Appendix B - Extra

 
          Humans have speculated about extraterrestrial life since antiquity. [1][2][3][4]  Sapient aliens in science fiction of the early twentieth century tended to be humanoid. Later, many writers conceived aliens that resembled some non-human Earth animal – e.g., a reptile, insect, or bird. More recently, aliens have assumed bizarre, other-earthly forms. [5][6]
          In 1976, Carl Sagan and Edwin Salpeter published a classic scientific paper [7] on the prospect of life in the atmosphere of Jupiter, which helped inspire the setting for Eternal Passage. An ecology was proposed with four types of organisms: sinkers, floaters, hunters, and scavengers. The sinkers are the primary autotrophs, performing photosynthesis and establishing the basis for a food chain. Mature sinkers passively descend from the upper troposphere down through the atmosphere, toward the scorching depths, where they perish in the heat. They reproduce along the way, and many of the tiny offspring rise on turbulent currents back to the top of the sinker range. The hunters evolved from sinkers, having acquired the ability to control depth. These quick, maneuverable, heterotrophic animals aggressively seek other organisms, and feed on them. The floaters likely evolved from hunters, and actively maintain their pressure level. They can be heterotrophic (filtering sinkers from the air), autotrophic (performing photosynthesis), or both. It might be advantageous for autotrophic floaters to dwell in the upper troposphere, just above the water clouds, and grow to kilometer proportions. The scavengers, also evolved from hunters, inhabit the lower reaches of the life zone, where they feed on organic detritus drifting downward. Television audiences were introduced to these Jovian life forms on the second episode of Sagan's television series Cosmos in 1980, featuring artwork by Adolf Schaller [8].
          Science fiction authors have proposed even less familiar life forms, not confined to a planetary biosphere. For example, in the1957 novel The Black Cloud [9] by astrophysicist Sir Fred Hoyle, a massive black cloud enters the solar system from interstellar space, blocking sunlight and threatening life on Earth. The erratic yet purposeful behavior of the cloud leads some scientists to speculate that it may be an intelligent life form. The scientists attempt to communicate with it using radio waves, and are surprised when they succeed. The cloud is actually a superorganism much more intelligent than humans, and is itself surprised to find sapient life on our solid planet. The cloud thinks via electrically charged dust particles, and is receptive to radio communication, as it already uses radio waves to coordinate its own thoughts and actions.
          The voidling (introduced in chapter 13) represents an attempt to envision a similarly unusual creature, but one not composed of ordinary matter, and inhabiting the extreme environs near black holes. Various writers have speculated on the possibility of life under conditions of ultrastrong gravity. A classic example is the 1980 novel Dragon's Egg [10], by Robert Forward. In this story, the surface of a neutron star is populated by Cheela – flat, amoeba-like creatures the size of a sesame seed, composed of highly compressed nuclear matter. Because nuclear reactions occur much more rapidly than ordinary chemical processes, the Cheela live and evolve a million times faster than humans. Gravitational time dilation does slow them from the viewpoint of an outside observer by about 10%, but this is negligible compared to the nuclear enhancement. The strange life processes of the voidling are also considerably faster than human, though not rooted in nuclear matter. Time dilation for the voidling is variable, however, since individual aspects of a collective can move vertically in their gravity well. In Dragon's Egg, humans discover the Cheela, and observe them from a safe orbit around the neutron star (approaching the star too closely would be fatal, as enormous tidal forces would rip a person apart). Over the course of a single month, Cheela civilization unfolds, from primitive agricultural communities to a space-faring society with superhuman technology.
          Stephen Baxter has envisaged life in even more intense gravity settings, similar to those encountered by the voidling – the environment near black holes. In his Xeelee Sequence, the building blocks of life are not limited to ordinary matter, but may include such exotic entities as quantum vacuum fluctuations, quarks, dark matter, even kinks in spacetime. [11]  Life arose soon after the Big Bang, and spawned civilizations through every phase of the universe's evolution. Mass extinctions occur at transitions between major epochs, such as the end of rapid inflation, but pockets of intelligence persist and adapt. In the novel Exultant [12], the Xeelee are descended from survivors of the recombination epoch, when the hot plasma that filled the early universe cooled enough for atoms to form. They first inhabited primordial black holes, which they harnessed for energy, tools and computation, but later migrated to supermassive black holes in galaxy cores. The most advanced baryonic life form (composed of matter whose mass derives primarily from protons and neutrons), the Xeelee wage ceaseless war with the Photino Birds, dark matter creatures that inhabit the gravity wells of stars. The Photino Birds seek to extend the lives of their stellar homes by shutting down nuclear fusion (thereby converting the stars to white dwarfs), even though the process will ultimately make the universe hostile to all baryonic life. Humans, who have no knowledge of this peril, encounter the Xeelee, but find their mysterious actions threatening. Just as the voidling seeks to exterminate the Los colony when it fails to understand the psyche and motivation of the interloping colonists, the humans launch a bitter war against the misunderstood Xeelee. The preoccupied aliens are driven from the galaxy periphery, and ultimately flee even the supermassive black hole at the center of the Milky Way, in order to preserve the exotic ecology there.
 
REFERENCES__________________________ 
1. Steven J. Dick, Plurality of Worlds: The Origins of the Extraterrestrial Life Debate from Democritus to Kant (Cambridge: Cambridge Univ. Press, 1982).
2. Steven J. Dick, Life on Other Worlds: The 20th-Century Extraterrestrial Life Debate (Cambridge: Cambridge Univ. Press, 2001).
3. Mark Brake, Alien Life Imagined: Communicating the Science and Culture of Astrobiology (Cambridge: Cambridge Univ. Press, 2013).
4. Stephen L. Gillett, "Alien Worlds," in The Greenwood Encyclopedia of Science Fiction and Fantasy: Themes, Works, and Wonders, Vol. 1, ed. Gary Westfahl (Westport, CT: Greenwood Press, 2005), 12-14.
5. Gary Westfahl,"Aliens in Space," in The Greenwood Encyclopedia of Science Fiction and Fantasy, 14-16.
6. David Toomey, "Weird Life in Science Fiction," in Weird Life: The Search for Life That Is Very, Very Different from Our Own (New York: W. W. Norton, 2013), 165-178.
7. Carl Sagan and Edwin Salpeter, "Particles, Environments, and Possible Ecologies in the Jovian Atmosphere," The Astrophysical Journal Supplement Series 32 (1976): 737–755.
8. Adolf Schaller, "Creating Life on a Gas Giant – On 'Hunters, Floaters, Sinkers' from Cosmos," The Planetary Society Blogs, posted 11/02/2013 (21:29 UTC), https://www.planetary.org/blogs/guest-blogs/2013/20131023-on-hunters-floaters-and-sinkers-from-cosmos.html .
9. Fred Hoyle, The Black Cloud (New York: Harper, 1957).
10. Robert L. Forward, Dragon's Egg (New York: Del Rey 1980).
11. "Xeelee," Spacebattles Wiki, accessed November, 2015, https://www.spacebattles.wikia.com/wiki/Xeelee .
12. Stephen Baxter, Exultant (London: Gollancz, 2004).