I've got a group of magical people living mostly incognito in an ancient society. They look and act exactly the same as regular people, but they are really magicians, and a side effect of having those powers is that they are two times as dense. E.g. a lithe woman who looks like 50kg/110lbs would really weigh 100kg/220lbs. They've got twice the muscle strength to compensate, but the mass is still there. It is congenital, they are born that way (perhaps even since conception).

What are things people could notice about them? It's not enough extra weight to make them fall through floors, but sitting on one end of a boat betrays them as it leans over more than it should. I think the extra inertia would also matter in some places, but I'm not sure where.

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    $\begingroup$ Welcome to worldbuilding.SE! When you have a moment, please take our tour and visit our help center to learn more about us. This is a good first question that fits nicely with our "I need a finite list of things" question type. Thanks! $\endgroup$ Jun 9 '18 at 21:15
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    $\begingroup$ Usually you find exceptionally dense people in university campuses.....oh, you mean physically dense.... $\endgroup$
    – Thucydides
    Jun 9 '18 at 21:32
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    $\begingroup$ Is the extra density magical or is there a physical basis for it? If it's physical, then you have to consider the fact that the human body is over 50% incompressible water, meaning that the extra density is even more highly concentrated than at first glance. $\endgroup$ Jun 9 '18 at 23:29
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    $\begingroup$ No high heels for you. $\endgroup$
    – Mazura
    Jun 10 '18 at 18:31
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    $\begingroup$ The first thing would be the MAGA hat. $\endgroup$
    – T.E.D.
    Jun 12 '18 at 14:08

23 Answers 23


They can't swim.

Normal humans are just barely buoyant enough to float in water. We need to generate some hydrodynamic lift to get far enough out of the water to breath.

The average human body has a relative density of 0.98 compared to water. Your humans would have a relative density of 1.96. That means while a normal human swimmer just needs to create a little bit of hydrodynamic lift in order to get their face high enough out of the water to breath, your dense humans would need to support half of their whole body weight with swimming motions.

To get an impression of how difficult that would be, imagine trying to keep your head above water while there is another person of the same weight as you standing on your shoulders. Even if you were twice as good of a swimmer, that would be impossible.

Normal people can't do that and your people wouldn't be able to do that either, even with twice the strength. They would sink like rocks. It would be next to impossible for any bystanders to get them back to the surface before they drown.

For that reason you will likely not get them into a boat. They would know that being so close to deep water would put them in mortal danger.

You would notice if they compete in contact sports

In sports like wrestling or rugby, a trained athlete quickly learns to judge the momentum of their opponent by how they look. This skill is crucial if one wants to succeed. When their opponent is twice as heavy as they should be, they will notice. A professional might even notice when they observe a match where one participant is heavier than they should be.

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    $\begingroup$ Can confirm as someone with prolonged martial arts and casual parkour experience, a trained/attentive person would notice, and not just during contact sports, even though they won't necessary understand what they're noticing: many movements would have to be slightly different to account for the larger inertia that any limb moving at the same speed would have. The faster the movement, the greater the tell. $\endgroup$
    – mtraceur
    Jun 12 '18 at 17:07
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    $\begingroup$ Hence the utility in tossing potential witches in pools of water... $\endgroup$
    – Jiminion
    Jun 12 '18 at 20:06
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    $\begingroup$ The makers of Lilo and Stitch did a good job showing Stich's increased density. $\endgroup$
    – Pureferret
    Jun 13 '18 at 12:41
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    $\begingroup$ @Jiminion Except the witches are the ones that are supposed to float. $\endgroup$
    – Ray
    Jun 13 '18 at 21:35
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    $\begingroup$ They would be also be really good at cycling due to low wind resistance relative to their mass and power. $\endgroup$ Jun 13 '18 at 21:35

A number of common situations could give them away.

If you ever paid attention to people getting in and out of your car, you notice that it shifts by noticeably different amount depending upon the weight of the person. Maybe the fact that I notice this makes me a bit of a rarity.

But there are other small things. How loud a floorboard or chair creaks. How much a cushion or mattress compress.

Again, these may be subtle, but the brain is good at pattern recognition -- and although you may not notice these things in in normal people, does not mean you would fail to recognize the exception to the pattern for high-density people.

Of course, early in-life people weigh babies, hold them, and even pass them around to friends and relatives. This would be instantly noticeable and all high-density people would be detected as infants.

If high-density people don't realize their condition, they would be detected in medical exams. Or broken toilet seats, chairs, etc. as they would not expect to cause damage by simple actions. If they try to conceal their condition, it will be harder for others to detect of course.

