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Physicists contemplate an alternative life, but miss the point entirely

Computer simulations show that dust particles in plasmas may come together and …

Okay, let's begin this article with a disclaimer: I was a big fan of artificial life. The field claimed that it was on the way towards greatness by explaining why and how life came to be the way it is. The central thesis was that life obeys sets of very simple rules that, when put together, give rise to astonishing complexity. Computer models that showed flocking behavior and other commonly seen animal behavior were manufactured and presented as triumphs. However, even during my A-life period, I always had a nagging suspicion that there was a missing link in there somewhere. That link became glaringly obvious when I discussed it with a friend just a year ago; none of the researchers (at the time) had shown any inclination to look for the existence of such rules in real organisms and thereby test their models against reality.

A forthcoming paper in the New Journal of Physics follows the A-life vein of research and should be treated with appropriate caution. Nevertheless, it is still important because it highlights our problems when contemplating life on other planets or even in the dusty realms of outer space. Stripped to its bare essentials—and without the nitpicking, thank you very much—life can be described as anything that can replicate and has, through replication, the ability to evolve so that an open-ended increase in complexity becomes possible. Once you accept this, then some minimum functionality is found to be necessary, namely the ability to accumulate and dissipate energy, the ability to store information, and a boundary.

A collaborative computer modeling effort has shown that dust in plasma may form structures that exhibit all these properties. Dust that is sitting in a plasma quickly becomes charged thanks to collisions with electrons and protons. The charged dust interacts and, provided the temperature is low enough, forms a stable structure. This structure will almost always end up helical. The only exception to this is when the plasma is spherically symmetric. The helical spiral automatically encourages the growth of a second helix that, in the absence of environmental noise, is a perfect copy of itself. The growth rate depends on how quickly the helix absorbs energy through electron and proton collisions from the plasma.

So far, what we have described is replication without evolution or memory. However, these too are present. The dusty helix has only three different radii that are stable and as a helix spontaneously forms, it can switch randomly back and forth between these radii. Furthermore, as it replicates, it replicates these switches in radii as well. The kicker, however, is that some structures are better at collecting energy from the surrounding plasma than others, setting up a competition for a limited resource and enabling a form of natural selection.

To be fair, the researchers don't claim that this is life, only life-like and I think they should have noted a couple of caveats to the work. These guys seem to intermingle evolution and origin of life issues, producing confused statements like this: "The well known problem in explaining the origin of life is that the complexity of living creatures is so high that the time necessary to form the simplest organic living structure is too large compared to the age of the Earth. Similarly, the age of the Universe is also not sufficient for organic life to be created in a distant environment (similar to that on the Earth) and then transferred to the Earth." They have not demonstrated that there is any selection pressure. For there to be selection pressure, the amount of energy gathered by a helix has to be limited by other helices and their simulations are not that sophisticated. More importantly, the experimental evidence is limited to the observation that something that might have been a helix has been observed in a plasma. All the rest is based on computer models, making it look like argument by analogy.

The final conclusion backs up something that was discussed on a recent Scientific American podcast. Our search for life is biased by our own observational evidence. We really don't know if life could have taken alternative pathways right at the beginning. When we manufacture probes to search for life on other planets, engineers and scientists tend to assume they are looking for carbon-based life that need water. The existence of extremophiles is one example that tells us that our net needs to be cast very widely if we are to be sure of success.

New Journal of Physics, 2007, DOI: unknown

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