For decades the main assumption about extraterrestrial intelligences is that our galaxy contains many civilizations much older than ours, perhaps millions of years older. The reason for this assumption is the fact that the universe is thousands of times older than the human race. Humanity is estimated to be only a few hundred thousand years old, but the universe is some 13 billion years old. Apparently intelligent life could have arisen on other planets any time during the past three or four billion years. A period of about three billion years is about 10,000 times longer than a period of only a few hundred thousand years. So it would seem that if intelligence arose in our galaxy at random times, it would have arisen mainly during the first 99% of this three-billion-year period, which would mean most extraterrestrial civilizations would have arisen millions of years ago. Under such a scenario, our species is a very inferior species, and there are extraterrestrial minds as superior to our minds as our minds are superior to mice or insects.
Such reasoning seems pretty solid, but there is one big problem with it: the fact that we do not see any evidence of other extraterrestrial civilizations (with the possible exception of UFO's, a matter of controversy). If many civilizations arose on other planets millions of years ago, we might expect that such civilizations would have left signs of themselves which we would have detected. But no such sign has been indisputably found. Our searches for extraterrestrial radio signals have not been successful; we have seen no evidence of extraterrestrials in deep space; and we see no artifacts from extraterrestrials anywhere in the solar system.
This discrepancy is known as Fermi's Paradox, the paradox that asks: where is everybody? I discussed various possible solutions to Fermi's Paradox in this earlier blog post. I would now like to suggest another possible solution. I will call this possible answer the SAGE hypothesis. SAGE is an acronym standing for Simultaneous Appearance of Galactic Extraterrestrials.
The idea behind the SAGE hypothesis is that all intelligent life that has appeared in the galaxy has appeared only in the past 300,000 years . Rather than asserting our galaxy has many civilizations millions or many thousands of years older than man, the SAGE hypothesis asserts that while our galaxy may have many civilizations, none of them are much older than mankind.
The answer that the SAGE hypothesis gives to the “Where is everybody?” question of Fermi's Paradox is: they exist, but we have not detected them because they appeared not very long ago; they are about as old as we are.
If this hypothesis is correct, it can adequately explain Fermi's Paradox. We would not expect that we would have received radio signals from extraterrestrial civilizations that are only about as old as our civilization, since our civilization has made almost no attempts yet to send radio signals to other civilizations. We also would not expect to see any signs of extraterrestrial civilizations in deep space if they are only about as old as we are, nor would we expect that they would have reached our planet with spacecraft from their planets.
The graph below illustrates the difference between conventional thinking about the origin date of extraterrestrial civilizations and the assumption of the SAGE hypothesis. Each dot represents the appearance of an extraterrestrial civilization at a point in time and space. The pattern of red dots illustrates the pattern we might expect under conventional assumptions, with extraterrestrial civilizations appearing at random intervals in the past billion years. The pattern of blue dots illustrates the pattern that might occur under the SAGE hypothesis, with all the civilizations appearing relatively recently.
Two Contexts in Which the SAGE Hypothesis Would Be Credible
Despite its success in answering Fermi's Paradox, one might argue that the SAGE hypothesis is not credible, because it seems to require too much of a coincidence for all intelligent life in the galaxy to have appeared only during the past small sliver of cosmic history (a period less than a thousandth of the total length of cosmic history). But there are two contexts in which the SAGE hypothesis would be entirely credible.
The first context in which the SAGE hypothesis would be credible is a theistic context. Let us imagine for a moment the possibility that the universe was specifically created billions of years ago by a cosmic designer, a possibility that cannot be casually dismissed in the light of all we know about the anthropic principle, apparent cosmic fine-tuning, and remarkable coincidences required for our existence. Under such a possibility it is plausible enough that the universe might be either programmed or controlled so that there is a widespread simultaneous appearance of intelligent life, all in the relatively recent past, rather than at random intervals over a span of billions of years.
