Book Review: Alone in the Universe: Why Our Planet Is Unique (Part 2)

[ I'm reviewing this book because I liked it, but also for a larger reason which will become evident at the end of Part 3 of the review, and in the weeks ahead. ]

[ Also, in case you missed it: Part 1 ]

Alone in the Universe: Why Our Planet Is Unique by John Gribbin

Asked about the likelihood of intelligent life elsewhere in the universe, or in the galaxy, or in the neighborhood (of a size for technologically-conceivable visits), most of us here would say it was possible. We wish it to be, want it to be, yearn for it to be. We might point to this or that argument from common sense, or common experience, or simply private hope, and proclaim even that it MUST be.

But in the same way we rein in our religious neighbors, drawing them away from all their wishes and wants and arguments from common sense, at some point we have to rein in ourselves, and look at, not just those factors that seem to make it likely, but those that seem to make it less than likely.

Gribben does that. But he does it carefully, almost reluctantly. The book is not a gleeful spoiler, a crowing of “Ha! You were wrong all along!” Instead, it is a clear-headed baring of facts and the probabilities that arise from them, touched with a hint of sadness at a conclusion that becomes more and more likely as the lengthy argument progresses.

Opening with a chapter on the Drake Equation and a couple of theoretical paradoxes bearing on the question, he follows with a mere seven chapters, each focusing on the question of life, and intelligent life, viewed at a particular scale.

What’s So Special About Our Place in the Milky Way? looks at the question from a galaxy-sized perspective. Stanton Freeman’s suggestion of super-advanced civilizations on ancient stars near the galactic core gives way to the realities of radiation, to the likelihood of cometary collisions, and even to stellar evolution and the elements necessary to life.

Because there is a close link between the metallicity of a star and the likelihood that it has planets, this had led to the idea of a ‘Galactic Habitable Zone’ (GHZ), the region around the thin disc where planetary systems like the Solar System and planets like the Earth are likely to be found. The crucial point, as far as the prospect of other intelligent beings existing in our Galaxy is concerned, is that this Galactic Habitable Zone slowly gets larger as time passes. According to some calculations, it also moves outwards through the disc as time passes; but the most up-to-date version of the idea, from Charles Lineweaver and his colleagues, suggests that it has always been centered on a ring about 26,000 light years from the galactic centre, began to emerge about 8 billion years ago, and at present extends from about 23,000 light years to about 29,000 light years. The sun is close to the centre of the GHZ, but not exactly at the centre. This is the region where the abundance of metals 5 billion years ago, when the Solar System formed, was sufficient to allow for the formation of planets like the Earth.

[...] The exact boundaries of the GHZ are not clear, but what is clear is that the inner regions of the Galaxy have plenty of metals but are hazardous for life, while the outer regions of the thin disc are safer, but metal-poor and unlikely to contain Earth-like planets. In between, there is a Goldilocks religion, the GHZ, that it just right for life. The Solar System sits near the centre of that zone.

What’s So Special About the Sun? looks at our own home star. We like to think of the Sun as average, and the formation of planets as a given, but Gribben lays out arguments why this is not so. Something like 95 percent of the stars in the Milky Way are less massive, and therefore less luminous, than the Sun, moving their individual Solar Habitable Zones – that area around a star between 0 degrees Celsius and 100 degree Celsius where liquid water can exist – so close-in that other factors such as solar radiation come into play to make life less likely. (A surprising percentage of stars are pairs, or even triplets, I was interested to discover, making planets much less likely.)

The Sun also appears to be unusually stable as stars go, a factor that plays into another concept in the subject, the CHZ, ‘Continuously Habitable Zone.’ This is the volume around a star not just where life might arise, but that volume through time, where conditions might be stable enough, and for long enough, for life to actually arise, and then evolve.

Even our Sun’s CHZ is smaller than might be expected, due to the fact that the life zone has moved outward as the Sun has brightened slowly over the past 4 billion years, making areas formerly habitable now deadly.

The [habitable] region that was on the outer edge of the zone (the cool edge) is now on the inner edge (the hot edge), and regions that used to be the hottest part of the zone, including the orbit of Venus, are now too hot for life.

