In this post, I wish to outline an alternative picture to the grabby aliens model proposed by Hanson et al. (2021). The grabby aliens model assumes that “grabby aliens” expand far and wide in the universe, make clearly visible changes to their colonized volumes, and immediately prevent life from emerging in those volumes.
In contrast, the picture I explore here involves what we may call “quiet expansionist aliens”. This model also involves expansion far and wide, but unlike in the grabby aliens model, the expansionist aliens in this model do not make clearly visible changes to their colonized volumes, and they do not immediately prevent life from emerging in those volumes — although they do prevent emerging civilizations from developing to the point of rivaling the quiet expansionists’ technology and power.
The reason I explore this alternative picture is that I think it is a neglected possible model for hypothetical alien expansion. I am not claiming that it is the most plausible model a priori, but I think it is too plausible for it to be altogether dismissed, as it generally seems to be.
1. What changes in the quiet expansionist model?
The most obvious change in this model compared to the grabby aliens model is that we would not be able to see a colonized volume from afar, and perhaps not even from up close. Likewise, the quiet expansionist model implies that there would be more instances of evolved life, including observers like us, since the expansionist aliens would not immediately prevent such observers from emerging within their colonized volumes; they could instead stay around and observe. Taken together, this means that quiet expansionist aliens could in theory be here already, and they could even have a lot of experience interacting with civilizations at our stage of development.
Note that the grabby aliens model and the quiet expansionist model need not be mutually exclusive, as they could in principle be combined. That is, one could have a model in which there are both grabby (i.e. clearly visible) and quiet expansionist aliens that each rule their respective volumes, and different versions of the model could vary the relative proportion of these different colonization styles. (The original grabby aliens model only involves clearly visible expansionist aliens, not quiet expansionist ones; that is a helpful simplifying assumption, but it is worth being clear that it may be wrong.)
2. Arguments against the quiet expansionist model
A reason the quiet expansionist model is rarely taken seriously is that there seem to be some compelling arguments against it. Let us therefore try to explore a couple of these arguments, to see how compelling they are and what they should lead us to conclude.
2.1 “Implausible motive”
One argument is that it is implausible that an expansionist civilization would not visibly change its colonized volume. In particular, it is difficult to see what kind of underlying motive could make sense of such cosmic silence. The default expectation appears to be that we should instead see overt signs of colonization.
How convincing is this as an argument against the plausibility of quiet expansionist aliens? In order to evaluate that, it seems helpful to first outline what could, speculatively, be some motives behind quiet expansion. For example, it is conceivable that quiet expansion could aid internal coordination and alignment in a civilization that spans numerous star systems and perhaps even countless galaxies. By staying minimally concentrated and diversified across its colonization volume, a civilization might minimize risks of internal drift and conflict.
Another potential reason to stay silent is to try to learn about emerging civilizations (cf. the “info gain” hypothesis explored here). This might seem like a far-fetched reason to stay quiet, yet if the value of information gained from emerging civilizations is high, it might be a sufficient or at least supporting reason.
Furthermore, there is the dark forest hypothesis, or something in that ballpark, which roughly posits that aliens would stay quiet so as to avoid detection by, and resulting conflicts with, other civilizations. Note that such a motive would not require certainty about hostility from other civilizations — mere uncertainty about the motives of other potential civilizations might be enough to justify such a quiet approach. This is similar to the arguments that some have made against human attempts to send signals to alien civilizations based on the potential risks of sending such signals (see e.g. Todd & Miller, 2017).
Another motive for being quiet might be that sufficiently advanced civilizations would tend to realize that quiet expansion is a stable win-win equilibrium that avoids large-scale conflict with other advanced civilizations. In that case, they may naturally decide to adhere to a quiet strategy, lest they eventually get beaten by a larger coalition. A loose analogy to the contemporary human world might be how states generally do not invade international waters, in part because they know that a larger coalition would seek to undo such invasions. (To be clear, I am not claiming that being quiet is necessarily a win-win equilibrium for expansionist civilizations; I am merely claiming that this is yet another speculative possibility that warrants some level of consideration.)
Finally, there is a category of motives that we could call “unknown unknowns”, namely motives that we cannot readily conceive of, yet which might make sense to agents who are more advanced and better informed than we are. After all, it seems that we should not be confident that we can readily list all the plausible motives that a highly advanced intelligence might have.
Note that the motives outlined above are not mutually exclusive. That is, an expansionist civilization could potentially be quiet due to a combination of these motives — for example, to maintain internal coordination, to stay hidden from potential adversaries, and to study emerging civilizations.
