[HN Gopher] Reversible computing escapes the lab
___________________________________________________________________
Reversible computing escapes the lab
Author : jasondavies
Score : 197 points
Date : 2025-01-10 21:42 UTC (4 days ago)
(HTM) web link (spectrum.ieee.org)
(TXT) w3m dump (spectrum.ieee.org)
| siver_john wrote:
| 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_3975148...
| colanderman wrote:
| 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 wrote:
| 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 wrote:
| 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 1/2CV2 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 wrote:
| Maybe this would work better with superconducting electronics?
| colanderman wrote:
| 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.
| mikepfrank wrote:
| There indeed has been research on reversible adiabatic logic
| in superconducting electronics. But superconducting
| electronics has a whole host of issues of its own, such as
| low density and a requirement for ultra-low temperatures.
|
| When I was at Sandia we also had a project exploring
| ballistic reversible computation (as opposed to adiabatic) in
| superconducting electronics. We got as far as confirming to
| our satisfaction that it is possible, but this line of work
| is a lot farther from major commercial applications than the
| adiabatic CMOS work.
| mikepfrank wrote:
| Hi, someone pointed me at your comment, so I thought I'd reply.
|
| First, the circuit techniques that aren't reversible aren't
| truly, fully adiabatic either -- they're only quasi-adiabatic.
| In fact, if you strictly follow the switching rules required
| for fully adiabatic operation, then (ignoring leakage) you
| _cannot_ erase information -- none of the allowed operations
| achieve that.
|
| Second, to say reversible operation "only saves an extra 20%"
| over quasi-adiabatic techniques is misleading. Suppose a given
| quasi-adiabatic technique saves 79% of the energy, and a fully
| adiabatic, reversible version saves you "an extra 20%" -- well,
| then now that's 99%. But, if you're dissipating 1% of the
| energy of a conventional circuit, and the quasi-adiabatic
| technique is dissipating 21%, that's 21x more energy efficient!
| And so you can achieve 21x greater performance within a given
| power budget.
|
| Next, to say "resistive losses dominate the losses" is also
| misleading. The resistive losses scale down arbitrarily as the
| transition time is increased. We can actually operate adiabatic
| circuits all the way down to the regime where resistive losses
| are about as low as the losses due to leakage. The max energy
| savings factor is on the order of the square root of the on/off
| ratio of the devices.
|
| Regarding "adiabatic circuits can typically only provide an
| order of magnitude power savings" -- this isn't true for
| reversible CMOS! Also, "power" is not even the right number to
| look at -- you want to look at power per unit performance, or
| in other words energy per operation. Reducing operating
| frequency reduces the power of conventional CMOS, but does not
| directly reduce energy per operation or improve energy
| efficiency. (It can allow you to indirectly reduce it though,
| by using a lower switching voltage.)
|
| You are correct that adiabatic circuits can benefit from
| frequency scaling more than traditional CMOS -- since lowering
| the frequency actually directly lowers energy dissipation per
| operation in adiabatic circuits. The specific 4000x number
| (which includes some benefits from scaling) comes from the
| analysis outlined in this talk -- see links below - but we have
| also confirmed energy savings of about this magnitude in
| detailed (Cadence/Spectre) simulations of test circuits in
| various processes. Of course, in practice the energy savings is
| limited by the resonator Q value. And a switched-capacitor
| design (like a stepped voltage supply) would do much worse, due
| to the energy required to control the switches.
|
| https://www.sandia.gov/app/uploads/sites/210/2023/11/Comet23...
| https://www.youtube.com/watch?v=vALCJJs9Dtw
|
| Happy to answer any questions.
| colanderman wrote:
| Thanks for the reply, was actually hoping you'd pop over
| here.
|
| I don't think we actually disagree on anything. Yes, without
| reverse circuits you are limited to quasi-adiabatic operaton.
| But, at least in the architectures I'm familiar with (mainly
| PFAL), most of the losses are unarguably resistive. As I
| understand PFAL, it's only when the operating voltage of a
| given gate drops below Vth that the (macro) information gets
| lost and reversibility provides benefit, which is only a
| fraction of the switching cycle. At least for PFAL the figure
| is somewhere in the 20% range IIRC. (I say "macro" because of
| course the true energy of information is much smaller than
| the amounts we're talking about.)
|
| The "20%" in my comment I meant in the multiplicative sense,
| not additive. I.e. going from 79% savings to 83.2%, not 99%.
| (I realize that wasn't clear.)
|
| What I find interesting is reversibility isn't actually
| necessary for true adiabatic operation. All that matters is
| the information of where charge needs to be recovered from
| can be derived _somehow_. This could come from information
| available elsewhere in the circuit, not necessarily the
| subsequent computations reversed. (Thankfully, quantum non-
| duplication does not apply here!)
|
| I agree that energy per operation is often more meaningful,
| BUT one must not lose sight of the lower bounds on clock
| speed imposed by a particular workload.
|
| Ah thanks for the insight into the resonator/switched-cap
| tradeoff. Yes, capacitative switching designs which are
| themselves adiabatic I know is a bit of a research topic. In
| my experience the losses aren't comparable to the resistive
| losses of the adiabatic circuitry itself though. (I've done
| SPICE simulations using the sky130 process.)
| mikepfrank wrote:
| It's been a while since I looked at it, but I believe PFAL
| is one of the not-fully-adiabatic techniques that I have a
| lot of critiques of.
|
| There have been studies showing that a truly, fully
| adiabatic technique in the sense I'm talking about (2LAL
| was the one they checked) does about 10x better than any of
| the other "adiabatic" techniques. In particular, 2LAL does
| a lot better than PFAL.
|
| > reversibility isn't actually necessary
|
| That isn't true in the sense of "reversible" that I use.
