If we wish to colonize another world, finding a planet with a gravitational field that humans can survive and thrive under will be crucial. If its gravity is too strong our blood will be pulled down into our legs, our bones might break, and we could even be pinned helplessly to the ground.
Finding the gravitational limit of the human body is something that's better done before we land on a massive new planet. Now, in a paper published on the pre-print server arXiv, three physicists, claim that the maximum gravitational field humans could survive long-term is four-and-a-half times the gravity on Earth.
Or, at least you could if you are an Icelandic strongman – and Game of Thrones monster – who can walk with more than half a metric ton on your back. For mere mortals, the researchers say, it would need to be a little weaker.
[...] For the maximum gravity at which we could take a step, the team turned to Hafþór Júlíus Björnsson, an Icelandic strongman who once walked five steps with a 1430 pound log on his back, smashing a 1,000-year-old record[*].
[*] YouTube video.
What's the Maximum Gravity We Could Survive?
(Score: 5, Interesting) by Runaway1956 on Saturday September 22 2018, @02:11PM (68 children)
Reaching sexual maturity and reproducing ensures survival of the species/race. But, at what cost?
At 4 gravities, any fall is far more potentially lethal. Babies learning to walk will be a far greater hazard than the same feat on earth. Imagine, planning for a family, going through a successful pregnancy, bringing that healthy little baby into the world, and nurturing him/her for several months. Baby begins to pull himself upright or the edge of a chair, or coffee table, and BANG! Baby falls over and breaks his neck.
Or just as bad, baby survives his first fall or ten - but his injuries just don't heal. A green tree fracture of a collar bone just gets worse, and worse, because of the added weight.
We may find that we need some genetically modified humans to settle high G worlds. Slowly adapting just may not cut it. It is far more likely that we can adapt to microgravities, than to higher gravities.
Now, if we could find a route to adaptation gradually, that would probably work out well. A generation or ten on a 1.25G world, then more generations on a 1.5G, and more generations on 1.75G. Eventually, you'll have a divergent race of humans who are well adapted to high gravity.
(Score: 2) by takyon on Saturday September 22 2018, @02:35PM (7 children)
I clicked on the story expecting to see 2g, not 4.5g.
Everything is heavier, you're under strain all of the time, simple actions that might slightly hurt your foot or leg on Earth could break them at 4.5g. Felt any pain in your feet or ankles lately? FATALITY. You're probably at a much greater risk of cardiovascular disease. Even the spit in your mouth would feel heavy.
It's not clear to me that we can find a habitable planet with such a high gravity. As you increase mass into super-Earth territory, acceleration due to gravity doesn't necessarily go up that much. For example, Kepler-452b [wikipedia.org] has an estimated 5 Earth masses and 1.9g (high uncertainty for the planet's parameters though). HD 40307 g [wikipedia.org] has 7.09 Earth masses and 2.39 Earth radii, so it should have 1.24g surface gravity. With increasing mass, eventually the planet will become a gas dwarf/mini-Neptune/giant with fatal atmospheric pressure, liquid/metallic hydrogen, etc. Chthonian planets [wikipedia.org] would probably be too hot and/or have no atmosphere.
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(Score: 3, Interesting) by bzipitidoo on Saturday September 22 2018, @03:01PM (2 children)
I read of an experiment in which chickens were raised in a 2G environment. (They used centrifugal force to mimic heavier gravity.) The chickens survived, growing much thicker legs and heavier bones and musculature.
We also have info from fighter plane pilots and NASA tests. I forget the exact figures, maybe 10G max, maybe up to 15G for a fraction of a second, but direction and duration matter a lot. You can take the most Gs when lying on your back. 4.5G could be okay for standing but too much if you trip. As I recall when looking into how fast a rail gun could safely accelerate human passengers, for launch into orbit, 6G was about the limit for longer durations.
(Score: 0) by Anonymous Coward on Saturday September 22 2018, @04:34PM (1 child)
Or maybe think in a ladder method. Say 2G steps. I am two Che the size of a average man so I am already at 2G. Yes my brother new are thicker but I run at 12 more n mile. But once the body / populating n live by full time in 2G, that will become in generations the new 1G. Then repeat.
But to me the new concern is eating and pooping. The structure of the body can hold up with a 2G mass but the only niter app plumbing becomes a issue. Since the soft organs will pull down by 2G not. In child bearing comes to issue since that large mass is on not held up by the pelvis and huts over at the end.
(Score: 3, Funny) by PartTimeZombie on Sunday September 23 2018, @11:45PM
Quick everyone run away, the AI are taking over!!!
Well, they will once they learn to form a coherent sentence.
(Score: 0) by Anonymous Coward on Saturday September 22 2018, @04:24PM (2 children)
(Score: 2) by takyon on Saturday September 22 2018, @04:43PM (1 child)
Forget birds. How about high gravity hailstones?
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 3, Insightful) by Pslytely Psycho on Monday September 24 2018, @12:56AM
Damn, good point. Having experienced softball sized hail that did almost $15K worth of damage to a $100K semi-truck that would be some 'biblical' hail indeed!
Alex Jones lawyer inspires new TV series: CSI Moron Division.
(Score: 2) by toddestan on Sunday September 23 2018, @02:29AM
The other place you might experience high gravity like that could be artificial "gravity" on a space ship that is underway at a constant acceleration. Though even then, there would be little reason to run your spaceship at 4.5 G (except maybe during some short maneuver) as a space ship that can operate at 1 G for any extended period of time is already pretty damn fast.
* A space ship that could do a constant 1 G acceleration could get to Mars in about 3 1/2 days, and would be traveling at about 0.005 C at the halfway point.
(Score: 2) by Arik on Saturday September 22 2018, @02:43PM (39 children)
And not so much a question of can we, but should we, I would think.
Even if it's possible to adapt to a high g world, why? Why take such a massive step backwards, after escaping out own gravity well, why would we imprison ourselves in another, stronger one? The US Constitution, at least, forbids such things.
Don't colonize high g worlds directly. If they have things you need, then colonize using High Orbital emplacements and robotics. Let the robots deal with the gravity well and pass whatever is needed back upstairs.
"Eventually, you'll have a divergent race of humans who are well adapted to high gravity."
Each and every member of which will dream of inventing a time machine with which to kill you before you could create them.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by crafoo on Saturday September 22 2018, @02:56PM (13 children)
Can you imagine the "humans" from such a world after 20 or so generations? They would come back to Earth and immediately take every riot cop and prison guard job available.
Yeah, for the first 20 or so generations everyone wears a robotic exoskeleton to deal with daily life. You'd have to keep the evolutionary pressure on to adapt to the environment though. I think even with exoskeletons, the massive strain on the heart, diaphragm, and circulatory system would kill quite a few people early in their life.
(Score: 2) by Arik on Saturday September 22 2018, @03:12PM (3 children)
What makes you think there would be any such jobs available on Earth at that time?
"I think even with exoskeletons, the massive strain on the heart, diaphragm, and circulatory system would kill quite a few people early in their life."
