A group of aliens are off to save the human race from extinction caused by a Lovecraftian monstrosity.

In order to accomplish this feat, they go to Earth in order to harvest as many humans as possible to restart the race while keeping as much diversity in the gene pool as possible.

The thing is, the aliens don't have time to introduce themselves and have the humans sort themselves out. So they arrive one day and start abducting people for the greater good. In order to store the humans they have acquired, they liquefy them in-order to save...how much space on their craft exactly?

I would like to know how much volume a liquefied person takes up if they were stored in the most spatially-economical vessel (a cube or rectangle, though cylinders might be needed if under pressure.)

The age groups I would like are:

  • Toddlers

  • Teenagers

  • Adults

(Don't question how they are liquefied only to come back normally afterwards. We are dealing with Clarketech here.)

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – L.Dutch - Reinstate Monica Apr 29 '20 at 19:28
  • $\begingroup$ The same volume they took before liquification. A change in the state of matter does not create or annihilate any matter. For back of envelope numbers, human density is approximately that of water so ~1litre/kg. $\endgroup$ – Bohemian Apr 30 '20 at 8:50
  • $\begingroup$ Can we address requirement the other way around? The liquifaction may not be to save space on each individual human. But on the whole group. To simplify the idea, human need space to breath and move, those on the bottom on the pile ended as liquid anyway. Only the crust, external layers were viable. The advantage of liquified human is that they don't have those requirement, you just need a container big enough and the shape do not matter, that also a big plus in spaceship design. In fact liquified human take more space we add a lot of lubrification fluid. it was sticky on the pipeline wall $\endgroup$ – Drag and Drop Apr 30 '20 at 14:04
  • $\begingroup$ Your FBI agent sends his regards. He was a bit scared to talk to you personally. $\endgroup$ – Blueriver May 1 '20 at 14:24

How good is liquefaction?

L.Dutch's answer is the right concept, but his numbers are wrong. 6 liters is the maximum inhalation of an average adult male; however, men have much larger capacity than women and normal respiration does not fully inflate the lungs. The 62 liter volume of an average adult assumes a resting inhalation volume which actually averages closer to 2.5 liters of air in your lungs (during normal at-rest breathing across genders). Volumes of gastro intestinal gases vary a lot throughout the day, but average about 1 liter. This means his equation should look more like 3.5/(62+3.5) = 5%; so, you only get a 5% reduction in absolute volume.

That said, the more important savings are in removing the empty spaces around the body. An average human is 160x39x23cm that is 143.52 liters. When you compare that to the 58.5 liter liquid state of a human, you get 143.52/(143.52+58.5) = 71%; so, your reduction in practical volume would be 71% compared to shoving us in boxes.

This will result in the following:

Age Group          | Avg. Whole Weight | Avg. Volume
2yr old Toddler      12,000 g            11,100 cm^3*  
13yr old Teenager    45,000 g            41,600 cm^3*
Adult                62,000 g            58,500 cm^3

*Due to lack of data, child volumes are based on mathematical ratios compared to adults.
Different childhood ratios of bone, muscles, organs, etc might impact these figures. 

Designing the packaging:

To package your humans this way, place thier remains in large plastic bags kind of like IV bags. This will keep your remains separate, sterile, and waste very little space.

That said, because some fluids such as stomach acid would react with other fluids such as brain chunks, you may in fact want to store certain biological substances separately rather than in on big bag to make sure you still have all the same compounds coming out as you had going in. This may mean a complex system of "disassembling" the human body into seperate bags rather than just throwing them into a blender. This can lead to some unexpected wasted space as you start needing to account lots of total bag materials, air gaps between bags, and possibly wasted space in whatever bins you use to keep all the liquid human sacs organized in. It's hard to say just how much space will be wasted without delving REALLY deep into human biochemistry and industrial design to determine how many bags and of what size you need; so, lets just say it will still be more efficient than boxing whole humans, but maybe closer to a 50-60% savings if you go this rought.

enter image description here

But, your aliens could do better

Generally I agree with Carl's assessment that you don't need to bring whole people, but cloning humans requires large artificial wombs, and lot of labor for your aliens to hang around baby sitting us for 20 years waiting for us to have a functional adult population while our DNA synthesizes all the complex compounds (proteins, fats, nucleic acids, carbohydrates, etc.) that make up an adult.

