3 ms·

The big bang only produced light elements and heavier elements were produced by nuclear fusion in stars. In particular, carbon and oxygen[1] would not have been

The big bang only produced light elements and heavier elements were produced by nuclear fusion in stars. In particular, carbon and oxygen[1] would not have been abundant until the first generation of very hot, very large stars went supernova. Our own star is a third-generation star[2]; it is only 4-5 billion years old, forming ~10 billion years after the big bang, so our own solar system is fairly rich. Earlier solar systems would have been less rich, and this means life would have been far less likely to arise. Also, 25% of lightspeed is fairly aggressive. Even 1% would require engineering and energy reserves way beyond anything we can realistically hope for, largely due to the tyranny of the relativistic rocket equation[1]. Note that if you want to stop, you have to carry your own fuel, which makes the problem quadratically worse. Proposals like Breakthrough Starshot[3] can hope for 10% largely because they will just do a flyby and don't have to carry fuel for braking at the destination. Similar projects[4] have used much more realistic velocities and discovered in doesn't really matter - it still takes less than 100 million years to completely colonize every star in the galaxy. But this model doesn't solve or address the Fermi Paradox - where is everybody? It actually makes it worse. We might overlook or not be able to see a single populated solar system halfway across the galaxy, but a civilization that has expanded to fill every nook and cranny of the galaxy should be fairly easy to spot, no? Obvious, even. Yet there is no sign - not in our solar system, not in radio signals, not in Dyson spheres, nothing. On the other hand, every time we still down and make reasonable assumptions about how long it would take a species to colonize the galaxy, we usually find that it should have happened hundreds of times over, billions of years ago. So where is everybody? [1]: https://wmap.gsfc.nasa.gov/universe/uni_life.html https://wmap.gsfc.nasa.gov/universe/uni_life.html [2]: https://www.physlink.com/education/askexperts/ae465.cfm https://www.physlink.com/education/askexperts/ae465.cfm [3]: https://en.wikipedia.org/wiki/Breakthrough_Starshot https://en.wikipedia.org/wiki/Breakthrough_Starshot [4]: https://www.extremetech.com/extreme/294051-scientists-simulate-human-colonization-of-the-milky-way https://www.extremetech.com/extreme/294051-scientists-simula...

m4rtink 6y ago
If the slightly insane Nuclear Salt Water rocket can be pertectec then couple percent light speed might be doable even without complex exotic tech: https://en.m.wikipedia.org/wiki/Nuclear_salt-water_rocket https://en.m.wikipedia.org/wiki/Nuclear_salt-water_rocket
- ngvrnd 6y ago
  "slightly"???
khafra 6y ago
Regarding your final paragraph, the Grabby Aliens model implies that we are within the Anthropic Shadow[1] of the event. E.g., the humanity that lives in the possible universe where the galaxy has already been eaten does not exist. [1] https://www.stat.berkeley.edu/~aldous/157/Papers/cirkovic.pdf https://www.stat.berkeley.edu/~aldous/157/Papers/cirkovic.pd...
sliken 6y ago
You are right, but very large stars have very short lifetimes, on the order of 10M years. So there would be areas of high concentrations of things further up the periodic table even in the first billion years. Keep in mind that while earth is rich in things like iron and other elements higher up the periodic table, that's far from the average for the solar system. I think the colonization problem is mainly a human perspective, we can't get their in our lifetimes so it's impossible. So it seems realistic to send a small probe to Proxima Centauri at 5-10% of the speed of light to get sensors much closer. We'd learn quite a bit getting even today's sensors 1M times closer as it zips by. Communication might be tricky, but say a 100 watt laser can beam to a decent portable telescope on a precise frequency even 0.01 light years apart. Just sent a new relay probe every year or so. So in 50-100 years we'd know much more about the planetary system. Number of planets, size, orbits, chemical composition, asteroid belts, even some idea of weather, clouds, magnetic fields, and some idea of the likelihood of life, and the potential for hosting life. Google earth would get it's first planet outside the solar system ;-). With that knowledge, and presumable some technology improvements we could send a large probe, even if it's slower say 0.5% of speed of light. While propulsion technology will likely improve (things like light sails, fission, fusion, antimatter, etc) maybe there's other ways to slow down, gas clouds, magnetic fields, chained gravitational assists, magnetic ram scoops, etc. Maybe it could allow for a few 100 kg in orbit around the most promising planet. Potentially autonomous manufacturing could turn some asteroids into mirrors, we could be used to help brake future probes. Said few 100 kg would also include improved sensors to tell us much more about the planets, increase our understanding of the presence of life, and the potential. Some 100s of years into the future it seems likely that bio-engineered bacteria, fungus, molds, and similar could be used to seed life, make the atmosphere friendlier, and extract useful minerals/fuels. Future deliveries would leverage braking/fuel/materials at the far side to get more mass there more easily. Instead of building mirrors (relatively easy) they start building solar cells. Mining kicks increases in scale, etc. Extracting methane, oxygen, and aluminum would be a good start. Bootstrapping the ecosystem (assuming there isn't one) starts with bacteria, mold, fungus, and similar on land and in the oceans. At some point the mirrors, communications, and energy available starts being an appreciable fraction of earth and non-trivial size ships can get up to 5-10% of light on this end, and decelerate down to zero on the far side and sending humans (or at least human DNA) starts becoming feasible. Say 1000 years from now, intelligence (human, semi-human, or artifical) on the far end starts communicating with earth at the speed of light. Does make one wonder what bandwidth you can get over 5 light years with say a small moon of mass to capture and redirect energy.

