The notion that quantum processes kick-started life may not be so far
fetched after all ZEEYA MERALI
AS IF they don't have enough on their hands tackling some of the biggest
questions about our universe, some physicists are muscling in on biology's
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 Schrödinger's 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
of Arizona State University (ASU) in Tempe.
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's critics, and reveal
a way in which quantum fluctuations might have sparked life. "We shouldn't
be too hasty in shrugging aside quantum effects in the origin of life,"
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
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 - most of which are not
self-replicators - could be made with the same starting ingredients. "That's
more than the number of electrons in the universe," he says. What's more,
life came about relatively soon after the planet formed, he says. "The
not only how life emerged, but how it emerged so fast."
McFadden believes that nature employed a quantum trick to speed up the process
of sorting through and discarding unwanted structures - the same trick quantum
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
McFadden thinks a similar process could have occurred in the chemical soup
that spawned it life. If many different chemical structures could exist
simultaneously in multiple, slightly mutated configurations, they could
essentially "test" 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. "McFadden has found a way in which the fragility
of quantum states actually helps amplify the process he is trying to achieve,"
he says. However, McFadden's 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. "We think they would be disrupted, but
in fact nobody really knows," he says. He points out that recent experiments
hint at quantum effects in large-scale biological systems.
For instance, quantum effects maybe needed to explain the speed with which
molecular "motors", the polymerase enzymes, crawl along unzipped strands
of DNA and forge the links that match up the strands' unpaired nucleotide
bases with complementary bases floating in the vicinity (New Scientist, 11
December, 2004, p28)
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 - 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.
"All we have done is bring together the ideas of other researchers," says
Mitra-Delmotte. "We 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
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 "It will be an important
and astonishing discovery if it is found to be true," he says.
Davies also finds the idea promising. "These guys may have found a niche
where quantum magic really could be at work "he says. "But it is conjecture
at this stage, just as all ideas for the origin of life are."
Antonio Lazcano, a biologist at the National Autonomous University of Mexico
in Mexico City and president of the International Society for the Study of
the Origin of Life, 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. "They are extrapolating quantum physics without
caring for this biological problem," he says.
Lazcano is not convinced quantum explanations are needed at all. "There is
an element of quantum mysticism in these theories that just doesn't entice
me," 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' 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't be terribly shocked. "People argue
that we've been struggling for 20 years with quantum computing and we haven't
got very far, so how can nature have been doing it? But of course nature
had billions of years to perfect its technique."