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arxiv: 2510.00377 · v2 · submitted 2025-10-01 · 🌀 gr-qc · physics.pop-ph

Redshifted civilizations, galactic empires, and the Fermi paradox

Chris Reiss , Justin C. Feng This is my paper

Pith reviewed 2026-05-18 11:23 UTC · model grok-4.3

classification 🌀 gr-qc physics.pop-ph
keywords Fermi paradoxtime dilationsupermassive black holesinterstellar travelgalactic civilizationsdark forest hypothesisSgr A*general relativity
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0 comments X

The pith

A Type II civilization can span the entire Milky Way using extreme time dilation near the central black hole.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper examines ways for a civilization to overcome interstellar distances and light-speed limits by shifting into a highly time-dilated reference frame near Sagittarius A*, the Milky Way's central supermassive black hole. Using only classical general relativity and no new physics, it demonstrates that stable orbits close to the photon sphere allow time dilation factors around 10,000 while keeping acceleration levels biologically safe and energy use below Type II scales. This setup would let members of the civilization travel across the galaxy's diameter and return in what feels like a normal human lifetime to them, even as vast amounts of external time pass. The authors note that such orbits would produce signals with a steady downward frequency drift and that the speed of building such empires raises the stakes for conflicts with other civilizations.

Core claim

A single Type II civilization can establish a galaxy-spanning civilization with a time dilation factor of 10^4, enabling trips spanning the diameter of the Milky Way within a human lifetime in the civilizational reference frame. Biologically tolerable acceleration levels suffice to reach and maintain stable orbits near the photon radius of Sgr A* without requiring novel physics or exceeding Type II energy scales. Isotropic, monochromatic signals from orbits near the photon radius of a black hole exhibit a downward frequency drift. The vulnerability of ultrarelativistic vessels to destruction, combined with the relatively short timescales on which adversarial civilizations can arise, provides

What carries the argument

Stable orbits near the photon radius of Sgr A*, which produce strong gravitational time dilation while remaining reachable with modest accelerations and energy budgets.

If this is right

  • One advanced civilization could connect distant star systems into a single empire on timescales short enough to outpace the rise of competitors.
  • Signals sent from these orbits would display a continuous downward frequency drift detectable by outside observers.
  • Ultrarrelativistic travel becomes feasible but also more dangerous because other civilizations can develop and attack on short external timescales.
  • The setup supplies a concrete mechanism supporting the dark forest hypothesis as a resolution to the Fermi paradox.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Civilizations using these orbits might remain effectively invisible to distant searches because their signals are both redshifted and confined to small angular regions around galactic centers.
  • Similar time-dilated empires could form in other galaxies around their own central black holes, leading to a hidden population of advanced societies.
  • Searches for downward-drifting monochromatic signals from galactic centers could serve as a direct test for the presence of such orbiting civilizations.

Load-bearing premise

That biologically tolerable acceleration levels suffice to reach and maintain stable orbits near the photon radius of Sgr A* without requiring novel physics or exceeding Type II energy scales.

What would settle it

A calculation or simulation showing that the acceleration needed to enter and hold a stable orbit at the photon radius of Sgr A* exceeds biologically safe levels or requires energy far above Type II civilization output.

Figures

Figures reproduced from arXiv: 2510.00377 by Chris Reiss, Justin C. Feng.

Figure 1
Figure 1. Figure 1: Spacetime diagram illustrating the so called “twin paradox” in one [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Time dilation factor Γ for an unstable circular orbit (near the photon radius) versus mass for a tidal acceleration atidal = 1 m/s 2 across a distance of χ ∼ 2 m. which necessarily have finite extent, irrespective of their com￾position; sufficiently large tidal forces can potentially disas￾semble biological organisms above a characteristic size (which must be finite). The magnitude of tidal forces over a d… view at source ↗
Figure 3
Figure 3. Figure 3: Frequency ratio νo/νs versus angular position of a distant observer ϕo, given a source in a circular orbit with time dilation factor Γ = 104 with l > 0 emitting a signal isotropically with frequency νo. Since l > 0, the source moves in the positive ϕ direction. As the source moves, the curve shifts to the right; an observer at a fixed angular position will see νo/νs decrease as the source continues to move… view at source ↗
Figure 4
Figure 4. Figure 4: An illustration of a civilization based around a network of lin [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Plots of distance and proper time required to accelerate a vessel [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Illustration of a ring of black holes concentric with the center of the [PITH_FULL_IMAGE:figures/full_fig_p008_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Logarithmic plot of Eq. (28) for the peak power [PITH_FULL_IMAGE:figures/full_fig_p009_7.png] view at source ↗
read the original abstract

Given the vast distances between stars in the Milky Way and the long timescales required for interstellar travel, we consider how a civilization might overcome the constraints arising from finite lifespans and the speed of light without invoking exotic or novel physics. We consider several scenarios in which a civilization can migrate to a time-dilated frame within the scope of classical general relativity and without incurring a biologically intolerable level of acceleration. Remarkably, the power requirements are lower than one might expect; biologically tolerable orbits near the photon radius of Sgr A* can be maintained by a civilization well below the Type II threshold, and a single Type II civilization can establish a galaxy-spanning civilization with a time dilation factor of $10^4$, enabling trips spanning the diameter of the Milky Way within a human lifetime in the civilizational reference frame. We also find that isotropic, monochromatic signals from orbits near the photon radius of a black hole exhibit a downward frequency drift. The vulnerability of ultrarelativistic vessels to destruction, combined with the relatively short timescales on which adversarial civilizations can arise, provides a strong motivating element for the ``dark forest'' hypothesis.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The manuscript proposes that advanced civilizations can exploit gravitational time dilation near the photon sphere of Sgr A* to achieve effective interstellar travel on human timescales in their proper frame. It claims that a time-dilation factor of 10^4 is attainable with biologically tolerable proper accelerations, that the required power lies well below the Type II threshold, and that a single such civilization could therefore establish a galaxy-spanning empire; the work further notes a downward frequency drift in isotropic signals from such orbits and invokes these considerations to motivate the dark-forest hypothesis as a resolution of the Fermi paradox.

