The invisibility cloak inventor now has better tricks up his sleeve

John Pendry’s kitchen is dominated by a huge photograph of what looks like the view through a kaleidoscope: dizzying shards of purple, green, yellow and white. Given that Pendry is famous above all else for inventing an invisibility cloak – a device that can bend light around objects – I wonder if I am looking at something related to that.

But no, he tells me, the image simply shows crystals of vitamin C magnified many times. All that invisibility-cloak stuff is in the past, he says, and he has moved on to “more exciting things”.

It is a throwaway remark, but it reveals something of why I have always found Pendry, who is based at Imperial College London, so interesting. This is someone who invented a device 20 years ago that sounds like magic, but his true legacy is barely appreciated. If engineers get their way, Pendry’s ideas will soon shape everything from earthquake protection to self-driving cars. Yet he seems to give the applications of his famous breakthrough barely a thought, instead turning his mind to the question of whether, for his next trick, he can bend light through time instead of space, and so build materials that can simulate the wild physics of black holes. It is these and other ideas that have brought me to his home for lunch.

Pendry’s career began in the 1970s. He trained as a theoretical physicist before working as a self-described jobbing scientist, focusing on rather unfashionable problems. Among other things, he was interested in the granular details of how electrons interact with solid matter.

Then, one day in the mid-1990s, a collaborator showed him a special piece of stealth technology that had been developed to hide British ships from radar. It was a polymer impregnated with carbon fibres, scattered chaotically in many layers. Something clicked. It wasn’t the carbon atoms, per se, that allowed the material to work so effectively, Pendry realised, but how they were structured in disordered filaments.

Pendry had stumbled into the science of metamaterials. In the broadest sense, a metamaterial is a substance that has properties that don’t occur naturally. A mechanical metamaterial, for example, might get thicker when stretched. Scientists had also proposed the concept of an optical metamaterial, which would be capable of bending and manipulating light in ways no natural lens could – but no one had ever found a practical way of making one. Pendry’s breakthrough was to formulate, for the first time, a comprehensive theoretical description of how metamaterials worked and to show they could be produced by etching tiny grooves, rings or pillars into an ordinary substance.

The invisibility cloak appears

Pendry recognised this was a route to revive a radical proposal from the Soviet physicist Victor Veselago. Decades earlier, in the 1960s, Veselago had imagined materials that would refract light in reverse, causing a simple slab to focus rather than disperse light. It was long assumed to be impossible, but Pendry worked out how to coax light into obeying the strange mathematical rules that Veselago had sketched out.

The invisibility cloak, unveiled in 2006, was the moment this abstract physics burst into public view amid an enthusiastic chorus of press coverage. But Pendry first described the idea a year earlier, at a conference in San Antonio, Texas, attended largely by defence researchers. “I was given the mission to ‘ginger things up’, which I did with a deadpan talk on the mathematical details of transformation optics,” he jokes. “Then, just as people might have been about to ask what the use of all this was, I wrote down a simple formula, together with a sketch of what a working invisibility cloak might look like. Then I sat down to see the room erupt.”

It was an uncharacteristic moment of flamboyance from someone as understated as Pendry, but the audience loved it. He went on to develop the first working prototype of an invisibility cloak with collaborators at Duke University in North Carolina, which hid the device and an object from microwaves – one of the simplest forms of electromagnetic radiation to corral. Sadly, its appearance is less theatrical than the name suggests: it looks like a circuit board, not a cape you might drape over your shoulders.

When it is time for lunch, Pendry puts on an apron, carefully microwaves mushroom soup and lays the table. It is an oddly mundane counterpoint to a man whose equations briefly convinced the world that Harry Potter physics might be real. I am told later that the soup is a last-minute thing and isn’t representative of his usual, much more confident standard of cooking. I believe it. His sitting room is dotted with coffee-table books on molecular gastronomy, many authored by Nathan Myhrvold, the San Francisco-based venture capitalist who also dabbles in photography and food science.

Myhrvold turns out to be an important figure in Pendry’s story: the two have shared a long professional relationship and it is Myhrvold’s huge photograph of vitamin C (pictured above) that graces the kitchen wall.

Myhrvold owns around 60 of Pendry’s metamaterials patents and has founded several companies built on his ideas. He envisions metamaterials embedded in everything from self-driving cars and humanoid robots to 6G communications satellites within the next decade. Analysts estimate the market he is chasing could be worth around £6 billion by 2033.

