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> Given the number of stars out there, it seems wildly improbable that we are alone This tells you nothing unless you also know the probability of (intelligent

> Given the number of stars out there, it seems wildly improbable that we are alone This tells you nothing unless you also know the probability of (intelligent) life emerging on a planet. As far as we can tell it could be very low, and earth could very well be a unique combination of factors that allows it. Remember, there are many more possible deck of 52 cards than there are planets in the universe.

DavidSJ 5y ago
There's also the possibility that the existence of one civilization in a cosmic neighborhood tends to preclude the emergence of other civilizations in that same neighborhood, due to the tendency of civilizations to rapidly expand and take resources that might have been used by others, before those others even get a chance to emerge. In that case we can't treat our existence as independent of the existence of other nearby civilizations.
- hokumguru 5y ago
  What makes you think other civilizations would be focused on rapid expansion like humanity?
  - bpodgursky 5y ago
    You don't have to assume that they all do. You can assume that .1% of them do, and it works out precisely the same.
    - light_hue_1 5y ago
      Worse. von Neumann probes show that none of them can be expansionist, otherwise the galaxy would have been overrun in half a million years. So then.. maybe only the civilizations that aren't expansionist survive? Or everyone changes their mind and no one is expansionist by the time they get the right tech? Or maybe it's physically impossible to build von Neumann probes for some reason we don't yet understand? Or who knows what else. In any case, it's got to be zero in the history of our galaxy.
      - cdelsolar 5y ago
        I mean, let's try to build a von Neumann probe. How? I don't believe that our knowledge will continue to increase exponentially. Hard AI may never be achievable (although von Neumann probes don't necessarily need it). In order to build a von Neumann probe, once you need the very first microchip or anything resembling one, you're screwed. Will the von Neumann probes also be able to build an entire fabrication lab?
      - pharke 5y ago
        There could be good reasons we wouldn't see von Neumann probes. They could be extremely dangerous to deploy similar to the arguments that are currently being made against autonomous weapons systems. That might result in them having many built in limitations such as needing to phone back periodically or being saddled with multiple redundant systems or safeguards that would prevent them from mutating into something that could harm the originating civilization. Also don't forget that the purpose of the probes is exploration and/or resource harvesting. For exploration you only need a handful of probes at each star system and they may depart after completing their survey which would result in a very small footprint. For resource extraction you need some means of transporting the resources back to where they will be used in a timely manner which puts limits on the effective distance at which they can operate. A civilization may even decide that it's pointless to explore the entire galaxy this way since it would take millions of years to gather and transmit the information, what government do you know of that's capable of planning over that kind of timescale?
  - DavidSJ 5y ago
    I'm only suggesting a possibility, not a certainty. That said, it only takes a tiny fraction of their civilization to do it, for it to happen.
  - sidlls 5y ago
    What evidence have we that they would not? Life on earth certainly expands as rapidly as the environment can support, or even faster than it can, in many cases. Also "rapid" is a relative term, right? If we humans start expanding to other planets even within 10,000 years that would be quite rapid relative to the length of time it took for us to evolve.
- addicted 5y ago
  But if we had precluded the emergence of other civilizations in our neighborhood, wouldn’t we have known about it when we were taking resources away from those other living creatures? Based on that theory, a prerequisite to preventing the arising of other civilizations is the knowledge of the existence of other living beings at the very least.
  - rolleiflex 5y ago
    The other end of the argument is also interesting. It is possible that this has already happened before the age of Homo Sapiens, and we lack the one crucial thing that makes fusion power possible, say, deuterium oxide (heavy water) in sufficient quantities. It’s a ‘you don’t know what you don’t know’ situation — we could be living on a stellar neighbourhood that is already tapped out of that crucial resource, forever doomed to travel the slow way, never able to go more than knee deep into the vast ocean beside us.
  - blueblisters 5y ago
    I think the argument is that if there’s an advanced enough civilisation in our neighbourhood, it would have precluded us from evolving.
  - DavidSJ 5y ago
    No, for two reasons: 1) The idea is that we will do it, not that we have done it already. (How does something we will do in the future affect what we see today? It doesn't, at least not causally. It's just that some civilization had to be first in the neighboorhod, and that civilization will be the one to preempt the others, at least according to this model. So it's more of a probabilistic conditioning effect than a causal effect: conditional on existing, that means no one preempted us, which means we're the first, which means we'll preempt everyone else.) 2) The preemption happens well before the other civilizations come into existence. For example, we might deplete their stars of energy so that evolution doesn't happen at all on their planet.
- vardump 5y ago
  "There's also the possibility that the existence of one civilization in a cosmic neighborhood tends to preclude the emergence of other civilizations in that same neighborhood" Interesting. That's a point I haven't heard before. Or perhaps it's my lucky 10,000 day. :-) Although our path through the galaxy is somewhat unique. Stars don't really move in unison in the greater timescales, but more like slip past each other. Assuming Sol was born as a binary star, its sibling could be other side of the galaxy by now. Another thought is that if WE do expand to the stars, how long until our distant ancestors aren't really the same civilization anymore, but something completely alien to each other? Evolution could take some rather unexpected steps in the long run.
