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> A core idea of this is that there are various filters that separate a new planet from one hosting spacefaring life. The most obvious, but least talked about

> A core idea of this is that there are various filters that separate a new planet from one hosting spacefaring life. The most obvious, but least talked about filter is time. Let’s assume there is a civilization just like us on the other end of the Milky Way galaxy, it’s not like we can just “look out” and observe them. Assuming they blasted out radio signals, those radio signals would have to have been sent 100,000 years ago for us to detect them today. Alternatively for that same civilization to detect our earliest radio signals it take another 999,900 years. If this technologically advanced civilization was in the closest galaxy instead of the opposite end of the Milky Way, then our ability to detect one another’s signals traveling at the speed of light would be separated by over 2.5M years.

messe 4y ago
> The most obvious, but least talked about filter is time. For good reason: there's been a lot of it so far. Even at slower than light speeds, it would be possible for a sufficiently advanced civilization to send probes to ever star in the galaxy (or even colonize it) in just a few million years. So why don't we see any evidence of any prior civilization having done that? It would only take one.
- pjmlp 4y ago
  Cough, Egyptian pyramids, jump doors with runes,... :) Now seriously, maybe we have and they just weren't interested.
- cloverich 4y ago
  How long would they have to last though? We don't just have to both be advanced but also overlap in time. When you consider there are hundred million+ years between advanced life forms and intelligent life, and even millions of years between humans and intelligent humans, any signals of any kind may have to last for millions of years or more to be detected. Then there's so much space, so it probably takes more than one. Perhaps a million+ more than one. Then the final but to me most important thing, is we often assume advanced life looks like us. I personally believe it generally does -- for a bit. But if we're just a stepping stone to AI and then (perhaps) we disappear, advanced life forms like us only exist for a blip anyways. We probably don't even know what to look for. The possibilities are fascinating and humbling.
  - eloff 4y ago
    I suspect that could be part of it, that we're the biological bootloader for AI and we last just a blink in that stage on the time scale of the universe. But then what does that AI do afterwards and why don't we see them. That doesn't really solve the dilemma.
    - cloverich 4y ago
      That is true although I suspect it might be like an ant and us -- the ant certainly interacts with us but does it, can it, know anything about us? Maybe the output of AI is all around us and we are simply (now and forever) incapable of "seeing" it. My other hunch is that communication at that level isn't actually required in the traditional sense, and anything that would need to be communicable is done so via truth seeking.
  - whimsicalism 4y ago
    It wouldn't have to be a signal, it could be physical artifacts.
- throwawaycities 4y ago
  > …it would be possible for a sufficiently advanced civilization to send probes to ever star in the galaxy (or even colonize it) in just a few million years. It’s “possible”, highlighted by the fact that we haven’t sent a single probe to another star system. We have a grand total of 2 probes that have made it outside our solar system, and only 3 more on the way. There are an estimated hundred thousand million stars in the Milky Way. At a rounded cost of $1B for the Voyager missions, “possible” starts to meet reality. There are far to many assumptions. Not only does a technological civilization exist, but it had a few million years head start on us and used their time/technology to colonize every star system in the galaxy with physical probes, when so long as we are making assumptions and can assume they have/had the ability to collect all the same data/information locally at the speed of light.
- canaus 4y ago
  I'm pulling information from an introductory astronomy class, but isn't the definition of what lot of time passing is, not agreed upon? /The Five Ages of the Universe/ by Adams and Laughlin theorize that new stars won't stop forming until trillions (possibly hundreds of trillions) of years after the universe's inception. We're currently on years 14-15 billion. If their theories are true we'd be, arguably, one of the first instances of intelligent life in the universe. Now, some astronomers theorize that the universe will end in 5 - 15 billion years, so that would change the timeline substantially.
cletus 4y ago
The oldest stars in our galaxy are >12 billion years old. Ours is 4.5 billion years old. We obviously don't have a lot (meaning more than 1) of data points here but that one data point is that life can evolve in 4 billion years. Whatever the variance is we've had ~3x that for other civilizations to arise in our galaxy alone. Yes we could be "first" (within our cone of spacetime). First of 3? That's possible. First of 1000? Way less likely. There's some BAyesian reasoning about probability spaces you can do here. The very fact that we can't seem to detect anyone else in our galaxy changes the probabilities making it much more likely (but not impossible of course) that we're effectively alone. Also the odds that another civilization evolves over 4B years and reaches spacefaring technology within 100,000 years of us is, statistically speaking, incredibly unlikely. It's way more likely they'll be way ahead of us or way behind us.
spfzero 4y ago
Also, who knows how long the window would last where a civilization uses electromagnetic waves to communicate, in the ways we would look for them? We've only used them for a hundred-plus years or so, maybe in another hundred we will be using something else. That would mean there is only a 200-year period where we emitted detectible radiation, which is only detectible within a certain radius, and the detector would have to be within that radius and listening during that 200-year window at exactly the right distance and time to catch it.
- deleted 4y ago
  [deleted]

