To know the unknowable

kw: book reviews, nonfiction, science, cosmology, philosophy

When I was a geology student in the late 1960s, the environmental movement was gaining traction, and the word "biodegradable" became fashionable. My classmates and I had just learned of the tectonic cycle, the understanding that on a scale of between 50 million and 200 million years, mountains rise, they are eroded to near sea level, all the sediments eventually wind up being subducted by trenches into the upper mantle, and new mountains arise. Somebody said, in a bull session, that there is a lot of waste "out there" that is not biodegradable. Someone else said, "Well, it is mostly geodegradable," to which I added, "and everything else is theodegradable."

Endings get better press than beginnings. A very popular country song of a few years ago crooned, "Let's go out in a blaze of glory," and quoted the proverb, "All good things must end." Just ask Chris Impey. In his book how it ends: from you to the universe (capitalization of the book's cover) he tells us not just that everything ends, but how it does so. Yet in the best tradition of the philosophy of science, you have to know what you have before you can predict where it is going, so much of the book is devoted to exploring what exists. It is a very good survey of the breadth of science as it relates to existence of people, species, planets, stars, galaxies, and universes. The doleful matter of how each might come to an end is nearly swallowed up in the discussions of how they are.

Let's begin with the biggest ending of all: the Universe. Can it end? Not too surprisingly, the jury is still out on that one. Hubble's discovery 80+ years ago that the universe is expanding led to much work (and speculation) about whether the expansion was being brought to a halt by gravity. Visible matter (stars and gas clouds) constitutes only a few percent of the mass needed to halt the expansion at any time. But star movements in galaxies and other lines of evidence indicate that a kind of matter we cannot detect except by its gravity, usually called dark matter, outweighs visible matter by a factor of six or seven. But that still falls short of the mass needed to "close" the universe. That would seem to answer the question negatively: the Universe cannot end; it will expand forever.

But wait, there's more. Just under twenty years ago, accelerated expansion was proffered to explain the unexpected dimness of distant supernovae. This would seem to emphasize the point, but some versions of "cosmic acceleration" postulate a singularity, perhaps one or two billion years from now, when the acceleration rate will rise infinitely (better stated as "without limit"), leading to a "Big Rip", after which spacetime cannot exist, at least not in any form that we can calculate (after all, the theory itself is simply a calculation). Dr. Impey follows his discussion of the big rip with a reference to data that it probably can't be so. Whew! So maybe something can be genuinely eternal after all.

Not so fast. Let us suppose that there is no cosmic acceleration, or that it stays within bounds, so that spacetime expands at some calculable rate, and just keeps doing so. In a few billion years, not much happens, but in a trillion years or so the galaxies have run out of non-star matter (gas and dust) to make new stars, and the oldest stars existing are running out of their own fuel. The lights go out and the universe cools, forever, toward absolute zero. Yet matter itself may also evaporate. In a trillion trillion trillion years (36 zeroes), half of existing matter will have turned into neutrinos and photons; add a few more zeroes and it is effectively all gone. Double the number of zeroes and most black holes will have evaporated via Hawking radiation. Do you dare to double the number of zeroes again? Spacetime may still be expanding, but there is no matter around to impede the passage of photons, most of which have wavelengths measured in billions or trillions of light years. Not too exciting. So photons are apparently eternal. Big whoop!

Well, with that for a backdrop, we can consider items with briefer existences, and more interesting ones. Stars, for example. The biggest stars that can exist burn off their nuclear fuel in a million years or less, briefly forge elements ranging to iron, then blow everything into space as a supernova. That allows planets to form that are made of something other than H+He. The smallest stars that can burn nuclear fuel might last a trillion years, but eventually just fade away as dimming cinders. In between, the Sun and similar stars can cook along for a number of billions of years, then they puff up into red giants and puff away a third of their mass into a planetary nebula before subsiding into white dwarfs, which slowly fade to black (in a few dozen billion years). But in midlife they provide a haven for planets that might harbor life for a while, say one to ten billion years.

But what of life? Earth has been a living planet for about four billion years. The Sun will probably cook all life off the Earth long before becoming a red giant. Theories differ: it may take as little as another half a billion years, or as many as 2-3 billion. Will humanity survive to that point? Here things get interesting. Will our technology allow us to overcome evolution, which so far seems to produce mammal species that last no longer than ten or twenty million years, and tend to average about two million years before going extinct or mutating beyond recognition, becoming a different species? Is there a "technological singularity," as Ray Kurzweil projects, that will make humanity into something different (and possibly part or all machine) within the lifetime of people a little younger than I am? Will these post-human creatures be longer-lived than we?

How long can a human live? Shigechiyo Izumi and Jeanne Calment are the only humans in the modern era who are thought to have lived more than 120 years. Darn few of us live more than 90 years. A few species of bird, turtle, and whale seem to have produced individuals that have lived 150 years or more, but the complex organ systems needed to keep a metazoan animal living are apparently not able to fend off irreparable damage more than 100-200 years.

There are two indicators of general senescence that, if you want to pay for a test or two, will probably simply cause depression. One is the Hayflick limit. Fetal cells in culture divide 40-60 times, then stop, enter senescence, and eventually all die. That 40-60 range is not quite absolute, but covers nearly all of us. Statistical analyses indicate that if nothing else gets you, you'll just wear out at some age between 60 and 120 years. The other test is to get an electron microscopic look at your mitochondria. Mitochondria look like crisp little sausages about two microns long, with baffles inside. They start looking rather ragged in your forties, and get positively snaggly with the passing decades. They are your energy system, and when they fall apart, so does everything else.

The amazing thing is, that we are continually driven to learn such things: the inner workings of mitochondria, the survival of species, the evolution of stellar interiors, and the structures of galaxies and universes. Even the least technical among us are interested in how things work, and indeed, many members of the local Astronomy club are not science majors. Same with the local Lapidary society. Humans are curious, and the best stimulation is to learn things. I read that Robert Feynman said on his deathbed, "I'd hate to die again. It is so boring." We are driven, and that makes us what we are.