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.Seventy years ago, physicists took up biology for two important reasons: (1) they were expecting to find new fundamental laws in biology, (2) they wanted to show biologists how smart they were.
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?.
They partially succeeded in the second goal since some of the most important work in molecular biology was done by physicists who started to work on biological problems. However, the biggest lesson from this experience was that you need to learn how to think like a biologist—and not like a physicist—in order to make progress in the messy field of living organisms.
This is a lesson that physicists need to relearn frequently. The latest attempt to understand biology, while thinking like a physicist, comes from Johnjoe McFadden. In this case, McFadden is not a physicist but a genuine molecular bioogist. He thinks that primitive self-replicating RNAs have to spring up out of the primordial ooze in one fell swoop.
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 puzzle is not only how life emerged, but how it emerged so fast."The creationists are going to love hearing about those kinds of improbable events.
Most biologists don't think that life began with the sudden formation of a 165 bp ribozyme. Instead, they would postulate much more probable scenarios, including scenarios that precede the RNA world.
But such thinking doesn't concern a physicist because physicists are used to dealing with five or six improbable things before having breakfast. McFadden believes that an extremely improbable ribozyme can form spontaneously by invoking a short-cut in the search algorithm.
McFadden believes that nature employed a quantum trick to speed up the process of sorting through and discarding unwanted structures - the same trick quantum computers employ.Thanks for your input, Dr. McFadden, but those kinds of hand-waving explanations don't cut the mustard in biology. They may be acceptable in physics but most biologists have higher standards these days.
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 "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.
However, in fairness, there are a few biologists who find the idea of quantum magic quite attractive. Ken Miller writes in Finding Darwin's God (p. 241).
Even the most devout believer would have to say that when God does act in the world, He does so with care and subtlety. At a minimum, the continuing existence of the universe itself can be attributed to God. The existence of the universe is not self-explanatory, and to a believer the existence of every particle, wave, and field is a product of the continuing will of God. That's a start which would keep most of us busy, but the Western understanding of God requires more than universal maintenance. Fortunately, in scientific terms, if there is a God, He has left himself plenty of material to work with. To pick just one example, the indeterminate nature of quantum events would allow a clever and subtle God to influence events in ways that are profound, but scientifically undetectable to us. Those events could include the appearance of mutations, the activation of individual neurons on the brain, and even the survival of individual cells and organisms affected by the chance processes of radioactive decay.Now you can add the formation of life itself to the list of subtle, scientifically undetectable, processes that can be used by God.
Johnjoe McFadden is the author of Quantum Evolution. As far as I can tell, McFadden is not promoting belief in the supernatural. Nevertheless, some of his writings appear to almost as mystical as those of Ken Miller. Here's a quotation from his website [Quantum Evolution].We have all been brought up on the neodarwinian synthesis of Darwinian natural selection with Mendelian genetics that states that the only significant lifestyle change to befall any microbe – mutations – are entirely random. The dogma states that mutations provide the raw material for evolution but natural selection provides the direction of evolutionary change. This dogma has been the central plank of evolutionary theory for nearly a century. But is it always true?Is this one of those times when a little knowledge of physics (and biology) proves to be a really dangerous thing?
The proposal that the genetic code may inhabit the quantum multiverse suggests that in some circumstances, it doesn’t hold. Mutations are the driving force of evolution; it is they that provide the variation that is honed by natural selection into evolutionary paths. Mutations have always been assumed to be random. But mutations are caused by the motion of fundamental particles, electrons and protons – particles that can enter the quantum multiverse – within the double helix.
When Watson and Crick unveiled their double helix more than half a century ago they pointed out that mutations may be caused by a phenomenon known as DNA base tautomerisation.
Tautomerisation is essentially a chemist’s way of describing a quantum mechanical property of fundamental particles: that they can be in two or more places at one. Quantum mechanics tells us that the protons in DNA that form the basis of DNA coding are not specifically localised to certain positions but must be smeared out along the double helix. But these different positions for the coding protons correspond to different DNA codes. At the quantum mechanical level, DNA must exist in a superposition of mutational states.
If these particles can enter quantum states then DNA may be able to slip into the quantum multiverse and sample multiple mutations simultaneously. But what makes it drop out of the quantum world? Most physicists agree that systems enter quantum states when they become isolated from their environment and pop out of the multiverse when they exchange significant amounts of energy with their environment, an interaction that is termed ‘quantum measurement’. Cells may enter quantum states when they are unable to divide and replicate – perhaps they can’t utilise a particular substrate in their environment. They may collapse out of those quantum states when their DNA superposition includes a mutation that allows them to grow and replicate once more. In this way the environment interacts with, and performs a quantum measurement on the cell, to precipitate advantageous mutations. From our viewpoint, inhabiting only one universe, the cell appears to ‘choose’ certain mutations.
"A little learning is a dangerous thing; drink deep, or taste not the Pierian spring: there shallow draughts intoxicate the brain, and drinking largely sobers us again."
Alexander Pope (1688 - 1744) in An Essay on Criticism, 1709
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