Australasian Science: Australia's authority on science since 1938

Learning about Life from Waves

By Stephen Luntz

Nail Akhmediev believes that the creation of rogue waves at sea could be a useful template for the conditions that gave rise to life on Earth.

In February this year a rogue wave hit the giant cruise ship Marco Polo in the English Channel, killing a passenger and injuring another. As tragic as the event was, it represented a vindication for Prof Nail Akhmediev who has spent years studying these sorts of waves, which were once thought not to exist. Now, however, Akhmediev is pushing into more metaphorically choppy waters, using waves to model the origins of life.

“A soliton can be used as a model for life because it displays the simplest and most essential functions of life,” says Akhmediev, who is based at the Australian National University’s College of Physical and Mathematical Sciences. The claim seems strange – waves may grow and die but we usually do no think of them breeding. However, Akhmediev says that “energy flows across these waves, and some parts absorb and others dissipate it. Some can divide into two, and the process can continue indefinitely.”

Solitons are single waves that keep the same shape as they travel. They exist in all sorts of media. In January, Nature published a report of the first observation of solitons on silicon chips by researchers at the University of Sydney’s School of Physics – a step towards the development of photonic chips.

The waves Akhmediev is studying are called dissipative solitons. While the conservative forms exist in systems with constant energy, dissipative solitons can gain and lose energy.

Akhmediev sees parallels between these and life forms. “Waves supported by energy continue as long as energy is supplied,” he says. “In the same way, life continues when there is energy from the Sun. If the Sun switches off, all life disappears.”

However, life is about more than energy. “A tree needs matter from the soil as well as energy from sunlight to survive,” Akhmediev says. “Some scientists are studying energy in waves and some are studying matter. We brought these together to provide a better model of life.”

Akhmediev admits that modelling of the first life on Earth is limited as we do not know the exact conditions in which it formed. Nevertheless, he argues: “The model is alive. It oscillates when there isn’t enough energy or matter, just like it’s breathing. When matter and energy stop flowing through the system, it dies. If these processes happen in simple formations like solitons, we can imagine how the very first basic forms of life were ‘born’ in nature from non-living elements, such as hydrogen and oxygen.

“The point is these waves are self-organised, so they don’t need external forces to start the process, just as would have been the case for the first life,” Akhmediev concludes.

He hopes to turn the research to the question of whether life exists on Mars and, if so, where it would be most likely to be found. “It depends on conditions on the planet,” he says. “First we do experiments on Earth. There have been many experiments in previous work for the energy parts and the matter parts. We have been able to combine this into a single model, closer to explaining first life than previous models, so in principle this could help but it needs work of course.”

Akhmediev says that solitons have been his life’s study. “Rogue waves are very weakly related,” he says. A wave is deemed a rogue when it is more than twice the mean wave height (trough to crest) of the highest one-third of the waves around it.

Rogue waves can apparently come from nowhere, leading generations of scientists to dismiss them as a myth spread by incompetent seafarers. However, in 2001 satellite images recorded waves 25 metres high when those around them were much lower. Akhmediev replicated them in water tanks (AS, June 2012, pp. 6–7) and with lasers. He hopes his work will lead to a better understanding of the conditions under which they form on the ocean, leading to alerts that could save lives.

“A crucial factor in the appearance of extreme events, whether in nature or a laser in the laboratory, is the existence of energy, or a background excitation in the system,” he says. On the high seas this energy comes from cannibalising smaller waves, and under the right conditions can rise even higher than previously realised. “What we’ve found is that extreme events happen much more often than people expect,” says Akhmediev, and he is making progress towards identifying the signs that a wave is building.

Akhmediev says he “studied well at school” but the origins of his interest in science may lie in his construction of a radio receiver.

His postgraduate degree at Moscow State University was on “non-linear dynamics and optics, laser pulses in technology,” he says. “I started with experimental work but started thinking more about solitons and non-linear waves, and step-by-step moved to more complicated objects.”