Instead of a slurry which is 60% water, you could dehydrate the human pulp into a "meat and bone meal". This is an industrial term referring to the dehydrated and ground up remains of an animal. Since any planet they are bringing us to would inevitably contain lots of water, they would just need to rehydrate our remains as part of the reconstitution process using the water from our new world. https://en.wikipedia.org/wiki/Meat_and_bone_meal says that meat and bone meal averages 4–7% water (I will use 5% to simplify the math); so, if you reduce the human body from 60% water to 5%, you are eliminating about 55% of a human's total mass.

According to calcert.com, loose meat and bone meal is has a density of 0.72 g/cm^3. This is a bit less than our liquid density because the powder will have room for air, but will still have a lower total volume than liquid humans while allowing the aliens to transport all of our complex compounds needed to put us back together.

This will result in the following:

Age Group          | Avg. Whole Weight | Avg. Dry Weight | Avg. Volume
2yr old Toddler      12,000 g                5,400 g        7,500 cm^3*  
13yr old Teenager    45,000 g               22,250 g       30,902 cm^3* 
Adult                62,000 g               27,900 g       38,750 cm^3*

*Due to lack of data, meat and bone meal density is based on animal meal.  Human meal 
might be slightly more or less dense.

If the remains are vacuum sealed like coffee, you could increase the density of your meal to be just a bit over 1 g/cm^3; however, vacuums cause most organic compounds to break down; so, depending on how advanced your alien tech is will determine how much they can safely compress your human remains.

Going back to the practical volume of a human, this means you will get somewhere between a 79 and 84% practical reduction in volume by converting people to meat and bone meal. That is about 34-53% more efficient than liquefaction (ignoring any differences in packaging processes). If you opt for liquefaction in your story, I would suggest giving some brief handwave explanation for why you can not dehydrate the human remains.

Designing the packaging:

Another possible advantage to removing water from the human body is that it makes freezing us far less destructive. Water expands when freezing which plays havoc on on the other molecules being frozen with it. The Arrhenius equation shows that as things cool, things that react at higher temperatures stop reacting with one another. This means you can deep freeze stomach acid and dehydrated brain chunks together without them reacting with one another such that you can get an even better efficiency out of your packaging by keeping us in one very cold container.

Even under low-vacuum states, vacuum sealed plastic and foil cubes are probably the best way to store and separate human remains because they maintain a sterile, light weight, easily stored, separate vessel for each human, and can be shaped into cubes for optimal space efficiency. To figure out how big these cubes have to be we should look at the top end of who the aliens might select for transport. If they want to save the species, they will probably select people based on health factors meaning the obese and dangerously tall may be excluded. This puts a reasonable upper limit of 115kg on your whole weight. If we assume a light vacuum seal will compress the meal density to about 0.85 g/cm^3, then we get a finished volume of about 60,882cm^3 or a cube that is about 39x39x39cm.

enter image description here

If it were me, I would describe the human storage room as being a cryogenically cooled cargo bay full of pallets of vacuum sealed blocks, all ~39x39cm at the base so that they stack nicely, but ranging from ~4-39cm tall. By mixing and matching people of various volumes, each pallet could be filled to the maximum height recommended by alien freight regulations.

In conclusion:

There are many factors that could play into how you could and should store a disintegrated human, and it all boils down to "how destroyed is too destroyed to reassemble." Hopefully this goes into enough (though be it disturbing) detail to figure out how compressed your humans should be.

