Are We Alone In The Milky Way?

When facts are few, speculations are most likely to represent individual psychology
   — Carl Jung

Let's go big or go home. Today I will talk about astrobiology, which is the study of the possibility of  life outside the Earth. This has been a preoccupation of mine for a long time now, for whenever I tire of human life on Earth, which is often, it is fun to speculate about the existence of technologically advanced alien (extra-terrestrial) civilizations. Astrobiology has been jokingly referred to as the only science without a subject because there is no observational evidence of any kind which suggests that we share the Milky Way (or the observable Universe) with other "intelligent" species. Even the question of whether single-celled bacteria exist on other worlds remains unanswered.

I intend to do a series of articles on astrobiology, and relate it to some of my other writing, so today's post serves as an all-too-brief introduction.

Let's get right to the heart of the matter and focus on Fermi's Paradox (and watch the video below)

The story goes that, one day back on the 1940's, a group of atomic scientists, including the famous Enrico Fermi, were sitting around talking, when the subject turned to extraterrestrial life. Fermi is supposed to have then asked, "So? Where is everybody?" What he meant was: If there are all these billions of planets in the universe that are capable of supporting life, and millions of intelligent species out there, then how come none has visited earth? This has come to be known as The Fermi Paradox.

And from here—

The drive to place humanity at the center of the universe has led to a stream of assumptions that, as facts have been collected, are shown to be ill founded. The Ptolemaic Earth-centered view was replaced by Copernican Sun-centered view which in its time was also replaced. The assumption that we are alone in the universe is also under threat of replacement. One of the more interesting aspects of our apparent aloneness was pointed out by Enrico Fermi and is know as Fermi's Paradox.

Fermi's Paradox may be succinctly stated as: Extraterrestrials should have colonized Earth long ago, but they have not. So where are they? Whether you agree with the point that Earth was colonized or not the fact remains that no concrete evidence has ever been found indicating a visitation of Earth by extraterrestrials. This is in itself is a very significant point...

Let me explain. The Milky Way is almost as old as the Universe itself, with a measured age of roughly 13.6 billion years (with a wide margin of error, 0.8 gya). By some estimates there were enough"metals" (elements more complex than hydrogen and helium) being generated by exploding stars to allow complex life to form by 7 billion years ago. Our solar system and the Earth are 4.6 billion years old. Propagation models suggest that it would only take between 5 to 50 million years for an alien species to colonize the entire galaxy, so there has been ample time for them to do so. These are the sort of calculations Fermi must have roughed out in his head right before he asked his famous question.

There is no positive evidence that aliens have ever visited Earth, nor is there any observational evidence (coming from the Hubble or other instruments) that suggests artificial (non-natural) heat sources or large-scale structures elsewhere in the Milky Way. Outside of old I Love Lucy TV shows, which have propagated to about 60 light years from our location, Earth's human civlization is effectively invisible to aliens who would thus have no reason to look for us. That was the premise of Carl Sagan's book (and the movie) Contact.

We can forestall some objections immediately. As the ever-optimistic SETI people (Jill Tarter, Seth Shostak) are fond of saying, absence of evidence is not evidence of absence. Therefore we can not prove that aliens have never visited the Earth, nor can we infer that they don't exist because of our failure to detect them with our instruments. We can't even prove they aren't watching re-runs of Battlestar Galactica right now from some unknown location in the asteroid belt. (They can't stop laughing.) In fact, you can never demonstrate that aliens don't exist. That's a logical fallacy (a faulty inductive conclusion based on a poor data sample). Just because all the swans you've seen are white doesn't entitle you to conclude that there are no black swans (as we have recently learned).

Even with these objections the existence problem suggested by Fermi's question still stands until some positive data falsifies it. Maybe some genuine evidence will turn up which shows aliens really have visited the Earth. There wouldn't been much to see until about 542 million years ago at the end of the Precambrian. Maybe we'll dig up a monolith on the Moon. Maybe E.T. will call in from his undisclosed Lagrangian orbital point in our solar system. Maybe some nasty aliens are actually on a rampage and they're due to arrive next week so they can blow up the White House. Maybe those illusive UFOs are definitive evidence of a massive government conspiracy (and cover-up) to deploy super-secret technology from outer space.

Who can say for sure?

