The Science of Doctor Who: What do Daleks smell like?

The Scientific Secrets Of Doctor Who duo on Benjamin Franklin and Dalek static electricity

Screen shot 2015-05-29 at 13.25.52

Screen shot 2015-05-29 at 13.25.52

What do Daleks smell like – and why would we even want to know? In fact, we’re told what they smell like in their very first story, as the Doctor and his friends puzzle out how to escape from a detention cell.

‘Let’s concentrate on the Daleks. Have you noticed, for example, that when they move about there’s a sort of acrid smell?’

‘Yes, yes, I’ve noticed that.’

‘I know – a fairground.’

‘That’s it. Dodgems.’

‘It’s electricity. I think they’re powered that way … I believe the Daleks have discovered a way to exploit static electricity. Very ingenious, if I’m right.’

The First Doctor, Susan, Ian and Barbara, The Daleks (1963-4).

From this detail about dodgem cars, the Doctor works out that the Daleks – at least in their first story – get their power through the metal floors of their city. This deduction helps the Doctor and his friends to escape from the cell, by using an insulator (a plastic cape) to cut off the supply from the floor to their Dalek jailor. Later, when the power source in the floor is destroyed so too are the Daleks – apparently for good. The Doctor uses the smell of the Daleks to defeat them.

In fact, it’s a good example of the Doctor being a scientist: looking carefully at a situation, asking questions and weighing up evidence to make sense of what’s going on and how he might solve a problem such as escaping from the cell. Science is a deductive process rather than a fixed body of sacred, unchanging facts.

There’s also something else going on in knowing what Daleks smell like. As we explain in The Scientific Secrets of Doctor Who, our sense of smell is linked to the parts of our brain that also process emotion and learn associations between things. That’s why smells can bring back sudden, vivid memories and feelings. As a result, being told what Daleks smell like can make us recall our own memories of dodgem cars – the excitement of the fairground, that sense of danger and fun – but now associated with the Daleks.

As we say in the book, “But this is a trick: television can only convey sound and images, not smells. We react emotionally to something we’re not actually sensing, which makes these alien [creatures] seem more vibrant and real.”

Do the Daleks still smell like dodgem cars today? No character says so in the story – but that absence of evidence doesn’t automatically mean that they don’t. What other evidence can we use to deduce an answer?


According to the Doctor in the scene we’ve been discussing, the smell is linked to the Daleks’ power source. However, when the Daleks returned for their second battle with the Doctor in The Dalek Invasion of Earth (1964), they had developed a new source of power. Small discs on their backs, we were told, gave them increased mobility. For their third story in 1965, BBC designer Ray Cusick added vertical slats below the Daleks’ grills which he thought would act like solar panels, and those slats remain part of Dalek design today. Unfortunately, whatever Cusick intended, it’s never been stated on screen in Doctor Who that the slats are – or aren’t – solar panels. We need better evidence.

However, even if the Daleks are now solar-powered, static electricity still seems important to them. In The Evil of the Daleks (1967), a Victorian scientist experimenting with static electricity unwittingly attracts Daleks to his house. More recently, in The Daleks in Manhattan / Evolution of the Daleks (2007) they use the Empire State Building as a lightning conductor to source power from the static electricity in the clouds – which we’ll discuss in a moment. If they’re still exploiting static electricity as a power source, perhaps they still smell like dodgem cars.

Except that, despite what the Doctor seems to say, dodgem cars don’t run on static electricity. Instead, the tall bar at the back of each car completes a circuit between the floor and the ceiling, allowing another kind of electricity – ‘current’ electricity – to flow through their engines, providing them with the energy needed to move the car. The distinctive ‘static’ smell, is just the smell of sparking, which happens when electricity, whether static or not, discharges through the air.

In fact, static electricity is an odd choice of power source. We tend to get our energy from current electricity, which flows through wires and transmits energy. By contrast, static electricity doesn’t ‘flow’, it’s simply an imbalance in electrical charges that remains where it is (hence ‘static’) until something else enables it to equalise in a sudden discharge or spark.

Static electricity is the cause of the tiny electric shocks that you sometimes experience when touching a metal door handle or railing. In this case, your own body has built up an excess of negatively charged particles, usually by the friction of walking around on a rough surface like a carpet. Because the soles of your shoes are usually made of rubber or some other insulating material, these negatively charged electrons can’t discharge through your feet. However, when your hand makes contact with a conducting material like metal they are suddenly free to flow away, often jumping the gap with a sharp crackle as soon as your hand is close enough.