We can imagine why a cosmic designer or controller might want the earth-like planets of the galaxy to produce intelligent life at roughly the same time – perhaps as a sign of that being's control over things, or perhaps to prevent one civilization from being able to take over the galaxy before other civilizations appeared. By arranging for civilizations to appear simultaneously throughout the galaxy, such a cosmic designer or controller might be guaranteeing a more even-handed distribution of things, so that each civilized planet gets a fairly equal share of the galactic pie.
The second context in which the SAGE hypothesis would be credible is a context in which the universe has some kind of information capabilities beyond any that we currently understand. Let us imagine that the universe has some strange capability in which the following astonishing thing happens: once a highly unlikely event occurs in one place in the galaxy, it then becomes radically more likely to start occurring in other places in the galaxy. This might happen if the galaxy had some type of information field or computational layer, a field perhaps allowing the universe to in some sense “learn” from great successes of the past . We can imagine some context under which the chance of intelligent life appearing on a planet is, say, 1 in a billion – until the time that it first appears, and then the probability changes to be vastly higher (perhaps only 1 in 10 or 1 in 100). It could be that for some information-related reasons, once some great but highly improbable event occurs, it is then almost as if the universe “learns” how to accomplish this thing; and once that happens it could then be relatively easy for the event to occur elsewhere.
Under this idea (which does not require any assumption of a divine creator or designer or controller, but which does require assuming some unusual computation-related feature of the universe), we have a second context in which this SAGE hypothesis could plausibly be true. If the probability of intelligent life appearing on a particular planet were somehow to be radically improved once it had occurred one time, there might be a significant chance of intelligent life appearing more or less simultaneously on many planets in the galaxy.
The Predictions of the SAGE Hypothesis, and How It Could Be Falsified
To many philosophers of science, a scientific idea should ideally be falsifiable, and it should make specific predictions. In this regard, the SAGE hypothesis is in good shape, because it can be falsified, and does make specific predictions.
The SAGE hypothesis would be falsified if we were to look for and receive radio signals or television signals from a very old civilization vastly older than ours. We might then learn that the civilization was far older than ours. That would instantly falsify the SAGE hypothesis, which maintains that no civilizations in our galaxy are very much older than ours. The hypothesis would also be falsified if our planet was to receive a spaceship from another planet, and those beings told us their civilization was very much older than ours.
Below are specific predictions that follow from the SAGE hypothesis:
- We will find no evidence of Dyson Spheres, or any other gigantic galactic engineering projects that would have required many thousands or millions of years to complete.
- If we receive extraterrestrial radio signals or television signals, they will not show us pictures of some vastly superior mega-civilization with godlike technology, but will merely show us a civilization not very much more advanced than our own.
- If we ever receive an extraterrestrial spaceship, it will not be from some civilization vastly older than ours, but will at most be from some civilization that only has started to explore the galaxy fairly recently.
We can imagine how the SAGE hypothesis could be pretty well verified in the next century. Looking in one direction of the sky, we might find radio or television signals from an extraterrestrial civilization only slightly more advanced than ours. Then looking in some opposite direction of the sky, to a completely different part of the galaxy, we might then find the same thing – signals from another civilization about the same age as ours. Once the same thing happened three or four times, we would have a choice between believing in a one in a billion coincidence, or believing in something like the SAGE hypothesis, which would pretty well clinch the hypothesis.
Do I personally think that the SAGE hypothesis is correct, and that civilizations have only recently appeared in our galaxy? No, I think it is somewhat unlikely that the SAGE hypothesis is correct. I still tend to prefer the idea that there are some civilizations in our galaxy much older than our civilization. However, I think that the SAGE hypothesis is a respectable hypothesis that might well be true, a hypothesis that deserves a mention in a discussion of Fermi's Paradox. I would say the SAGE hypothesis is rather unlikely to be true, but perhaps not very unlikely to be true. I also think that the SAGE hypothesis has some good aspects, particularly the fact that it is falsifiable and the fact that it makes specific predictions that we might well be able to verify in a reasonable time frame.