The Keys of Marinus

I wouldn’t think of asking you to travel in such an absurd way.

Teleportation – moving from place to place near-instantly, without having to travel through the intervening space – has long had a hold on the human imagination. From the Arabian Nights to the Ring Cycle, it appears as a magical ability to disappear here and reappear there, and is still invoked in this way by various mystics to this day (as well as, bizarrely, being studied seriously by US military intelligence). Even when it comes into science fiction, it is at first as a mystical or psychic power, whether as John Carter’s sudden trip to Mars or Gully Foyle’s jaunting.

But science fiction inevitably seeks to translate mystical marvels into technological devices, and teleportation is no exception. It’s most famous from Star Trek, of course, and apart from a few sad fans no one knows or cares that Doctor Who got there first.

So how could the technology of teleportation work?

Naively, you could imagine doing teleportation by measuring the position and all the other properties of every particle in the body, then transmitting that information to somewhere else where the body is reassembled. This is the usual explanation of Star Trek-style teleportation. It is, unfortunately, impossible. It’s generally said that this impossibility is due to the Heisenberg Uncertainty Principle, which says that physical variables at the quantum level come in matched pairs, such as position and momentum, and the more accurately you measure one the less accurately you can know the other. This is quite true, and in itself a fatal blow to this model of teleportation (one which later Trek series hilariously handwaved away by invoking “Heisenberg compensators”), but there’s a deeper version of this idea that we need to understand before going on to see how quantum teleportation can work.

In quantum mechanics, systems of particles exist in quantum states, which cannot be measured directly. A single measurement only gives us partial information, and it destroys the quantum state in the process. If you have a load of systems in the same quantum state you can measure all of them, and build up an approximate description of the underlying state – the more of these systems you measure, the more accurate the description. What you can’t do is directly measure the complete quantum state of a single system, such that you could then transmit that information somewhere else and recreate the system.

Quantum teleportation solves these problems, but with some restrictions and subtleties. It involves the use of particles that have been made to interact in some way so that they are each part of the same quantum system, then separated such that they are still part of the same quantum state even though they are some distance apart. This is called entanglement.

Imagine a setup where two people, let’s call them Arbitan and Barbara, share in advance a pair of particles that have been put into an entangled state. Now Arbitan has a third particle, that is in some quantum state of its own. This is the particle he wishes to teleport. By making certain cunningly-contrived measurements on this third particle in conjunction with his entangled particle, Arbitan manages to extract a set of information about his combination of particles, which he sends to Barbara by conventional means. Barbara can then use this information to put her half of the entangled pair into the same state as the particle that Arbitan wanted to teleport. So the net effect is that the quantum state of Arbitan’s particle is destroyed, and transferred to Barbara’s particle. Crucially, it is the complete quantum state that is transferred, not just the partial information that Arbitan could glean by measuring his particle’s quantum state directly. That’s really the clever bit.

An interesting philosophical wrinkle here is that it is not quite right to say that a quantum state is transferred from one particle in Arbitan’s possession to a different particle in Barbara’s possession. Elementary particles are indistinguishable from one another. Electrons aren’t like cars. Even though cars are mass-produced and come in production runs of apparently identical cars, there is a real sense in which my dark blue Vauxhall Astra is not the same as your dark blue Vauxhall Astra, even before they get scratched and grimy and the passenger sides covered in the muddy footprints of our respective spouses. Electrons are different. They don’t have number plates or identifying marks. If we each have an electron, and we swap them, the electrons remain in the same physical state: as far as the laws of physics are concerned, nothing has changed. This is really, really important. The behaviour of matter depends on how electrons and other particles behave as a statistical aggregate, and those statistics become very different if this isn’t true. Among the many, many things that depend on this are semiconductors, such as the chips that drive the computer or phone or whatever device you’re using to read this blog.

The upshot of this, as far as teleportation is concerned, is that there’s no sense in saying “you haven’t teleported the particle, you’ve just transferred its quantum state to another particle far away”. These two things are identical.

We also don’t need to worry about this apparent duplication process giving rise to multiple identical copies. Arbitan’s measurement destroys the quantum information in his version of the system – there is only ever one copy at a time.

There is still the question of  – assuming we can scale this up from the spin state of one particle to the entire quantum ensemble of 1029 particles that make up your typical living, breathing human in such a way that the teleported person is still living and breathing at the end of the process – whether the teleported person (let’s call her Susan) is copied as a single, continuous entity or whether she is killed by Arbitan and resurrected by Barbara as a new person with only the memories of the original Susan. The argument that the particles are indistinguishable, so she should just chill out, might not seem so compelling to the Susan in Arbitan’s clutches, as she experiences her quantum information being destroyed. It’s as much a question of philosophy as physics, and it’s philosophers we turn to for an answer.

In a recent survey of 931 philosophers, one of the questions they were asked was precisely this: does teleporting Susan result in her death and the creation of a copy, or her survival in Barbara’s far-off location? The results were as follows:

Survival: 36.2%



I guess that’s why they get paid the big bucks.