You're correct, and only scratching the surface. Forget about things that kill. Think about things that fail to kill you, but cause agonizing pain every second of your misbegotten life. Think about joints wearing out before you hit puberty. Think about having to plan each and every movement carefully, knowing that a simple misstep, a stubbed toe on earth, would be a broken ankle or worse here. Think about how that ankle would never heal unless you stay completely off it for months. Think about how if you stay off your feet for months, then once the ankle is healed, you wouldn't have the strength left to stand up on your own.
No, this is the exact opposite of what we should do. Don't colonize high g planets. Colonize weightless spaces. Escape all of those burdens, and then adapt to freedom, not to heavier restrictions.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by takyon on Saturday September 22 2018, @03:21PM (2 children)
By the time we have the technology to go interstellar, we'll have great anti-aging and regenerative medicine. Meaning that you can fix your joints, bones, heart, etc. faster than it would take for them to wear out.
The 4.5g mentioned in TFS is atypical. 1.25g is more common for exoplanets, with maybe 2g possible although exoplanets could become Neptune-like before reaching that surface gravity. 0.5g to 1g is also possible. It will be interesting to see the health effects of 0.8g. Might be a great vacation spot.
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 2) by Arik on Saturday September 22 2018, @05:14PM
That's your assumption, but I see no proof for it. Might turn out that way, might not.
If laughter is the best medicine, who are the best doctors?
(Score: 1) by ChrisMaple on Sunday September 23 2018, @05:19AM
Bones, joints, and muscles aren't a problem. People weighing twice as much as average already exist on Earth without problem; they have sturdier bodies because they've been grown and trained that way. One body system that doesn't automatically adapt is the circulatory system; human beings aren't far from the margins of what can be tolerated for blood pressure difference between the brain and the feet. Tall animals like giraffes have special evolved adaptations that required thousands of generations to appear; that's not going to happen quickly in humans without gene editing.
(Score: 4, Insightful) by takyon on Saturday September 22 2018, @03:26PM (7 children)
There will be no need to wait for 20 generations before adaptation can occur.
First of all, humans won't evolve those adaptations if natural or artificial selection isn't occurring.
Second, you can just use gene editing to make those adaptations.
Finally, 4.5g is not typical. And if we did need to adapt to that, we could create very tiny pygmy/dwarf humans rather than Icelandic troll-gods.
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(Score: 0) by Anonymous Coward on Saturday September 22 2018, @03:48PM (6 children)
This is extremely delusional.
(Score: 2) by takyon on Saturday September 22 2018, @04:08PM (5 children)
Yes you are. When do you think we will reach an exoplanet? 20 years from now?
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: -1, Troll) by Anonymous Coward on Saturday September 22 2018, @05:43PM (4 children)
Is it even proven that there are exoplanets? All they see is flickering stars... If you saw a flickering star and didn't know about planets, would that be the first explanation you came up with?
(Score: -1, Redundant) by Anonymous Coward on Saturday September 22 2018, @10:06PM
What is trolling about this?
(Score: 1) by khallow on Sunday September 23 2018, @04:23AM (2 children)
To what standard of evidence? In addition to said flickering stars, we have detected motion of the stars and spectral lines from some of the transiting planets. That doesn't mean a planet is going to be nice enough to live on. Most of it is pretty nasty.
If you don't know about planets, then you don't know enough to have an opinion on flickering stars.
(Score: 0) by Anonymous Coward on Sunday September 23 2018, @01:01PM (1 child)
The standard should be that they use those methods to predict something that is verified some other way. Obviously actually getting an image of the planet would be best.
(Score: 1) by khallow on Monday September 24 2018, @01:25PM
I noted three such methods. The flickering of stars (usually strongly periodic, I might add) is actually a very reliable measure. And it's not like the Solar System is going to be unique in the universe.
(Score: 2) by krishnoid on Sunday September 23 2018, @01:54AM
... fixing the overpopulation and social security bankruptcy problems a lot faster, anyway.
(Score: 2) by Runaway1956 on Saturday September 22 2018, @03:13PM (1 child)
I think you are suffering a simple case of projection. You can't imagine a rewarding life on a high-G world, so you are projecting your expectations upon this hypothetical race of man. I suggest that we wait until we find this hypothetical race, abduct one of it's members, and probe him/her to find out how happy they are. I understand that they really like anal probes.
https://en.wikipedia.org/wiki/Cartman_Gets_an_Anal_Probe [wikipedia.org]
(Score: 2) by Arik on Saturday September 22 2018, @05:22PM
You're wrong, and I can.
I can definitely imagine a rewarding life on a high-G world for a species which evolved on that world. To them, it would be normal, expected. But I wouldn't expect such a species would resemble us physically, or even to resemble what we would become after some generations there.
What I don't imagine would be very enjoyable in any case is the regression involved in first mastering weightlessness - then diving not just back onto a planet, but a high g planet at that. THAT doesn't seem like a very rewarding life at all.
More likely, adaption will work out to be a one-way trip in practice. Once a human is adapted to zero-g, they will not willingly go back to a full g, let alone 4.5. The medical risks will be severe, not insurmountable in abstract perhaps, but who would want to face them personally? And for what gain? What is it that you need done down there that you can't build a machine to do for you remotely?
If laughter is the best medicine, who are the best doctors?
(Score: 2) by takyon on Saturday September 22 2018, @03:15PM (1 child)
If we have the technology to go to another star system, we probably can get out of a stronger gravity well whenever we want to.
It's galactic real estate. If you want to live in the far future, you can live on the overcrowded oasis that is on Earth, imperfect solar system objects such as the Moon, Mars, Ceres, and Titan, on a space station, possibly spinning to simulate gravity, or you can go interstellar if technology allows it. It may be possible for individuals to reach other star systems without generation ships by using anti-aging and suspended animation. Settling on the surface of a planet (with breathable atmosphere and correct temperature) can have a lot of advantages over an orbiting station (if I break a wall in your house, you won't die).
As I wrote above, we probably don't need to adapt to 4.5g because there will be very few suitable exoplanets with that surface gravity. 1.25g seems more likely, and may not require any genetic modification to adapt to it, although you will get a little buffer living there.
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 4, Funny) by Arik on Saturday September 22 2018, @05:28PM
It's galactic real estate. If you want to live in the far future, you can live on the overcrowded oasis that is on Earth, imperfect solar system objects such as the Moon, Mars, Ceres, and Titan, on a space station, possibly spinning to simulate gravity"
The last option is the one you should be thinking about.
Oh give me a locus
where the gravitons focus
Where the three-body problem is solved.
Where the microwaves play
down at three degrees K
and the cold virus never evolved.
Home, Home on LaGrange
Where the space debris always collects
We possess so it seems
two of man's greatest dreams.
Solar power and zero-gee sex.
If laughter is the best medicine, who are the best doctors?
(Score: 3, Interesting) by wisnoskij on Saturday September 22 2018, @04:00PM (20 children)
Why would a human dislike being stronger, fitter, and more able to travel over land and through space?
