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Mercury, September/October 2002 Table of Contents

Ben Zuckerman Responds:

My friend Seth Shostak presents a spirited defense of SETI. But of course this was not entirely necessary since the title of my article was "Why SETI Will Fail," not "Why SETI Should Be Terminated." If Seth, Jill Tarter, Frank Drake, and other SETI pundits can entice well-to-do individuals to fund their SETI efforts, then I say great, go for it, sail on. Heck, even I contribute a modest dollar amount each year to support the efforts of the SETI Institute.

It appears that Seth and I agree, albeit for different reasons, that should SETI eventually be successful, then it will be because it received signals from distant stars. Where we clearly disagree is where Seth has misstated my arguments and, in so doing, has made a subtle, but important, mistake in his own argument. In the first sentence of "Going All the Way," Seth says that I consider only "a first generation of interstellar expansion." But if you re-read the first three paragraphs of my "Pessimists are Optimists" section, you will see that this is not true. In the first paragraph I extend what Seth calls a local "sphere of influence" to "distant times and places." And then, in the third paragraph, I extrapolate the argument to the "galaxy as a whole."

A problem with Seth's "sphere of influence" idea is that the Galaxy is not a solid object like Earth. Different stars pursue different sized and shaped orbits around the galactic center. Over the course of hundreds of millions of years, planetary systems in any initial sphere of influence will spread out over a huge volume of the Galaxy. This natural expansion process comes in addition to any exploratory trips between living worlds and would, over time, bring civilizations close together. Thus, regions "untouched by aliens," if they exist at all, will be very few and far between.

Seth belittles my argument as a mere "special edition" of the Fermi Paradox. Quite the contrary, the SETI literature has never mentioned the fact that a technological civilization has the ability to investigate in detail planets orbiting millions of stars without ever leaving its own planetary system. This ability totally changes the rules of the SETI game as they have been propounded until now by SETI enthusiasts and skeptics alike (as exemplified in the papers I cited by Newman/Sagan and Howard/Horowitz).

I have one final thought. In Seth's section "Going All the Way," he refers to "colonization" because he is refighting battles between SETI true believers and skeptics from decades past. For example, Seth argues that colonization often is not a very compelling motivation for large-scale expansion of a terrestrial civilization. But I am talking about intellectual curiosity, not colonization (which becomes an incidental consequence of intellectual curiosity). That is, when intellectual curiosity sends explorers like Captain Cook to far-flung places, they can easily return home if they so choose, whereas Cook's interstellar counterparts, like Captain Kirk, cannot. Even should most people (or aliens) be passive stay-at-home types, just a few curious, intrepid adventurers like Columbus or Cook can open grand new vistas from which there can be no turning back.

The same curiosity that motivates Seth and other SETI seekers will propel human beings, or whatever we become, to overcome all technological and physiological obstacles and thus to sail on and fill the Milky Way Galaxy.

Seth Shostak Responds:

I appreciate Ben's support of SETI, both moral and monetary. The intention of my article, however, as stated explicitly at the end of the first section, was to take issue with his argument as to why SETI will fail. It is somewhat disingenuous of Ben to strongly claim that SETI cannot succeed, and then plead that it wasn't his intent to suggest that SETI should be terminated. Methinks he wants it both ways, and that bespeaks uncertainty.

Ben is telling us that SETI experiments will come up dry because the Galaxy can be easily and quickly occupied. Despite his disclaimers, this really is the Fermi Paradox argument of old. It is revealing that Ben has objected to my characterizing his argument as a "special edition" of this scenario, implying that he does, indeed, assume such Galaxy-wide enterprise. He prefers to think of "intellectual curiosity" as the motive that drives advanced beings to visit (and not return from) other suns, rather than "colonization." But can he really argue that the former is more prevalent than the latter given our less-than-impressive current knowledge of alien sociology?

Still, I'll give credit where it's due. Ben has added two ingredients to the venerable Paradox recipe: stellar shuffling and planet-finding telescopes. Lamentably, the former is a slow way to bring worlds in contact. Even slow rockets could do the job much more quickly.

As for Ben's second ingredient, planet-sniffing telescopes, it's true that these might allow peripatetic aliens to limit their travels to worlds with established biology. But perhaps they prefer to travel to worlds where biology is not already under way, as a matter of safety or ethics. We simply don't know.

Let's add a new spice to this mix. Within a century or two, we will have the technical capability to search for artificial signals from any star system in the Galaxy. And just as we can assume that advanced extraterrestrials would wield planet-finding telescopes, so too would they have advanced SETI transmitters and receivers. If intellectual curiosity is truly their bag, then perhaps the best course of action is to eschew the interstellar tourism and explore the Galaxy for intelligent signals. After all, radio antennae could tell the curious a great deal about distant worlds, and with far less effort then transporting themselves across hundreds of light-years.

The bottom line is simple. While I enjoy this conceptual arm wrestling with my buddy Ben, the facts are that no matter what you, the reader, may think of these essays, they won't settle the question that underlies this debate. In fact, neither argument nor experiment can prove Ben right.

But SETI could prove him wrong.