  - DavidSJ 5y ago
    The concept of "cosmic neighborhood" is deliberately left a bit vague in my description, but it definitely doesn't mean the stars that were near the sun when the sun was born. Rather, it refers to those stars which are within reach of us, now, in a timescale that is short relative to the typical interval between births of civilizations that distance apart. That could be anything from a corner of a galaxy to a galactic supercluster, depending on the speed with which civilizations can expand and the frequency with which new ones arise in the universe. Note that if civilizations expand at sufficiently close to the speed of light, then there is only a tiny window of time between when their light arrives and when their colony ships do. So under this model, it is quite unlikely that a new civilization waking up for the first time would look around and see anyone. Most likely, either the light from those other civilizations hasn't yet gotten here, in which case we see nothing, or their colony ships have already gotten here, in which case we wouldn't be born in the first place.
- tzs 5y ago
  Are you assuming FTL travel? If a civilization doesn't have FTL then expansion beyond their solar system seems unlikely. Yes, it is still possible with sub-light travel, but then you run into the problem of motivation. When limited to sub-light speed trade between colonies and the home system is so slow that you probably can't usefully import resources from the colony systems. When you are stuck with sub-light, colonizing another system (unless perhaps you are in a place with a lot of stars close together) is more accurately described as spending a whole lot of effort to establish another system that then won't really have much interaction with or effect on your system. Even the old classic of kicking out your undesirables who then go on to start a new civilization doesn't really work, because it is so expensive. If you dislike them so much that exile is the only answer and you don't have someplace in your system to exile them to you are far more likely to just kill them.
  - kingsuper20 5y ago
    This assumes that the expanding intelligence isn't machine-based.
    - 7thaccount 5y ago
      This. Paul Davies (prominent SETI researcher) states in one of his books that he wonders if biological life is a transitory phenomena.
  - deeviant 5y ago
    > If a civilization doesn't have FTL then expansion beyond their solar system seems unlikely. Yes, it is still possible with sub-light travel, but then you run into the problem of motivation. > When limited to sub-light speed trade between colonies and the home system is so slow that you probably can't usefully import resources from the colony systems. I mean this seems to disregard our entire history as a species. There have always been "others" within a population that seek, above anything else, to find a new place to go in order to live life they way they want to. We are also moving into an age where data and knowledge are raising to supreme importance. Both of these things can be transported at the speed of light, so a multi-solar system civilization that is able to increase is total resources available to acquire new information and knowledge will be at an advantage. Then, of course, there is the desire to preserve the human species as a whole by "spreading our seeds" so to speak.
randerson 5y ago
Isn't the universe potentially infinite?
- vardump 5y ago
  We don't really know. It might be. But the region we can observe is definitely finite. What we can causally affect (light cone) is a subset of that. And where we can travel given the Ultimate Technology is a small subset of the previous.
crazypython 5y ago
A bunch of self-replicating patterns in a physics simulation believe other self-replicating patterns must exist elsewhere.
jk7tarYZAQNpTQa 5y ago
> This tells you nothing unless you also know the probability of (intelligent) life emerging on a planet Life is not only probable, it's inevitable. Given the proper conditions, it's just a matter of time. And the same happens with intelligent life, it just needs more time without being hit by a meteor.
- goatlover 5y ago
  Where do you get that intelligent life is inevitable from a sample size of one?
  - splistud 5y ago
    Because we're not working from a sample size of one. But if we were, then what other possible conclusion would there be?
    - goatlover 5y ago
      We are, since Earth has the only life known in the universe to date. The other possible conclusions are any probability < 1, which means not inevitable.
  - jk7tarYZAQNpTQa 5y ago
    Life is inevitable + Evolution is a universal law = Intelligent life is inevitable Given the proper conditions, that is. A planet that is just a ball of magma won't see life (as we know it) until it cools down.
    - goatlover 5y ago
      Given the proper conditions, life might form once in a thousand planets, and intelligent life might be one in a billion. We don't know, but there's some probability for both. It could be really low, or it could be relatively high. The Rare Earth solution to the Fermi Paradox is as good a guess as any. Life of some kind might be relatively common, but intelligent life could still be really rare. We are the only species on Earth in 3.5 billion years to make radio telescopes and spacecraft. On other worlds, it might never happen because of the thousand different factors that led to hominid evolution which might be different elsewhere. For example, If the non-avian dinosaurs hadn't gone extinct from a large meteor impact, who knows whether any technological civilization would have ever formed. At any rate, mammalian evolution would have gone differently, and it's anyone's guess whether some non-hominid intelligent species would have evolved instead. They didn't during the age of the dinosaurs. We don't even know whether multicellular life is a low probability event. Maybe Cambrian explosions don't happen very often. There's no inevitability here, only unknown probabilities.

