Jupiter’s Great Red Spot may get its colour from an unexpected quantum effect – one that we could use to generate power from clouds here on Earth
FORTY years ago, in what was then the Soviet Union, physicist Mark Perel’man had an outlandish thought. It took him a further seven years to show that his thought might have substance, and 30 or so more years to be taken seriously. The problem for Perel’man was that his idea overturned the established view of a familiar physical process, one that occurs every time a gas condenses into a liquid or a liquid freezes solid.
It might sound esoteric, yet if Perel’man’s theory is correct it will have far-reaching consequences. It could transform the way we manufacture materials such as metals, help explain why Jupiter’s Great Red Spot is red, and provide the basis of an early-warning system for storms and tornadoes on Earth. It might even unlock an untapped source of renewable energy hidden in the sky.
Advertisement
Perel’man emigrated to Israel in 2006, and he was working at the Hebrew University of Jerusalem when he died in August this year. By then, though, others had become convinced that he was on to something and are now keen to explore it. “I definitely intend to continue to investigate this, particularly with energy and environmental issues in mind,” says Quinn Brewster of the University of Illinois at Urbana-Champaign. “I am confident that it is a real effect,” says physicist Peter Townsend of the University of Sussex in Brighton, UK. Yet other researchers contacted by żěè¶ĚĘÓƵ remain sceptical: “My take on it is that it’s wrong,” says Graeme Ackland at the University of Edinburgh, UK. So what is going on?
The argument hinges on the details of a process called a phase transition. Phase transitions occur all around us: as ice cubes melt in a glass of gin and tonic, for example, or as water vapour condenses to form clouds.
What specifically interested Perel’man were condensation and freezing. These are both exothermic phase transitions, involving the release of heat. Freeze water, for instance, and as ice starts to form, the water molecules become locked into crystals where they can only vibrate. As a result they lose some energy of motion, releasing it as heat.
It had always been assumed that this so-called latent heat could escape via two processes: thermal conduction – as atoms or molecules knock into each other and pass on their excess heat energy – or as black body radiation, the radiation given off by all objects, with a characteristic spectrum that depends on the object’s temperature.
In the 1960s, however, Perel’man began to suspect that another mechanism was involved. He was thinking about the quantum mechanics of condensation and freezing, and started to wonder how the electrons in the material might be affected. Quantum theory tells us that these electrons occupy discrete energy levels, and that they can emit photons if they make a jump to a lower energy level.
Perel’man speculated that this mechanism could provide another way for a material to lose heat as it condenses or freezes. It was a notion that ran counter to mainstream physics. “At the time these ideas seemed completely fantastical and heretical,” Perel’man told żěè¶ĚĘÓƵ shortly before his death. Yet his thinking caught the attention of the prominent Soviet physicist Andrei Sakharov. Buoyed by his support, Perel’man published his idea in the journal ).
Perel’man realised that he needed clear experimental evidence to back up his theory. Time and again he and his colleagues ran careful experiments in which they froze water or condensed steam, but each time they failed to detect the faintest glimmer of electromagnetic radiation. Nevertheless, Sakharov maintained his interest and at one stage even suggested conducting experiments in his own kitchen, Perel’man recalled.
After much brainstorming, Perel’man finally worked out where he might have been going wrong. The photons were there, he reckoned, but they were being absorbed by water vapour in the air before they could reach the detector. He froze water again, this time in a partial vacuum, and sure enough, the detector spotted infrared radiation at wavelengths between 28 and 40 micrometres. He redesigned the apparatus to study water vapour condensing and, as droplets formed, he recorded another infrared burst, this time between 4 and 8 micrometres. In both cases, he showed that black body radiation alone could not explain the results. Perel’man and his colleagues presented their findings in several Russian-language publications and at conferences in the Soviet Union. Yet the results received little attention elsewhere, even when published in Physics Letters A in 1977 ().
