How Far Beyond Earth Could Humanity Travel?
Summary
This episode explores the maximum extent of human expansion if intergalactic travel becomes possible, defining the "affectable universe" as a 165-billion-light-year sphere containing billions of galaxies. It analyzes how dark energy and cosmic expansion limit our reach, noting that delaying departure or traveling slower significantly reduces the number of accessible stars and planets. The discussion also covers the inevitable "era of isolation," where causally disconnected colonies can no longer communicate, and examines the trade-offs between travel speed and the potential for maintaining …
Topics discussed
Sponsor reads: LinkedIn and Gatorade
Introduction: How big can humanity get?
Recap of previous episode and cosmological limits
Assumptions for intergalactic travel thought experiment
The fundamental limit of our influence bubble
Spacetime diagrams and light cones explained
Future light cone and inaccessible regions
Expansion, gravity, and the Hubble horizon
Dark energy and the shrinking Hubble horizon
Conformal coordinates and the event horizon
Crossing the cosmological event horizon
The accessible universe and maximum reach
Estimating the number of galaxies and stars
Potential population and the cost of waiting
Travel speed and the era of isolation
The ultimately observable universe
Causal disconnection of future colonies
Limits on two-way communication
Communication frequency vs. travel speed
Strategies for maximizing cosmic legacy
Conclusion and Earth Month promotion
Sponsor reads: LinkedIn, Gatorade, Uber Eats, Anthropic, Verizon
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