In light of the potential motives outlined above, the “implausible motive” argument is hardly a decisive argument against quiet expansionist civilizations. There is a wide range of possible motives that might make sense of quiet expansion. Some of these motives appear at least somewhat plausible individually, and the broader category of such motives is more plausible still.
2.2 “Implausible convergence”
Another argument against a quiet expansionist model is that it would require an implausible degree of convergence, both within any single quiet expansionist civilization and across civilizations with different origins. After all, the argument goes, it would seemingly only require a single defiant faction to break the quiet policy and become a grabby civilization.
Would convergence toward being “quiet” within a single expansionist civilization be implausible? There are some reasons not to think so. For one, an advanced civilization could presumably be extremely capable, including when it comes to maintaining internal stability and alignment (cf. Finnveden et al., 2022).
Second, there might be strong strategic reasons to remain quiet that would be compelling to any rational sub-agent within the expansionist civilization (e.g. some of the specific motives outlined above, or an “unknown unknown” motive).
Third, it seems plausible that occasional defiants could be kept permanently in check if they are greatly outnumbered and overpowered by the pro-quiet faction, similar to how a few revolutionaries are unlikely to gain independence within a large nation-state. For example, if a small defiant faction tries to escape, they might be chased by a much larger faction that would prevent the defiant faction from accomplishing much.
What about convergence toward being “quiet” across civilizations? First, it is worth reiterating that, as a general matter, models with quiet expansionist civilizations do not require such convergence across civilizations. In particular, the above-mentioned combined models that involve both grabby and quiet expansionist civilizations obviously entail no such convergence. However, for the sake of argument, we can list some reasons why de facto convergence toward being “quiet” might be plausible even across civilizations.
Some of the reasons that could apply to convergence within civilizations might also apply to convergence across civilizations. For example, perhaps there are strong strategic reasons for being quiet that will be obvious to any advanced civilization. Or maybe there is a kind of cosmic selection pressure that pushes all civilizations toward being quiet.
Or perhaps quiet expansionist civilizations will tend to be so numerous that they are able to keep all budding grabby civilizations in check. In other words, scenarios with a sufficiently low ratio of grabby-to-quiet expansionist civilizations might eventually become de facto quiet everywhere. (The same might apply in reverse: for a sufficiently high ratio of grabby-to-quiet expansionist civilizations, the universe may converge toward an overall grabby equilibrium.)
Similarly, if we restrict our focus to (large) local regions of the universe, a state of purely quiet expansion could occur if the earliest expansionist civilization within a large radius happened to be a quiet one. By virtue of its earliness, such a civilization could impose its quiet rule on a vast cosmic volume — potentially spanning a billion light years or more — even if not all civilizations converge toward being quiet on the largest scale.
In light of these considerations, the “implausible convergence” argument is hardly that convincing either. In particular, it does not seem to be a decisive argument against models that involve quiet expansionist civilizations, including models that involve de facto convergence toward quiet expansion, whether in a large local vicinity or (less probably) across the entire universe.
Lastly, in our efforts to think clearly about these matters, it is worth being aware of our tendency toward belief digitization: our tendency to round the probability of less likely possibilities down to zero (see also Gettys et al., 1973; Fernbach et al., 2010). Thus, even if scenarios involving quiet expansionist civilizations do not seem to be the most likely ones — even if they only deserve, say, a 10 percent prior probability conditional on alien expansion — this should not lead us to altogether disregard this class of scenarios.
3. Arguments in favor of the quiet expansionist model?
Having explored two key arguments against the quiet expansionist model, it is worth asking whether there are any arguments that positively favor this model. It seems to me that there are. In particular, it seems that certain anthropic considerations — i.e. considerations relating to observation selection effects — support quiet expansionist models, at least relative to the “standard” grabby model.
For example, if we assume a mixed model that involves both grabby and quiet expansionist civilizations, there would be more observers like us (e.g. observers living in civilizations at our current stage of development) in scenarios with a higher proportion of quiet expansionist vs. grabby civilizations. By extension, there would be far more observers like us in a pure quiet expansionist versus a pure grabby model.
This is illustrated in the three toy figures below, in which the green stars represent civilizations at roughly our stage of development. In each of the figures, time increases along the vertical axis while space extends along the horizontal axis; the grey areas represent quiet expansionist colonizations while the black areas represent grabby colonizations. The green stars become increasingly prevalent over time because we here assume the hard-steps model described by Hanson et al. (2021, pp. 3-4).
