The Fermi Paradox and Are We Alone in the Universe?

The Fermi paradox is something like this. The Universe is enormous, and there are an astronomical number of planets. Accordingly, the potential for intelligent life somewhere should be enormous, but we find no evidence of anything. The Seti program has been searching for decades and has found nothing. So where are these aliens?

What is fascinating about this is an argument from Daniel Whitmire, who teaches mathematics at the University of Arkansas and has published a paper in the International Journal of Astrobiology (doi:10.1017/S1473550417000271 ). In it, he concludes that technological societies rapidly exterminate themselves. So, how does he come to this conclusion. The argument is fascinating relating to the power of mathematics, and particularly statistics, to show or mislead.

He first resorts to a statistical concept called the Principle of Mediocrity, which states that, in the absence of any evidence to the contrary, any observation should be regarded as typical. If so, we observe our own presence. If we assume we are typical, and we have been technological for 100 years (he defines being technological as using electricity, but you can change this) then it follows that our being average means that after a further 200 years we are no longer technological. We can extend this to about 500 years on the basis that in terms of age a Bell curve is skewed (you cannot have negative age). To be non-technological we have to exterminate ourselves, therefore he concludes that technological societies exterminate themselves rather quickly. We may scoff at that, but then again, watching the antics over North Korea can we be sure?

He makes a further conclusion: since we are the first on our planet, other civilizations should also be the first. I really don’t follow this because he has also calculated that there could be up to 23 opportunities for further species to develop technologies once we are gone, so surely that follows elsewhere. It seems to me to be a rather mediocre use of this principle of mediocrity.

Now, at this point, I shall diverge and consider the German tank problem, because this shows what you can do with statistics. The allies wanted to know the production rate of German tanks, and they got this from a simple formula, and from taking down the serial numbers of captured or destroyed tanks. The formula is

N = m + m/n – 1

Where N is the number you are seeking, m is the highest sampled serial number and n is the sample size (the number of tanks). Apparently this was highly successful, and their estimations were far superior to intelligence gathering, which always seriously overestimated.

That leaves the question of whether that success means anything for the current problem. The first thing we note is the Germans conveniently numbered their tanks, and in sequence, the sample size was a tolerable fraction of the required answer (it was about 5%), and finally it was known that the Germans were making tanks and sending them to the front as regularly as they could manage. There were no causative aspects that would modify the results. With Whitmire’s analysis, there is a very bad aspect of the reasoning: this question of whether we are alone is raised as soon as we have some capability to answer it. Thus we ask it within fifty years of having reasonable electronics; for all we know they may still be asking it a million years in the future, so the age of technological society, which is used to base the lifetime reasoning, is put into the equation as soon as it is asked. That means it is not a random sample, but causative sample. Then on top of that, we have a sample of one, which is not exactly a good statistical sample. Of course if there were more samples than one, the question would answer itself and there would be no need for statistics. In this case, statistics are only used when they should not be used.

So what do I make of that? For me, there is a lack of logic. By definition, to publish original work, you have to be the first to do it. So, any statistical conclusion from asking the question is ridiculous because by definition it is not a random sample; it is the first. It is like trying to estimate German tank production from a sample of 1 and when that tank had the serial number 1. So, is there anything we can take from this?

In my opinion, the first thing we could argue from this Principle of Mediocrity is that the odds of finding aliens are strongest on earth-sized planets around G type stars about this far from the star, simply because we know it is at least possible. Further, we can argue the star should be at least about 4.5 billion years old, to give evolution time to generate such technological life. We are reasonably sure it could not have happened much earlier on Earth. One of my science fiction novels is based on the concept that Cretaceous raptors could have managed it, given time, but that still only buys a few tens of millions of years, and we don’t know how long they would have taken, had they been able. They had to evolve considerably larger brains, and who knows how long that would take? Possibly almost as long as mammals took.