A more extreme version of this effect is often achieved in physics classrooms and science centres using a Van der Graaf generator. This device uses the friction of a moving belt to build up equal and opposite electrostatic charges on two metal globes. When you touch one of the globes the charged particles spread into your body but, as long as you’re insulated from the ground, they are unable to travel any further. As the charge continues to build, your hair will begin to stand on end because the charged particles in each strand of hair repel each other.

This is one reason why static electricity seems like a rather unscientific choice of power source for the Daleks: if they were all full of static charge from the floor of their city, the Daleks wouldn’t be able to get close to one another because electrostatic repulsion would force them apart. Worse, if they ever touched anything outside the city they would discharge themselves –catastrophically with an almighty spark. Perhaps this explains why the Daleks are so bad tempered. If this element of the story is more science fiction than science fact, what’s more realistic is the way the Doctor works from the observed evidence – the smell of electrical sparking – to deduce what’s going on, and then uses this information to devise a way of immobilising the Dalek. (He does this by using a plastic cape to insulate the Dalek from the power source in the floor.)


When lightning strikes, what’s happening is very similar to the example of a person discharging through a door handle, just on a much larger scale. When the ground is heated by the sun, in turn it heats the air above it. Warm air rises, expanding and cooling as it goes, and causing any water vapour that it contains to condense into droplets, forming a cloud. The more warm air that’s created, the bigger the cloud gets.

The top of a large cloud can reach high into the atmosphere, where temperatures are cold enough for some of the water droplets to turn icy. As pieces of ice and droplets of water bump against each other, they transfer electrical charge. The lighter ice particles gain a positive charge as they rise to the top of the cloud, while the heavier water droplets gain negative charges as they sink toward the bottom. This creates a huge charge imbalance between the upper and lower parts of the cloud.

Because opposite charges attract, the positive and negative charges would like to flow together and cancel each other out, but they are prevented from doing so by the insulating properties of the air. However, eventually the charge imbalance becomes too great, and a spark forms across the gap, discharging the imbalance in a huge release of energy: a lightning strike.

Often, lightning occurs only in the clouds themselves. But a spark can also be created if the negative charge at the bottom of a cloud discharges into the ground. The closer the cloud base is to the ground the easier it is for a spark to form, which means that lightning often ‘strikes’ tall things such as trees, buildings and – when there’s nothing else about – even people.

Until we understood this process, lightning was a scary and apparently random phenomenon that could set buildings on fire and kill people. But then, in 1750, an American called Benjamin Franklin published an account of a simple experiment – almost as simple as the hand and the door handle, but a lot more dangerous.

The experiment involved flying a kite in a thunderstorm. The kite would act like a tall tower, reaching up from the ground. From the kite protruded a metal wire of about 30 centimetres, which would form a convenient point for the lightning to strike, allowing the cloud to discharge itself through  the kite, via the string reaching down to the person holding it on the ground. Franklin was lucky his experiment didn’t kill him – as it did some of those who tried it for themselves.

But Franklin’s experiment proved that lightning was made of electricity, and could be manipulated. He invented the lightning conductor, which saved tall buildings by ‘bypassing’ the connection between the clouds and the ground. It saved countless properties and lives.

More than that, the kite experiment made Franklin famous round the world. This meant people listened to him, so he was sent on a number of diplomatic missions to England and France, and found himself at the heart of a political storm about the way English people governed parts of America. The science-fiction writer Isaac Asimov even argued in his book The Kite That Won the Revolution that Franklin’s key role in America gaining independence from Britain is a direct result of his experiments with lightning.

Of course, Franklin couldn’t have known what his experiment would lead to. He couldn’t even know, when he first devised it, whether or not it would show that lightning was composed of electricity. But that’s not the point. The important thing is that he came up with a question – is lightning made of electricity? To learn the answer, he devised a test and that test led him – and all of us – to new knowledge and understanding of natural processes, which we can use to solve problems and transform the world.

That is science. And it’s why, when the Doctor is trapped in a Dalek detention cell with his friends, he is being a scientist when he asks if they’ve noticed the smell.

The Scientific Secrets of Doctor Who by Simon Guerrier and Dr Marek Kukula is published by BBC Books on 4 June. Simon and Dr Kukula will be speaking at The Planetarium at Royal Observatory Greenwich on Friday 5 June. More information and how to book tickets can be found here.