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What is Life? Is there Life beyond Earth? Is there Intelligent Life beyond Earth? From the daily news, I sometimes wonder if there is intelligent life anywhere. On the possibility of extraterrestrial intelligent life (ETI), Nobel Laureate Enrico Fermi, my father’s mentor, said something like: “If they do exist, why aren’t they here?” This simple statement has resonated through generations of ETI enthusiasts, becoming known as the Fermi Paradox. A recent paper by Westby and Conselice of the University of Nottingham estimates ETI’s capable of interstellar radio communication are extremely rare, with only 36 in our entire Milky Way galaxy. They say the nearest one may be 17,000 light-years away, and most likely orbiting a low-mass M-dwarf star — a type of star that is notoriously unstable. These guys sound more like the Sheriff of Nottingham, rather than Robin Hood. Another recent paper by retired UCLA astronomer Benjamin Zuckerman, a devotee of space exploration, is more optimistic. Yet he claims ETI cannot exist anywhere “nearby”, by which he means within 100 light-years. He says SETI, the Search for Extra-Terrestrial Intelligence, is wasting money by looking too close to home. 
Zuckerman thinks we should instead fund the Terrestrial Planet Finder (TPF), a proposed NASA project that was un-funded for budget reasons. TPF envisions an array of infrared telescopes, shown here, employing interference to cancel a distant star’s intense radiation, allowing analysis of orbiting planets’ atmospheres for telltale signs of life — perhaps news reports of their budget cuts. Since oxygen is highly reactive, oxygen-rich atmospheres must be continually replenished. Astrobiologists generally agree plant life is the only plausible long-term oxygen source. Within the next 20 years, Zuckerman says, TPF could find any life-bearing planet within 30 light-years of Earth, with subsequent missions extending that to at least 100 light-years. Zuckerman makes the startling claim, without explanation, that our spacecraft will eventually reach velocities of “a few percent of the speed of light”. He says a 100-light-year voyage would take “only” 3000 years and cost $10 trillion, which is “not really” expensive. He thinks anything within 100 light-years is “nearby”, but more distant space travel is not “practical”. He says the Sun’s nearest neighbors typically pass by at 20,000 mph, so stellar systems within 100-light years remain “nearby” for millions of years, and millions of Sun-like stars have been “nearby” Earth in the last two billion years, since our atmosphere first announced the existence of plant life. He says we should assume space-capable ETIs are far more advanced than us. Hence, those residing within a few 100 light-years long ago discovered life on Earth.  ETIs may have studied Earth, and possibly come here. It would be foolish, he says, to assume more intelligent life is less curious and less eager to explore the cosmos than we are. If they did come here, why would they leave — “it’s a long way home”, which was Fermi’s point.
Zuckerman concludes: “The fact that, evidently, no technological creatures have come to investigate Earth during the past several billions of years is strong evidence that few such creatures exist in our galaxy.” He says SETI’s search for ETI around nearby stars will surely fail, and we must plan much longer voyages that, I suppose, would be “really expensive”. I wonder how we can be sure Earth hasn’t been visited in the past several billion years. I contacted SETI, asking if they wish to respond. So far, I haven’t detected any sign of life at SETI. I prefer a more analytical approach. My books list 14 remarkable life-supporting characteristics of our planet. Based on NASA/JPL/Caltech data on 4100 exoplanets, we can estimate the probability of a planet having 7 of those characteristics (comparative data for the other 7 is not yet measurable). I find Earth-like planets are probably extremely rare — we might need to search many billions of cubic-light-years to find one — and planets with intelligent life are likely rarer still. Lastly, you might wonder who funds SETI. They get many public donations and also NASA funding. Over the past 25 years, NASA says it gave SETI $1.6 million specifically for searches for extraterrestrial intelligence. SETI also conducts more conventional astrophysics research, education, and outreach. Per NASA’s Inspector General, in 2018, SETI was engaged in 85 NASA-funded projects totaling $81 million. Best Wishes, Robert 
June, 2020
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