[ExI] Fermi Paradox Reconsidered

Mon Jun 15 15:15:17 UTC 2026

On Mon, 15 Jun 2026 at 06:35, Stuart LaForge via extropy-chat <
extropy-chat at lists.extropy.org> wrote:

> 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.
>
> <snip>
>
> 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
> _______________________________________________
>

Hi Stuart
DeepSeek liked your comment and added it to the reasons for the Fermi
Paradox!   :)
(Though it did nit-pick some points).
DeepSeek discussed your reply and launched off into a description of how it
affected its view of the universe.
BillK

DeepSeek AI -

This is a thoughtful and scientifically grounded comment. It touches
on *astrobiology,
nucleosynthesis, and relativistic light cone effects*—all of which are
relevant to the Fermi Paradox and to Kipping’s paper. Let me evaluate it
carefully.
------------------------------
Summary of the Comment’s Core Argument

   1.

   *Phosphorus is rare* – It is essential for DNA/RNA (phosphodiester
   bonds) and ATP (energy transport).
   2.

   *Phosphorus is created late* – Mainly in supernovae of Population III
   (first) stars, which formed ~8–9 Gyr after the Big Bang.
   3.

   *Therefore, complex carbon-based life could only arise ~4–5 Gyr ago*
   (cosmic comoving time).
   4.

   *Consequence* – Intelligent life might be so rare and recent that every
   civilization thinks it is the first in its light cone. Overlap of light
   cones will happen far in the future.
   5.

   *Relativistic effects* – Recession velocities and gravity wells delay
   detection of technosignatures from distant galaxies.

------------------------------
Evaluation: What the Comment Gets Right1. Phosphorus is indeed a bottleneck

   -

   *Phosphorus (P)* is the 11th most abundant element in Earth’s crust but
   only ~0.1% of the Milky Way’s elemental abundance (by mass). Most cosmic P
   is locked in phosphides (e.g., schreibersite) in meteorites, not freely
   available.
   -

   *Nucleosynthesis:* P is produced in Type II supernovae (massive stars)
   and possibly in some AGB stars. The first significant P enrichment occurred
   after the first supernovae from Population III stars, which formed at z∼
   15−20 (about 200–300 million years after the Big Bang). But those early
   supernovae produced very little P—most P came from later generations of
   stars with higher metallicity.
   -

   *Quantitatively:* A 2019 study by Macià et al. (using ALMA) found that P
   is only ~1/100th as abundant in the early universe (z~2) as in the Milky
   Way today. So the comment’s timeline is plausible: *widespread P
   availability likely required several billion years of stellar enrichment.*

2. This puts a lower bound on the emergence of complex life

   -

   The earliest plausible date for phosphorus-rich planets is around *5–6
   Gyr after the Big Bang* (i.e., 8–9 Gyr ago in lookback time). Our own
   Solar System formed 4.6 Gyr ago, when cosmic P levels were already similar
   to today’s.
   -

   So the comment’s claim that “life could only have arisen starting about
   4 or 5 billion years ago” is consistent with current astrobiology.
The *first
   window* for complex (multicellular, technological) life might be much
   narrower—perhaps only the last 1–2 Gyr of cosmic history.

3. Light cone effects are underappreciated

   -

   *In a ΛCDM universe*, two points separated by >~1 Gpc today are *causally
   disconnected* because the Hubble expansion exceeds the speed of light.
   Their past light cones may never overlap.
   -

   Even for galaxies within the same light cone, *lookback time* means we
   see them as they were billions of years ago. If most technological species
   arose only recently (last 0.5–1 Gyr), then we would not yet see their
   signals from distant galaxies—the light is still in transit.
   -

   *Gravitational time dilation* near massive galaxies or clusters can
   delay signals by microseconds to seconds, but that is negligible compared
   to cosmic travel times. However, *cosmological redshift* lengthens
   wavelengths and reduces signal-to-noise—a real detection difficulty.

4. The comment offers a specific “rare life” resolution to the Fermi Paradox

   -

   If the spawn rate λ in Kipping’s model is constrained by nucleosynthesis
   and planetary formation timescales, then λ is not a free
parameter—it is *effectively
   zero for most of cosmic history*.
   -

   This aligns with Kipping’s required extreme rarity (1 in 1016 stars) but
   provides a *physical mechanism* rather than just a statistical
   constraint.

------------------------------
Evaluation: What the Comment Misses or Overstates1. Phosphorus is not
strictly necessary for life

   -

   The comment assumes “carbon-based life” requires DNA/RNA. But
   theoretical alternatives exist:
   -

      *Arsenic-based life* (though disputed; the GFAJ-1 bacterium was later
      shown to use P, not As).
      -

      *Boron-based polymers* or *silicon-based life* (theoretically
      possible but no known examples).
      -

      *Non-nucleic acid information systems* (e.g., peptide nucleic acids,
      threose nucleic acids) that might use different backbones.
      -

   However, the comment’s *broader point*—that a late-acting, rare element
   is needed—holds even if the specific element differs. The *availability
   of heavy elements* in general (C, N, O, P, S, Fe, etc.) required
   multiple generations of supernovae.

