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I once read a novel about a prison-planet which was chosen to make the prisoners suffer. One of the different "tortures" was a gravity three times higher than that on Earth.

Would the human body support living under such a gravity? It is known that living under no-gravity conditions for long periods of time has negative consequences for the body. Would a high-gravity environment also be negative, or it will only make individuals stronger over time?

NOTE: There is a discussion here about whether questions on already existing worlds are on-topic.

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  • $\begingroup$ Heavy-world planets and humans adapted to live on them are a pretty standard sci-fi trope. So whether or not it's a specific existing world doesn't really matter. $\endgroup$ – Bobson Sep 17 '14 at 14:33
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    $\begingroup$ Quote from The Biology of Human Survival: Life and Death in Extreme Environments, Claude A. Piantadosi: Human volunteers have tolerated 1.5g for seven days with no apparent ill effects. However, after just twenty-four hours at 2g, evidence of significant fluid imbalance is detectable. At 3g to 4g fatigue is limiting, and above 4g cardiovascular factors limit g tolerance. -- I have not read the full text so I felt it inadequate to list it as a full answer. books.google.com/books?hl=fr&id=Lqz-4XU5m28C $\endgroup$ – Keeta Feb 18 '16 at 19:21
  • $\begingroup$ @Keeta you should really turn this into a complete answer it is the best one so far just for the source. $\endgroup$ – John Oct 12 '17 at 17:25
  • $\begingroup$ Side thoughts though: A 3G world requires a good reason not to have an impossibly thick atmosphere. To thin an atmosphere, you need either to react it to form rocks (The biggest part of CO2 on earth is in carbonate rocks - Venus, not so much.) or you need to give it escape velocity. The latter is very sensitive to gravitation. $\endgroup$ – Sherwood Botsford Dec 26 '17 at 19:37

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The simple answer is "yes".

The more complex answer is "it depends" and "how much heavier".

Over time you could expect evolution to help, bones would thicken. Height would decrease, people might even move back towards shorter legs and great-ape-style 4-legged movement.

That doesn't help the first poor victims though so lets think about this.

Lets say an adult male weighs 80kg on earth.

In 2G they would weigh 160kg; at 3G they would weigh 240kg.

Those are starting to be serious weights, you could still move but it would be an effort. Assuming you were fed enough you would build up serious muscle strength but you can still expect bones and joints to feel the strain. The heart and lungs would need to work harder, bed sores would develop faster.

Even minor trips and falls would become much more serious, a simple trip could easily lead to multiple broken bones and a slip on the stairs could be fatal. In fact there would be unlikely to be stairs and certainly no ladders.

Sleep would be a problem and floating in water with a breathing device might become a popular way to sleep. Swimming would certainly be a popular recreation as the water would support your weight (you should still be buoyant).

Pregnancy would be a major risk, even on earth people experience back trouble and other pain from the weight. Even if the pregnancy proceeded normally (and I'm not aware of any studies that would provide evidence either way on that) there would be a high risk of injury and mishap.

The environment would be placing a constant strain on you, so you can expect lifespans to be shortened (weak hearts would be fatal, bones tend to weaken as you age).

So the immediate conclusion is that young healthy adults would survive. Everyone else is in trouble....

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    $\begingroup$ 'over time you could expect evolution to help': Only if people survive. And if you're constantly sending colonists to a heavy planet expecting a proportion of them to die so the ones that survive can breed more suited children what you're doing is technically eugenics. Brutal, gravity assisted eugenics. $\endgroup$ – Joe Bloggs Mar 22 '16 at 10:38
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    $\begingroup$ @JoeBloggs Yep. I never said it was a nice thing to do :) $\endgroup$ – Tim B Mar 22 '16 at 11:20
  • $\begingroup$ I'm glad we agree on that point! :D $\endgroup$ – Joe Bloggs Mar 22 '16 at 11:20
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    $\begingroup$ You'll want to clear up the weight issue. Mass never changes; weight does. So the mass will always be 80kg, but the weight will not. $\endgroup$ – HDE 226868 Apr 5 '16 at 0:46
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    $\begingroup$ I would think having to adapt to a heavy gravity environment would require much more time than adapting to a low gravity environment. Thus, if people did adapt to a heavy gravity environment, leaving to a low gravity environment would likely be a bad idea if they wished to return to their high gravity environment later. Thus, physical visits between people from low and high gravity planets would be unlikely, I would think, unless they planned to stay. Just a neat aspect of human interaction, or lack thereof, that could potentially develop. $\endgroup$ – Iter Aug 6 '17 at 21:15
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Your 3g location would kill most unenhanced humans pretty quickly - in a matter of days to weeks, depending upon the starting fitness level of the human in question. The amount of extra strain that this places on the heart is quite large for any position that does not involve lying down, akin to running near-flat-out all the time, and even lying down would put pressure on the heart similar to walking constantly.