DavidSJ 5y ago

There's also the possibility that the existence of one civilization in a cosmic neighborhood tends to preclude the emergence of other civilizations in that same neighborhood, due to the tendency of civilizations to rapidly expand and take resources that might have been used by others, before those others even get a chance to emerge. In that case we can't treat our existence as independent of the existence of other nearby civilizations.

hokumguru 5y ago
What makes you think other civilizations would be focused on rapid expansion like humanity?
- bpodgursky 5y ago
  You don't have to assume that they all do. You can assume that .1% of them do, and it works out precisely the same.
  - light_hue_1 5y ago
    Worse. von Neumann probes show that none of them can be expansionist, otherwise the galaxy would have been overrun in half a million years. So then.. maybe only the civilizations that aren't expansionist survive? Or everyone changes their mind and no one is expansionist by the time they get the right tech? Or maybe it's physically impossible to build von Neumann probes for some reason we don't yet understand? Or who knows what else. In any case, it's got to be zero in the history of our galaxy.
    - cdelsolar 5y ago
      I mean, let's try to build a von Neumann probe. How? I don't believe that our knowledge will continue to increase exponentially. Hard AI may never be achievable (although von Neumann probes don't necessarily need it). In order to build a von Neumann probe, once you need the very first microchip or anything resembling one, you're screwed. Will the von Neumann probes also be able to build an entire fabrication lab?
    - pharke 5y ago
      There could be good reasons we wouldn't see von Neumann probes. They could be extremely dangerous to deploy similar to the arguments that are currently being made against autonomous weapons systems. That might result in them having many built in limitations such as needing to phone back periodically or being saddled with multiple redundant systems or safeguards that would prevent them from mutating into something that could harm the originating civilization. Also don't forget that the purpose of the probes is exploration and/or resource harvesting. For exploration you only need a handful of probes at each star system and they may depart after completing their survey which would result in a very small footprint. For resource extraction you need some means of transporting the resources back to where they will be used in a timely manner which puts limits on the effective distance at which they can operate. A civilization may even decide that it's pointless to explore the entire galaxy this way since it would take millions of years to gather and transmit the information, what government do you know of that's capable of planning over that kind of timescale?
- DavidSJ 5y ago
  I'm only suggesting a possibility, not a certainty. That said, it only takes a tiny fraction of their civilization to do it, for it to happen.
- sidlls 5y ago
  What evidence have we that they would not? Life on earth certainly expands as rapidly as the environment can support, or even faster than it can, in many cases. Also "rapid" is a relative term, right? If we humans start expanding to other planets even within 10,000 years that would be quite rapid relative to the length of time it took for us to evolve.
addicted 5y ago
But if we had precluded the emergence of other civilizations in our neighborhood, wouldn’t we have known about it when we were taking resources away from those other living creatures? Based on that theory, a prerequisite to preventing the arising of other civilizations is the knowledge of the existence of other living beings at the very least.
- rolleiflex 5y ago
  The other end of the argument is also interesting. It is possible that this has already happened before the age of Homo Sapiens, and we lack the one crucial thing that makes fusion power possible, say, deuterium oxide (heavy water) in sufficient quantities. It’s a ‘you don’t know what you don’t know’ situation — we could be living on a stellar neighbourhood that is already tapped out of that crucial resource, forever doomed to travel the slow way, never able to go more than knee deep into the vast ocean beside us.
- blueblisters 5y ago
  I think the argument is that if there’s an advanced enough civilisation in our neighbourhood, it would have precluded us from evolving.
- DavidSJ 5y ago