As we can see, the further we get toward a pure quiet expansionist scenario, the more observers there are like us.
Similarly, in terms of where we should expect to find ourselves within a specific scenario that contains both grabby and quiet expansionist civilizations, there would generally be more observers like us in the parts of the universe that are ruled by quiet expansionist civilizations.
We can phrase these points in terms of the two canonical assumptions in anthropic reasoning, namely the Self-Indication Assumption (SIA: updating based on observer prevalence across different hypothetical scenarios) and the Self-Sampling Assumption (SSA: updating based on observer prevalence within a fixed scenario). That is, SIA generally pushes us toward believing in a higher ratio of quiet expansionist to grabby civilizations, while SSA generally pushes us toward thinking that we find ourselves inside a quiet expansionist volume (at least this latter claim would hold true in a wide range of mixed scenarios that are not close to being purely grabby).
3.1 Qualifications to this argument
Some key qualifications are worth stressing about the anthropic argument outlined above. First, it is notoriously difficult to know what to make of anthropic arguments, which suggests that we should be cautious in drawing strong inferences from such arguments. Thus, to be clear, I present this argument as one that is worth pondering, not as a definitive argument from which we should draw any strong conclusions.
Second, the argument presented above is by no means exhaustive in terms of the possibilities it explores. The argument only compares two simple models, or rather a continuum of simple models between the two extremes of fully grabby and fully quiet expansionist models. Yet there are, of course, many other options than these. For example, another model might say that large-scale space colonization is simply impossible (such a model would have its own strengths and weaknesses).
We should thus be clear that the anthropic argument outlined above only favors (simple) quiet expansionist models in comparison to (simple) grabby models (e.g. it favors models with a higher prevalence of quiet expansionist relative to grabby civilizations). It does not necessarily say much about the plausibility of the quiet expansionist model compared to other competing colonization models, or about the plausibility of this quiet expansionist model in absolute terms.
These qualifications notwithstanding, the argument does seem to pose a challenge to the simple grabby aliens model as proposed by Hanson et al.
4. Objection: Fails to explain earliness
An objection to the anthropic argument outlined above is that the quiet expansionist model fails to explain our apparent earliness in cosmic history. For example, Hanson et al. argue that humanity has appeared surprisingly early in cosmic history, and they propose their grabby aliens model as a way to explain that earliness, since grabby aliens would prevent new civilizations from emerging (Hanson et al., 2021, sec. 2). But in the quiet expansionist model, it is not clear how this earliness is explained.
I see at least two reasons why this objection should not lead us to dismiss quiet expansionist models. First, it is unclear whether there indeed is an earliness problem. On some assumptions about what kinds of star systems can give rise to life, our appearance date may in fact be quite typical, and thus not particularly early (see e.g. Burnetti, 2016; 2017). If these assumptions are correct, there is no earliness problem. And since it is highly uncertain which stars can give rise to life, it seems that we should place a substantial probability on there being no earliness problem to begin with.
Second, quiet expansionist civilizations could, like grabby ones, imply a deadline on the emergence of new civilizations at some point, even if they would not do so initially. Such a deadline need not be mysterious, and it could even be a clear strategic necessity, at least within some plausible versions of the quiet expansionist model. For example, we can imagine a version of the model in which the quiet expansionists prevent any further life from emerging once they encounter other expansionist civilizations that originated elsewhere, or when they encounter hostile expansionists in particular. In that case, some of the motives for being quiet and not using all resources available to them might no longer apply (e.g. the motive of trying to remain hidden from potential cosmic adversaries).
In sum, the purported earliness problem does not seem to be a valid reason to dismiss quiet expansionist models, nor is it a valid reason to dismiss the anthropic argument that supports such models relative to the pure grabby aliens model.
5. Conclusion
The quiet expansionist model is a conjecture that could simultaneously:
Answer the Fermi question: according to this model, they are most likely out there, and probably even here (cf. the illustration above).
Account for (much of) the great filter that prevents visible colonization of the cosmos: quiet expansionist civilizations would generally impose a future filter on civilizations like ours.
Be favored by anthropic considerations and make us typical observers (of our kind), in line with the Copernican Principle.
Help explain the hardest (seemingly) anomalous UFOs: they might be silent cosmic rulers.
To be clear, my claim here is not that the quiet expansionist model is in fact true. But as a conjecture, I submit that it deserves more consideration than it has received so far.
