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I read the paper and I find it highly unserious how frivolously they assigned some probability to the question how many intelligent civilizations there are in t

I read the paper and I find it highly unserious how frivolously they assigned some probability to the question how many intelligent civilizations there are in the universe. Their key assumption is: "We assume that if an SP remains in the circumstellar Habitable Zone (HZ) for a time equal to the current age of the Earth it will develop intelligent, communicative life." (page 5 at https://arxiv.org/ftp/arxiv/papers/2004/2004.03968.pdf https://arxiv.org/ftp/arxiv/papers/2004/2004.03968.pdf) Why? Why do you assume a planet will develop intelligent life when it remains in the Habitable Zone long enough? Just because it happend on Earth? And they continue with: "[...] according to the Copernican Principle – we propose that the likelihood of the development of life, and even intelligent life, should be broadly uniformly distributed amongst any suitable habitats" We have no clue how likely it was at Earth that life developed at all. Maybe it was just a chain of many lucky coincidences that happen once in 10 billion years. How is distribution any relevant then?

bhaak 6y ago
With other assumptions, they would arrive at 0 intelligent civilisations in the galaxy. That would make the rest of the paper void. :-) Nobody knows how life is distributed in the galaxy. Assuming that we are not special (the Copernican Principle) is a valid prerequisite. As it neither can be proved or disproved, it's not unserious to just state what the unproven assumptions are.
dahfizz 6y ago
One thing that bothers me is that papers like this always assume alien life will look exactly like life on Earth. It must be the same distance from the sun as us, have water and proteins like us, etc. If we effectively limit the definition of "life" to "the types of organisms we see on Earth", then of course we will never find life anywhere else. Maybe there are aliens that live on a gas giant and they "eat" the lighting rather than food, and their bodies look more like circuitry than the chemical life on Earth. Maybe there is a planet with a very strong magnetic field, and the life there is kind of like an electromagnet. They have bodies high in copper and the current of the ocean moves them through the magnetic field and generates electrical energy. It makes sense that we restrict our search for life forms we know to be possible while we are stuck with limited tools at our disposal. But I don't want us to overlook some amazing discoveries because we have put blinders on.
- learnstats2 6y ago
  It's reasonable to understand that 'life' here means 'we can meaningfully communicate across space with', since that is the intended purpose here. It seems almost infinitely more likely that we will be able to communicate with life that is like us. Even if that turns out not to be essential, it is a better starting place to spend your limited resources looking.
  - teknopaul 6y ago
    I think this very article disproves your hypothesis. Life like us is probably so far away and so short-lived that we will never be able to communicate. An intelligence that is near enough to reply & able to survive millions of years (so its lifespan crosses ours) might provide some results. If we start sending out signals and ask how long will it take for a reply? 17,000 years from something like us. Thats no use. Might be better to phone every star in the neighbourhood starting with the nearest, and see if anyone picks up.
    - Balgair 6y ago
      Our understanding of the universe and physics is still young. We're reasonably sure about 'normal' matter, things like you, a beer, or a star. Unfortunately, that's only about 5% of the universe that we know of today. Things like Dark Matter, well, we know it falls down. That's about it, really. There's a lot of theories about it though. More unfortunately, we think Dark Matter is about 20% of the universe. Then there's Dark Energy. It makes things fall up (?!). And we're not super sure about that, either. Most unfortunately, Dark Energy is about 75% of the universe. We don't have a clue if any intelligence is even using photons to communicate anymore. Most of the universe doesn't seem to really interact with them anyways. And that's with this limited understanding of 'Dark' things. We're still standing at the shore of a vast ocean.
