AS if they don鈥檛 have enough on their hands tackling some of the biggest questions about our universe, some physicists are muscling in on biology鈥檚 greatest endeavour. Life, say the physicists, began with a quantum flutter.
The idea that quantum mechanics is key to explaining the origin of life was first raised as far back as 1944 in Erwin Schr枚dinger鈥檚 influential book What is life?.
More than 60 years later, this bold prediction has still to be confirmed. Its proponents have struggled to find a way round the fact that quantum effects lose all their handy weirdness in the probable crucible for life. As a result, many scientists are sceptical of ideas that set up quantum mechanics as the midwife of life, says physicist Paul Davies of Arizona State University (ASU) in Tempe.
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Yet, perhaps the quantum midwife idea ought to be taken more seriously. Delegates at a conference on quantum effects in biology at ASU this week certainly think so. Two separate studies claim to answer the theory鈥檚 critics, and reveal a way in which quantum fluctuations might have sparked life. 鈥淲e shouldn鈥檛 be too hasty in shrugging aside quantum effects in the origin of life,鈥� says Davies.
The first person to strike a blow for the theory was Johnjoe McFadden at the University of Surrey in the UK, who reckons he has a way to harness the problematic fragility of quantum states.
The problem with most theories for the origin of life, says McFadden, is that even with all the ingredients needed to build life in some primordial soup, the odds of them combining in the right sequence to create a primitive self-replicating structure are slim. Chemists and biologists look for ways that a primitive self-replicating structure, such as a rudimentary RNA enzyme, or ribozyme, might spring up naturally.
鈥淭he problem with most theories for the origin of life is that the ingredients are unlikely to combine in the right sequence鈥�
Yet even a primitive ribozyme is a complicated structure, McFadden explains, requiring 165 base-pair molecules to be strung together in the right order. In fact, 4165 possible structures 鈥� most of which are not self-replicators 鈥� could be made with the same starting ingredients. 鈥淭hat鈥檚 more than the number of electrons in the universe,鈥� he says. What鈥檚 more, life came about relatively soon after the planet formed, he says. 鈥淭he puzzle is not only how life emerged, but how it emerged so fast.鈥�
McFadden believes that nature employed a quantum trick to speed up the process of sorting through and discarding unwanted structures 鈥� the same trick quantum computers employ.
Quantum bits, or qubits, can take on many different values simultaneously, since the properties of particles are not set until they are observed. This means that quantum computers can, in theory at least, exploit this ability to whip through their calculations much faster than their classical counterparts.
McFadden thinks a similar process could have occurred in the chemical soup that spawned life. If many different chemical structures could exist simultaneously in multiple, slightly mutated configurations, they could essentially 鈥渢est鈥� a range of possibilities at once until they hit a self-replicating molecule. This could trigger the act of replication, he says, which could be violent enough to collapse the delicate quantum states, fixing that structure as a self-replicator.
Davies likes that idea. 鈥淢cFadden has found a way in which the fragility of quantum states actually helps amplify the process he is trying to achieve,鈥� he says. However, McFadden鈥檚 theory does not fully get around the problem of the fragility of quantum effects.
In the past, critics of a quantum origin for life have argued that heat would disrupt the fragile states because biological processes tend to take place in warm environments.
Davies thinks that this is not enough of a reason to dismiss such theories out of hand. 鈥淲e think they would be disrupted, but in fact nobody really knows,鈥� he says. He points out that recent experiments hint at quantum effects in large-scale biological systems.
For instance, quantum effects may be needed to explain the speed with which molecular 鈥渕otors鈥�, the polymerase enzymes, crawl along unzipped strands of DNA and forge the links that match up the strands鈥� unpaired nucleotide bases with complementary bases floating in the vicinity (New 杏吧原创, 11 December, 2004, p 28)
Nonetheless, to be taken seriously, any credible quantum theory for the origin of life would need to show that there are natural environments in which quantum processes can occur unhindered even in warm temperatures.
Another recent study that gained attention before the ASU quantum life conference claimed to have found such a shelter 鈥� at the bottom of the ocean. Asoke Nath Mitra, a physicist at the University of Delhi in India, and independent researcher Gargi Mitra-Delmotte, were inspired by an idea proposed by Michael Russell at the University of Glasgow, UK.
In 1994, Russell and his colleagues showed that the molecules needed to build a primitive RNA will chemically react with iron sulphide on hydrothermal mounds, becoming trapped in crystal chambers near the vents and increasing the chance of the molecules self-assembling into a primitive RNA structure.
Mitra and Mitra-Delmotte say that these chambers could allow quantum effects to occur without disruption. Their calculations show that small magnetic fields generated by the iron sulphide mineral greigite, which makes up the chambers, could maintain the quantum states of molecules despite the heat.
They argue that this is an established effect; physicists attempting to build quantum computers already use magnetic fields to control the quantum property of entanglement in qubits.
鈥淎ll we have done is bring together the ideas of other researchers,鈥� says Mitra-Delmotte. 鈥淲e were so excited when we found that actually they all fit together perfectly, like the pieces of a jigsaw puzzle. This seems to indicate an important role for magnetism in the theories of the origin of life.鈥�
Vlatko Vedral, an expert on quantum computing at the University of Leeds, UK, says that the idea needs experimental support, but he is optimistic about the prospects for testing it using existing technology. 鈥淚t will be an important and astonishing discovery if it is found to be true,鈥� he says.
Davies also finds the idea promising. 鈥淭hese guys may have found a niche where quantum magic really could be at work,鈥� he says. 鈥淏ut it is conjecture at this stage, just as all ideas for the origin of life are.鈥�
Antonio Lazcano, a biologist at the National Autonomous University of Mexico in Mexico City and president of the , is less impressed. He believes that the Russell mound scenario is itself flawed.
For example, the researchers suggested that bacteria and archaea emerged from the chambers independently then somehow joined to create the third class of life, the eukaryotes. This sequence of events conflicts with how biologists think early life evolved. 鈥淭hey are extrapolating quantum physics without caring for this biological problem,鈥� he says.
Lazcano is not convinced quantum explanations are needed at all. 鈥淭here is an element of quantum mysticism in these theories that just doesn鈥檛 entice me,鈥� he says. In a upcoming paper in Chemistry and Biodiversity, he argues that attempts to find a quantum explanation for life will end up in the same dustbin as physicists鈥� earlier attempts to explain the riddle using magnetism, surface tension and radioactivity.
Vedral is reserving judgement, pending experimental evidence, though if such an idea were to prove correct he won鈥檛 be terribly shocked. 鈥淧eople argue that we鈥檝e been struggling for 20 years with quantum computing and we haven鈥檛 got very far, so how can nature have been doing it? But of course nature had billions of years to perfect its technique.鈥�
鈥淲e have been struggling for 20 years with quantum computing but nature had billions of years to perfect its technique鈥�
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