By the standards of most of his close family members, Steven Chu was a pretty mediocre student. The son of two Chinese immigrants who went to graduate school at the Massachusetts Institute of Technology in the US, he had an elder brother who set a record grade at high school and went on to study at Princeton, while two of his cousins attended Harvard. Chu’s good but not Earth-shattering school results were not enough for the Ivy League universities and he instead went to the University of Rochester in New York State.
Not that it did him much harm, however. Graduating from Rochester with a degree in maths and physics in 1970, he went on to share the 1997 Nobel Prize for Physics for his work on using lasers to cool atoms to just a few thousandths of a degree above absolute zero – a process that allows physicists to study the behaviour of ultracold atomic gases. He then adapted this technique to study the properties of individual DNA molecules – an approach that is now used by hundreds of researchers across the world and that could have medical applications such as finding a treatment for Alzheimer’s disease.
Now, aged 59, Chu is hoping to help save the planet from the perils of global warming. He is currently director of the Lawrence Berkeley National Laboratory in California, where he oversees major programmes of basic research in everything from particle physics to biology. However, his lab is also involved in projects to develop renewable energy resources, including the $500 m Energy Biosciences Institute, sponsored by oil giant BP, which aims to create new, environmentally friendly biofuels.
"Scientists love to do basic research, but there are times when they are willing to work towards a specific goal," Chu told Physics World ahead of a recent talk he gave in Rome on the world’s need for sustainable energy. "Just as in the Second World War, when there were scientists who worked on radar or the bomb because they felt there was an emergency, so there are scientists today who want to work on the energy problem. But this one feels better because I think we’re all on the same side."
Experimental prowess
Part of the reason for Chu’s unspectacular high-school career was boredom – the rote memorization of reams of facts meant that schoolwork was a chore, not a delight. There were one or two courses at Garden City High, New York, that were different, however. One was English. Another was geometry, which appealed to him because he could use logic to derive theorems from just a few intuitive postulates. Subsequent courses in physics and calculus had a similar impact on him.
While at Rochester, Chu became increasingly interested in maths and theoretical physics. But while doing his doctorate at the University of California, Berkeley, which he started in 1970, he realized he was more suited as an experimentalist as he enjoyed tinkering in the lab. He demonstrated his experimental prowess by building a state-of-the-art laser that he and his supervisor used to search for subtle asymmetries in the polarization of laser light predicted by the unification of the weak and electromagnetic interactions.
Although the pair were scooped by a much larger high-energy-physics experiment at Stanford, Chu’s talents were recognized by Berkeley, which wanted to promote him from postdoc to assistant professor in its physics department. Despite this attractive offer, Bell Labs in New Jersey was able to entice him to move back east in 1978. It was there that Chu carried out his Nobel Prize-winning work.
Having already proved his worth by making some painstaking measurements of the energy levels of positronium – an atom made up of an electron and a positron – as well as various other laser-based studies of condensed-matter systems, Chu began exchanging ideas with his colleague Art Ashkin in 1983 about how to trap and slow atoms with light. Investigating the detailed properties of atoms is impossible at room temperature because they move at about 4000 kmh–1.
By 1986 Chu was able to slow down – and therefore chill – atoms by colliding with them photons in a laser beam of just the right energy. In doing so, he managed to cool them to 0.25 mK. Chu was recognized with the award of a Nobel Prize 12 years later, alongside physicists Claude Cohen- Tannoudji and William Phillips, who extended Chu’s basic technique to lower temperatures. Laser-cooling and atom-trapping techniques have since led to the development of ultraprecise atomic clocks and the creation of Bose–Einstein condensates, in which large collections of atoms collapsing into the lowest quantum state.
In 1986 Ashkin had shown how the tiny attractive or repulsive forces generated by laser beams could be used to hold micron-diameter plastic spheres in water. Chu reasoned that if lasers could be used to trap both atoms and micron-sized objects, then his trapping technique also ought to apply to intermediate-sized objects, namely molecules. By 1990, now at Stanford University, Chu had managed to manipulate individual DNA molecules in water at room temperature, thus allowing him to study what happens inside live cells, including how viruses invade a cell.
Chu carried on this work when he moved back to Berkeley in 2004. He is now using single-molecule techniques to study the protein "nerve growth factor", which stimulates the growth of neurons. He and his colleagues have shown that this molecule is transported through nerve cells more slowly in mice that have the human equivalent of Alzheimer’s disease or Down’s syndrome, suggesting it may be possible to cure these kinds of conditions.
