4 ms·

While we're speculating, allow me to throw my 2 cents in. The biochemistry of life is likely to be common, the conditions for complex or even intelligent tool

by lumost 4y ago

While we're speculating, allow me to throw my 2 cents in. The biochemistry of life is likely to be common, the conditions for complex or even intelligent tool using life are likely to be rare. To have an earth, you need to have a moon comparable in mass to the planet to avoid atmospheric stripping. A temperature regime stable enough to support long term life development between 0 and 100 C. A star that doesn't blasttge planet in radiation every few thousand years. Along with a reasonable balance of materials, and a stellar neighborhood which wont swing the balance too badly every few million years. Lastly, although untested, To have tool use, you likely need a planet with gravity thats strong enough for the atmosphere to be stable, but weak enough for organic molecules to hold together complex life and enable the construction of material objects. A super earth covered in algae is interesting, but may not be capable of traditional human intelligence.

EForEndeavour 4y ago
> To have an earth, you need to have a moon comparable in mass to the planet to avoid atmospheric stripping. Could you elaborate on this? I'm aware that magnetospheres protect atmospheres from solar wind stripping (e.g., https://science.nasa.gov/science-news/news-articles/earths-magnetosphere https://science.nasa.gov/science-news/news-articles/earths-m...), but have never heard of the role of moons, and can't find anything via Google right now.
pasabagi 4y ago
My preferred speculation is simply that faster-than-light travel is impossible, so all the tool-using aliens out there are not visiting us because they can't, and we can't hear their signals because it gets lost against the background noise. I mean, would we be able to detect our own civilization from a few lightyears out? Apparently, unless you're pointing a radio telescope right at something, you woudn't be able to pick up human civilization levels of radio from more than a lightyear out. Say there's one smart tool-using civilization per 5000 lightyear volume, then they're unlikely to meet.
- spfzero 4y ago
  Even if a civilization out there had faster-than-light travel, they would most likely not know we were here. They would need to decide to come explore near us, probably need to expensively slow down to sub-light speeds to look for signs of life near here and pick up our emissions on some old archaic piece of equipment they happened to bring along. Would a much more advanced civilization spend their exploration budget to look over uninteresting primitives like us, or would they go off in search of other more advanced civilizations like their own?
corrral 4y ago
You also need plate tectonics. And exactly the right level of stellar radiation for the carbonate-silicate cycle to work, if you want photosynthesis, and without that you likely won't have anywhere near enough energy available for complex life. Get any of it wrong and life either won't develop, or will wreck its own biosphere in an unrecoverable way very early on and get wiped out (if there was ever life on Mars, that's my bet for why traces of it are elusive—it wasn't around very long, wasn't very complex, and it was a very long time ago).
- lordnacho 4y ago
  Can you elaborate? What's the reason it wouldn't work if all the plates were frozen?
  - corrral 4y ago
    Maybe not strictly necessary for any life, but the broad principal is that any process that recycles material is going to be really helpful to life, with big bonus points for it working in a dynamic fashion so it tends to self-stabilize—plate tectonics don't have that quality, but other processes do, like any chemical process where the concentration affects the rate at which the process occurs, or how our climate tends to find stable points rather than having runaway freezing or runaway heating. In the Earth's case, vulcanism is critical to balancing atmospheric CO2 levels. Over time (not on human timescales) carbon tends to get trapped in ways that make it unavailable to life, so you need something to undo that, and that's a major mechanism for it. Life may be (probably is) possible without some elements of what makes life work on Earth, but with the wrong environment may destroy itself relatively quickly (as life on Earth nearly did, during the oxygenation crisis) or fail to capture enough energy for the development of complex life (think: a planet where the only energy available to life comes from a few undersea vents, photosynthesis being impossible for any of several reasons). For this reason, a planet being in the "Goldilocks zone" around its host star is just the bare minimum required for widespread, complex life. The planet itself must also be more-or-less the right size, and must have the right composition of surface and atmosphere and various processes occurring (geological and otherwise) to keep those in balance, and so on. It's possible there are certain very hardy chemistries possible for life that we simply don't see on Earth because they're easily outcompeted by what we've already got, but those pretty much by definition won't provide as much energy to the host body's biosphere, so complex life is less likely. It's also possible there are planets far more amenable to life than Earth (though perhaps wholly incompatible with Earth-like life), with unknown-to-us chemistries that are only viable in that kind of even-better environment.
noasaservice 4y ago
But you're assuming that life must contain good quantities of water, and in all 3 phases on the planet. Silicon life could definitely be a thing.. However silicon bonds are a lot lower energy than carbon bonds are, for most substances. (I would argue that oxygen would be toxic to silicon based beings, due to Si-O.). So, I'd theorize that silicon based living beings would have to be in an atmosphere of, say, methane. And the phasegraph of methane ( https://www.engineeringtoolbox.com/methane-d_1420.html https://www.engineeringtoolbox.com/methane-d_1420.html ) would seem to show that -175c and around there would be ideal temps for silicon life. However, if we're exclusively only looking for carbon/oxygen/water based lifeforms, then I think the 0-100c is a reasonable assumption.
- lordnacho 4y ago
  Don't you need carbon because the C-C bonds won't be disrupted by O2? I read that somewhere iirc in Larry Gonick's cartoon about chemistry.
  - scrumbledober 4y ago
    can't be disrupted by O2 if there's no O2 in your environment
cletus 4y ago
The law of large numbers comes into play here. There are at least 100B stars in our galaxy. Over the last 20+ years we've gained a lot data on exoplanets. Exoplanetary systems seem to be really common. So stability, the right elements, etc no doubt all play a role but we may be talking over WWhata trillion planetary bodies (including large moons). What's more, our understanding of where live can evolve, survive and thrive has greatly expanded in recent decades and now includes volcanic vents on the ocean floor, for example. So yes a lot of things have to go right but we're rolling an awful lot of dice.
- lumost 4y ago
  Yes, but the fermi paradox focuses on intelligent life. Even if there are ~10 trillion of possible planets in the galaxy for intelligent life to evolve on, that is only 10^14th power. If each of the circumstances described above is a 1 in 100 event, then that leaves only 10^5 habitable planets for intelligent life to evolve across the entire galaxy. If you then consider that there is a 5 in 4.5 billion chance that such a planet currently has an intelligent life form on it, then it's quite possible that there are no other intelligent life forms in the galaxy. However there may be millions or billions of planets with evolved forms of algae. Now, I do not believe that these are uncorrelated probabilities - and as such I'd place the odds quite a bit higher. But the more we learn about planetary physics, the more unique earth appears to be. Meanwhile, it appears that the biochemistry of life is incredibly common.
- AareyBaba 4y ago
  "but we're rolling an awful lot of dice." but are the odds better than 2^256 ? https://youtu.be/S9JGmA5_unY?t=38 https://youtu.be/S9JGmA5_unY?t=38

