# Gravity alteration as extermination tool viable?

An alien race was rubbed the wrong way by humans being humans and decided that humankind has to go. However, unlike many other science fiction stories, they do not intend to give the humans even a semblance of a sporting chance by sending their equivalent of an invasion force. These aliens are capable of manipulating the fundamental interactions and instead have decided on using gravity as their tool.

Before humanity can realise the gravity of their situation, the aliens will flip a switch, at which point the strength of Earth's gravitational pull will be multiplied by 10 without any alteration of mass for a period of 24 hours. So for instance a person weighing 60kg will suddenly become 600kg with no prior warning and no other change. After this 24 hour period, Earth's gravity will return to its prior normal level of 1G.

Is this sufficient to guarantee the extinction of the human race? Will this also end all life as we know it on Earth?

• The small problem is that the force pulling the Earth towards the Sun will also increase by a factor of ten, with very unhappy consequences for Earth's orbit... Mar 13 '19 at 9:26
• @AlexP I'm not sure that would happen (note that OP posited changing only the gravity of Earth), but even if it did, in 24 hours the Earth moves only about a degree in its orbit around the Sun, so you'd end up with the Earth in a slightly but not likely significantly different orbit. I suspect it could be modelled as a simple propulsive maneuver toward zenith in a Sun-centric reference frame (away from the Sun, opposite of nadir; the resultant thrust would push Earth toward the Sun, same as an increase in gravity would).
– user
Mar 13 '19 at 9:45
• assuming any creature with lungs survives those 24 hours, they would surely die afterwards. The reason being that the increased gravity increases atmospheric pressure, too. So after switching off, the decompression should clean up any survivors Mar 13 '19 at 9:56
• @aCVn: Increasing Earth's gravity increases the force with which Earth attracts the Sun. By Newton's third law, this force is equal to the force with which the Sun attracts Earth. Earth would behave as a spacecraft executing a 24 hour long burn; the current position of the Earth will remain the aphelion point, with the perihelion point moved quite a bit towards the Sun. Mar 13 '19 at 9:57
• @AlexP what about Earth's "innards"? Won't Earth just collapse on itself? Mar 13 '19 at 13:02

https://en.wikipedia.org/wiki/G-force#Human_tolerance According to Wikipedia, 16g for a minute are already deadly. For a day 10g are very much lethal for humans, as well as for any large animal. Insects, bacteria will fare better, as may various marine life.

• That article is g-force, the question is pertaining to gravity per se.
– Mr.J
Mar 13 '19 at 7:49
• @Mr.J, g-forces and gravity are indistinguishable from the inside. Mar 13 '19 at 7:57
• @Separatrix after reading the content, I get it, I have to revise my answer (or maybe delete it)
– Mr.J
Mar 13 '19 at 8:07
• Nope, even marine life would die. Hydrostatic pressure would rise tenfold, killing off everything except maybe bacteria and jellyfish. Mar 13 '19 at 8:50
• @DarthDonut - hydrostatic pressure increases with depth. It would change the depths at which various lifeforms could survive, but pretty much any marine life could still find a depth they are comfortable with. And as much marine life is capable of living at a wide range of depths, I would bet that a significant portion would not be too adversely affected by the sudden switch. Mar 13 '19 at 14:53

In addition to other effects, there is atmospheric compression to consider.

With gravity increased by a factor of 10, the atmospheric pressure at sea level will become (about) 10 times greater, and the altitude at which air becomes unbreathable will drop by (about) a factor of 10.

It's well-known that prolonged exposure on Mt Everest is not survivable, so let's put 30,000 feet as a killer altitude. With 10 times the gravity, the same air density will now be found at 3,000 feet, and anybody much above this will be in big trouble.

The altitude limit is not exactly a factor of 10, though. At scales of 3000 feet the earth is not a uniform sphere. Higher-altitude areas will have no lower-altitude areas at all, so the death zone will be somewhat higher than a simple calculation indicates.

I'd put a rough estimate for the 30,000 foot equivalent at about 4,000 feet.

Fortunately (if you're looking for good news), a x10 increase in atmospheric pressure is not quite enough to produce lethal oxygen toxicity in most people.

• Of course, a lot of those higher locations will very rapidly cease being higher locations. Dirt and rock has weight too, now 10× as much... Mar 13 '19 at 20:05
• @derobert - Yeah. The angle of repose gets a lot shallower. Mar 14 '19 at 17:13

a very very small chance of no

Thanks to the corrections given by the moderators, the most viable answer that "some" humans will survive is if they take a trip to space before the gravity alteration occured. That's the only chance some humans might have survived...

