4 ms·

This line of logic doesn’t hold. Star spanning structures requires the ability to move mass at scale which requires enormous but diffused in time and space amo

This line of logic doesn’t hold. Star spanning structures requires the ability to move mass at scale which requires enormous but diffused in time and space amounts of controlled energy. Moving between stars requires immense energy focused on a single thing. The amount of acceleration required to any meaningful mass to speed necessary to travel between stars and maintain a coherent civilization is extraordinary and implies many things about the mass being accelerated as well. Most things would simply be crushed instantly, including any organism. The speed of light is also a major impediment as is time dilation, as is the need to decelerate, which require equal and opposite energy away from the destination. Ok - accelerate with large lasers based at home - how do you then stop? You first need to build large lasers both at home and destination. The problems expand, and this only helps for very local travel between close stars. It’s difficult but plausible with today’s technology scales up to build star spanning structures because they’re built incrementally and the need for near light speed travel doesn’t exist. Further the existence of a star spanning structure might enable interstellar travel, but not intergalactic. I’d also note that SF is meant to entertain with a story that is possible given some assumptions of progress or hidden nature of reality or small modifications to what is. It’s not meant to be built on magic and other absurdities (not meant as a pejorative!). Many science fiction stories become true and many more will. Often science fiction inspires us to achieve what doesn’t exist today but could. To couch it in something that’s dismissible as say Gandalf the Wizard fighting a Balrog is to greatly underestimate what science fiction is. It’s a roadmap to the future that helps us understand what to avoid on the road.

pfdietz 3y ago
Building a starship reaching 1% of the speed of light seems quite reasonable without substantial technological advance (Dyson's 1968 H-bomb propelled Orion). What it would need would be lots of deuterium, but that's just a matter of large scale industry, which this putative civilization would have. If you are saying this civilization does its work over very extended periods of time, you're saying they're comfortable with efforts that take centuries or millenia or even longer. That alone makes interstellar travel and colonization much easier; the energy needed scales as the inverse square of the travel time (assuming Isp optimized for the travel time chosen and assuming non-relativistic travel). We (or they) do not need close to light speed travel for interstellar colonization.
- HarHarVeryFunny 3y ago
  Typical distance between any two stars in the Milky Way is 5 light years, which at 1% speed of light would take 500 years to get there. Assuming 25 years per generation, that represents a travel time of 20 human generations. That's like a family from the 1500's committing for their children and 19 following generations to live on a shitty rocket. They'd have just arrived. I wonder what 500 years of food, water, and oxygen looks like for a civilization-founding crew. What's the backup plan if the target planet isn't livable? Cyanide tablets?
  - pfdietz 3y ago
    Colonization wouldn't be aimed at planets, it would be aimed at structures in space. You know, like we're assuming this star-spanning civilization has been building in astronomical numbers? Food and air would be manufactured during the trip. All that's needed is a source of energy. At 1% c, that probably means a nuclear source (or beamed power), but at higher speeds they could simply exploit the energy being deposited by interstellar matter. At 1 proton/cm^3 and .1 c, the power is 22 W/m^2.
    - HarHarVeryFunny 3y ago
      If we're talking inter-stellar travel then it doesn't seem to matter what the destination is (planet or space habitat). The travel time remains the same, and the only source of materials (incl. food etc) would be what you bring with you until you arrive at a planet (i.e. at nearest star that has a planet that has useful resources). Even if this were a robotic terraforming mission, it's hard to see humans committing to the expense of such an endeavor with no payoff for generations to come. Heck, we're reluctant to act to save the planet our lives depend on right now.
      - pfdietz 3y ago
        If we're talking about a species that has exploited the resources of its star system, and done so at a scale that includes noticeably blocking the light from its star, then said economy has billions of times the energy we're currently consuming. Proportionally, the cost of an interstellar spacecraft would be less than one week of your salary.

pfdietz 3y ago

Building a starship reaching 1% of the speed of light seems quite reasonable without substantial technological advance (Dyson's 1968 H-bomb propelled Orion). What it would need would be lots of deuterium, but that's just a matter of large scale industry, which this putative civilization would have. If you are saying this civilization does its work over very extended periods of time, you're saying they're comfortable with efforts that take centuries or millenia or even longer. That alone makes interstellar travel and colonization much easier; the energy needed scales as the inverse square of the travel time (assuming Isp optimized for the travel time chosen and assuming non-relativistic travel). We (or they) do not need close to light speed travel for interstellar colonization.

HarHarVeryFunny 3y ago
Typical distance between any two stars in the Milky Way is 5 light years, which at 1% speed of light would take 500 years to get there. Assuming 25 years per generation, that represents a travel time of 20 human generations. That's like a family from the 1500's committing for their children and 19 following generations to live on a shitty rocket. They'd have just arrived. I wonder what 500 years of food, water, and oxygen looks like for a civilization-founding crew. What's the backup plan if the target planet isn't livable? Cyanide tablets?
- pfdietz 3y ago
  Colonization wouldn't be aimed at planets, it would be aimed at structures in space. You know, like we're assuming this star-spanning civilization has been building in astronomical numbers? Food and air would be manufactured during the trip. All that's needed is a source of energy. At 1% c, that probably means a nuclear source (or beamed power), but at higher speeds they could simply exploit the energy being deposited by interstellar matter. At 1 proton/cm^3 and .1 c, the power is 22 W/m^2.
  - HarHarVeryFunny 3y ago
    If we're talking inter-stellar travel then it doesn't seem to matter what the destination is (planet or space habitat). The travel time remains the same, and the only source of materials (incl. food etc) would be what you bring with you until you arrive at a planet (i.e. at nearest star that has a planet that has useful resources). Even if this were a robotic terraforming mission, it's hard to see humans committing to the expense of such an endeavor with no payoff for generations to come. Heck, we're reluctant to act to save the planet our lives depend on right now.
    - pfdietz 3y ago
      If we're talking about a species that has exploited the resources of its star system, and done so at a scale that includes noticeably blocking the light from its star, then said economy has billions of times the energy we're currently consuming. Proportionally, the cost of an interstellar spacecraft would be less than one week of your salary.