Theory:Doctor Who television discontinuity and plot holes/Kill the Moon


 * Mass is constant. That means that the moon will not have grown any larger or gotten heavier. That the moon "gained weight" because the creature grew larger suggests that mass was created out of thin air, which is impossible.
 * Remember that mass only remains constant if there is no change to the object itself. Since the creature grew larger, its mass would obviously increase. However in this case, the subject of mass does not apply here, since we're talking about the moon gaining weight. Mass and weight are not the same, as weight is affected by the force of gravity. Since the creature grew larger, its weight would obviously have increased, which in turn affects the moon's weight as well.
 * The problem is still there. Where did that extra mass come from? The creature growing larger would only increase its volume. The gravitational effect of it would actually be smaller on the moon's surface since they would be further from the centre of mass, and some of the mass would have spread further away, unless extra mass was added. Where did that mass come from?
 * maybe the moon was hollow to an extent. This would allow for an increase in mass due to dividing cells in the womb.
 * The problem is not the necessary space into the moon core, but the fact that matter cannot be created from nothing. In fact, when a single cell splits into two cells, the sum of the two cells mass is equal to the mass of the original cell. So, the extra matter can only be gained if the creature has "eaten" something, maybe even energy (solar ?) then converted into matter...
 * That is probably the case. Being an alien egg, we have no idea how it works.