In fact, metamaterials appear to be finally taking off. Many have reached commercial maturity, with some of the most striking advances appearing in so-called metalenses. Rather than bending light through curved glass, metalenses shape light directly using surfaces patterned with dense forests of nanoscale structures, each acting like a tiny antenna. The result is a paper-thin lens, just micrometres thick, that can outperform traditional optics. Instead of stacking heavy glass elements inside a camera, a single flat layer can do the job. “One application is to put them in these drones,” says Pendry. “You can have tiny, tiny drones that still have very, very good optics, because they have these extremely light lenses.” Smartphones and virtual-reality headsets can also now carry high-performance optical systems without the usual weight penalty.

Myhrvold is also using Pendry’s ideas to reimagine autonomous vehicles. Most self-driving cars rely on lidar – a light-based radar that scans the environment by sweeping laser beams across it to build up a detailed 3D picture. Today’s lidar systems typically achieve this by physically rotating mirrors or entire sensors, which makes them bulky, fragile and expensive. Myhrvold thinks metamaterials could change that, and he is developing lidar systems that steer laser beams electronically, with no moving parts at all.

There are even metamaterials out there that can control the seismic waves that pass through Earth. At a mathematical level, such waves behave much like light, and so the same principles that govern optical metamaterials can be used to divert an earthquake from a building’s foundations.

Commercialisation, though, isn’t what Pendry cares about. “I know what I’m good at, and I know what I’m not very good at,” he says. “And developing products was not something I ever got excited about.” In any case, in the early days, he wasn’t sure his ideas would ever make money.

Given that this is a man who finds joy in the minutiae – both of science and everyday life – perhaps it makes sense that he has lost interest in the invisibility cloak. The technology has grown too large and diffuse for his tastes. Entire industries are still catching up with its implications, but for Pendry, the intellectual work is done. “There comes a point when your research starts running away from you,” he tells me. “It’s all very interesting, but I can’t add very much any more. So, let’s do something really new and exciting.”

Temporal metamaterials

And what is that new thing? Well, metamaterials have traditionally been used for controlling how light moves through space. But ever since Albert Einstein’s general theory of relativity, we have known that space and time are really two sides of the same coin: space-time. Some years ago, Pendry began to wonder if there could be such a thing as temporal metamaterials, which would control how light moves in time, too.

He gestures towards my phone, which is recording as we sit in his living room. Inside every smartphone screen, he says, there is a material called indium tin oxide. Strike it with a laser and it turns from opaque to transparent on ultrafast timescales. To a light wave travelling through the material, that change appears almost instantaneous, which breaks one of the most basic assumptions of optics: that energy is conserved as light passes through matter. The upshot of this is that a temporal metamaterial can inject energy into a wave, or drain it away, shifting its frequency. Red light becomes blue. Microwaves become infrared. They are a kind of philosopher’s stone that can transmute one type of electromagnetic wave into another.

These new metamaterials could be highly revealing. In particular, they could become a way to explore otherwise inaccessible physics that usually comes into play only under extreme circumstances. Take black holes. In 2023, Pendry calculated what would happen if you built a material whose internal pattern shifts in time so that it appears to move at almost the speed of light. Under those conditions, the mathematics produces points that light cannot cross – in other words, an analogue of a black hole’s event horizon. He says that an experimental realisation of his ideas could provide a new way to study black holes in a lab.

An even stranger example involves the Casimir effect. Place two metal plates a few nanometres apart in a vacuum and, counterintuitively, they will be pushed together. The effect arises thanks to the fluctuations of quantum fields in a vacuum. But Pendry has pointed out that changing a material’s electromagnetic properties in time may produce a dynamic version of the same phenomenon, where this subtle pressure can be dialled up to produce a never-before-seen quantum analogue of friction. Several separate research groups are now exploring how to test this in real temporal metamaterials.

None of this is straightforward. The equations of optics were built on the assumption that materials stay still. Once they begin to change on femtosecond timescales, the mathematics starts to fray. Moreover, many of the effects Pendry is predicting hover at the edge of detectability. But it is exactly this territory – where theory, experiment and intuition briefly lose alignment – in which Pendry seems most at home.

Before I leave, Pendry lifts a small frame off the floor by the fireplace. He explains that, like Myhrvold, he enjoys taking photographs, and this is one of his snaps that his wife has repurposed into a firescreen. It shows some butterflies he photographed on a walk, the most impressive of which is an Adonis blue, its wings flashing an electric, iridescent azure. The colour, he explains, isn’t a pigment: it is the result of the butterfly’s wing being a natural metamaterial, with the nanoscale architecture scattering light.

“I always like using butterflies when I’m explaining metamaterials to new people,” says Pendry. For a moment, I’m surprised he doesn’t use his world-famous invisibility cloak as the ultimate introduction to the power of metamaterials. But then I realise that this is Pendry all over – a man who prefers not to dwell on his breakthroughs, but rather vanish back into the lab and make some more.