Why Stephen Hawking is Wrong

(If this post had a subhead, it would be: Dr. Strangehawking, or How I Learned to Stop Worrying and Love the Aliens.)

The Discovery Channel’s new series Into the Universe with Stephen Hawking debuted last night with an episode about Aliens. I’ll plead guilty to not having seen it—the clips appearing on Discovery’s web site seemed full of both CGI goodness and speculation relatively unencumbered by annoying facts, so I’m not sure what to make of it. But one of the claims that Hawking apparently makes in the program has drawn considerable media attention, as in this BBC story:

Aliens almost certainly exist but humans should avoid making contact, Professor Stephen Hawking has warned.

In a series for the Discovery Channel the renowned astrophysicist said it was "perfectly rational" to assume intelligent life exists elsewhere.

But he warned that aliens might simply raid Earth for resources, then move on.

…

Prof Hawking thinks that, rather than actively trying to communicate with extra-terrestrials, humans should do everything possible to avoid contact.

He explained: "We only have to look at ourselves to see how intelligent life might develop into something we wouldn't want to meet."

Hawking’s concern seems to be the Independence Day scenario: that spacefaring species might roam the universe in gigantic motherships, pillaging planets for their resource wealth and exterminating those worlds’ inhabitants in the process. (So for the rumored sequel to Independence Day in the works, does this mean Hawking could take Jeff Goldblum’s role? Or Brent Spiner’s?)

Naturally, Stephen Hawking’s speculations on most matters are probably far more likely to be right than are mine, but in this case I’ll argue that he’s most probably wrong about alien conquests of this sort being a meaningful danger. First, though, I have to make two asides.

• If we’re suppose to start worrying about dangers from space, I refuse to give one second’s attention to the possibly dubious threat from aliens until after humanity starts taking seriously the statistical certainty that an asteroid will eventually cause a catastrophe on earth again unless we avert it.
• Back in the ‘70s, Carl Sagan argued in The Cosmic Connection, as other scientist-authors did elsewhere, that any alien civilization advanced enough to contact and visit us would surely have evolved past its own barbaric, warlike phase and would therefore meet us in peace. That view may seem naïve in retrospect, but given how little the available facts have changed, the current bent toward a more paranoid outlook probably says something about how society has changed in recent decades.

Most biologists and astronomers would probably agree with Hawking’s analysis that, in so far as we can make informed guesses about the odds, alien life is probably out there: the Milky Way alone probably brims with at least tens of billions of planets and unguessable numbers of moons; niches conducive to life’s evolution are likely to be legion; the galaxy’s 14 billion year age offers plenty of time for civilizations to rise (and fall). In fact, the numbers so lopsidedly favor extraterrestrial life that the greater conundrum is the Fermi paradox: why haven’t we already seen clear evidence of alien intelligence? But put that question away for now.

Let’s also assume that Sagan was wrong and that an advanced alien civilization can be hostile to us, either through active malevolence and desire for conquest or through the utter disregard we would show for an anthill on a lot zoned for a shopping mall. Let’s completely stipulate the existence of Hawking’s resource-hungry aliens. When would they be trouble?

If the hypothetical aliens are motivated purely by malice and must on principle exterminate us if they know about us—Daleks, ahoy!—then by definition they are a threat. But that argument begs the question: it just posits the existence of the baleful aliens we’re wondering about. They’re not impossible, but we know nothing about their probability a priori.

On the other hand, if these aliens are motivated by a need for resources, we can ask, “What resources do we Earthlings have that they would want so much?” And in those terms, it’s not obvious we have much to offer.

Water? The Oort cloud is lousy with the stuff. Earth’s oceans of water probably came from cometary bombardments during the early days of the solar system. Why wouldn’t they go to the original aquifer?

Minerals? University of Arizona planetary scientist John S. Lewis has estimated [pdf] that just one asteroid about a kilometer wide would contain about 30 million tons of nickel, 1.5 million tons of metal cobalt and 7,500 tons of platinum. The solar system may have a million asteroids of roughly that size. One good-sized metallic asteroid could contain dozens of times as much metal as has ever been mined out of the earth. True, the asteroids are dispersed across a huge volume of interplanetary space—but for an alien civilization capable of getting to our solar system, finding, capturing and mining an asteroid should be elementary. And remember, all this mineral wealth is instantly available to them without the trouble of pulling it all back out of Earth’s gravity well.

Uranium? The inner solar system may be richer in uranium than the asteroids and outer planets are. But that would mean the aliens would have the options of going to Mercury, Mars and our moon, all of which are smaller and lower gravity and where they wouldn’t be faced with a pest eradication problem, as on earth.

Would the aliens want to conquer earth so they could eat our biomass? That’s hard to imagine. I’m not at all sure that truly alien life would be able to metabolize terrestrial meat or vegetation: their biology could be based on different amino acids, sugars with different stereochemistry or countless other subtle differences.

Would they want humans as slave labor? Surely they would have the ability to build robots or other machines (or genetically engineer new organisms, if you prefer) that could work for them much more efficiently and under a far wider range of environmental conditions.

That seems to leave the possibility that the aliens might just earth for its real estate value. Might they be driven by uncontrollable population pressures? Maybe, but it seems like special pleading to imagine that the advanced aliens would see conquering other planets as a simpler, better solution than either reining in their reproduction or just building more of those giant spaceships.

Yet once again, even if we grant hypothetically that the aliens would want earth for its land (or for its other resources), I think it only highlights where Hawking is most incorrect: in recommending that “humans should do everything possible to avoid contact.” If the aliens want earth for its resources, contact with us will be irrelevant to them. The aliens won’t bother to listen for radio signals or other evidence of intelligence in the universe; they will scan the cosmos for earthlike planets around yellow suns, ones with atmospheres that show evidence of photosynthesis and oxygen production, and so on. After all, primitive as we humans are, we’re already on the verge of building telescopes and other instruments capable of finding other earths. The aliens will have detected earth long before our own communications technology existed; if they want our resources, they will have target our planet no matter what we do.

So perversely, Hawking’s reasoning leads me to almost the opposite conclusion: we should definitely be trying to contact any aliens within the sound of our radio voice. Because if those resource-hungry, planet-poaching alien invaders are out there, we may want to line up some other alien allies in a hurry.

Update: Phil Plait and Sean Carroll have their own reactions to Hawking's argument. Oh, and also Ethan Siegel at Starts with a Bang.

Update, Part Deux: This story has more legs than a Denebian sandspider, my friends. Here's still more divergent  commentary on Hawking and the aliens from Chad Orzel, PZ Myers, and ERV. I'd agree with the possibilities of alien contact having disruptive or destructive effects on our species in various incidental ways, but those differ mightily from the misplaced concern that maybe Mars Needs Coal.