messe 4y ago

> The most obvious, but least talked about filter is time. For good reason: there's been a lot of it so far. Even at slower than light speeds, it would be possible for a sufficiently advanced civilization to send probes to ever star in the galaxy (or even colonize it) in just a few million years. So why don't we see any evidence of any prior civilization having done that? It would only take one.

pjmlp 4y ago
Cough, Egyptian pyramids, jump doors with runes,... :) Now seriously, maybe we have and they just weren't interested.
cloverich 4y ago
How long would they have to last though? We don't just have to both be advanced but also overlap in time. When you consider there are hundred million+ years between advanced life forms and intelligent life, and even millions of years between humans and intelligent humans, any signals of any kind may have to last for millions of years or more to be detected. Then there's so much space, so it probably takes more than one. Perhaps a million+ more than one. Then the final but to me most important thing, is we often assume advanced life looks like us. I personally believe it generally does -- for a bit. But if we're just a stepping stone to AI and then (perhaps) we disappear, advanced life forms like us only exist for a blip anyways. We probably don't even know what to look for. The possibilities are fascinating and humbling.
- eloff 4y ago
  I suspect that could be part of it, that we're the biological bootloader for AI and we last just a blink in that stage on the time scale of the universe. But then what does that AI do afterwards and why don't we see them. That doesn't really solve the dilemma.
  - cloverich 4y ago
    That is true although I suspect it might be like an ant and us -- the ant certainly interacts with us but does it, can it, know anything about us? Maybe the output of AI is all around us and we are simply (now and forever) incapable of "seeing" it. My other hunch is that communication at that level isn't actually required in the traditional sense, and anything that would need to be communicable is done so via truth seeking.
- whimsicalism 4y ago
  It wouldn't have to be a signal, it could be physical artifacts.
throwawaycities 4y ago
> …it would be possible for a sufficiently advanced civilization to send probes to ever star in the galaxy (or even colonize it) in just a few million years. It’s “possible”, highlighted by the fact that we haven’t sent a single probe to another star system. We have a grand total of 2 probes that have made it outside our solar system, and only 3 more on the way. There are an estimated hundred thousand million stars in the Milky Way. At a rounded cost of $1B for the Voyager missions, “possible” starts to meet reality. There are far to many assumptions. Not only does a technological civilization exist, but it had a few million years head start on us and used their time/technology to colonize every star system in the galaxy with physical probes, when so long as we are making assumptions and can assume they have/had the ability to collect all the same data/information locally at the speed of light.
canaus 4y ago
I'm pulling information from an introductory astronomy class, but isn't the definition of what lot of time passing is, not agreed upon? /The Five Ages of the Universe/ by Adams and Laughlin theorize that new stars won't stop forming until trillions (possibly hundreds of trillions) of years after the universe's inception. We're currently on years 14-15 billion. If their theories are true we'd be, arguably, one of the first instances of intelligent life in the universe. Now, some astronomers theorize that the universe will end in 5 - 15 billion years, so that would change the timeline substantially.

cletus 4y ago

The oldest stars in our galaxy are >12 billion years old. Ours is 4.5 billion years old. We obviously don't have a lot (meaning more than 1) of data points here but that one data point is that life can evolve in 4 billion years. Whatever the variance is we've had ~3x that for other civilizations to arise in our galaxy alone. Yes we could be "first" (within our cone of spacetime). First of 3? That's possible. First of 1000? Way less likely. There's some BAyesian reasoning about probability spaces you can do here. The very fact that we can't seem to detect anyone else in our galaxy changes the probabilities making it much more likely (but not impossible of course) that we're effectively alone. Also the odds that another civilization evolves over 4B years and reaches spacefaring technology within 100,000 years of us is, statistically speaking, incredibly unlikely. It's way more likely they'll be way ahead of us or way behind us.

spfzero 4y ago

Also, who knows how long the window would last where a civilization uses electromagnetic waves to communicate, in the ways we would look for them? We've only used them for a hundred-plus years or so, maybe in another hundred we will be using something else. That would mean there is only a 200-year period where we emitted detectible radiation, which is only detectible within a certain radius, and the detector would have to be within that radius and listening during that 200-year window at exactly the right distance and time to catch it.

deleted 4y ago
[deleted]