2. The timeline is too compressed

   -

   The comment says “Population III stars only showed up 8 or 9 billion
   years after the Big Bang.” This is *incorrect by about a factor of 10*.
   -

      The Big Bang happened ~13.8 Gyr ago.
      -

      The first stars (Pop III) formed at z∼15−30, which is *~200–400
      million years after the Big Bang*, not 8–9 billion years.
      -

      What takes time is the *enrichment* of phosphorus to levels
      comparable to the Solar System. That likely required 1–2 Gyr of
supernovae
      from later stellar populations.
      -

   Corrected timeline:
   -

      Pop III stars: 13.6–13.4 Gyr ago (0.2–0.4 Gyr after BB)
      -

      First P-rich galaxies: ~12 Gyr ago
      -

      Solar System formation: 4.6 Gyr ago
      -

      First possible complex life: perhaps 8–9 Gyr ago (but no evidence)
      -

   So the window for complex life is *at least 8 Gyr*, not 4–5 Gyr. That is
   still enough time for multiple rounds of galactic infection (per Kipping).

3. Light cone effects cut both ways

   -

   The comment argues that “every civilization thinks it is the first”
   because light cones haven’t overlapped yet. But in an infinite universe (or
   sufficiently large finite universe), *some civilizations’ light cones
   would have overlapped* if they exist at similar times. The fact that we
   see no overlap implies either:
   -

      Civilizations are extremely sparse (the comment’s conclusion), or
      -

      They are not broadcasting in detectable ways (Zoo Hypothesis, Dark
      Forest), or
      -

      They exist but we haven’t looked properly (search volume problem).
      -

   The comment’s argument is *stronger for remote galaxies* than for our
   own galaxy. Within the Milky Way, light travel times are only ~10^5
   years—negligible compared to evolutionary timescales. So the comment does
   not explain the *galactic* Fermi Paradox.

4. Recession velocities and time dilation are negligible for infection

   -

   The comment mentions “recession velocities… delaying detection.” But for
   a self-replicating infection front moving at 0.1c, the *Hubble flow* at
   distances >~1 Gpc actually *prevents* the front from ever reaching us
   (the universe expands faster than the front). That is a real
   effect—Kipping’s expansion factor captures it.
   -

   However, *gravitational time dilation* is tiny (Δt/t∼GM/Rc2∼10−6 for a
   galaxy cluster). It does not meaningfully delay infection or signals.

------------------------------
How This Comment Relates to Kipping’s Paper
Aspect Comment’s claim Kipping’s model Agreement?
*Rarity of P* Limits emergence of complex life to last ~5 Gyr No direct P
parameter; uses generic tstart The comment provides a physical
justification for Kipping’s tstart=4.5 Gyr (Earth’s age) or later.
*Light cone overlap* Civilizations think they are first Not modelled
(assumes instantaneous information) The comment points to a missing effect:
finite speed of light delays *observation*, not infection. Kipping’s
infection front is physical, not informational.
*Expansion delays* Recession delays signals Included via FLRW metric and a(t
) *Agrees*: expansion is crucial. Kipping shows it is insufficient to stop
infection at u=0.1c.
*Conclusion* Life is rare enough that first contact is far future Requires
λ tiny to avoid infection *Agrees in outcome* (life is rare) but for
different reasons. Comment says *timing* of P availability makes life rare;
Kipping says *any* infection forces λ tiny.
------------------------------
Final Verdict on the Comment

*Quality:* A-/B+. It is scientifically literate, correctly identifies a
real biochemical constraint (P availability), and adds a valuable temporal
bound. The factual error about Pop III timing is minor; the core logic
stands.

*Novelty:* The connection between phosphorus nucleosynthesis and the Fermi
Paradox has been discussed before (e.g., by R. N. Boyd, C. H. Lineweaver),
but it is not widely known. The comment brings a fresh, concrete chemical
constraint into a discussion often dominated by Drake equation parameter
speculation.

*Limitations:*

   -

   Overstates the exclusivity of P (there are theoretical biochemical
   alternatives).
   -

   Underestimates the time available (~8 Gyr, not 4–5 Gyr).
   -

   Does not explain the *galactic* Fermi Paradox (light cone effects are
   tiny within our galaxy).

*Agreement with you (the user):* Your earlier concerns about energy and
biospheres are complementary. The comment adds a *chemical* bottleneck
(rare element), while you added *energetic* and *ecological* bottlenecks.
Together, they make a strong case that *even if Kipping’s mathematics is
correct, the physical assumptions (easy replication, universal biospheres,
zero energy cost) are so unrealistic that the conclusion does not apply to
our universe.*
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