  • $\begingroup$ Nice answer but when reach in "separate human remains..." I cant leave to think in human microbiome and how the reconstituition of individuals will deal with each different life being inside each one of us. $\endgroup$ – Rodolfo Penteado Apr 29 '20 at 16:19
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    $\begingroup$ Hmm... I was just thinking about keeping remains separate as an organizational tool, but you are right that there may be some philosophical issues too. The aliens may see a person as the sum of THEIR parts, so they may see this as the difference between putting a person into thier own equivalent of a medically induced coma and murdering people and replacing them with clones. $\endgroup$ – Nosajimiki Apr 29 '20 at 16:31
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    $\begingroup$ I was scrolling down until I found someone who gave the answer I would have given (except I don't have the time to do the research). Essentially "instant human, just add water". Beautiful. Well, disgusting, but beautiful from a science/engineering standpoint. $\endgroup$ – manassehkatz-Moving 2 Codidact Apr 30 '20 at 17:07
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    $\begingroup$ @manassehkatz-Moving2Codidact 'Beautiful. Well, disgusting ' lol! Funny thing about WB.SE is if you spend too much time on here, you eventually find yourself treating some very disturbing things way to matter of factly... $\endgroup$ – Nosajimiki Apr 30 '20 at 17:35
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    $\begingroup$ Thank you! This has been a real help! Right now I’m picking which idea to go too; liquefaction would be more akin to my original image of a man crawling out of a pool of goo, but the picture of people getting sorted into mini bags or drained of fluids before being freeze dried really hammers in some very disgusting ( entertaining) scenes. $\endgroup$ – Seraphim May 1 '20 at 6:31

The average volume of an adult human is about 62 liters.

Assuming that the aliens don't use any process that causes the loss of volatiles elements, the only saving from liquefying a human body would come from the air volume taken by the lungs and bowels.

In an average adult the lungs account for about 6 liters of air, while the bowels I wasn't able to find accurate values, so I would go for the same volume as the lungs.

That would save about $12/(62+12)=16\%$ of the volume taken by a normal body.

Since we are at it, the same page I linked above calculates the volume of entire mankind is about half a cubic kilometer

If you stacked everyone together into a Human Cube (hmmm, I should trademark that), it would be about 770 meters on a side.

Since the average above covers adults, teenagers and toddlers, I won't go into further calculations.

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    $\begingroup$ You don't only save the air inside the body, you salso save in the air between the bodies. Packing inefficiencies! $\endgroup$ – Grollo Apr 29 '20 at 7:22
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    $\begingroup$ @Grollo true, this answer completely misses that humans are not efficient in shape, needs, or behaviour, to facilitate packing. If we assume (as an example) that the smallest space a live conscious human can reasonably be kept in is an economy airline seat, then the space saved is the volume between that seat and the one in front, minus 62 litres. Quite a saving! $\endgroup$ – Grimm The Opiner Apr 29 '20 at 7:28
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    $\begingroup$ @GrimmTheOpiner, I have been on Tokyo metro during rush hours. When you float because of the hydrostatic pressure of the crowd, you understand what "packing" means. $\endgroup$ – L.Dutch - Reinstate Monica Apr 29 '20 at 7:57
  • $\begingroup$ I'd imagine that a column of humans ~770m high would mean the lower ones were fairly effectively squashed into a block with no air gaps... While there might be air gaps among the top few layers, things would pretty quickly compress. I also thought we were talking about blended humans here. $\endgroup$ – Caius Jard Apr 29 '20 at 10:41
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    $\begingroup$ Your link asserts that "The average total lung capacity of an adult human male is about 6 litres of air." but you compared mens' lungs to average human volumes. Men have much higher maximum lung capacity than women and higher average body volumes than 62 liters. 6 liters is also not the at rest capacity of lungs which is where human volumes are typically calculated from. I reran your calculations along with a source that claimed average GI gases are 1 liter and came up with closer to 5%. $\endgroup$ – Nosajimiki Apr 29 '20 at 14:25

Since we know that the density of a human is very close to 1kg/l (we float in water, but only just), a human’s volume in litres is pretty much the same as their weight in kilogrammes.