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    $\begingroup$ Which raises the question: are their relatives (especially their mothers) magical, too? If so, they’d keep the secret. $\endgroup$
    – Davislor
    Jun 9 '18 at 22:21
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    $\begingroup$ They’d better not play teeter-totter. $\endgroup$
    – Davislor
    Jun 9 '18 at 22:22
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    $\begingroup$ Little kids do enjoy being picked up. So the mother of the dense child will need to make sure only those in the know try to pick them up. $\endgroup$
    – Anketam
    Jun 10 '18 at 2:00
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    $\begingroup$ @KeizerHarm after carrying around a 15 pound (7 kilo) baby at term and then a growing behemoth at nursing, the mothers might not have any energy left to properly aid hiding them (or they might help the assassins) :-p $\endgroup$ Jun 10 '18 at 3:04
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    $\begingroup$ @Sumyrda "In an ancient society" - even stick-shifts weren't common then. $\endgroup$ Jun 11 '18 at 10:30

In addition to the answers listed, here are some more things that these people will need to be careful about, otherwise it could put them in a situation that could result in their exposure:


Their vocal cords are also twice as dense. The length, size, and tension of the folds in the vocal cords affect the pitch of ones voice. It is doubtful that the tension will go unchanged as a result of the density doubling. Unfortunately I could not find any studies on what happens if you change the density of the larynx. So, I cannot say for sure if it would cause them to naturally have higher or lower pitch voices. For example, if the density increases the tension, then it will cause their voices to have a higher pitch. If they get scared or excited it would increase the tension even further, resulting in them hitting some rather high pitch notes you would not expect a person to reach (specially if it is a man).

Getting Their Hair Cut

Their hair is going to be twice as dense as regular hair. Any barber or hair stylist will notice something is wrong. Specially when their scissors or clippers start having trouble cutting through their hair or become blunt faster. They might not be able to conclude that the person is twice as dense, but they will know something is different with these people.

Corset and Brassiere Problems

Corsets, brassieres, and other types of clothing are designed and intended to provide women with support. Unfortunately for any women that is twice as dense, means their clothing will need to provide twice as much support. As such the extra unexpected weight could damage corsets and cause more flimsy outfits to struggle and break leading to wardrobe malfunctions. This would not directly reveal them as being more dense, but it could put them in a situation which could easily lead to their discovery if someone tries to help them.

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    $\begingroup$ If it's literally every part of them is twice as dense, also wonder how differently (/if?) they hear due to the bones/fluids in the ear... and likewise how the circulatory/respiratory/digestive/renal systems and sweat will be impacted. $\endgroup$ Jun 10 '18 at 4:13
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    $\begingroup$ @JeopardyTempest I don't think sweat and the like would be included. Otherwise all the world's water would slowly be replaced by dense water. $\endgroup$
    – KeizerHarm
    Jun 10 '18 at 7:58
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    $\begingroup$ @JeopardyTempest how everyone hears is slightly different because everyone has variations in their ear structure. We have learned to process what we are hearing, and our brain does some amount of post processing on it to figure out things like direction from it. Things might sound different to them, but they would not even notice. $\endgroup$
    – Anketam
    Jun 10 '18 at 10:44
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    $\begingroup$ @Anketam That's probably the solution I would go with if it ever had to come up, but I don't think examining everyone's waste products would be attractive story-wise :P $\endgroup$
    – KeizerHarm
    Jun 10 '18 at 11:38
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    $\begingroup$ You could even think that their modified vocal folds is the very thing that ables them to cast spells $\endgroup$ Jun 11 '18 at 9:03

Besides what everyone has already said: their steps would be generally louder. They would impact the ground with twice the energy on each step, for the same footfall used by a person of regular density.

Also, they would be putting twice the pressure on the ground when standing. Their feet will sink a little bit on beach or desert sand. Their footprints will be deeper in any soil. And on snow, depending on the environment, they might sink anywhere from less than an inch to more than their full height depending on how compact the snow is.

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    $\begingroup$ > "They would impart the ground with twice the energy on each step." - Do note however that this assumes that they place their feet with the same care as an average person. Twice the energy of a light footfall may still be less than a heavy footfall. $\endgroup$
    – TLW
    Jun 10 '18 at 22:09
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    $\begingroup$ @TLW I think that someone making an effort to keep doing lightfalls might be even more noticeable than louder footsteps on most kinds of flooring in a city, unless they have practiced for years. $\endgroup$ Jun 11 '18 at 11:40
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    $\begingroup$ @Renan -- and they would have years of practice. I'm a big guy, and I am frequently accused of sneaking up on people simply because I step lightly (it was a mom thing, she forbade us to clomp around the house because that was not the right way to do it) $\endgroup$ Jun 11 '18 at 13:50
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    $\begingroup$ @Renan some children of the same height/weight/build move lightly, some clump around like baby elephants. Many can do either depending on mood/tiredness. This is without years of practice, because they haven't been walking at all for many years. $\endgroup$
    – Chris H
    Jun 11 '18 at 15:35
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    $\begingroup$ "Their steps would be louder" might well be one of those things that gives magicians their '"Presence".. $\endgroup$
    – JeffUK
    Jun 11 '18 at 16:41

They would also likely need to consume a fair chunk more food to account for the increased energy needed to move. You mentioned the extra inertia, well coincident with that is larger amounts of energy needed to move, such as in kinetic ($\frac{1}{2}mv^2$) and potential ($mgh$) energy.

