will always be emitted and needs to go somewhere. If 1MWh of that heat is dumped into district heating how would that be less efficient than the 1MWh being dumped in the atmosphere to (hopefully) be reclaimed by a heat pump elsewhere? Or, alternatively, that 1MWh could be absorbed by the already existing datacenter AC coils which could ultimately still be used to heat up district water as it cools the refrigerant. (People actually do this with swimming pools, using the coils from their AC to heat the pool).
    - Klaus23 2y ago
      istjohn is right. Using a heat pump instead of resistive heating (which is basically what a data centre is) is many times more efficient. That doesn't mean we shouldn't use the heat a data centre provides. It just means that it is not a good idea to neglect the development of energy-saving technology because the heat produced can be used somewhere else.
      - witch-king 2y ago
        the issue is that there is an upper limit to how much heat can be removed from a system each cycle, so even if you have a way to disperse the removed heat in a useful way you still can't grow compute beyond a certain point. And because scaling is exponential even immersing the whole rack into liquid nitrogen would only buy a few years of computing growth post-Moore's law.
DonHopkins 2y ago
https://news.ycombinator.com/item?id=30735397 https://news.ycombinator.com/item?id=30735397 DonHopkins on March 19, 2022 | parent | context | favorite | on: Ask HN: What book changed your life? Cellular Automata Machines: A New Environment for Modeling Published April 1987 by MIT Press. ISBN: 9780262200608. http://mitpress.mit.edu/books/cellular-automata-machines http://mitpress.mit.edu/books/cellular-automata-machines http://www.researchgate.net/publication/44522568_Cellular_automata_machines__a_new_environment_for_modeling__Tommaso_Toffoli_Norman_Margolus http://www.researchgate.net/publication/44522568_Cellular_au... https://donhopkins.com/home/cam-book.pdf https://donhopkins.com/home/cam-book.pdf https://github.com/SimHacker/CAM6/blob/master/javascript/CAM6.js#L41 https://github.com/SimHacker/CAM6/blob/master/javascript/CAM... themodelplumber on March 20, 2022 | prev [–] I'm curious, how did the book change your life? What kind of problems did the authors model using their approach? I'm new to the topic, thanks for any input. DonHopkins on March 22, 2022 | parent [–] It really helped me get my head around how to understand and program cellular automata rules, which is a kind of massively parallel distributed "Think Globally, Act Locally" approach that also applies to so many other aspects of life. But by "life" I don't mean just the cellular automata rule "life"! Not to be all depressing like Marvin the Paranoid Android, but I happen to think "life" is overrated. ;) There are so many billions of other extremely interesting cellular automata rules besides "life" too, so don't stop once you get bored with life! ;) https://www.youtube.com/watch?v=CAA67a2-Klk https://www.youtube.com/watch?v=CAA67a2-Klk For example, it's kind of like how the world wide web works: "Link Globally, Interact Locally": https://donhopkins.medium.com/scriptx-and-the-world-wide-web-link-globally-interact-locally-1995-38f35e32ea2f https://donhopkins.medium.com/scriptx-and-the-world-wide-web... It's also very useful for understanding other massively distributed locally interacting parallel systems, epidemiology, economics, morphogenesis (reaction-diffusion systems, like how a fertilized egg divides and specializes into an organism), GPU programming and optimization, neural networks and machine learning, information and chaos theory, and physics itself. I've discussed the book and the code I wrote based on it with Norm Margolus, one of the authors, and he mentioned that he really likes rules that are based on simulating physics, and also thinks reversible cellular automata rules are extremely important (and energy efficient in a big way, in how they relate to physics and thermodynamics). The book has interesting sections about physical simulations like spin glasses (Ising Spin model of the magnetic state of atoms of solid matter), and reversible billiard ball simulations (like deterministic reversible "smoke and mirrors" with clouds of moving particles bouncing off of pinball bumpers and each other). Spin Glass: https://en.wikipedia.org/wiki/Spin_glass https://en.wikipedia.org/wiki/Spin_glass >In condensed matter physics, a spin glass is a magnetic state characterized by randomness, besides cooperative behavior in freezing of spins at a temperature called 'freezing temperature' Tf. Magnetic spins are, roughly speaking, the orientation of the north and south magnetic poles in three-dimensional space. In ferromagnetic solids, component atoms' magnetic spins all align in the same direction. Spin glass when contrasted with a ferromagnet is defined as "disordered" magnetic state in which spins are aligned randomly or not with a regular pattern and the couplings too are random. Billiard Ball Computer: https://en.wikipedia.org/wiki/Billiard-ball_computer https://en.wikipedia.org/wiki/Billiard-ball_computer >A billiard-ball computer, a type of conservative logic circuit, is an idealized model of a reversible mechanical computer based on Newtonian dynamics, proposed in 1982 by Edward Fredkin and Tommaso Toffoli. Instead of using electronic signals like a conventional computer, it relies on the motion of spherical billiard balls in a friction-free environment made of buffers against which the balls bounce perfectly. It was devised to investigate the relation between computation and reversible processes in physics. https://en.wikipedia.org/wiki/Reversible_cellular_automaton https://en.wikipedia.org/wiki/Reversible_cellular_automaton >A reversible cellular automaton is a cellular automaton in which every configuration has a unique predecessor. That is, it is a regular grid of cells, each containing a state drawn from a finite set of states, with a rule for updating all cells simultaneously based on the states of their neighbors, such that the previous state of any cell before an update can be determined uniquely from the updated states of all the cells. The time-reversed dynamics of a reversible cellular automaton can always be described by another cellular automaton rule, possibly on a much larger neighborhood. >[...] Reversible cellular automata form a natural model of reversible computing, a technology that could lead to ultra-low-power computing devices. Quantum cellular automata, one way of performing computations using the principles of quantum mechanics, are often required to be reversible. Additionally, many problems in physical modeling, such as the motion of particles in an ideal gas or the Ising model of alignment of magnetic charges, are naturally reversible and can be simulated by reversible cellular automata. Also I've frequently written on HN about Dave Ackley's great work on Robust-First Computing and the Moveable Feast Machine, which I think is brilliant, and quite important in the extremely long term (which is coming sooner than we think). https://news.ycombinator.com/item?id=22304110 https://news.ycombinator.com/item?id=22304110 https://news.ycombinator.com/item?id=22300376 https://news.ycombinator.com/item?id=22300376 https://news.ycombinator.com/item?id=22303313 https://news.ycombinator.com/item?id=22303313
DonHopkins 2y ago