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    $\begingroup$ This is a bit tricky, given the lungs. For instance, I have a fairly low body fat percentage, and so will float when I take a deep breath, but sink when I exhale. A good ballpark answer, though! $\endgroup$ – jamesqf Apr 28 '20 at 16:04
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    $\begingroup$ -1 - This answer is predicated on the assumption that the volume of a liquefied human is equivalent to the volume of a normal human, which is exactly the assumption that the OP is trying to evaluate. This is a slightly more complicated way of saying "the volumes are the same", without any supporting argument whatsoever. As a rough approximation of the volume of a human, it's OK, but completely inadequate to calculate the space savings from liquefaction. $\endgroup$ – Nuclear Hoagie Apr 28 '20 at 16:14
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    $\begingroup$ The answer does in fact give an argument why the volumes should be roughly the same—namely that the density of a human and the density of water are almost the same. The fact that wood floats very easily or that steel sinks rapidly means that those densities are not very close to the density of water, and so such an argument would not apply to them. — The one step in the argument that could be articulated is the assumption that liquid human has a similar density to water (or to regular human). In theory liquid human could sink rapidly, for example, although that seems unlikely. $\endgroup$ – Greg Martin Apr 28 '20 at 16:36
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    $\begingroup$ You're missing the emperical observation "we float in water, but only just". That observation would not hold if human density were much higher than water density. $\endgroup$ – Greg Martin Apr 28 '20 at 16:49
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    $\begingroup$ This answer is intuitive... but it's not quite correct. You can see this if, when at a pool, you exhale as much air from your lungs as you can - you will begin to sink. And no matter how hard you try, you won't be able to exhale all the air in your body - so 'liquified', you'd be even more dense. I think if you put a disclaimer about this, and said that it's a reasonable approximation, you'd be in much steadier ground. $\endgroup$ – Kevin Apr 29 '20 at 15:19

The whole concept is wrong. If you want to save the species and the diversity of the species all you need is a couple bottles full of cryogenically stored eggs and sperm. And a decent artificial womb, but if they can travel from wherever to Earth, that shouldn't be a big problem.

Resurrecting actual people is a huge waste of mass and effort, and further it'll be a lot easier to acclimatize newborns to the alien planet than to try to get native Earth-born folk to adjust.

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    $\begingroup$ perhaps they endeavour to also save the human cultures $\endgroup$ – crobar Apr 28 '20 at 20:32
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    $\begingroup$ @crobar An alien race capable of reconstituting a person from pulp would need to be able to map a person's mind before disintegrating them so that they could know how to reassemble it. If they can do that, then they could just grow a bunch of clones at the new world, then disintegrate the clones and reassemble them with stored mind maps. I'd say the real limit here is far more the extra labor and equipment required. $\endgroup$ – Nosajimiki Apr 29 '20 at 13:23
  • $\begingroup$ Storing adults would be a good idea if you have the technology and are trying to maintain a breeding population. If you just store embryos you lose all culturally-passed on information, including how to raise offspring and how to survive in the wild. This is really bad for humans, whose behavior is primarily cultural, not instinctive. Otherwise these humans are just fancy zoo animals. Similar concerns exist today with trying to clone intelligent, social animals like mammoths, because the behavioral knowledge is lost and the clones may not know how to survive on their own. $\endgroup$ – user2352714 May 19 '20 at 20:17

Liquification won't be all that effective. Basically, you reduce the problem to "what is the volume of a human being?"

One can find this volume via Archimedes' principle. Fill a tub with water, put the human in the tub, letting the water spill over, and measure how much water left the tub. However, we can do this faster. The human body is roughly the same density as water. Thus, for every kg of human, you have roughly 1 liter of water. Get any growth chart of your preference, and you find out how many liters they are (in particular, toddlers grow freaking fast, so there's no one number).

Now if these aliens mean business, they need to then put the liquid in a dehydrator, to concentrate the humans. Orange juice concentrate gets about a factor of 4 size reduction (which is why you add 3 cans of water to bring it back). The human body is only about 60% water, but you should be able to squeeze a bit more out of it!

Freeze dried humans are probably the most effective form of packaging. It works for ice cream!

