Redshifted civilizations, galactic empires, and the Fermi paradox

Chris Reiss; Justin C. Feng

doi:10.1016/j.actaastro.2026.04.003

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arXiv · 2510.00377

Redshifted civilizations, galactic empires, and the Fermi paradox

Chris Reiss·Justin C. Feng

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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.

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Chris Reiss, Justin C. Feng. 2026-04-18. Redshifted civilizations, galactic empires, and the Fermi paradox. https://doi.org/10.1016/j.actaastro.2026.04.003

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