Now there are three big restrictions on this kind of teleportation. The first is that Arbitan still has to send the results of his measurements to Barbara before she can perform the teleportation at her end. That’s maybe not such a big deal, but it does mean that you can’t use this to travel faster than light. The second is that Barbara has to have a suitable supply of appropriate particles to complete the teleportation. Easy enough if we’re talking about individual electrons, but quite how you would store and use the raw material for a complete Susan is a trickier question.

The biggest problem of all, though, is that this can only work at all if Arbitan and Barbara have previously shared between them enough particles in entangled quantum states to allow them to do the teleport at all. And each entangled pair is a one-use, disposable item – when they’re gone, they’re gone and Barbara has to go back to Arbitan the slow way so they can share another batch. This means you can only teleport between pre-arranged locations that have been visited by someone carrying entangled particles from the home station, and these need to be resupplied or else they will run out of entangled particles and become useless.

Let’s be honest, it’s starting to sound a bit shit.

Could there be another way?

In the post for An Unearthly Child, we talked about distorting spacetime with the use of exotic matter. We can do something similar for teleportation.

The idea, basically, is to cut out a small region of spacetime at the departure point, and an identical region of spacetime at the arrival point, and join them together so that they become one. You then have a portal in spacetime through which you can simply step from one region into another.

Physicist Matt Visser has done a lot of work on these sorts of traversable wormholes. In one of his papers he lays out a simple design: a cuboidal frame into which the traveller can step and be instantly transported to another place. The edges of the frame are made of exotic matter, and the clever bit is that all the immense stress-energy needed to rupture spacetime in this way is concentrated along these edges: as long as you just step through the faces of the cuboid, you should feel no ill effects.

This is a crucial piece of progress. Most wormholes, such as those that may be created by rotating black holes, subject anyone who comes near them to such overpowering tidal forces that the hapless traveller becomes, in general relativity jargon, spaghettified. Which is about as pleasant as it sounds. If any wormhole is to be actually useful for travel, it must be set up so as to avoid this danger.

That said, it’s still not something that we have any idea how to set up in practice. How to manufacture exotic matter with negative mass is still an open question (though one that we may return to for The Evil of the Daleks), as is the amount of such matter that would be needed to create this frame. Visser’s earlier calculations suggest that making a human-sized frame would require a quantity of exotic matter roughly comparable to the mass of Jupiter, though he reckons he has since come up with a way to do it with much less.

These niggling technical details aside, this kind of travel through wormholes – let’s call it “classical teleportation” – has real advantages over the trendier quantum teleportation. There are no questions of whether you are killed in the process, for a start: you simply step through the portal as if you were stepping through a door, and any philosophical questions about whether you are the same person on the other side of the teleporter become no more pressing than the question of whether the you that gets off a bus is the same as the you that got on it. (In other words, actually quite a tricky philosophical problem if you think about it, but not one that keeps most people awake at night.) Also, we don’t have to worry about continually replenishing the supply of entangled particles to keep the process going: once the wormhole is set up, you can go back and forth as much as you please, and if you want to close it and reopen it somewhere else you just need your original supply of exotic matter.

So perhaps we should assume that the travel dials that Arbitan provides to our time travellers somehow generate a frame of exotic matter that punches a hole in spacetime that opens out onto the destination. To my mind it’s a more pleasing solution: having teleportation work along similar scientific principles to the Tardis gives a pleasing sense of coherence to this science-fictional world. Which, let’s face it, is more than can be said for Terry Nation’s plots.

Marco Polo

We shall all die of thirst.

A body lies in the desert sands. A desiccated corpse, stretched out in the vast, baking emptiness. A lost traveller, found by chance. Found too late.

The body has scant clothing and few possessions. Everything that was not essential long since discarded in the exhausting struggle against the desert heat. Only one precious object remains – a water bottle.

It’s still half full.

This is more common than you might think. People often die of thirst in the desert long before they run out of water. This is because they make the mistake of rationing their water supply. It seems like common sense: you only have so much water, and you want it to last as long as possible. But if you’re sweating water out and not replacing it, you will get more and more dehydrated, and eventually die.

Water isn’t like food. If you ration out your food, you’ll feel hungry, sure, but you can keep going for a very long time while taking in fewer calories than you are expending. Your body just starts using up its reserves, extracting energy from stored fat to make up the difference. You lose weight, but you stay alive. Even when all the fat is gone, your body will keep going by cannibalising its own muscle tissue. In the end, of course, you will die if you don’t get enough food, but if you carefully eke out your remaining supplies you can put that day a long way off.

When it comes to water, you have much less room for manoeuvre. Your body temperature must be kept within a fairly narrow band, within about half a degree of 37 °C. If it gets much higher than this, you begin to suffer heat exhaustion and eventually, if it gets past 40 °C, heatstroke. At this point, you either get emergency medical treatment to cool you down rapidly, or you die. (Getting too cold can be just as dangerous, but we won’t deal with that here.)

