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Comment by jccalhoun | Hacker News Reader

Space is just so unimaginably huge that although I think aliens exist, I don't think it is likely that multi-solar system civilizations exist or there is a lot of organic life traveling between solar systems. The fastest man-made object is Helios 2 which went a little over 250,000 km/h https://en.wikipedia.org/wiki/Helios_(spacecraft) So if I did my math right, that's 0.02% of the speed of light. So we would have to go 50 times that fast to just be 1% of the speed of light. The nearest star is 4 light years away. So even at the speed of light it would take 4 years to get there.

So a civilization would have to develop some way of going faster than light to realistically go to other solar systems which, even if possible, would likely take unimaginable amounts of power.

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Space is big, but Helios isn’t us trying to go as fast as possible, it’s going the speed it is because that’s a requirement of orbital dynamics.

If we really really wanted, nuclear options could get us to a few percent of c with current tech and no breakthroughs.

On the other hand, if someone builds a von Neumann probe that eats sunlight and Mercury (the planet), it could make a Dyson swarm in a human lifetime, and that would enable us to colonise most of our causal future light cone directly from Sol: https://youtu.be/zQTfuI-9jIo

Just speculation (I am not a physicist or astrobiologist), but this is my thinking also. If anything is traveling between the stars, it's either inorganic (an AI), or it has a natural lifespan several orders of magnitudes longer than humans. Without FTL travel, to conquer space you also have to conquer time.

Organic life is fragile and ill-suited for space travel, at least organic life as we know it. Perhaps the destiny of all sufficiently advanced organisms is either to die off or replace itself with AI.

Anyway, while I find it impossible to believe there's nothing out there, I find it nearly equally impossible to believe anything that's ever visited our rock resembled little green men.

I certainly like the idea of traveling at 1G better than living in a rotating ring-like spaceship. (On the other hand, in my imagination I keep seeing this huge sign at the end of a journey to another galaxy that took forty years saying “Nothing to see here, move along...”)

They wouldn't need FTL. Sufficiently[0] powerful rockets with a sufficiently dense fuel source could reach relativistic speeds, allowing the travelers to experience the journey in less time than the trip takes according to an outside observer.

For instance, accelerating at 1G toward our nearest neighboring star for half the distance, then slowing down for the other half, a traveler could arrive in 3.5 years instead of the "minimum" 4.3. Of course, from Earth's perspective it took 5.9 years, but that's not important. The effect is exponential, such that a trip to the center of the Milky Way, ~30kly, would only take 20yrs ship time (30,002yrs Earth time).

[0] "Sufficiently" in this case meaning "pretty ludicrously".

Humanity only ventured into space in the last few centuries, and Helios 2 is the best current effort, not a fundamental limit.

Also, the real obstacles are not physical speed limits, but the huge cost of getting materials into space. If we ever got enough material into space to provide a true, self-sustaining industry (i.e. non-terrestrial power and materials) then we'd see a space-building boom that could rapidly improve on space exploration.

The earth is relatively close to the sun, better use of solar wind: both the light and the plasma might help accelerate without the high energy/fuel costs, see: https://en.wikipedia.org/wiki/Magnetic_sail

>> So a civilization would have to develop some way of going faster than light to realistically go to other solar systems

That is a very human mindset. "Civilization" would include machine civilizations. For a machine, a few thousand years of transit time would be irrelevant given the advantages a new star system might offer.

Are machines immune to entropy? If not, I suspect that a few thousand years of transit time still pose an obstacle, even for a machine civilization.

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