“How many angels can dance on the head of a pin?” is often asked rhetorically, to indicate disdain at a silly question, or to indicate amusement at the foolishness of early religious thought.

Although, Catholic theologians tell us the question is both misquoted and misunderstood. The original form of the question asked how many angels could occupy an arbitrarily small point in space  – there was no dancing involved. It was a serious philosophical thought experiment that touched on subtle questions about the nature of infinity, space, and divine nature. No theologian seriously proposed answers like 17 or 22. The only possibilities seriously considered were zero, one, and as “many as God wills.”

It’s ironic that this question is so often quoted to indicate the superiority of modern thought over medieval ignorance, when in fact it indicates a lack of historical and philosophical understanding among moderns. We cite this as an example of cultural bias, which one must always be on against when considering alien ideas.

Which brings us to our real subject – a recent press release by the SETI Institute, in which SETI Institute founder and former director Dr. Jill Tarter takes issue with physicist Stephen Hawking.

Dr. Tarter disagrees with recent statements by Dr. Hawking, who has warned that alien civilizations might harbor hostile intentions toward Earth. She states, “While Sir Stephen Hawking warned that alien life might try to conquer or colonize Earth, I respectfully disagree. If aliens were able to visit Earth that would mean they would have technological capabilities sophisticated enough not to need slaves, food, or other planets.  If aliens were to come here it would be simply to explore.”

We agree that conquering Earth for food or slaves doesn’t make much sense. Any civilization that has the technology to travel between the stars could easily produce such things much closer to home, at far less cost. Even planets are iffy. As the late Dr. Gerard O’Neill and Professor Freeman Dyson have shown, planets are not the only form of real-estate available to an advanced civilization, and in some ways not even the best. It’s far easier to build space habitats closer to home than to travel between the stars to steal someone else’s planet.

It’s hard to imagine what humans might have that alien civilizations would find valuable enough to take from us, given the enormous energies required to travel between the stars.

On the other hand, the same argument can be made against exploratory missions. It’s equally hard to imagine why aliens would find us so interesting that they would make the enormous investment of resources required merely to visit. No human society would invest that much for pure exploration – we have enough trouble just funding NASA  – so we should not presume to understand the motives of an alien society that would choose to make the investment.

Considering how much trouble we have understanding Medieval philosophers from our own civilization, who lived just a few hundred years ago, we should be very careful about making assumptions about truly alien minds.

There’s also another possibility, which Dr. Tarter fails to consider. An alien civilization might attack us not to steal our resources but to eliminate a possible threat or rival – a preemptive strike. That scenario may be more likely than either the extraterrestrial raiding party or the peaceful scientific expedition. It would certainly be cheaper.

An advanced civilization would not need to send a large starship to wipe out humanity – much less the giant armadas of science fiction. A small probe, carrying microorganisms or nanorobots, would suffice. Such an attack might be incredibly subtle. We might not even recognize its extraterrestrial origin.

The late Dr. Robert Forward produced a conceptual design called the Starwisp, a laser-propelled interstellar probe weighing just 16 grams. Advanced civilizations would no doubt have other means of propelling such small probes between the stars, and they could launch billions of probes for the price of one starship.

If SETI scientists are right, our galaxy should be home to a number of technological civilizations, some of which are millions of years old. If one of those civilizations began sending out probes several millions of years ago, it could have wiped out every potential rival in the galaxy. That could explain why SETI has not detected any radio signals – perhaps we are the only ones left.

Perhaps an alien invasion of Earth is already underway. Perhaps we should be looking for extraterrestrials with microscopes instead of telescopes.

All of this is purely speculative. SETI scientists have long held a secular religious belief that any advanced civilization must be inherently peaceful and benevolent. We hope they’re right, but right now we have no evidence for either alien hostility or alien benevolence. We need to keep an open mind to all possibilities and, above all, try to find some actual data. Perhaps that data will come from the SETI Institute, from NASA, or from an unexpected source such as our High Altitude Astrobiology Challenge. In any case, until we actually discover alien life, we’re simply debating how many aliens can dance on the head of a pin.


Written by Astro1 on June 12th, 2012 , Astrobiology

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