“Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.” Arthur C Clarke, sci-fi author.
Graham writes …
The question as to whether intelligent life exists elsewhere in the Universe is a fascinating one. As someone who was captivated by the sciences, and astronomy in particular, from a young age I have been always intrigued by this mysterious, unresolved issue. Everyone, including myself, is able to express an opinion, but evidence is lacking to be able to arrive at a definitive conclusion. The two major stumbling blocks are, firstly, no one knows how life began on planet Earth, and secondly no direct evidence of alien life has been found despite decades of searching by programmes such as SETI (the search for extraterrestrial intelligence).
The first of these issues is that we do not have a working theory or understanding of the process of abiogenesis, which is the means by which living organisms arise from inorganic material (the proverbial ‘primaeval soup’). Despite intense research activity over many years, this has evaded satisfactory resolution. Some authors have expressed a view that ‘evolution did it’, but of course this only comes into play when there is an existing living population for evolution to act upon. Darwin’s process of natural selection can say nothing about the origin of life. So without an appreciation of how life began here, and in particular how likely or unlikely is the process of abiogenesis, it is difficult to assess whether the Universe is devoid of other life, or conversely teeming with life. The second issue related to SETI raises the question – if intelligent life is abundant in the Universe why has there been a total lack of evidence in the form of direct communication. Where are they all?
Our lack of success in making contact is not just about the vastness of space, but there is also a time-related aspect. There is good evidence to suggest that the Earth was formed around 4.6 billion years ago, and it has taken most of that time for intelligent life to arise. The human species, Homo sapiens, arose about 250,000 years ago, and it is only in recent times that we have developed the technology to potentially communicate across interstellar distances. Although we don’t know how typical our development is compared to extraterrestrial civilisations, we can indulge in a hypothetical comparison to make a point. We can suppose that an alien technological society would discover the energy of the atom, and potentially develop the capability to wipe itself out. Also if we assume that their society, like ours, is energy-hungry, this may result in the threat of a run-away greenhouse effect destroying their biosphere. This raises the question – how long typically would a technological civilization exist? It might be only of the order of 200 years between the development of communications technology and a potentially catastrophic demise. So here’s the point. If we collapse the 4.6 billon year history of planet Earth into a 24 hour period, then 200 years would be equivalent to a very brief 4 milliseconds (four thousandths of a second) – much shorter than the blink of an eye. So the window of opportunity, in time, to communicate with an alien society may be very brief indeed. And furthermore, how likely is it that our window of reception is synchronized with their window of transmission, given the huge sweep of cosmic history?
Without breakthroughs in both of these areas, we come back to the notion that all we can do is express an opinion. I think at the moment it’s ‘fashionable’ to express a view that intelligent alien life is abundant. And a great many ‘celebrity scientists’ do. The argument goes that given enough planets and enough time, life will happen everywhere, despite the fact that abiogenesis appears to be very unlikely. An example is American astronomer and science communicator Carl Sagan, who presumably believed the view expressed by Ellie Arroway, the lead fictional character in his excellent novel Contact (1). Talking to a group of children, she expressed what has become a commonly held view: “I'll tell you one thing about the universe, though. The universe is a pretty big place. It's bigger than anything anyone has ever dreamed of before. So if it's just us... seems like an awful waste of space. Right?” I have to say that over the majority of my lifetime, I too have expressed this belief.
In recent years, I have attempted to gain more of an understanding of the problem of abiogenesis. It is fair to say that I have spent a career effectively as a physicist, so my background is not exactly ideal in allowing me to understand the complex biological issues associated with the origin of life. However, working with John Bryant in writing the book, and co-leading conferences, has spurred my interest in biology. I now find myself reading books about organic chemistry, life and the origin of life! I do however have to choose the authors I read very carefully, as I don’t have a lifetime’s experience of the topic to determine the authority, or otherwise, of what I read. Having said that, I now find that doubts about a Universe teeming with life have crept in. From what I grasp from my attempts to understand the biology of life, I have begun to appreciate the magnitude of the problem. Even my rudimentary knowledge gives me an appreciation of the beauty, elegance and especially the complexity of the mechanisms involved in the creation and sustenance of a living organism. In trying to understand how it all started are the enigmas of the curious but vital relationship between nucleic acids (information) and proteins (the molecular work horses) and the apparently irreconcilable ‘chicken-and-egg’ type issues that John has explained so well in his contributions to the book. At this stage of our scientific understanding of abiogenesis we have to say that it remains a mystery.
So what are the chances of life arising from inanimate material? Many years ago mathematician and physicist Fred Hoyle (of Steady State Theory fame) likened the probability of abiogenesis as comparable to “the chance that a tornado sweeping through a junkyard might assemble a Boeing 747 jumbo jet.” His estimate of the odds of this happening is one in 10 to the power of 40,000 (that’s 1 with 40,000 zeros) – an extremely low probability. I have no idea how he came to such an estimate, but the truth is that we are not able to estimate the probability of abiogenesis occurring on this, or any other planet. Hoyle’s argument is now accepted as erroneous as it considers the unlikely scenario of advanced life forms arising directly from inorganic material.
One thing we do have some idea about is the number of planets in the visible Universe. Our home galaxy The Milky Way comprises around one hundred billion stars, and we can estimate the number of galaxies also as approximately one hundred billion. This suggests the number of stars in the visible Universe is approximately 10 to the power 22 (that’s ten thousand billion billion, if that means anything to anyone). We also know that most stars have a planetary system, so if we suppose that each star has one planet orbiting in the circumstellar habitable zone that is a huge number of planets where, potentially, life may arise. However, this too is not straightforward.
As John writes in Chapter 5, cradle Earth that has nurtured complex life is itself special. It orbits a star, the energy output of which has remained relatively stable over billions of years. The Earth is at the ‘right’ distance from its star, so that water may exist in liquid form. Its size is just sufficient to allow it to retain its atmosphere and oceans over billions of years. It possesses a radiation shield by virtue of its magnetic field. It supports tectonic activity which recycles material, especially carbon. The Earth is also accompanied by a relatively large moon, which helps stabilise Earth’s spin axis producing steady climatic conditions. Among the many planets existing in the visible Universe, the Earth may indeed be very rare. The notion of the ‘rare Earth’ was formalised in 2000 by Peter Ward and Donald Brownlee (2).
At the end of all this, we really have no other option than to say the existence of life elsewhere in the Universe is still open to speculation. Frank Drake wrote down an equation in 1961 (the Drake Equation) to estimate the number of communicative extra-terrestrial civilisation in our galaxy. And now, after 60 years of effort, we still do not know the values of the parameters in this equation to allow us to make a definitive judgement.