Silent cosmic rulers
In this post, I wish to outline an alternative picture to the grabby aliens model proposed by Hanson et al. (2021). The grabby aliens model assumes that “grabby aliens” expand far and wide in the universe, make clearly visible changes to their colonized volumes, and immediately prevent life from emerging in those volumes.
In contrast, the picture I explore here involves what we may call “quiet expansionist aliens”. This model also involves expansion far and wide, but unlike in the grabby aliens model, the expansionist aliens in this model do not make clearly visible changes to their colonized volumes, and they do not immediately prevent life from emerging in those volumes — although they do prevent emerging civilizations from developing to the point of rivaling the quiet expansionists’ technology and power.
The reason I explore this alternative picture is that I think it is a neglected possible model for hypothetical alien expansion. I am not claiming that it is the most plausible model a priori, but I think it is too plausible for it to be altogether dismissed, as it generally seems to be.
1. What changes in the quiet expansionist model?
The most obvious change in this model compared to the grabby aliens model is that we would not be able to see a colonized volume from afar, and perhaps not even from up close. Likewise, the quiet expansionist model implies that there would be more instances of evolved life, including observers like us, since the expansionist aliens would not immediately prevent such observers from emerging within their colonized volumes; they could instead stay around and observe. Taken together, this means that quiet expansionist aliens could in theory be here already, and they could even have a lot of experience interacting with civilizations at our stage of development.
Note that the grabby aliens model and the quiet expansionist model need not be mutually exclusive, as they could in principle be combined. That is, one could have a model in which there are both grabby (i.e. clearly visible) and quiet expansionist aliens that each rule their respective volumes, and different versions of the model could vary the relative proportion of these different colonization styles. (The original grabby aliens model only involves clearly visible expansionist aliens, not quiet expansionist ones; that is a helpful simplifying assumption, but it is worth being clear that it may be wrong.)
2. Arguments against the quiet expansionist model
A reason the quiet expansionist model is rarely taken seriously is that there seem to be some compelling arguments against it. Let us therefore try to explore a couple of these arguments, to see how compelling they are and what they should lead us to conclude.
2.1 “Implausible motive”
One argument is that it is implausible that an expansionist civilization would not visibly change its colonized volume. In particular, it is difficult to see what kind of underlying motive could make sense of such cosmic silence. The default expectation appears to be that we should instead see overt signs of colonization.
How convincing is this as an argument against the plausibility of quiet expansionist aliens? In order to evaluate that, it seems helpful to first outline what could, speculatively, be some motives behind quiet expansion. For example, it is conceivable that quiet expansion could aid internal coordination and alignment in a civilization that spans numerous star systems and perhaps even countless galaxies. By staying minimally concentrated and diversified across its colonization volume, a civilization might minimize risks of internal drift and conflict.
Another potential reason to stay silent is to try to learn about emerging civilizations (cf. the “info gain” hypothesis explored here). This might seem like a far-fetched reason to stay quiet, yet if the value of information gained from emerging civilizations is high, it might be a sufficient or at least supporting reason.
Furthermore, there is the dark forest hypothesis, or something in that ballpark, which roughly posits that aliens would stay quiet so as to avoid detection by, and resulting conflicts with, other civilizations. Note that such a motive would not require certainty about hostility from other civilizations — mere uncertainty about the motives of other potential civilizations might be enough to justify such a quiet approach. This is similar to the arguments that some have made against human attempts to send signals to alien civilizations based on the potential risks of sending such signals (see e.g. Todd & Miller, 2017).
Another motive for being quiet might be that sufficiently advanced civilizations would tend to realize that quiet expansion is a stable win-win equilibrium that avoids large-scale conflict with other advanced civilizations. In that case, they may naturally decide to adhere to a quiet strategy, lest they eventually get beaten by a larger coalition. A loose analogy to the contemporary human world might be how states generally do not invade international waters, in part because they know that a larger coalition would seek to undo such invasions. (To be clear, I am not claiming that being quiet is necessarily a win-win equilibrium for expansionist civilizations; I am merely claiming that this is yet another speculative possibility that warrants some level of consideration.)
Finally, there is a category of motives that we could call “unknown unknowns”, namely motives that we cannot readily conceive of, yet which might make sense to agents who are more advanced and better informed than we are. After all, it seems that we should not be confident that we can readily list all the plausible motives that a highly advanced intelligence might have.
Note that the motives outlined above are not mutually exclusive. That is, an expansionist civilization could potentially be quiet due to a combination of these motives — for example, to maintain internal coordination, to stay hidden from potential adversaries, and to study emerging civilizations.