Or else they'd become tired and start losing weight/look emaciated.

Certainly the existing range in metabolism may make it difficult for many notice, similar to Gary's answer. Indeed I've certainly had "smaller" friends who ate nonstop, weren't all that active, and somehow didn't gain weight. But it might at least make people suspicious.

You could use this calculator to get a rough idea of how much additional energy consumption would be needed.

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    $\begingroup$ @arp you can handwave any and all effects from all the answers. $\endgroup$ Jun 10 '18 at 2:18
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    $\begingroup$ @arp why would you want to? This brings up "what if"s that can help round out your world. How do the regulars react to this? Are they careful not to be seen over indulging in food, so as not to be mistaken for (or simply similar to) mages? How do the mages hide how much additional food they need to eat? How do they pay for it all? $\endgroup$
    – Morgen
    Jun 10 '18 at 3:55
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    $\begingroup$ @arp Even though the source of the extra weight is magic, it still takes energy to move that weight. So yep, they'd be big eaters. $\endgroup$
    – KeizerHarm
    Jun 10 '18 at 7:55
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    $\begingroup$ @arp I am the OP :-) And it's magic. These people are magicians, and they are able to manipulate various forces of physics including gravity, density, and momentum and such, but they cannot manipulate themselves, and their increased mass is simply a side-effect of having those powers. That's all I want to leave it at for now. $\endgroup$
    – KeizerHarm
    Jun 10 '18 at 11:43
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    $\begingroup$ I think the calorie intake wouldn't increase too much, most of your calories are spent on heating your body. Maybe 40% increase. $\endgroup$
    – gnasher729
    Jun 10 '18 at 11:44

Physical contact between humans is not rare, especially on sports teams but also in other social situations.

  • High five: normally the momentum of both people's arms cancels out. It might be possible to simulate a less dense arm by using your muscles, but even this could give you away.

    A simple hand-shake might not be a give-away if the person is well-practiced at making their hand easy for the other person to pump up and down. Sometimes a handshake starts with a slap or hand-clasp that could give it away.

  • Hugs, especially a "man-hug" that starts with a handshake and involves pulling the other person in until you bump shoulders. The other person's inertial mass is readily apparent. Illustration from this article: enter image description here

    Holding someone's shoulders as you greet them with air kisses next to their cheek (like in some parts of Europe) might give things away. The more touchy-feely the culture, the harder it will be to go undetected.

  • slap someone on the shoulder or give them a friendly push: if it's at all forceful, you expect their body to move some.

  • non-friendly pushes or fighting: it will be very obvious if you punch, push, or kick someone. Physical play between children might not be a "fight" per-se, but any kind of roughhousing will be a giveaway even to other children unless they're very young.

  • dancing with a partner: you don't push/pull your partner around the dance floor, but I think you would notice the difference just touching them while they move. Any "spin your partner" move where you hold on to each other and spin around a common centre of mass would be a dead giveaway.

Even in non-contact sports like Ultimate [frisbee], it's not rare to accidentally bump in to someone. A factor of 2 mass increase will be very obvious. You'll bounce off and they'll barely move.

At walking speed in a crowd, you sometimes jostle with other people a little bit, and even that could be enough to notice something was weird.

If a dense person is trying to stay undetected, just being physically near other people is a big risk. You never know when one will bump into you accidentally or touch you on purpose and notice the difference.

If you slip and someone tries to help catch you, they'll notice. If someone thinks you slipped or might need help, they might grab your hand and notice that it has twice the inertia it should.

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    $\begingroup$ That picture looks like the dude in the red suit put his hand all the way through the other guys chest. I thought, for a second, you were trying to say that the extra mass and inertia might lead to accidental impaling of "muggles" $\endgroup$
    – Kevin
    Jun 13 '18 at 14:37
  • $\begingroup$ @Kevin: hehe, after reading your comment it looked that way to me, too, until I realized that's his left hand, slightly awkwardly drawn. $\endgroup$ Jun 13 '18 at 14:55
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    $\begingroup$ Many people are not aware that a common handshake is a motorical difficult task. To exert force on the other persons arm and hand to move them your body has to provide muscle tension from your feet to your hand and move your center of balance accordingly. This only works without falling over, because our motor cortex calculates the exact muscle tension we need for the expected contact - if this calculation is off, we will struggle and feel out of balance - you would probably recognize something is off with every handshake. $\endgroup$
    – Falco
    Jun 13 '18 at 15:33

They will sink like a stone in water.