There are three main ways a body can lose heat: radiation, convection and evaporation. Of these, there’s not much your body can do about the first two. The rate at which a body radiates heat is (to a good approximation) simply a function of its surface temperature and surface area, and there’s not a lot you can do to change those. Convection is a little more hopeful. This is when your body transfers heat to the air next to the skin, and as the air moves the heat is carried away. A good breeze will help with this, if you can find one, or a fan – although fanning yourself will generate more heat than it carries off. When you’re in the desert, your best bet to maximise convection is to wear loose clothing and hope for the best.

That leaves evaporation. Your body emits droplets of water from the skin, and as these evaporate they carry away heat. Crucially, this is something your body is able to control directly, increasing the rate of water emission in response to heat, so as to keep its core temperature within that narrow band of safety.

In other words, when it’s boiling hot, you sweat buckets.

This brings us to the crucial point. You need to sweat a certain amount to prevent heatstroke, and if you deprive your body of water you deprive it of the means to regulate its temperature. There is no sweat reserve that your body can use in an emergency, as it uses up fat reserves when food is scarce. If you sweat out more water than you drink, you will die pretty quickly. And before you die you’ll suffer the early symptoms of heatstroke, including confusion and disorientation, making it all the harder for you to correct this mistake in time.

So you shouldn’t ration your water, but when you’re out in the desert and you use up your water you’re going to die anyway, so what should you do? Apart from “be somewhere else”, which in fairness is the obvious solution.

The answer is to reduce your body’s need to sweat. That way, you can keep going longer with less water, because your body isn’t using so much to keep its temperature down.

The single simplest way to do this is to rest and sleep during the hot day, in as much shade as you can find or contrive, and do your travelling in the cooler periods of early morning, late evening and night. Keeping your mouth closed as much as possible will help you to retain moisture – one traditional trick is to suck on a small, smooth round pebble. It also helps if you can avoid eating: digestion requires water, and you need to save as much of your water as possible for sweating.

You should certainly avoid the temptation to drink your own urine. Your body will just use up even more water trying to flush out all the excess salts you’ve just consumed. That’s not to say your piss is useless, however. If you can save it up until you are ready to rest for the day, then pee into some small depression and rest on top of it, the damp ground will help to keep you a little cooler.

We don’t see these techniques in use when Marco Polo is dragging our time travellers through the Gobi Desert, and in some ways that’s just as well. The sight of the Doctor settling down for the day in a bed of his own piss might have been educational, but it is unlikely to have been welcomed. Instead, our intrepid heroes manage to survive by extracting water from their surroundings using the phenomenon of condensation.

There is a way you can do this in the real world. It’s called a condensation trap, and it works like this. Dig a decent-sized hole, about a metre across, deep enough that it goes down into damp ground. You can even pee into the hole for extra moisture. Pop a cup down at the bottom of the hole, somewhere near the middle, and cover the hole with a clear plastic sheet. Make sure the sheet is weighted down with stones all around its circumference so as to seal the hole, and place a rock on top of the sheet above the cup. Then wait.

As the sun heats the damp earth, water will evaporate, then condense on the underside of the plastic sheet. It will drip down from the low point created by the rock, and be caught in the cup. At the end of the day, uncover the hole and have a good drink.

It’s a sound enough theory, and popular in survivalist circles, but unfortunately it’s not all it’s cracked up to be. It generates water, sure, but you’ll be doing well to get more than 100 ml or so out of it – and you’ll sweat out more than that digging the damn thing in the first place.

Still, this seems to have provided the inspiration for the Doctor’s life-saving discovery of condensation in the Tardis. And it also gives us some indication of why that doesn’t seem to make a whole lot of sense. For a start, you need a source of moisture, and it’s not clear where that is coming from in the Tardis. (Viewers of later series might suggest the Tardis swimming pool, but if the Tardis has a swimming pool at this point then why not just drink directly from that?) Secondly, how do you collect this condensation from the Tardis walls? Mop it up with J-cloths and wring it out into a pint mug? All suggestions gratefully accepted.

So if you must head out into the desert, plan ahead to avoid having to resort to these desperate measures. Take enough water for your daily consumption, and enough transport to carry it all. And avoid travelling with sinister villains if you can at all help it. That never goes well.

The Edge of Destruction

What is inside, madam, is most important at the moment


The Belgica, marooned in Antarctic ice

In 1898, the Belgian Antarctic Expedition ship, the Belgica, spent eight desperate months trapped in polar ice. The entire crew became depressed, demotivated, hardly able to work or even to sleep. One man became convinced his crewmates were trying to kill him, and would sleep wedged into a small recess in the ship so as to remain hidden. Another became deaf and mute through psychosomatic illness. Only through the unstinting efforts of the ship’s doctor, Frederick Cook, were the crew able to shake off their maladies enough to blast the ship free of the ice and escape their terrible frozen prison.

Antarctic science is now a well-established part of national research institutions across the globe, and yet with all this professionalism things still go wrong. A study of Antarctic researchers in 1957-8 found that several experienced fugue states, leaving their quarters then coming back to consciousness some time later in another part of the station with no idea how they had got there or what they had been doing. In 1979, one crew member at South Pole station burst into the galley wreaking havoc with a two-by-four, smashing up crockery and his apparent rival for the affections of a female colleague, before charging out berserk into the freezing polar darkness. And there are many more tales that are not in the public record, as you’ll find out if you go for a few beers with an Antarctic scientist.