In addition, lying down in these conditions would rapidly cause pressure sores that would necessitate some sort of movement.

Even movement would be dangerous, a fall when standing would be equivalent to falling from a second floor balcony in 1g, and a fall when on all fours - not impossible given that the subject's effective weight would be triple normal, when humans can typically lift only their own weight to double their own weight - would be the same as a fall from their own height in 1g.

It sounds like a pretty effective torture to me...

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    $\begingroup$ Are you sure about this? I think you are overstating the effects of 3g considering there are people alive today weighing over 600kg...it wouldn't be pleasant but I think 3g would be on the limits of survivable. I'd like to know where the 2nd floor balcony figure comes from too. $\endgroup$ – Tim B Sep 17 '14 at 17:47
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    $\begingroup$ @celtschk Google will provide plenty of examples. en.wikipedia.org/wiki/List_of_the_heaviest_people - two have a peak weight over 600kg and the third is only 3kg lower. One had an unconfirmed peak weight of over 700kg. $\endgroup$ – Tim B Oct 11 '14 at 9:55
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    $\begingroup$ @mike3, 2g would probably be survivable to most, though there would be significantly increased mortality. On the other hand, I'm not sure that would be such a great punishment despite the unpleasantness of the situation - making the survivors as muscular and strong as a body builder... $\endgroup$ – Monty Wild Nov 18 '14 at 21:25
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    $\begingroup$ The 600kg people still 'just' have to pump blood at 1g like everybody else. They might have to pump more, but the blood itself doesn't weigh 3x as much... $\endgroup$ – fgysin Feb 18 '16 at 10:09
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    $\begingroup$ And how many of those 600 kg people ever stand unassisted? $\endgroup$ – WGroleau Apr 27 '16 at 16:16
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I think we're missing some factors in this conversation. The effect wouldn't be the same as weighing more on this planet. Yes, the gravitational pull would be pulling you down onto a scale at... let's say 600kg. Well it would also be pulling all the liquid in your body down toward your feet at a higher rate. Your heart would be working not only against your own body weight, but to pull the blood away from the ground as well. I say, ignore the fact that a scale would report you weighing more. The important thing is that all matter is being pulled to the core of the planet. Even water would be compressed into a thick syrup. Even air molecules would be pulled down toward the surface and be much harder to breath in. Your eyes and brain tissue would be compressed flatter, and not function the same. Even a strong person's blood vessels would collapse. Noone would live for long at 3 Gs.

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    $\begingroup$ Minor nitpick: kilograms are units of mass, not force - that would be Newtons. $\endgroup$ – HDE 226868 Jun 3 '15 at 23:28
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    $\begingroup$ Water would be compressed into a thick syrup? Can you explain further please - I thought the compressibility of water was very low! $\endgroup$ – Kimball Dec 17 '15 at 6:43
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    $\begingroup$ I think the only change in a body of water, would be that splashes and sprays would not travel far, and I think waves would dissipate rapidly. $\endgroup$ – Michael Richardson Mar 13 '16 at 18:54
  • $\begingroup$ I have never seen any argument for why the heart would have to work harder. Blood isn't pumped one way, it's circular. So the blood on its way down is helping. People don't black out under high g load (e.g. jets) because their heart can't handle it, it's because the blood is centrifuged out of their head. And that takes more than 3g. $\endgroup$ – Vectorjohn Sep 11 at 22:41
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I would start with a thought experiment. If I was sent to a 3G planet I think it would kill me within a couple days, at least without being prepared ahead of time. I would weigh over 600 lbs., the mere act of sitting up in bed would be like doing a crunch with my wife sitting on my chest and a bowling ball attached to my head.

I think 2G would be pushing it and even there one would need a bit of training and plenty of trained medical expertise. 1.5G would be torture enough.

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One answer is that we don't know the effect of high-G in the long term.

We do know the effects of high blood pressure. Not good. Under 3G, standing or sitting, your brain needs a certain normal pressure so you do not black out. Your heart is about 40 cm lower in your body. Two extra G adds a pressure on your heart of 80 cm of water or about 60 mmHg. You'll die quite a bit sooner on average. As for the added pressure on the arteries in your legs ...

It's also known that tall people are at greater risk of brain injury if they fall over. Falling in 3G will be life threatening even for short people. Broken limbs far more common. Long term arthritis awaits.

So if it's not lethal in the short term I'm quite sure it would wreck your health in the longer term.

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Think how a jet pilot feels in his seat during a somewhat routine turn. That's how you would feel all the time.

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I think it would require compression clothing to keep the blood from trying to all settle in the legs. Compression clothing would substantially reduce the strain placed on the heart.