https://news.ycombinator.com/item?id=35366971 https://news.ycombinator.com/item?id=35366971 Tipler's Omega Point cosmology: https://en.wikipedia.org/wiki/Frank_J._Tipler#The_Omega_Point https://en.wikipedia.org/wiki/Frank_J._Tipler#The_Omega_Poin... >The Omega Point cosmology >The Omega Point is a term Tipler uses to describe a cosmological state in the distant proper-time future of the universe.[6] He claims that this point is required to exist due to the laws of physics. According to him, it is required, for the known laws of physics to be consistent, that intelligent life take over all matter in the universe and eventually force its collapse. During that collapse, the computational capacity of the universe diverges to infinity, and environments emulated with that computational capacity last for an infinite duration as the universe attains a cosmological singularity. This singularity is Tipler's Omega Point.[7] With computational resources diverging to infinity, Tipler states that a society in the far future would be able to resurrect the dead by emulating alternative universes.[8] Tipler identifies the Omega Point with God, since, in his view, the Omega Point has all the properties of God claimed by most traditional religions.[8][9] >Tipler's argument of the omega point being required by the laws of physics is a more recent development that arose after the publication of his 1994 book The Physics of Immortality. In that book (and in papers he had published up to that time), Tipler had offered the Omega Point cosmology as a hypothesis, while still claiming to confine the analysis to the known laws of physics.[10] >Tipler, along with co-author physicist John D. Barrow, defined the "final anthropic principle" (FAP) in their 1986 book The Anthropic Cosmological Principle as a generalization of the anthropic principle: >Intelligent information-processing must come into existence in the Universe, and, once it comes into existence, will never die out.[11] >One paraphrasing of Tipler's argument for FAP runs as follows: For the universe to physically exist, it must contain living observers. Our universe obviously exists. There must be an "Omega Point" that sustains life forever.[12] >Tipler purportedly used Dyson's eternal intelligence hypothesis to back up his arguments. Cellular Automata Machines: A New Environment for Modeling: https://news.ycombinator.com/item?id=30735397 https://news.ycombinator.com/item?id=30735397 >It's also very useful for understanding other massively distributed locally interacting parallel systems, epidemiology, economics, morphogenesis (reaction-diffusion systems, like how a fertilized egg divides and specializes into an organism), GPU programming and optimization, neural networks and machine learning, information and chaos theory, and physics itself. >I've discussed the book and the code I wrote based on it with Norm Margolus, one of the authors, and he mentioned that he really likes rules that are based on simulating physics, and also thinks reversible cellular automata rules are extremely important (and energy efficient in a big way, in how they relate to physics and thermodynamics). >The book has interesting sections about physical simulations like spin glasses (Ising Spin model of the magnetic state of atoms of solid matter), and reversible billiard ball simulations (like deterministic reversible "smoke and mirrors" with clouds of moving particles bouncing off of pinball bumpers and each other). Spin Glass: https://en.wikipedia.org/wiki/Spin_glass https://en.wikipedia.org/wiki/Spin_glass >In condensed matter physics, a spin glass is a magnetic state characterized by randomness, besides cooperative behavior in freezing of spins at a temperature called 'freezing temperature' Tf. Magnetic spins are, roughly speaking, the orientation of the north and south magnetic poles in three-dimensional space. In ferromagnetic solids, component atoms' magnetic spins all align in the same direction. Spin glass when contrasted with a ferromagnet is defined as "disordered" magnetic state in which spins are aligned randomly or not with a regular pattern and the couplings too are random. Billiard Ball Computer: https://en.wikipedia.org/wiki/Billiard-ball_computer https://en.wikipedia.org/wiki/Billiard-ball_computer >A billiard-ball computer, a type of conservative logic circuit, is an idealized model of a reversible mechanical computer based on Newtonian dynamics, proposed in 1982 by Edward Fredkin and Tommaso Toffoli. Instead of using electronic signals like a conventional computer, it relies on the motion of spherical billiard balls in a friction-free environment made of buffers against which the balls bounce perfectly. It was devised to investigate the relation between computation and reversible processes in physics. Reversible Cellular Automata: https://en.wikipedia.org/wiki/Reversible_cellular_automaton https://en.wikipedia.org/wiki/Reversible_cellular_automaton >A reversible cellular automaton is a cellular automaton in which every configuration has a unique predecessor. That is, it is a regular grid of cells, each containing a state drawn from a finite set of states, with a rule for updating all cells simultaneously based on the states of their neighbors, such that the previous state of any cell before an update can be determined uniquely from the updated states of all the cells. The time-reversed dynamics of a reversible cellular automaton can always be described by another cellular automaton rule, possibly on a much larger neighborhood. >[...] Reversible cellular automata form a natural model of reversible computing, a technology that could lead to ultra-low-power computing devices. Quantum cellular automata, one way of performing computations using the principles of quantum mechanics, are often required to be reversible. Additionally, many problems in physical modeling, such as the motion of particles in an ideal gas or the Ising model of alignment of magnetic charges, are naturally reversible and can be simulated by reversible cellular automata. Theory of Self-Reproducing Automata: John von Neumann's Quantum Mechanical Universal Constructors: https://news.ycombinator.com/item?id=22738268 https://news.ycombinator.com/item?id=22738268 [...] Third, the probabilistic quantum mechanical kind, which could mutate and model evolutionary processes, and rip holes in the space-time continuum, which he unfortunately (or fortunately, the the sake of humanity) didn't have time to fully explore before his tragic death. >p. 99 of "Theory of Self-Reproducing Automata": >Von Neumann had been interested in the applications of probability theory throughout his career; his work on the foundations of quantum mechanics and his theory of games are examples. When he became interested in automata, it was natural for him to apply probability theory here also. The Third Lecture of Part I of the present work is devoted to this subject. His "Probabilistic Logics and the Synthesis of Reliable Organisms from Unreliable Components" is the first work on probabilistic automata, that is, automata in which the transitions between states are probabilistic rather than deterministic. Whenever he discussed self-reproduction, he mentioned mutations, which are random changes of elements (cf. p. 86 above and Sec. 1.7.4.2 below). In Section 1.1.2.1 above and Section 1.8 below he posed the problems of modeling evolutionary processes in the framework of automata theory, of quantizing natural selection, and of explaining how highly efficient, complex, powerful automata can evolve from inefficient, simple, weak automata. A complete solution to these problems would give us a probabilistic model of self-reproduction and evolution. [9] [9] For some related work, see J. H. Holland, "Outline for a Logical Theory of Adaptive Systems", and "Concerning Efficient Adaptive Systems". https://www.deepdyve.com/lp/association-for-computing-machinery/outline-for-a-logical-theory-of-adaptive-systems-efsWyqMa1l https://www.deepdyve.com/lp/association-for-computing-machin... https://deepblue.lib.umich.edu/bitstream/handle/2027.42/5578/bac4296.0001.001.pdf?sequence=5 https://deepblue.lib.umich.edu/bitstream/handle/2027.42/5578... https://www.worldscientific.com/worldscibooks/10.1142/10841 https://www.worldscientific.com/worldscibooks/10.1142/10841 perl4ever on Dec 26, 2017 | root | parent | next [–] Tipler's Omega Point prediction doesn't seem like it would be compatible with the expanding universe, would it? Eventually everything will disappear over the speed-of-light horizon, and then it can't be integrated into one mind. DonHopkins on Dec 26, 2017 | root | parent | next [–] It also wishfully assumes that the one mind can't think of better things to do with its infinite amount of cloud computing power than to simulate one particular stone age mythology. Then again, maybe it's something like the 1996 LucasArts game Afterlife, where you simulate every different religion's version of heaven and hell at once. https://en.wikipedia.org/wiki/Afterlife_(video_game) https://en.wikipedia.org/wiki/Afterlife_(video_game) The primary goal of the game is to provide divine and infernal services for the inhabitants of the afterlife. This afterlife caters to one particular planet, known simply as the Planet. The creatures living on the Planet are called EMBOs, or Ethically Mature Biological Organisms. When an EMBO dies, its soul travels to the afterlife where it attempts to find an appropriate "fate structure". Fate structures are places where souls are rewarded or punished, as appropriate, for the virtues or sins that they practiced while they were alive.