Since there are older stars out there, why haven’t we found evidence? That question should be rephrased into, how would we? The Seti program assumes that aliens would try to send us messages, but why would they? Unless they were directed, to send meaningful signals over such huge distances would require immense energy expenditures. And why would they direct signals here? They could have tried 2,000 years ago, persisted for a few hundred years, and given us up. Alternatively, it is cheaper to listen. As I noted in a different novel, the concept falls down on economic grounds because everyone is listening and nobody is sending. And, of course, for strategic reasons, why tell more powerful aliens where you live? For me, the so-called Fermi paradox is no paradox at all; if there are aliens out there, they will be following their own logical best interests, and they don’t include us. Another thing it tells me is this is evidence you can indeed “prove” anything with statistics, if nobody is thinking.

Biogenesis: how did life get started?

Early next year I have been invited to give a talk on biogenesis. How life gets started is of interest, because now we know there are a number of planets around other stars, if we know how it can get started, we can know whether life could or should form on a given planet. Of course, nobody actually knows, which has the obvious benefit is that if I get something a little wrong, nobody (including me) will know, and the second one is, one can use logic to cut away a lot of some rather silly stuff being said elsewhere. The most obvious silly suggestion (in my opinion) to me is panspermia, which is when life came from somewhere else, travelled through space on a meteor, and landed on Earth, whereupon the life form flourished in a new environment. Supporters of this theory point out that very primitive life forms can survive in a vacuum, and that DNA has been shown to be able to survive through extended time in vacuum and radiation, if buried inside a rock.

So, what is wrong with this theory? First, let us think about “extended periods of time”. A number of meteorites have been found that originated on Mars, and these have taken millions of years to get here. (Not there has been any sign of viable life on them.) We have no evidence whatsoever that life forms could last that long, nor have we any reason to believe that Mars was a better place for life to get started than here. Had the life come from another solar system, it had to survive for hundreds, or thousands of millions of years, because of the huge distances in space. This also shows another problem: if they take that long to arrive, and there is not that many of them, the concentration of them is very low. Why does it take that long? Basically, because ejecta that escapes Mars goes into orbit around the sun, and stays in that orbit indefinitely until it hits something else. Compared with the size of the solar system, Earth is a tiny microscopic dot. If it comes from another star system, it will arrive with a velocity greater than the escape velocity of our star, so it will come in at extreme velocity and either hit the Earth or never pass it again.

The fact that DNA can survive (although it has hardly been shown to be viable for that length of time) is insufficient to bring life here. Life will contain a set of enzymes, and they get denatured on warming. Yes, there are special enzymes in hot pools, but these have evolved there. Most enzymes denature and then refuse to work if heated half-way to boiling, and a meteorite coming into the Earth’s atmosphere will get a lot hotter than that. But let us suppose it survives and either hits land or water. Now what? A life form has to support itself by consuming what it needs from its environment. It needs a boundary to contain it (skin, in our case), it needs chemicals to replace it, it needs some means of obtaining energy, and it needs chemicals to enable it to use energy. If any of these are missing, then the life form will die.

Energy for life on Earth comes from the sun, via photosynthesis. We know that on Earth life may well have been around in some form or other for something like a billion years before photosynthesis evolved. That means that if the original life forms came from space, they had no means of using solar energy that we know of, hence they would have to rely on chemical processing. There would then be the problem of finding nitrogen-rich organic compounds from which to make things like protein and more nucleic acids. Either those things were around or they were not. If they were not, the life form would die out, as it would be impossible to reproduce. If they were around, then why did they not evolve to form life? Thus any conditions present that would permit an alien life form to grow would also be sufficient for the life form to evolve from what is there. I cannot prove it did, but from Occam’s razor, life coming from outer space is an unnecessary assumption unless there is proof, and since it is sufficient for life to form here if the chemicals required for alien life to survive are here, it is simpler to assume that is what happened. I am convinced we are ourselves, and not some remnants of some space catastrophe.

