For the past half a century, Japan has led the world in neutrino science. In the 1980s the Japanese physicist Masatoshi Koshiba masterminded the construction of a huge neutrino detector located 1000 m underground in a lead and zinc mine in Japan in Hida, Gifu Prefecture. Called Kamiokande, it was an enormous water tank surrounded by photomultiplier tubes to detect the flashes of light produced when neutrinos interacted with atomic nuclei in water molecules.

Koshiba famously used the experiment to detect neutrinos from a distant supernova explosion – in the process becoming one of the founders of neutrino astronomy. The work led him to sharing the 2002 Nobel Prize for Physics for the detection of cosmic neutrinos.

Takaaki Kajita – who was still a physics student when Koshiba did his Nobel-prize-winning work – was intrigued by the study of these ghostly particles and decided to carry out a PhD at the University of Tokyo under the supervision of Koshiba. The work fascinated him enough such that in 1988, Kajita joined the Institute for Cosmic Ray Research (ICRR) at the University of Tokyo where he spent the next two decades working on neutrino physics.

In 1996, Kamiokande’s successor – the Super-Kamiokande experiment – began operation and two years later, Kajita played a key role in using the facility to show that the ratio of electron to muon neutrinos coming from opposite sides of the Earth were different. This meant that these neutrinos – created when cosmic rays interact with nuclei in the upper atmosphere – were changing flavour as they passed through the Earth. This showed, for the first time, that neutrinos must have mass, albeit at only about 0.1 eV.

Science has become so important for deciding the direction of society – or even the future of the Earth

For the work, Kajita followed in Koshiba’s footsteps and in 2015 shared half that year’s physics Nobel with the neutrino physicist Arthur McDonald “for the discovery of neutrino oscillations, which shows that neutrinos have mass”. Experiments at the Sudbury Neutrino Observatory (SNO), led by McDonald, determined how many of the electron neutrinos produced in the Sun change into muon neutrinos or tau neutrinos as they travel to the Earth. SNO data were able to confirm the fact that about two-thirds of the solar electron neutrinos change flavour by the time they reach the Earth.

Switching fields

Despite adding to Japan’s rich legacy in neutrino physics, in 2008 – before Kajita was awarded the Nobel prize – he made a bold decision to switch research fields. “After many years of neutrino research, I wanted to do something new that would be important and exciting,” Kajita told Physics World. “Fortunately, our institute had been planning a gravitational-wave project as the next major project to come after Super-Kamiokande.” That facility was the KAGRA gravitational-wave observatory, which would be based underground nearby Super-Kamiokande.

Kajita became director of ICRR in 2008 and played a major role in getting KAGRA funded and constructed. KAGRA is a huge interferometer in which a laser beam is split down two 3 km-long arms. The beams are reflected multiple times between mirrors suspended at the ends of each arm and then combined at a detector. A gravitational wave is a ripple in space–time and when it passes through an interferometer, it can change the distances between the mirrors. This is detected as a change in how the laser light interferes at the detector.

Construction of KAGRA, which is based 200 m underground, began in 2010 and became operational in 2020. Given the impact of COVID-19, KAGRA is expected to join the international hunt for gravitational waves next year. Kajita is currently the project’s principal investigator.

As well as switching research fields, Kajita also delved into other aspects of science, becoming a member of the Science Council of Japan (SCJ) in 2017. The role of the SCJ is to make recommendations to the government and wider society about certain issues. In 2020 he was nominated by the other SCJ members as its president. “I do not know why many of them voted to me,” admits Kajita. “But I guess that the Nobel prize had some influence on the vote!”

Kajita says he joined the SCJ to communicate the importance of basic science to the public and indicates that can be as important as doing the science itself. “Science has become so important for deciding the direction of society – or even the future of the Earth,” he says. “Physics is clearly one of the important parts of science. So I hope that physicists dedicate their time for other activities such as science policy.”

With a Nobel prize under your belt and unshackled by the need to “prove” yourself, it must be tempting to set off in new directions – to try your hand at topics beyond the area in which you originally made your name. One Nobel-prize-winning physicist who has perhaps veered off the conventional path more than any other is Brian Josephson, who leads the self-styled Mind-Matter Unification Project at the University of Cambridge in the UK. It aims to understand “from the viewpoint of the theoretical physicist, what may loosely be characterized as intelligent processes in nature, associated with brain function or with some other natural process”.