| Look at the structure of the word -- reverse-able. _Able_
| to be reversed. It isn 't essential that the very same
| computation that computed some given data is actually
| applied in reverse, only that no information is obliviously
| discarded, implying that the computation always _could_ be
| reversed. Unwanted information still needs to be
| decomputed, but in general, it 's quite possible to de-
| compute garbage data using a different process than the
| reverse of the process that computed it. In fact, this is
| frequently done in practice in typical pipelined reversible
| logic styles. But they still count as reversible even
| though the forwards and reverse computations aren't
| identical. So, I think we agree here and it's just a
| question of terminology.
|
| Lower bounds on clock speed are indeed important; generally
| this arises in the form of maximum latency constraints.
| Fortunately, many workloads today (such as AI) are limited
| more by bandwidth/throughput than by latency.
|
| I'd be interested to know if you can get energy savings
| factors on the order of 100x or 1000x with the capacitive
| switching techniques you're looking at. So far, I haven't
| seen that that's possible. Of course, we have a long way to
| go to prove out those kinds of numbers in practice using
| resonant charge transfer as well. Cheers...
| colanderman wrote:
| PFAL has both a fully adiabatic and quasi-adiabatic
| configuration. (Essentially, the "reverse" half of a PFAL
| gate can just be tied to the outputs for quasi-adiabatic
| mode.) I've focused my own research on PFAL because it is
| (to my knowledge) one of the few fully adiabatic
| families, and of those, I found it easy to understand.
|
| I'll have to check out 2LAL. I haven't heard of it
| before.
|
| No, even with a fully adiabatic switched-capacitance
| driver I don't think those figures are possible. The
| maximum efficiency I believe is 1-1/n, n being the number
| of steps (and requiring n-1 capacitors). But the
| capacitors themselves must each be an order of magnitude
| larger than the adiabatic circuit itself. So it's a
| reasonable performance match for an adiabatic circuit
| running at "max" frequency, with e.g. 8 steps/7
| capacitors, but 100x power reduction necessary to match a
| "slowed" adiabatic circuit would require 99 capacitors...
| which quickly becomes infeasible!
| EncomLab wrote:
| 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 wrote:
| Sounds like a good time :)
| colanderman wrote:
| The reverse computing is independent of the energy storage
| mechanism. It's used to "remember" how to route the energy for
| recovery.
| IIAOPSW wrote:
| 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 wrote:
| 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 wrote:
| This is glorious.
| nine_k wrote:
| Cars specifically dissipate energy on deformation of the
| tires; this loss is irreversible at any speed, even if all
| the bearings have effectively zero losses (e.g. using
| magnetic levitation).
|
| A train spends much less on that because the rails and the
| wheels are very firm. A maglev train likely recuperates
| nearly 100% of its kinetic energy during deceleration, less
| the aerodynamic losses; it's like a superconducting
| reversible circuit.
| psd1 wrote:
| A pub in Cambridge, perhaps! I doubt you'd overhear such talk
| in some Aldershot dive.
|
| The Falling Edge, maybe? The Doped Wafer?
| 082349872349872 wrote:
| The Flipped Bit? The Reversed Desrevereht?
|
| (I once read a fiction story about someone who, instead of
| having perfect pitch, had perfect winding number: he couldn't
| get to sleep before returning to zero, so it took him some
| time to realise that when other people talked about
| "unwinding" at the end of the day, they didn't mean it
| literally)
| PaulHoule wrote:
| Notably the physical limit is
|
| 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
|
| as, to complete cycles, the demon has to clear its memory.
| Y_Y wrote:
| Does it not take energy to process information? Can any
| computable function be computed with arbitrarily low energy
| input/entropy increase?
| colanderman wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| Also an Edward Fredkin
| https://en.wikipedia.org/wiki/Edward_Fredkin interest
| https://en.wikipedia.org/wiki/Fredkin_gate .
| DonHopkins wrote:
| 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-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 computing:
|
| 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/h...
| entaloneralie wrote:
| 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
|
| 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
| jheriko wrote:
| 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
| EncomLab wrote:
| The miniscule amount of energy retained from the "reverse
| computation" will be absolutely demolished by the first DRAM
| refresh.
| fintler wrote:
| 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 wrote:
| SRAM is actually very architecturally similar to some
| adiabatic circuit topologies.
| iamnotagenius wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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.
| d3ckard wrote:
| Wait, you mean there is no central hot water infrastructure in
| the world? Poland is not ex-USRR but it is common place and I
| always assumed this is a normal thing everywhere.
| DonHopkins wrote:
| 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://www.researchgate.net/publication/44522568_Cellular_au...
|
| https://donhopkins.com/home/cam-book.pdf
|
| 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
|
| 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...
|
| 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
|
| >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
|
| >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
|
| >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=22300376
|
| https://news.ycombinator.com/item?id=22303313
| DonHopkins wrote:
| https://news.ycombinator.com/item?id=35366971
|
| Tipler's Omega Point cosmology:
|
| 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
|
| >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
|
| >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
|
| >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
|
| >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
|
| [...] 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-machin...
|
| https://deepblue.lib.umich.edu/bitstream/handle/2027.42/5578...
|
| 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)
|
| 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 wrote:
| Reversible Computing (2016) [video] (youtube.com)
|
| https://news.ycombinator.com/item?id=16007128
|
| 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/Reversible_cellular_automaton
|
| 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/resear...
|
| https://www.wired.com/2012/04/soldier-crabs/
|
| 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 wrote:
| The concept completely flummoxed me but how does this play with
| quantum computers? That's the direction we are going aren't we?
| fallingfrog wrote:
| 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 wrote:
| > 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 wrote:
| 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 wrote:
| Interesting, thanks!
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