- fennecfoxen 6y ago
  The start of life is basically a statistics game waiting for a system to spontaneously enter the right self-reproducing state, and it is relatively easy for a system combining water and various mostly-carbon-based molecules to enter into that state. We thus suppose that life looks like life on Earth because life on Earth has several properties which allowed it to come into existence. By contrast, there are no known states that cause a strong planetary electromagnetic field to rearrange copper into self-reproducing patterns: if anything, such electromagnetic fields are more likely to disrupt any spontaneous order that happens to arise. So it's true there may be other systems of life out there, but too much handwaving about that fact can obscure the fact that the other candidates for ordered systems arising from chaos are weak candidates. It would be unwise to rely on this wild speculation while trying to responsibly and conservatively estimate how much life there is.
lolc 6y ago
Habitable for who anyway? We shouldn't assume that life can only develop in the habitable (for us) zone. But we do anyway because we don't know anything else. Why would other sentient beings even want to communicate with those self-centered carbon-breathers? Why not just laugh about their hubris and that woefully incomplete definition of life? Telling them would spoil it!
- morganvachon 6y ago
  http://www.eastoftheweb.com/short-stories/UBooks/TheyMade.shtml http://www.eastoftheweb.com/short-stories/UBooks/TheyMade.sh...
rwmj 6y ago
> We have no clue how likely it was at Earth that life developed at all. Maybe it was just a chain of many lucky coincidences that happen once in 10 billion years. How is distribution any relevant then? Incidentally this is the "Rare Earth" hypothesis. There's a rather depressing book on this: https://www.amazon.co.uk/Rare-Earth-Complex-Uncommon-Universe/dp/0387952896 https://www.amazon.co.uk/Rare-Earth-Complex-Uncommon-Univers...
the8472 6y ago
Only providing averages is crazy given the huge variance of the underlying factors. https://arxiv.org/abs/1806.02404 https://arxiv.org/abs/1806.02404
zackees 6y ago
Dude - Mars billows out CO2 and methane during it's seasons, indicating that there is microbial life on that planet as well. The media has told us that life is rare and that WE ARE ALONE IN THE GALAXY. I saw it with my own eyes of Neil deGrasse Tyson explaining in an authoritative way that we as a human species have to accept that we are alone in this galaxy. Yet another lie pushed by the mainstream media. Also a glaring breakdown in logic to assert to a definitive negative, especially on the concept of life existing on one of the 100 billion or so star systems in the galaxy. They can't even get their story straight. The US military is already acknowledging UFO's and the POTUS has hinted that the truth is a really big deal. How many times will the story change and the goal posts be moved until we acknowledge that ET's have visited earth and have been for a very long time?
- hyperman1 6y ago
  At this point, i wouldn't believe the POTUS if he claimed it was raining, so you might want to remove that from your list of evidence.
- pharke 6y ago
  Personally, I think they are just overreacting to their excessive optimism about the prevalence of life in our solar system before any of the probe missions to Mars and Venus. If you read old astronomy books from that period they were full of speculation and hope that we would easily establish contact with other forms of life. They were burnt badly by the discovery that all other planets and moons in our solar system are much harsher environments than we initially expected and they received a lashing from the media after headlines full of starry eyed promises. It seems to be a similar effect to an AI winter where initial progress and optimism is met with challenges and limitations that turn fickle public opinion against the science, the researchers then internalize these beliefs or they become fringe pariahs. Thankfully some brave souls persevere and eventually prove the field isn't worthless after all.