In light of the potential motives outlined above, the “implausible motive” argument is hardly a decisive argument against quiet expansionist civilizations. There is a wide range of possible motives that might make sense of quiet expansion. Some of these motives appear at least somewhat plausible individually, and the broader category of such motives is more plausible still.
2.2 “Implausible convergence”
Another argument against a quiet expansionist model is that it would require an implausible degree of convergence, both within any single quiet expansionist civilization and across civilizations with different origins. After all, the argument goes, it would seemingly only require a single defiant faction to break the quiet policy and become a grabby civilization.
Would convergence toward being “quiet” within a single expansionist civilization be implausible? There are some reasons not to think so. For one, an advanced civilization could presumably be extremely capable, including when it comes to maintaining internal stability and alignment (cf. Finnveden et al., 2022).
Second, there might be strong strategic reasons to remain quiet that would be compelling to any rational sub-agent within the expansionist civilization (e.g. some of the specific motives outlined above, or an “unknown unknown” motive).
Third, it seems plausible that occasional defiants could be kept permanently in check if they are greatly outnumbered and overpowered by the pro-quiet faction, similar to how a few revolutionaries are unlikely to gain independence within a large nation-state. For example, if a small defiant faction tries to escape, they might be chased by a much larger faction that would prevent the defiant faction from accomplishing much.
What about convergence toward being “quiet” across civilizations? First, it is worth reiterating that, as a general matter, models with quiet expansionist civilizations do not require such convergence across civilizations. In particular, the above-mentioned combined models that involve both grabby and quiet expansionist civilizations obviously entail no such convergence. However, for the sake of argument, we can list some reasons why de facto convergence toward being “quiet” might be plausible even across civilizations.
Some of the reasons that could apply to convergence within civilizations might also apply to convergence across civilizations. For example, perhaps there are strong strategic reasons for being quiet that will be obvious to any advanced civilization. Or maybe there is a kind of cosmic selection pressure that pushes all civilizations toward being quiet.
Or perhaps quiet expansionist civilizations will tend to be so numerous that they are able to keep all budding grabby civilizations in check. In other words, scenarios with a sufficiently low ratio of grabby-to-quiet expansionist civilizations might eventually become de facto quiet everywhere. (The same might apply in reverse: for a sufficiently high ratio of grabby-to-quiet expansionist civilizations, the universe may converge toward an overall grabby equilibrium.)
Similarly, if we restrict our focus to (large) local regions of the universe, a state of purely quiet expansion could occur if the earliest expansionist civilization within a large radius happened to be a quiet one. By virtue of its earliness, such a civilization could impose its quiet rule on a vast cosmic volume — potentially spanning a billion light years or more — even if not all civilizations converge toward being quiet on the largest scale.
In light of these considerations, the “implausible convergence” argument is hardly that convincing either. In particular, it does not seem to be a decisive argument against models that involve quiet expansionist civilizations, including models that involve de facto convergence toward quiet expansion, whether in a large local vicinity or (less probably) across the entire universe.
Lastly, in our efforts to think clearly about these matters, it is worth being aware of our tendency toward belief digitization: our tendency to round the probability of less likely possibilities down to zero (see also Gettys et al., 1973; Fernbach et al., 2010). Thus, even if scenarios involving quiet expansionist civilizations do not seem to be the most likely ones — even if they only deserve, say, a 10 percent prior probability conditional on alien expansion — this should not lead us to altogether disregard this class of scenarios.
3. Arguments in favor of the quiet expansionist model?
Having explored two key arguments against the quiet expansionist model, it is worth asking whether there are any arguments that positively favor this model. It seems to me that there are. In particular, it seems that certain anthropic considerations — i.e. considerations relating to observation selection effects — support quiet expansionist models, at least relative to the “standard” grabby model.
For example, if we assume a mixed model that involves both grabby and quiet expansionist civilizations, there would be more observers like us (e.g. observers living in civilizations at our current stage of development) in scenarios with a higher proportion of quiet expansionist vs. grabby civilizations. By extension, there would be far more observers like us in a pure quiet expansionist versus a pure grabby model.
This is illustrated in the three toy figures below, in which the green stars represent civilizations at roughly our stage of development. In each of the figures, time increases along the vertical axis while space extends along the horizontal axis; the grey areas represent quiet expansionist colonizations while the black areas represent grabby colonizations. The green stars become increasingly prevalent over time because we here assume the hard-steps model described by Hanson et al. (2021, pp. 3-4).
