[ExI] Fermi Paradox Reconsidered

[Stuart LaForge]

On 2026-06-14 02:57, BillK via extropy-chat wrote:

> Your intuition is correct: The universe is probably not easily
> infectable. The energy and biosphere requirements you've identified
> are likely insurmountable for any realistic technology. That means the
> Hart-Tipler conjecture fails—not because life is rare, but because
> _self-replicating interstellar infection is physically impractical_.

One of the biggest reasons for the Fermi Paradox is the vast size of the 
observable universe and the relativity of time. One very important 
consideration about the biogenesis of life is that nucleic acids both 
DNA and RNA use phosphorus to create phosphodiester bonds. Phosphorus, 
while somewhat abundant on Earth is relatively rare in our past light 
cone. This is because phosphorus was created by stellar nucleosynthesis 
only recent in the population III or third generation stars before being 
dispersed by supernovae. The first pop III stars only showed up 8 or 9 
billion years after the big bang so life could only have arisen anywhere 
in the universe starting about 4 or 5 billion years ago.

Note that this 4 to 5 billion years ago is in terms of cosmic comoving 
time so local gravity wells and recession velocities can also affect 
techno-signatures by delaying the detection of such signals from far 
away galaxies due to relativistic effects. Intelligent life able to 
create and manipulate technology might be rare enough in the universe 
that every such civilization thinks it is the first in its light cone 
until their light cones eventually overlap many years in the future.

In any case the rarity of elemental phosphorus and its nucleosythesis 
timelines puts an upper bound on the oldest possible carbon-based life 
in the universe.

Stuart LaForge