If we assume a space faring future, any humans adapted to space would be stuck in their backyard for life as they would be unable to take any acceleration. And since mass still exists in space, it would be an incredibly dangerous for anyone with the type of bones that would develop in space. To do anything in space, you need to spend 99% of your life in high Gs. And the higher the Gs, the better.
In any space faring society. The people who grew up on the the highest G world will have an overwhelming military and space faring advantage, and will be able to subjugate or simply outperform everyone else.
(Score: 0) by Anonymous Coward on Saturday September 22 2018, @04:47PM (2 children)
Because they are American? Probably best to ask some of the fat bastards you see, I was going to say walking, but you're more likely to find them in a car, around in the USA.
(Score: 1) by Arik on Saturday September 22 2018, @05:36PM
If laughter is the best medicine, who are the best doctors?
(Score: 0) by Anonymous Coward on Saturday September 22 2018, @05:46PM
If you are fit and strong, and able to do stuff, someone might ask/force you to do something. So the best way to avoid being asked is to not look like you can achieve anything. Eg, you cant be drafted if your health is too poor.
(Score: 1) by Arik on Saturday September 22 2018, @05:56PM (16 children)
Big assumptions there. Interstellar space travel will not necessarily involve great acceleration. If we're talking about sleep ships, or generational ships, they can simply accel at a constant 1g or less until they reach speed. With sleep ships in particular, it may be possible to shield the humans from the affects of the accel anyway.
Another assumption is that those who adapt to zero-g will be 'unable to take any acceleration" there's a kernel of truth to this one obviously but that's way too far. HOMEs as planned would spin to generate effective gravity, with concentric rings with different effective levels. So up to something around 1g would still be within their regular experience - journeying to the outer ring regularly for exercise, or to perform maintenance or whatever.
Under those conditions, we clearly would not completely lose our ability to deal with acceleration. You're right that someone from a high g world would have an advantage on that one specific measure, but I'm not convinced it would be all that important in the bigger picture. Your existence would be so much more efficient, from beginning to end. You could eat less yet be able to do more. Your body parts might last many times as long, given the lack of the constant burden that gravity represents to the circulatory system and so on. You have lower tolerance for accel? Ok, but you don't NEED to start off your journey by lifting off from a planet. What an incredible head start! Do you have any idea how many calories it takes to put a capsule capable of supporting life for a few hours on an escape trajetory? Take a look at the old Saturn V.
"The people who grew up on the the highest G world will have an overwhelming military and space faring advantage"
Well, if you're imagining them landing troops on a planet and going door to door, sure.
I don't imagine conflicts between people with those levels of technology are very likely to look like that though.
To put it in in strategy game terms;
Landing your high-g stormtroopers on my planets is pointless - there's nothing for them to fight but my robots, who are just fine with the gravity.
Boarding my HOMEs? Well sure, I guess if you get that close I'm probably toast anyway, but your physical advantages won't help much if you haven't spent a LOT of time training these guys to deal with low and zero-g also. Without that training, they'll be breaking their own arms, legs, and necks as they attempt to maneuver down through the inner rings, where resistance would be waiting. No, I think if you got that close you'd still be better off just to use your guns, of whatever type you possess, and destroy the HOMEs rather than try to take them.
Defending your planet against my troops? Well obviously I am not sending anyone to the surface for you to defend against. If we really have to, we'll bombard from orbit, and send down robots afterwards to collect anything of sufficient value.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by HiThere on Saturday September 22 2018, @06:41PM (1 child)
I consider permanent space habitats which are mobile to be a lot more likely than sleep ships. I won't deny the possibility of sleep ships, but why?
When I say "space habitat", think of it as a mobile city, though mobile doesn't imply able to move very fast. I expect that 0.01g would be considered excessive. It's a place to live more than a vehicle. You need to keep moving so that you can get to new resources, but you don't want to move at a speed much different from drift because you don't want to deal with high speed meteors. This does assume nuclear power, and probably fusion, and it assumes a nearly closed ecology, and it assume a long-term stable society. The last is probably the most difficult, but with a government operated by an AI and good virtual reality to allow stresses to be eliminated it seems plausible. A lot of people may spend most of their life gaming, but why not. Reproduction would be strongly controlled except when the entire community decided to build a new city and the population forked into two cities. This would only happen when in contact with an exceptionally rich source of resources.
Note: A single habitat, even one the size of a city, probably doesn't contain enough expertise to maintain a civilization. But laser communication should be feasible. (Though maybe with an AI it could contain enough expertise.)
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 1) by Arik on Saturday September 22 2018, @07:00PM
At that point it really becomes feasible to exploit resources that are easily accessible from zero-g, the asteroid belt for instance. And once sufficient capital is built up there, a sort of mega-HOME could be built, large enough to be pretty darn self-sufficient.
It would not go at a La Grange point, but into it's own solar orbit, and would be able to shift that orbit, even to escape it over time, if desired.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by wisnoskij on Saturday September 22 2018, @07:15PM (1 child)
> Well, if you're imagining them landing troops on a planet and going door to door, sure.
More like I imagine High G accustomed soldiers to be anywhere they want to me 10 times faster than low G accustomed soldiers. Sure, your "spend 90% of their lives in free fall" people can get to Planet X given 100 years of low acceleration. But my high G accountomed colonists can get their in their own lifetimes and with enough time to spare to erect satellite defences before you arrive.
Acceleration is everything in space, the ship with more A wins every encounter.
(Score: 1) by Arik on Saturday September 22 2018, @07:45PM
Really, you now seem to be assuming not just that acceleration will not only continue to be a limiting factor in space movement, but will become even more important with time. This seems far from assured.
Currently, the limiting factor is light speed, and while higher accel *will* cut some time off a given trip, it's really not much on a long journey when you figure the large majority spent at light speed regardless.
There's no reason that technology to exceed light speed would not also imply technology to modify inertial forces and shield humans from extremes of it as well, but you're implicitly implying nothing of the sort develops.
You're *also* assuming that your guys have effectively infinite resources behind them. And this is where our estimates drastically diverge. You won't have infinite resources, nowhere close. You'll have effectively *fewer* resources, because your development is planet centered, most of your resources aren't "available" properly without spending incredible amounts of energy to boost them out of the gravity well. While ours are mined, refined, and manufactured in zero-g, much more efficiently.
And you're assuming that getting there before my humans is enough. It isn't. You need to beat my *robots* there. Robots manufactured from materials and energy gathered at greatly reduced energy costs, outside the gravity well.
More likely, by the time your guys can afford to send a probe, we have robotic manufacturing and defenses setup already.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Immerman on Sunday September 23 2018, @04:07PM (11 children)
There is a significant military application for high-G troops in space combat though. Unless your combat ships are all fully autonomous drones, the light-speed delays means you'll need at least some troops to be right in the thick of the fight. In which case they will be the limiting factor on the maneuverability of any ship they're on. A ship that can only accelerate at 0.1 g is a sitting duck in a fight against ships that can handle a sustained 4g.