There are lots and lots of solutions to Fermi's Paradox, and I've heard and considered them all. But I've taken so long to lay out the basics that I'm going to have to discuss them next time. To whet your appetite, I should note that the default (null) hypothesis is that Homo sapiens is alone in the Milky Way, which implies that the evolution of "intelligent" life is extremely improbable. Occam's razor alone tells us this, for that's the simplest explanation for the lack of evidence for extraterrestrial civilizations. Any other explanation requires further elaboration based on guesswork and assumptions which may turn out to be bogus. However, it is still possible to do some highly informed guesswork while making what appear to be reasonable assumptions, which is what makes astrobiology so much fun for oddballs like me. We must of course work with a small, inadequate data sample (of size = 1, us).

Suppose we are alone in the galaxy. If we could somehow prove this conclusion, which we can't, how would that affect the way our species conducts itself? Or what if other "intelligent" extraterrestrial civilizations once existed—this is the teaser—but all of these were extremely short-lived because these aliens ended up destroying themselves or losing their advanced technology—just as we appear to be doing. In short, one solution to Fermi's paradox says that all intelligent species self-destruct, coming into being and then disappearing in far less than the blink of an eye on cosmological time scales.

For the more ambitious among you, watch The Eerie Silence, an hour-long lecture by Paul Davies, Director of the Beyond Center and Co-Director of the Cosmology Initiative at Arizona State University. The best book on the Fermi Paradox is Stephen Webb's If the universe if teeming with aliens—where is everybody? (fifty solutions to the Fermi paradox and the problem of extraterrestrial life). Also see my post Will The Human Species Grow Up?

So stay tuned. I have far more to say about astrobiology.

Bonus Video — Nick Bostrom talks about Fermi's Paradox

 

Comments

[eugene12]

For me the answer is simple: The distances are enormous and the speed of travel is slow in comparison. I think statements, like Fermi's are simply naive. I used to be very amused by the Star Trek films showing stars rapdily passing by. I'd have to check but I think the nearest star is something like 9 yrs away at the speed of light. Which means at the speed of light, for nine yrs, we would not pass a single star. Course at "warp 4" it would only take 2+ yrs but you get the point.

In addition, to think we are worth visiting is more than a bit arrogant. After all, we are still in a very primitive,intertribal warfare stage of development. We really, really need to get over ourselves.

[Wanooski]

Is it truly technologically feasible to become a space faring and colonizing civilization? Hypothetically sure, but really?

Perhaps intelligent species have a very limited window of resource availability and technological sophistication that would allow such development, and perhaps most intelligent species miss such a window.

But I don't know, I'm hardly an expert.

[Dave Cohen]

@eugene

"Getting over ourselves" as you so eloquently put it is a subject of future posts, not this one.

FYI, the closest star to our own is a red dwarf called Proxima Centauri. It is about 4.2 light years away.

The question of whether interstellar travel is possible obviously looms large in any discussion of Fermi's question. Technological optimists -- are there any other kind? -- want to believe humans will be colonizing the galaxy in the far-flung future. Whenever I hear this, I can't stop laughing.

-- Dave

[Ben]

"In short, one solution to Fermi's paradox says that all intelligent species self-destruct, coming into being and then disappearing in far less than the blink of an eye on cosmological time scales."

I'm reminded of something Ernst Mayr said: the human form of intellectual organization may not be favored by selection. The history of life on Earth refutes the claim that it is better to be smart than to be stupid, at least judging by biological success: beetles and bacteria, for example, are vastly more successful than humans in terms of survival. Mayr also made a rather somber observation that the average life expectancy of a species is about 100,000 years.

[The Practician]

Maybe, just maybe, there is intelligent life in the galaxy that hasn't screwed up their own planet and is doing just fine not exploring the galaxy. Honestly It seems a bit more likely than faster than light travel to me.

[Paul]

"Maybe, just maybe, there is intelligent life in the galaxy that hasn't screwed up their own planet and is doing just fine not exploring the galaxy."

Of course, that's it! I've been musing on this for years too but had never considered a world populated by populations of beings with the same considerations, culture and intentions as, say, the Inuits, Australian Aborigines or American Indians.
That has to be the answer. Thanks.

[Dave Cohen]

@Paul, @ The Practician

Sorry, but making a romanticized appeal to the supposed virtues of hunter-gatherers don't get you out of this.

