Assume there's a colonized or partially colonized galaxy. What are the features and requirements that can provide chance for various technological levels (from industrial age up to utopistic future) to coexist? How these various levels can appear instead of a constant and unified tech level?
closed as too broad by Pavel Janicek, James♦, mjr, Hohmannfan, Aify Mar 7 '16 at 17:24
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A galaxy is a pretty big place. (citation needed)
Even supposing widespread colonization, Without cheap, efficient FTL travel, every inhabited planet is going to be very isolated - we're talking generations of time just to visit another world. If relativistic travel exists, individuals can make it to other planets, but at the cost of leaving everyone they knew behind, knowing they will probably not see them again until they are old or dead. In that kind of galaxy, it would be harder to justify a unified tech level than a varied one - chances are good each planet's culture and civilization would develop more or less independently.
If there is cheap, efficient FTL travel, you could justify it by saying that different civilizations are distrustful of each other, possibly due to vast separation. It is likely that some planets may develop technologies that others could not because of their different resources or circumstances, and they may be less than interested in sharing technologies for fear of that technology being used against them.
Generational ships and non-interference laws for colonies
At the start of the space colonization age, the people decide they like freedom and also don't want to compete for resources. They pass a law stating that each generational ship can claim a destination solar system or cluster and no other ship is allowed to enter that system unbidden.
Over hundreds of years technology at the origin planet(s) advances much faster than inside the generational ships. Every few years, faster ships are launched, containing more advanced tech. They have to travel farther, but will arrive roughly at the same time due to increased speed. This provides a tech gradient where the closer colonies are actually lower-tech and the farther colonies higher tech.
To add more mixing, let's assume ships are only launched at destination considered viable (not too much of a stretch). Advancing astronomy tech at the origin will discover that some closer systems previously skipped because they were deemed nonviable may have become viable with the new tech level. Those colonies will actually be established the earliest, starting at a higher tech level and allowing more development compared to neighbors who launched earlier but will arrive later.
Finally, Murphy's Law applies to space colonization, so not all destinations will actually be viable and not all ships will arrive unscathed. Conditions might be only barely survivable or a large part of the resources needed for colonization may be missing.
- The Nth generation on a ship may go luddite or hippie and stop teaching their children the vital skills passed down for generations because "Big Brother" (the ships's AI) runs everything anyway and can teach generation N+20 in time for arrival... or so they think.
- An unlucky ship might be hit by a radiation burst, losing their database or the seeds in their DNA banks. All that survived are... enhanced soy beans.
- The colonized planet isn't quite as viable as thought with anything from poison atmosphere to predatory acid-for-blood natives. The colonists may survive but not until they've lost a good part of their people, leaving them in barely-getting by limbo.
These scenarios will result in your lowest tech-level colonies, at any location you choose.
Invention of FTL
This is when all your colonies may get into contact, assuming they want to. There may also be another rush to claim solar systems now that it's feasible to fly there, check it out and go for the next one if it's not viable. The technology level of these ships and their colonies will be much, much higher than those of ships launched thousands of years ago, leading to your utopian future tech colonies... hopefully.
If you want to apply a Human/Earth touch, the multi-award winning book Guns Germs and Steel by Jared Diamond cuts to the root of why earthly civilizations have risen and fallen or failed to rise at all. It has much to do with Tech and the variables needed to evolve tech. The rules for expansion are more insightful than one could imagine (with out a degree in that line of conversation). Seed/Animal packages, exposure to endemic germs, human need for sustenance all play a part in how much energy humans put in to tech innovations. The Native tribes of America had plenty of food that could be obtained with primitive weapons and little real competition and zero exposure to European germs. If they were a "planet" and we added 2000 years with out outside contact, their tech may still be considerably lower than high competition planets.
The factors promoting different rates (and limits) of technical progress in different civilizations of a galaxy are:
1- Different Levels Of Intellect
Different planets would undergo different courses of evolution, resulting in sentient species who/which would be vastly different in intellect and understanding of the world around them.
2- Different Sensory Potentials
This is related to point 1, but is not the same. Consider a species who has eyesight matching that of an eagle (20 times higher resolution than human eye). Their understanding of cosmological phenomena would be far more detailed and accurate than another species with equal IQ, but human (or lower) eyesight.
3- Collaboration And Social Bonds
Things such as complex language, writing, trade, complex society etc appear to be a direct result of higher IQ, but things are not so simple. What if we (humans) had slightly higher IQ but did not have a tongue and larynx system capable of complex sounds like we have now? Civilizations with stronger social bonds tend to progress technically much faster than those with equal level of intellect but lesser degree of social behavior (humans versus neanderthals, remember?)
4- Planetary Composition
Chemical composition of planets varies greatly. No two planets have more than 60% matching chemical composition even in our own solar system! Consider how vast the difference would be at the extent of a galaxy! If a planet does not contain iron, copper or titanium in its crust in vast quantities, how would it affect the pace of technological progress? How about a planet where the intelligent beings do not get any type of fossil fuel. Would they still be able to bring about an industrial revolution as we had on Earth?
5- Interests And Preferences
We, humans have progressed so far due to a combination of ecological challenges. We progressed so vastly in medical sciences because we have encountered diseases which were troublesome, horrific and lethal. We invented bows, arrows, knives and axes because we were physically weaker than both the predators (sabretooths, lions, tigers, wolves) and mega prey (wildebeests, cape buffaloes, deer, gazelles) in our ecosystem. Would we have made the same technological progress if we were the apex predators in our ecosystems? What if we had no pathogens and acquiring a bow and an arrow meant you had a perpetual supply of game meat to eat and hide to cover ourselves with? Would we still continue to invest our time and effort in alchemy and physics?
There are a lot of factors affecting the technological progress and limit of an intelligent civilization. At the extent of a galaxy, you are likely to encounter civilizations stuck at, and progressing at ALL the stages of biological and technological evolution we have passed through so far. And with better senses, longer lifespans and higher intellect levels, some civilizations might be hundreds of thousands of years in advance than us.
Cultural difference in priorities would be sufficient to explain technological diversity
Each human culture places emphasis on different attributes and will advance their local technology to meet that end, while ignoring other technological venues.
Consider the Japanese. They have a strong aversion to importing lower wage workers but still need to perform those tasks, so the Japanese have gone all-in on robots. Robots of every shape, size, color, or task-fitness can be found in Japan.
Consider the Egyptians. They had a strong cultural emphasis on preserving the dead, particularly, the rich dead. Their priests and embalmers develop highly sophisticated techniques for preserving the dead. To my knowledge, no other culture has pushed preservation as far as they did or over as long a time as they did.
Humans are tool makers. Any other species that makes it into space will also be toolmakers. Tools are always adapted to the needs of the moment. No planet will be exactly the same, nor will the cultures on those planets be the same. The tools will always adapt to the needs of the user.