[Ultra-Tech] Conservative hard SF... but not implausibly conservative

[Michael Thayne]

Originally Posted by sir_pudding

In this case, I think "a set of cultural institutions that are distinct and haven't suffered a major collapse or technological discontinuity" fits the requirement. Even if you count the PRC as the same civilization as started agriculture in Chengtoushan, it is still a 100th of the age of your proposed civilization. This is a stretch, though, the PRC today is the result of nine thousand years of emigration, unrest, war, and foreign conquest. No institutions survive from 9000 years ago, and three relativity recent discontinuities: the Mongol conquest, the Manchurian conquest, and the Communist Revolution had profound, transformative, effects on the cultures of the region.

You are proposing a civilization that is able to maintain the technological and economic infrastructure necessary for a Type II civilization with a Class B stellar engine for nearly five times as long as anatomically modern humans even existed.

What is "proven to exist" are a few rare institutions that have continuously operated for about 1500 years. Claims can be made for slightly older, but can't be substantied, and many (the Japanese Emporer, the lineage of Elizabeth Windsor) are clearly political fiction.

Okay—I'm not really interested in how long institutions survive, as long as technological advances continue to accumulate. You wouldn't claim that the problems you cite are a barrier to moving up the Kardashev scale, correct?

[Anthony]

Originally Posted by sir_pudding

There are fairly complex organisms with significant longevity, so even if senescence can't be completely eliminated in multicellular organisms, it almost certainly can be delayed quite a bit.

A problem for sapient beings is that brains have limited storage capacity; our learning rates vary significantly with age (the older you are, the slower you learn) and also involve a lot of forgetting. Basically any means for storing immortal memory in a finite brain involves some combination of extremely limited ability to form new memories and extremely aggressive purging of old memories.

[Michael Thayne]

The more I think about it, the less sure I am what a conservative design for a von Neumann probe looks like. If the interstellar impact rules in Spaceships 5 are a reasonable approximation of reality, then going faster significantly cuts into your range. The difficulty (impossibility?) of shielding space sails against impact hazards is also a major issue.

[sir_pudding]

Originally Posted by Michael Thayne

Okay—I'm not really interested in how long institutions survive, as long as technological advances continue to accumulate. You wouldn't claim that the problems you cite are a barrier to moving up the Kardashev scale, correct?

Depends on the discontinuity, extinction certainly does.

At any rate, if this isn't a continuous civilization, the "million years" is meaningless. There is a difference between a civilization that is living in the same habitats they built a million years ago (at least the same in the axe paradox sense) and one that has recently rebuilt habitats after recovering from a global nuclear war and dieback to minimal population a million years ago.

Originally Posted by Anthony

A problem for sapient beings is that brains have limited storage capacity; our learning rates vary significantly with age (the older you are, the slower you learn) and also involve a lot of forgetting. Basically any means for storing immortal memory in a finite brain involves some combination of extremely limited ability to form new memories and extremely aggressive purging of old memories.

Yes, and there is a question about whether a five hundred year old person is still the same person (its not the same river and he's not the same man) but I think people would still recognize a continuity of existence. Regardless, it isn't biologically insurmountable.

[David Johnston2]

Originally Posted by Michael Thayne

What do you mean by "civilization"? How old is Chinese civilization, by your reckoning?

I suspect we Westerners tend to over-extrapolate from the case of Rome. Rome's problem was heavy dependence on grain from Egypt, leaving it vulnerable to catastrophic collapse. That sort of collapse is actually fairly rare AFAICT.

Not especially. Every civilized culture experiences it. Including China.

https://www.thoughtco.com/why-did-ha...ollapse-195115

Of course civilization collapses rarely destroy more than a few peripheral technologies. The successors rebuild and continue onward, at least preserving if not advancing on the technologies of the former culture. But if if they lasted for a million years with the same civilization and with technological advancement having ground to a halt, then my guess is they went to some trouble to genetically engineer the capacity for original thought and rebelliousness out of themselves.

[Ulzgoroth]

Originally Posted by Michael Thayne

The more I think about it, the less sure I am what a conservative design for a von Neumann probe looks like. If the interstellar impact rules in Spaceships 5 are a reasonable approximation of reality, then going faster significantly cuts into your range. The difficulty (impossibility?) of shielding space sails against impact hazards is also a major issue.

Shielding space sails shouldn't usually be a problem - they're diffuse by nature so punching holes in them doesn't actually compromise them in any significant way until it adds up quite a lot.

Laser-driven light sails are really simple conceptually - just point a laser array to put extra push on your lightsail, especially at much greater distances from the star than natural light would allow (even if said natural light isn't blocked by a dyson swarm...)

Ideally, you also can have a huge collector in-system to catch and recover some of the light reflected back off the sail, but that's cannonball polishing.

[AlexanderHowl]

I doubt that we will reach a Class II civilization ever. That is 3.8e26 W, which is around 2e14 times as much energy as we consume right now (by comparison, we have only increased our per capita energy consumption by x115 over the past two million years). If we assume that the per capita energy consumption will only increase by a similar factor over the next two million years, the population of humanity would need to increase by 1.7e12 in the Sol System to reach a Class II civilization within two million years.

One possible reason why advanced civilizations may not leave their home systems would be due to virtual reality. A TL11 civilization could support a virtual world with a complete cast of realistic characters for every inhabitant for as much expense as it would be to send a small colony to another star system via STL travel. If they have biological immortality and advanced non-volitional AI, they would probably prefer their virtual worlds within a connected virtual galaxy over the boredom and risk associated with STL travel to another star system. With biological immortality, there is also little need for reproduction beyond replacement through cloning, so the alien civilizations would probably cap out at 1 trillion people when their virtual worlds become a reality.

[Anthony]

Originally Posted by Ulzgoroth

Shielding space sails shouldn't usually be a problem - they're diffuse by nature so punching holes in them doesn't actually compromise them in any significant way until it adds up quite a lot.

The interstellar impacts issue is mostly about very fine dust that erodes the surface, not larger impacts that punch holes. Sails won't survive that very well. On the other hand, there's no a lot of reason to have sails open after the launch phase, they're kinda useless in deep space and unless there's a laser array at the destination, also useless for stopping, so you'd either fold or discard them.

[Michael Thayne]

Originally Posted by David Johnston2

Not especially. Every civilized culture experiences it. Including China.

https://www.thoughtco.com/why-did-ha...ollapse-195115

Of course civilization collapses rarely destroy more than a few peripheral technologies. The successors rebuild and continue onward, at least preserving if not advancing on the technologies of the former culture. But if if they lasted for a million years with the same civilization and with technological advancement having ground to a halt, then my guess is they went to some trouble to genetically engineer the capacity for original thought and rebelliousness out of themselves.

<Reads Wikipedia>

Huh. I didn't realize the end of the Han dynasty coincided with a population collapse. Nevermind then.

Note, though, that I'm assuming technological advance grinds to a halt because we're being pessimistic about what's possible in the future, and eventually possible innovations are exhausted.

[Michael Thayne]

You know, I plucked the 10 million years figure out of a hat, but I just realized at 1% C, you're not actually going to colonize the entire galaxy in that time. Hmmm...