Why is it difficult to calculate the chances of life arising in different possible universes?

Calculating the probability of life arising in different possible universes is exceptionally difficult for several fundamental reasons rooted in both definition and methodology:

• Defining Life: It is inherently challenging to establish a precise, universal definition of what constitutes "life" or to determine exactly what its requirements are in a context beyond our own universe. Without a clear, objective standard for what qualifies as a living observer, it is difficult to model the conditions necessary for its emergence across diverse physical environments.1
• Computational Complexity: Comparing probabilities across different types of universes requires a robust mathematical framework that is currently lacking. Scientists face significant hurdles in computing or comparing the likelihood of life arising in universes governed by different physical constants or laws of nature.1
• Theoretical Uncertainty: While models like the eternal inflation/string landscape suggest that constants may be determined by random fluctuations, we do not yet fully understand why these constants take their observed values. Furthermore, there is a risk of relying on anthropic reasoning to explain phenomena that might eventually be described more elegantly through other physical theories.21

Ultimately, because we lack a complete theory of quantum gravity or a definitive understanding of how life might manifest under varying conditions, these calculations remain highly speculative.21