DonHopkins 2y ago
Reversible Computing (2016) [video] (youtube.com) https://news.ycombinator.com/item?id=16007128 https://news.ycombinator.com/item?id=16007128 https://www.youtube.com/watch?v=rVmZTGeIwnc https://www.youtube.com/watch?v=rVmZTGeIwnc DonHopkins on Dec 26, 2017 | next [–] Billiard Ball cellular automata, proposed and studied by Edward Fredkin and Tommaso Toffoli, are one interesting type of reversible computer. The Ising spin model of ferromagnetism is another reversible cellular automata technique. https://en.wikipedia.org/wiki/Billiard-ball_computer https://en.wikipedia.org/wiki/Billiard-ball_computer https://en.wikipedia.org/wiki/Reversible_cellular_automaton https://en.wikipedia.org/wiki/Reversible_cellular_automaton https://en.wikipedia.org/wiki/Ising_model https://en.wikipedia.org/wiki/Ising_model If billiard balls aren't creepy enough for you, live soldier crabs of the species Mictyris guinotae can be used in place of the billiard balls. https://www.newscientist.com/blogs/onepercent/2012/04/researchers-build-crab-powered.html https://www.newscientist.com/blogs/onepercent/2012/04/resear... https://www.wired.com/2012/04/soldier-crabs/ https://www.wired.com/2012/04/soldier-crabs/ http://www.complex-systems.com/abstracts/v20_i02_a02.html http://www.complex-systems.com/abstracts/v20_i02_a02.html Robust Soldier Crab Ball Gate Yukio-Pegio Gunji, Yuta Nishiyama. Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501, Japan. Andrew Adamatzky. Unconventional Computing Centre. University of the West of England, Bristol, United Kingdom. Abstract Soldier crabs Mictyris guinotae exhibit pronounced swarming behavior. Swarms of the crabs are tolerant of perturbations. In computer models and laboratory experiments we demonstrate that swarms of soldier crabs can implement logical gates when placed in a geometrically constrained environment.
yalogin 2y ago
The concept completely flummoxed me but how does this play with quantum computers? That’s the direction we are going aren’t we?
- fallingfrog 2y ago
  Quantum computations have to be reversible , because you have to collapse the wave function and take a measurement to throw away any bits of data. You can accumulate junk bits as long as they remain in a superposition. But at some point you have to take a measurement. So, very much related.
amelius 2y ago
> The main way to reduce unnecessary heat generation in transistor use—to operate them adiabatically—is to ramp the control voltage slowly instead of jumping it up or down abruptly. But if you change the gate voltage slowly, then the transistor will be for a longer period in the resistive region where it dissipates energy. Shouldn't you go between the OFF and ON states as quickly as possible?
- colanderman 2y ago
  The trick is not to have a voltage across the channel while it's transitioning states. For this reason, adiabatic circuits are typically "phased" such that any given adiabatic logic gate is either having its gates charged or discharged (by the previous logic gate), or current is passing through its channels to charge/discharge the next logic gate.
  - amelius 2y ago
    Interesting, thanks!
stevage 2y ago
Wow. This whole logic sounds like something really harebrained from a Dr Who episode: "It takes energy to destroy information. Therefore if you don't destroy information, it doesn't take energy!" - sounds completely illogical. I honestly don't understand from the article how you "recover energy". Yet I have no reason to disbelieve it.
- kibwen 2y ago
  Someone else here compared it to regenerative braking in cars, which is what made it click for me. If you spend energy to accelerate, then recapture that energy while decelerating, then you can manage to transport yourself while your net energy expenditure is zero (other than all that pesky friction). On the other hand, if you spend energy to accelerate, then shed all that energy via heat from your brake pads, then you need to expend new energy to accelerate next time.
- EncomLab 2y ago
  If the concept has existed for 60 years and no one has capitalized it yet - you can bet it's more Dr. Who than reality.
Jean-Papoulos 2y ago
>it is producing a chip that, for the first time, recovers energy used in an arithmetic circuit. The next chip, projected to hit the market in 2027, will be an energy-saving processor specialized for AI inference. The 4,000x energy-efficiency improvement is on Vaire’s road map but probably 10 or 15 years out. How I wish I could place bets on this never happening. >In the following years, Vaire plans to design the first reversible chip specialized for AI inference. These guys are cashing in on AI hype. Watch them raise VC money, give themselves 6 figures salaries and file for bankruptcy in 3 years.
- EncomLab 2y ago
  You are exactly correct - the combination of deep belief in the ability to obtain quick riches by investing in the "next big thing" aligned with a large gap of knowledge between reality and hype, all mixed into a milieu of in-group speak and customs always leads to the proliferation of the con. It's the next "Long Blockchain Corp!"
  - robertlagrant 2y ago
    It's also how proliferation of advances happen. Nothing advances unless someone tries it, and trying it costs money.
- z3t4 2y ago
  4000x cost saving would bring operation costs for compute down close to zero, meaning marginal costs for data centers would go down as well, meaning data centers would buy a shit ton of these chips. Think the valuation of Nvidia x 1000 I still think the technical challange is too big, but it's high reward for early investors.
  - EncomLab 2y ago
    This is insanity - "compute" is a tiny fraction of energy usage compared to memory, data storage, and data retrieval.
    - 2y ago
lkm0 2y ago
All of quantum computing is reversible by nature (until you measure the state, of course). Yet, there'some research in the field focusing on irreversible ("non-unitary") quantum algorithms and it appears there is some advantage in throwing away, algorithmically speaking, the reversibility. See https://arxiv.org/abs/2309.16596 https://arxiv.org/abs/2309.16596 It's interesting that classical and quantum computing researchers are each looking in the direction of the other field.
IgorPartola 2y ago
This is probably a dumb question, but where does this fail: what happens if I run something like the SHA256 algorithm or a sudoku solver backwards using these techniques? I assume that wouldn’t actually work, but why?
- Enginerrrd 2y ago
  I'm speaking out of my depth, but as I understand you'd need the extra information that was accumulated along the way (as shown in the XOR gate example) If you had that you certainly could run sha 256 in reverse but for the starting hash + info, you have at least as many bits as the starting information that was hashed.

