I am a fan of Doctor Who but last Saturday's episode annoyed me a lot. It wasn't that the premis was bad, quite the opposite it was really cool, but the violation in logic and science made much of the plot nonsensical which ends up making the big climatic decision confusing and stupid.
But let's start at the beginning:
We start off with the shuttle landing on the moon, a task it is not designed or equipped to manage. The shuttle is designed for re-entry to Earth where we have a nice thick atmosphere to slow the descent and nice flat smooth runways for it to land on. The hyper-massive moon from Dr Who has the same gravity as earth but no atmosphere so the shuttle would come in way too fast and would be very difficult to control. Plus its careful coat of heat-resistant panelling is perfect for resisting the heat created by the friction with the air but is no protection from the ripping damage from landing belly-first on pointy moon rocks rather than landing-gear first on a tarmac runway.
But at least our world-in-danger plot is off to a good start, with the Doctor's explanation that a super-heavy moon would cause huge problems on Earth by causing higher tides, which considering 40% of the world's population lives within 100km of the coast would result in lots of death and destruction.
However, the astronauts, who presumably had to factor in the increased lunar gravity into their landing plans, seem confused or surprised that the Doctor would diagnose the problem as the Moon "putting on weight". Strike one! The Doctor brought two companions with him who could have expressed surprise and questioned the possibility of this, one of which is a 15 year old kid, but nope they had the astronaut say it.
Then we have the 'explanation' or more accurately the lack-there-of of their solution to the problem: set off a bunch of nuclear bombs to blow-up.. something... which would of course solve the problem of 'something being wrong with the moon' which the astronauts admit nobody knows what that something is. If we instead say that the astronauts are just a bunch of flunkies that don't need to understand what their mission is about then why are they there at all? Why not just send a remote control robot ship? Surely they can't expect the crew to fix any potential problems or roadblocks to completing the mission if they don't even know what the point of the mission is. Then off we go to the Mexican mining station, where some mysterious thing went wrong then suddenly there were massive high tides on Earth.
The problem is we later find out that the 'thing' that is wrong with the moon is that it was an egg that caused the gravity increase and thus the high tides by growing. If we accept this premise there are still some very fundamental problems. (1) Eggs don't gain mass when the offspring grows/develops inside, eggs are self contained: the embryo grows by converting the nutritious yolk and albumen into the new organism the only inputs into the system are oxygen which is converted into carbon dioxide (gains a carbon) to generate the energy needed for the embryo to grow, as such the egg actually loses some mass while growing. (2) Even if we let that slide because this is some alien-egg so maybe it can somehow create matter as it grows that still leaves the problem of speed. Growth and development takes time so the sudden increase in tides which caused so many problems wouldn't have been all that sudden. Indeed later on the Doctor says it has been growing for a hundred million years. (3) There is never any attempt to explain what any of the egg-business had to do with the Mexican mining station, rather the thing that went wrong is revealed to be just an attack of bacteria-spider-mite-things which just happen to be living on the moon-egg. So I guess that was all just a coincidence?
The moon-walk is also the first introduction of the idea that the natural disaster on Earth wasn't super-high-tides like the Doctor suggested but that it was "high-tide everywhere at once". Firstly high-tide everywhere at once wouldn't actually cause anymore damage than regular high tides (unless those tides were unusually high) so it most certainly wouldn't be the "greatest-natural disaster in history". Secondly, that's not how tides work. To have high-tides everywhere at once you'd actually be talking about a massive flood (a la Noah). Tides exist because the moon's gravity pulls on the water in the oceans causing the water to flow toward it and bulge out slightly toward it (because the earth is more of less spherical water on the opposite side will also flow together into an opposite bulge). So increasing the mass (and thus gravity) of the moon would just cause more extreme tides (higher high tides and lower low tides) but still keep the 12h pattern and thus that only part of the earth would experience high tide at any one moment.
Then we have another hilarious scene of conversation between the astronauts where they reveal not knowing how to even turn on the nuclear weapons which appears to be the only reason they are on the bloody mission?! Again if this is the 'biggest natural disaster in history' you would think they could find some competent people to send on the mission to save the day? Instead we get a throw away comment that it is a 2nd rate shuttle and 3rd rate astronauts off on this mission to save the world. Then we get some more space-exploration incompetence with the fact that the Mexicans put the expense and effort into building a permanent mining base without confirming there actually are minerals worth extracting.
