Planetary Life

 

A long time ago - maybe in the 1970s - Carl Sagan and Pat Morrison explained that the Search for Extra-Terrestrial Intelligence (SETI) involves a simple calculation, a multiplication of odds. The calculation states (a lengthy list of) factors thought to be involved in the evolution of life forms, and the odds for each factor to happen. This is like estimating the odds of throwing a six, a three and then a ten with dice: the cumulative probability is the multiplication of the odds of each event. In the case of Homo sapiens, the chances of our existence are less than one in a million. Nonetheless, we think we exist; at least, I think I exist.

The problem of SETI is a matter of luck. If contacting an ET requires technology, probably on both ends, what are the odds of two or more technological civilizations thriving simultaneously and long enough to complete a circuit? To skeptics, especially, this must seem truly stupendous foolhardiness: betting on the longest of long shots to win.

But, is it?

Since the odds were first stated, a lot has changed. For example, it now appears planetary systems are far more abundant than was thought in the absence of discovery. In the course of stellar evolution, planets may be formed 25-40% of the time. 25 years ago, that probability was considered far less than 1%.

We now know a lot more about genetics than just 2 decades ago. It seems likely that, once evolution gets going, it "inevitably" (is very likely to) produces ever more hardy organisms. Evolution is not simply the result of adaptation to geological changes, but also arises from inter- and intra-species competition. In the presence of a variety of species, there are endless experiments on the environment, some of which endow the experimenters with a relative advantage in survival or reproduction. Thus, it is in the "nature" of organisms to improve themselves, as well as adapt to external forcing events.

We still don't know exactly how life got started on this wonderful planet, our Gaia. But, however lowly our origins, the process of living seems likely to produce very competent creatures, even such as ourselves. Moreover, it is not as far-fetched as it once seemed that different planets could mother different life forms.  So, the likelihood of technical civilizations is probably far greater than Sagan et al thought a quarter-century ago. If so, this is a great reward for those farsighted innovators.

The one thing that hasn't changed is the likelihood of co-existence. This involves three factors: the probability of relativistically simultaneous civilizations, the probability of technical capability, and the duration of capability. We don't control the first factor, have only some control over the second, but are completely responsible for the third.

The first factor is the probability that a star has had the right kind of planets in the same time frame as our Sol. Due to the vast distances between solar systems, "time frame" has to be understood in Einsteinian terms. Assuming face-to-face contact unlikely, "contact" will be made over hundreds or thousands of light years, so "now" is a very slippery, if calculable, term. What we learn of our correspondents will be quite old news of them. We will only be able to guess what is happening to them in our "now," today.

The distances make communication a long process, but it also makes it more difficult because messages will be lost or corrupted in transmission. So, there is not just the difficulty of finding an ET about the same age and ability as ourselves, but the further difficulty of one on the same space-time trajectory as ourselves. Despite these problems, I think the overall probability of possible contact can be calculated, once we have a reasonable estimate of how likely it is for life to form on a planet, and how long life forms persist on planets.

In order to contact an ET, those capable of contact have to be around at the same time long enough for the signals to make a round trip. The signal circuit time is probably much longer than a century or two, longer than we have had radio, TV and satellites. Thus, a major constraint on the problem is how long a technical civilization can endure. I believe this factor is the one in our control. In fact, whether we control our social longevity probably determines whether we will ever contact an ET. That is, if we haven't the good sense to control our own destiny, then natural circumstances will probably bring our civilization to an end before contact is made or confirmed. The point of this remark is to establish a criterion for ETs and ourselves capable of interstellar contact: they are sufficiently intelligent to control their own destinies.

Homo sapiens is on the threshold of  meeting this requirement. I don't think we have reached that stage. In looking over the events of our times, we should ask ourselves which things hasten the day of a enlightened, permanent civilization capable of meeting ETs, and which do not. I think this question sheds light on many issues of our time, pointing the way for our further activities.