The text discusses the potential future of human exploration and expansion into the universe. It begins by noting that humanity's exploration is limited on Earth but opens up with the vastness of the cosmos. It suggests that future generations may explore other galaxies and wonders how far this expansion could go.
The text then introduces a thought experiment where intergalactic travel at a reasonable fraction of the speed of light is assumed. It discusses the possibility of hopping between galaxies and the preservation of explorers for thousands of years per jump.
The text then introduces the concept of the future lightcone, which defines all the spacetime points a signal sent today could possibly reach. It explains that as time progresses, our future lightcone moves up, and more of spacetime slips out of our possible reach.
The text then discusses the Hubble horizon, a boundary in space beyond which galaxies are moving away from us faster than light can travel. It explains that in a universe expanding at a constant speed, we could never reach the Hubble horizon from within. However, in our universe, the Hubble horizon is moving towards us due to dark energy.
The text then introduces the concept of the cosmological event horizon, a boundary beyond which light cannot reach us. It explains that the horizon can be crossed in one direction but not the other.
The text then discusses the theoretical upper limit on the distance our civilization could spread, referred to as the "affectable universe". It estimates that the affectable universe contains around 20 billion galaxies and around a sextillion stars.
The text then discusses the potential size of humanity's future, considering different travel speeds. It concludes by discussing the potential cultural and social implications of such an expansion.
1. Humans have always been explorers, and future generations may explore the cosmos and even settle other galaxies .
2. There is a hard limit to how much of the universe humans can expand into .
3. If we manage to survive current existential perils and master interstellar and even intergalactic travel, we could potentially explore many planets .
4. There are unpredictable factors such as sociological, technological, political, and environmental factors that could impact human exploration .
5. Physics and cosmology provide a clear limit to how big our future could be .
6. The maximum extent of our potential view of the universe from the Milky Way is around 63 billion light years .
7. Intergalactic travel at a reasonable fraction of the speed of light is possible .
8. If hopping between stars is possible, then hopping between galaxies may also be possible .
9. The size of the affectable universe is approximately proportional to our speed .
10. At half the speed of light, our affectable universe is around half the radius .
11. If we're traveling at least 20% light speed on average, we'll have access to around a billion galaxies or more .
12. In the far future, our observable universe will be around