  Normally one thinks of the motion of the planets around the Sun as a highly
classical phenomenon, so that one can neglect quantum gravity in the Solar
System. However, classical chaos in the planetary motion amplifies quantum
uncertainties so that they become very large, giving huge quantum gravity
effects. For example, evidence suggests that Uranus may eventually be ejected
from the Solar System, but quantum uncertainties would make the direction at
which it leaves almost entirely uncertain, and the time of its exit uncertain
by about a billion billion years. For a time a billion billion years from now,
there are huge quantum uncertainties whether Uranus will be within the Solar
System, within the Galaxy, or even within causal contact of the Galaxy.
