Iron Stars

Posted on May 20, 2011 by Steve

Freeman Dyson put the zap on my head.

Halfway through a nerdy article about physics and the long-term future, I tracked down a 1979 paper it cited (3MB PDF). In it, Dyson observes that the early history of the universe is a respected field of study, but very little serious consideration has been given to the distant future. Given his inveterate curiosity and disregard for convention, he proposed to apply his understanding of physics to describe as clearly as possible the ultimate fate of everything, with a view to considering what challenges any living things will face.

Appropriate for publication in Reviews of Modern Physics, the paper includes plenty of formulae, which I mostly glossed over. I have found that authors are usually kind to their readers, and a slight effort to follow a formula is usually adequate to catch the gist. However, I am usually reading books that take the time to explain exponential notation early on. In this case the gist was hard to grasp, and presumably gets proper treatment in the cited external sources. Dyson merely provides cursory guidance like "where χ is a space coordinate moving with the matter," and other variables seem to be of the if-you-don’t-know-don’t-ask variety.

The imagery, however, is arrestingly clear. Never mind the inconvenient destiny of the sun to swell up and engulf our planet; that's just a few billion years off. The real problems come later. Planets will be ripped from their orbits by close encounters with other celestial bodies, or gravitational radiation will cause their orbits to decay until they plunge into their mother stars. Stars will be torn from their home galaxies, and eventually fizzle out and become inhospitable white dwarfs, neutron stars, or black holes. Solid objects will lose their shape -- as Dyson puts it, on a long enough time scale, "matter is liquid at zero temperature." Atoms in a rigid structure occasionally shift and rearrange themselves. So asteroids, planets, Voyager I -- all will eventually flow into spherical shapes under the force of their own gravity, like water droplets. But wait, there's more. Radioactive elements relatively quickly break down into smaller atoms. But the product elements are not perfectly stable either. Over the time scale of 101500 years, "ordinary matter is radioactive" and decays. Smaller atoms tend to fuse and larger atoms split, and all of them settle on a middling stable element: iron. So the Pleiades, Cassiopeia, Orion -- if they avoid other fates all will become cold perfect spheres of pure iron, sailing through the darkened reaches of space.

By now the reader is not surprised to learn that even this is not the end of the story. Matter in an iron star is not in its lowest energy state, and could release a spectacular amount of energy by collapsing into an ultradense neutron star. This takes quite a while longer, and may result in either a supernova or at least a vigorous outburst of neutrinos, x-rays, and visible light. These "occasional fireworks" will light up the universe after a passage of time too large to be expressed with a single level of exponentiation.

Skinner woke once, or seemed to, and struggled to sit up, calling, Yamazaki thought, for the girl.
“She isn’t here,” Yamazaki said, his hand on Skinner’s shoulder. “Don’t you remember?”
“Hasn’t been,” Skinner said. “Twenty, thirty years. Motherfucker. Time.”
“Time. That’s the total fucking motherfucker, isn’t it?”
Virtual Light

I read the paper two weeks ago, and it rather upset my habitual focus on ephemera. Earlier that week I missed a big news story while watching a ten-minute video of mesmerizing ballistic impacts which span, in total, a hundredth of a second. I watched it twice -- a welcome distraction from a 30-year mortgage, domestic responsibilities, and a looming midlife crisis. First Dyson turned my time perspective inside out, then someone close to me suffered a spasm of ennui and started asking those impossible, existential questions, all of which seem to be variations of the sentiment, "What's the point?" Even on a good day, I'm not well-equipped with satisfying answers. My head began a long, slow spin.

Dyson's paper, like the man, is upbeat, playful, irreverent. He can tell his wife, concerned about global warming, that "the polar bears will be fine," while knowing that every existing milligram of polar bear is destined to become a bit of iron near absolute zero. The second half of his paper is a quite optimistic analysis of the prospects for life, in some form, in the same distant future which had just appeared so gloomy, despite the occasional fireworks. There are good future prospects not just for life, but also for communication, the essential ingredient that makes our species social, that preserves our shared memory, that is the basis of every relationship. I took hope in this hope, felt new appreciation for those close to me, and recalled a touching passage written by a man I used to associate with hopeless doomsday scenarios.

Perhaps there is scarcely a man who has once experienced the genuine delight of virtuous love, however great his intellectual pleasure may have been, that does not look back to the period as the sunny spot in his whole life, where his imagination loves to bask, which he recollects and contemplates with the fondest regrets, and which he would most wish to live over again. The superiority of intellectual to sensual pleasures consists rather in their filling up more time, in their having a larger range, and in their being less liable to satiety, than in their being more real and essential.
Thomas Malthus

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Posted by RWH | May 25, 2011 | 14:43:24

did Freeman Dyson put the zap on your head steve.

did he put it on there.

Thinking about the long horizon is a good way to give yourself a case of the screaming willies.

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