Nanotech, specifically theorized universal constructors/destructors. They've been proposed in sci-fi as a general tool. But I started thinking about using them in a home environment for rooms that reshape themselves and their furniture arbitrarily, and I got stuck on energy and heat requirements. It seems like all the dissassembly and reassembly would absorb or produce a lot of energy, enough that they really would not be feasible for a home environment. Do others agree with that analysis? Or is there a way the tiny machines could cache their waste energy to vent away from nearby humans?

[EDIT] Smart matter and universal constructors are both nanomachines that achieve similar effects at macro scale, but very different function when examined at nanoscale. Smart matter is a substance that, by reconfiguring itself, mimics other substances at the macro scale. Think like butterfly wings taking on different colors depending upon the angle the cells are set, only in this case, changing nanoscale arrangement allows for different friction, conductivity, color, phase state, etc. A universal constructor, on the other hand, actually takes apart molecules and rearranges atoms to build things. Near-tech constructors could only rearrange available atoms. Far-fetched sci-fi proposes nanobots that can fission or fuse atoms to create other elements as needed (clearly higher power level needed). This question is about universal constructors of the near or far tech variety. Can any sort of universal constructor operate at a low enough heat level to be regularly used in a home environment? Or are they strictly for industrial environments with heavy radiation shielding?

PS: at some point, you need the constructors to make smart matter. :-)

  • $\begingroup$ I expanded the question details. $\endgroup$
    – SRM
    Sep 8, 2016 at 18:09
  • $\begingroup$ Ok, so you specifically want to know about molecule-scale. Like, microbots won’t be suitable for making food or chemicals (and the microbots themselves), right? $\endgroup$
    – JDługosz
    Sep 8, 2016 at 18:31
  • $\begingroup$ Nuclear fusion nanobots that can produce and handle those quantities of energy without radiation. How? Not possible with matter. $\endgroup$ Sep 8, 2016 at 19:39

5 Answers 5


A look at molecular assembly

I think molecular assembly will resemble the growth of plants or animal organs. I believe Drexler used the example of a rocket engine in Engines of Creation, a landmark book well worth reading if you are interested in this subject! The engine can’t simply be made from modular reconfigurable microbots and be able to function. But it is built by such devices. A growth chamber is filled with fluid and swarms of microbots are introduced: they grab on to each other to form a circulatory system and any needed scaffolding. Then raw material is presented in the fluid, and the microbots break up the feedstock to get the individual atoms they need, and start assembling the device. The fluid also bears the fuel and carries away the heat.

So imagine how “bone” is grown. The naturally occurring microbots (called osteoblasts) crawl along a protein matrix and deposit material.

[O]steoblasts produce a calcium and phosphate-based mineral, hydroxyapatite, that is deposited, in a highly regulated manner, into the organic matrix forming a very strong and dense mineralized tissue…

Leaving the circulatory system in place provides for continued self-repair and modification, if provided with power and materials. And the composite structure might be desired for most uses, even with capillaries leaving gaps. After all bone is a very good lightweight material.

But for more solid pieces, the circulatory system can simply be filled in last as part of the retreat of the bots.

※ Having the microbots covered in and contain programmable matter might change this!

About heat

The existence of circulatory fluid bearing raw material and carrying away waste will help matters because it can also carry away the heat.

But what is heat, anyway? It’s random stray motion of atoms. If the atoms and molecules are placed into position very carefully there will be no heat generated! Well, not at the site where it was deposited anyway; it’s a case of Maxwell’s Demon. The circulatory fluid will carry away the extra entropy in some form, to spill heat somewhere else like another vat that needs heating, or a heat sink. (And of course the use of this kind of technology means that energy reclamation systems can spring into existence wherever hot/cold borders exist at the moment.)

So, it’s possible to deposit material rapidly without leaving the workpiece hot. It will be cooled molecule by molecule by damping the excess vibration. Any such assembly needs materials and fuel coming in and waste going out, and excess heat (or entropy) can be among the waste products.

Home environments?

The question specifies “…in home environments”, presuming that home use will be different from business, professional, or industrial use. But the very technology we’re talking about eliminates any such distinction! You won’t have “industrial” installations if the infrastructure is conjured up on demand by microbots. So having, say, a huge vat with pipes and pumps is not something that you won’t have available at home, but will be created on the spot as a kind of temporary scaffolding for the job underway. Any bootstrapping and intermediate steps will simply be taken and not rely on permanent installations of support equipment.

The only real limits will be the logistics of bringing power, feedstock, and microbots to the jobsite. Since the distribution may use the same technology as well, the system will simply add or widen pipes and wires to meet the demand in your location. If you’re conjuring up a house, and need an order of magnitude more supplies than the typical user in that neighborhood, the supplier can enlarge the delivery pipes on the fly because they are made and maintained using the same principles.


N.B. The question was edited

The question was edited to disallow this specifically. It’s good to keep as a reference though, since the Q and other As will need to refer to the distinction between microbots and full molecular assembly.

original answer

There is no real problem.

Instead of thinking about assembling everything from scratch or disassembling everything into atoms, you should think about rearranging larger blocks of matter.

There are roughly 1012 atoms in an object 1×1×1 μm (micron size object) — construction from blocks of this size is very precise, and for utilitarian uses such as furniture or buildings it is overkill precision. Manipulating blocks of that size rather than individual atoms saves you 12 orders of magnitude individual operations in whole process.

