One thing that a few science fiction films seem to get wrong: it is extremely unlikely for two civilizations to evolve completely independently and yet be within a few hundred years of each other technologically when they make contact. They are more likely to be millions or billions of years apart.

Could this be made more likely by some large-scale catastrophe that affects both star systems, causing mass extinctions in both at the same time, or by some other means?

I was thinking of two stars, say 5 to 20 light years apart. Planetary life emerged in both at roughly the same time in terms of billions of years - still not very likely but possible. Then both stars drift through the same cloud of interstellar debris, or pass close to the same massive object or other star (maybe each other?) - this causes a mass extinction in both star systems (still no civilization). At that time, maybe the lifeforms at star A were more advanced biologically by millions of years than at star B, but the mass extinction brings both down to the same level. Could events like that, or something else, synchronize the development of civilizations at different stars so that they are at a similar technological level (within about 300 years)?

More specifically, could one of those planets be Earth?

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    $\begingroup$ are you assuming biological or technological advancement in both civilizations goes at the same pace? Because that is very unlikely too $\endgroup$
    – guido
    Commented Oct 16, 2014 at 13:54
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    $\begingroup$ 300 years is a pretty huge gap. We went from not-flying-at-all to landed-on-the-moon in like 70 years. $\endgroup$
    – corsiKa
    Commented Oct 16, 2014 at 22:40
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    $\begingroup$ Is this a serious question, or are you looking for a justification for an idea of yours? The concept is written about often for the same reason numerous genres repeat ideas. Common situations are boring, so few authors write about them. The unusual or uncommon situations are written about more often. Otherwise stories would be about everyday stuff, and who would want to read them? It might happen rarely and be written about constantly. $\endgroup$ Commented Oct 17, 2014 at 8:00
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    $\begingroup$ @professorfish: I don't think you can realistically assert that the aliens from either film were "100-300 years ahead of us". The culture and physiology of both were clearly entirely different from ours. In the former case, does the possibility that the aliens would have had to sit tight in their spaceship for potentially hundreds or thousands of years to get here help? $\endgroup$ Commented Oct 17, 2014 at 11:03
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    $\begingroup$ If your story relies on them being at similar tech levels, but it's not particularly important why, this might be a good place for lampshading. You can peripherally mention all the reasons it's so implausible and say it's been keeping biologists and psychologists and philosophers flummoxed ever since the civilizations met. It still does a lot to flesh out your world even if (as in real life) you don't have all the answers. $\endgroup$
    – octern
    Commented Oct 18, 2014 at 19:48

14 Answers 14


Evolution is an essentially random, undirected process, so even if you synchronize things with a planet-wide extinction, it seems extremely unlikely that both planets would evolve intelligent life at the same time after that (or that both planets would evolve intelligent life at all since evolution doesn't have goals).

So, instead of trying to mess with the starting conditions, what if we change the ending conditions: What if there's an incredibly difficult piece of science or technology that you need to advance significantly beyond where we are now?

So, one species evolves on one planet, reaches approximately our current tech level and then stagnates for a few tens (or hundreds) of millions of years. Then another species evolves on a nearby planet. Maybe the ability to contact the nearby planet leads to a massive breakthrough for both species, leading to interstellar travel and a giant leap in understanding of physics.

This also sets you up with nicely contrasting cultures:

The older species has had hundreds of millions of years to perfect their technology, so everything we can do, they can do much better.. but they probably hit the pinnacle of technology a long time ago and haven't needed scientists for millions of years. The younger species is still behind the older one technologically, but has a strong culture of science, engineering, and novelty and will likely catch up quickly, and perhaps come up with less predictable tactics.

