There's a long way to go before building permanent structures on the Moon is a possibility (meteoroid detection/destruction, understanding seismic activity, etc.), but its far side would be a great place for building data centers.
Not really. (Disclaimer: I'm not an expert at all, much of what I say is wrong)
Consider your CPU's heat sink. The CPU gets hot, but it can transfer that heat to your metallic heat sink (thermal conduction?), which in turn can dissipate that heat to its surrounding air (thermal convection?).
If you're in space, the only way to get rid of that heat is by radiating it as light (radiation; the same way a metal glows white hot) but that's much less efficient. You can't transfer it to another mass because there isn't other mass in a vaccuum.
to give brudgers as much credit as possible, space is a pretty good heat sink, in that it can absorb all of the heat you can ever produce, without changing temperature. (and since heat transfer is proportional to temperature difference, your transfer rate will never drop because of it.)
but it is terrible for heat transfer.
the metal widgets we stick onto our CPUs aren't really heat sinks, they're for reducing the thermal resistance between the CPU body and the atmosphere, which is the "final" destination for the heat.
One of the issues with the LM was getting rid of heat from the electronics. The Aft Equipment Bay was mounted external to the LM[1], and had to use active cooling (some sort of sublimation system according to [2]).
Are you implying that the far side of the moon receives no sunlight? It does, just as much as anywhere else on the moon. Note also that communication with earth would be tricky (aside from the 3 second ping time you'd already get due to the distance)
I recently scored a copy of Maxwell's Demon, a book containing a collection of (among others) Landauer and Bennett's papers. As I was skimming them, I couldn't help but think that if there is a correspondence between heat and information erasure, can that be used to move "heat" in a fundamentally different way?
The idea would be you do some computation at point A, the related information erasure at point B, and the heat associated with it get "transported" faster than it would be by moving pipes around. The hope is that sending the bits along something like an optical network would be faster than laminar fluid flow.
I'm sure HN's more knowledgeable folks will tell me exactly where I'm wrong, but it seemed like an intriguing possibility.
There's a comment on the post by Tim Tyler talking about "digital heat", which seems to be close to your idea. He's written more about it here: http://cell-auto.com/reversible/
I've long wondered something similar about energy storage: could you store energy by spending to learn the times when you should open the doors (in the Maxwell's Demon though experiment) to sort the molecules?
In that case, you could get much better energy storage densities because you'd only be limited by how densely you can store information.
(It's know that you can't generate energy by opening doors in a chamber at just the right times to let fast molecules go on one side and slow on the other. This is because you'd have to spend just as much energy learning when to open the doors. However, that's not a barrier to using this technique to store rather than generate energy.)
Hanson needs to brush up on his thermodynamics. Reversible computers need not generate any heat. But they do need to grow larger as they are operated (their size scales with the number of operations performed). This means SPACE = TIME, which is a pretty sad state of affairs and probably the reason why all practical computers and known lifeforms are irreversible machines.
That's an interesting animal, but its unusual life cycle in no way negates the fact that its metabolism is irreversible (both at the cellular and ensemble level).
It's not a good bet that data centers will need to build out at a constant rapid pace into the future to keep pace with demand. A lot of the work in servers in recent years has been about improving utilization of available resources, and I expect that there is still a lot of headroom left for improvement. It's probably safe to say that across all datacenters, the vast majority of heat is generated while servers are mostly idle and have too little to do.
I don't think that it's safe to anticipate reaching some kind of fundamental limit on power efficiency, either. Nobody has come up with a viable replacement for the silicon transistor, despite decades of trying, and current CPU technology has practically stopped generating any improvements for the past several years. I think the important quantity to measure is the energy that goes into powering up the cpu for one clock cycle, because clock cycles are what drive computation forward and their individual energy usage basically just add together. For decades after the invention of the transistor, this energy dropped rapidly due to shrinking the wires. However, the wires reached a point where their capacitance began to fall off with decreasing size, and there have been no significant energy improvements since. Solving that problem requires either a revolutionary discovery about the physics of conductivity, a completely novel mode of doing computation that isn't based on electronics (photons?), or a fundamentally novel principle of organizing a cpu that somehow avoids being clock-bound (I heard about an effort over ten years ago, but I have not heard of it since). Any of those improvements could have surfaced at any time in the past few decades and been eagerly pursued, but none did, so the odds don't favor the miraculous appearance of one of them in the foreseeable future.
> The future of computing, after about 2035, is adiabatic reservable hardware. When such hardware runs at a cost-minimizing speed, half of the total budget is spent on computer hardware, and the other half is spent on energy and cooling for that hardware. Thus after 2035 or so, about as much will be spent on computer hardware and a physical space to place it as will be spent on hardware and space for systems to generate and transport energy into the computers, and to absorb and transport heat away from those computers.
Not almost. It is alive. The only fundamental difference between computers and "life as we know it" is that the computer's genetics are encoded on magnetic media rather than DNA.
>Thus in future cities crammed with computer hardware, roughly half of the volume is likely to be taken up by pipes that move cooling fluids in and out
Presumably those would be domed cities like you see in futuristic predictions from the 1960s. That's why you can measure their volume and predict the percentage that will be dedicated to pipes to carry waste heat from computers.
The author assumes the demand for CPU cycles is elastic in the long term (i.e. as prices of cycles drop, people will continue to use more and more of them).