It wasn’t until Perel’man arrived in Israel, 30 years after his original experiments, that he was able to put his ideas on a firmer theoretical footing. And it was then that Vitali Tatartchenko, a Russian crystallographer working at glass manufacturer Saint-Gobain in France, contacted him.
It turned out that Tatartchenko had been studying the same idea independently, also for over 30 years. In the 1970s, while at the Institute of Solid State Physics in Moscow, he had emitted by various metals and salts, and even sapphire – a form of aluminium oxide – when they crystallised out from a molten state. These experiments were hugely challenging, since the phase changes took place at high temperatures. “Sapphire was especially difficult because it has a melting point of 2050 °C,” Tatartchenko recalls.
What intrigued him was the possibility that this radiation could offer a new way to control the manufacture of certain materials. Imagine a molten metal or semiconductor that can solidify into several different types of molecular structure, each with its own associated latent heat. He reasoned that it might be possible to steer the solidification process towards a specific structure by beaming in light at a specific wavelength related to the transition energy. This would stimulate emission from the melt, he thought, in much the same way as photons inside a laser cavity stimulate an avalanche of light emission, and at the same time trigger the desired phase change.
Tatartchenko wanted to work with Perel’man to develop a theoretical model of the process, more to convince others that the effect was real than to find any sort of practical application. The pair began by collating previous research on electromagnetic radiation in phase transitions, and compared the data with standard results in laboratory handbooks. In 2007, they published their conclusion – that the effect is genuine ().
Ackland is not so sure. “I’m unconvinced by their experimental evidence,” he says. He says that any changes in atomic or molecular motion during phase transition are too gradual “to produce any kind of effect needed to generate electromagnetic radiation at a characteristic frequency”.
Bradley Stone, a physical chemist at San José State University in California, is keeping an open mind. He says there is no particular reason why latent heat should not be released directly as infrared radiation. “But I’d like to see independent corroboration by others before I am absolutely convinced,” he says.
Roy Sambles at the University of Exeter, UK, says that Perel’man and Tatartchenko’s idea is plausible. The electronic energy levels in atoms can be modified by neighbouring atoms, he says, though he suspects any shift in the levels would be tiny. “The problem is to compute what effects this may have,” he says.
A recent study by Brewster and graduate student Kuo-Ting Wang goes some way towards doing this. They have come up with a model that seems to explain how electromagnetic radiation can be emitted when water condenses, and they even calculate the spectra that we should see.
According to Brewster, when a molecule of water vapour condenses – by attaching itself to the surface of a water droplet via a hydrogen bond – its sudden loss of mobility, combined with a change in the distribution of electric charge across the molecule, force it to lose a relatively large amount of energy. The best way for it to do that is to kick out a photon. “There is a lot of energy that needs to be liberated and this model provides the possibility of photon release,” says Brewster. Using his model, he calculates that condensing water vapour will emit infrared radiation at wavelengths between 4 and 8 micrometres (). “Theory suggests the probability of this is very low, which is why many scientists are sceptical, but we have to keep an open mind.”
Tatartchenko says the finding explains why clouds emit infrared radiation at wavelengths between 6.5 and 7 micrometres – a range monitored by weather satellites recording cloud formation. Until Brewster’s model linked these wavelengths with water vapour condensing, there had been no detailed physical mechanism to explain why clouds emit so much radiation in this range.
Tatartchenko calculates that up to 5 per cent of the latent heat released when water condenses could be in the form of radiation. And with vast quantities of water vapour in the atmosphere, he believes that this process represents a significant yet previously ignored energy pathway. If confirmed, says Stone, “this mechanism might need to be taken into account in atmospheric and climate models”.
“This mechanism might need to be taken into account in atmospheric and climate models”
This is not, however, a line of reasoning that convinces Joshua Wurman, an atmospheric scientist from the Center for Severe Weather Research in Boulder, Colorado. There is already a perfectly good explanation for the infrared radiation we see in Earth’s atmosphere, Wurman says. It is simply black body radiation. Atmospheric water vapour emits this radiation mainly in the infrared range, he says, and that is what satellites are detecting. “Their idea makes no sense,” he says.