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    $\begingroup$ That end scenario is explored in a great book series called WorldWar by Harry Turtledove. Aliens invade Earth in 1941 (during World War 2), but while they are super-advanced relative to the humans, they only improve their technology on a scale of thousands of years. (They actually sent a probe to Earth in the Middle Ages, expecting us not to have advanced much in 1000 years). Meanwhile the various human nations are more primitive, but they're advancing fast in competition with the aliens and each other. $\endgroup$
    – Nerrolken
    Commented Oct 16, 2014 at 22:25
  • $\begingroup$ I like this idea. Instead of relying on assumptions about life or intelligence, it relies on an (as yet unfalsifiable) postulate about how any intelligence would run up against the underlying nature of reality. Lateral! $\endgroup$
    – octern
    Commented Oct 17, 2014 at 2:29
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    $\begingroup$ Evolution is neither random nor undirected. It is non-deterministic in the computational sense. The next step of evolution is limited by both basic chemistry and the already happened evolution. And which paths of evolution stick and which become extinct depends both on external circumstances and other paths of evolution. Sorry to nitpick (isn't important to your answer), but there are two reasons this is important enough to correct. 1. Perception of evolution as random is the most common reason it is rejected. 2. If NP=P then the path of evolution could feasibly be directed or predicted. $\endgroup$ Commented Jan 13, 2015 at 19:13
  • $\begingroup$ This has been done more or less with Turtledove's Worl War series $\endgroup$
    – user4239
    Commented Jan 13, 2015 at 20:32
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    $\begingroup$ @BrendanLong I know, understand, and agree. This issue just annoys me so much I just had to comment anyway... $\endgroup$ Commented Jan 13, 2015 at 22:25

Could events like that, or something else, synchronize the development of civilizations at different stars so that they are at a similar technological level (within about 300 years)?

The well-trod trope of humans being "seeded" on the planet by an advanced civilization is the first thing that comes to mind that would lead to this sort of behavior, though might not be as sufficiently independent as you'd like.


  • The advanced civilization could "meddle" in affairs to speed or slow technological advancement to keep the two close.
  • If the seeding was done ubiquitously, the odds that some pair of civilizations remain at parity is much more likely due to the birthday paradox. According to this link, there are ~17 stars in 20ly that possibly have habitable worlds. If you were in a more populous region of space, or expanded your radius, it would be even more common. (note that this applies to non-seeded life evolving as well).
  • There's also the (somewhat) well-trod trope of a colonization gone wrong. In this scenario the "advanced" civilization doing the seeding is the same as the developing one. Since there are likely ruins (if only a ship) it's a much shorter path from subsistence to inter-planetary discovery.

The odds of two separate planets developing at the rate are essentially zero.

Time is bigger than space. Two sentient species would have to evolve within few hundred thousand years of each other just to be able to recognize the other as sentient.

Multicellular life has been on earth for billion years. If you seeded two identical planets with multicellular life at the exact same time, and it took roughly a billion years for sentients to evolve, the sentient species would have evolve within a 0.001% of the total span of multicellular life for both to be sentient at the same time.

Technology equilibrium is even more impossible. Look at earth's history. At any given time, one area has been far more advanced than others. As technology accelerates, the rate of change in the power of technology accelerates as well.

Two hundred years is nothing in evolutionary terms but compare the power and scope of 2014 technology to 1814. Even more dramatic, compare the difference between the military technology of 1935 to that of 1945. Even excluding the Atomic Bomb, the planes, tanks, ships etc of 1945 would simply annihilate their 1935 counter parts.

In sum, the total time scales are so vast and the time windows for overlap are so small, that the odds that two roughly equivalent civilizations would evolve at the same time in sync, would be virtually zero. In fact, I rather doubt that any two equivalent civilizations could evolve in the same galaxy.

Given the timing issues, I don't think any natural phenomena could reasonably lead to equivalent civilizations. Natural disasters don't have effects lasting longer than a few thousand years which is trivial in evolutionary time scales.

You would need some kind of artificial mechanism, something that synchronized evolution and technological development.

The obvious solution is to have something communicating between the planets, carrying information of some kind back and forth so that changes in life forms and technology on one planet propagate to the next. Perhaps a stargate could connect the two, or perhaps an elder species leaves AIs to guide younger species and they communicate.

I think the likely scenario would be that planet A evolve sentient life first and they go exploring. They find planet B with proto-sentient species and decide to try and uplift. They start the process but some cataclysm overtakes them knocking them back to more primitive level. While they recover, the uplifted sentients of planet B build their civilization, perhaps with some information left behind from planet A's expeditions.

By the time each makes it to star travel and they bump into one another, both have forgotten the other's existence. They appear to have found an equivalent civilization despite all the odds.