  No, for two reasons: 1) The idea is that we will do it, not that we have done it already. (How does something we will do in the future affect what we see today? It doesn't, at least not causally. It's just that some civilization had to be first in the neighboorhod, and that civilization will be the one to preempt the others, at least according to this model. So it's more of a probabilistic conditioning effect than a causal effect: conditional on existing, that means no one preempted us, which means we're the first, which means we'll preempt everyone else.) 2) The preemption happens well before the other civilizations come into existence. For example, we might deplete their stars of energy so that evolution doesn't happen at all on their planet.
vardump 5y ago
"There's also the possibility that the existence of one civilization in a cosmic neighborhood tends to preclude the emergence of other civilizations in that same neighborhood" Interesting. That's a point I haven't heard before. Or perhaps it's my lucky 10,000 day. :-) Although our path through the galaxy is somewhat unique. Stars don't really move in unison in the greater timescales, but more like slip past each other. Assuming Sol was born as a binary star, its sibling could be other side of the galaxy by now. Another thought is that if WE do expand to the stars, how long until our distant ancestors aren't really the same civilization anymore, but something completely alien to each other? Evolution could take some rather unexpected steps in the long run.
- DavidSJ 5y ago
  The concept of "cosmic neighborhood" is deliberately left a bit vague in my description, but it definitely doesn't mean the stars that were near the sun when the sun was born. Rather, it refers to those stars which are within reach of us, now, in a timescale that is short relative to the typical interval between births of civilizations that distance apart. That could be anything from a corner of a galaxy to a galactic supercluster, depending on the speed with which civilizations can expand and the frequency with which new ones arise in the universe. Note that if civilizations expand at sufficiently close to the speed of light, then there is only a tiny window of time between when their light arrives and when their colony ships do. So under this model, it is quite unlikely that a new civilization waking up for the first time would look around and see anyone. Most likely, either the light from those other civilizations hasn't yet gotten here, in which case we see nothing, or their colony ships have already gotten here, in which case we wouldn't be born in the first place.
tzs 5y ago
Are you assuming FTL travel? If a civilization doesn't have FTL then expansion beyond their solar system seems unlikely. Yes, it is still possible with sub-light travel, but then you run into the problem of motivation. When limited to sub-light speed trade between colonies and the home system is so slow that you probably can't usefully import resources from the colony systems. When you are stuck with sub-light, colonizing another system (unless perhaps you are in a place with a lot of stars close together) is more accurately described as spending a whole lot of effort to establish another system that then won't really have much interaction with or effect on your system. Even the old classic of kicking out your undesirables who then go on to start a new civilization doesn't really work, because it is so expensive. If you dislike them so much that exile is the only answer and you don't have someplace in your system to exile them to you are far more likely to just kill them.
- kingsuper20 5y ago
  This assumes that the expanding intelligence isn't machine-based.
  - 7thaccount 5y ago
    This. Paul Davies (prominent SETI researcher) states in one of his books that he wonders if biological life is a transitory phenomena.
- deeviant 5y ago
  > If a civilization doesn't have FTL then expansion beyond their solar system seems unlikely. Yes, it is still possible with sub-light travel, but then you run into the problem of motivation. > When limited to sub-light speed trade between colonies and the home system is so slow that you probably can't usefully import resources from the colony systems. I mean this seems to disregard our entire history as a species. There have always been "others" within a population that seek, above anything else, to find a new place to go in order to live life they way they want to. We are also moving into an age where data and knowledge are raising to supreme importance. Both of these things can be transported at the speed of light, so a multi-solar system civilization that is able to increase is total resources available to acquire new information and knowledge will be at an advantage. Then, of course, there is the desire to preserve the human species as a whole by "spreading our seeds" so to speak.

