BackLife in universe, the immortal paradox
Just by looking around our place in the universe and making some reasonable calculations, it seems very likely that extraterrestrial life must exist somewhere
PremiumIt’s fascinating how a single film stimulates thought in different directions. In this case, Oppenheimer. In my last column, I touched on the connection between the Galton-Watson process and Oppenheimer’s Manhattan Project colleague Leo Szilard’s work. Time, this week, for a look at another Oppenheimer colleague, the physicist Enrico Fermi.
Specifically, this is about a conversation Fermi and a few other scientists had at Los Alamos in 1950. The Manhattan Project and the bomb were in the past, so perhaps not so much on their minds by then. But there had been several reports of UFO sightings. I don’t think these thinkers believed these were actually extraterrestrial visitors, but it got them discussing space travel, and the possibility of it happening at speeds close to or even faster than the speed of light. For at least from how we humans look at it, visiting other stars would have to happen at those kinds of speeds. After all, even at the speed of light it will take over four years to travel between Earth and our nearest stellar neighbour, Proxima Centauri.
The men sat down for lunch, and Enrico Fermi suddenly asked, “But where is everybody?" His colleagues laughed, because given the context, they knew exactly what he was referring to. Not that the lunch-room was empty, but that there was no evidence anywhere of extraterrestrial life.
Thus was born what we now know as the Fermi Paradox. Just by looking around our place in the universe and making some reasonable calculations, it seems very likely that extraterrestrial life must exist somewhere. Yet in 1950, there was no sign of it anywhere. Not in 2023 either. (There are those who might contest that; of that, more later.)
Spend a few moments taking in the numbers and the reasoning.
To start with, we live our lives on a planet that orbits a star, our Sun. That is, it’s the Sun that makes life possible on Earth. Yet, we have known for centuries now that there is nothing special about the Sun. It’s a fairly nondescript star. In our Milky Way galaxy alone, there are many billion other stars like it. That number increases dramatically if we consider the many billion other galaxies out there, but let’s confine ourselves to the Milky Way.
Plenty of those billions of stars must also have planets orbiting them—why should the Sun be uniquely blessed? Given distances and the luminosity of stars compared to any planets they might have, it’s hard to detect the presence of planets. But there are clever techniques astronomers use to do so. So, by now, we have identified many stars that have planets. As I mentioned in my column “Nothing to do, planet Earth is blue", we have a list of over 5000 such “exoplanets". Astonishingly, we found the first exoplanet on that list only in 1992. Which means that when Fermi and his friends were lunching in 1950, they didn’t even know for certain that there were planets out there, other than those in our solar system.
But that a random star has one or more planets does not itself suggest life. After all, of the eight in our Solar System, only one is known to have life. (Ours, in case you were wondering.) Why that one? Because it orbits in what’s called a “Goldilocks" zone—at a distance from its parent star that makes it neither too hot nor too cold for life. Certainly, there might be life forms we don’t know about that can survive in the furnace of Mercury or the freezer of Uranus. But that’s just the point. We don’t know about that kind of life, so we focus on life as we know it.
Here on Earth, we have found fossils that are 3.7 billion years old. Clearly then, life began at least that long ago. Since our planet is itself about 4.5 billion years old, it didn’t take very long—well, at least geologically speaking—for life to emerge here. If we assume life anywhere evolves as it has on Earth—we have no other benchmark anyway—then we’re looking at about 4 billion years for intelligent life to emerge. In particular, life forms that are capable of looking out at the universe and asking questions about other possible life forms.
Well, many of the stars with exoplanets are much older than 4 billion years, much older even than our Sun (about 14 billion years). So, certainly, some of those 5,000 exoplanets may have produced intelligent life—call them civilizations—long before we did. Thus, it is reasonable to believe that there are civilizations somewhere in space that are, just like us, considering how to travel widely through space; that may, unlike us, have attempted and mastered it already.
But wait, this reasoning takes us still further. The Milky Way is about 100,000 light years across. If some advanced civilization has figured out how to travel at even a tenth of the speed of light, its members will need a million years to traverse the galaxy. That seems to us like an impossibly long time. But thinking geologically again, it’s a mere wink of an eye compared to the several billion years the civilization has existed and evolved. What this suggests is that a civilization like this might have worked out how to sustain travel for that long, and in fact might already have visited most parts of the Milky Way.
Including our Solar System. Including our Earth.
Seems reasonable? Yet, here’s Fermi’s Paradox in all its bald glory: we have found zero evidence of any such visit.
I could stop there. But as I explained in my column “Call me the wanderer, I roam around", the Harvard astronomer Avi Loeb believes we do indeed have such evidence, and in two different ways.
First: the mysterious object, ‘Oumuamua, that shot past Earth in 2017. Loeb has made a serious case that it is a probe from another civilization. Second: in June, he led an expedition to a spot off the coast of Papua New Guinea, where an apparent meteor crashed into the sea in 2014. From the ocean floor there, he retrieved tiny spherules that he claimed as evidence that the meteor came from beyond the galaxy - which, he also claimed, meant the meteor was a “technological gadget".
Many of Loeb’s peers disagree vehemently with his claims. No doubt you have your opinions too. Fermi’s Paradox, you see, lives on.
Once a computer scientist, Dilip D’Souza now lives in Mumbai and writes for his dinners. His Twitter handle is @DeathEndsFun.
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