Karel Schrijver
- Published in print:
- 2018
- Published Online:
- July 2018
- ISBN:
- 9780198799894
- eISBN:
- 9780191864865
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/oso/9780198799894.003.0002
- Subject:
- Physics, Geophysics, Atmospheric and Environmental Physics, History of Physics
This chapter briefly reviews some the challenges encountered in the search for extraterrestrial life. So far, no signs of extraterrestrial life have been found. The search started with radio ...
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This chapter briefly reviews some the challenges encountered in the search for extraterrestrial life. So far, no signs of extraterrestrial life have been found. The search started with radio telescopes, looking for technology-based civilizations, but new strategies have emerged that take on the primary challenges in this search: the enormous distances to exoplanets and the question of the true nature of life. The author outlines the development of new tools for the search, and why the present focus is on Earth-sized exoplanets with a potential for liquid water on their surfaces. Not having been visited by an alien civilization presents us with a paradox: if life develops as quickly elsewhere as on Earth, then why have we not been contacted? Is the speed of light too slow to cross interstellar distances, is life intrinsically rare, or should we conclude that civilizations are intrinsically short-lived?Less
This chapter briefly reviews some the challenges encountered in the search for extraterrestrial life. So far, no signs of extraterrestrial life have been found. The search started with radio telescopes, looking for technology-based civilizations, but new strategies have emerged that take on the primary challenges in this search: the enormous distances to exoplanets and the question of the true nature of life. The author outlines the development of new tools for the search, and why the present focus is on Earth-sized exoplanets with a potential for liquid water on their surfaces. Not having been visited by an alien civilization presents us with a paradox: if life develops as quickly elsewhere as on Earth, then why have we not been contacted? Is the speed of light too slow to cross interstellar distances, is life intrinsically rare, or should we conclude that civilizations are intrinsically short-lived?
Emily C. Parke
- Published in print:
- 2020
- Published Online:
- June 2020
- ISBN:
- 9780190915650
- eISBN:
- 9780197506066
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/oso/9780190915650.003.0005
- Subject:
- Biology, Bioethics
This chapter argues that the concept of “life” is used in several rather distinct ways: sometimes as an all-or-nothing phenomenon and other times as a matter of degree; sometimes referring to ...
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This chapter argues that the concept of “life” is used in several rather distinct ways: sometimes as an all-or-nothing phenomenon and other times as a matter of degree; sometimes referring to individual organisms and other times to communities; sometimes based on specific chemistries and other times on functions. In contrast to biologists in general, astrobiologists cannot take the status of their subject matter as living or nonliving for granted. There are at least two reasons to think astrobiologists need an understanding of what counts as life. The first is to set search criteria for finding “life as we don’t know it” in the universe. The second is to set success conditions conducive to agreement about when life has been found and when it has not. In addition to particular cases like the recent Mars finding by NASA, the meaning of “life” figures into a broader agenda in astrobiology: looking for biosignatures.Less
This chapter argues that the concept of “life” is used in several rather distinct ways: sometimes as an all-or-nothing phenomenon and other times as a matter of degree; sometimes referring to individual organisms and other times to communities; sometimes based on specific chemistries and other times on functions. In contrast to biologists in general, astrobiologists cannot take the status of their subject matter as living or nonliving for granted. There are at least two reasons to think astrobiologists need an understanding of what counts as life. The first is to set search criteria for finding “life as we don’t know it” in the universe. The second is to set success conditions conducive to agreement about when life has been found and when it has not. In addition to particular cases like the recent Mars finding by NASA, the meaning of “life” figures into a broader agenda in astrobiology: looking for biosignatures.