bhaak 6y ago

With other assumptions, they would arrive at 0 intelligent civilisations in the galaxy. That would make the rest of the paper void. :-) Nobody knows how life is distributed in the galaxy. Assuming that we are not special (the Copernican Principle) is a valid prerequisite. As it neither can be proved or disproved, it's not unserious to just state what the unproven assumptions are.

dahfizz 6y ago

One thing that bothers me is that papers like this always assume alien life will look exactly like life on Earth. It must be the same distance from the sun as us, have water and proteins like us, etc. If we effectively limit the definition of "life" to "the types of organisms we see on Earth", then of course we will never find life anywhere else. Maybe there are aliens that live on a gas giant and they "eat" the lighting rather than food, and their bodies look more like circuitry than the chemical life on Earth. Maybe there is a planet with a very strong magnetic field, and the life there is kind of like an electromagnet. They have bodies high in copper and the current of the ocean moves them through the magnetic field and generates electrical energy. It makes sense that we restrict our search for life forms we know to be possible while we are stuck with limited tools at our disposal. But I don't want us to overlook some amazing discoveries because we have put blinders on.

learnstats2 6y ago
It's reasonable to understand that 'life' here means 'we can meaningfully communicate across space with', since that is the intended purpose here. It seems almost infinitely more likely that we will be able to communicate with life that is like us. Even if that turns out not to be essential, it is a better starting place to spend your limited resources looking.
- teknopaul 6y ago
  I think this very article disproves your hypothesis. Life like us is probably so far away and so short-lived that we will never be able to communicate. An intelligence that is near enough to reply & able to survive millions of years (so its lifespan crosses ours) might provide some results. If we start sending out signals and ask how long will it take for a reply? 17,000 years from something like us. Thats no use. Might be better to phone every star in the neighbourhood starting with the nearest, and see if anyone picks up.
  - Balgair 6y ago
    Our understanding of the universe and physics is still young. We're reasonably sure about 'normal' matter, things like you, a beer, or a star. Unfortunately, that's only about 5% of the universe that we know of today. Things like Dark Matter, well, we know it falls down. That's about it, really. There's a lot of theories about it though. More unfortunately, we think Dark Matter is about 20% of the universe. Then there's Dark Energy. It makes things fall up (?!). And we're not super sure about that, either. Most unfortunately, Dark Energy is about 75% of the universe. We don't have a clue if any intelligence is even using photons to communicate anymore. Most of the universe doesn't seem to really interact with them anyways. And that's with this limited understanding of 'Dark' things. We're still standing at the shore of a vast ocean.
fennecfoxen 6y ago
The start of life is basically a statistics game waiting for a system to spontaneously enter the right self-reproducing state, and it is relatively easy for a system combining water and various mostly-carbon-based molecules to enter into that state. We thus suppose that life looks like life on Earth because life on Earth has several properties which allowed it to come into existence. By contrast, there are no known states that cause a strong planetary electromagnetic field to rearrange copper into self-reproducing patterns: if anything, such electromagnetic fields are more likely to disrupt any spontaneous order that happens to arise. So it's true there may be other systems of life out there, but too much handwaving about that fact can obscure the fact that the other candidates for ordered systems arising from chaos are weak candidates. It would be unwise to rely on this wild speculation while trying to responsibly and conservatively estimate how much life there is.

lolc 6y ago

Habitable for who anyway? We shouldn't assume that life can only develop in the habitable (for us) zone. But we do anyway because we don't know anything else. Why would other sentient beings even want to communicate with those self-centered carbon-breathers? Why not just laugh about their hubris and that woefully incomplete definition of life? Telling them would spoil it!

morganvachon 6y ago
http://www.eastoftheweb.com/short-stories/UBooks/TheyMade.shtml http://www.eastoftheweb.com/short-stories/UBooks/TheyMade.sh...

rwmj 6y ago

> We have no clue how likely it was at Earth that life developed at all. Maybe it was just a chain of many lucky coincidences that happen once in 10 billion years. How is distribution any relevant then? Incidentally this is the "Rare Earth" hypothesis. There's a rather depressing book on this: https://www.amazon.co.uk/Rare-Earth-Complex-Uncommon-Universe/dp/0387952896 https://www.amazon.co.uk/Rare-Earth-Complex-Uncommon-Univers...

the8472 6y ago

Only providing averages is crazy given the huge variance of the underlying factors. https://arxiv.org/abs/1806.02404 https://arxiv.org/abs/1806.02404

zackees 6y ago

Dude - Mars billows out CO2 and methane during it's seasons, indicating that there is microbial life on that planet as well. The media has told us that life is rare and that WE ARE ALONE IN THE GALAXY. I saw it with my own eyes of Neil deGrasse Tyson explaining in an authoritative way that we as a human species have to accept that we are alone in this galaxy. Yet another lie pushed by the mainstream media. Also a glaring breakdown in logic to assert to a definitive negative, especially on the concept of life existing on one of the 100 billion or so star systems in the galaxy. They can't even get their story straight. The US military is already acknowledging UFO's and the POTUS has hinted that the truth is a really big deal. How many times will the story change and the goal posts be moved until we acknowledge that ET's have visited earth and have been for a very long time?

hyperman1 6y ago
At this point, i wouldn't believe the POTUS if he claimed it was raining, so you might want to remove that from your list of evidence.
pharke 6y ago
Personally, I think they are just overreacting to their excessive optimism about the prevalence of life in our solar system before any of the probe missions to Mars and Venus. If you read old astronomy books from that period they were full of speculation and hope that we would easily establish contact with other forms of life. They were burnt badly by the discovery that all other planets and moons in our solar system are much harsher environments than we initially expected and they received a lashing from the media after headlines full of starry eyed promises. It seems to be a similar effect to an AI winter where initial progress and optimism is met with challenges and limitations that turn fickle public opinion against the science, the researchers then internalize these beliefs or they become fringe pariahs. Thankfully some brave souls persevere and eventually prove the field isn't worthless after all.