I don't believe that human (sentient creatures) progress or its speed is a stable process, so I would find such an occurrence very, very unlikely. Moreover, even by asking your question you assume that their technological level would be comparable. Of course, there are things like Kardashev scale, but it doesn't say very much about the civilization itself (and I get the feeling that it's not exactly the kind of "similar technological level" you had in mind).

However, the whole idea is not lost at all. Should you synchronize them in any way (e.g. 5 light years away should be close enough to manage some form of communication), then such a thing might be possible, or even certain, unless the civilization would decide on keep the balance off at all costs.

To give some examples:

  • Observe how companies catch up with each other with regard to technology, unless the leader is very secretive about it (and even then the gap is not that big).

I hope this helps ;-)

Edit: I'll try to find better examples soon.

  • $\begingroup$ Two additional problems to add to this great response 1) the catastrophe would have to destroy all recorded knowledge otherwise A gets to Bs technology level then keeps going because they have books to work off 2) you would have to explain why race A never moved beyond the affected area. $\endgroup$ Commented Oct 16, 2014 at 16:50
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    $\begingroup$ @dtldarek How exactly did the Great Wall affect the progress of China? The Wiki article makes no mention of economic impact other than a throwaway line or two about taxing trade routes. $\endgroup$
    – TylerH
    Commented Oct 16, 2014 at 20:45
  • $\begingroup$ @ShaneCourtrille, that assumes they will be able to read (and understand) them. I think proffessorfish wants to annihilate them down to bacterias, but if you left them at people level, it would be interesting to leave traces from the past that are completely misinterpreted (such as scientific descriptions treated as poems or religious texts). $\endgroup$
    – Ángel
    Commented Oct 17, 2014 at 9:41
  • $\begingroup$ @TylerH From what I remember, ancient China was quite ahead in civilization progress, but then it isolated itself too much and lost its edge (perhaps the Great Wall was an effect, not a cause, I don't know). $\endgroup$
    – dtldarek
    Commented Oct 17, 2014 at 11:46
  • $\begingroup$ @dtldarek China got too big for the bureaucracy to work well enough (and the very act of joining all the states in one country limited diversity on its own). The adoption of taoism and the "status quo is the best!" attitude probably had a lot to do with China's stagnation. The Great Wall was a building spread out over centuries and arguably it helped a lot in maintaining security, which probably promoted the economy, rather than hindering it. It's not like it prevented contant - you need to man the walls for them to be useful at all, and you build gates in the walls. $\endgroup$
    – Luaan
    Commented Oct 17, 2014 at 12:52

The short answer here is sort of a long one.

For two separately developed species on different planets to exist either near, or billions of light years away at the same time is highly improbable. So improbable in fact that if it did happen, both civilizations would be too far away to communicate with any known technology. So for them to exist at the same time whilst developing independently and reaching the same technological milestones at the same time is near impossible. There are too many variables even if the planets were identical, the organisms would be unique in how previous generations of organisms developed. They may develop in different climates on the planets and adapt their future generations to fit the environment. 4-billion years of that will not produce the same results, ever.

It has been theorized that the time it takes a civilization to develop the technology to create and control radio waves , and the time it takes them to annihilate themselves by nuclear means, is so minute on the galactic time table that millions of advanced civilizations could have come and gone before ours without us ever knowing. Even if by some miracle two civilizations had the same technology at the same time and could communicate through known telecommunication methods, both civilizations would most likely have become extinct before a communication was received due to the extreme time it would take radio waves to get to and back from the other planet.


The short answer is: no.

Even on one small planet such as ours, we can see that some civilizations are thousands of years apart (western civilization vs amazonian tribes for ex.), yet all the "big" events such as dinosaurs' extinction happened on the whole planet and it was only a few millions years ago (65).

There was another clash of civilizations when the European invaders met the Central America people. The former had firearms, horses, vehicles, and the later did not yet invent the wheel.

The only reason why there is a similar civilization level across most of our planet is the communication level.

Until your 2 civilizations can communicate with each other for a long time, there is absolutely no chance they would have any similar (a few hundreds years apart) technological level.

On a biological point of view, the whole human history is a 3-4 million years story. Just an instant for the life history on the planet. We don't know what triggered the evolution of a lineage of primates in Africa at that time, but there is absolutely no chance that the same event or events would happen at the same time on a different planet.