In other words, Josephson, 81, spends his days thinking about how the brain works, investigating topics such as language and consciousness, and pondering the fundamental connections between music and the mind. Most controversially, as far as physicists are concerned, he also carries out speculative research on paranormal phenomena, a field known as parapsychology. Josephson’s interests even touch on homeopathy and cold fusion – two areas in which few physicists would dare to dabble.

But Josephson’s interest in consciousness and the mind is nothing new. In fact, it began long before his Nobel Prize for Physics, which he won in 1973 for work done in the early 1960s during his PhD at the Cavendish Laboratory, Cambridge. Under the supervision of Brian Pippard, Josephson had predicted that a superconducting current can tunnel through an insulating junction, even when there is no voltage across it, with the current oscillating at a well-defined frequency when a voltage is applied (Phys. Lett. 7 251). Such “Josephson junctions” are central to superconducting quantum interference devices (SQUIDs), which can measure magnetic fields with exquisite sensitivity.

But almost as soon as his PhD was over, Josephson’s attention quickly switched elsewhere. During a year-long postdoc at the University of Illinois at Urbana-Champaign, John Bardeen (still the only person ever to have won two Nobel physics prizes) tried to persuade Josephson to continue his work in on superconductivity. Unconvinced, he decided to work instead with Leo Kadanoff on critical phenomena. “But after that I felt that the easier and more interesting aspects of many-body theory had been done and I started trying to understand brain function,” Josephson says.

I felt that the easier and more interesting aspects of many-body theory had been done and I started trying to understand brain function

Brian Josephson

His interests were piqued further after returning to Cambridge, when Josephson got to know the mathematical geneticist George Owen, who in his spare time investigated poltergeist claims. “He talked to me about parapsychology generally and got me interested in that, particularly as I could see parallels between psi phenomena and quantum mechanics,” Josephson recalls. In 1974, shortly after picking up his Nobel prize in Stockholm, Josephson was invited by Owen to a conference on “psychokinesis” in Toronto, where he saw demonstrations of metal bending. “I did some research on this but have always regarded it as a sideline,” Josephson says.

Still, Josephson’s new line of interest was clearly established. He went on to give a course on “creative intelligence” at the Cavendish and even collaborated with Hermann Hauser – the physicist and technology entrepreneur who helped set up Acorn Computers – on a paper on the logic of developmental processes. As the years went by, Josephson began getting invited to conferences concerned with mind processes. “I then started trying to link concepts such as semiosis with quantum physics. Currently I’m working with a quantum physicist who is developing the maths side,” he says.

Looking back on his career, Josephson thinks he would have moved into studying the mind even if he had never received his Nobel prize. “Having tenure would probably have given me freedom to work on it,” he says. Still, despite the prestige that a Nobel brings, life outside the mainstream has not been easy. “The Nobel prize didn’t stop the department being very hostile,” Josephson claims, citing incidences of potential collaborators being discouraged from working with him and having their promised funding withdrawn.

Recognition that mind is fundamental rather than matter will be as significant step for physics as the step from classical to quantum physics.

Brian Josephson

He has also faced criticism from the likes of geneticist David Winter, who have accused him of suffering from “Nobel disease” – the notion that a Nobel prize gives a scientist who is an expert in one area an “unfounded confidence” to speak on subjects they know nothing about. Winter believes the affliction encourages sufferers to “spout anti-scientific rubbish”, citing the Nobel-prize-winning chemist Linus Pauling who thought that high doses of vitamin C are medicinally useful.

Such comments do not seem to deter Josephson, who believes that, on the contrary, it’s his critics who are in the dark. “It is people such as Winter who speak with unfounded confidence, on subjects they know essentially nothing about such as telepathy, or memory of water,” he insists. “In the latter case, fallacious arguments are frequently used to dismiss the possibility.”

Indeed, Josephson told Physics World he thinks his present work is “much more important than my superconductivity work” even though it has not been finalized. “The point is that recognition that mind is fundamental rather than matter will be as significant step for physics (and for science generally) as the step from classical to quantum physics,” he says. “A number of people have asserted this in the past of course and the question is when we will reach the ‘tipping point’ when ’the club’ will start to take note?”