General-purpose desktops and laptops today often don't come close to using all of the CPU horsepower available to them, and many server applications are limited by memory, network bandwidth, and storage.
It seems conceivable to me that at some point, before reaching thermodynamic limits, CPU cycles will stop being scarce for many application spaces, and future computing investments will mainly be in networking, memory, storage and software.
Is it "SPACE = TIME", or is the limitation actually set by the surface area of the volume enclosing the machine? In space-time coding for communications, the limitation on achievable spectral efficiency is related to the surface area of the volume enclosing the antenna array, in units of wavelength. It would seem sensible if this was reflected in a fundamental property of information.
Maybe a fundamental limit of the universe is that the minimum surface area of a volume containing a subatomic structure is related to the information required to define that structure? My maths is a bit fuzzy, but isn't there a fundamental relationship between a volume its boundary, involving a Fourier Transform? That could then mean that a limitation on surface area is equivalent to a limitation of the (4-dimensional?) volume occupied by some other quantity?
The above is speculation on my part, but is there a HN reader our there who can say whether such thoughts are garbage, or whether they have some basis?
30 comments
[ 4.4 ms ] story [ 72.2 ms ] threadConsider your CPU's heat sink. The CPU gets hot, but it can transfer that heat to your metallic heat sink (thermal conduction?), which in turn can dissipate that heat to its surrounding air (thermal convection?).
If you're in space, the only way to get rid of that heat is by radiating it as light (radiation; the same way a metal glows white hot) but that's much less efficient. You can't transfer it to another mass because there isn't other mass in a vaccuum.
to give brudgers as much credit as possible, space is a pretty good heat sink, in that it can absorb all of the heat you can ever produce, without changing temperature. (and since heat transfer is proportional to temperature difference, your transfer rate will never drop because of it.)
but it is terrible for heat transfer.
the metal widgets we stick onto our CPUs aren't really heat sinks, they're for reducing the thermal resistance between the CPU body and the atmosphere, which is the "final" destination for the heat.
[1] http://www.hq.nasa.gov/alsj/LM04_Lunar_Module_ppLV1-17.pdf
[2] http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/1972001...
The idea would be you do some computation at point A, the related information erasure at point B, and the heat associated with it get "transported" faster than it would be by moving pipes around. The hope is that sending the bits along something like an optical network would be faster than laminar fluid flow.
I'm sure HN's more knowledgeable folks will tell me exactly where I'm wrong, but it seemed like an intriguing possibility.
In that case, you could get much better energy storage densities because you'd only be limited by how densely you can store information.
(It's know that you can't generate energy by opening doors in a chamber at just the right times to let fast molecules go on one side and slow on the other. This is because you'd have to spend just as much energy learning when to open the doors. However, that's not a barrier to using this technique to store rather than generate energy.)
Not necessarily true. There is that 'immortal' jellyfish that basically reverts back to a polyp and then grows again.
http://en.wikipedia.org/wiki/Turritopsis_dohrnii
mm maybe I ought to dust off those old steam tables eh.
I don't think that it's safe to anticipate reaching some kind of fundamental limit on power efficiency, either. Nobody has come up with a viable replacement for the silicon transistor, despite decades of trying, and current CPU technology has practically stopped generating any improvements for the past several years. I think the important quantity to measure is the energy that goes into powering up the cpu for one clock cycle, because clock cycles are what drive computation forward and their individual energy usage basically just add together. For decades after the invention of the transistor, this energy dropped rapidly due to shrinking the wires. However, the wires reached a point where their capacitance began to fall off with decreasing size, and there have been no significant energy improvements since. Solving that problem requires either a revolutionary discovery about the physics of conductivity, a completely novel mode of doing computation that isn't based on electronics (photons?), or a fundamentally novel principle of organizing a cpu that somehow avoids being clock-bound (I heard about an effort over ten years ago, but I have not heard of it since). Any of those improvements could have surfaced at any time in the past few decades and been eagerly pursued, but none did, so the odds don't favor the miraculous appearance of one of them in the foreseeable future.
like asynchronous circuits?
CPUs based on them have been around, and more can certainly be done. they're just a lot more complicated.
The computer almost sounds alive...
A lot of this post reads like nonsense.
General-purpose desktops and laptops today often don't come close to using all of the CPU horsepower available to them, and many server applications are limited by memory, network bandwidth, and storage.
It seems conceivable to me that at some point, before reaching thermodynamic limits, CPU cycles will stop being scarce for many application spaces, and future computing investments will mainly be in networking, memory, storage and software.
Maybe a fundamental limit of the universe is that the minimum surface area of a volume containing a subatomic structure is related to the information required to define that structure? My maths is a bit fuzzy, but isn't there a fundamental relationship between a volume its boundary, involving a Fourier Transform? That could then mean that a limitation on surface area is equivalent to a limitation of the (4-dimensional?) volume occupied by some other quantity?
The above is speculation on my part, but is there a HN reader our there who can say whether such thoughts are garbage, or whether they have some basis?
You might be thinking of Stokes's theorem [0] or one of its special cases.
0. http://en.m.wikipedia.org/wiki/Stokes%27_theorem
My physics abilities are far from what I'd want them to be, but it does sound to me that there may be some insight in what you're saying.