Actually, it is most probable that the first civilization destroys itself, or is destroyed by some external event BEFORE the second civilization arises. If it arises.

More specifically about our neighborhood (< 50 light years away), if any civilization there would exist and would have invented electricity, we would know already...


While it could happen that a large scale catastrophe influences two nearby solar systems (A supernova or planetary nebula are the first things that come to mind), it is unlikely that this would leave anything alive apart from a very advanced space traveling race, or very primitive form of life. The first possibility, obviously doesn't qualify and the second is problematic as well, since there is no telling how long it will take for simple life to develop into complex (and even intelligent) life.

One thing I can think of is an asteroid. It is believed by some that the sun passes wobbles during its orbit around the center of the galaxy and that this movement periodically makes the sun pass through a dust cloud. This causes periodic meteor strikes.

If we assume that these two solar systems move along roughly the same pattern (which doesn't seem like a huge stretch), it's not entirely unlikely that they would experience enormous meteor strikes periodically around the same time. Which would cause an impact winter.

If up until that point, both planets had large creatures as the dominant lifeforms (much like our dinosaurs). It is likely that the rule of these creatures were ended with that impact winter. With these huge creatures gone, there would be the possibility for more intelligent, smaller animals to flourish and start their path to eventually become an actually intelligent species. (After a bunch of branches of course.)

An additional advantage of this scenario is that the frequent meteor strikes make panspermia more likely, a good explanation for why life is found in two solar systems so close together.

This still leaves a massive gap though. It took us 65 million years to get to the point we are since the dinosaurs died and even the smallest variation there would have one planet able to explore the galaxy (or having destroyed themselves) and the other still swinging from trees. Quite frankly, 300 years is nothing.

The only option I see is to have a more advanced race (or a deity, but what's the difference really?) occasionally help both planets out with getting to the next step in their advancement towards space exploration. Here, directed panspermia is worth looking into. The reason why a more advanced being would do this could vary from scientific research to boredom (but what's the different really?).


There is one scenario that hasn't been considered much. It's the scenario where technology does not continue advancing in a quasi exponential fashion, but rather reaches some sort of stasis, where further advance is no longer assimilated by the society. This seems ridiculous to us, living as we do on the cusp of the end of the industrial age and the beginning of the digital age. But it's an imaginable possibility.

Brain Wave, by Poul Anderson, dealt with a slightly different topic. (See Wikipedia article). Here, it wasn't technology but intelligence that stopped evolving past a certain point. Except that earth, due to an anomaly, passes from a zone that inhibits the operation of intelligence into a zone that does not. The result is that earth acquires a level of intelligence that can't be reached by normal evolutionary processes. And suddenly.

If technological advance does reach some kind of stasis point, then it becomes very likely that two civilizations will be at approximately the same level, even if their ages differ by billions of years. I admit that this is far fetched, but hey.


I'm happy to say yes! Not only is it possible, but it is certain to happen infinitely many times.

While I agree with other answers that the probability of such an aggregate of events is vanishingly small, it is a non-zero probability.

There is a compelling argument that says that in an infinite universe subject to ergodicity any configuration with a non-zero probability will not only occur, but will occur infinitely often.

Our current science strongly supports an ergodic view of our own universe.

It has become mainstream to consider our universe to be infinite, either via eternal inflation or via a multiverse interpretation.

Therefore I must conclude that there are infinitely many such neighbouring civilizations. They are probably at each others throats right now!


I agree with the others that it is highly unlikely (virtually impossible) for two cultures to develop to the same technology over any reasonable period of time, because "the same" is not how technology works. Cultures will find what benefit them the most, and it will be hard to compare a culture that just invented fire against a culture that just invented arithmetic but has no fire.

I think the challenge is that your question involved a single event to initiate things, and then both cultures freewheel. If, instead, the event is a long drawn out thing (such as a decrease in radiation levels over hundreds of years), it is more likely that both cultures will run into comparable walls at the same time. As long as the long drawn out thing is WAY more powerful than either culture, it will appear that both are in lockstep with eachother, when the real answer is that both are simply running up against the same wall.


Given the enormous amount of galaxies with billions of stars and the assumption that life will start on most planets that are neither too hot, cold, heavy or light(1).

