In this XKCD What If, an indestructible hairdryer outputs 2 GW of power, turning the earth under it into gas:
Periodic explosions of gas beneath the box launch it into the air, and it starts fires and forms a new lava pool where it lands.
At 20 GW:
The box begins to be tossed around by the powerful updrafts it’s creating.
Later it outputs 11 PW, turning the surface of an entire lake into plasma and launching itself into space:
Is this really accurate, though?
The energy is being emitted isotropically, so the energy itself shouldn't cause any net thrust in any direction, right?
If the object were surrounded by a fluid on all sides, would there be net force upward? Due to creating convection currents that push upwards against it? Does this depend on the density of the object?
Or does the thrust upward only exist when it's on a boundary between air and earth/water? The liquid/solid material below the box is greatly increasing in volume due to the phase changes, while the air above is not changing in volume as much, so the gases and plasma are rushing upward overall and carrying the box with it?
But that effect would drop off with height, leading to the case of it being surrounded by air on all sides again.
In what conditions does the superhot object launch upward into space, and in what conditions does it melt its way into the center of the earth?