Using different shapes, sizes, or materials of blocks for different roughness of surface, or different size objects if needed. Do not dissemble things when you do not have to. When you need specific ideal properties and don't already have the needed blocks you can manufacture those blocks from scratch rather than the entire object. As example, when ideal shape is needed, object can be approximated with pre-manufactured 1 μm blocks, and everything what needed to get ideal shape after that is to produce blocks for surface layer. Thickness of that layer will be under 1 μm, and for spoon as example it will be minuscule amount of work(individual operations) needed for that spoon polishing compared to producing from scratch.

The blocks themselves can be designed for specific properties; strength, softness, etc. Optimization is key - don't make or change things you don't have to, but be ready to make things you may need to. What and how you make or assemble blocks is like software optimization; there are many possible ways of getting your end result.

When moving blocks you do not have move each block individually; moving a string of connected blocks requires or dissipate less energy than moving each block by itself. Strings could be prebuilt tubes as well, which you can assemble together on fly, and anywhere you might use ordinary coolants you can use assembled blocks as coolants (string or coolant conducted through the tubes, Peltier-like modules, or high heat conductive modules etc. etc.)

Nanotech, at least reasonable nanotech, does not mean assembling everything from individual atoms, it is about flexibility of construction that may occasionally requires this. Even magical grey goo might use tricks like this. Assembling from blocks allows nanotech to build things more efficiently than just assembling from grey goo alone; at least until we have the technology to control individual molecules without some nanotech effectors we have built to manipulate them (i.e. until we invent real space-time magic for atom level sizes).

As in a clock where you can only see the face but not what moves the hands; this doesn't mean there is nothing behind the clock face. So instead of old beds and other junk stored in your basement you could instead store a few cubic meters of spare nanotech blocks for your nanotech system which are not used at the moment. If thee system works and doesn't waste energy that's all we care about.

  • $\begingroup$ Like transformium $\endgroup$ Sep 8, 2016 at 5:33
  • $\begingroup$ This whole answer is similar to "Collapsium" (novel title) and other stories involving forms of "smart matter", but isn't quite the same as actually constructing products at the molecular level. I've marked it as "answer" because it indirectly answers my question: no, universal constructors aren't feasible in any environment, much less home environment. $\endgroup$
    – SRM
    Sep 8, 2016 at 13:42
  • 1
    $\begingroup$ @SRM You could wait few days, I'm myself would like to see the others answers. You could improve the question to define universal constructors. I do not see some strict border between blocks and atoms assembly - we need them both and as we have one we have another (blocks to atoms is not so obvious - at the moment we are kinda block stage - but we can directly manipulate atoms with our tools - atm it is more knowledge problem). From physical stand point of view only atom assembly have Maxwell's demon problem - to move single atom with group of atoms - we move group+1 atoms and generate heat $\endgroup$
    – MolbOrg
    Sep 8, 2016 at 14:31
  • $\begingroup$ @srm I think programmable matter will be used in conjuction with micro-scale modular reconfirable robots. Maybe on the surface to control the finish. $\endgroup$
    – JDługosz
    Sep 8, 2016 at 17:47

If you have a net heat output, there would seem to be two main possibilities:

Take it slow - you can always just slow the processing down to a point where the heat output drops to acceptable levels, or

Use the heat - most houses require heating some of the year, and you need a way to cook things in your kitchen. So put your active universal constructors in the nanotech equivalent of an Aga cooker / storage heater. With good insulation (vacuum flask equivalent) around your working area, raw materials with a high heat capacity as working stock/heat sink for your constructors, you can use the heat generated to heat up your heat sink materials to store the heat, then heat pipe it out when you need it for cooking, hot water, or room heating.

You could also use the heat to drive power generation for your electricity.

  • 1
    $\begingroup$ It would be reclaiming power, not generating it, since you are giving it power to do the assembly. $\endgroup$
    – JDługosz
    Sep 9, 2016 at 2:19

Yes, this is feasible

If such constructors do in fact produce a lot of waste heat, then perform the operations in a manner and/or location that captures and stores said heat.

Heat could be vented to air for air temp control, vented to liquid for heated water reserves, and to energy storage banks (liquid salt or similar) much as solar energy can be stored and later vented as heat or converted to electrical energy.

Thus, this could be feasible in even a residential environment.

Edit for new question content

Should universal constructors produce waste radiation in a non-heat form (ie: not photons) this is more difficult, but still not infeasible. Such units would probably reside in the foundation of every structure built by this civilization. Incorporated into the foundation would be the requisite shielding as well as properly isolated and protected input and output ports and storage spaces.

Again, waste heat (produced by any method) can still be siphoned off and used to heat gases or liquids, or stored for later use and/or conversion. After all, this is much the method used in most nuclear power plants. With as high a tech base as is being proposed, any potential radioactive material can be deconstructed and recombined with the atomic components necessary to render it inert.


Efficiency is key

Paraphrasing your (edited) question:

Does waste heat from molecular reassembly make it impractical or home use?

Assuming that you have Maxwell's Demon to help you, the only heat you have to worry about comes from the difference in potential energy of your feedstock and result. By using the right feedstock, this can balance out to "no difference".

In reality, the heat generated is likely to be substantial if you're breaking and forming bonds in bulk, and ridiculous if you're using fission/fusion. Instead, using existing material with a similar structure will minimise the need for these bonds to be broken and re-formed.

A practical solution will try to use "traditional" programmable matter as far as possible, and may well use conventional construction techniques such as slicing off "large" sections. Most objects (food and combustibles aside) are easily made with a thin veneer of "the real thing" over a smart-matter underlay. For food and combustibles (which are chemically decomposed), the right set of reactions can assemble them with a minimum of waste heat.


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