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In the near future, an alien race finds Earth, learns how it and everything on it works, and begins to tamper with it. Somehow they figure out a way to flip the pull of Earth's gravity on only humans so we fall into space instead of falling to the ground.

They do this instantaneously to the entire human race and a theoretical half of the entire population is pushed into space and dies immediately (one half is sleeping inside, the other half is awake outside). Those who survive are now standing on whatever was above them and mad because they didn't get enough sleep. The survivors must figure out new means of transportation and general living techniques among many other things. Also, a vast majority of existing structures will be rendered useless.

Assuming the human race doesn't just decide to burrow into the ground and set up camp there, would we be able to adjust to this change in time to be able to survive? If so, how?


Notes:

  1. Gravity's properties still work the same way. For example, you step out from under a platform and you fall upwards, accelerating at 9.8 m/s^2 until you reach terminal velocity and run out of oxygen.
  2. Since only humans are put through this, all other living things stay the same. This means your cat is now on the ceiling (relative to you).
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    $\begingroup$ Do you want this to be grounded in hard science? Consider adding a hard-science or science-based tag $\endgroup$ – DonyorM Oct 27 '15 at 16:58
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    $\begingroup$ That would give a whole new meaning to having one's underwear ride up on them... $\endgroup$ – Cort Ammon Oct 27 '15 at 17:26
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    $\begingroup$ Going to the toilet becomes immensely risky task best undertaken with specialist training... $\endgroup$ – Joe Bloggs Oct 28 '15 at 10:12
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    $\begingroup$ " accelerating at 9.8 m/s^2 until you reach terminal velocity " Nope. As you rise the air gets thinner, so your terminal velocity increases. You'll get out of the atmosphere before the gravity starts to fall in any major way, so you'll keep accelerating. Final velocity will be on the order of 11 km/sec. $\endgroup$ – WhatRoughBeast Jun 4 '16 at 0:54
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    $\begingroup$ @Adam - "That's hardly my concern since I'm no physics guru" Sorry, but if you're going to invoke something like terminal velocity it is your obligation to understand it. Rejecting correction by claiming ignorance is not a great response. $\endgroup$ – WhatRoughBeast Jun 4 '16 at 1:53
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Note that you will surpass terminal velocity, because you will rather quickly fall up through the atmosphere and continue on accelerating. Human flesh powered spacecraft, the Solar System is ours.

Apart from that, once the original confusion clears out, the best bet is to use weights - slightly more than your weight of lead (or rocks in low tech environments) will give you some very nice powers, like human powered flight. I imagine everyone using something like 120% of their body weight (to give some safety margin) of lead garment. People would generally prefer to stand inside, though.

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  • $\begingroup$ I think that weighted clothing is the answer like you say. They'd probably want to wear evenly distributed weights which have 200% the mass of their body, though: this would make the overall weight the same as what it used to be. $\endgroup$ – Max Williams Oct 27 '15 at 9:46
  • $\begingroup$ Very good idea, you'll still need some adaptions to your house though. Think of changing your clothes, you'll need some special room for that. $\endgroup$ – Snake Oct 27 '15 at 11:30
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We'd use weights to keep ourselves attached to the ground. It would be a pain and require a lot of work, but it's doable. For example, let's say you weigh 150kg. You could have two weights, each 80kg, attached to your wrists with a rope. You can now use those to "walk" upside down. Lots of people would probably never leave their house though, or would use motorized devices.

There's also nothing stopping you from driving a car as-is. It would be extremely difficult, but the car isn't going to float up, so it's a matter of reworking control surfaces to be upside down. The vast majority of parking garages would be reworked to be indoors, or at least have structurally strong ceilings. You might see ceilings over roads too, or at least over the sides so people can get out and do something to a vehicle.

There would be an adjustment period. I'd estimate a lot of people would die during this as crucial services are disrupted, but we'd adjust using the techniques above.

More interesting applications, however, are in the fact that humans now act as buoyancy devices.

Personal flight? Is now possible and cheap. A 200kg flying device that carries a 180kg human only has to "lift" 20kg worth of weight. This makes it pretty trivial, vastly reducing the power requirements while increasing longevity.