Energetic thoughts
While Chu may have made great strides in applying his physics to the problems of biology, his main concern since leaving Stanford has been energy. The principal motivation for this has been his increasing sense that global warming is both real and pressing. He believes that the evidence for anthropogenic warming has become compelling, and that society must therefore take action. "We don’t need absolute certainty that the dire consequences of climate change will occur," he says.
Chu believes that, if anything, the climate-change scenarios laid out by the Intergovernmental Panel on Climate Change in its assessment last year may be on the conservative side. In particular, he points out, the panel did not include in its analysis a number of "tipping points", beyond which the climate becomes dangerously and irreversibly out of control. One such tipping point would be the release, through a small rise in the planet’s temperature, of huge quantities of methane and carbon dioxide contained within the frozen Arctic tundra, the heating effects of which could cause sea levels to rise by several metres.
Chu believes it is also vital to develop new energy sources, which requires further research in basic science. He points out that the incremental improvements to traditional silicon solar cells could halve the cost of these devices within the next decade, but that the price will have to come down by around a factor of 10 before utility companies in the US would consider installing many hectares of solar farms without subsidies.
"Some people say that producing new energy sources is just a matter of engineering," he says. "That’s actually not true." As Chu points out, even today’s inefficient photovoltaic devices could satisfy the world’s current electrical needs by covering less than 1% of the planet's desert area (although ways must be found to store and transmit the energy).
At Berkeley, Chu has enviable resources to draw on. Altogether, more than 100 top scientists and their students and postdoctoral fellows are, or will shortly start, working on a range of different solar-energy projects. Prominent among these initiatives is the Energy Biosciences Institute, a collaboration between the University of California Berkeley, the University of Illinois and BP, which will use $50 m of BP’s money per year for 10 years to investigate increasing the green energy yield from biofuels.
Biofuels, such as ethanol derived from corn, can help reduce greenhouse-gas emissions because although they release carbon dioxide when they are burned, the plants themselves absorb a similar amount from the atmosphere as they grow. The problem with these fuels is that corn is also used for food. Indeed, the growing demand for biofuels is one reason why global food prices are rising as increasing amounts of farm land are given over for corn destined for ethanol production.
One of the main aims of the Energy Biosciences Institute is to try and make cellulose-based fuels. The advantage of this material as a fuel is that it is not used for food. Chu and his colleagues are also looking at ways of improving the conversion of plant material into biofuels, for example by studying how the microbes in the gut of a termite convert woody material into energy.
Scientists at the Berkeley lab are even looking at ways of bypassing biology altogether in their pursuit of tapping the Sun’s energy, through artificial photosynthesis. Plants and algae split water into hydrogen and oxygen, and reduce carbon dioxide into carbon monoxide in order to create the complex polymer sugars that constitute a major part of the cell walls. As Chu points out, artificial photosynthetic devices will not be limited like their natural counterparts by the need to use materials that are compatible with the life and reproduction. The principal challenge in creating these artificial devices is to generate high catalytic rates using materials that are readily available, such as cheap metals.
Worth the sacrifice
Chu has been encouraged by the fact that so many – several hundred – of the lab’s scientists are keen to tackle the energy problem. He says that the problem is appealing because it is an intellectual challenge and also because its solution would bring great benefits to society. "It was pretty easy to sell," he adds. "People were ready."
But having to oversee the lab’s other activities – as well as heading the Energy Biosciences Institute – does not leave Chu with much spare time. He is still involved in research into single-molecule biophysics, atom interferometry and novel states of matter based on Bose condensates, but usually only gets to speak to his fellow researchers in the evenings and at weekends. He admits that his work life is "a little bit crazy" and that he has no time any more to exercise. "I also spend far less time with my wife," he adds.
Despite the strains it may be placing on him personally, Chu believes that his job is worth the personal sacrifice. The climate problem is so urgent that what politicians, scientists and the public do in the next few years, he thinks, will affect the planet’s future for decades – if not centuries – to come. It therefore makes perfect sense to him that he and his colleagues at Berkeley should pull out all the stops in the pursuit of new energy sources. "There are a lot of very smart people who want to save the world," he says. "I hope that some combination of this desire and wanting to get rich can help guide us towards a sustainable future for the world."