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Let's say some magic aliens come and prank us. They, in one step, remove out the innards of the earth, and put everything on the surface on the inside. They make some artificial gravity so we stay on the surface. They also put a giant light bulb in the middle that acts like the sun. Besides the artificial gravity, its physics as normal.

What would happen? Short term and long term.

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    $\begingroup$ Your aliens are mean. $\endgroup$ – Jimmy360 Jun 3 '15 at 1:15
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Short term: Pain and Zero Gravity

This lightbulb would keep heating your sphere. How would heat escape. Heat flows from hot to cold. As long as the molten outside layer is hotter than the inside, the layer with humans will get extremely hot. The only form of cooling will be radiation, but it will be slow because the outside layer will absorb it. Also, the outside layer will not cool quickly due to radioactive decay. There are radioactive isotopes in the earth's mantle. There decay will continue to heat the mantle and to bake us alive. We would either be weightless or we would have to stand on the lightbulb, depending on how massive you have made your lightbulb. This is due to Newton's Shell Theorem. It says that in a hollow sphere, gravity cancels out, making the inside experience zero gees.

Short term: Death

The heat on the inside would bake the earth. Everyone dies. Your aliens turned the earth into an oven.

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  • $\begingroup$ What if its an LED lamp, that doesn't produce much heat? $\endgroup$ – PyRulez Jun 3 '15 at 1:20
  • $\begingroup$ @PyRulez The radioactive heating of the mantle would still lead to death, although more slowly. $\endgroup$ – Jimmy360 Jun 3 '15 at 1:22
  • $\begingroup$ What about artificial gravity? $\endgroup$ – BartekChom Jun 3 '15 at 10:40
  • $\begingroup$ @PyRulez A LED light, aside from the minor detail of putting out different amounts of light in different directions (let's handwave that away), luminous enough to illuminate the surface of the Earth from the distance of Earth's core, would still be putting out quite a decent chunk of light. LEDs are efficient light-producers compared to other types of light sources available to us at present, but that will still be quite a bit of heat. With nowhere really for the heat to go, the result will be the same. $\endgroup$ – a CVn Jun 3 '15 at 13:00
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Gravity, whether artificial or not, falls off as the square of the distance. That means the inside will be zero-g, even of you lined the rind with superdense matter (or artificial equivalent).

I think if the gods or aliens did what you describe, it would require a lot of subtle details to make it work at all. So wouldn't they make make "everything" work, as part of the total effort?

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    $\begingroup$ If the artificial gravity is made for us to stay on the surface, it should not leave us weightless. Maybe the gravity force will be directed to the outside, e.g. the bulb in the middle will have negative mass. For each spacetime curvature, there can be stress–energy tensor that allows for it, even if very strange. $\endgroup$ – BartekChom Jun 3 '15 at 10:47
  • $\begingroup$ Good point: negative gravity would do it. So would some way of bending spacetime that falls off faster than the square of distance. Although GR can describe arbitrary curvatures, is there any arrangement of mass-energy on the "wood" side, or what new type of wood would be necessary? $\endgroup$ – JDługosz Jun 3 '15 at 18:51
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It depends if you mean that you turn it inside out like one of the rubber poppers or the molten lava on the outside and the surface in the inside. If you live in the inside or the outside then it really depends. if you live in the inside, the earth won't be the same cause you can't see anything and your sun is shining another son, aka the molten lava and the plants will die with no sunlight (Vitamin D). If you live on the molten lava side

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