With the advent of space flight, these breakdowns took on a new importance. The psychological challenges faced by Antarctic researchers, and people in other confined environments such as nuclear submarine crews, have long been used as models for the stresses to be expected in long-term space travel. Since the advent of long-duration space missions on the Russian space station Mir, followed by the International Space Station, psychologists have real data from astronauts and cosmonauts to add to their insights from terrestrial observations about how human beings can cope with extreme isolation.

To be cooped up in a tiny space with a small number of other people, who you may not know well and certainly might not like very much, is bound to be tricky, as even a cursory viewing of the Big Brother franchise will indicate. Really, the remarkable thing is not that people in these environments sometimes crack up – it’s that so few of them do.

Simply being stuck inside a glorified tin can is bad enough. In the early days of the US space programme, the astronauts who were due to fly the Mercury missions insisted that the capsules should have windows. This developed into an almighty tussle with the engineers, who quite sensibly pointed out that windows would weaken the structure and the astronauts didn’t actually have anything to do in flight that would involve seeing outside. But the astronauts won, and became the first Americans to see Earth from orbit. Window time remains a valued necessity on the ISS, and even on submarines crew members are given scheduled periscope time to catch a precious glimpse of the world outside. We humans have a deep need to see the wide world: in one experiment, it was found that even paintings can have psychological benefits to isolated crews, provided they are realistic depictions of spacious landscapes. Antarctic research stations are at least well supplied with windows, but the frequent white-outs at Halley, the British station on the Brunt ice shelf, gave rise to the blank, distant gaze known as the “Halley Stare”.

It’s how people get on in small, isolated groups, though, that really interests the psychologists, and that’s where the biggest problems can lie. Whether at the poles or in space, living and working for months on end with the same few colleagues can foster intense solidarity and friendship – or resentment, bitterness and misery.

The International Biomedical Expedition to the Antarctic was a comprehensive study of how human beings cope in Antarctica, both physically and mentally. It followed twelve men on a 72-day traverse of the polar plateau in French Antarctic territory, with laboratory studies before and after the expedition. On the trip, serious group conflicts and tensions arose: some individuals found themselves ostracised due to nationality, and the observers even had to step in and intervene when the resentments got to the stage of scientists threatening to disrupt their rivals’ experiments. The mutual animosity persisted for many years after the study.

As you may have noticed, this was an all-male group. There were understandable reasons for that at the time – the study required experienced polar researchers, and in those days that was an overwhelmingly male activity, but these days we would expect a mixed-sex crew by default. Whether the presence of females increases or reduces the conflict level within the group depends one one major factor: whether or not the men are sexist arseholes. In one notorious case, a female cosmonaut boarding the Mir space station was greeted by her male colleagues presenting her with a dustpan and brush, with an announcement that she would be doing all the cleaning. As far as I can tell, her response is not recorded.

In less misogynistic teams, female members often play a positive role as mediators and peacemakers within the group, helping to reduce tensions and improving the group’s performance. Indeed, studies in isolation experiments have shown that all-female teams perform at least as well as, and often better than, all-male teams, with more sensitivity to individual concerns and less macho bullshit. Having settled the argument about whether women should be on long-term isolation missions, perhaps we should start asking  whether men should.

The size of the crew is also important. A larger group is generally better than a smaller one, as individuals are less likely to find themselves isolated or singled out, and an odd number of members is better than an even number, as it reduces the potential for deadlock in joint decision making. Clear leadership makes a big difference: the leader’s role must be well-defined, with no confusion as to who is in charge, and he or she must make decisions that the group can understand and go along with. Above all, there must be only one leader: one consistent finding is that there are problems if two crew members have a high need for dominance.

All this matters, not only because these people are stuck with each other for an extended period, but because they are in a dangerous environment in which they have to perform complex technical tasks. Individual psychological problems or toxic group dynamics only serve to increase stress. This can cause acute psychological reactions, psychosomatic illness such as fatigue or apparently inexplicable pain, and may end up with people making mistakes under pressure, with serious or even fatal consequences. Keeping busy helps, provided it is meaningful work: it’s when you’re bored that you begin to notice your colleagues’ annoying habits and irritating mannerisms.

Having said all this, severe emotional or behavioural problems are uncommon in astronauts. This is probably because they are highly screened before being allowed to go into space, and those who are unlikely to get on with others don’t make it onto the launch pad. In less highly screened isolated populations, such as Antarctic winterers, severe emotional problems have occurred at a higher rate than in the general population.