The unlikely event of two relative neighbouring planets will have nearly the same development stage become not so unlikely due to the huge amount of star systems(2).

That Earth is one of these cases is incredible unlikely as the chance that for a given planet instead of any planet will have such a neighbour is extremely unlikely due to the huge lifespan of the planets.

Could events like that, or something else, synchronize the development of civilizations at different stars so that they are at a similar technological level (within about 300 years)?

More specifically, could one of those planets be Earth?

A super nova in the neighbourhood could reset any advanced technology with a massive EMP. But there is a high risk that it also wipes out all life or all larger lifeforms, in which case the same stage is unlikely again due to the million of years of evolution needed.

Another synchroniser is if two systems are hit by a meteor, the sun moves between the 2 spiral arms in approximately 65 million year cycles, and the risk of disturbing the meteors is higher when other stars are near. Again a high risk to wipe out all higher lifeforms or all life. And its unlikely that two neighbour systems are hit in the same time frame setting them back to approximately the same technological level.

From the list (1) these are the only synchronizers I can think of.

A third possibility of having the same technological level would be if there is a finite maximum level to technology, then a society could develop and hold the same level for a long time while another civilization can arise to the same level much later.
That there is some limit to technology is almost certain, that a long lasting civilization doesn't try to destroy itself every 100-1000 year is more of an uncertainty. And the higher level of technology the more likely they succeed in extinguishing themselves.

1) The chance that life emerges and develops is more limited than that, for an increased chance to reach a high technological level the following will among others help:

  • it has to happen at a 3rd generation Sun, to have the right chemical elements.
  • a relatively stable galactic neighbourhood so that not too many meteors drops nor supernovas explode too often nearby.
  • it must have an atmosphere and it must not be too dense or thin.
  • an ample supply of liquid water but not too much.
  • it must not be too light or heavy
  • it must not be too hot or cold
  • a reasonable low amount of radiation, especially outside water to enable higher lifeforms.
  • an usable form of intelligence must develop
  • survive themselves, no self extinction
  • not be neighbours to an advance race who would either colonise the planet or destroy it.

See also

2) if the chance that life does not develop beyond a certain microscopic level is high, as I believe, then the chance of creating intelligence is increasingly unlikely.

  • $\begingroup$ As more and more planets are discovered, our own system of planets seems more and more of an outlier. This might change as different methods of planet detection are developed that aren't weighted towards detecting large planets in close orbits, but it also may not. Jupiter's position greatly reduces the amount of bombardment that the Earth would otherwise suffer, and having such a large protector may be a significant factor in allowing intelligent life to develop. $\endgroup$ Commented Jan 26, 2023 at 21:01


-There are three aspects to it

Planetary formation

For your question Galaxies have a production rate of stars per year (In the Milky Way 3 to 7 per year, but much greater in the past). Two planets can form from the same stelar cloud in two similar mass stars with the metalicity to produce terrestial planets in stable orbits within similar habitable zones, However this stars are likely to remain toguether for at most a few hundred million years. Now to have two solar systems with similar age and conditions unrelated to each other in close proximity is possible but very unprobable.

So my guess is that the chances of two planets near each other with similar civilizations is not very likely as per the fact of different starting points or resets to evolution due to extinctions. If the planets would be at a few thousand light years away it maybe more likely as per the stages in evolution of stars (you will find more stars of high metalicity). However this stars and planetary systems will be separated in their creation by tens to a billion years and again if habitability is reset in their evolution this makes predicting it not possible. However if enough space the whole galaxy is taken it is possible to find two planets that were created at the same time with similar conditions.

Biological Evolution

A-Biology reset by large cataclisms Evolution even if with similar conditions on inception are the same it is 100% sure that both have had different and at different times large catastrophies so creating a difference in the timing and possibly also in the biologica development paths between the two worlds. Therefore biologically distancing them in terms of evolutionary complexity and possibly even afecting the types of biological entities.

