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Blueberry Earth

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Here’s a gedankenexperiment (that’s German for “thought experiment”) that ought to interest you.

A gedankenexperiment is a way that physicists ask questions about how something in our universe works, for the joy of working out it’s consequences. The experiments don’t need to be practical, although many do lead to advances in physics. Famous examples of gedankenexperiments that led to new ideas in physics include Schrödinger’s cat and Maxwell’s demon.

Blueberry Earth: The Delicious Thought Experiment That’s Roiling Planetary Scientists
“A roaring ocean of boiling jam, with the geysers of released air and steam likely ejecting at least a few berries into orbit.”

Sarah Zhang, The Atlantic, 8/2/1018


Image from pxhere.com, 517756, CC0 Public Domain

Sarah Zhang, in The Atlantic, 8/2/1018, writes

Can I offer you a thought experiment on what would happen if the Earth were replaced by “an equal volume of closely packed but uncompressed blueberries”? When Anders Sandberg saw this question, he could not let it go. The asker was one “billybodega,” who posted the scenario on Physics Stack Exchange. (Though the question was originally posed on Twitter by writer Sandra Newman.)

A moderator of the usually staid forum closed the discussion before Sandberg could reply. That didn’t matter. Sandberg, a researcher at Oxford’s Future of Humanity Institute, wrote a lengthy answer on his blog and then an even lengthier paper that he posted to arxiv.org, a repository for physics preprints that have not yet been peer reviewed. The result is a brilliant explanation of how planets form.

To begin: The  1.5 x 1025 pounds of “closely packed but uncompressed” berries will start to collapse onto themselves and crush the berries deeper than 11.4 meters – or 37 feet – into a pulp. “Enormous amounts of air will be pushing out from the pulp as bubbles and jets, producing spectacular geysers,” writes Sandberg. What’s more, this rapid shrinking will release a huge amount of gravitational energy—equal to, according to Sandberg’s calculations, the energy output of the sun over 20 minutes. It’s enough to make the pulp boil. Behold:

“The result is that blueberry earth will turn into a roaring ocean of boiling jam, with the geysers of released air and steam likely ejecting at least a few berries into orbit. As the planet evolves a thick atmosphere of released steam will add to the already considerable air from the berries. It is not inconceivable that the planet may heat up further due to a water vapour greenhouse effect, turning into a very odd Venusian world.”

Deep under the roiling jam waves, the pressure is high enough that even the warm jam will turn to ice. Blueberry Earth will have an ice core 4,000 miles wide, by Sandberg’s calculations. “The end result is a world that has a steam atmosphere covering an ocean of jam on top of warm blueberry granita,” he writes.

The process is not so different from the birth of a planet out of a disc of rotating debris. The coalescing, the emergence of an atmosphere, the formation of a dense core—all of these happened at one point to the real Earth. And it is currently happening elsewhere in the universe, as exoplanets are forming around other stars in other galaxies.

What happens-if-the-earth-instantly-turned into a mass of blueberries? The Atlantic

An interview with the author on Slate.com

Article by Anders on his blog

Blueberry Earth by Anders Sandberg, on Arxiv


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