But all these isolated environments are still at least within sight of Earth. People are still in touch with home in some fashion, however distant. The psychological impact of being totally cut off is still not understood – but it could be devastating. According to astronauts, the direct visual link to Earth is of immense importance. It is not known what the psychological effect will be of this link being broken for extended periods, such as on a human mission to Mars. In Space Psychology and Psychiatry, Kanas and Manzey speculate: “At a minimum, this experience will add to the feelings of isolation and loneliness within the crew. Beyond that, it seems possible it will induce some state of internal uncoupling from the Earth, Such a state might be associated with a broad range of individual maladaptive responses, including anxiety and depressive reactions, suicidal intention, or even psychotic symptoms such as hallucinations or delusions. In addition, a partial or complete loss of commitment to the usual (Earth-bound) system of values and behavioural norms may occur. This can result in unforeseeable changes in individual behaviour and crew interactions.”

So in the light of all this, how does our Tardis crew stack up in terms of psychological risk?

We have a small, even-numbered group. There are cultural divisions – the mix of males and females is a positive thing, but there are profound differences between the mysterious time travellers and the two school teachers. They have had no training, preparation or screening for their roles, and no testing for compatibility between crew members. They are cut off completely from home, with no knowing when they might return. Leadership is erratic, unreliable and untrustworthy, when it is not being actively contested. Only one crew member has any work to do on board, though how much of that is meaningful as opposed to fussing and busywork we don’t know. The ship keeps malfunctioning, and although they are not always confined on board, whenever they do go outside people try to kill them.

It’s a wonder they don’t all crack up.

The Daleks

We know that there are survivors. They must be disgustingly mutated.

Flowers began to grow back in Hiroshima less than a month after Little Boy incinerated the city. But this was no comforting return of nature after humanity’s terrible flash of technological sorcery. The distorted and malformed blooms were a haunting sign that the world would never be the same again.

Both the wielders and the victims of the atom bomb knew about the lethal potential of radiation. Survivors of the blast told lurid tales of the black rain that brought radioactive sludge from the atmosphere back down to earth, and doctors recognised the low white blood cell counts of their dying patients as a symptom of something similar to an X-ray overdose. Babies who were in their mothers’ wombs at the time of the explosion were born with cruel deformities and genetic maladies.

The Americans were keen to play down the radiation story. To be fair, the radiation levels dropped rapidly after the explosion, and fears that Hiroshima might be uninhabitable for decades were swiftly proved to be unfounded. Seizing on this, the US military spin machine presented their atom bomb as just another high explosive,  certainly more powerful than any yet created, but not fundamentally different from a stick of dynamite.

They maintained this stance for the best part of nine years, and for all the vague fears among the general public radiation was mostly seen by solid, no-nonsense types as a relatively minor hazard of warfare in the atomic age. Nuclear fallout was recognised and studied, but with most atomic test explosions taking place high enough off the ground to avoid drawing radiation-blasted soil up into the mushroom cloud, it didn’t seem like a major worry.

Castle Bravo changed all that. Operation Castle was the US attempt to develop a hydrogen bomb that could be practically delivered to the enemy. The preceding programme, Operation Ivy, saw the first ever explosion of a hydrogen bomb in the Ivy Mike detonation. At over ten megatons, this was more than six hundred times more powerful than the Hiroshima bomb, but as an experimental setup – a huge, cryogenically-cooled storage tank – it wasn’t something you could readily drop on Moscow. Castle Bravo swapped the cumbersome liquid deuterium that fuelled Ivy Mike’s fusion explosion for solid lithium deuteride, creating a bomb that could be readily transported – and dropped.

Mushroom cloud from the Castle Bravo test

Castle Bravo detonation

It was detonated on Bikini Atoll on 1 March 1954. The explosive yield was 15 megatons – three times higher than expected, thanks to an incomplete model of the fusion process. The wind had shifted eastward, blowing the radioactive fallout outside of the designated zone. The fallout plume spread out over a hundred miles, shrouding inhabited islands in radioactive dust. Most famously, the Japanese fishing vessel Daigo Fukuryu Maru was caught in the plume, radioactive coral debris raining down as white ash. Its 23 crewmen all became seriously ill, and one died. This was too big a calamity for the official US denial machine to brush aside. Along with the dreadful effects on the many islanders and fishermen subjected to this calamity, and the strain the event put on US diplomatic relations with Japan and in the wider Pacific region, Castle Bravo showed, publicly and undeniably, the far-reaching lethality of nuclear fallout from the new hydrogen bombs.

Not only would nuclear warfare devastate cities, destroy countries, turning nations to rubble in a few hours or days like World War II on fast-forward. It would also poison the soil, contaminate the sea, fill the air with lethal dust, covering the world in a deadly shroud that would linger for years – centuries – millennia. The Earth would become a dead planet.

Which brings us to Skaro.

The dead planet with its petrified forest is Terry Nation’s surreal vision of a planet long since ravaged by nuclear war. If we’re going to understand what happens to our four time travellers once they step out onto the ruined surface, we have to look at exactly why radioactivity is so bad for you.

When we talk about radiation, as in the intangible killer that blighted the survivors of Hiroshima, Castle Bravo and Skaro, we’re really talking about ionising radiation. That is, rays of light or subatomic particles that have enough energy to knock electrons out of atoms when they collide with them. This matters, because chemical processes are all about the interactions between electrons belonging to different atoms, and ionising radiation is radiation that is powerful enough to screw up chemistry. The more complicated the chemistry, the more ways there are to screw it up, and the most complicated chemical phenomenon we know about is life. So, ionising radiation is particularly relevant if you are alive, especially if you plan to stay that way.