• I'd have to do the math, but I'm pretty sure planes wouldn't fall down even if gravity suddenly increased tenfold. Airplanes in cruise don't use full engine power, and the typical airplane has a glide ratio on the order of 10-15 to 1. Even if the plane had no excess power (not likely) and there are no other mitigating factors, the plane would descend at an angle of 30-45 degrees. Hardly nice for the passengers, but only one order of magnitude worse than a standard landing approach, and much less so than an expediated flight level change, which is a standard (if unusual) procedure.
– user
Mar 13 '19 at 7:39
• I am not sure that your legs crush differently under 9000 N just because you leave a secluded life out of society.
– L.Dutch
Mar 13 '19 at 7:54
• @L.Dutch No, my point about living a secluded life is you don't have to avoid something falling on your head.
– Mr.J
Mar 13 '19 at 8:02
• Even the astronauts in space around Earth are going to die, as the sudden increase in gravity changes the orbits of everythin around Earth. I would even asume that the orbit of the moon would be affected! So, as long as noone is on Mars, there is noone to survive. Mar 13 '19 at 8:48
• 30 degrees down would be fine for a few minutes, but 30 degrees down is still "down". In short order, all of the planes will crash into the ground. Even if a plane was close to an airport, there's no way it could generate enough lift to level off during landing. Apr 2 '19 at 16:08

Humanity and life will die, that is for sure, but maybe not because of the g-force alone. As AlexP pointed out in the comments of the original post :

The small problem is that the force pulling the Earth towards the Sun will also increase by a factor of ten, with very unhappy consequences for Earth's orbit...

Temperature

While a day might not be enough to make Earth plunge into the sun with such force, the orbit will be off-course by a lot. I have no idea how to do the calculation, but I'm convinced usual users might know how to prove it.

Anyway, the Earth orbit is in a very small spot where the temperature is balanced, having a span of temperature of -30ish°C in the coldest places in winter to 40ish°C in hot places on summer. This relatively small span of temperature allows fauna & flora to adapt to winter and be reborn / wake-up in spring.

Having a larger orbit because of the 24h gravitational shift will increase this temperature span, and thus killing every life being that can't adapt enough.

EDIT : As pointed out by ThisIsMe, this schematic is wrong in its naming. Instead of Summer and Winter (which is influenced by the inclinaison of Earth and NOT by the distance to the Sun), let's call them "Hot phase" and "Cold phase".

There is a 25ish°C temperature gap between the 2 seasons in continental contries as is, imagine the temperature gap now that summer and winter are so far appart from what they were.

The moon

Even if Earth won't pludge into the sun because of the distance between them and the short duration, the moon will plundge into Earth (can't prove it once again, but I'm pretty sure being pulled during a full revolution will drag it down).

And even if I'm mistaken and the moon doesn't crash, it will at least pass very close to Earth, generating some big waves.

Conclusion

If the goal is just to destroy humanity, yes, it's a good way to do it (for the most part, some could escape), but if aliens plan to colonise Earth afterward, that's a big no.

• Actually, this is incorrect. Firstly, seasons are not caused by our distance from the sun (if they were, the US and australia would have summer at the same time, instead of half a year apart). The altered orbit would change temperatures, and perhaps equalise seasongs, but not to such a degree that it would become uninhabitable. secondly, this "tiny sliver" where humans could live is rather large: Earth could be anywhere between Venus and Mars and remain habitable (albeit uncomfortable) for humans. Mar 13 '19 at 11:04
• The distance in itself isn't the right word, you're right. I rather meant the influence of the sun on Earth. During winter, the exposure is shorter than in summer, less radiation is reaching the surface and being conserved within the atmosphere, hence the reduced heat. But if you're further away, the radiations will have a lesser influence on Earth, it will be colder. Same goes for heat if you're closer. Mar 13 '19 at 12:46
• the exposure on that half of the earth, yes. the tilt of earths' rotation is what affects this exposure. Making the earths' orbit more eccentric could make summers in the north warmer than the summers in the south (or reversed). If the new highest/lowest point happens to be during the equinox, barely anything would change. Simply attracting the sun a bit more for a day won't have such a dramatic effect, it won't change the orbital extremes more than the difference between the extremes and the average (aphelion and semi-major axis); we are talking less than a percent here... Mar 13 '19 at 13:03

Extinction is almost certainly inevitable.

