r/IsaacArthur

https://preview.redd.it/7da2xy82vdwg1.png?width=1532&format=png&auto=webp&s=620b9a3f634f9ad8830d2a21e26eac3eb7c4fbe2

How could an advanced civilization forcibly oxygenate gigaliters of water per day? Assume we're stuck with fission reactors but we're making hundreds per day off of factory assembly lines. The fuel is U233 mass produced from an on-shore Thorium enrichment industry.

Equatorial waters are the warmest at the surface where exposed to air, so I think that is why you get large equatorial dead zones, and the coastal ones in the Gulf of America. One idea might be to have large floating hoops containing hundreds of thousands of floating aluminumized shadeballs each. This would shade the water below and thus cool it down, but also they could have spongey cores that soak up seawater and evaporate it for evaporative cooling on solar thermal energy and ocean breezes alone, conducting this cooling to the other aluminum shadeballs and increasing surface area in these slightly cooler waters. This would have the added side benefit of increasing rainfall, which could help with landside water shortages as well as contribute to further evaporative cooling climate-wide. This would require an absolutely mind boggling amount of shadeballs to be produced and released, and their lifespans would have to be extremely long.

Another idea is to simply pump air down to the thermocline's naturally cooler waters and force it through aeration nozzles to bubble up to the surface. An alternative design might be to condense oxygen into cryogenically cold LOX and naturally drain down to the thermocline into cisterns, and then release pressurized squirts of it into the ocean directly to rapidly boil off, cooling the water and simultaneously forming millions of bubbles of pure oxygen to be absorbed by the water. This would probably be less disruptive to marine life which are highly responsive to bubbles in the water. So a big wall of bubbles from the former option is probably not the best approach.

Any other ideas?

Last week I posted about Mercury as a potential energy hub in r/energy. The response pushed me to dig deeper — and the deeper I went, the more genuinely uncertain I became.

JAXA has been researching Space-Based Solar Power for 40+ years. ESA launched their SOLARIS program more recently. Institutional patience at that scale deserves attention — but longevity alone doesn't validate an idea. So I ran the numbers myself.

Using the IPCC SRES A1 scenario, global electricity demand in 2100 reaches approximately 898 EJ/year — roughly 250,000 TWh/year, or 28.5 TW of continuous power.

Using De Castro et al. (2013), which measured real-world utility solar at 3.3 W/m², meeting that demand entirely with ground PV would require approximately 8.6 million km² —roughly comparable to the combined area of India, Mexico, Argentina and Egypt.

Then I ran the same calculation using LBNL 2022 data, which shows modern US utility solar achieving 12.6 W/m². The land requirement dropped to approximately 2.3 million km² — roughly two Mexicos. Still enormous by any measure.

But here's what stopped me: that 78% reduction happened in just nine years of technological progress.

We have 74 more years until 2100. If solar density improved fourfold in under a decade, what becomes possible across seven more decades of human ingenuity? Physics has ceilings — but we don't yet know where that ceiling is for solar.

This is genuinely where my thinking broke down. I came in favoring space-based solar. The numbers complicated that.

Is SSPS a rational next layer for a civilization scaling toward unprecedented energy demand — or an expensive solution to a problem Earth will quietly solve on its own?

I'm curious what you think. Not looking for a verdict — just honest perspectives from people who've thought about this longer than I have.

Slower-than-light travel is the only kind of interstellar travel that is feasible using foreseeable terrestrial technology. Slower-than-light interstellar travel at speeds that could be accomplished using foreseeable technology imply travel times that exceed a human lifetime. As a result, interstellar travel using foreseeable technology necessarily implies multiple human lifetimes, namely, generation ships.

A generation ship is an artificial human habitat specialized for interstellar travel. Artificial habitats are likely to be developed to provide places to live within the solar system in order to accommodate a human population that might theoretically reach 100 billion people. (Imagine mass production of kilometer-scale habitats at Uranus and Neptune with plastic hulls made using atmospheric hydrocarbons, a kind of Levittown in space.) Therefore, it seems likely that interstellar generation ship designs will be artificial habitat designs adapted to the environment of interstellar travel (perhaps using an “interstellar railroad” network of lasers placed between star systems to accelerate and decelerate ships using light sails, because light sails are the only foreseeable means of reactionless propulsion and the rocket equation tells us that reaction-mass propulsion is unavailable for interstellar travel).

On a separate but related note, in my opinion, common sense tells us that pervasive artificial intelligence would be integral to such artificial habitats and generation ships. In fact, the habitats and ships may ultimately resemble a kind of symbiosis between humans and artificial intelligences. One corollary of that symbiosis would be that putting people into suspended animation for interstellar travel (arguably not a foreseeable technology) wouldn't work in practice. The smooth functioning of a generation ship would be an ongoing collaboration between the humans on the ship and the artificial intelligences that comprise the ships’ systems. If the humans are in hibernation while the artificial intelligences are actively operating the ship for, say, a century of interstellar travel to Alpha Centauri (even if a top speed of 0.10c could be reached, acceleration and deceleration imply an average speed of 0.05c or less), then there would be only a limited basis for the necessary symbiosis upon arrival. Artificial habitats and generation ships would, in effect, be living things.

Sorry for posting something right after another.

But I think people take the human element out of it. I am not certain if most people would be willing to live in a rotating tin can in space. Even if it is theoretically more safe, most people would still prefer planets. Similar to how people feel safer in cars than in planes despite statistics saying otherwise.

I have heard that only some configurations cause CTCs (time travel). It’s fine for normal use and it’s possible those configurations might not even work.