I don't think a doubled strength could fully compensate for a doubled density, as the buoyancy force is not doubled. If they can swim at all, it will be obvious that they're making a huge effort just to stay afloat.

Of course, knowing that, and also knowing about drowning, they'll avoid deep water like lava. Especially around outsiders. They won't stand out for it either, since "I don't know how to swim" is a perfectly valid excuse. But any accidents with them falling on water will surely reveal that they sink unnaturally.

  • $\begingroup$ Good point! Swimming may be the only activity where a person's density (not their weight or mass) matters directly $\endgroup$
    – KeizerHarm
    Jun 9 '18 at 22:51
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    $\begingroup$ The best part - dunking, which was historically used to "detect" witches, would actually work on these people, though in the opposite sense. If they sink, they're a witch. $\endgroup$
    – Obie 2.0
    Jun 11 '18 at 2:00

You also need to think of things like body heat. You'll have the same surface area through which you emit heat, but you'll have muscles -- and I assume other body/cell functions -- that are emitting twice as much heat. Someone very near to or touching you would feel the unnaturally high heat. Perhaps your metabolism could somehow be twice as efficient, but... (Also, if your metabolism is higher, even things like breathing would be an issue, since you'd need more oxygen but you have normal-sized nostrils and lungs, so you might be "out of breath" a lot.)

In terms of your remark on inertia, imagine bumping into a normal person on a sidewalk -- a situation where extra strength wouldn't help them because you wouldn't have time to use that strength to oppose your inertia. People would naturally assume from the force of the impact that you purposely put your shoulder into them. And this is assuming you possibly could use your strength to modify the situation, so imagine a situation where you're ballistic -- jumping, falling -- where no amount of muscle action could compensate. (This would apply to accidental impacts with anything, not just people, so you would be more likely to knock things over or destroy them if you bumped into them.)

You would also wear out horses pretty rapidly as an adult. I don't think horse stamina falls off linearly, so you'd wear out a horse more than twice as fast as someone else of your size. And your horse would generally be slower than those of any companions.

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    $\begingroup$ Not everything is doubling. Think of it more as them wearing an invisible backpack of their own body weight, that is distributed evenly over their body; and they get extra muscle strength to compensate. Their organs are not duplicated, so any extra heat would come from the muscles alone. $\endgroup$
    – KeizerHarm
    Jun 10 '18 at 16:21
  • $\begingroup$ @KeizerHarm muscles alone would include everything from breathing to blood circulation, from sitting upright or walking to talking. So if "extra muscle strength" implies twice the calories expended (and hence heat created) that might add up to noticeable heat. $\endgroup$
    – Wayne
    Jun 12 '18 at 2:50
  • $\begingroup$ Not quite twice the heat, since most body heat comes from digestion, but yep, noticeably more. $\endgroup$
    – KeizerHarm
    Jun 12 '18 at 11:30
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    $\begingroup$ The heat effect would likely be enough to make living in warm regions downright deadly to these super-dense people: It would significantly reduce the ambient temperature that they are able to endure. Any caring parent would try to move to polar regions as fast as possible. $\endgroup$ Jun 16 '18 at 13:41

In the movie Shallow Hal, Jack Black's character sees a woman who is extremely over weight as skinny an petite.

Some things the film did to show his perception of her wasn't accurate-

  • Getting in to a car, it sinks much more than her weight would suggest it should.
  • A chair that looks like it could easily manage her weight fails under the stress.
  • After she gets out of bed, Hal rolls over to where she was laying and falls into a deep recession in her mattress.
  • $\begingroup$ how does this answer the question? $\endgroup$
    – L.Dutch
    Jun 11 '18 at 17:22
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    $\begingroup$ It rather neatly illustrates some of the things that you might encounter if the person was substantially heavier than expected., I think it's a good answer, if a little oblique. $\endgroup$
    – Ruadhan
    Jun 12 '18 at 9:48
  • $\begingroup$ @L.Dutch if you've seen the movie, this answer makes a lot of sense. Screenshots are probably not permitted but they're visible at IMDB link $\endgroup$
    – Criggie
    Jun 16 '18 at 0:02

They would eat a lot

You could expect these people to need many more calories than a normal human. It takes energy to start and stop the additional mass, even if the enhanced muscle ability make the movement look completely normal. Additionally, even at rest, muscle take more calories to maintain than other tissues in the body. I imagine the enhanced muscle would need a similarly enhanced flow of calories in upkeep.
Net result: these people probably spend much more time eating than others, or possibly would only eat calorie dense foods

Note: a similar effect might be found with their breathing. Even a professionally athlete is going to get tired and breathe heavily if they carry around another person's weight all the time. Lung capacity / efficiency might increase to compensate, but if it plays out like this, I think it unlikely that these people would spend much, if any, time at high elevation where the air is thinner.

