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In my world, a 16 year old boy has gained ghost-like properties, invisible to the naked eye and able to flit through objects as if they were not there. Like a man trapped in a room with an endless expanse of stark white tile, with projections showing him what's happening in the world around him. He passes right through the holograms, but in this story, the boy is technically still there.

When his feet reach grass, he starts free falling to the Earth's core and swings back and forth until he is resting in the exact center of the core.

My question is this: If the boy was suddenly able to interact with the environment once more, what would happen? He is technically taking up the space that the core is, so he would most likely displace it, and I was thinking that maybe, like a gopher's tunnel, there would be an impression in the earth directly above him that looks like his body, because he doesn't instantly get incinerated by the sun. Would this be plausible?

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  • $\begingroup$ That sounds completely implausible. For one thing, he's at the exact center, so everywhere is directly above him. For another thing, his body is completely insignificant in size compared to the rest of the stuff inside the earth. He would just be crushed and it wouldn't affect anything else. $\endgroup$ – sumelic Apr 7 '16 at 22:33
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    $\begingroup$ The idea of the indentation assumes that the Earth's core is incompressible, which is not at all the case. Furthermore, while he wouldn't be "incinerated by the sun", he would be simultaneously melted and crushed by the high temperatures and pressures. $\endgroup$ – HDE 226868 Apr 7 '16 at 22:34
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    $\begingroup$ Why would he come to rest at the center of the Earth if there's no friction to slow his oscillating cycles of speeding up as he approaches the center, than slowing down and halting once he pops out the surface on the opposite side, then falling back down again? $\endgroup$ – Hypnosifl Apr 7 '16 at 22:59
  • $\begingroup$ @Hypnosifl - It's because he's magic. He moves horizontally not because he can apply force (he doesn't interact with the physical world), but because he wants to. When he touched the grass, for some reason he became aware of his height above the center of the earth with no support, so he started falling. He became frightened by his speed, so he wanted to slow down. So he did. And came to rest. $\endgroup$ – WhatRoughBeast Apr 7 '16 at 23:48
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I have two main points.

  1. Compressibility. Your idea of his body forming an indentation rests on the assumption that the Earth's core is incompressible. This is not true. While it is thought to be solid, this does not mean that it can't be compressed. I find it highly unlikely that any sizable indentation would be formed, especially given the size difference: The inner core is about 1,220,000 meters in radius. Your average boy probably doesn't top two meters in height.
  2. Temperature and pressure. Again, working from Wikipedia's numbers, I find that the temperature at the edge of the inner core is about 5,700 K, about as hot as the surface of the Sun. The boy will be burned to a crisp . . . unless he is crushed by 3,300,000- to 3,600,000-atm pressure all around him.

Also, keep in mind that the boy's initial gravitational potential energy at the surface has now been converted into kinetic energy, meaning that he's moving at a speed of . . . oh, I'm not going to do the calculations, but it's really, really, really fast. The result of suddenly finding himself rushing through a solid object at this speed could be compared to building a brick wall across the track during the Indy 500, but that doesn't quite do it justice.

You do say that he's stopped his oscillations, which didn't occur to me when I wrote the above paragraph. However, Hypnosifl's concerns are also my own. There's no mechanism to dissipate his energy if he isn't interacting with anything.

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  • $\begingroup$ Since there is no friction to root him in place, how far would he oscillate each time he came around, and would it eventually stop? $\endgroup$ – White Fang Apr 8 '16 at 4:29
  • $\begingroup$ @WhiteFang Funny thing. You answered your own second half of your question. You said frictionless. Friction is what stops things. Without friction, he does not stop. First half. 42.2 minutes. The answer is the solution to the "gravity train" equation. $\endgroup$ – Aron Apr 8 '16 at 9:36
  • $\begingroup$ The gravity train/boy will be travelling at 7900m/s. So no, hitting a brick wall during the Indy 500 is orders of magnitude off base. Its much closer to turning a Saturn V sideways and launching it into a brick wall. $\endgroup$ – Aron Apr 8 '16 at 9:39
  • $\begingroup$ @Aron And even the Saturn V (or any Earth-orbit capable spacecraft, rather; 7900 m/s is pretty much exactly what you need for low Earth orbit) needed several minutes to get to that velocity. $\endgroup$ – a CVn Jun 27 '16 at 17:54
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The Earth's core is already compressed to well beyond normal densities of the materials, it can and will compress more in response to his emergence. You're not looking at immovable object meets irresistible force, even the small fusion boom from his emergence (nuclei too close to ones that were there) will be a localized effect.

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The guy would vaporize almost istantly and cause a little tiny explosion inside the core due to vapor trying to get away and pressure.

The explosion would have no relevant effect, it'be strong enough to break a glass or burn a piece of papper but nothing more.

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