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In my short story ghosts are much like the movie, "Ghost," where they can interact with each other and also have a very tiny bit of power to move something small (like a penny, or slam a door).

However one of my ghosts just pushed the other ghost, who fell through a wall, but my ghosts don't accidentally fall through the floor (or the Earth).

What is a pseudo-scientific explanation for why ghosts don't fall downward?

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  • $\begingroup$ I'm confused... why did you label this as anatomy - the science of living (now or sometime in the past) beings bodies? Or is there another meaning of anatomy I never heard about? $\endgroup$ – Confused Merlin Jun 14 '16 at 6:07
  • $\begingroup$ I don't think this has anything whatsoever to do with anatomy of any kind, and have edited to that effect. (I still think "anatomically correct X" is a lousy question title, FWIW.) If you disagree strongly, feel free to roll back. (I'm also surprised we don't seem to have any tag for ghosts or spirit-beings, so I made one.) $\endgroup$ – a CVn Jun 14 '16 at 7:14
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    $\begingroup$ How would a ghost in a lift behave? $\endgroup$ – Donald Hobson Jun 15 '16 at 15:09
  • $\begingroup$ By the way, you could try to ask Dr Egon Spangler who has theoretical and (sadly) practical knowledge of ghosts. :) $\endgroup$ – Alexander von Wernherr Dec 8 '16 at 17:56
  • $\begingroup$ They do - that's why you don't see them around. They are all stuck together at the earth's core, fueling with their souls the planet's magnetic field. $\endgroup$ – T. Sar Dec 9 '16 at 19:27
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Gravity does not apply to ghosts. Maybe it is because they have no mass, which makes interaction with real-world things difficult. It raises the question though why ghosts move and interact the way we do. Maybe it's habit or convention.

It also makes me wonder how ghosts interact with the real world objects like push them.

Maybe they can willingly choose to not fall through stuff. However when pushed they oftentimes do not react quickly enough, or willingly fall through a wall in order to prevent "hard impacts".

This could be the issue as to why ghosts have trouble moving real world entities. Because they have no mass. However they can willingly choose to collide with other masses, but they have no/barely any counter-mass themselves.

All in all it the following assumptions would make "sense":

  • Ghosts have a mass density of air (drafts can shut down doors or knock stuff over), and can create smaller pressure fields. (Talk about 21 grams, you can use that reference)

  • Ghosts by default do not collide with anything, but can willingly choose to interact with other masses and therefore collide with them.

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  • $\begingroup$ "Ghosts by default do not collide with anything, but can willingly choose to interact with other masses and therefore collide with them." - and since everyone is just SO used to the floor being solid, most ghosts instinctively "choose" to collide with it because they can't even imagine not doing so - or at least not quickly enough while falling $\endgroup$ – Syndic Jun 14 '16 at 11:49
  • $\begingroup$ If gravity doesn't apply to ghosts, shouldn't they be thrown away from Earth by centrifugal force? $\endgroup$ – user8808 Jun 14 '16 at 14:52
  • $\begingroup$ Ghosts have roughly the same density has the air around them, so they would technically float by default. If you want to change the 21 grams to a more realistic number and screw the reference, assuming that the mass of air is 1,9g per liter, and a human on average has about 80l of volume, feel free to correct that to 152g per average human ghost. $\endgroup$ – InstantMuffin Jun 14 '16 at 15:28
  • $\begingroup$ Only if ghosts collide with and displace air $\endgroup$ – Donald Hobson Jun 15 '16 at 15:02
  • $\begingroup$ That would fall under point 2 of my answer. If you like you could make collisions with gases mandatory and not a property by choice. $\endgroup$ – InstantMuffin Jun 15 '16 at 15:08
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Upon disincarnation, consciousness remains, but it is no longer "attached" to the physical body. Consciousness is not made of matter, and therefore is not bound by "two bodies cannot occupy the same space at the same time". No matter means no mass, so no gravity.

So far so good, right?

For some reason, though, the disincarnate mind still retains most, or even all of the memories if had while attached to a body. And here is the thing about not falling through the floor: the living have a habit of not falling past a perceived ground. And habits are harder to break than atoms, so your ghosts stick around because they think that is what is natural, even for ghosts.

If a very pedantic, very physics-savvy person dies and realizes that they are now a ghost, and therefore not bound by gravity, while at the same time remembering that the orbital speed of our planet around the sun is around sixty-seven thousand miles per hour... They would shoot out into space at thrice the escape velocity for Earth's surface. This could be hilarious to some people, though not so much for the poor ghost. Most people don't know [expletive] about rocket science, though, so they don't have this problem.


Let's put a little more science into it.

Planets and stars "deform" spacetime around them. In very laysman terms, that's how gravity works (warning: boring to people who don't like quantum physics), when you think about it in relativity terms. We've all seen graphics like this:

Now let's throw more fantasy science into it.

Ghosts, as well as the living, exist in more than three dimensions - or four, if you count time (but I don't want bring relativity into the topic for now). And the three spatial dimentions are not the only ones distorted by gravity.