B-Evolution of Brain size The development of large brains as per number of neurons. (brains developed in three or four different stages and the history of it is burried in the structure of our brain. (A nervous system evolving to a primitive reptilian brain and then evolving into a mamalian brain). This last part happen arround 300million years ago. For this to happen all previous dominant species had to be extinct possibly because in this way large populations could develope and by means of adaptation and intermixing a new genera was created better adapted. Mamals have the longest life spands of animals on earth and also the longest expands in terms of maternity and the long periods of defensiveness of the offspring until maturity is achieved. (It is this long maternity - learning from parents, that created the need for large size brains so their offspring could learn from their parents - This is an smart way nature provided animals means of adaptation to the environement as adaptation possibly is better as it occurs across the life of an individual and is not as determined by the previous genes that were passed to you only although nature prudently keept our ancestral brains also in place so they interis very eact in creating adaptation.

Now if evolution has a set of rules (we do not know as we are the only example on earth of a path of evolution) However thre appear to be hints that there are laws to evolution. If this laws are the same every where that of adaptation it is very probable that life evolves in a similar way across the universe. Then if this is the case the containment of brain development is subject to population explossions, extinctions and the development of new species with traces of those prior with the hability to evolve rapidly large brains. In the Genus homo it took 46 million years of monkeys with arms to manipualte things to develop into apes and then 6 millon from this last to the present to grow brains our size. However across time there were 15 maybe more homo genus types with different brain sizes and each specie had a slightly larger brain from the few species only three or four developed suffciently large brains as to evolve into us. They all shared and imnproved certain technology along the way. Humans have 3x to 4x more neurons than the largest brains in the animal kingdom.

There is another caveat and is that genuis homo Primitive pre-civilization species tended to be small in numbers even after hundreds of thousands of years Only homo sapiens has multiplied exponentially in the past 50 thousand years and is the only surviving species. So we can see to that to develop a civilization a large population has to exists as to multiply the speed of complexity and thus speed evolution. So as long as there is no explosion in population of any single specie there will be no social development and technology even if large brain exists (case for Neanderthals). Even in the case of neantherthals they had their chance to develop agriculture in the previous interglacial period (130K to 120K years ago) but they did not. There is one issue with this and is social complexity as they were never more than 100,000 individuals at that time while in Homo sapiens there were 4 to 5 million at the time of the neolithic.

proximity as a relative term

A- Proximity in Space However closeness is relative as per our understanding of the size of the unverse and above all the fastest method of transportation at one time. So 100 years ago we imagined selenites or martians, today habiatable worlds at 50 ly radious and in 10000 years maybe 1/4 of the size of our galaxy. So I would treat proximity with attemtion as it is dependant on our perception of our world.

B-Proxmity in Time I think that two similar civilizations could only be able to recognize each other if they both have pursued similar purpose broad goals across their development which are derived from their needs. Could we say that those that were able to make fire a million years ago could recgnize a light bulb (sure) but they will find very difficult to understand how the ligh is generated. So this two civilizations will not be separated by evolution that mach. I think in one million years light may be still in use and possibly in 100 million years. So this is a partial answer as there may be some parts that could be undertood but others not. Could we say that this two civilizations are close in proximity yes because their needs and goals are the same (food, light, heat, raw materials, communication, medicines, etc). However if you expect to find two civilizations developing the plane that will brake the sound barrier at the same time you will not find them. (Space establishes relations between objects in space and time relates them in evolution).

However if we would find an extremely advanced civilization it is possible that all his needs will not exist in a more primitive civilization (as would be the case of meeting a computer machine civilization or a non phisical entity) in that case it is very difficult that they understand each other at all. This two civilizations will be separated by billions of years. So as long as there are biological entities they will recognize each other and their goals and needs aklthough it will become wirder and wirder.

A ultimate case would be that of an extremely advanced biological civilization that may reach a plateau lasting for millions to hundreds of millions of years where a civilization that dominates and perfects a technology has diminished returns from his development and has evolutionary limits on how it can achive this. Imagine for example a biological civilization that has been able to dominate and manipulate all the existing laws of physics. This civilization may find any further advance is halted by limits by the laws of nature or by the required engineering to an scale which is unachievable or that requires extremely long periods of time or unatainable resources In this case two temporary different advanced civilizations will converge at one point and their differences will became smaller and smaller as the more advanced will find it harder to progress while the younger civilization will get closer to the development point of that more advanced so they become similar. (However for an outside observer there will allways be a difference between the two stages of development but they will resemble more the closest the get).