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    $\begingroup$ The average human density you are using accounts for any empty pockets inside the body; but liquefying someone should remove those voids, so density would increase and this technique wouldn't be accurate. $\endgroup$ – JMac Apr 28 '20 at 18:13
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    $\begingroup$ Now there is the matter of the volume of the lungs (and GI tract), but that is so small that we're getting into details that are dwarfed by the fact that people aren't the same size. $\endgroup$ – Cort Ammon Apr 28 '20 at 18:34
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    $\begingroup$ @Nosajimiki-ReinstateMonica But that's pretty much the entire crux of the question and it's being dismissed with handwavyness. There's only one answer that even seems to try to account for those numbers, and quite frankly it's the only part of the question that isn't totally trivial IMO. $\endgroup$ – JMac Apr 28 '20 at 18:36
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    $\begingroup$ @CortAmmon The question doesn't even suggest liquifying humans is a good idea at all. It isn't looking for the best way to process the humans to fit them in the least space. It's specifically asking how much volume you could save and how well you could pack with a liquid. A 19% change in volume for liquification is very relevant to the question as posed, whereas a 95% change due to freeze drying (which is not the question, it's not asking for best methods) is not relevant. $\endgroup$ – JMac Apr 28 '20 at 18:54
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    $\begingroup$ @JMac You are absolutely right; however, on this site there is a kind of answer called a Frame Challenge. It is where a person reframes the question based on possible oversights made by the OP to give suggestions that would better answer the core of the question than the question seems to allow for. It is then up to the OP to decide if said suggestions expand on or go against what he is trying to ask. In this case, freeze drying is a valid frame challenge to a question about aliens trying to fit people into a smaller space for transport. $\endgroup$ – Nosajimiki Apr 28 '20 at 19:09

How much volume does a liquefied human take?

Just over 1 litre per kg of mass.
Close packed in a rectangular sided form (cubes or other).


Rather than looking at materials, lets look at some attributes of "real people".
The average person will float in fresh water with air in their lings and will usually sink if all air is expelled.

The density of fresh water is 1 kg per litre.
So the density of "just sinking" people is just over 1 kg/litre.

If you allow 1 lite per kg = 1 cubic metre per tonne (or ton) in rectangular sided shapes you get a slightly higher than absolutely minimal volume.
Add whatever allowances you need for storage (shelves, protection, ... . )

Most of the body is liquid which is incompressible.
If the technology allows you may gain a little more packing density by compressing no fluid materials.


It really depends on the pressure, because liquids are, contrary to common belief, compressible, it just takes much more pressure than gases. In fact, everything is compressible, even the most incomprehensible thing there is, a neutron star, can develop into a black hole.

So, I say, for maximum compressiblility, the minimum volume occupied by the liquefied people is only dependent on the mass, and is a sphere with radius r = 2GM/c², where G is the gravitational constant, M is the mass, and c is the speed of light (this is the Schwarzschild radius), which is very small for the whole population of Earth. Subatomic, in fact.

People compactified into black holes should not lose their original information, according to the outcome of a bet between Stephen Hawking and Leonard Susskind, so the aliens may be able, in principle, to reconstruct the people from the information in the black hole.

  • $\begingroup$ While this is in theory true, one should stipulate that you stop having a liquid state of matter LOOONG before you can compress a substance down to a black hole. Also, the stages of compression between normal liquid and black hole destroy all nuclear and atomic bonds meaning that the conservation of information is irrelevant to the usability of said information. In other words, the raw elements of the planet you are going to will generally be in a more useful state for synthesising humans than anything you can get back out of the black hole. $\endgroup$ – Nosajimiki Apr 29 '20 at 16:12
  • $\begingroup$ If they can take the information of the quantum state of the matter in the black hole, and simulate it backwards, they can get the exact subatomic and macroscopic structures of the matter before compression. If you already have to reconstruct proteic and celular structure from a liquid, it is just a few step further to have to reconstruct baryonic matter and atomic structure from just information. Both seems equally impossible, from where we stand. $\endgroup$ – lvella Apr 29 '20 at 16:24

What you want is a justification for liquifying the human body. Since some answers have already pointed out, the act of liquefying itself is useless, I will try pointing some other things

If you only want to save volume and not mass why not make them denser?

Why not extract only the nervous system and then liquefy it? Wouldn’t that make them more self-righteous...

In absence of logic the reasoning you choose can be arbitrary. If you are hell-bent on liquefaction to save humanity from galactic extinctionists go with the second soln.


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