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2 results

  • Abiogenesis: the Carter argument reconsidered

  • Daniel P. Whitmire
  • Journal:
    International Journal of Astrobiology / Volume 22 / Issue 2 / April 2023
    Published online by Cambridge University Press:
    23 September 2022, pp. 94-99
    • Article
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  • The observation of life on Earth is commonly believed to be uninformative regarding the probability of abiogenesis on other Earth-like planets. This belief is based on the selection effect of our existence. We necessarily had to find ourselves on a planet where abiogenesis occurred, thus nothing can be inferred about the probability of abiogenesis from this observation alone. This argument was first formalized in a Bayesian framework by Brandon Carter. Though we definitely had to find ourselves on a planet where abiogenesis occurred, I argue here that (1) the Carter conclusion is based on what is known as the ‘Old Evidence Problem’ in Bayesian Confirmation Theory and that (2) taking this into account, the observation of life on Earth is not neutral but evidence that abiogenesis on Earth-like planets is relatively easy. I then give an independent timescale argument that quantifies the prior probabilities, leading to the inference that the timescale for abiogenesis is less than the planetary habitability timescale and therefore the occurrence of abiogenesis on Earth-like planets is not rare.

  • 19 - The Biological Universe

  • from Part V - Beyond the Milky Way
  • Wallace Arthur, National University of Ireland, Galway
  • Book:
    The Biological Universe
    Published online:
    24 September 2020
    Print publication:
    24 September 2020, pp 300-317

  • Summary

    Here, I use a particular type of mental picture to contemplate the possible extent of the biological universe. The idea is that at various levels of spatial scale we can use green to depict entities with life. Such entities could be planets with life, stars that have planetary systems with life, or galaxies that include one or more such planetary systems. Whatever the extent of the biological universe, another question is: what form does it take? A pessimistic answer is that we have no idea because so far we only have a sample size of a single inhabited planet. However, I advocate a more optimistic view by recommending what I call Copernican biology. This is the view that life on Earth is more likely to be ordinary than special. I consider which laws of science should apply to the biological universe and which should not. I then ask to what extent alien life-forms would be expected to resemble terrestrial ones in their construction, at both cellular and morphological levels. I end by outlining a view of the extent and nature of the biological universe that I call the Huge hypothesis.