Your body is made up of many different kinds of cells, each performing its own specialised function. The effects of ionising radiation depend not just on what kind of cell it hits, but also on whether the cell is killed outright or merely damaged. Large doses of radiation will kill a load of cells at once, leading to radiation sickness, while lower doses can damage the reproductive mechanisms of cells, causing cancers or genetic mutations. The radiation levels that we encounter on Skaro are high enough to give the time travellers acute radiation sickness, while the natives seem to only be suffering the chronic effects of mutations. Evidently cells on Skaro are made of sterner stuff than on Earth.

How susceptible a cell is to radiation damage depends mainly on how quickly it reproduces: the higher the reproduction rate, the greater the chance that the cell will be screwed up by radiation. In our bodies, blood cells reproduce quickly, nervous system cells reproduce slowly, and the cells in your gut are somewhere in between. And right enough, at low (but still damaging) levels of radiation exposure it’s the blood cells that show the first sign of damage. At this stage you just feel fatigued, though if the radiation has affected the skin there may also be sunburn, and hair loss as the hair follicles are damaged. As the dose gets higher, the damage increases and the gastrointestinal cells begin to suffer. First nausea, then vomiting and diarrhea as the dose level increases. At the highest levels, the central nervous system crumbles, leading to loss of coordination, confusion, coma, shock, convulsions – the sort of symptoms that vomiting and diarrhea seem like a blessed condition.

The lower levels of damage can be treated – blood transfusions or bone marrow transplants can provide for a full recovery from blood disorders. If the gut is too badly damaged, however, death is inevitable, and pretty nasty. And if the radiation dose is high enough to take out the central nervous system, there’s not much in the way of medical treatment beyond one last, heavy dose of morphine.

Older people will tend to be more susceptible to radiation sickness, so it’s no surprise that the Doctor is the first to succumb. We can be thankful his symptoms do not progress beyond the first stages of fatigue: the sight of Billy Hartnell shitting his guts out all over Lime Grove Studio D is not one that anyone wants to see on a Saturday teatime.

If you get your radiation dose from fallout, rather than the direct radiation blast from the explosion itself, how much damage it does depends on the precise chemical makeup of the fallout that you breath in or ingest with your food, as well as the level of radiation it gives off. In the aftermath of a nuclear war, a wide range of radioactive isotopes would be present in the fallout. Project Gabriel, a US Atomic Energy Commission study in the 1950s, determined that the most dangerous isotope would be strontium-90. This isotope emits beta radiation – fast-moving electrons – but what makes it really nasty is where it sits while it’s doing the emitting. Strontium is chemically similar to calcium – it’s directly beneath it in the periodic table – and because of this it is readily absorbed into bones, where it hangs around giving the unfortunate victim bone cancer or leukemia. It was evidence that levels of strontium-90 in children’s teeth had massively increase due to nuclear testing that convinced President Kennedy to sign the partial test-ban treaty that put an end to above-ground nuclear test explosions.

But one of the major horrors of radiation that we haven’t touched on much yet is mutation. Whether by damaging DNA molecules directly, or by upsetting the mechanisms within the cell that enable DNA to replicate, radiation can make cells and even whole organs develop in strange and unexpected ways. There is ample evidence of this kind of mutation happening in human fetuses, from Hiroshima onwards. Whether a single  radiation dose can cause mutations in subsequent generations is a more vexed question. Studies of survivors of the Hiroshima and Nagasaki bombs suggest not, but laboratory studies on mice and fruitflies have found second-generation effects. In any case, to be sure of getting mutation continuing down the generations, you really need the radiation to stick around as a long-lasting environmental feature. continuing mutation effects, you need to have the radiation as a long-lasting environmental feature. The nastiest isotopes of fallout, like strontium-90 or caesium-137, decay with half-lives of the order of tens of years, so after a few generations they would be practically gone. However, there are some fallout isotopes like plutonium-239 and carbon-14 that hang around for tens of thousands of years, and are readily taken up in food and absorbed into the body. These could raise the mutation rate for a very long time indeed.

Even so, it is unlikely to produce a race of Aryan supermen in kinky pants. Most mutations are trivial, and most of the non-trivial ones are harmful. These mutations lead to cancers, genetic diseases, disabilities and severely shortened lifespans. So, although we need some mutations to drive natural selection, producing new variations that may be better suited to their environment, too high a mutation rate does not simply give us evolution on fast forward. Rather, it results in the entire population dying out before it has much chance to adapt to anything. Unless, of course, these poor, crippled mutations have the technological capability to build themselves protective cocoons with mobility and manipulation devices that allow them to survive the debilitating effects of genetic degradation. Yeah, that sounds feasible.