Hi everyone, I’m a huge fan of SFIA and Isaac’s deep dives into megastructures and future history. Inspired by these concepts, I’ve been building a project called Libernova a simulation designed to model the economic logic of a Type-II civilization.

Instead of 'magic money,' I’m coding trade algorithms based on actual thermodynamic costs (Joules as currency) and accounting for information lag due to light speed. I want to see how a galactic market functions when decentralized nodes are separated by light-years.

I’d love to hear your thoughts: In a world of Dyson Spheres and automated labor, what would be the primary driver of 'value'? Let's discuss the physics of finance

This links to my Wordpress blog which in turn links to my Skyhook Equator web-page script program which animates selected sizes of skyhooks launching from equatorial skies to Earth orbits and which calculates launch G-forces etc.

https://preview.redd.it/tfrob36370wg1.jpg?width=3840&format=pjpg&auto=webp&s=6bf892e584bd51391423ea7c8ec31e100601b70d

Skyhook Equator demonstration video

Related - my spreadsheet of calculations for lunar skyhooks which suggests that a skyhook radius of 250km to 300km would be right for landing on and taking off from the Moon with only 1G so the skyhook could also serve as a 1G lunar space station.

If the 1887 Michelson-Morley Experiment was a success and the Luminiferous ether was verified to be real. What would humanity's technological and scientific progress between then ( 1887 ) and let's say... 2016 look like?

I'm not just interested in knowing what kind of technology we would invent but when it would come about.

Obviously I'm not talking about soft sci fi, because I'm not too concerned about how humanity conquered the galaxy in 500 years when the in universe FTL method is space surfer jesus literalry surfing on spacetime itself to create ripples in the galaxy that allow for the laws of physics to be bent (actual sci fi but I cannot remember the name of it).

This is about hard sci fi settings, and how sci fi universes don't seem to understand how human progress works, with humans thousands of years from now somehow only slightly more advanced than us, or humans in the next 200 years becoming unrecognisable technological gods able to traverse all of space and time.

Sure some Sci fi is always gonna be weird, but even many more grounded or realistic settings still don't understand how timespans work.

Modern humanity is progressing faster than ever, and more has been accomplished in the last 450 years of history than the previous 12,000 years of civilisation.

Setting where 1,000 years of human progress still see humanity as just modern humanity with slightly more sci fi is weird as at modern rates of progress and exponetial growth, in 400 years we will become a type 1 civilisation, and by the year 4,000, the world energy demand could be as much as 10,000,000,000 TWH, which would see a humanity so advanced that the construction of megaprojects isn't unbelievable.

Sci fi settings either seem of overestimate or underestimate/ underutilize the time that has passed from modern day and ignore what can be achieved by a humanity with centuries of technological progress.

I don't have a strong opinion as at the end of the day it's sci fi and it's fiction, but I still wish as someone who loves looking at human movement and settlement pre recorded history, that people would appreciate the impact of scales of time, whether incredibly long or short, and implement that into sci fi, as I find that super cool.

There's a joke that practical fusion is at least 30 years away — and it always will be. Meanwhile, fission exists, though it's less efficient. And even if fusion is commercialized, there are likely to be applications where fission is a better option (just as we still use coal for some things, even though other fuels are now available). The solar system is surprisingly low in fissionable materials (including among the asteroids), with the Earth and Moon being the only known sources of significance. By contrast, the Alpha Centauri system is higher in metals and is predicted to be higher in fissionable metals. If that is confirmed by exploratory probes, then fissionable materials could be exported from the Alpha Centauri system to the Sol system.

I know currently due to limitations, nuclear reactors can only be put in larger vehicles. But theorically, with future technologies, how small can a nuclear powered machine be? Be it to travel on land, air, sea, and space.

For example, can it made to be the size of a car like the Ford Nucleon concept? Would it have practically unlimited endurance?

I didn't come up with the idea of interstellar highways comprised of laser stations to push laser-sail-equipped vessels between star systems, but it seems to me that a network of laser-driven light sails through interstellar space would be the best way to get around the limitations of the rocket equation. The lasers would probably have to be fusion-powered lasers similar to rocket dynamic lasers. The first step would be to build the network by using a solar system-based laser to push another laser platform to a predetermined location in interstellar space and then push a third laser platform further out, and so forth until the destination star system is reached. After the network was in place, ships could use it to move through interstellar space, paying a fee. Fuel and other supplies needed by the laser platforms (nodes) could be shipped using light sails, and the platform infrastructure could serve as waystations to resupply ships moving along the network.

The virtue of such a network would be that it wouldn't require reaction-mass space drives and therefore wouldn't be limited by the rocket equation. It would be more analogous to a railroad than to ocean-going vessels, because it would facilitate movement only along the network infrastructure. Such a project might seek out ice giants among the exoplanets, which are among the most common type of exoplanet, because they have valuable resources. Such infrastructure would not be cost effective to build to enable a single vessel to move through interstellar space, but it may be cost-effective to build to enable thousands of vessels to move through interstellar space. If rogue planets with valuable resources are identified, they could be sites for laser stations. At some point, maybe the Lagrange point between the Sun and the galactic center (about 4 light years towarda the galactic center from the Sun) could also a site for a laser station on the network. Vessels and laser stations could be mass produced, and new manufacturing sites for vessels and laser stations could be established in destination star systems using local resources.

Unfortunately, one essential thing which is currently lacking is the economic justification for traveling between the stars. That's likely to change before the technical capability exists to build an interstellar railroad, but it's essential because something on such a large scale can't work unless it generates a profit.