277 points by jasondavies 2y ago

The miniscule amount of energy retained from the "reverse computation" will be absolutely demolished by the first DRAM refresh.

fintler 2y ago
I doubt it would use DRAM. Maybe some sort of MRAM/FeRAM would be a better fit. Or maybe a tiny amount of memory (e.g. Josephson junction) in a quantum circuit at some point in the future.
- colanderman 2y ago
  SRAM is actually very architecturally similar to some adiabatic circuit topologies.

siver_john 2y ago

This is really cool, I never expected to see reversible computation made in electrical systems. I learned about it undergrad taking a course by Bruce MacLennan* though it was more applied to "billiard ball" or quantum computing. It was such a cool class though. *Seems like he finally published the text book he was working on when teaching the class: [https://www.amazon.com/dp/B0BYR86GP7?ref_=pe_3052080_397514860][https://www.amazon.com/dp/B0BYR86GP7?ref_=pe_3052080_397514860] https://www.amazon.com/dp/B0BYR86GP7?ref_=pe_3052080_3975148...

colanderman 2y ago

Nice, these ideas have been around for a long time but never commercialized to my knowledge. I've done some experiments in this area with simulations and am currently designing some test circuitry to be fabbed via Tiny Tapeout. Reversibility isn't actually necessary for most of the energy savings. It saves you an extra maybe 20% beyond what adiabatic techniques can do on their own. Reason being, the energy of the information itself pales in comparison to the resistive losses which dominate the losses in adiabatic circuits, and it's actually a (device-dependent) portion of these resistive losses which the reversible aspect helps to recover, not the energy of information itself. I'm curious why Frank chose to go with a resonance-based power-clock, instead of a switched-capacitor design. In my experience the latter are nearly as efficient (losses are still dominated by resistive losses in the powered circuit itself), and are more flexible as they don't need to be tuned to the resonance of the device. (Not to mention they don't need an inductor.) My guess would be that, despite requiring an on-die inductor, the overall chip area required is much less than that of a switched-capacitor design. (You only need one circuit's worth of capacitance, vs. 3 or more for a switched design, which quadruples your die size....) I'm actually somewhat skeptical of the 4000x claim though. Adiabatic circuits can typically only provide about a single order of magnitude power savings over traditional CMOS -- they still have resistive losses, they just follow a slightly different equation (f²RC²V², vs. fCV²). But RC and C are figures of merit for a given silicon process, and fRC (a dimensionless figure) is constrained by the operational principles of digital logic to the order of 0.1, which in turn constrains the power savings to that order of magnitude regardless of process. Where you can find excess savings though is simply by reducing operating frequency. Adiabatic circuits benefit more from this than traditional CMOS. Which is great if you're building something like a GPU which can trade clock frequency for core count.

itissid 2y ago
Can one define the process of an adiabetic circuit goes through like one would do analogusly for the carnot engine? The idea being coming up with a theoretical cieling for the efficiency of such a circuit in terms of circuit parameters?
- colanderman 2y ago
  Yes a similar analysis is where the above expression f²RC²V² comes from. Essentially -- (and I'm probably missing a factor of 2 or 3 somewhere as I'm on my phone and don't have reference materials) -- in an adiabatic circuit the unavoidable power loss for any individual transistor stems from current (I) flowing through that transistor's channel (a resistor R) on its way to and from another transistor's gate (a capacitor C). So that's I²R unavoidable power dissipation. I must be sufficient to fill and then discharge the capacitor to/from operating voltage (V) in the time of one cycle (1/f). So I=2fCV. Substituting this gives 4f²RC²V². Compare to traditional CMOS, wherein the gate capacitance C is charged through R from a voltage source V. It can be shown that this dissipates ½CV² of energy though the resistor in the process, and the capacitor is filled with an equal amount of energy. Discharging then dissipates this energy through the same resistor. Repeat this every cycle for a total power usage of fCV². Divide these two figures and we find that adiabatic circuits use 4fRC times as much energy as traditional CMOS. However, f must be less than about 1/(5RC) for a CMOS circuit to function at all (else the capacitors don't charge sufficiently during a cycle) so this is always power savings in favor of adiabatics. And notably, decreasing f of an adiabatic circuit from the maximum permissible for CMOS on the same process increases the efficiency gain proportionally. (N.B., I feel like I missed a factor of 2 somewhere as this analysis differs slightly from my memory. I'll return with corrections if I find an error.)
pfdietz 2y ago
Maybe this would work better with superconducting electronics?
- colanderman 2y ago
  Possibly, that's an interesting thought. The main benefit of adiabatics as I see them is that, all else being equal, a process improvement of the RC figure can be used to enable either an increase in operating frequency or a decrease in power usage (this is reflected as the additional factor of fRC in the power equation). With traditional CMOS, this only can benefit operating frequency -- power usage is independent of the RC product per se. Supercondition (or near-superconduction) is essentially a huge improvement in RC which wouldn't be able to be realized as an increase in operating frequency due to speed of light limitations, so adiabatics would see an outsize benefit in that case.

EncomLab 2y ago

Calling the addition of an energy storage device into a transistor "reverse computing" is like calling a hybrid car using regenerative braking "reverse driving". It's a very interesting concept - best discussed over pints at the pub on a Sunday afternoon along with over unity devices and the sad lack of adoption of bubble memory.

perching_aix 2y ago
Sounds like a good time :)
colanderman 2y ago
The reverse computing is independent of the energy storage mechanism. It's used to "remember" how to route the energy for recovery.
IIAOPSW 2y ago
Well actually, "reversible driving" is perfectly apt in the sense of acceleration being a reversible process. It means that in theory the net energy needed to drive anywhere is zero because all the energy spent on acceleration is gained back on braking. Yes I know in practice there's always friction loss, but the point is there isn't a theoretical minimum amount of friction that has to be there. In principle a car with reversible driving can get anywhere with asymptotically close to zero energy spent. Put another way, there is no way around the fact that a "non-reversible car" has to have friction loss because the brakes work on friction. But there is no theoretical limit to how far you can reduce friction in reversible driving.
- immibis 2y ago
  Actually, a non-reversible car also has no lower energy limit, as long as you drive on a flat surface (same for a reversible one) and can get to the answer arbitrarily slowly. An ideal reversible computer also works arbitrarily slowly. To make it go faster, you need to put energy in. You can make it go arbitrarily slowly with arbitrarily little energy, just like a non-reversible car.
- EncomLab 2y ago

PaulHoule 2y ago

Notably the physical limit is https://en.wikipedia.org/wiki/Landauer%27s_principle https://en.wikipedia.org/wiki/Landauer%27s_principle it doesn't necessarily take any energy at all to process information, but it does take roughly kT work of energy to erase a bit of information. It's related to https://en.wikipedia.org/wiki/Maxwell%27s_demon https://en.wikipedia.org/wiki/Maxwell%27s_demon as, to complete cycles, the demon has to clear its memory.