by lumost 4y ago

EForEndeavour 4y ago

> To have an earth, you need to have a moon comparable in mass to the planet to avoid atmospheric stripping. Could you elaborate on this? I'm aware that magnetospheres protect atmospheres from solar wind stripping (e.g., https://science.nasa.gov/science-news/news-articles/earths-magnetosphere https://science.nasa.gov/science-news/news-articles/earths-m...), but have never heard of the role of moons, and can't find anything via Google right now.

pasabagi 4y ago

My preferred speculation is simply that faster-than-light travel is impossible, so all the tool-using aliens out there are not visiting us because they can't, and we can't hear their signals because it gets lost against the background noise. I mean, would we be able to detect our own civilization from a few lightyears out? Apparently, unless you're pointing a radio telescope right at something, you woudn't be able to pick up human civilization levels of radio from more than a lightyear out. Say there's one smart tool-using civilization per 5000 lightyear volume, then they're unlikely to meet.

spfzero 4y ago
Even if a civilization out there had faster-than-light travel, they would most likely not know we were here. They would need to decide to come explore near us, probably need to expensively slow down to sub-light speeds to look for signs of life near here and pick up our emissions on some old archaic piece of equipment they happened to bring along. Would a much more advanced civilization spend their exploration budget to look over uninteresting primitives like us, or would they go off in search of other more advanced civilizations like their own?

corrral 4y ago

You also need plate tectonics. And exactly the right level of stellar radiation for the carbonate-silicate cycle to work, if you want photosynthesis, and without that you likely won't have anywhere near enough energy available for complex life. Get any of it wrong and life either won't develop, or will wreck its own biosphere in an unrecoverable way very early on and get wiped out (if there was ever life on Mars, that's my bet for why traces of it are elusive—it wasn't around very long, wasn't very complex, and it was a very long time ago).