m4rtink 6y ago

If the slightly insane Nuclear Salt Water rocket can be pertectec then couple percent light speed might be doable even without complex exotic tech: https://en.m.wikipedia.org/wiki/Nuclear_salt-water_rocket https://en.m.wikipedia.org/wiki/Nuclear_salt-water_rocket

ngvrnd 6y ago
"slightly"???

khafra 6y ago

Regarding your final paragraph, the Grabby Aliens model implies that we are within the Anthropic Shadow[1] of the event. E.g., the humanity that lives in the possible universe where the galaxy has already been eaten does not exist. [1] https://www.stat.berkeley.edu/~aldous/157/Papers/cirkovic.pdf https://www.stat.berkeley.edu/~aldous/157/Papers/cirkovic.pd...

sliken 6y ago

You are right, but very large stars have very short lifetimes, on the order of 10M years. So there would be areas of high concentrations of things further up the periodic table even in the first billion years. Keep in mind that while earth is rich in things like iron and other elements higher up the periodic table, that's far from the average for the solar system. I think the colonization problem is mainly a human perspective, we can't get their in our lifetimes so it's impossible. So it seems realistic to send a small probe to Proxima Centauri at 5-10% of the speed of light to get sensors much closer. We'd learn quite a bit getting even today's sensors 1M times closer as it zips by. Communication might be tricky, but say a 100 watt laser can beam to a decent portable telescope on a precise frequency even 0.01 light years apart. Just sent a new relay probe every year or so. So in 50-100 years we'd know much more about the planetary system. Number of planets, size, orbits, chemical composition, asteroid belts, even some idea of weather, clouds, magnetic fields, and some idea of the likelihood of life, and the potential for hosting life. Google earth would get it's first planet outside the solar system ;-). With that knowledge, and presumable some technology improvements we could send a large probe, even if it's slower say 0.5% of speed of light. While propulsion technology will likely improve (things like light sails, fission, fusion, antimatter, etc) maybe there's other ways to slow down, gas clouds, magnetic fields, chained gravitational assists, magnetic ram scoops, etc. Maybe it could allow for a few 100 kg in orbit around the most promising planet. Potentially autonomous manufacturing could turn some asteroids into mirrors, we could be used to help brake future probes. Said few 100 kg would also include improved sensors to tell us much more about the planets, increase our understanding of the presence of life, and the potential. Some 100s of years into the future it seems likely that bio-engineered bacteria, fungus, molds, and similar could be used to seed life, make the atmosphere friendlier, and extract useful minerals/fuels. Future deliveries would leverage braking/fuel/materials at the far side to get more mass there more easily. Instead of building mirrors (relatively easy) they start building solar cells. Mining kicks increases in scale, etc. Extracting methane, oxygen, and aluminum would be a good start. Bootstrapping the ecosystem (assuming there isn't one) starts with bacteria, mold, fungus, and similar on land and in the oceans. At some point the mirrors, communications, and energy available starts being an appreciable fraction of earth and non-trivial size ships can get up to 5-10% of light on this end, and decelerate down to zero on the far side and sending humans (or at least human DNA) starts becoming feasible. Say 1000 years from now, intelligence (human, semi-human, or artifical) on the far end starts communicating with earth at the speed of light. Does make one wonder what bandwidth you can get over 5 light years with say a small moon of mass to capture and redirect energy.