Read Jared Diamond's Guns, Germs And Steel for more insight.

If Inuits ran the world and they had the technology, the story would be largely the same. They drive motorized vehicles and over-hunt game species too.

http://www.cbc.ca/news/canada/north/story/2009/09/29/nwmb-baffin-bay-hearing.html

I should add that I too would like to think there are technologically advanced species living gracefully without colonizing the galaxy.

-- Dave

[Mike Roberts]

I guess this has already been covered by other comments but it may just be that interstellar travel, for humans, is impossible. There may be practical reasons (perhaps that filter that was talked about in the video) why it's just not possible to colonise other planets, especially ones that would take generations to reach. Maybe it's like those early settlers to my country, New Zealand, who would have set out in their small boats not know if they would reach any habitable land mass. If humans eventually reached Proxima Centauri and found there was no habitable planet there, where would they then go, for a further multi-generational journey? It could be that any species can't exist for very long in an artificial ecosystem. It could be that there isn't a propulsion system that can reach across tens of light years.

The other aspect is the notion of "intelligent life". This assumes, I think, that we are somehow "intelligent". But how is that measured? If there was an objective measure of intelligence, would humans come up to the mark?

Isn't speculation wonderful? I wonder if humans are the only species that is capable of speculation.

[Charlie Brown]

Lucy, in a Peanuts column, when asked if she believed in extraterrestrial life, answered no, and when queried why, replied:

"Because they haven't tried to contact me."

;)

[Joy]

"technologically advanced species"
If that is the metric, yes I am quite willing to entertain the possibility that there are no other planets in this galaxy inhabited by beings doing the things we do. We are unique in this respect even on our home planet. Even the very closely related Neanderthals we interbred with did not build radio transmitters. And our own brief little experiment with technological sophistication is ending badly.

I also agree that interstellar travel is beyond our species and possibly beyond any species due to the problems of energy, time, and distance.

"The other aspect is the notion of "intelligent life". This assumes, I think, that we are somehow "intelligent". But how is that measured?"
Indeed. Whatever metric of intelligence one adopts, it is impossible to isolate humans from several other species on this planet. Even some birds seem able to learn to use symbolic language in context, and memorize hundreds of words of vocabulary, and the New Caledonian crow is a clever tool user. Not to mention the impressive brains and cognitive skills of the cetaceans and elephants. Some ethologists would argue that we are not "alone" on this planet Although we eventually may be if we damage the Earth's environment so severely that the more complex lifeforms all go extinct. It is a sad commentary on Homo sap that we now have the capability to spy on all human communications all of the time but have not used the supercomputers to analyze dolphin vocalizations.

[Brian]

I think even scientists do not properly estimate how rare earths really are. Why isn't there signs of complex life on mars?
1. Mars has no molten core and cannot stop the onslaught of particles from the sun.
2. Mars moon is too small and so mars flips over on it axis all the time, i.e. the north pole sometimes practically faces the sun.
3. The moon is believed to have formed from an early planetary collision that was just the right angle to blow off the top of the earth, which makes it perfect for all the heavy stuff to be relatively near the surface of the earth instead of buried deep. Making it perfect for industrial civ.
4. Some scientist conjecture that our moon is of the proper size and distance to soak up a lot of asteroids that would have done serious damage to life's chances.
5. The bad for future intelligence on earth if we don't make it: Our moon is leaving us, the water is getting locked up in rock formations, most primary suns in our galaxy burned hot and fast and then exploded killing any life in near by stars and a big star near by could do this to earth.
Just saying that maybe life really is more rare than we think.

[Diogenes]

Hi Dave,

Fabulous topic.

On your post of Jan 17, commenter RobM linked to a presentation by Eric Smith called Ineveitable Life (very grateful to Rob).

Although I haven't yet had the chance to give Smith's work the time and attention it deserves (for me, at least), I found his ideas fascinating and initially persuasive (my degree is in biochemistry).

Taking the step of accepting those ideas as having some basis in science, we can infer a universe teeming with life; by necessity. I love taking that step since it blends with what I have "known" intuitively as far back as I can remember. And it's fun.

I really love this shit Dave - looking forward to your "far more to say". As I have pondered all this, much music has come to mind - but I won't go there here.

Here is that link in case anyone's curious:

http://fora.tv/2007/04/18/Inevitable_Life

Regards