Even if it's only a single drone-oversight command ship with a crew in any given encounter, that ship is the limiting factor on how fast the entire fleet can move.
(Score: 2) by Arik on Sunday September 23 2018, @05:26PM (10 children)
"Unless your combat ships are all fully autonomous drones"
Why wouldn't they be? Start with off-the shelf autonomous mining drones, upgrade weapons and logic, program for mission and launch.
"the light-speed delays means you'll need at least some troops to be right in the thick of the fight."
Ok, I'll actually give you a point here. While of course we'd do as much of any fighting that had to be done as possible with autonomous military bots, yes there still might be a need to have a human relatively near for C&C overwatch.
"In which case they will be the limiting factor on the maneuverability of any ship they're on. A ship that can only accelerate at 0.1 g is a sitting duck in a fight against ships that can handle a sustained 4g."
But again, I still don't see this as being so important. Acceleration? Maneuverability, essentially, in a vacuum. Why do you think that is so blamed important?
If there's no FTL, then c is still your speed limit. Greater accel could get you there faster, get you back down faster, but interstellar distances being what they are most of the trip would be spent at c either way, and your advantage is small. And that's assuming we don't come up with some nice sleep ships that can first suspend us and then safely accelerate more rapidly than your guys can do.
It would be handy in a tactical situation in that it might give you the ability to flee, or to preclude flight, by the enemy. Assuming you detect them from outside of either sides effective weapons range, at least. Ok, that's actually pretty big. But still not nearly as big as you seem to think.
And again, if we have FTL, we almost certainly have some associated tech to render this moot.
But beyond that it's pretty nearly useless. Space combat would be taking place at astronomical distances. The likely weapons include lasers, and there's no way to dodge a laser (short of time-machine level stuff.) And another likely sort of attack would be to launch a wave of autonomous weapons - call them suicide drones, or just guided missiles, it's the same thing. They set a collision course, get as much speed as possible, and then self destruct at the last moment, turning into an expanding cloud of shrapnel. Moving at a significant fraction of light speed, anything they touch would be toast.
Who can detect the other first, who can launch an effective strike first, would almost certainly determine who won. Little, perhaps nothing, else matters.
So I don't think your accel is likely to come into it, even under your best scenarios.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Immerman on Monday September 24 2018, @12:01AM (9 children)
No one's getting anywhere close to c for anything other than interstellar voyages - at 1g it'd take almost a year to get to that speed, in which time you'd have long since exited the solar system. Even at 10g you'd have traveled about 50x the diameter of Neptune's orbit before you reached relativistic speeds.
And I'm guessing most people would want to avoid releasing fully autonomous killing machines in as free-flowing a battle-ground as space, unless they're actually conscious AIs (which brings up a whole different set of problems). It's just too easy to lie to a machine. And too easy to extract its knowledge if captured (at the very least you get it's tactical/strategic decision-making algorithm, rendering it easy to exploit.) The friend-versus-foe identification system alone would be ripe for exploitation.
Now, for the importance of acceleration, suppose we have two armies of roughly equal size, but once can handle 10x the acceleration of the other. I'll call them F(ast) and S(low)
F decides they want to capture a location, so they launch their entire military at a juicy-enough target in the opposite direction. S launches at least most of their military to the same spot - anything less would be a pointless suicide mission. Halfway there, F changes course to attack the original location. They get there long before S can hope to do so, capture it, and then proceed to the next target - all while S is stranded in the interplanetary void unable to do anything remotely useful
Meanwhile, S decides to attack, and F can consolidate their armies at their destination from anywhere remotely close - when your army's movements can't be hidden, the faster army wins. F's army can effectively be in multiple places at once.
It all boils down to the equation of motion: d=1/2*a*t^2, or t = sqrt(2d/a). 10x the acceleration, means you can traverse 10x the distance in the same amount of time, or the same distance in a third the time.
(Score: 1) by Arik on Monday September 24 2018, @04:38AM (8 children)
Those would be the voyages that are important here though. That's the limiting factor for exploration, for colonization, and yes for invasion.
If you're talking about tactical mobility; again, little if any advantage actually accrues there, because our robots still don't have any difficulties with accel, and they're the tactical pieces, not manned ships.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Immerman on Monday September 24 2018, @02:27PM (7 children)
Acceleration is largely irrelevant for interstellar invasion. Unless you're imagining combat between galaxy-spanning empires - but without FTL such a thing even existing seems extremely unlikely.
Distances are so vast that the time taken to reach cruising speed is largely irrelevant, top speed is determined by propellants specific impulse and the rocket equation. And it's relatively easy to hide in interstellar space, so nobody is going to see you coming. Well, not until your braking burn announces your position I suppose - in which case the Slows give 10x as long a warning to get ready to fight them. But that's going to be months or years even for the fasts - making it strictly relevant to how many additional defenses can be built.
It's warfare within a solar system where acceleration matters. If you really think tactical AIs will be so advanced that human insight has no value in a military engagement, then perhaps it's not important. But with several minutes to hours of communication lag, probably relatively easily jammable locally, if human insight has anything to offer then you're going to want humans nearby.
(Score: 2) by Arik on Monday September 24 2018, @06:22PM (6 children)
Yes.
"And it's relatively easy to hide in interstellar space, so nobody is going to see you coming."
Not so sure about that. New detection methods might be in play by that point, and even with 1960s tech we should be able to spot an incoming fleet just fine once they start their decel burn.
"If you really think tactical AIs will be so advanced that human insight has no value in a military engagement, then perhaps it's not important."
Given the distances and velocities involved I suspect ONLY a tactical AI will be able to function in traditional front line roles.
Yes you'll want and need human oversight at the strategic level but that's a relatively small issue. Ok, our command ships are slow beasts that can't really run. Just gives our guys more incentive to make sure they win. And if you take a command ship out, sure, that's human casualties, I'm sure it will piss us off more than losing the robots, but we lose one command ship and you lose a whole manned fleet, we're still going to feel ok about the way things are going I am thinking.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Immerman on Monday September 24 2018, @08:47PM (5 children)
You want to spot a broad-spectrum vanta-black ship coasting against the blackness of interstellar space? Good luck - we can barely spot things the size of a planet when we get *extremely* lucky. But maybe eventually - which would rob high-acceleration ships of their advantage on that front. Until then though, they're likely invisible until they start their deceleration burn - at which point the Slows would give their target 10x as much warning as the Fasts. How much of an advantage that would really be though? How much additional military can you you really build in a year or three? Especially compared to the size of fleet necessary for a credible shot at an interstellar invasion?
Yeah, but you're not going to be throwing your automated fleets against their manned ones - you're going to be throwing your automated fleets against their automated fleets, in an effort to take out each other's strategically important command ships. And ultimately, while people get upset over casualties, it appears to be cost of replacing hardware that wins modern wars. Soldiers are cheap until things have been going really badly for a while.
(Score: 2) by Arik on Tuesday September 25 2018, @04:21AM (4 children)
Sure, and your stealth-paint isn't going to make it any harder. If anything, it might make it easier.