What’s So Special About the Solar System? carries that same zone argument a step further, but adds in the hazardous mechanics of planetary formation, and the vast billiard game of solid bodies and gravitational break-shots that ensues.

Computer simulations show that by about a million years after the collapse of the cloud from which the Sun and planets formed, there would have been twenty or thirty objects in the region between the Sun and the present orbit of Mars, ranging from about the size of the Moon (roughly 27 percent of the diameter of the Earth today) to about the size of Mars, (roughly 53 percent of the diameter of the Earth today). They would have been accompanied by a huge number of smaller planetisimals, which would have been swept up by the larger objects in a series of collisions, while the larger objects themselves collided with one another and merged until eventually only four or five large objects were left – the objects that became Mercury, Venus, Earth and Mars, plus at least one other Mars-sized object.

[ Continued in Part 3 ]

Beta Culture: Being Grownups on Planet Earth
Book Review — Alone in the Universe: Why Our Planet Is Unique (Part 3)
The Book of Good Living: How to Avoid Being Killed By A Train
Book Review: Alone in the Universe: Why Our Planet Is Unique (Part 1)
  • Stephen “DarkSyde” Andrew

    Nice review. I don’t know if I buy the element idea though, a galactic habitable zone, at least not universally. Stars wander, galaxies swarm and collide, waves of star formation rip through the dust and gas churning out iron and gold. Radiation and comets might be bad for us, but there might be places where the entire ecosystem utterly depends on them for survival. Provocative topic in any case.

  • Daniel

    ‘This is the religion where the abundance of metals 5 billion years ago…’

    Region, surely. Dare I mention Freud?

    • Hank Fox

      Good catch! Fixed.

      • Yoritomo

        The Freud is strong with this one:

        In between, there is a Goldilocks religion, the GHZ…

  • Pieter-Jan van der Veld

    It is called the rare earth hypothesis,and this book is not the first to mention this theory. It explains the Fermi paradox (if the universe is so full of life, were the fuck is everybody), for this reason I believe it is a probably true.
    It does not mean that we are alone in the Universe, but more that life in general, and much more so intelligente life, is extremely rare.

    • jamessweet

      I think the Fermi paradox can be handily explained without invoking the Rare Earth hypothesis or similar.

      Assume for a moment that interstellar travel is impractical, that almost no intelligent civilizations ever do it, and those that do are limited to maybe sending a few probes to very nearby stars.

      Now also assume for a moment that the progression of natural radio visibility on our planet is typical: For a century or two after radio communication is developed, the planet becomes radio-bright — though still not tremendously so, with the unintentional visibility only extending a few light years — after which lower-energy digital communication starts to take over. The model is: very low power digital radio signals for short distances (i.e. Wi-Fi), a planet-spanning network of wired cables for long distance/high-bandiwdth (i.e. transcontinental fiber optic), and highly attenuated digital signals for communicating with satellites, interplanetary probes, etc. None of that shit is radio-visible outside the solar system!

      So what’s left then? One race has to be intentionally beaming radio signals directly at another star (i.e. Active SETI) at the same time (relativistically speaking, of course) that another race orbiting that same star is intentionally listening to the source star! Again assuming that our planet is typical, funding and support for SETI and Active SETI-type projects would tend to wax and wane — so even if two relatively nearby intelligent civilizations a) overlapped in time, and b) engaged in active searches for intelligent life, and even c) at times looked for intelligent life in each other’s star systems, it still could be overwhelmingly likely that neither of them ever happened to be listening while the other was talking.

      Space is absolutely, inconceivably, unimaginably huge. I sometimes like to say that if we imagine the largest distance we as humans can conceive of, we cannot even conceive of how woefully short that conception falls of capturing the distance to the nearest star. Intelligent life could be remarkably common, and we still might very well not ever make contact.

  • StevoR

    Sounds like the ‘Rare Earth’ hypoethesis :

    advanced in the eponymous book by Ward and Brownlee.

    But consider it added to my reading list nonetheless – although with that aforesaid ‘Rare Earth’ one which I keep meaning to find a copy of somewhere.

    The fermi paradpox and teh billennia of Earth’s history without intelligent or at leats technological life around are powerful arguments supporting this idea in my view.