In another answer, I addressed the effects of atmospheric compression. I failed to extend the analysis to the interior.

With a 10x increase in gravitational attraction, the apparent weight of the entire planet will increase by at least a factor of 10, as will the pressures at any given (proportional) depth.

With increasing pressure, density increases, so the planet will become smaller. Exactly how much is going to depend on the depth of the rock involved, and the exact composition. I'm not willing to do the effort required to determine the exact pressure/density relationship of rock at these pressures (it's rather an obscure field) so let's take a target density increase of 100% overall.

In this case, the volume of the earth will decrease by 50%, which means the radius of the earth will decrease by about 20%. Note that this will decrease the area of the earth by about 30%, but the surface material density will not increase at all (relatively speaking). This means that the earth's crust will massively wrinkle, with essentially a complete destruction of all surface features.

Worse, the transition from 100% to 80% radius (about 800 miles) will essentially occur in freefall, at least the early stages. This will have two effects: first, everything on the surface will be pulverized by the equivalent of a fall of several hundred miles at 10 times the current gravitational acceleration. Second, the kinetic energy released by the impact will liquefy the crust into an incandescent mass of molten rock. The energy released by the fall of 1 kg 100 km in a 10g field is about 1 MJ, which is enough to raise granite or basalt by more than 1000 degrees K. Since 100 km is about 60 miles, a 20% radius reduction (800 miles) will produce temperatures more than 10 times as great.

When 24 hours is up, the reverse (rebound) effect will occur, with the reduced-area crust ripped apart as the area of the earth increases by 45%. The crust will redistribute over a fairly short period, even if it has cooled to the point of solidifying in the 24-hour grace period - which simply isn't going to happen.

Granted, the 100% density increase is fuzzy at best, but two things should be kept in mind:

1) Since the earth becomes significantly smaller, the pressure increase becomes even greater, since gravitational attraction gets greater as distance to the point of attraction (the center of the earth, in this case) decreases. This will increase the amount of density enhancement.

2) Given the catastrophic nature of the results, even if the density does not increase as much, the effects will remain catastrophic.

• Thanks, and just in time. Astonished noone explored this previously, it seemed to answer all the OP's question's concerns. Much appreciated. Apr 2 '19 at 19:04

Since it is a given that these aliens can manipulate gravity however they like:

Would not be easier just to 'switch off' gravity entirely?

• I am really curious to know how you can delete gravity with a science based method, per question tags. Can you detail that out?
– L.Dutch
Mar 14 '19 at 13:44
• @L.Dutch they take the sciency thing they built to increase gravity x10, and dial it up to eleven, obviously. Mar 14 '19 at 16:08
• They are able to manipulate gravity, but not necessarily with zero constraints as "however they like" seems to suggest Mar 15 '19 at 10:07

If I was the head of Aliens I d rather invert gravity to -1G and happily watch those humans fly into space.

Not sure why this bounty hasn't been rewarded yet but perhaps it is because the answers are not direct enough, so I will give it a shot.

Q1) "Is this sufficient to guarantee the extinction of the human race?"

A1) No, based on your question, you have not detailed if the aliens have accounted for dependencies such as: "Is all of humanity currently on the Earth?" how could they eliminate all human life by only targeting the planet if not all of human life currently exists on the planet? However, increasing the gravity by a factor of 10 would most definitely kill all human life on the planet assuming that humans have no way of altering gravity on their own. The human body can withstand roughly 40 g's:

A man named John Stapp demonstrated a human can withstand 46.2 g's for just an instance. I say 40 g's for the average human (probably an overestimate) because the average human has no training as John Stapp did.

The Earth's gravitational field push's on the surface at 9.8 m/sec^2 == 1 g, 9.8x10 = 98, 98 >> 40.

Q2) Will this also end all life as we know it on Earth?

A2) No, there are many organisms on this Earth which could withstand 98 g's or greater for 24 hours, humans just aren't one of them.

Hope that helps!

• @Agrajag Sure, I went ahead and edited my answer a bit.
– Rob
Apr 2 '19 at 16:10

Nope, they will all die, except for those in space. However, if they are in orbit the orbit may become destabilized and they could die from atmospheric reentry or hurtling into space.