We aren't likely to detect it directly, reflected light or radio waves or whatever, even if you mirror-polished it instead. That's just not going to be the method of detection, so the countermeasures against it won't matter either.
How will we spot it? One of two ways. Either via occultation (we notice that this one star blinked out at this time, and then this one a little later, and then this one a little later... ohhh I see a pattern here!) or a direct detection once the decel burn starts.
The decel burn, whatever type of engine you use, is still going to involve releasing massive amounts of energy, and that's visible, there's no way to avoid it.
"How much of an advantage that would really be though? How much additional military can you you really build in a year or three?"
Obviously that depends on how long ago you got the colony started and how efficiently you've worked it, what's on hand, etc. But 1-3 years might well be enough time to prepare, or to evacuate if necessary. Even with lower accel tolerance.
Remember we don't colonize planets. We live in HOMEs and exploit the surface robotically. We'll have a relatively small human population to worry about, and none or virtually none will need to worry about packing up or reaching escape velocity - we're already packed and ready to go. HOMEs can be moved just like any other spacecraft.
"And ultimately, while people get upset over casualties, it appears to be cost of replacing hardware that wins modern wars"
Sure.
And war machines made in zero-g, from materials mined in zero-g, are just going to require orders of magnitude fewer calories to produce than machines made on a planet and then boosted to space, or even those made in space using raw materials boosted from a planet.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Immerman on Tuesday September 25 2018, @02:18PM (3 children)
Yes, I've twice agreed with the decel burn - that's when you light the "here we come" beacon and give the targets not only warning of your coming, but a probably pretty good estimate of your mass. Unless you approach out-of-plane with
And again I say - we're barely able to detect entire planets by occultation when we get very, very lucky, we don't see any of the probably billions of Oort cloud objects that way. You really think we'll be able to detect something as tiny as space ships?
Also, infrared would probably be the bigger giveaway, but sufficient layers of directional reflective shields should render ships effectively invisible at the distances involved.
And what makes you think calories will matter? If you're talking about civilizations capable of launching credible interstellar invasion fleets fast enough that their technology won't be hopelessly obsolete by the time they arrive, then the energy required to get a ship off a planet won't even be a rounding error. The limiting factor in rapidly expanding a fleet is industrial capacity and raw materials.
(Score: 2) by Arik on Tuesday September 25 2018, @02:44PM (2 children)
Planets many light years away, oort cloud objects much closer but also much smaller. Your space ships can't afford to be too tiny - smaller than a planet but probably a good bit larger than a comet. Yes, I suspect that even our current feeble astronomical capabilities are quite capable of spotting something like that. Especially if you're talking about an 'invasion fleet' of dozens, even hundreds of such ships, I suspect there would be a noticeable pattern of occultation at considerable distance.
Today, it's my understanding that much of that data only winds up being analyzed months after it's been gathered, but that's an issue that could be solved very quickly and not very inexpensively, were there a will to do it.
"Also, infrared would probably be the bigger giveaway, but sufficient layers of directional reflective shields should render ships effectively invisible at the distances involved."
I don't see why you think infrared would be a bigger giveaway than occultation, but that aside, it is definitely another potential detection mechanism, and you CANNOT stealth it with shielding as you're proposing. You would cook. Everything you're doing in there, from biological movement to mechanical, even just powering the computers, all generates heat, and if there is no heat escaping then the temperature will rise until everyone is dead and everything is melted.
"And what makes you think calories will matter?"
What makes me think energy matters?
You realize that besides matter, energy is literally the only thing that matters? :)
Calories = joules = energy.
E=mc^2
Literally nothing else matters.
"If you're talking about civilizations capable of launching credible interstellar invasion fleets fast enough that their technology won't be hopelessly obsolete by the time they arrive, then the energy required to get a ship off a planet won't even be a rounding error."
Ok, so how did you to that level of technology to begin with then?
Certainly not by thinking that calories don't matter.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Immerman on Tuesday September 25 2018, @11:29PM (1 child)
Hence *directional* shields - you can radiate anything you want away from enemy observation posts.
And yes, counting energy matters during development. But compared to the cost of getting ships out of the Sun's gravitational well, much less up to interstellar speeds, the cost of getting them off a planet is so close to zero as to make no difference. It's not going to be a limiting factor in building out additional combat capacity in a survival situation. The limiting factor will be your industrial capacity to convert non-essential resources into defenses.
(Score: 2) by Arik on Wednesday September 26 2018, @01:18AM
Perhaps, as long as you're sure where they are.
"And yes, counting energy matters during development. But compared to the cost of getting ships out of the Sun's gravitational well, much less up to interstellar speeds, the cost of getting them off a planet is so close to zero as to make no difference. "
*Perhaps* that's true, at the end of the tech tree. Even there I'm skeptical.
But at the tech levels we were talking about, this is just the most important thing. Because the challenge is the transition. Going from being a planet bound species to being a species that travels space and can spread from one star to the next. And the next, and the next.
Bridging that gap means large and intricate construction in space. And it's going to be many orders of magnitude more difficult to do if you don't get away from the idea of boosting stuff off the planet to work.
So we bridge the gap much more quickly than you, we have a dozen systems or more before you manage to go anywhere... that really seems a big enough advantage to cover any potential disadvantages.
If laughter is the best medicine, who are the best doctors?
(Score: 0) by Anonymous Coward on Saturday September 22 2018, @07:26PM (19 children)
Doesn't sound as difficult as breaking the known laws of physics to get there.
(Score: 2) by Runaway1956 on Saturday September 22 2018, @09:50PM (18 children)
Apparently, you haven't read the REST of this discussion. Lots of ideas being thrown out there, some of which may work. The fact is, we don't know if we can put living human beings into other star systems yet. With today's tech, no we can't. As soon as we make a serious attempt to colonize even one other body in our own solar space, we begin to find potentially important ideas for exploring further.
No one can say what will work, and what will not work, 200 years from now. I'm kinda partial to the generation ship idea. No laws of physics, as we understand them today, need be broken.
(Score: 2) by Arik on Saturday September 22 2018, @10:45PM (17 children)
Nonsense. We had the tech to do it in the 60s.
The issue is not having the tech to do it. The issue is having the will to commit the resources. And there's been nowhere near that, so far.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Runaway1956 on Saturday September 22 2018, @11:54PM (6 children)
Yes, and no, to that. Let's just say that 50, 100, or 150 years after we plant our first space colony, the local residents will still be remarking about how stupid the earthmen who first came here were. Necessity being the mother of invention, tech will be invented on the spot, to solve problems that earth dwellers never imagined.
(Score: 1) by khallow on Sunday September 23 2018, @12:33AM (2 children)
Won't matter if we plant our colonies in space 50, 100, or 150 years from now.
(Score: 2) by Runaway1956 on Sunday September 23 2018, @12:55AM (1 child)
I'm not sure we're communicating very well.
