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There are a lot of solutions for living in low gravity environments. (e.g. centripetal acceleration, linear thrust, etc.)

But what about living on high gravity planets? Is there anyway to build or simulate 1-G in a planet that has 4-g, for example?

This is a stretch, but I recall that if one were to submerge themselves in a fluid it will negate the effects of high g forces. Is it possible to build, say, an underwater habitat on a 4-g ocean planet and utilize buoyancy to offset the high g forces? Say a dome underwater with a sealed environment with pressurized air?

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Well, There are four ways.

One way would be a plane like the 'vomit comet'. It would slowly climb and then dip into freefall, giving you a minute of low G. Planes in 4 G would be pretty expensive, mind, but if the atmosphere were thick enough they should be possible. You can get longer times with a vertical launching rocket, like Blue Origin's New Shepard, but rockets in 4g with all that atmosphere would be even more tricky.

Another way would be to sink/dig halfway to the core of the planet. The gravity should be about 1g down there. Of course if the planet has a molten core this may not be advisable :), and regardless the shafts heading down would need scads of airlocks to prevent the air pressure down there from being too high. If you happen to like the idea, I'd be happy to run the numbers.

You could put the thing that needs low gravity physically in water to give it the buoyancy effect, but having it in an underwater city filled with air sadly wouldn't do.

And finally, do what we do and go to orbit!

Best of luck with your water world.

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  • $\begingroup$ That only gives very temporary 1G at the cost of increased weight while climbing, I don't think it's really a solution. $\endgroup$ – Tim B Jan 21 '18 at 13:22
  • $\begingroup$ @TimB expect that is how we do it in the here and now, and the original question technically doesn't ask for how long. $\endgroup$ – Xavon_Wrentaile Jan 21 '18 at 15:23
  • $\begingroup$ Digging to the core of a planet with anything but a cold core could be lethal as you hit extreme pressure and thermal gradients - try descending into a mine and discover how much hotter it is down a thousand feet. $\endgroup$ – StephenG Jan 21 '18 at 17:40
  • $\begingroup$ @StephenG as noted in answer, it may not be advisable with a molten core :). There's some atmospheric heating effects as well going so low, hence the airlocks. Lots of 'em! $\endgroup$ – Michael Irving Jan 21 '18 at 22:55
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No.

If you want buoyancy to lower the influence of gravity on your body, you have to be in the fluid. There, your body will get an upward push equal to the weight of the displaced fluid, i.e. if you displace 1000 N of water, that is about 100 liters with 1 g gravity, you will get an upward push of 1000 N.

But if you are in a sealed dome filled with air, you are displacing air, thus you get a much lower buoyancy. If you want hydrostatics to help, you have to swim.

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  • $\begingroup$ Even when submerged in fluid, upward pull from buoyancy is affecting your body from the outside - your blood and internal organs still experience a higher gravity... $\endgroup$ – G0BLiN Jan 21 '18 at 11:35
  • $\begingroup$ @G0BLiN, I agree. But if NASA used swimming pools to train astronauts it means it a fairly good approximation of the "touch and feel" of microgravity $\endgroup$ – L.Dutch Jan 21 '18 at 11:59
  • $\begingroup$ Fairly good may be an overstatement, but well, it's best we have for a reasonable price, and good enough for its purpose. $\endgroup$ – Mołot Jan 23 '18 at 12:24
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As mentioned in other answers, orbit is the only practical solution for long term simulation of lower gravity. But what about impractical solutions? I can think of two that allow you to stay on the surface.

The first is essentially the same trick as orbiting. Build a train track that goes all the way around the planet. It works best at the equator. Run a train along this track at a significant fraction of orbital speed. The size of the planet will effect how fast you will need to go. The train track will almost definitely need to be a vacuum tunnel. The train is in effect a centrifuge that encircles the planet. When the centrifugal force is 3g, the total force experienced by passengers will be 1g. This solution has the obvious issue that exiting the train to interact with the surface is as difficult as de-orbiting.

The second only works if you have an especially dense kind of unobtainium. Building a super heavy roof over top you colony will cancel out some of the planets gravity. For the roof to avoid being nearly as heavy as the planet, the mass it is composed of must be mech closer, which is why the density must be quite high and even then the roof will be unimaginably heavy. Probably the only candidate materials are neutronium, minature black holes, and strangelets. Though it seems difficult to take this approach seriously, it is notable that it has appeared in hard science fiction at least once. It is used by Robert Forward's Dragon's Egg in order to cancel the extreme tidal forces experienced by a space station in a close orbit around a neutron star.

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1) Antigravity! Just handwave the problem away!