One stereotypical pastime of prisoners is to spend a lot of time in the weight room. This prison is a 24/7 weightroom. Any prisoner who finished the prison term would be extremely muscuclar. Perhaps a control collar and automatic enlistment in the Space Marines would be required upon release?

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I will buck the trend and say it could, without too much trouble, provided that it has adequate supporting technology.

The key tech is:

  • Compression suits – @MichaelRichardson pointed out that these would prevent the circulation-induced problems.

  • Swimming would be almost unaffected. Indeed, it would be a preferred means of locomotion. I suspect that the human body could survive in 3G just fine, if it almost never had to leave the water.

  • The amount of muscle that would be developed would be massive. There are wieght lifters who can lift 3 times there own body weight, I believe. A person in this circumstance only needs to lift twice their weight.

But none of those is the real solution.

The Solution: Powered Exoskeletons

Powered exoskeletons are the real solution. By supporting and moving the body from the outside the problems of higher gravity are mostly eliminated.

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Have you ever been on a roller coaster? The G-force felt on the average roller coaster sits at about 1.67 g's. Now double the feeling you felt being mashed into the back of your seat and whipped around corners and apply it directly down, constantly. To say it was used as torture would not be unreasonable.

I remember reading somewhere that the the average human would be fine and even thrive in gravity +/-20% of what Earth's gravity is. But Remember our bodies are specifically adapted for what we consider 1 g. of course lower gravity is more easily adapted. But even if we had long term housing on Mars it would likely have pretty severe consequences for our health over long periods of time. Its why any manned missions to Mars would be one way trips.

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Actually I looked into this a while back. The chances are some of the side effects are less serious if atmosphere has a higher concentration of oxygen than ours. Seems that if you have more O2 a smaller more compact body is likely to be feasible, also makes other modifications like a hemocyanin and as mentioned aquatic intelligence feasible existing in a relatively small region close to or at the surface. High G isn't actually a big problem if the life forms evolved to tolerate it, I think there would be life forms similar to dolphins, surfacing to breathe that thin layer of oxygen close to surface.

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  • $\begingroup$ Welcome to WorldBuilding! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$ – Secespitus Mar 26 '18 at 7:55
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Surviving? How about living? And shelter construction? Unloading cargo? Then ultimately food production, equipment repair. We'd be invalid at best. And procreation? That's an unlikely success outcome given the difficulties under normal circumstances. As for swimming I think one would drown very fast due to the crush on the abdomen.

Prolonged 1.5 - 2 g not doable. Even a multi year gradual acclimatization program would washout all but the very few.

IMO

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According to Surface gravity, no planet in our solar system has 3g on surface (Jupiter is not a pretty comfortable place for living, but stands at 2.5g; living on the sun, leaving apart extreme radiation and heat, is another story, with 28g on "surface").

Your torture device at 3g is awesome! Think on a fighter jet pilot at 3g all the time...

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  • $\begingroup$ Interesting way of showing why it is not an issue in our solar system, but it is not directly answering the question. $\endgroup$ – Hohmannfan Mar 22 '16 at 18:54
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After reading some of these answers, and only some, I think one thing is being taken for granted. Increasing the gravity would increase the pressure on the fluid in your body. Your blood, the fluid around the brain, your stomach acid, every liquid in your body would become heavier. Your skin would also become heavier, making it pull and tear. MAYBE 1.5x Earth's normal gravity would be survivable, but I don't think anything more than that would be plausible.

...unless you were able to manipulate your "energy" (Chi/Ki/life force) to enhance your physical abilities. Then you could possibly handle more of an increase.

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  • $\begingroup$ Source one removed from the original article, but citations provided: Could Humans Colonize a Planet with Stronger Gravity? The assertion here (apparently backed up by NASA is that the absolute survivability threshold is a constant 4Gs, and that up to 3Gs would probably be something to which residents could adapt. So you're broadly right, but have to dial up your plausibility level a bit. $\endgroup$ – jdunlop Aug 7 '17 at 0:29
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3g? Almost impossible, 2g also is probably not very doable but maybe 1.5-1.8..I think there are some drugs and breathing/mental exercises that could make the transition a lot more tolerable physically and mentally. Cocaine for example if administered intravenously immediately gives the subject a euphoric high and raises the blood pressure as the blood vessels constrict. That, combined on and off with psychedelic tryptamine (acting often like a reset button on the nervous system) might help the body accelerate/facilitate the transition necessary to adapt. That's just one thought.

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  • $\begingroup$ at 3G id b shocked if any organism native to earth survives that pressure pain. The kinetics at that level of Gforce are hopelessly disorienting. Thats a system of governing dynamics that is entirely absurd to even imagine anything happening except stuff falling super fast. even that is hard to picture $\endgroup$ – John Mueller Oct 12 '17 at 13:34

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