But there’s one last twist in the tale, when the Daleks realise they need radiation to survive. This seems an odd notion – we’ve seen how damaging ionising radiation can be to biological tissues. It is not, however, wholly without foundation. At high doses, radiation is just a bad idea and best avoided. The evidence for what effect, if any, radiation has on us at very low dose levels is sparse. If you drop a nuclear bomb on some people, and they all either die or get cancer, that’s a big effect that’s easy to measure. If you give someone a small radiation dose, and they get cancer thirty years later, separating out the effects of the dose from background radiation, passive smoking, pollution and various other carcinogens is pretty hard. So for now we have to extrapolate, and there are two main theories. One is the straightforward linear extrapolation: draw a straight line through the graph, all the way down to zero. The other is the threshold theory, which is that below a certain level of radiation there is no harm done. People involved in radiological protection argue about this a lot: the linear theory is the standard one, on which standards for radiation dose limits are based, but if the threshold theory is true then those limits are too conservative and we are throwing away money on over-cautious protection.

There is a third, rather more interesting theory. Hormesis is the phenomenon whereby a small amount of something is beneficial, while large doses are harmful. Take any household painkiller, for example – but only as directed on the packet. Since the eighties, there has been something of a cottage industry of scientists trying to establish that radiation might have a hormetic effect, through aiding DNA repair, reducing free radicals or stimulating the immune system. This theory is not widely accepted, and the opinion of official bodies ranges from cautiously interested (France) to patently unconvinced (US). So it’s possible there’s something in it, but there’s a pretty good chance it’s bollocks.

So if you do wind up as the desperate survivor of a nuclear apocalypse, horribly mutated beyond recognition, don’t count on the radiation ever doing you any good, and certainly don’t count on being able to sit around waiting to evolve into something prettier. Instead, get to work building yourself an electric wheelchair with a grabby arm and an eyestalk, and make the best of things. And it’s probably worth sticking some kind of gun on it as well. Just in case.

The Tribe of Gum

The tribe say you are from Orb and when you are returned to him on the stone of death, we will have fire again.

A stone age tribe, struggling for survival. A cave of skulls, imbued with supernatural power. Human sacrifice to the Sun God. A society where political power goes to the man who can make fire. It’s a perilous situation that our time travellers find themselves pitched into after their abrupt flight from London, forced to contend with the superstitious fanaticism of a stone age people.

Human beings are the only animals to have religion. The origins of this idiosyncratic phenomenon are obscure. Although other apes are not religious, they do have social rituals that help to bind their tribe together and create peaceful relationships with other tribes. These range from the ceremonial scrotum-grab of male baboons, to the ritualised group-greeting behaviours of chimpanzees, to the notorious bonobo gang-bangs.

It seems – and we’re never going to get definitive answers on this, so informed speculation is the best we can do – that early humans had ecstatic group rituals of their own, and that these were the first steps towards religion.

Any kind of shared activity can promote group cohesion and bonding. Music, chanting and rhythmic movement all help to build the group identity in the course of the ritual – and these all predated the development of speech. Drugs help, too. There doesn’t need to be any supernatural element. Rock concerts and football matches will do just fine.

These elements persist in modern religions. I still remember the full-on Catholic masses of my youth in St Aloysius Chapel, the great organ resounding around the cavernous, mosaic-covered church, the choir singing, the incense wafting across the congregation as they stepped through the ritual dance of kneeling, standing, genuflecting. And the rituals remain potent even without the theological content: even Richard Dawkins goes carol-singing.

Bonding rituals would certainly have been important in the Paleolithic era, that vast panorama of time that stretches off into the partially-glimpsed origins of our species some hundreds of millennia ago, and which ends around ten thousand years ago with the domestication of plants and animals. Early humanity consisted of small family tribes, thinly scattered across the east of Africa, and their need for rituals to bind their own tribe together and establish peaceful relations with other tribes would have been just as strong as it is for our ape cousins.

But something changed. These rituals became something darker, deeper, more profound. The earliest signs of this are hundreds of thousands of years old – collections of skulls, cracked open in ways that match more recent practices of ritual cannibalism. By eating the brains of the dead, their kin would seek to absorb some of their power and spirit. These skulls also bear the marks of flint knives that show that the flesh was thoroughly removed from them. Later defleshed skulls show signs of staining with red ochre. This naturally-occurring iron oxide is found in the form of a soft rock that can be made into a powder or used directly to make marks like a pencil. It became increasingly used by our ancestors for marking sacred objects and buried corpses, and remains popular to this day in some tribes who use it for body painting.

These early rituals indicate some kind of spiritual attitude concerning the dead, but they are rudimentary compared to the elaborate religious practices found in every human society in the present day. At some point between then and now something changed in human consciousness, and we became a species with the full panoply of supernatural beliefs.

It’s generally reckoned that this change took place around 50,000 years ago. Even with just the fragmentary evidence we have, it seems like a switch suddenly flips in people’s heads, and immediately we have music and art of a recognisably modern form. Indeed, there are etchings on ice-age animal bones showing artistic techniques that seemed revolutionary when Picasso reinvented them in the last century.