In year XXXX we plant our first colony. In year XXXX +a month or two, the colonists discover an unforseen problem. They solve it. In year XXXX +1 they discover a couple more unforeseen problems, and solve them. In time, these solutions add up to "new technology", some of which would have been pretty useless on earth. That is, they build an entire new body of science, which earthdwellers would not, and in some cases, could not, have found.
In year XXXX +50, or +100, or whatever, the residents will be looking back, and mocking earth men and early colonists, much as people today mock medieval Europeans. "They were so BACKWARDS!! I'm sure glad I wasn't born then!"
(Score: 1) by khallow on Sunday September 23 2018, @04:10AM
(Score: 2) by Arik on Sunday September 23 2018, @02:16AM (2 children)
This is what I was referring to, only I'll quote more of it: " The fact is, we don't know if we can put living human beings into other star systems yet. With today's tech, no we can't."
No one would deny there will be new problems once we get there, for sure. But we developed the necessary technology to put people there and find out many decades ago. Had the political will existed to do it, the project could have been planned before 1970, and even with many delays launched for Alpha Centauri (or wherever, sorry Sid) by now, had there been the political will to do so.
Does it get easier and more likely as technology improves? Sure. But don't pretend we're waiting for some crucial technology to make it possible. It's already possible, and has been for a long time.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Runaway1956 on Sunday September 23 2018, @03:12AM (1 child)
Ohhhhh-kay, I think I can see what you're saying, and I can even accept the possibility. But, had we launched a ship to any of the closest stars in 1970, that ship would most likely only be exiting our own solar system, today. It might be near about where the Voyager craft are today, albeit on a different heading. Personally, I can't see us building such a ship on earth, then launching it. Nor do I see us launching the materials into space, then building it. I think it necessary to develop space mining, smelting, forging, and assembly, before we can build such a ship. Whether we are considering a generational ship, or a really fast ship, the ship is going to be massive, and the fuel requirements just as massive.
We'll have to get up there, before we can start getting things done. The idea of launching an interstellar ship from earth is just a pipe dream, IMO.
I'll readily give you the point that, if we had launched space mining endeavors in 1970, we would now be 48 years closer to launching an interstellar ship today. For far too long, we've been hung up on that silly space plane, and the ISS. It's time, and past time, to move beyond a shuttle and a low orbit space camp for a privileged few.
(Score: 2) by Arik on Sunday September 23 2018, @05:08AM
It would be a colossal waste of calories, yes. Much better to build it in orbit, using materials mined from space insofar as possible.
"I think it necessary to develop space mining, smelting, forging, and assembly, before we can build such a ship."
Precisely. And we knew that then, and we had the technology then. But not the funding. That would have to wait until we won the cold war.
So we won the cold war, where's that peace dividend? It could have paid for a full set of HOMEs and plenty of mining startups as well.
Nope, can't afford space exploration, not possible. (Quick, someone start another war!)
"I'll readily give you the point that, if we had launched space mining endeavors in 1970, we would now be 48 years closer to launching an interstellar ship today. For far too long, we've been hung up on that silly space plane, and the ISS. It's time, and past time, to move beyond a shuttle and a low orbit space camp for a privileged few."
Indeed. It's nothing but bread and circuses for the science-loving crowd, and I'm afraid we're not a very important demographic so there isn't even a lot of that.
We can't claim to have even begun a serious space program while the LaGrange points sit uninhabited.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Immerman on Monday September 24 2018, @09:21PM (9 children)
I must disagree. We don't have the technology today to get a colony ship to the nearest star in decades. Probably not even in centuries. You can't just keep making a rocket go faster by loading it with more propellant - the rocket equation means you get diminishing returns, and an effective top speed based on the propellant's specific impulse.
Nor do we have a good enough understanding of managing a closed ecosystem to keep the colonists and their ecosystem alive for hundreds, maybe thousands of years between stars with no possibility of getting any additional supplies. Heck, we haven't even managed to do it for a few years yet. Nor are we even remotely close to having the hibernation or cryogenics technology for "sleeper ships" that could avoid those problems.
Alternate drive technologies could shorten the trip to something potentially manageable, with nuclear-powered ion drives probably the most promising technology, but we still don't have ion drives up to the task, though we have some promising things in the lab. Nor are we anywhere close to having the sort of ridiculously high-powered lasers that could accelerate a light-sail anywhere near hard enough to reach interstellar speeds before it was too far away to maintain focus.
(Score: 2) by Arik on Tuesday September 25 2018, @04:31AM (8 children)
Arrival within decades was not one of the specified parameters, you can't just tack on extra requirements afterwards.
"Probably not even in centuries."
No, definitely within centuries. With 1970s tech, it would be ~300 years to Alpha Centauri. If the project had been funded and planned back then, likely improvements available before completion would have reduced it to ~100 years, possibly even less.
"Nor do we have a good enough understanding of managing a closed ecosystem to keep the colonists and their ecosystem alive for hundreds, maybe thousands of years between stars with no possibility of getting any additional supplies. "
To the degree that's true it's simply because we have NOT been working on a project where we would have gained that experience.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Immerman on Tuesday September 25 2018, @02:08PM (7 children)
My point was that we don't have the technology to keep people alive for the duration of the voyage. Not today, and definitely not in the 70s.
And sure, *if* we had started seriously developing the technology in the 70s, *maybe* we'd have it ready today. But that dioesn't change the fact that the technology doesn't yet exist, and thus we couldn't then, and still can't today, establish an interstellar colony. Rocketry is the easy part.
(Score: 2) by Arik on Tuesday September 25 2018, @02:29PM (6 children)
I guess that's a fundamental disagreement then. I think you're simply wrong. We knew how to do it then and we certainly know how to do it now. ANY time you do something new of course there are things you will only learn by doing, so you can ALWAYS say that you lack the technology to do ANYTHING new by that standard.
If that's your standard then by that standard you're right, I just don't think it's a useful standard.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Immerman on Tuesday September 25 2018, @11:37PM (4 children)
No, we *don't* know how to do it now. When it comes to managing complex closed ecosystems all we have is theory, and even that still has serious known gaps in it - and who knows how many unknown ones. As the saying goes "In theory there's no difference between theory and practice. In practice there is." Technology is what you get after you've distilled theory to practice.
The few attempts we've made at managing closed ecosystems have ended badly within a couple years. Had we launched a colony ship in the 70s it wouldn't have exited the solar system yet, and the colonists would likely already mostly be dead.
(Score: 1) by Arik on Wednesday September 26 2018, @01:28AM (3 children)
Again, with our actual timeline of technology, we could easily have 40 years of experience with long-term space habitations, more than enough time to work out the details of engineering and practice that are always lacking when you start to apply a new technology.
I didn't suggest launching an interstellar colony ship in the 70s, I suggested *planning* and *commencing* the project to produce it as early as that decade.
That's not something you just do in one stage. First you need HOMEs, and then... well it doesn't matter. We still haven't gotten to step 1, but not because we lacked any essential technology.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Immerman on Wednesday September 26 2018, @02:08PM (2 children)
I think we have a disagreement over what the word technology means. I say it's not just the hardware - you're right that we had the necessary hardware. It's *also* the practical knowledge (both beyond and preceding theory) on how to do a thing. Democracy is a social technology. Irrigation is an agricultural technology. Managing a closed ecosystem is a bio-ecological technology - one that we don't have, and that we'd need a lot of practice to develop.