Abnormal body temperature

Or at least, that's how it would likely feel. I'm interpreting twice as dense to mean that there's literally twice as much physical stuff in the same space. This would mean there is effectively twice as much surface area for purposes of thermal transfer.
Net result: with any physical contact (say, shaking hands, for instance) both parties would feel any temperature differences much more acutely. It's possible these people would have constant hot/cold hand syndrome, or at least be perceived that way by normal people.

No static electricity(possibly)

Higher material density decrease electrical conductivity, all other thing bring equal. (I'm using compression of air as a logical reference point, so this might not even apply since people are made of solids and incompressible fluids). These people would effectively be electrically insulated.
Net result: tasers, Van der Graff generators, etc might not work as well on these people. It could also protect them from electrical magic you have them wield, if that's a thing in your world.

They don't get sick

Traditional diseases rely on germs bring suspended in a person's blood or cells. If these people are twice as dense, this simply would not happen. It's like the swimming problem in the other answers, except in reverse. Normal diseases would simply float and collect in certain points of the body where they would be quickly eliminated. If magical traits are at all genetic, you could expect their immune system to eventual center around (or even create) these points. Perhaps the magical community have their own unique set of diseases that normal people can't get?

Deep footprints

This one is pretty simple. Heavy people would displace more dirt/mud when walking

Biological waste

If everything in their bodies is twice as dense, it's fair to assume that their... excrement would be as well. This would create a problem if they needed to use modern plumbing, as it's entirely possible moving water would simply not have enough mass to clear a toilet bowl.

Note: hair is interesting to consider as a non living component of a person. Either the hair is just as strong as normal (limiting it's length due to the extra weight) or it doubles in strength like everything else so it would look sort of normal. Sort of, because if it's denser, it wouldn't blow in the wind as much as a normal person's. It's possible normal people would want to use it for making rope, given its strength. Or if it is just denser but not stronger, normal people might grow their own hair past that point to prove, immediately and visually, that they are not magical (useful for a diplomat, say for instance, since the couldn't then be a magical assassin)

I'm sure there's more, but that's all I can think of off the top of my head. Cheers!

  • $\begingroup$ The diplomat idea sounds awesome. $\endgroup$ Jun 12 '18 at 0:09
  • $\begingroup$ They do have unique diseases. Dragon pox, vanishing sickness, spattergroit, etc. They are wizards!!! $\endgroup$
    – user51857
    Jun 12 '18 at 12:04
  • $\begingroup$ I imagine a wizard would be able to cast a charm that allows them to grow long hair, so long hair by itself could not prove that someone is not magical. $\endgroup$
    – forest
    Jun 12 '18 at 22:03
  • $\begingroup$ Humans conduct electricity because we're bags of dirty water, with salts and other ionic compounds dissolved. Density should have no effect here: ions can still move in solution. Air is totally different: it's an insulator: to conduct it has to break down and ionize. Denser air means an electron will bump into something sooner if it is torn away from an atom, so it will pick up less energy from the electric field (on average: mean free path times volts per metre). This means we need higher volts / metre for an en.wikipedia.org/wiki/Electron_avalanche breakdown to cause arcing. $\endgroup$ Jun 12 '18 at 22:14
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    $\begingroup$ The hair idea is very good - excellent "outside the box" thinking. Finger/toe nails too. $\endgroup$
    – Criggie
    Jun 16 '18 at 0:04

You would notice the difference in children at a playground. Almost all playground sets use weight as a factor of play with the exception of the climbing sets.

Sets like the swings, seesaw, rope bridge, bouncy horses and the roundabout. You could see the difference if a children who was twice as heavy played with a normal child on a set.

A person with a keen eye could even spot the difference in the sand as the children ran and jumped.

Children could also not play contact sports like soccer, football, rugby or basketball without revealing their weight difference.

If a segment of the population was prosecuted for this difference, then it would be interesting to see how places like playgrounds would change. Instead of being an open place at the park and welcome to everyone. There might be police there keeping an eye out for heavy children. We might find that strange, but for parents living in that world it might be a necessary thing to ensure their children are safe.