randerson 5y ago

Isn't the universe potentially infinite?

vardump 5y ago
We don't really know. It might be. But the region we can observe is definitely finite. What we can causally affect (light cone) is a subset of that. And where we can travel given the Ultimate Technology is a small subset of the previous.

crazypython 5y ago

A bunch of self-replicating patterns in a physics simulation believe other self-replicating patterns must exist elsewhere.

jk7tarYZAQNpTQa 5y ago

> This tells you nothing unless you also know the probability of (intelligent) life emerging on a planet Life is not only probable, it's inevitable. Given the proper conditions, it's just a matter of time. And the same happens with intelligent life, it just needs more time without being hit by a meteor.

goatlover 5y ago
Where do you get that intelligent life is inevitable from a sample size of one?
- splistud 5y ago
  Because we're not working from a sample size of one. But if we were, then what other possible conclusion would there be?
  - goatlover 5y ago
    We are, since Earth has the only life known in the universe to date. The other possible conclusions are any probability < 1, which means not inevitable.
- jk7tarYZAQNpTQa 5y ago
  Life is inevitable + Evolution is a universal law = Intelligent life is inevitable Given the proper conditions, that is. A planet that is just a ball of magma won't see life (as we know it) until it cools down.
  - goatlover 5y ago
    Given the proper conditions, life might form once in a thousand planets, and intelligent life might be one in a billion. We don't know, but there's some probability for both. It could be really low, or it could be relatively high. The Rare Earth solution to the Fermi Paradox is as good a guess as any. Life of some kind might be relatively common, but intelligent life could still be really rare. We are the only species on Earth in 3.5 billion years to make radio telescopes and spacecraft. On other worlds, it might never happen because of the thousand different factors that led to hominid evolution which might be different elsewhere. For example, If the non-avian dinosaurs hadn't gone extinct from a large meteor impact, who knows whether any technological civilization would have ever formed. At any rate, mammalian evolution would have gone differently, and it's anyone's guess whether some non-hominid intelligent species would have evolved instead. They didn't during the age of the dinosaurs. We don't even know whether multicellular life is a low probability event. Maybe Cambrian explosions don't happen very often. There's no inevitability here, only unknown probabilities.