Next we get the revelation that the Moon is in the process of falling to apart. Because apparently the geologist working on this mining project didn't notice the moonquakes or new gaping fissures opening up on the surface. Now presumably the plan was to use the nuclear weapons to blow-off a chunk of the moon to reduce its mass and restore normal moon-gravity to get rid of the abnormally high tides which are causing destruction, so news that the moon is breaking apart on its own should be a happy surprise!
But before anyone has time to realize this we have a germ-spider-thing attack and the stupidest thing in the whole episode happens: our rebellious teenager Courtney (who ends up having more of a clue about what is going on than the astronauts) starts floating like a hot-air balloon only a few feet away from the rest of the group who are still experiencing earth-normal gravity. Now if this was a spaceship/space-station with artificial gravity that would be one thing, but no the whole episode is about the fact that the gravity is due to the super-massive moon, so it is completely impossible for that gravity to just disappear in one small location while remaining unchanged just a few feet away. The Doctor later explains this away as the creature inside the egg moving which 1) would cause just a slight decrease in gravity not enough to cause a person to float off the ground weightless and 2) wouldn't be so tightly localized, everyone should have been floating not just Courtney.
After Courtney kills the germ-spider thing by spraying it with disinfectant, which again wouldn't have worked because disinfectant kills germs and not people purely because of the size difference (drinking bleach will kill your insides just as effectively as wiping a counter with it kills the germs) and these germs are the size of a badger, we get one of the best/worst lines I've heard the Doctor spout to date: "it's a prokaryotic unicellular organism with non-chromosomal DNA". This is just so wrong on so many levels (1) it can't be unicellular because to be able to run around requires communication which is much faster and more efficient than any known intracellular mechanisms. Animals can walk and run because they have nerves which act like electrical wires. Transmitting electricity requires an isolated insulated system to funnel and guide the charge, requiring a separate cell. (2) Prokaryotes have chromosomes, sure they often look very different from eukaryotic chromosomes (often circular, are a lots smaller etc...), but they are still chromosomes! What prokaryotes don't have that eukaryotes do is a nucleus where the chromosomes are stored separate from the rest of the cell. (3) Not all germs are prokaryotes, for instance the germ that causes malaria is a eukaryote. Thus the fact that disinfectant spray killed the organism does not tell you whether it is a prokaryote or a eukaryote but actually indicates a particular sensitivity to something in the disinfectant because such a small amount on such a large organism shouldn't have been enough to kill it.
Lastly we have the transmission to Earth, and voting by lights. Again we are reminded that things a getting 'pretty bad' on Earth in some unclear indescribable way for who knows what reasons. Then Clara asks the world for their opinion but providing them pretty much no information to base the decision on and asking them to vote by turning their lights off or leaving them on because for some unexplained reason they won't be able to communicate with Earth again. Problem is lights are only visible on the night side of the Earth which of course means only the half of the planet where most people are probably sleeping can vote. Plus a large portion of the light is from street lamps or spotlights or signage which are automated control so couldn't easily be turned off. The blanket blackness seen in the episode only happens when there is a mass power outage. However if things were getting 'pretty bad' because of huge tides flooding many major cities surely the power grid would be pretty severely affected because of powerplants having to be turned off because of flood damage (see Japan post-tsunami), so many lights probably wouldn't be under anyone's control anyway so this 'voting' isn't going to work at all.
To be nit picky I could also point out that the liquid within an egg is not amniotic fluid it is 'albumen' and the fact that Courtney is still sitting the right way up unhurt after the shuttle and the TARDIS fall nose first into a crevasse.
These logical/scientific failings ruin the climax and the ethical dilemma because it isn't clear what the consequences are of each choice. What exactly is the cause of the problems on Earth and how would setting off the nuclear weapons solve it? Wouldn't the moon hatching solve the problems on Earth or would it get ride of tides completely and cause a whole other set of problems? The astronaut suddenly seems worried about bits of the moon flying off and hitting the Earth but surely that was part of the plan for the nuclear weapons? Also couldn't they wait until after the thing hatched before setting off the nukes, the bombs are still going to be sitting there in close proximity aren't they? Didn't the drilling and cracks let the bacteria-spiders into the egg to rot & kill the thing living inside it (the Doctor made it into the liquid around the embryo)? If the audience doesn't understand the stakes they won't care about the outcome of the decision.
If they wanted to have a kill or don't kill decision why not just set it up as Russians or Americans secretly militarizing the moon when it starts to hatch or have a moon-base powered by a nuclear reactor with artificial gravity generators. That would give you the means to kill the creature, and a reason for people to be up there without all the contradictory nonsense about tides and gravity.
