Probability of Advanced Life Forms in our Galaxy

It is almost an article of faith among many ufologists that, of course, the ufos are piloted by beings from distant star systems.

Some go further and make sweeping statements about Pleiadean beamships and Sirian motherships.Sirius and all the stars in the Pleiades cluster are, by the way, only a fraction of the age of our Earth and Sun.

But let us address two questions. Is there anyone out there, and, if so, could they come here? The answer to the first question, of course, is that we don't know for sure, and, while it seems likely in such a vast universe that someone is out there, there are reasons to believe that technological civilizations are few and far between.

As to the second question, most certainly they could come here, if they exist and have sufficient wealth (interstellar flight is likely to be an expensive undertaking) and are sufficiently advanced.

As discussed in another article, even if faster than light speeds or "warp drive" prove impossible, and even if the tenuous interstellar medium, composed mainly of hydrogen, makes near light speed travel impossible, immense "space arks," rotating to produce artificial gravity and containing entire ecosystems, with cities and farms, would allow "manned" interstellar flight, although such voyages could take centuries or even millions of years, and generations would be born and die on the way.

But the first question is more difficult. Are they out there? Astronomers estimate the number of stars in our galaxy at 100 to 400 billion, say 200 billion, and they estimate that there may be 100 billion other galaxies in our universe. Bear in mind that without some kind of "warp drive" intergalactic voyages are problematic at best.

Our galaxy is believed to have a dense nucleus and six spiral arms, with a halo of dense globular star clusters surrounding the nucleus. We are thought to be about a third of the way out on what is called the Orion Arm, and our galaxy is believed to be about 100,000 light years across. So, at first glance, you would expect us to have plenty of company.

Not so fast. Most of the stars are packed into the globular clusters and the dense central regions of the galaxy. Most of these are so closely surrounded by other stars that their planets would have no night, so bright would the starlight be.

Even if they were not too hot from all that energy, any life forms there, or at least advanced life forms, would be periodically wiped out by nearby supernovae. These are hostile environments.

In addition, our Sun is a second generation population one star, with enough of the elements heavier than hydrogen and helium, or enough "metallicity" as astronomers put it, to have solid planets like the Earth end elements like carbon and oxygen for life as we know it. The first stars, population three, apparently no longer exist, and the later population two stars are still so poor in heavier elements that they could not have solid planets or carbon based life forms.

So out of our 200 billion stars, we have perhaps 20 billion that might have advanced life forms. Bear in mind that this is just an educated guessing game, an updated version of Drake's Equation, formulated in 1961 by Dr. Frank Drake.Stars much more massive than our Sun fuse their hydrogen more rapidly and go off the Hertzsprung Russell diagram's main sequence sooner; that is, they become unstable, and, depending on their mass, either swell up into red giants or explode as supernovae.

Either way, their planets are destroyed and any life is wiped out. It has taken us four point six billion years to "evolve," and, while as an advocate of intelligent design I can't say it is impossible for civilizations to develop in only one or two billion years or less, it seems unlikely. Stars much less massive than our Sun, red dwarves, are unstable.

To receive enough light and warmth for life, a planet would have to orbit very close to its star (one such system has recently been discovered) where it would periodically be blasted by solar flares.

Also, the steep tidal gradient would probably induce heating of the planet's interior (like Jupiter's moon Io), which, added to the heat already generated in the interior of any near Earth sized planet, would cause too much vulcanism for anything to survive.

Eventually the planet would become tide locked, like our own Moon, with one side always burned by its parent star and the other side frozen in eternal night. Being very generous, we are now down to about two billion stars with the right luminosity.

Most stars are multiples, with two or three or (rarely) more stars orbiting a common center of gravity. If the two stars of a binary system are either very close together or very far apart, one or both might have a planet with a stable orbit receiving the right amount of energy.Otherwise, no dice.

This brings us down to perhaps a billion stars. But it turns out that, far from us being the new kids on the block, our Sun is one of the oldest population one stars. So now we are down to perhaps a hundred million stars with habitable planets old enough for civilizations to have developed.

Since our Sun, like all stars, slowly gets hotter as it ages, it will destroy all life long before it goes off the main sequence.Also, the craters we see on every solid world in our Solar System show that we are in a shooting gallery, and it is just pure luck (or Divine Providence) that we have not been destroyed by asteroid or cometary impacts, and that we "evolved" before our Sun became too hot.

So now we are down to maybe ten million stars suitable for advanced life forms. If a tenth of those have advanced civilizations on their planets, we would have the company of one million worlds out of a galaxy of 200 billion stars.

That is one in 200 thousand.

Bear in mind that most of the solar systems we have yet discovered are very different from our own, with gas giants orbiting very close to their stars, and that many astronomers believe that our Moon, formed by Earth's freakish and improbable collision with a large planetismal, may be essential to keeping our axial inclination stable enough for us to live here.

Still, a million is not bad. But where are they?

The SETI people, who mock us ufologists who have nothing but radar and visual sightings and videotape, have been listening for radio messages from other planets for decades. They have checked hundreds of stars on many wave lengths, and have never yet detected a single message.

Consider this.

If only one star in a million in our galaxy, or 200,000, had a planet with a technological culture, and only one in a hundred of those was broadcasting radio, that would be 2,000 message senders.

If only one in ten of those was within radio range, we should be listening to 200 other civilizations.

So where are they?

It is beginning to look as though we don't have very much company out there after all. Perhaps the ufos come from much, much closer to home.

William B Stoecker