What is antimatter? The science of Doctor Who explained

During the course of the episode the Doctor discovers an antimatter drive powering a hospital spaceship, and rhapsodises about its conceptual beauty while filling in Yaz (Mandip Gill) on the science behind it.

But what actually is antimatter? How accurate is the science in this episode? Could humanity really have our own antimatter drives by the 67th century? And when has antimatter turned up in Doctor Who before?

To find out, we asked some experts.

What is antimatter?

"Antimatter is the opposite – or 'partner' – of particles’ regular matter," Simon Guerrier, co-author of The Scientific Secrets of Doctor Who, tells RadioTimes.com.

"It has the same mass but opposite electrical charge. For example, electrons – on which anything electronic depends – are subatomic particles with a negative electrical charge.

"The idea was first seriously proposed by theoretical physicist Paul Dirac in 1928, and first seen by Carl D Anderson in 1932; it was Anderson who coined the term ‘positron’."

So there you have it: the Doctor's explanation in the episode is pretty bang on.

Could antimatter actually be used as fuel?

At the moment, humans have only been able to create miniscule amounts of antimatter – but that doesn’t mean scientists haven’t already been considering the possibilities of an antimatter drive like the one in this episode.

"Where antimatter is useful as a fuel source (and for Doctor Who stories) is that if an antimatter particle collides with its matter equivalent, the result is 'mutual annihilation' – a technical term – and the release of energy," Guerrier says.

"NASA have already funded some investigation of possible antimatter drives," Giles Sparrow, a bestselling astronomy and physics author, added.

"Even though a practical drive is way beyond current technology, the potential benefits are just too big to ignore, and you've got to start somewhere.

"Compared to other fuels, antimatter is incredibly efficient in terms of how much energy you can get out of a small amount of fuel – about 39 per cent of the fuel ends up being released as pure energy.

"One study calculated that you could power a trip to Mars with just 1/10,000th of a gram of antimatter, but that's still billions of trillions of times more than modern particle accelerators can create.

"By the 67th century, however, who knows? If you can make enough antimatter you can keep on accelerating your spaceship nearly all the way to light speed."

If anything, then, the spaceship in this episode is practically idling compared to its full capacity. Pull your fingers out, Tsuranga!

How accurate is the use of antimatter in The Tsuranga Conundrum?

During the episode, Whittaker’s Doctor explains how the Tsuranga rescue craft’s antimatter drive actually works, involving a miniaturised particle accelerator (basically an extremely advanced version of the Large Hadron Collider at CERN, described as "the iPhone version of CERN") storing positrons in electromagnetic fields.

"The particle accelerator smashes the atoms together, like a little antimatter factory, to produce positrons, which are stored very carefully inside electric and magnetic fields," the Doctor says.

"The positrons interact with the fuel materials to produce heat, which produces thrust."

It all sounds very informative – but is it accurate?

"This all seems pretty much on-the-mark," Sparrow tells us.

"Positrons are the antimatter version of electrons, the lightweight negatively charged particles that orbit inside every atom and create the flow of electricity.

"Because they're lightweight, positrons are one of the easiest types of antimatter to make, and another bonus is that they don't release so much deadly high-energy radiation when they collide with normal electrons and annihilate.

"Once you've got your antimatter, you obviously need to store it safely out of contact with normal matter, and electromagnetic fields are the best way of doing that."

Apparently, real-life plans for antimatter drives currently involve using “found” antimatter out in space (a practice the Doctor alludes to in the episode) or pre-making it on Earth – but Sparrow says the futuristic technology of this episode is still possible.

"So far, most plans for antimatter drives envisage either making antimatter pellets in accelerators on Earth, or sweeping small numbers of particles up from space, where they zip around in so-called ‘cosmic rays’," he explains.

"But if you could shrink down a particle accelerator into a compact unit and generate enough energy to power it, then why not make your fuel where you need it?"

Why indeed? Unless, of course, a ravenous alien creature was trying to get to it…

Has antimatter been in Doctor Who before?

This isn’t actually antimatter’s first Doctor Who outing, with the substance featuring in a number of stories with, shall we say, 'varying' levels of scientific accuracy.

"In Planet of Evil (1975), the Fourth Doctor says: 'Antimatter in collision with matter causes radiation annihilation [and] a release of energy more powerful than nuclear fission,'" Guerrier tells us.

"The science of that story is a bit wobbly, though: at one point, the Doctor carries around some antimatter in a bucket."

The first reference to antimatter comes a few years earlier, though, in team-up special The Three Doctors.

"Antimatter first appears in Doctor Who in 1972-3 story The Three Doctors," Guerrier says, "when the first three Doctors travel through a black hole to a universe of antimatter to face a renegade Time Lord called Omega."

"'The mere fact of our being here should cause a colossal explosion,' says physicist Dr Tyler to the Third Doctor.

"'Yes, well,’ says the Doctor, 'our bodies have been converted, processed in some ways, so that we can exist here.' But the Second Doctor's recorder is inside a force field when this conversion takes place so isn't converted – and when Omega knocks it out of the force field there's a big explosion."

And the last appearance of antimatter in the series prior to The Tsuranga Conundrum led to a truly tragic sequence of events.

"In Earthshock (1982), the Cybermen crash a space freighter powered by antimatter into Earth, causing a colossal explosion and wiping out the dinosaurs," Guerrier says.

"Also killed in the explosion is the Doctor's companion Adric. His name was, purposefully, an anagram of Dirac [the man who first mooted the idea of antimatter particles, as explained above]."

Adric is, famously, one of the few Doctor Who companions to actually die while travelling with the Doctor – so perhaps it makes sense that it took a few decades before the Time Lord started to express an interest in antimatter again…

Doctor Who continues on BBC1 on Sundays