Y_Y 2y ago
Does it not take energy to process information? Can any computable function be computed with arbitrarily low energy input/entropy increase?
- colanderman 2y ago
  No, and yes, so long as you don't delete information. Think of a marble-based computer, whose inner workings are frictionless and massless. The marbles roll freely without losing energy unless they are forced to stop somehow, but computation is nonetheless performed.
  - Y_Y 2y ago
    I don't know how to compute with marbles without mass and stopping. Marble computers I've seen rely on gravity and friction, though I'd love to see one that didn't.

pama 2y ago

The ideas are neat and both Landauer and Bennet did some great work and left a powerful legacy. The energetic limits we are talking about are not yet relevant in modern computers. The amount of excess thermal energy for performing 10^26 erasures associated to some computation (of say an LLM that would be too powerful for the current presidential orders) would only be about 0.1kWh, so 10 minutes of a single modern GPU. There are other advantages to reversibility, of course, and maybe one day even that tiny amount of energy savings will matter.

leoc 2y ago

Also an Edward Fredkin https://en.wikipedia.org/wiki/Edward_Fredkin https://en.wikipedia.org/wiki/Edward_Fredkin interest https://en.wikipedia.org/wiki/Fredkin_gate https://en.wikipedia.org/wiki/Fredkin_gate .

DonHopkins 2y ago
As well as Tommaso Toffoli, Norman Margolus, Tom Knight, Richard Feynman, and Charles Bennett: Reversible Computing, Tommaso Toffoli: https://publications.csail.mit.edu/lcs/pubs/pdf/MIT-LCS-TM-151.pdf https://publications.csail.mit.edu/lcs/pubs/pdf/MIT-LCS-TM-1... >Abstract. The theory of reversible computing is based on invertible primitives and composition rules that preserve invertibility. With these constraints, one can still satisfactorily deal with both functional and structural aspects of computing processes; at the same time, one attains a closer correspondence between the behavior of abstract computing systems and the microscopic physical laws (which are presumed to be strictly reversible) that underly any concrete implementation of such systems. According to a physical interpretation, the central result of this paper is that it is ideally possible to build sequential circuits with zero internal power dissipation. A Scalable Reversible Computer in Silicon: https://www.researchgate.net/publication/2507539_A_Scalable_Reversible_Computer_in_Silicon https://www.researchgate.net/publication/2507539_A_Scalable_... Reversible computing: https://web.eecs.utk.edu/~bmaclenn/Classes/494-594-UC-F17/handouts/LNUC-II.C.pdf https://web.eecs.utk.edu/~bmaclenn/Classes/494-594-UC-F17/ha... >In 1970s, Ed Fredkin, Tommaso Toffoli, and others at MIT formed the Information Mechanics group to the study the physics of information. As we will see, Fredkin and Toffoli described computation with idealized, perfectly elastic balls reflecting o↵ barriers. The balls have minimum dissipation and are propelled by (conserved) momentum. The model is unrealistic but illustrates many ideas of reversible computing. Later we will look at it briefly (Sec. C.7). >They also suggested a more realistic implementation involving “charge packets bouncing around along inductive paths between capacitors.” Richard Feynman (Caltech) had been interacting with Information Mechanics group, and developed “a full quantum model of a serial reversible computer” (Feynman, 1986). >Charles Bennett (1973) (IBM) first showed how any computation could be embedded in an equivalent reversible computation. Rather than discarding information (and hence dissipating energy), it keeps it around so it can later “decompute” it back to its initial state. This was a theoretical proof based on Turing machines, and did not address the issue of physical implementation. [...] >How universal is the Toffoli gate for classical reversible computing: https://quantumcomputing.stackexchange.com/questions/21064/how-universal-is-the-toffoli-gate-for-classical-reversible-computing https://quantumcomputing.stackexchange.com/questions/21064/h...

entaloneralie 2y ago

Henry G. Baker wrote this paper titled "The Thermodynamics of Garbage Collection" in the 90s about linear logic, stack machines, reversibility and the cost of erasing information: https://wiki.xxiivv.com/docs/baker_thermodynamics.html https://wiki.xxiivv.com/docs/baker_thermodynamics.html A subset of FRACTRAN programs are reversible, and I would love to see rewriting computers as a potential avenue for reversible circuit building(similar to the STARAN cpu): https://wiki.xxiivv.com/site/fractran.html#reversibility https://wiki.xxiivv.com/site/fractran.html#reversibility

jheriko 2y ago

interesting. on a basic level, with the gates, it seems, if you have at most two input amounts of work, and get at most one out, then storing the lost work for later reuse makes sense

iamnotagenius 2y ago

The simplest, dumbest alternative to for reversible computing is to install datacenters in ex-USSR, where there is still (slowly disappearing) rich infrastructure for central hot water. Instead of charging people, utilities can charge both people and datacenters and yet lower the carbon footprint.

istjohn 2y ago
I believe it would be more efficient to use a heat pump for the district heating even if the datacenter heat is just dumped. Heat pumps can get up to 400% efficiency.
- cogman10 2y ago
  What do you mean by efficient? The heat emitted by the electronics will always be emitted and needs to go somewhere. If 1MWh of that heat is dumped into district heating how would that be less efficient than the 1MWh being dumped in the atmosphere to (hopefully) be reclaimed by a heat pump elsewhere? Or, alternatively, that 1MWh could be absorbed by the already existing datacenter AC coils which could ultimately still be used to heat up district water as it cools the refrigerant. (People actually do this with swimming pools, using the coils from their AC to heat the pool).
  - Klaus23 2y ago
    istjohn is right. Using a heat pump instead of resistive heating (which is basically what a data centre is) is many times more efficient. That doesn't mean we shouldn't use the heat a data centre provides. It just means that it is not a good idea to neglect the development of energy-saving technology because the heat produced can be used somewhere else.
    - witch-king 2y ago
      the issue is that there is an upper limit to how much heat can be removed from a system each cycle, so even if you have a way to disperse the removed heat in a useful way you still can't grow compute beyond a certain point. And because scaling is exponential even immersing the whole rack into liquid nitrogen would only buy a few years of computing growth post-Moore's law.

