The race to absolute zero
In the early 1900s, a Dutchman and a Briton battled to create the coldest place on earth
WORDS: ANDY ROUND
ILLUSTRATIONS: HAN HOOGERBRUGGE
At 0°C, water freezes. Few of us can imagine temperatures more than a few degrees lower. The lowest natural temperature ever recorded is -89.2°C, at Russia’s Vostok research station in Antarctica, in 1983. But this doesn’t even scrape the frosty surface in terms of cold. Down at -190°C, it gets so cold that the air turns to liquid. So, how low can you go?
More than a hundred years ago, this simple question tormented two of the world’s greatest scientists. And, like all great rivalries, the race to create the coldest place in the world was packed with endless drama.
It was a tale of terrible explosions, horrific injuries, blind egotism, colourful characters and the obsessive pursuit of absolute zero. One scientist would win the Nobel Prize, the other would reject cold science to study soap bubbles. You couldn’t make it up.
James Dewar was a hot-headed Scottish scientist who enjoyed great success but made enemies quickly and guarded his secrets jealously. Heike Kamerlingh Onnes, in The Netherlands, was much younger, more inclusive, used teams of collaborators and shared his research publicly.
Their characters and approaches were diff erent, but they both had their eyes on the same prize – being the first to achieve absolute zero, or -273.15°C.
Why this number? Well, as far back as 1703, physicist Guillaume Amontons had believed that a total lack of heat was possible, but it was not until 1848 that the concept of absolute zero became internationally recognised when William Thomson – later Lord Kelvin – established his ‘absolute temperature scale’ setting zero Kelvin (-273.15°C) as the coldest anything could ever be.
Today we know that, at this level of cold, electricity flows without resistance. Some atoms are so confused and drained of energy that they lose their identity to become neither solid, liquid nor gas.
Fascinatingly, when light tries to enter this fourth state – known as ‘Bose-Einstein condensate’ – it slows down to the speed of a bicycle, and compresses to almost nothing. Which is all very well and good, but at the time of Onnes and Dewar, every degree colder brought new discoveries; the race was on to be the first to reach absolute zero.
So in laboratories more than 100 years ago, and through the liquefying of what were known as the permanent gases – oxygen, nitrogen and hydrogen – the two men searched for their Holy Grail.
Oxygen had been the first to fall earlier in the 19th century, followed by nitrogen at almost -200°C.
All that was left was hydrogen, or ‘Mount Hydrogen’ as Dewar preferred to call it. Liquefying this gas would be the greatest achievement of the age. And he wanted to make sure Heike Kamerlingh Onnes didn’t get there first.
Dewar was ahead of the Dutchman in many ways. He had demonstrated the liquefaction of air before an amazed public in the late 19th century and invented the revolutionary idea of the vacuum flask. “He was a brilliant experimenter and could build his own instruments,” says Dirk van Delft, curator of Museum Boerhaave (the Dutch National Museum for the History of Science and Medicine).
“But Onnes had a totally different approach. He was the beginning of ‘big science’. He had taken over the physics laboratory in Leiden when he was only 29, and his inaugural speech was about making Dutch physics famous abroad by liquefying gases. He was amazingly far-sighted.”
The methods both men used to transform hydrogen were similar. By using diff erent gases that would liquefy at lower and lower temperatures through a series of cooling coils, a cascade was established until the final stage – when hydrogen would be as cold as possible and be put under giant pressure before being released though a valve, triggering a huge drop to -252°C.
“The apparatus was very fragile, under very high pressure, and Dewar took the most amazing risks,” Simon Schaffer, professor of science history at Cambridge University, tells the PBS documentary The Conquest of Cold. There were plenty of explosions as a result. On many occasions, assistants suffered terrible injuries as shattered glass flew through the air. Several were blinded in one eye.
In The Netherlands, the authorities were so afraid of explosions that they closed Onnes’ cryogenic laboratory for three years. “Dewar was already working towards liquefying hydrogen while Onnes had lost the battle before it began, even though he had all the equipment he needed,” says Van Delft .
In 1898, Dewar was successful. He produced the coldest liquid on earth and beat the Dutchman. He waited to be feted, but there were no celebrations. “Imagine you’ve just climbed the highest peak and, just as you get to the top, there is an even higher mountain just beyond,” says Schaff er.
That mountain was newly discovered helium, a gas that would only liquefy at a temperature lower than hydrogen – just five degrees above absolute zero. And Dewar’s luck had just run out.
He refused an offer from Onnes to collaborate on this latest challenge, and after making enemies of the pioneers who discovered the new gas, could not find a reliable supply. Then, after an assistant turned a knob the wrong way and his precious helium supply disappeared into thin air, Dewar had to close his laboratory for six months.
For Onnes, it was all the chance he needed, and years of meticulous testing, research and careful documentation finally paid off on July 10, 1908. That morning, the scientist gathered together his researchers, confident that a breakthrough would be achieved. But despite the frenetic pace (his wife fed him lunch to avoid losing time), by 6.30pm the temperature was still stubbornly stuck.
“Onnes didn’t know why this was,” writes Tom Shachtman in his book Absolute Zero and the Conquest of Cold. “But then a colleague came in and suggested that perhaps they had already succeeded. So Onnes looked underneath the apparatus and there it was, liquefied helium.”
The temperature had reached -268°C. For this staggering achievement, Onnes was awarded the Nobel Prize. Dewar abandoned research into low temperatures, preferring to focus, among other phenomena, on the science of soap bubbles.
For Onnes, there were other discoveries in this new world of ultra-cold. At four degrees above absolute zero, all resistance to electricity in frozen mercury disappeared. Onnes christened this phenomenon superconductivity.
The Dutchman’s achievements with helium paved the way for other extraordinary discoveries too. Later, it was discovered that at two degrees above absolute zero, liquid helium has no viscosity and appears unaffected by gravity.
It can actually climb out of the walls of its container and escape.
Absolute zero remains a theoretical temperature. Magnetic cooling achieved the coldest ever recorded temperature in a laboratory in Helsinki – one tenth of a billionth of a degree above absolute zero – but scientists believe it could take all the time in the universe to remove that last tiny bit of heat. And you would need an apparatus the size of the universe to achieve it. But that’s another story.