  • $\begingroup$ I agree on most playground sets, but swings won't give the child away: On a swing, there is only gravity and inertia that control movement, and they are both proportional to mass. The swing would need to hold twice the weight, but it won't move any faster/slower for it. The frequency at which the swing swings is only dependent on its length. $\endgroup$ Jun 16 '18 at 13:48
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    $\begingroup$ @cmaster you just watch the person pushing the child on the swing or trying to stop the child from swinging. $\endgroup$
    – Reactgular
    Jun 16 '18 at 17:55

The every day sign, especialy in an ancient time.

Chair, Ladder, and Car:

Every things is build and design with a weight limitation. Take a good old wooden chair, A average man of 80Kg will not break a chair by sitting on it. A Dense Joe will easy break it, especialy if he give it a little swing. For a 50Kg woman the sign will be the floor wear. In ancient time floor were wood or dirt, this will be easly noticable.

For bench, once a normal man sit down, a dense one can catapult him just by sitting to fast or getting up too fast. If he goes slowly you will notice the weigth simply by the bench vribration and bend. On a bench you can notice if a kid(light) or an grown up sit on it even with your eye close.

For car and transport, this will be fun. They will either break the horse back or make a noticable shift in the car balance. Old vehicule don't have the sweet car suspension we have now. And even car suspension will give them away, same test for bench close your eye and ask someone to sit next to you. You should be able to tell witch is 50kg or 100Kg.

Ask Dense Joe to use a teen bicycle for fun.

In general every they use will wear faster, If those dense live together like a familly they should not invite people home.

When we build thing we trend to build them so they can be use in normal usage. 2 people usage instead of 1 is more than -50% life time, it could be imediat failure. Things like ladder won't like your Dense Joe.

The one that don't Knock:

They also never knock on door. You can have physical expectation when earing a door knock. You will notice that the 50 Kg girl knock like a 100Kg man.

Dense Joe don't drink booze:

There is nothing that test its own inertia on object like a drunk man. Any one that even encounter a drunk Dense joe can tell: "You don't pick them up."

Dense Joe sleep on the floor:

He will tell you that it's good for hes back. But Dense Joe simply break the bed every time. (50kg+80kg)x2 in the middle of the bed.

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    $\begingroup$ And they don't walk in mud. $\endgroup$ Jun 11 '18 at 9:29
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    $\begingroup$ The bed should be fine. Two adults sleeping together on the same part of the bed is a supported use case for many beds. $\endgroup$
    – bdsl
    Jun 16 '18 at 13:00
  • $\begingroup$ @bdsl, well clasical today bed have a best use at 200/250Kg "slowly distribued" quoting from my own bed notice... (50kg+80kg)x2 is 260Kg. Now if D.Joe and D.Jane are on the same side, they better not be moving to fast. Any one that already break a woden bed frame can tell you. It would have been easier if they weight Twice more. Things are build for common use, If you double use weight thats not normal any more. It will not be 80Kg perfectly safe 160Kg immediat failure. But it will wear faster. $\endgroup$ Jun 16 '18 at 17:42
  • $\begingroup$ Ah I think I didn't read your answer fully - you're talking about an issue with two dense people sharing a bed, not that one dense individual wouldn't be able to use a normal bed on their own. $\endgroup$
    – bdsl
    Jun 16 '18 at 18:13
  • $\begingroup$ Dense Joe wouldn't have too much problem drinking; it would take a lot more drink for him to get drunk. $\endgroup$
    – Spudley
    Jun 17 '18 at 19:44

They'd ask you to speak louder. Their denser ear and bone tissues would require a higher sound frequence in order to perceive clearly our speaking. Also, while eating, they should pay more attention if eating meat with bones. They could accidentally shard a bone and end up with mouth wounds.

  • $\begingroup$ Speaking louder wouldn't be a giveaway though because plenty of people are hard of hearing. $\endgroup$
    – JustinCB
    Jun 15 '18 at 19:11

Any time they need to get on a vehicle—in an ancient society, probably some kind of cart or chariot—or ride a horse, it will go much slower than it should. And if you know how much your own horse can carry, you’d at the least be worried that something’s the matter with your horse. In any situation where you have to balance a load, say by putting two people the same size on opposite sides of the cart, it becomes obvious that it takes twice as much weight as it should.

Someone who knows the strategies wizards use to stay inconspicuous might therefore look for the person who always makes very sure to sit in the middle of the wagon, not on either side, but also to sit directly over the legs of a bench, not in the middle.