DonHopkins 2y ago

https://news.ycombinator.com/item?id=30735397 https://news.ycombinator.com/item?id=30735397 DonHopkins on March 19, 2022 | parent | context | favorite | on: Ask HN: What book changed your life? Cellular Automata Machines: A New Environment for Modeling Published April 1987 by MIT Press. ISBN: 9780262200608. http://mitpress.mit.edu/books/cellular-automata-machines http://mitpress.mit.edu/books/cellular-automata-machines http://www.researchgate.net/publication/44522568_Cellular_automata_machines__a_new_environment_for_modeling__Tommaso_Toffoli_Norman_Margolus http://www.researchgate.net/publication/44522568_Cellular_au... https://donhopkins.com/home/cam-book.pdf https://donhopkins.com/home/cam-book.pdf https://github.com/SimHacker/CAM6/blob/master/javascript/CAM6.js#L41 https://github.com/SimHacker/CAM6/blob/master/javascript/CAM... themodelplumber on March 20, 2022 | prev [–] I'm curious, how did the book change your life? What kind of problems did the authors model using their approach? I'm new to the topic, thanks for any input. DonHopkins on March 22, 2022 | parent [–] It really helped me get my head around how to understand and program cellular automata rules, which is a kind of massively parallel distributed "Think Globally, Act Locally" approach that also applies to so many other aspects of life. But by "life" I don't mean just the cellular automata rule "life"! Not to be all depressing like Marvin the Paranoid Android, but I happen to think "life" is overrated. ;) There are so many billions of other extremely interesting cellular automata rules besides "life" too, so don't stop once you get bored with life! ;) https://www.youtube.com/watch?v=CAA67a2-Klk https://www.youtube.com/watch?v=CAA67a2-Klk For example, it's kind of like how the world wide web works: "Link Globally, Interact Locally": https://donhopkins.medium.com/scriptx-and-the-world-wide-web-link-globally-interact-locally-1995-38f35e32ea2f https://donhopkins.medium.com/scriptx-and-the-world-wide-web... It's also very useful for understanding other massively distributed locally interacting parallel systems, epidemiology, economics, morphogenesis (reaction-diffusion systems, like how a fertilized egg divides and specializes into an organism), GPU programming and optimization, neural networks and machine learning, information and chaos theory, and physics itself. I've discussed the book and the code I wrote based on it with Norm Margolus, one of the authors, and he mentioned that he really likes rules that are based on simulating physics, and also thinks reversible cellular automata rules are extremely important (and energy efficient in a big way, in how they relate to physics and thermodynamics). The book has interesting sections about physical simulations like spin glasses (Ising Spin model of the magnetic state of atoms of solid matter), and reversible billiard ball simulations (like deterministic reversible "smoke and mirrors" with clouds of moving particles bouncing off of pinball bumpers and each other). Spin Glass: https://en.wikipedia.org/wiki/Spin_glass https://en.wikipedia.org/wiki/Spin_glass >In condensed matter physics, a spin glass is a magnetic state characterized by randomness, besides cooperative behavior in freezing of spins at a temperature called 'freezing temperature' Tf. Magnetic spins are, roughly speaking, the orientation of the north and south magnetic poles in three-dimensional space. In ferromagnetic solids, component atoms' magnetic spins all align in the same direction. Spin glass when contrasted with a ferromagnet is defined as "disordered" magnetic state in which spins are aligned randomly or not with a regular pattern and the couplings too are random. Billiard Ball Computer: https://en.wikipedia.org/wiki/Billiard-ball_computer https://en.wikipedia.org/wiki/Billiard-ball_computer >A billiard-ball computer, a type of conservative logic circuit, is an idealized model of a reversible mechanical computer based on Newtonian dynamics, proposed in 1982 by Edward Fredkin and Tommaso Toffoli. Instead of using electronic signals like a conventional computer, it relies on the motion of spherical billiard balls in a friction-free environment made of buffers against which the balls bounce perfectly. It was devised to investigate the relation between computation and reversible processes in physics. https://en.wikipedia.org/wiki/Reversible_cellular_automaton https://en.wikipedia.org/wiki/Reversible_cellular_automaton >A reversible cellular automaton is a cellular automaton in which every configuration has a unique predecessor. That is, it is a regular grid of cells, each containing a state drawn from a finite set of states, with a rule for updating all cells simultaneously based on the states of their neighbors, such that the previous state of any cell before an update can be determined uniquely from the updated states of all the cells. The time-reversed dynamics of a reversible cellular automaton can always be described by another cellular automaton rule, possibly on a much larger neighborhood. >[...] Reversible cellular automata form a natural model of reversible computing, a technology that could lead to ultra-low-power computing devices. Quantum cellular automata, one way of performing computations using the principles of quantum mechanics, are often required to be reversible. Additionally, many problems in physical modeling, such as the motion of particles in an ideal gas or the Ising model of alignment of magnetic charges, are naturally reversible and can be simulated by reversible cellular automata. Also I've frequently written on HN about Dave Ackley's great work on Robust-First Computing and the Moveable Feast Machine, which I think is brilliant, and quite important in the extremely long term (which is coming sooner than we think). https://news.ycombinator.com/item?id=22304110 https://news.ycombinator.com/item?id=22304110 https://news.ycombinator.com/item?id=22300376 https://news.ycombinator.com/item?id=22300376 https://news.ycombinator.com/item?id=22303313 https://news.ycombinator.com/item?id=22303313