  • StevoR

    D’oh! Typos. Sorry. Capital “F’ Fermi Paradox and ,well, y’all know and get the gist I hope.

    The alternative “Life is everywhere” camp is well championed here :

    Which I have also read and would recomend too btw.

  • StevoR

    Personally, between the Rare Earth vs Life everywhere camps its hard to know.

    Insufficient evidence as yet I have to conclude.

    There’s a lot of speculation and statistics and argumenst on each side and xenobiology is a fascinating field with huge implications whose area of study may or may not even exist – bit like theology except a bit more fascinating in my view! ;-)

    • Pieter-Jan van der Veld

      Indeed, it is an interesting discussion. My personal hero, Carl Sagan, was a “Live is everywhere” man, but I am more inclined to the rare Earth theory, because it solved the Fermi paradox and it´s sub-item, The Great Silence.
      The Drake equation can be used to get any number, from extremely high (life is everywhere) to less than one (and then we should not be here – but in comes the anthropic principle).
      So as you said, we do not have enough information to decide between the two possibilities.
      We should continue to look for extraterrestrial life, but handle our Earth with care, it is the only planet we are sure there exist life (I am not so sure if there is intelligent life).

      • jamessweet

        (I am not so sure if there is intelligent life).

        As I said in the other thread, we have tendency to be self-deprecating, but with a sample size of one there is no reason really to think so. As depressing an idea as it is, it could very well be the case that a) the universe is teeming with sapient life, and b) the majority of sapient races are even more warlike and boorish and tribalistic and short-sighted than we are. With a sample size of one, it’s no more likely or unlikely than the alternative!

        It’s extremely possible that we represent one of the most enlightened and egalitarian civilizations in the universe. I sure hope not, but… with a sample size of one, it’s impossible to say otherwise.

      • jamessweet

        And of course the null hypothesis is that we are average.

        • Pieter-Jan van der Veld

          Good points, all of them, James. I know there are other ways to explain the Fermi paradox. Maybe there is something like an intergalactic civilization with a none-interference agreement for solar systems with life, even microbial life. Something like, let life run its own course, give it the change to become sapiens and meet us on its own terms. Who knows? There can be other explanations. Still, I think the Rare earth Theory is the most probable.
          You mentioned the possibility of self-destruction of sapiens life (Carl Sagan also mentioned this). Maybe evolution equips sapiens life with instincts that work very well for stone-age civilizations but are not suited for are not suited for an civilization that can make atomic bombs or cause global warming. Even so, if intelligent life arises on a regular base in this Universe, some of them should have survived.
          About radio, you are right; maybe radio communication is just a very small time-window. I can imagine an isolated tribe in a tropical forest who say something like: “We know that there are no other intelligent beings in the world, because when we have sent our best drummers to the edge of our hunting ground, and nobody answered our talking drums”. All the while, they are surrounded by radio waves that are carrying messages around the globe. If sapiens life is abundant, some may choose to remain silent or use communication methods we cannot image. On the other hand, some of them will want to communicate and use all techniques possible, even something as outdated as radio communication, just the make it easier for primitives like us. Why don´t we hear them? If sapiens life is rare it explains the Great Silence. The few civilizations that chose radio communication are just too few and too far away.
          Interstellar Space travel may be impractical, as you mentioned, but as far as we know, not impossible. If sapiens life is abundant, maybe most of them will be content to stay home, but some of them will try. A civilization that is just a few hundred or thousand year ahead (and that is not much in Deep Time) of us should be able to construct much faster space ships then we have. They do not need to reach the light of speed to explore the Universe, nor do they need to establish colonies. Imagine a scheme of self-replicating robot spacecraft who reach say a tenth of the speed of light. They arrive from a nearby star in an unexplored solar system, start harvesting natural resources to make other robots to explore this solar system, build a communication system to send messages back home and after a few hundred years build new interstellar spaceships to go to the next nearby stars. A scheme like this will explore a Galaxy in just a few millions of years. And what are a few millions of years in Deep Time. If sapiens life is abundant in this Galaxy, it should have been around when life on earth was dominated by dinosaurs.
          Just a few thoughts, it all remains speculation.

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