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    $\begingroup$ I disagree. I very definitely notice the performance difference between just me in the car and a car full of passengers. There is basically no change in the speed on flat ground, though--what's noticeable is acceleration and hills. $\endgroup$ Jun 11 '18 at 5:20
  • $\begingroup$ Not to mention deceleration. Braking, that is. $\endgroup$
    – Mr Lister
    Jun 15 '18 at 13:25
  • $\begingroup$ @LorenPechtel I think if you had to push the car yourself, you'd notice quickly! (Or pull a cart, as some people still do in South Asia.) If your horse is carrying or pulling the weight, it both exerts less force than the car engine and also gets tired. Too soon. Carrying one woman shouldn't tucker a horse already; wonder what's wrong with it. $\endgroup$
    – Davislor
    Jun 15 '18 at 16:36

They would need to eat more for the same growth (unless the extra weight magically clings to them upon absorbtion in the body).

Besides swimming, they would have trouble jumping/falling and have a lot of problems with steep stairs or climbing up/going down. Even with double muscle strength and equivalent bones, the impacts would be immense and because they have twice the mass but the same shape they would accelerate to terminal velocity twice as fast (and have higher terminal velocity), so their bones and muscles would need to be about 4x stronger for the same height jump/step.

They would basically move around the world like geriatrics. A simple stumble can break their arm or leg. A crash with a car (or even a simple bicycle) would be lethal far sooner. In reverse, it takes more force to start moving their body so you need something bigger to hit them and get a damaging response. Even that has downsides as you'll absorb more energy in less time as well.

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    $\begingroup$ I don't think terminal velocity is relevant; falls anywhere near high enough for air drag to be relevant are typically fatal for regular humans. But good point that increased muscle strength would require increased bone strength / durability to deal with jumping. $\endgroup$ Jun 10 '18 at 21:32
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    $\begingroup$ Very wrong about drag: If anything I think it would take them a bit longer to reach terminal velocity than for an ordinary human--most of the time taken is simply how long it takes gravity to accelerate you to that speed. Since they are heavier terminal velocity is higher and gravity needs more time to act. This would only be noticeable if they went skydiving, though--they need double-sized parachutes. $\endgroup$ Jun 11 '18 at 5:24
  • $\begingroup$ @Loren Pechtel a feather in a vacuüm falls as fast as a bowling Ball because the acceleration stays the same and gravity pulls equally on each molecule of a piece of mass. A piece of mass of 70kg with air resistance of 1 (for example) will accelerate slower than a 140kg mass with the exact same air resistance because of the same shape and surface area touched by the air that slows the acceleration stays the same. $\endgroup$
    – Demigan
    Jun 11 '18 at 6:06
  • $\begingroup$ @Demigan: Right, but the 140kg mass has about twice the terminal velocity (if drag is linear with speed). So it needs twice as much delta-v. Since some of that time spent accelerating is when drag is negligible, I think Loren is right and it will take longer to reach say 99% of terminal velocity. (In theory you only approach TV asymptotically, except that TV decreases with altitude because of the air pressure gradient, so maybe you do actually reach it...) $\endgroup$ Jun 11 '18 at 16:03
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    $\begingroup$ @Demigan At the realm that skydivers operate drag goes at the square of speed. Thus you get pretty close to terminal velocity before drag becomes meaningful. Divide it into two phases: The first part is near free fall and will go up linearly with terminal velocity. The final creep-up should be pretty much the same regardless of terminal velocity. (And body position and increasing drag as you fall are far bigger factors anyway.) $\endgroup$ Jun 11 '18 at 16:35

I thought I could write something about how changing direction (walking around a corner) would look weird, but turns out that since F = m * a is a linear relationship between force (twice as strong) and mass (twice as dense), so they should be able to accelerate/decelerate just as normal people do.

They also likely won't skid when trying to slow quickly, since friction is calculated as F = u * m * g, so the available friction to excert the force needed to decelerate them also grows linearly with the mass.

Thus, the only new thing that I can still mention is... That they would buy very sturdy shoes (nothing with a middle sole that would be compressed by their extra weight, ruining the shoe quickly, or a sole profile that would suffer similarly) and would have to replace them more often than normal since all that extra friction they need to accelerate/decelerate with every step will eat the rubber quickly.

So, people could notice strange (footwear) fashion choices, and a quicker-than-usual (for this kind of shoes) need to replace them. Might be something that makes for an amusing quirk to their friends :)

  • $\begingroup$ Reading all the other answers again, I was just about to go back and add one talking about their shoe wear would be a big key (and perhaps even clothes, due to stronger friction). Good job catching it! :) $\endgroup$ Jun 14 '18 at 1:44
  • $\begingroup$ Although, rubber shoes are anachronistic for an ancient society, unless possibly it's set in a tropical climate where rubber trees grow natively and also economic history took a different path. $\endgroup$
    – Davislor
    Jun 15 '18 at 16:31
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    $\begingroup$ Also they could counteract this by buying an extra pair & claiming that the two pairs are the same one & so the wear would seem normal. $\endgroup$
    – JustinCB
    Jun 15 '18 at 19:13

Playing contact sports

If they played say gridiron or rugby, they would be like the bowling ball and normal people would be like bowling pins.