C-Proximity in brain processing capacity What is the procesing capacity of a civilization individuals - The difference of our brain with that of an octopus is 4x more neurons. (And the brain is already prety packed with neurons to the point of saturation). Now if as Paul Davis says biological evolution is only a brief space of time towards any biological entity building machines with incredible intelligence and being surpased by them as per intelligence and capabilities. So far machines have been better than humans in specifc tasks and it is understandable as our brain is the product of an extremely long time spand of well over a hundred billion sucessfull evolutionary steeps and trillions upon trillions of experiments on variable dynamic environements that yields the best possible evolution for survival.

So yes intermediate Kardashev_scale from I to III given the interpretation of similarity in time and that of space provided it will be able to recognize each other although we may find each other culturaly in oposite extremes.

Yes possible for the most advanced possible civilizations (hibrid or post biological or non even physical) as they reach a plateau of knowledge where further knowledge and technology progress is limited or capeed.


Absolutely no chance, whatsoever.

Had the ancient greeks figured out electromagnetism, which really isn't that hard (in hindsight), Jesus might just have used the internet.

Even on Earth, there are places where travel was possible for millennia, yet technological development was often much more than 300 years apart, e.g. Zulus vs Imperialist Europe.

The only way to achieve what you want is extraterrestial or divine intervention, a.k.a. meddling.

  • $\begingroup$ I disagree, you could say that the Zulus were at the same tech level as the North American Indians in spite of the distance between them. It was the Europeans who were the anomaly. $\endgroup$
    – Separatrix
    Commented Feb 24, 2016 at 14:40
  • $\begingroup$ @user16295 If Europe was the anomaly, please explain how some places in Asia, India, and Arabia were also many centuries if not millennias ahead of the Zulu, technologically - even before imperialist times. Also, some Central American Indians were far more than 300 years ahead of some North American Indians, in terms of technological development. By the way, I'm in no way intending to insult the Zulu, I just picked them because they are relatively well known. $\endgroup$
    – Peter
    Commented Feb 24, 2016 at 15:31
  • $\begingroup$ My criticism is not of the different relative technologies, it's of your statement that there's "absolutely no chance". Europe was an anomaly because we'd had the industrial revolution, nobody else had the geography for that. The chance might be vanishingly small, but it exists. There's nothing saying they can't be the same, the two civilisations are completely independent, they could be completely identical or utterly unrecognisably different. $\endgroup$
    – Separatrix
    Commented Feb 24, 2016 at 15:42
  • $\begingroup$ @user16295 If we don't count Europe, that leaves us with hundreds of other anomalies - almost every subculture anywhere becomes an anomaly. In the Zulu example, they didn't even have writing, so they were far more than 300 years behind even the ancient Mediterranean civilizations, which were only on a somewhat equal level to each other due to trade. Start 2 human civilizations with similar preconditions, cut all communications, and 2000 years later they are almost certainly not within 300 years of each other, technology wise. The question asked about a period much longer then 2000 years. $\endgroup$
    – Peter
    Commented Feb 24, 2016 at 16:39

I doubt it would be possible with a civilization composed of people like humans - too often, we advance by leaps and bounds because one random person had a really good idea. And it didn't take all that many really great ideas to get to where we are now, so each one had a huge proportional effect.

So let's slow it down. Make both civilizations out of herd animals - slow, incurious, group-thinkers. Give them a slow rate of reproduction and an environment with plenty of resources - necessity is the mother of invention, so let's make invention an orphan. In such a civilization, presumably technological advancement would still happen, because people are still a little curious. But it would happen extremely slowly, and ideas would be generated not by a Swiss patent clerk stuck in an office but by the community as a whole, in a painfully slow fusion-like process. This would make technological advancement slower and more predictable - provided that the two civilizations got started around the same time, there would be a reasonable chance that they'd stay at similar levels for a long while.

Now, how do we start them at the same time? Here I'll borrow an idea from Jack McDevitt - omega clouds. In McDevitt's universe, the galaxy is plagued by massive clouds that are attracted to angular structures, and cause destruction when they arrive on a planet. Say we have some sort of similar phenomenon here. Planets A and B start out with civilizations in two wildly different technological positions - but our omega cloud or similar phenomenon comes tearing through and wipes them out roughly simultaneously. Now both worlds are starting from scratch (in terms of civilization, not biology) and we have the synchronization we wanted.


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