As we can see, the further we get toward a pure quiet expansionist scenario, the more observers there are like us.
Similarly, in terms of where we should expect to find ourselves within a specific scenario that contains both grabby and quiet expansionist civilizations, there would generally be more observers like us in the parts of the universe that are ruled by quiet expansionist civilizations.
We can phrase these points in terms of the two canonical assumptions in anthropic reasoning, namely the Self-Indication Assumption (SIA: updating based on observer prevalence across different hypothetical scenarios) and the Self-Sampling Assumption (SSA: updating based on observer prevalence within a fixed scenario). That is, SIA generally pushes us toward believing in a higher ratio of quiet expansionist to grabby civilizations, while SSA generally pushes us toward thinking that we find ourselves inside a quiet expansionist volume (at least this latter claim would hold true in a wide range of mixed scenarios that are not close to being purely grabby).
3.1 Qualifications to this argument
Some key qualifications are worth stressing about the anthropic argument outlined above. First, it is notoriously difficult to know what to make of anthropic arguments, which suggests that we should be cautious in drawing strong inferences from such arguments. Thus, to be clear, I present this argument as one that is worth pondering, not as a definitive argument from which we should draw any strong conclusions.
Second, the argument presented above is by no means exhaustive in terms of the possibilities it explores. The argument only compares two simple models, or rather a continuum of simple models between the two extremes of fully grabby and fully quiet expansionist models. Yet there are, of course, many other options than these. For example, another model might say that large-scale space colonization is simply impossible (such a model would have its own strengths and weaknesses).
We should thus be clear that the anthropic argument outlined above only favors (simple) quiet expansionist models in comparison to (simple) grabby models (e.g. it favors models with a higher prevalence of quiet expansionist relative to grabby civilizations). It does not necessarily say much about the plausibility of the quiet expansionist model compared to other competing colonization models, or about the plausibility of this quiet expansionist model in absolute terms.
These qualifications notwithstanding, the argument does seem to pose a challenge to the simple grabby aliens model as proposed by Hanson et al.
4. Objection: Fails to explain earliness
An objection to the anthropic argument outlined above is that the quiet expansionist model fails to explain our apparent earliness in cosmic history. For example, Hanson et al. argue that humanity has appeared surprisingly early in cosmic history, and they propose their grabby aliens model as a way to explain that earliness, since grabby aliens would prevent new civilizations from emerging (Hanson et al., 2021, sec. 2). But in the quiet expansionist model, it is not clear how this earliness is explained.
I see at least two reasons why this objection should not lead us to dismiss quiet expansionist models. First, it is unclear whether there indeed is an earliness problem. On some assumptions about what kinds of star systems can give rise to life, our appearance date may in fact be quite typical, and thus not particularly early (see e.g. Burnetti, 2016; 2017). If these assumptions are correct, there is no earliness problem. And since it is highly uncertain which stars can give rise to life, it seems that we should place a substantial probability on there being no earliness problem to begin with.
Second, quiet expansionist civilizations could, like grabby ones, imply a deadline on the emergence of new civilizations at some point, even if they would not do so initially. Such a deadline need not be mysterious, and it could even be a clear strategic necessity, at least within some plausible versions of the quiet expansionist model. For example, we can imagine a version of the model in which the quiet expansionists prevent any further life from emerging once they encounter other expansionist civilizations that originated elsewhere, or when they encounter hostile expansionists in particular. In that case, some of the motives for being quiet and not using all resources available to them might no longer apply (e.g. the motive of trying to remain hidden from potential cosmic adversaries).
In sum, the purported earliness problem does not seem to be a valid reason to dismiss quiet expansionist models, nor is it a valid reason to dismiss the anthropic argument that supports such models relative to the pure grabby aliens model.
5. Conclusion
The quiet expansionist model is a conjecture that could simultaneously:
Answer the Fermi question: according to this model, they are most likely out there, and probably even here (cf. the illustration above).
Account for (much of) the great filter that prevents visible colonization of the cosmos: quiet expansionist civilizations would generally impose a future filter on civilizations like ours.
Be favored by anthropic considerations and make us typical observers (of our kind), in line with the Copernican Principle.
Help explain the hardest (seemingly) anomalous UFOs: they might be silent cosmic rulers.
To be clear, my claim here is not that the quiet expansionist model is in fact true. But as a conjecture, I submit that it deserves more consideration than it has received so far.
Acknowledgments
Many thanks to Tristan Cook for helpful comments.