Researchers follow Hannes Alfvén's path of discovery
50th anniversary of KTH professor's Nobel Prize
On the 50th anniversary of Hannes Alfvén’s Nobel Physics Prize, researchers reflect on the KTH scientist’s contributions to our understanding of space, and the paths of discovery they continue to forge.
He’s revered as one of the founders of the field of plasma physics, yet Hannes Alfvén had to earn his 1970 Nobel Prize the hard way. At the height of the Second World War, the late KTH physicist published a brief paper in the letters section of Nature which would change the course of space physics, but not before years of dismissal and resistance from his peers.
“Alfvén was working out what is happening with sun spots,” says Andris Vaivads, professor of space physics at KTH. “And he found that there is a form of electromagnetic wave that moves through plasma, including the solar winds, which he called magnetohydrodynamic (MHD) waves.”
Alfvén’s extensive contributions to plasma physics are the basis for work that continues to this day at the KTH Space and Plasma Physics Division, where Vaivads and others are currently involved in space missions to the Sun, Mercury, Jupiter and near Earth space.
Widely held belief about electromagnetic waves
As late as the late 1940s, electromagnetic waves were widely believed to penetrate only a short distance in a conductor. The better the conductor, the less these waves could propagate.
Years after publishing his discovery, Alfvén delivered a lecture at the University of Chicago where Enrico Fermi was working on cosmic rays, and he presented his idea that these low frequency oscillations could propagate in a perfect conductor, such as the ionized gas of a star, or our own Sun.
According to accounts of the event, the audience was skeptical. Could these MHD waves exist? Fermi replied, “Of course”, giving the audience the validation Alfvén’s theory had been denied.
Now known as Alfvén waves, the phenomenon has provided generations of scientists a breadcrumb trail through key areas of space study, including Earth’s aurora, planetary magnetospheres, solar wind and radiation belts, among other subjects.
“The universe is more than 99.9 percent plasma, a kind of charged gas, so space is not a void … there are structures throughout the space plasma regions and within there are these waves,” Vaivads says.
New understanding of aurorae
The most familiar example of their effect is the Northern Lights, which Alfvén studied and described in groundbreaking papers that provided a path forward for generations of physicists, including his own student, Göran Marklund, who today is Professor Emeritus of plasma physics at KTH.
Even though Alfvén’s laboratory simulations and measurements proved to be accurate, “Alfvén argued strongly for measuring electric fields in space,” Marklund says. “He suggested that static electric fields are responsible for creating aurorae. This was in 1958, before there were any space missions or satellites to measure the particles.”
Unsupported by space observations, the idea would remain unproven until 1960. Later, in the 1990s, researchers at KTH were able to detect surprising activity in auroral electric fields thanks to the higher resolution measurements taken with satellites such as Viking, Freja and Cluster.
Working with space mission observations
Drawing on data from a series of space missions spanning some 40 years, Marklund is one of several space plasma physics researchers who carry on the work at the Alfvén Laboratory, helping to shed new light on how Earth' magnetosphere interacts with solar flares or ejections, and the dynamics of aurorae formation.
The Parker Solar Probe is one of the latest platforms the KTH scientists are working with, examining measurements the spacecraft collects on its path closer to the Sun. “One of the big surprises is this huge amount of high amplitude Alfvénic waves coming from the sun,” Vaivads says. “They’re probably heating up the solar atmosphere, or corona, which drives space weather,” he says.
One of the big questions they hope to answer is, why and how is this happening?
Today with higher and higher resolution measurements from missions run by Sweden’s own space program as well as ESA and NASA, Marklund, Vaivads and their colleagues enjoy an advantage Alfvén lacked in the pre-space age. Though even years after his Nobel award, the legendary theorist still tussled with his critics.
“I remember that when I was about to publish my first paper,” Marklund recalls asking his then-supervisor in the early 1980s. “I said, ‘Will you be on my paper as co-author?’ And he replied. ‘Oh no. You’d have no chance of being published if I’m on the paper.’
“He suggested that I submit the paper in Nature, where it got published”.
“Alfvén broke new ground and provoked many scientists over his career – he essentially declared war on some of his opponents,” Marklund says.
Story and photos:
Existence of Electromagnetic-Hydrodynamic Waves . Nature (1942) doi: 10.1038/150405d0
The Heritage of Hannes Alfvén , Physics and Chemistry of the Earth (1997) doi: 10.1016/S0079-1946(97)00182-1