Planets for alien life (2)

My last post gave an estimate of how many stars were suitable for having planets with life, if they had rocky planets in the right place. The answer comes out very roughly as one per every five hundred cubic light years. At first sight, not very common, but galaxies are very big, and we end up with about a hundred billion in this galaxy. The next question is, are there further restrictions? Extrasolar planets are reasonably common, according to recent surveys, however most of these found are giants that are very close to the star, and totally unsuited for life. On the other hand, there is a severe bias: the two methods that have yielded the most discoveries favour the finding of large planets close to the star.

To form stars, a large volume of gas begins to collapse, and as it collapses to form a star, it also forms a spinning disk. Three stages then follow. The first stage involves gas falling into the star from an accretion disk at a rate of a major asteroid’s mass each second. The second involves a much quieter stage, where the star has essentially formed, but it still has a disk, which it is accreting at a much slower rate, about a thousandth as fast. Finally, the star has “indigestion” and in a massive burp, clears out what is left of the disk (technically called a T Tauri event). The standard theory has the planets forming in the second stage or, for rocky planets, even following the T Tauri cleanout.

There are two important issues. As the gas falls into the star, both energy and angular momentum must be conserved. The fate of energy is simple: as the gas falls inwards, it gets hotter, and it is simple gravitation that heats the star initially, until it reaches about 80 million degrees, at which point deuterium starts to fuse and this ignites stellar fusion. However, the issue with angular momentum is more difficult. This is like an ice skater – as she brings her arms closer to herself, she starts spinning faster; put out her arms and the spin slows. As the gas heads into the star, the star should spin faster. The problem is, almost all the mass of the solar system is in the star, but almost all the angular momentum is in the planets. How did this happen?

Either all the mass retained its original angular momentum or it did not. If it did, then the sun should be spinning at a ferocious rate. While it could have lost angular momentum by throwing an immense amount of gas back into space, nobody has ever seen this phenomenon. If the stellar mass did not retain its angular momentum, it had to exchange it with something else. In my opinion, what actually happened is that the forming planets took up the angular momentum from gas that then fell into the star. If that is true, every star with enough heavy elements will form planets of some description because it helps stellar accretion. If so, the number of planet-bearing stars is very close to the number of stars.

There is, however, another problem. In my theory (Planetary Formation and Biogenesis for more details) planets simply keep growing until the stage 3 disk clear-out. If they get big enough, mutual gravitational interactions disrupt their orbits and something like billiards occurs. The planets do not collide, but if they come close enough one will be thrown out of the system (astronomers have already detected planets floating around in space, unattached to any star) and the other will end up as a giant very close to the star. A considerable number of such systems have been found. This would totally disrupt Earth-like planets, so stars with planets suitable for life must have had a shorter stage 2.

How short? Stage 2 can last up to 30 million years, although that is probably an exception, while the shortest stage 2 is less than a million years. The answer is, probably no more than a million years, i.e. our planetary system was formed around a star that had a relatively short secondary accretion. The reason I say that is as follows. The rate of accretion of a gas giant should be proportional to how much gas there is around it, and for how long. The amount of gas decreases as the distance from the star increases, and if you double the distance from the star, the gas density decreases somewhere between a half and a quarter. Now the three million year old star LkCa 15 is slightly smaller than our sun but it still has a second stage gas disk. This star has a planet nearly five times as big as Jupiter about three times further away from the star. This almost certainly means that Jupiter must have stopped growing well within three million years. (As an aside, standard theory requires at least 15 million years to start a gas giant.) Fortunately, it appears that about half the stars have such a short secondary stage. If we then say that about half the stars will be in the wrong part of the galaxy, then the estimate of stars that could be suitable for life reduces to about 25 billion. If we further reduce the total by those that are simply too young, or do not have sufficient metallicity, we could reduce the total to about 10 billion. These numbers are very rough, but the message remains: there are plenty of stars suitable to sustain life-bearing planets in the galaxy. The next question is, how many stars will have rocky planets?