We absolutely could have started building space habitats in the 70s if we had the will. But there's a lot of decades developing ecological technologies, not to mention orbital manufacturing technologies, before we would be anywhere close to ready to start building an interstellar ark.
(Score: 2) by Arik on Wednesday September 26 2018, @02:50PM (1 child)
To me, we had the tech - we had all the necessary pieces to get it going. The stuff you're talking about, the experience, well the only way you get that is by doing. And we just haven't been doing.
"We absolutely could have started building space habitats in the 70s if we had the will. But there's a lot of decades developing ecological technologies, not to mention orbital manufacturing technologies, before we would be anywhere close to ready to start building an interstellar ark."
Only way to know would be to go, but I suspect "decades" might even be an exaggeration. For sure, though, it's a stage that we could have passed by now, but one we still have to start at this point.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Immerman on Thursday September 27 2018, @03:19AM
The Wright brothers had all the necessary pieces to build an aircraft - but you wouldn't want to try to cross the Atlantic in the plane they first flew from Kitty Hawk. You need some steps in between to work the inevitable kinks out of the system, optimize, etc. They didn't have the tech for the job - they only had the beginnings of the tech, it took another 25 years to develop it to the point where someone managed to cross the Atlantic.
I think you're grossly underestimating the complexity of managing a closed ecology complex enough to support us. I don't forsee any serious problems in building off-world ecologies. A rough start for sure, but I don't think there'll be any insurmountable problems, primarily because they'll have relatively easy access to whatever ecological supplements they discover they need (mineral and/or biological). However, I don't think we will have even discovered all the problems, much less solved them, in only a few decades. And I doubt anyone will even be seriously *thinking* about closed ecologies - they'll be importing resources at a breakneck speed as they grow.
An interstellar voyage is just far too expensive to even consider launching before you've got every last detail hammered out. Just the raw kinetic energy required is E= 1/2*m*(10%*300,000,000m/s)^2 = 4.5x10^14J/kg = 125GWh/kg. For an 80kg average American, that's about 10TWh of kinetic energy in their body - without any supporting ship, or any losses to the hideous inefficiencies of existing propulsion systems. About 1/1,000th of annual global energy consumption. And you probably want to add at least two or three zeros to the end of that if you're using any existing propulsion system- at which point you're taking the entire annual global energy consumption to accelerate one person ('s frozen corpse) to interstellar speeds. Multiply that by enough people to make a viable colony (at least a few hundred, assuming lots of frozen gametes to reintroduce genetic diversity at the other end) , plus enough ship and ecology to keep them alive for many decades of interstellar travel (the ISS masses about 100,000kg per person, with no attempt at being self sufficient), PLUS - and this is where it gets REALLY bad - enough energy and propellant to do the same exact maneuver in reverse to stop at the remote star, with no external infrastructure. That probably adds at least a couple more zeros right there.
So, call it imparting probably many millions, maybe billions of times annual global energy consumption to something, for a minimally viable colony ship. Not something to do lightly. You want to be *sure* those colonists reach their destination alive and healthy. And you need a massively larger energy-base than anything this planet has ever seen.
(Score: 2) by Immerman on Tuesday September 25 2018, @11:41PM
Oh, and as for
>ANY time you do something new of course there are things you will only learn by doing
Absolutely. And we need a lot of time doing, with access to additional resources to fix our mistakes, before we'll have the mature technology required to survive the decades or centuries journey through the void to another star. Had we started seriously building off-world settlements in the 70s, we might have the technology today. But we didn't have it then, and we still don't have it now.
(Score: 3, Interesting) by bzipitidoo on Saturday September 22 2018, @02:35PM (2 children)
An old space conquest game, Spaceward Ho!, with goofy cowboy hats on the planets, used 2.53 times as an upper limit. I have not seen any design notes for that game, but I'd guess they just pulled that number out of the air.
(Score: 2) by Snotnose on Saturday September 22 2018, @03:38PM
Wow, that was a fun game. I played it what, 20 years ago? I remember a co-worker also played it, puts it at about 2000. I was only at that company for less than a year (didn't want to join them, got talked into it, realized almost immediately I'd made a mistake).
When the dust settled America realized it was saved by a porn star.
(Score: 1, Insightful) by Anonymous Coward on Saturday September 22 2018, @03:56PM
You're incorrectly assuming this "study" is anyway better than a dice roll. It's not. Doctors didn't foresee the problems astronauts had in zero gravity so they sent dogs. And they still missed a whole lot of stuff.
Go ask a sports doctors who treats strength and power athletes what they think about that 4x claim. Give them a good laugh.
(Score: 0) by Anonymous Coward on Saturday September 22 2018, @03:45PM (5 children)
"We" barely colonized this world, why colonize another one?
(Score: 2, Insightful) by Anonymous Coward on Saturday September 22 2018, @03:54PM (4 children)
And there are about 1+ billion cows, 1 billion sheep, 1 billion pigs, 19 billion chickens.
The weight of all the ships in the sea is already in the same magnitude as the weight of all the fish in the sea. Some estimates have the ships as weighing more.
We've gone past colonizing this world and moved to doing anal, bondage and submission on it.
(Score: 0) by Anonymous Coward on Saturday September 22 2018, @04:00PM (2 children)
Two football fields per person is huge. A person only needs a couple cubic meter tube to survive (see japan, astronauts, or submariners). Also, people barely live underground or under the sea yet. Finally, there is an entire moon to colonize.
(Score: 3, Insightful) by Runaway1956 on Saturday September 22 2018, @04:09PM (1 child)
A couple cubic meter cube sounds great - in theory. In real life, you can't fit a long term biosphere within that cube. You might replace plants for recycling oxygen with equipment, but how much room does that take? Where's your food source? How are you recycling water?
Fact is, it takes a few magnitudes more than a couple cubic meters to support a single human being on earth.
(Score: 0) by Anonymous Coward on Saturday September 22 2018, @05:49PM
There's still almost no vertical agriculture. Or, instead of that, the entire surface can be used for agriculture and we can move underground or into floating cities.
(Score: 0) by Anonymous Coward on Saturday September 22 2018, @04:08PM
Seasteading!
(Score: 0) by Anonymous Coward on Saturday September 22 2018, @04:16PM (2 children)
(Score: 1, Redundant) by takyon on Saturday September 22 2018, @04:53PM
We could live in microgravity or on Ceres if we could counteract the negative health effects.
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 3, Insightful) by Immerman on Saturday September 22 2018, @05:48PM
Zero.
There may be higher minimum limits for healthy multi-generational, but centrifugal cities can make up any difference needed if we're ambitious enough. And it gets a lot easier if we just need intermittent exposure, or for key developmental stages (gestation? Infancy? Puberty?) Or are in freefall to start with - huge centrifuges are a lot more complicated to build on a planet.
