 PLOT: When Cal and Ruth are on the ship, some of the aliens are  leaving the compression tubes in preparation for Metalunas  atmosphere. Cal and Ruth then go into the tubes to undergo the same  process. But, if Cal and Ruth were not yet compressed, and the  aliens were, they should not logically be able to be in the same  room at the same time, as the pressure would not be hospitable to  one group or the other.