DonHopkins 2y ago

https://news.ycombinator.com/item?id=35366971 https://news.ycombinator.com/item?id=35366971 Tipler's Omega Point cosmology: https://en.wikipedia.org/wiki/Frank_J._Tipler#The_Omega_Point https://en.wikipedia.org/wiki/Frank_J._Tipler#The_Omega_Poin... >The Omega Point cosmology >The Omega Point is a term Tipler uses to describe a cosmological state in the distant proper-time future of the universe.[6] He claims that this point is required to exist due to the laws of physics. According to him, it is required, for the known laws of physics to be consistent, that intelligent life take over all matter in the universe and eventually force its collapse. During that collapse, the computational capacity of the universe diverges to infinity, and environments emulated with that computational capacity last for an infinite duration as the universe attains a cosmological singularity. This singularity is Tipler's Omega Point.[7] With computational resources diverging to infinity, Tipler states that a society in the far future would be able to resurrect the dead by emulating alternative universes.[8] Tipler identifies the Omega Point with God, since, in his view, the Omega Point has all the properties of God claimed by most traditional religions.[8][9] >Tipler's argument of the omega point being required by the laws of physics is a more recent development that arose after the publication of his 1994 book The Physics of Immortality. In that book (and in papers he had published up to that time), Tipler had offered the Omega Point cosmology as a hypothesis, while still claiming to confine the analysis to the known laws of physics.[10] >Tipler, along with co-author physicist John D. Barrow, defined the "final anthropic principle" (FAP) in their 1986 book The Anthropic Cosmological Principle as a generalization of the anthropic principle: >Intelligent information-processing must come into existence in the Universe, and, once it comes into existence, will never die out.[11] >One paraphrasing of Tipler's argument for FAP runs as follows: For the universe to physically exist, it must contain living observers. Our universe obviously exists. There must be an "Omega Point" that sustains life forever.[12] >Tipler purportedly used Dyson's eternal intelligence hypothesis to back up his arguments. Cellular Automata Machines: A New Environment for Modeling: https://news.ycombinator.com/item?id=30735397 https://news.ycombinator.com/item?id=30735397 >It's also very useful for understanding other massively distributed locally interacting parallel systems, epidemiology, economics, morphogenesis (reaction-diffusion systems, like how a fertilized egg divides and specializes into an organism), GPU programming and optimization, neural networks and machine learning, information and chaos theory, and physics itself. >I've discussed the book and the code I wrote based on it with Norm Margolus, one of the authors, and he mentioned that he really likes rules that are based on simulating physics, and also thinks reversible cellular automata rules are extremely important (and energy efficient in a big way, in how they relate to physics and thermodynamics). >The book has interesting sections about physical simulations like spin glasses (Ising Spin model of the magnetic state of atoms of solid matter), and reversible billiard ball simulations (like deterministic reversible "smoke and mirrors" with clouds of moving particles bouncing off of pinball bumpers and each other). Spin Glass: https://en.wikipedia.org/wiki/Spin_glass https://en.wikipedia.org/wiki/Spin_glass >In condensed matter physics, a spin glass is a magnetic state characterized by randomness, besides cooperative behavior in freezing of spins at a temperature called 'freezing temperature' Tf. Magnetic spins are, roughly speaking, the orientation of the north and south magnetic poles in three-dimensional space. In ferromagnetic solids, component atoms' magnetic spins all align in the same direction. Spin glass when contrasted with a ferromagnet is defined as "disordered" magnetic state in which spins are aligned randomly or not with a regular pattern and the couplings too are random. Billiard Ball Computer: https://en.wikipedia.org/wiki/Billiard-ball_computer https://en.wikipedia.org/wiki/Billiard-ball_computer >A billiard-ball computer, a type of conservative logic circuit, is an idealized model of a reversible mechanical computer based on Newtonian dynamics, proposed in 1982 by Edward Fredkin and Tommaso Toffoli. Instead of using electronic signals like a conventional computer, it relies on the motion of spherical billiard balls in a friction-free environment made of buffers against which the balls bounce perfectly. It was devised to investigate the relation between computation and reversible processes in physics. Reversible Cellular Automata: https://en.wikipedia.org/wiki/Reversible_cellular_automaton https://en.wikipedia.org/wiki/Reversible_cellular_automaton >A reversible cellular automaton is a cellular automaton in which every configuration has a unique predecessor. That is, it is a regular grid of cells, each containing a state drawn from a finite set of states, with a rule for updating all cells simultaneously based on the states of their neighbors, such that the previous state of any cell before an update can be determined uniquely from the updated states of all the cells. The time-reversed dynamics of a reversible cellular automaton can always be described by another cellular automaton rule, possibly on a much larger neighborhood. >[...] Reversible cellular automata form a natural model of reversible computing, a technology that could lead to ultra-low-power computing devices. Quantum cellular automata, one way of performing computations using the principles of quantum mechanics, are often required to be reversible. Additionally, many problems in physical modeling, such as the motion of particles in an ideal gas or the Ising model of alignment of magnetic charges, are naturally reversible and can be simulated by reversible cellular automata. Theory of Self-Reproducing Automata: John von Neumann's Quantum Mechanical Universal Constructors: https://news.ycombinator.com/item?id=22738268 https://news.ycombinator.com/item?id=22738268 [...] Third, the probabilistic quantum mechanical kind, which could mutate and model evolutionary processes, and rip holes in the space-time continuum, which he unfortunately (or fortunately, the the sake of humanity) didn't have time to fully explore before his tragic death. >p. 99 of "Theory of Self-Reproducing Automata": >Von Neumann had been interested in the applications of probability theory throughout his career; his work on the foundations of quantum mechanics and his theory of games are examples. When he became interested in automata, it was natural for him to apply probability theory here also. The Third Lecture of Part I of the present work is devoted to this subject. His "Probabilistic Logics and the Synthesis of Reliable Organisms from Unreliable Components" is the first work on probabilistic automata, that is, automata in which the transitions between states are probabilistic rather than deterministic. Whenever he discussed self-reproduction, he mentioned mutations, which are random changes of elements (cf. p. 86 above and Sec. 1.7.4.2 below). In Section 1.1.2.1 above and Section 1.8 below he posed the problems of modeling evolutionary processes in the framework of automata theory, of quantizing natural selection, and of explaining how highly efficient, complex, powerful automata can evolve from inefficient, simple, weak automata. A complete solution to these problems would give us a probabilistic model of self-reproduction and evolution. [9] [9] For some related work, see J. H. Holland, "Outline for a Logical Theory of Adaptive Systems", and "Concerning Efficient Adaptive Systems". https://www.deepdyve.com/lp/association-for-computing-machinery/outline-for-a-logical-theory-of-adaptive-systems-efsWyqMa1l https://www.deepdyve.com/lp/association-for-computing-machin... https://deepblue.lib.umich.edu/bitstream/handle/2027.42/5578/bac4296.0001.001.pdf?sequence=5 https://deepblue.lib.umich.edu/bitstream/handle/2027.42/5578... https://www.worldscientific.com/worldscibooks/10.1142/10841 https://www.worldscientific.com/worldscibooks/10.1142/10841 perl4ever on Dec 26, 2017 | root | parent | next [–] Tipler's Omega Point prediction doesn't seem like it would be compatible with the expanding universe, would it? Eventually everything will disappear over the speed-of-light horizon, and then it can't be integrated into one mind. DonHopkins on Dec 26, 2017 | root | parent | next [–] It also wishfully assumes that the one mind can't think of better things to do with its infinite amount of cloud computing power than to simulate one particular stone age mythology. Then again, maybe it's something like the 1996 LucasArts game Afterlife, where you simulate every different religion's version of heaven and hell at once. https://en.wikipedia.org/wiki/Afterlife_(video_game) https://en.wikipedia.org/wiki/Afterlife_(video_game) The primary goal of the game is to provide divine and infernal services for the inhabitants of the afterlife. This afterlife caters to one particular planet, known simply as the Planet. The creatures living on the Planet are called EMBOs, or Ethically Mature Biological Organisms. When an EMBO dies, its soul travels to the afterlife where it attempts to find an appropriate "fate structure". Fate structures are places where souls are rewarded or punished, as appropriate, for the virtues or sins that they practiced while they were alive.