Footprints in sand

They would leave much deeper impressions is sand (IIRC the depths is proportional to the square root of the weight of the person - citation needed)

Martial arts

Especially sports like Judo - attempting to throw someone of twice the mass as you expect to the floor wouldn't work so well

Anywhere you are weighed

When flying in commerial light aircraft (less than about 20 passengers), they weigh you beforehand so they can distribute passengers mass evenly in the small cabin to provide safer flying

Jockeys, boxers, etc are also weighed


They will have significant problems walking on non-solid grounds.

Since their feet sizes are the same, they will be applying twice as much pressure per foot than a normal person.

If they walk on soft ground, they will sink much further in than the next guy of the same size. Assisting them out of the hole will also reveal their extra weight.


To the other excellent answers I would add that there are a number of areas where the difference in inertia would be apparent.

Any sport that involves sudden stops and starts like tennis or baseball would be affected. More dense people would slide farther. (There's a whole science of mastering sliding on clay or grass courts.) Dense children would be at a disadvantage in games like tag.

I don't know about the climate in your world, but if they do things like sledding, ice skating or skiing I think the difference would be noticeable.

Their greater strength would be apparent in tasks that don't involve moving around much of their body weight. If I understand correctly, their legs would be strong enough to jump about as high as a normal person. That means that their kicking power would be much greater. If they can do chin-ups as well as a normal person, they would be great at arm-wrestling.

Magicians would probably be very picky about footwear. Unless their feet were magically tough, they would be more prone to foot problems due to twice the weight being spread out over the same area. Sitting on a hard bench would be twice as uncomfortable. Falling would hurt twice as much.

  • $\begingroup$ You could then tell them apart by having worse callouses. $\endgroup$
    – JustinCB
    Jun 15 '18 at 19:15

One slightly unfortunate impact would be on social activity.

  • Raves/dances - a bunch of these people dancing or jumping (social or to escape something) on the floor above you.... Crunch?

  • Sex - uh oh! Those forceful passionate quickies will have to go. They'll probably have enough inertia/momentum to break shower panels/tiles, destroy car suspension, crack thin dividing walls between hotel/motel rooms, and break beds. They'll have to be gentle and languid!

  • Running - you run, you tread on a plank or paving slab, and it has to withstand twice the impact force. Crack!

  • Scuba - requires strict control of weight neutrality using belts around the waist.

  • Lifts/elevators/escalators/hot air balloons - have weight limits. Oops!

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    $\begingroup$ Any sexual partner will instantly notice if a dense person is on top. $\endgroup$ Jun 12 '18 at 14:14
  • $\begingroup$ Have you ever managed to overload a lift?!? The lifts I know are more like this: If they are rated for twelve people, you'll be hard put to pack six into them. I can't remember any lift that could be overloaded by people only. $\endgroup$ Jun 16 '18 at 14:03

Alcohol Tolerance

A dense person has more tolerance for ethanol and will take more booze to get drunk.

For a real-world example consider Andre the Giant.


It has been estimated that Andre the Giant drank 7000 calories worth of booze every day. That's about 46 beers a day.

Andre the Giant once admitted once on Letterman to having consumed 119 beers in a single sitting and passed out in a hotel hallway, and that wasn't even his record.

from https://www.stuff.co.nz/entertainment/celebrities/82494695/

Admittedly he was physically big as well as muscular, so the quantity of fluid vs the potency of the alcohol content could be a factor. That is, fitting a lot of beer inside the torso could be a challenge so they'd prefer higher-proof spirits.

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    $\begingroup$ Combined with the dietary suggestion for high calorie foods (usually quite greasy) this could amount to a substantial alcohol (and poison) resistance. $\endgroup$
    – Vorac
    Jun 18 '18 at 19:20

Just another addition:

Put them into / onto any vehicle such as a car or a motorized bike that has suspensions

In 'X-Men Origins', Wolverine, now with a freshly adamantized skeleton, gives himself away by just sitting on the motorbike and pressing it all the way down due to his unusual weight.


If they are a secret society, then definitely you will not know to look for such signs to recognize them. As well they likely use magic to conceal.

Additionally imagine in a technocrat society nobody would believe any strange signs. Most people would rather think they are going crazy than thinking the other person is a magician.

There was an old movie where a robotic young man/boy went to college and there were all sorts of funny moments when others hit him, the bed broke, etc. I don't remember the name of the movie but you can search for it.

Update: I think movie was "Still Not Quite Human"


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