A spaceship (internal pressure and temperature to standard Earth sea level conditions) is in interstellar space enroute to Arcturus. It is manned by space aliens who are balloon shaped and filled with helium. As the spaceship accelerates in one direction at a value equal to gravity at the surface of the Earth, which way do the space aliens move relative to acceleration? Hint, if the spaceship lands on the surface of the Earth its occupants are subject to the effects of the Earth’s gravitational field. This causes the space aliens to float about the ceiling of their spaceship just as a tethered helium filled balloon. The spaceship, enroute to Arcturus, experiences explosive decompression resulting from a skin rupture. Which way do the space aliens move relative to acceleration? Select the correct answer below.

In interstellar space, the gravity field is very weak. The principle of equivalence, from the relativistic theory of gravity, postulates that a uniform pseudo-gravitational field exists in the opposite direction of acceleration for observations conducted in an accele-rated chamber. Events that take place in a real gravitational field will be experienced in an artificial field as well. (See Figure 25 .) Thus, the aliens move in the direction of acceleration before explosive decompression. After explosive decompression, the aliens are now heavier than the vacuum introduced from the outside and therefore move in the opposite direction.