Stephen Hawking has created a new Discovery Channel show called Into the Universe with Stephen Hawking, which covers some of the possibilities of life beyond our own home world. A few excerpts from the British press have lit a storm of comment across the web, so I thought I’d join the fun.
Here’s a key sample of Hawking’s thoughts from Times Online:
He suggests that aliens might simply raid Earth for its resources and then move on: “We only have to look at ourselves to see how intelligent life might develop into something we wouldn’t want to meet. I imagine they might exist in massive ships, having used up all the resources from their home planet. Such advanced aliens would perhaps become nomads, looking to conquer and colonise whatever planets they can reach.”
He concludes that trying to make contact with alien races is “a little too risky”. He said: “If aliens ever visit us, I think the outcome would be much as when Christopher Columbus first landed in America, which didn’t turn out very well for the Native Americans.”
While it’s probably not the full content of Hawking’s argument, it’s a good start for discussion. On broad principles, I agree with a broad argument of his: a direct encounter with an intelligent civilization of extrasolar origin is likely to be unpleasant, and should probably be avoided if possible. However, on many of the specifics, there is a good degree of disagreement.
I will start by looking at Hawking’s conception of likely alien visitors. I agree that the vast majority of species that have developed interstellar travel would arrive with colonization in mind. With the distances and costs involved with such a voyage, a return trip would be costly and unlikely to achieve much.
However, if a civilization had used up the resources of its home planet, it would also find it difficult to muster the resources necessary to make such a grand interstellar voyage. As such, I don’t think that we’re likely to see refugees from a spoiled planet. It seems to me that such a civilization would be more likely to collapse than to maintain the structure necessary to launch such an expensive venture.
That said, a civilization facing a looming catastrophe—solar system instability, the expansion of their host star, or a runaway greenhouse effect for example—may muster the resources necessary to send out a colony ship to another solar system. The problem is that even then, only a small fraction of the inhabitants of the planets will be able to make the trip, making me think that it is perhaps more likely for the voyage to be “elective”. That is, most likely, a civilization sending out interstellar colony ships will not do so out of duress but rather from a position of strength. Of course, that may make them all the more fearsome.
Because of these difficulties, science fiction writers often postulate the manipulation and use of entities that are theoretically allowed by general relativity: wormholes. Hawking uses them himself in describing the potential threat we face from alien civilizations. I, however, discount the possibility, as it seems to me unlikely that wormholes would behave in a manner conducive to travel—that is, they would be far to unpredictable even if it were possible to make them, as they require folds in the very fabric of space, and thus where the other end of the wormhole was directed would very much be a matter of chance. Given the possible places to end up, a wormhole would likely lead one the lonely expanses of intergalactic space—hardly making it conducive to interstellar travel.
Hawking also sees them as possessing big ships. While the ships would likely be large enough to carry sufficient cargo to build a successful permanent colony in another solar system, the bigger the ship, the more costly the transportation. As there are limits to the amount of energy that could be harvested and used, there would be enormous barriers to carrying enough of a population to mount a full scale invasion of Earth.
We face quite a bit of uncertainty regarding the natures of alien civilizations with capacity for interstellar travel, so it is difficult to model their behavior in ways that stray too far from that of the species most close to such capabilities, humanity. As such, Hawking uses humans as a template in arguing that an alien invasion is likely to mirror European conquests upon arriving in the New World.
While that model may seem attractive, I think that it has several flaws that change the picture entirely. The first relates to environmental advantage. The Earth’s lower atmosphere has just the right partial pressures of oxygen and carbon dioxide for us to survive. If this seems like a remarkable coincidence, it’s not. Through a long process of natural selection, our genes have been honed to work best with the environment in which they operate, which in our case is the Earth.
A species of extraterrestrial origin would not have the advantage of billions of years of adaptation to Earth’s peculiarities and would likely find our planet to be quite hostile relative to that of its origin, and the challenges arising from the incompatibility of biological adaptation and environment would dwarf those facing the early European settlers of the New World.
Now, even if, as a wise group of interstellar explorers, our hypothetical invaders had taken the appropriate steps to neutralize this difficulties, they would have to face our own defenses, which though likely primitive compared to their own technological achievements would be more than enough to threaten their entire enterprise. As much as technological innovation can put one ahead in the rat race of fighting capability, a nuclear weapon striking the colony ship would likely have a devastating effect on the would-be invaders.
This raises another point: Would a sufficiently foresighted species even risk the voyage to our particular solar system? Hawking advocates avoiding contact with aliens because of the risks involved. While aliens capable of interstellar travel are likely to be much more technologically advanced than us, thus holding multiple advantages over us beyond our wildest imaginations, the sheer presence of a radio-capable species may convince them that the trip isn’t worth the risk.
An interstellar voyage an expensive endeavor, requiring vast amounts of resources and energy to make the voyage and to protect the ship’s contents against the dangers of cosmic radiation, while storing enough energy to keep everything operational for what is bound to be a very long trip—at one tenth the speed of light, a trip from the nearest star system, α Centauri, to here would take 43 years.
It should be noted that the Europeans were able to conquer the New World so easily because they were faced with a relatively diffuse set of peoples that were wracked with illnesses the Europeans had brought and because the Europeans came in waves. The round trip between Europe and the Americas was significantly less that a year. In contrast, the colony ship sent by our intrepid extrasolar conquerors would likely be alone without hope of back-up and with much decreased ability to communicate with their home world. A return signal from α Centauri would take 8.6 years to receive. Meanwhile,
Another disadvantage is that unlike the aliens portrayed in science fiction such as V, alien invaders are unlikely to understand humanity well at all. While we would obviously have some similarities to any intelligent spacefaring species, they would be based upon a completely different biological substrate from our own. The differences between us would probably be difficult to exaggerate and thus it would be difficult for them to decode our transmissions and use the knowledge gained in such a way as to manipulate us like a Machiavellian prince. Instead, we would be as alien to them as they are to us.
Of course that leads to a question of how such an alien race would analyze the situation, and it becomes clear that predictability is not a quality of extrasolar life forms with the intelligence required to create societies (if they are indeed organized into societies) capable of interstellar travel.
Finally, this brings us to what is perhaps the most important aspect of this whole issue and that is the probability of contact. According to the Times Online article:
Hawking’s logic on aliens is, for him, unusually simple. The universe, he points out, has 100 billion galaxies, each containing hundreds of millions of stars. In such a big place, Earth is unlikely to be the only planet where life has evolved.
While this is true, the existence in life in other galaxies is not likely to increase the odds of contact. Instead, contact is only likely to occur with life originating from our own galaxy or perhaps one of its satellite dwarf galaxies. Intergalactic travel makes interstellar travel look like child’s play and compounds the difficulties described above to an absurd extent. As such, contact scenarios only deal with the stars in our own Milky Way.
Now, that’s not a trifling amount; the low end estimate is 100 billion. But that raises the Fermi paradox: If there exists a species willing and capable to cross interstellar divides and colonize new solar systems within our galaxy, then why is there no evidence of them within our own solar system? Humans have only been within the past million or so years, most of that time without the slightest understanding of the universe beyond our parochial needs.
If a star-colonizing species existed, it would be unlikely that it would reach us within the very narrow window when humanity is beginning to contemplate its own ability to do so. As such, I suspect that the chance of an encounter at any time within my lifetime or even those of my great great grandchildren is vanishingly small.
Thus, it’s hard to take Hawking’s warning about contacting aliens seriously—we’re unlikely to meet them any time soon, and in many ways, the damage is already done. We’ve been broadcasting radio signals into space for over 70 years and we have even sent signals designed to make contact in the past.