lordnacho 4y ago
Can you elaborate? What's the reason it wouldn't work if all the plates were frozen?
- corrral 4y ago
  Maybe not strictly necessary for any life, but the broad principal is that any process that recycles material is going to be really helpful to life, with big bonus points for it working in a dynamic fashion so it tends to self-stabilize—plate tectonics don't have that quality, but other processes do, like any chemical process where the concentration affects the rate at which the process occurs, or how our climate tends to find stable points rather than having runaway freezing or runaway heating. In the Earth's case, vulcanism is critical to balancing atmospheric CO2 levels. Over time (not on human timescales) carbon tends to get trapped in ways that make it unavailable to life, so you need something to undo that, and that's a major mechanism for it. Life may be (probably is) possible without some elements of what makes life work on Earth, but with the wrong environment may destroy itself relatively quickly (as life on Earth nearly did, during the oxygenation crisis) or fail to capture enough energy for the development of complex life (think: a planet where the only energy available to life comes from a few undersea vents, photosynthesis being impossible for any of several reasons). For this reason, a planet being in the "Goldilocks zone" around its host star is just the bare minimum required for widespread, complex life. The planet itself must also be more-or-less the right size, and must have the right composition of surface and atmosphere and various processes occurring (geological and otherwise) to keep those in balance, and so on. It's possible there are certain very hardy chemistries possible for life that we simply don't see on Earth because they're easily outcompeted by what we've already got, but those pretty much by definition won't provide as much energy to the host body's biosphere, so complex life is less likely. It's also possible there are planets far more amenable to life than Earth (though perhaps wholly incompatible with Earth-like life), with unknown-to-us chemistries that are only viable in that kind of even-better environment.

noasaservice 4y ago

But you're assuming that life must contain good quantities of water, and in all 3 phases on the planet. Silicon life could definitely be a thing.. However silicon bonds are a lot lower energy than carbon bonds are, for most substances. (I would argue that oxygen would be toxic to silicon based beings, due to Si-O.). So, I'd theorize that silicon based living beings would have to be in an atmosphere of, say, methane. And the phasegraph of methane ( https://www.engineeringtoolbox.com/methane-d_1420.html https://www.engineeringtoolbox.com/methane-d_1420.html ) would seem to show that -175c and around there would be ideal temps for silicon life. However, if we're exclusively only looking for carbon/oxygen/water based lifeforms, then I think the 0-100c is a reasonable assumption.

lordnacho 4y ago
Don't you need carbon because the C-C bonds won't be disrupted by O2? I read that somewhere iirc in Larry Gonick's cartoon about chemistry.
- scrumbledober 4y ago
  can't be disrupted by O2 if there's no O2 in your environment

cletus 4y ago

The law of large numbers comes into play here. There are at least 100B stars in our galaxy. Over the last 20+ years we've gained a lot data on exoplanets. Exoplanetary systems seem to be really common. So stability, the right elements, etc no doubt all play a role but we may be talking over WWhata trillion planetary bodies (including large moons). What's more, our understanding of where live can evolve, survive and thrive has greatly expanded in recent decades and now includes volcanic vents on the ocean floor, for example. So yes a lot of things have to go right but we're rolling an awful lot of dice.

lumost 4y ago
Yes, but the fermi paradox focuses on intelligent life. Even if there are ~10 trillion of possible planets in the galaxy for intelligent life to evolve on, that is only 10^14th power. If each of the circumstances described above is a 1 in 100 event, then that leaves only 10^5 habitable planets for intelligent life to evolve across the entire galaxy. If you then consider that there is a 5 in 4.5 billion chance that such a planet currently has an intelligent life form on it, then it's quite possible that there are no other intelligent life forms in the galaxy. However there may be millions or billions of planets with evolved forms of algae. Now, I do not believe that these are uncorrelated probabilities - and as such I'd place the odds quite a bit higher. But the more we learn about planetary physics, the more unique earth appears to be. Meanwhile, it appears that the biochemistry of life is incredibly common.
AareyBaba 4y ago
"but we're rolling an awful lot of dice." but are the odds better than 2^256 ? https://youtu.be/S9JGmA5_unY?t=38 https://youtu.be/S9JGmA5_unY?t=38