DonHopkins 2y ago

Reversible Computing (2016) [video] (youtube.com) https://news.ycombinator.com/item?id=16007128 https://news.ycombinator.com/item?id=16007128 https://www.youtube.com/watch?v=rVmZTGeIwnc https://www.youtube.com/watch?v=rVmZTGeIwnc DonHopkins on Dec 26, 2017 | next [–] Billiard Ball cellular automata, proposed and studied by Edward Fredkin and Tommaso Toffoli, are one interesting type of reversible computer. The Ising spin model of ferromagnetism is another reversible cellular automata technique. https://en.wikipedia.org/wiki/Billiard-ball_computer https://en.wikipedia.org/wiki/Billiard-ball_computer https://en.wikipedia.org/wiki/Reversible_cellular_automaton https://en.wikipedia.org/wiki/Reversible_cellular_automaton https://en.wikipedia.org/wiki/Ising_model https://en.wikipedia.org/wiki/Ising_model If billiard balls aren't creepy enough for you, live soldier crabs of the species Mictyris guinotae can be used in place of the billiard balls. https://www.newscientist.com/blogs/onepercent/2012/04/researchers-build-crab-powered.html https://www.newscientist.com/blogs/onepercent/2012/04/resear... https://www.wired.com/2012/04/soldier-crabs/ https://www.wired.com/2012/04/soldier-crabs/ http://www.complex-systems.com/abstracts/v20_i02_a02.html http://www.complex-systems.com/abstracts/v20_i02_a02.html Robust Soldier Crab Ball Gate Yukio-Pegio Gunji, Yuta Nishiyama. Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501, Japan. Andrew Adamatzky. Unconventional Computing Centre. University of the West of England, Bristol, United Kingdom. Abstract Soldier crabs Mictyris guinotae exhibit pronounced swarming behavior. Swarms of the crabs are tolerant of perturbations. In computer models and laboratory experiments we demonstrate that swarms of soldier crabs can implement logical gates when placed in a geometrically constrained environment.

yalogin 2y ago

The concept completely flummoxed me but how does this play with quantum computers? That’s the direction we are going aren’t we?

fallingfrog 2y ago
Quantum computations have to be reversible , because you have to collapse the wave function and take a measurement to throw away any bits of data. You can accumulate junk bits as long as they remain in a superposition. But at some point you have to take a measurement. So, very much related.

amelius 2y ago

> The main way to reduce unnecessary heat generation in transistor use—to operate them adiabatically—is to ramp the control voltage slowly instead of jumping it up or down abruptly. But if you change the gate voltage slowly, then the transistor will be for a longer period in the resistive region where it dissipates energy. Shouldn't you go between the OFF and ON states as quickly as possible?

colanderman 2y ago
The trick is not to have a voltage across the channel while it's transitioning states. For this reason, adiabatic circuits are typically "phased" such that any given adiabatic logic gate is either having its gates charged or discharged (by the previous logic gate), or current is passing through its channels to charge/discharge the next logic gate.
- amelius 2y ago
  Interesting, thanks!

stevage 2y ago

Wow. This whole logic sounds like something really harebrained from a Dr Who episode: "It takes energy to destroy information. Therefore if you don't destroy information, it doesn't take energy!" - sounds completely illogical. I honestly don't understand from the article how you "recover energy". Yet I have no reason to disbelieve it.

kibwen 2y ago
Someone else here compared it to regenerative braking in cars, which is what made it click for me. If you spend energy to accelerate, then recapture that energy while decelerating, then you can manage to transport yourself while your net energy expenditure is zero (other than all that pesky friction). On the other hand, if you spend energy to accelerate, then shed all that energy via heat from your brake pads, then you need to expend new energy to accelerate next time.
EncomLab 2y ago
If the concept has existed for 60 years and no one has capitalized it yet - you can bet it's more Dr. Who than reality.

Jean-Papoulos 2y ago

>it is producing a chip that, for the first time, recovers energy used in an arithmetic circuit. The next chip, projected to hit the market in 2027, will be an energy-saving processor specialized for AI inference. The 4,000x energy-efficiency improvement is on Vaire’s road map but probably 10 or 15 years out. How I wish I could place bets on this never happening. >In the following years, Vaire plans to design the first reversible chip specialized for AI inference. These guys are cashing in on AI hype. Watch them raise VC money, give themselves 6 figures salaries and file for bankruptcy in 3 years.

EncomLab 2y ago
You are exactly correct - the combination of deep belief in the ability to obtain quick riches by investing in the "next big thing" aligned with a large gap of knowledge between reality and hype, all mixed into a milieu of in-group speak and customs always leads to the proliferation of the con. It's the next "Long Blockchain Corp!"
- robertlagrant 2y ago
  It's also how proliferation of advances happen. Nothing advances unless someone tries it, and trying it costs money.
z3t4 2y ago
4000x cost saving would bring operation costs for compute down close to zero, meaning marginal costs for data centers would go down as well, meaning data centers would buy a shit ton of these chips. Think the valuation of Nvidia x 1000 I still think the technical challange is too big, but it's high reward for early investors.
- EncomLab 2y ago
  This is insanity - "compute" is a tiny fraction of energy usage compared to memory, data storage, and data retrieval.
  - 2y ago

lkm0 2y ago

All of quantum computing is reversible by nature (until you measure the state, of course). Yet, there'some research in the field focusing on irreversible ("non-unitary") quantum algorithms and it appears there is some advantage in throwing away, algorithmically speaking, the reversibility. See https://arxiv.org/abs/2309.16596 https://arxiv.org/abs/2309.16596 It's interesting that classical and quantum computing researchers are each looking in the direction of the other field.

IgorPartola 2y ago

This is probably a dumb question, but where does this fail: what happens if I run something like the SHA256 algorithm or a sudoku solver backwards using these techniques? I assume that wouldn’t actually work, but why?

Enginerrrd 2y ago
I'm speaking out of my depth, but as I understand you'd need the extra information that was accumulated along the way (as shown in the XOR gate example) If you had that you certainly could run sha 256 in reverse but for the starting hash + info, you have at least as many bits as the starting information that was hashed.