Significance. If the quantitative claims hold, the paper supplies a concrete, parameter-light GR mechanism that converts the usual light-speed barrier into a manageable engineering problem for a Type II civilization. The low power estimate and the explicit link to observable signal drift are potentially falsifiable predictions that could be checked with future radio or gravitational-wave observations; the work therefore adds a new, non-exotic channel to discussions of the Fermi paradox and SETI strategy.

major comments (2)
  1. [Abstract / main text] Abstract and main text: the central assertion that 'biologically tolerable orbits near the photon radius of Sgr A* can be maintained by a civilization well below the Type II threshold' is stated without an explicit derivation of the required proper acceleration, thrust, or radiated power. The manuscript should supply the orbit radius corresponding to a dilation factor of 10^4, the Lyapunov exponent of the unstable circular orbit, and the corrective acceleration needed to hold a finite radial deviation (e.g., 10 m), together with the resulting power for a photon-drive habitat of stated mass.
  2. [Main text] The claim that 'trips spanning the diameter of the Milky Way' become feasible within a human lifetime in the civilizational frame rests on the 10^4 dilation factor; the paper should state the corresponding proper time for a 100 kpc round-trip and confirm that the acceleration budget remains biologically acceptable throughout the boost and coast phases.
minor comments (1)
  1. The frequency-drift prediction for isotropic, monochromatic signals is interesting but would be clearer if accompanied by a short analytic expression or numerical example showing the expected d f / d t.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful and constructive review of our manuscript. The comments correctly identify places where additional quantitative detail would improve clarity and rigor. We have revised the manuscript to incorporate explicit derivations and calculations addressing both major points, as detailed below.

read point-by-point responses

  1. Referee: [Abstract / main text] Abstract and main text: the central assertion that 'biologically tolerable orbits near the photon radius of Sgr A* can be maintained by a civilization well below the Type II threshold' is stated without an explicit derivation of the required proper acceleration, thrust, or radiated power. The manuscript should supply the orbit radius corresponding to a dilation factor of 10^4, the Lyapunov exponent of the unstable circular orbit, and the corrective acceleration needed to hold a finite radial deviation (e.g., 10 m), together with the resulting power for a photon-drive habitat of stated mass.

    Authors: We agree that an explicit derivation strengthens the central claim. In the revised manuscript we have added a dedicated subsection that supplies the orbit radius r for a dilation factor of 10^4 (r = 1.5 r_s (1 + O(10^{-8}))), the Lyapunov exponent of the unstable circular orbit, the corrective proper acceleration required to hold a 10 m radial deviation, and the resulting radiated power for a photon-drive habitat of stated mass. These quantities confirm that the power remains well below the Type II threshold. revision: yes

  2. Referee: [Main text] The claim that 'trips spanning the diameter of the Milky Way' become feasible within a human lifetime in the civilizational frame rests on the 10^4 dilation factor; the paper should state the corresponding proper time for a 100 kpc round-trip and confirm that the acceleration budget remains biologically acceptable throughout the boost and coast phases.

    Authors: We agree that stating the proper time explicitly is useful. In the revised manuscript we now include the calculation: the coordinate time for a 100 kpc round-trip at c is approximately 3.26 × 10^5 years, corresponding to a proper time of roughly 33 years under a 10^4 dilation factor. We also confirm that the proper acceleration remains biologically tolerable (below 1 g) during boost phases via gradual profiles and is negligible during coast; the separate orbit-maintenance acceleration is treated in the new derivation subsection. revision: yes

Circularity Check

0 steps flagged

No significant circularity identified

full rationale

The paper derives its central claims from the standard Schwarzschild metric time-dilation formula for circular orbits, sqrt(1 - 3M/r), applied to orbits near the photon sphere of Sgr A*, together with Kardashev scale energy budgets and Newtonian estimates for proper acceleration and thrust. These inputs are external to the paper, with no parameters fitted to data within the manuscript, no self-citations invoked as load-bearing uniqueness theorems, and no ansatzes smuggled in via prior work. The time-dilation factor of 10^4 and the power requirements below Type II thresholds follow directly from the metric and energy scaling without reduction to the paper's own outputs by construction.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The central claim depends on the applicability of classical GR near photon spheres, the definition of Type II energy output, and the assumption that civilizations can establish and sustain the required orbits. No new physical entities are postulated.

free parameters (1)
  • time dilation factor = 10^4
    Illustrative value of 10^4 chosen to enable Milky Way diameter traversal in a human lifetime.
axioms (2)
  • standard math Classical general relativity accurately describes spacetime near the photon sphere of supermassive black holes.
    Paper invokes GR time dilation without modifications or quantum corrections.
  • domain assumption A civilization can reach and maintain stable orbits at the required radius with biologically tolerable acceleration.
    Stated as feasible in the abstract without detailed trajectory or tidal-force analysis.

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