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.
 * Most eggs have a slightly permeable outer shell that allows small particles, like oxygen and CO2, to pass through it. Perhaps this alien egg indeed had absorbed bits of space dust, or solar energy, or even neutrinos over 100 million years through a similar permeable outer shell.


 * This story has several scientific errors: The moon is not hollow, eggs do not have lactic fluid, spacefaring creatures would not need wings and a creature cannot lay an egg that is bigger than itself. Furthermore, the establishing that the moon is an egg is a continuity error with several earlier silurian stories
 * Not true. A) The whole point of this episode is that until 2049 we didn't know the moon was hollow. It seems like ti isn't, and we have no reason to think it is. That might change in 2049. B) The Doctor specifically said it was amniotic fluid, not lactic fluid. (How he knows that from dipping his yo-yo in it is a different problem.) Certain eggs do indeed have an amniotic shell holding in nutritional fluid (see http://www.biologyreference.com/A-Ar/Amniote-Egg.html). C) Not sure where you are getting your information on the needs of spacefaring creatures. They could very well need wings. Perhaps they unfurl and act as a solar sail to ride the solar winds. Perhaps they are useless in space, but the creature spends a portion of its life cycle in an gas giant like Jupiter and using its wings then. D) No one said how big the new egg-moon was, and there was certainly nothing to suggest it was bigger than it used to be (ie the size of the creature.) Perhaps it was smaller. Additionally, it was never shown how the new egg formed. It didn't have to be 'laid' in the traditional sense. Maybe those wings weren't wings at all, and they were really parts of the eggshell. The create could have deposited a tiny zygote in space, and then wrapped it's "wings" around it creating the shell in which the baby grows, and then flew off without wings.


 * 1.3 billion tons is not enough to increase the moon's gravity to match that of Earth
 * Maybe it didn't. Maybe it just had enough of an effect to make a noticeable difference, but it was still less (ie 2/3 Earth gravity instead of 1/6).


 * When the lights go off, we see that the night side of the planet is facing the moon, but shortly after we see the moon hatch and it's day on Earth
 * There are no evident problems with the tides on the beach at the end of the episode.
 * Perhaps the beach wasn't a beach. Maybe the tides had already swelled and flooded a previously landlocked area and it WAS a "high tide". Instead of them standing on the beach in Dorsey, they were really standing on top of the Dover cliffs and it just looked like a beach.