Tornado warning
Tatartchenko agrees that some of the infrared radiation detected by satellites will be black body radiation, but insists that phase transitions make a significant contribution too, particularly when clouds are forming at extreme altitude or in the polar regions, where the atmosphere is very dry. In these situations the radiation will be able to reach weather satellites easily as there is little water vapour en route to absorb it. “The amount of infrared radiation emitted from cloud droplets is still not adequately explained,” he says.
“The amount of infrared radiation emitted from clouds is still not adequately explained”
If Perel’man and Tatartchenko have stumbled across a genuine effect, is it anything more than just a minor curiosity? Tatartchenko certainly thinks so. He suggests that watching for intense atmospheric infrared emissions could provide early warning of hurricanes and other violent storms. Observations with radar or in visible light can’t warn us that a storm is brewing until it is too late, he says: the storm clouds are already there by the time we can detect their water vapour. He thinks infrared observations could reveal a storm before it has fully formed, provided the contribution from black body radiation can be untangled (). “I think that the intensity of the radiation is proportional to the speed of the cloud formation,” he says.
And why should this mechanism be confined to our skies? Tatartchenko suggests it could help explain the colour of the Great Red Spot, the vast storm whirling around in Jupiter’s southern hemisphere. He thinks that when ammonia and water vapour condense and solidify in the planet’s upper atmosphere, they give off radiation that extends from the infrared into the long-wavelength end of the visible spectrum – in other words, red light.
Tatartchenko has an even more radical proposal. He thinks that a beam of infrared photons at precisely the right wavelength could stimulate emission from moisture in the air and trigger cloud formation. It’s not the clouds themselves he is interested in, though: his idea is to harness the energy locked up in moist air. The trick, he says, would be to set up a pair of parallel mirrors with a constant supply of cool, moist air flowing between them. Shining a beam of infrared photons into this space should trigger the formation of water droplets, releasing more infrared radiation in the process.
If the mirrors are carefully aligned, the radiation should bounce back and forth through the moist air, stimulating even more emission. Tatartchenko says this will amplify the incoming beam. In other words, it will create a sort of cloud laser. By extracting a little of the beam – perhaps by making one mirror slightly transparent, as in a regular laser – he suggests that such a device could be used to generate usable energy. Assuming about 8 per cent of the light emitted by the water is kept inside the cavity, Tatartchenko calculates that a pair of 1-square-metre mirrors would produce 2000 watts – an output 20 times as great as that of a typical silicon solar cell of the same size ().
Ackland is sceptical that it could ever work. Using this putative mechanism to drive a laser would require consistent conditions over time, he says. “Clouds and fog are not noted for this property,” he points out. And even if there is something to it, says William Rossow at the NASA Goddard Institute for Space Studies, this process is insignificant, since it would have to compete with the very efficient thermal emission process.
Townsend, who studies light emission from semiconducting crystals, also doubts the cloud laser is practical, but he is certain Tatartchenko’s emission mechanism is genuine. Consider how many molecules there are in a raindrop, he says. If just one-millionth of the drop’s latent heat of condensation goes into infrared radiation by Perel’man and Tatartchenko’s mechanism, “there would be millions of photons released”, he says.
Clearly Tatartchenko needs more evidence. In the past few months he returned to Russia to talk to the Russian Space Agency in the hope of organising further experiments. If funds materialise, he will make additional measurements of the spectrum of radiation emitted as water vapour condenses. He also wants to test his cloud laser concept by building one “on the slopes of a mountain, at an altitude of around 3000 metres”. Brewster too plans experiments, but on a less ambitious scale. “To start with I’d like to do simple cloud chamber experiments and measure the radiation for myself,” he says. It’s hardly surprising that researchers are sceptical, he says, but no one should dismiss new ideas out of hand. “Theory is always evolving in the face of experimental evidence.”