Consider going to orbit. This doesn't help as you might think, because a lot of the "get to orbit" part is increasing your speed, not just gaining height. But you can still use humans to get vastly larger payloads into orbital ranges, substantially reducing fuel requirements.

Also, merely the knowledge that gravity can be manipulated on this level would lead to scientific inquiry into the subject, possibly jumping our understanding of physics by decades or centuries.

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    $\begingroup$ That's a great point about flying. Keep in mind, though, the amount of basic (and extremely dangerous) infrastructure work that would be required to even begin to develop systems like that. $\endgroup$ – Adam Oct 27 '15 at 19:10
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    $\begingroup$ Hmm.. Not sure what would happen with orbits (or even what the concept would mean in this world), because there is no possible way to put a human in orbit if they're being repelled from the planet (as they have a negative orbital speed on account of experiencing negative g). If you have a ship with exactly matched masses of human/non human then it has an 'orbital speed' of 0, and can be pushed into 'orbit' with a desk fan and a couple of roman candles. Which would be epic, but not actually orbiting... $\endgroup$ – Joe Bloggs Oct 28 '15 at 10:09
  • $\begingroup$ Though the astronauts would have to watch out for de-orbit burns caused by pooping.... Eww.. $\endgroup$ – Joe Bloggs Oct 28 '15 at 10:10
  • $\begingroup$ @JoeBloggs: Orbits would be different, but still exist. Normal (current) orbits work because objects are falling just fast enough to miss. As long as the ship out-weighs the humans it will still fall overall, just at a different acceleration. $\endgroup$ – Dan Smolinske Oct 28 '15 at 13:15
  • $\begingroup$ @DanSmolinske: I know that, my issue was more with the definition of 'orbit'. Can it be considered to be orbiting, or is it powered flight that uses human 'gravity' to make up the missing engine thrust? $\endgroup$ – Joe Bloggs Oct 28 '15 at 13:20
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Basically, we're screwed. We would fall up into space and suffocate. Or we would be trapped inside and potentially starve to death. If one was asleep in a huge bunker full of canned food, they might be fine, but...

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    $\begingroup$ Welcome to the site AussieJo $\endgroup$ – James Oct 28 '15 at 14:46
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The other answers are quite fine, but it's worth noting that every human being now has the potential to generate a considerable quantity of power according to the formula:

E = 1/2 m v² / t

Which if I do my maths right is about 4.8kW for myself, not a inconsiderable amount of power. So while the initial transitional period is going to be horrific, likely worse than many apocalypse films one sees, the future is very interesting.

Go to sleep? In 8 hours I've generated 38.4kWh of electricity locally.

Building a space empire? The mechanics may be a little complicated, but you suddenly have both huge lifting capacity, and a reliable source of energy. Thanks to the rocket equation, these are both hard to obtain through conventional means.

So on and so forth, it's like a limited quantity of perpetual motion.

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  • $\begingroup$ Harvesting your own energy would require equipment that no common man has laying around. You'd have to figure out how to mass produce something like that and get it distributed while accounting for the world around you that's just descended into pure chaos. $\endgroup$ – Adam Jun 4 '16 at 1:02
  • $\begingroup$ @Adam you may have missed the part where I mention the transitional time would be awful. But I figure a few lucky nerds will spend their first few hours developing all kinds of contraptions in their minds, while waiting for rescue. $\endgroup$ – NPSF3000 Jun 4 '16 at 1:27
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Best way of transportation? Well that would be like old days - animals. As you said, it won't affect them, you can just use an elephant or horse or cattles for transportation, just tie yourself to them (like swing in a park), and train them just like you train a dog to do certain things.

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  • $\begingroup$ What about people in urban areas where big animals most likely wouldn't be? You'd need some way to go out and get them first. $\endgroup$ – Adam Oct 27 '15 at 18:37
  • $\begingroup$ It doesnt effect car.. Does it? Strap urself into it... $\endgroup$ – Kesh Oct 28 '15 at 11:37
  • $\begingroup$ That could work, but if you sat normally in a car you would be upside down. There's always a chance of passing out. $\endgroup$ – Adam Oct 28 '15 at 15:33

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