Your ghosts move in the 4th, 5th, 6th, up until the nth dimension if you want, and that's how they go through walls. These dimensions are distorted differently by gravity - so rather than accelerating towards the center of mass of the planet, you tend to stay put at the same point relative to that center of mass. That's why ghosts not only do not fall through the ground (and shoot out into space), they also need a willed effort to float up and down.

This could also explain how they disappear in one place and reappear in another. They are moving on other dimensions.

Last but not least, they interact with "physical" objects by reaching out to the boundary between whatever dimenions they are in and the three classical spatial ones. They can never go past the boundary (lack of a body and all), which is why they sometimes have a hard time pulling a respectable poltergeist.

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  • $\begingroup$ Why does the motion of our planet around the sun matter? The sun itself moves relative to other stars, the galaxy moves relative to other galaxies. According to the answers to this Physics.SE question there is no unique rest frame of reference. $\endgroup$ – sumelic Dec 8 '16 at 19:24
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Ghosts of humans are the remnants of humans, and of the human mind in particular. This means that they operate according to the rules of human comprehension. They can only exist in ways that a person can understand or imagine. They stand on the ground and expect to remain standing there instead of sinking, and so that's what happens. They expect to be subject to gravity, also, and so that happens.

If surprised, they might disobey some of these rules by accident, momentarily going through a wall for instance (perhaps because it's more preferable than just passing through the other ghost), but that's much better than sinking into the depths of the earth, an experience basically no human has ever experienced or imagined experiencing.

If a ghost were to spend some time pondering why they are still standing on the ground, well... let's just say that's probably a bad idea.

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Posit that the ghosts have a defined volume (roughly equal to their body's volume, at time of death, less lost parts) and that they have a density equal to that of the ambient air (or very close.) Now they float and have a tiny bit of mass to work with, but only a little bit: Roughly one thousandth their original mass -- and I'll posit that strength similarly scales. So if a man could lift 200 lbs, his ghost can exert ballpark 0.2 lbs, or a few ounces/100 grams.

Giving them the ability to resist being sucked into any nearby open flame or otherwise blown around the planet may be harder. For now, I'll further posit (magical handwavium) that ghosts can Anchor themselves to objects, so as not to be at the mercy of the winds.

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The netherworld in which the ghosts abide does not have walls around them like our corporeal plane has, but it does have a planet under their feet. By concentration, ghosts, mediums and psychics can pull the nether and corporeal worlds closer together so that minor interaction is possible within a local area.

With nothing more than their expectation that they will be seen, ghosts pull the planes close enough that some of the light reflecting of them in their plane passes over into our plane, making them sort of visible. During such times, some of our corporeal side light passes over to them, so they can see our world a little bit too. (Maybe some of the light from our side always bleeds through to theirs, otherwise the ghosts would not be able to navigate our world.)

A little more concentration can bring the planes close enough that sound waves can pass back and forth, allowing ghostly ease-dropping and brief conversations.

With even more concentration, they can bring the planes so close that they can touch and move small objects. But such concentration levels are very difficult to maintain so this ability is never very reliable.

With this setup in place, a ghost would have to concentrate hard to lean on a wall in our world. Most of the time when they try, they fall over and land on the ground. But the ground that they land on is on their plane, not ours.

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    $\begingroup$ But what about a floor. They fall through walls, but not the floor. $\endgroup$ – Mikey Jun 14 '16 at 5:15
  • $\begingroup$ The floor is the planet beneath their feet and it exists in both planes. There is a planet in the netherworld and there may even be some structures which have bled over from corporeal space. Maybe when a building burns down in our world, it becomes real in theirs. If you are asking if they fall through the floor boards, sure they do. But they stop when they hit the ground a few inches below. They don't fall into basements because the basements don't exist in their world. Neither can they climb stairs (unless the house has burnt down and been rebuilt). $\endgroup$ – Henry Taylor Jun 14 '16 at 15:18
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    $\begingroup$ Nah, it would lead to tropes about ghosts only being onnthe ground floor. $\endgroup$ – JDługosz Jun 15 '16 at 17:27
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The reason we don't fall into the ground is because of the electromagnetic force. If the electromagnetic force stopped affecting us, we'd be unable to touch anything. In fact, we wouldn't be able to see or be seen by anything as well, because light works due to the electromagnetic force too.

Sound familiar? Because not only are these properties of ghosts, but of dark matter as well.

Perhaps your ghosts are strange amalgamations of dark and normal matter, able to shift between the two forms at will or instinctively. By turning into "normal" matter, your ghosts are able to interact more with our world. By turning more of their being into dark matter, they interact less (and become harder to see).

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Give your ghosts gravitational but not inertial mass. With no inertial mass there is no kinetic energy. Ghosts can't fall because there is no other form of energy for the potential energy to become.

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    $\begingroup$ This doesn't answer the OPs wall-push example, specifically why the ghost would not fall through the ground. $\endgroup$ – InstantMuffin Jun 15 '16 at 15:11
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Ghost are able to interact with their environment as they like. Most ghosts can slam doors and walk through walls. They can be seen but also remain invisible. And: They can walk on the floor and decide not to fall through. And since it would be considered most impolite to fall through the floor when talking or ghosting.

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