At this point though, we have basically no idea what healthy minimums might be. We need to do research, and currently we have no facilities to do so. All we have right now is Earth and the ISS in freefall, anything in between would require establishing biology labs on other planets, or more likely, orbital centrifuges. Until we do that, everything else is just pure speculation.
We know that freefall (and/or orbital radiation exposure) causes health and developmental problems in lab animals that don't exist on Earth. But with only two data points we really can't say anything whatsoever of the shape of the curve between them. Could be serious problems start appearing anywhere below 0.99g. Could be just the orientation and types of motion present in even 0.01g is enough to eliminate virtually all problems. At this point all we have is wild conjecture from pet theories about what exactly is causing the problems.
(Score: 3, Interesting) by VLM on Saturday September 22 2018, @05:46PM (4 children)
I wouldn't worry too much about bones, we have four legged dogs running around from cat sized to pony sized, not to mention comparing "people of walmart" scooter drivers to marathon runners, I think we're all good over a 4G range. Bone isn't smart, it doesn't know the difference between 1 and 4 G planet anymore than it knows the difference between 400 pound vs 100 pound person.
The real problem is likely fluid dynamics. Like whats the NPSH of a human heart, could the vascular pressure required result in pulling a vacuum on leg veins? Could your brain blood vessels survive even the weakest tap if they had to run at 30 PSI blood pressure for high-G? Would it be expected that everyone who lays down for awhile automatically faints when they stand suddenly? Tensile strength of skin and stuff? Most importantly, I would guess boobs would be droopy to an unimaginable level, just tuck em in your belts, ladies.
Strange thought: Sweat "works" because it evaporates slowly on skin; does it work as an adaptive measure if 4G are pulling every droplet of sweat off like a salad spinner centrifuge dries lettuce? People might evolve to stop sweating since all it does is make your shoes wet and slippery, and evolve toward panting like a dog with long tongues, or maybe we'd evolve floppy ears.
Even something like chewing... imagine something pulling your jaw down with 3x the weight of your jaw every time you chew food, might be weird.
(Score: 2) by Immerman on Saturday September 22 2018, @05:55PM (3 children)
>Bone isn't smart, it doesn't know the difference between 1 and 4 G planet anymore than it knows the difference between 400 pound vs 100 pound person.
Umm, bone *absolutely* knows the difference between a 100 and 400 pound person. It doesn't need to be smart for that, it just needs to be subjected to the constant microfractures inflicted upon it by normal life, and the associated repair and reinforcement mechanisms. A 400lb person is going to either inflict more and larger microfractures in the course of performing the same activity.
(Score: 2) by VLM on Tuesday September 25 2018, @11:35AM (2 children)
Not under varying gravity. A femur can't tell the difference between the force applied from the body above of 100 Kg at 1G or 50 Kg at 2G, its the same number of newtons of force.
(Score: 2) by Immerman on Tuesday September 25 2018, @02:03PM (1 child)
Well not too much at least, there's probably still some differences in stress profiles just due to the sort of activity you'd engage in.
But that wasn't the assertion I was refuting - which was that bone didn't know the difference between 1 and 4g, OR between 100 and 400lb. It absolutely "notices" that sort of stress difference, regardless of whether the cause is a difference in gravity or mass.
(Score: 2) by VLM on Tuesday September 25 2018, @06:25PM
Ah I think I see the confusion. I'm implying the euler buckling column strength of a femur is affected the same from 400 pounds of potbelly at 1G as 100 pounds of potbelly at 4G, it can't "know" where the identical number of newtons of force come from. From your point of view yes separately a bone experiences different forces at 100 vs 400 pounds or 1 vs 4 G
(Score: 0) by Anonymous Coward on Saturday September 22 2018, @09:45PM
And that would be inside, of your CELLS.
(Score: 0) by Anonymous Coward on Sunday September 23 2018, @02:39PM (2 children)
"what's the maximum gravity (acceleration) we could survive?"
reading the conclusion then the posted question means naked or unassisted.
however with a exo-skeleton we could probably do 20 G (pull-out-of-ass-number)?
the trick is probably to BUFFER the human body in the same material that it is made of, that is water.
if the container -aka- exo-skeleton is strong enough to hold water at 20 G then the human body inside will probably not feel much of the gravity.
imagine a 1G planet and the human body to be like the body of a jellyfish. the jelly-human is perfectly content being made of 99% water and floating inside the ocean. remove it from the ocean and it collapses.
now transfer the REAL human to the 20G planet and it collapses like the jellyfish ... so just add water!
ofc the exoskeleton would need a water-tight control interface (and phone charging port to be sure) and assistive motors to lift stuff "outside" the exo-skeleton.
curiously enough, there's no difference between standing on a planet with 20 G and sitting in a spaceship going 20 G or so, so if the exoskeleton works for the planet it would also work for the super-fast spaceship (or dog fighting jet?).
ofc goku, like all real men, balks at the solution and rather prefers to train until 20 G feels like 0.5 G : ]
(Score: 2) by Immerman on Sunday September 23 2018, @05:13PM (1 child)
The problem is that there's a considerable amount of density variation within the human body, and no matter how perfectly you support the outside of the body, the inside will still feel every G of acceleration. Blood and most organs are within a few percentage of water density, so they could *probably* take some serious acceleration - though then again, they're designed to operate when that similarity means there's essentially no sustained uneven stresses between cells, so who knows what the long term consequence of sustained exposure might be.
Bone though is 3x-4x denser than muscle. Your skeleton is typically about 15% of your body mass, so at 20gs of acceleration that 2-3x of "excess density" would translate to around 15%*(2.5/3.5)*20 = 2.1 times your normal weight being supported by just the tissues and organs that lay between bottom and your "bottom" outside surface at any point.
(Score: 0) by Anonymous Coward on Sunday September 23 2018, @06:47PM
well, we could simplify the human body to a simple "T" to make some conjuring easier. they do this all the time just look up radioactive exposure stuff ... so bear with me.
the two arms of the "T" are rubber ballons filled with water and attached to a steel rod.
place "T" on land and the rod supports the sagging water ballons.
place "T" in water and the ballons support the rod.
the stresses at the connection point (where the two arms) connect to center rod is not same in both cases.
if true then it says something how the stresses inside the body would look like between "very watery tissue" and less "watery" tissue, so maybe like between muscle and bone.
the main problem might just be the (closed) cavities that exist in human body. these might get compressed: one meter of water at 20 g might then feel like 20 meters at 1G? ofc theres no need to surround the body with that much water. if the exoskeleton is engineered well enough then maybe a 1 cm layer of water from all body surfaces to internal surface of exo suit would suffice?
(Score: 0) by Anonymous Coward on Tuesday September 25 2018, @07:50AM
Human adaptability is easy to underestimate. There arealready many people who wear 100kg on their backs uphill in difficult terrain whole day every day, when they are supplying mountain huts or camps. It does not need extraordinary muscle and bone development, just training and proper posture. I would expect people living in 4g to be actually very small and nimble.