The cause of this change is still a matter for speculation. It isn’t linked to any physical change that we can see in fossilised bones: our ancestors were anatomically modern, indistinguishable from ourselves, well before this cultural revolution.

However it happened, we can see in the art our ancestors left behind, in the location of their sacred spaces and in their careful burials of the dead, a new religious sensibility. We can also fill in the gaps by looking at the religious beliefs and practices of modern-day people who live in isolated, tribal societies. You can’t blithely assume that religion has somehow been transmitted unaltered down fifty millennia, but where contemporary practices of people living the closest anyone comes these days to a Paleolithic lifestyle match up to the fragmentary evidence from the lives of our ancient common ancestors it would be perverse not to allow that to inform our speculation.

Figurative art from this period is largely concerned with animals – horses, bison, birds of prey. There are also sculptures of humans – some realistic, some stylised. But some of the most striking art depicts human/animal combinations, such as a man with the head of a lion. This blurring of the boundaries between human and animal is typical of shamanistic religion, and the shaman might well have appeared as a lion-man during rituals, wearing a lion’s head as a head-dress, and there is cave art showing human figures in animal hides apparently dancing and playing musical instruments, similar to shamanistic rituals that have been observed in Siberia and North America. Bears also feature prominently, and it may be that these animals, that seem so close to human when they walk upright, were considered to be the spirits of dead people.

So we have a picture of a shamanistic religion, with important rituals involving communing with animals and with the realm of the dead. Ritual healing would also be a key part of this. Faith healing is, of course, nothing more than the placebo effect – but when the placebo effect is all you have, it starts to look more attractive. The shaman would use his magic to cure or alleviate pain, from injured limbs to gastric infections to childbirth – pain is a phenomenon of the mind, and thus susceptible to the deployment of placebos. Rituals are a vital part of making the placebo effect work – the patient must believe that the magic will help them, and the ritual sells that belief. In the modern world, while old rituals like acupuncture can still deliver an effective placebo, we also find that many patients will feel their symptoms alleviated by a sugar pill if delivered in a suitably earnest medical context. It’s even been found that the colour of the pill influences the mental effect of the placebo, and a more extreme-looking treatment like an injection with saline solution is a more effective placebo than a benign-seeming pill. We can be sure that the stone age shamans were as expert in enhancing the placebo effect through impressive ritual as our own modern charlatans are today. And in a world without any more effective medicine, the man who could accomplish even that much healing would be powerful indeed. Just don’t get bother him when a lion’s taken your hand off – in that case, you’re pretty much on your own.

As the millennia pass, ancestor worship becomes the dominant aspect of religion. And with this comes a shift in political power. By analogy with present-day tribes, we can presume that Paleolithic societies were not just egalitarian, but aggressively so. Every man was equal, and any who tried to set himself up above the rest would be cut down – literally.

But ancestor worship provided the means to change this. The man with the greater ancestors had access, therefore, to the most powerful spirits, and could lay claim to more temporal power on that basis. This became the foundation for hereditary rule, and hierarchical societies.

So how does the Tribe of Gum fit into this picture? I’m afraid the answer is not very well. The Cave of Skulls does bring to mind the shattered skulls left behind by ritual brain-eaters, but there is little sign of shamanism, let alone the reverence and awe with which our forebears regarded animals. Aggressive egalitarianism has been replaced by the dictatorship of the fire-maker, and ancestor worship is nowhere in sight.

To an extent this is fair enough. We only have physical evidence from a few of our ancestors, and this sorry lot don’t look as though they’re going to be around long enough to leave much. But there’s one thing that really doesn’t fit with any of our understanding of prehistoric religion, and it literally couldn’t be any more glaring.

Sun worship.

It is perhaps surprising how rare sun worship actually is in ancient cultures. The Sun is the most powerful and impressive object in human experience, responsible not only for the cycles of day and night but also for all the processes of growth and development that sustain human life. And yet actual solar religions only appear in a few cultures – Egyptian, Meso-American and Indo-European – and only when these had developed urban civilisations governed by holy kings. In these cases, the Sun as a singular, unapproachable, dominant higher power fits with the ruling ideology – and we might speculate that a greater emphasis on agriculture as the primary occupation of the people led to a greater appreciation of the Sun’s overwhelming power and importance. Paleolithic people never worshipped the Sun – indeed, there is no sign of any attention to astronomy in any of their extant remains. Our Paleolithic ancestors instead venerated – and carved beautiful images of – migratory birds like swans and wild geese, whose comings and goings marked the seasons. It was not until agricultural settlement gave rise to the need to predict and understand the seasons in detail that our ancestors became astronomers, from the Egyptians predicting the flooding of the Nile to the ancient inhabitants of Britain creating Stonehenge.

So if you should find yourself dragged off to Paleolithic times by a silver-haired git in checked trousers, don’t panic. They’re more likely to invite you to a night of dancing and drugs than to attack you for the secret of fire, and they will certainly not strap you to a rock and sacrifice you to the Sun. Just don’t try to explain how they are really your ancestors – that could cause a religious debate that would make the Council of Nicea look like a parish church tombola.