2) Live deep underground where the gravity drops to 1g, you will need a way to counter the extreme pressure

3) Live in a gravity train; you can build a gravity train at an angle that will give the occupants 1g gravity constantly

MASSIVE ENGINEERING REQUIRED:

4) Live above ground, but not in orbit, just build a supraworld on top of many space fountains and you're done

5) Spin the hell out of the planet and live on the equator after you corrected the apparent gravity to 1g

6) Suspend a superdense mass above you colony using space fountains or a space elevator, then live directly below it

7) Build your colony on an orbital ring, have it revolve at suborbital speed to get 1g gravity on the surface of the colony

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Do it the way NASA did it in the 1960s -- with ropes and pulleys!

No, really. I distinctly recall seeing a video clip, but can't recall exactly where, of how Apollo astronauts trained for walking on the Moon, with its lower gravity.

What they had was what looked like (but likely wasn't, at least not exactly) a suited-up astronaut, attached to a system of ropes and pulleys that presumably offered a counterweight corresponding to 5/6 of the astronaut's total weight. This would reduce the weight experienced by the astronaut as they moved around to 1/6 of normal, which just so happens to match the Moon's gravity pretty well.

There are two obvious downsides with this:

  • It's difficult to make it work in two dimensions over any significantly sized area. It's pretty easy if you can live with the limitation of only being able to move any significant distance in a single dimension, though. Lineworld, anyone?
  • Any object the astronaut needs to manipulate will retain its normal weight, so you will need some other way of reducing their weight if you want to capture a fuller experience. Less dense props instead of the real thing, tools made specifically from lighter material because they don't need to be as durable anyway, or what have you.

You will also need to adjust the counterweight for the specific astronaut, but that's plenty doable. If you're training multiple astronauts, they will also need to stay aware of the ropes attached to their colleagues to avoid getting tangled.

The clear upside is that you can adjust the level of resistance from gravity to whatever level you prefer that is less than the surface gravity on your planet. Want 1 G on a 4 G world? Or 1/6 G on a 1 G world? Not a problem, just select the counterweights appropriately and hook your people up!

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None we know of.

But of course if you had managed to develop technology to travel to another planet with a 4g surface gravity you'd already have interstellar flight and maybe FTL or anti-gravity (as we're on on Worldbuilding).

So maybe you already have tech to manipulate gravitational fields locally.

Maybe you don't have that tech, but you might have the tech to make Dyson Swarms and self replicating machines that could e.g. use the planet to build something else, like two planets or lots of space stations (like IM Bank's Orbitals). Planets are just a nuisance to a space-faring race. :-)

The only other way I can think of (apart from digging down towards the core, which I already commented on) would be to build a platform (connected with the ground) at about one planet radius height, which would be an unimaginable engineering task (although perhaps no more difficult than digging down towards the core to the required depth). But that would have 1G.

Note that even if you can manipulate local gravity, you'd still need to live in sealed environments because a high gravity atmosphere would almost certainly be a higher pressure atmosphere. You'd likely have an atmosphere that was at something like 4 standard atmospheres, which would be lethal to humans in a short time.

With the physics we have, a 4G world is off-limits and, in practical terms anything more than, say, 1.2G is probably not practical - human physiology limits us for long term use (and we won't adapt to it - that's a common myth of sci-fi).

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  • $\begingroup$ The correlation you assume between gravity and pressure is wrong. There are several other factors involved in atmospheric pressure. Venus has 0.9g and 90 atm. Mars has 0.376g and 0.00628 atm $\endgroup$ – Lex Jan 22 '18 at 6:39
  • $\begingroup$ @lex There is no direct correlation between atmospheric pressure and gravity, but you're using extreme examples. If a 4G world is expected to be at all attractive for habitation by humans then it needs something like an air-like atmosphere and I think it's unlikely a 4G world would not retain a larger atmosphere of that type and hence have a higher surface pressure. If you're willing to try and live on Venus or Mars, why would you also make it even harder to survive (if not impossible) by adding high gravity as well ? $\endgroup$ – StephenG Jan 22 '18 at 6:51
  • $\begingroup$ Your points are inconsistent. Why would you care about Earth-like air if the higher pressure makes it unbreathable. If you are postulating a planet that is ideally habitable other than high gravity, real world examples show a wide enough range of atmospheric pressures that you might as well assume your planet has 1 atm. $\endgroup$ – Lex Jan 22 '18 at 7:02
  • $\begingroup$ @lex Seems a lot easier to find near-1G worlds without a suitable atmosphere and live in sealed environments that accepting high-G worlds with about 1 atm pressure. However, from my point of view this is not a real issue as I don't believe any interstellar capable civilization would care about planets at all except to find other life and for scientific purposes. YMMV. $\endgroup$ – StephenG Jan 22 '18 at 7:07

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