4 ms·

> This seems very inefficient due to the high energy cost and the long timescales in the proposal. This is efficient for what the paper is about: A solution to

> This seems very inefficient due to the high energy cost and the long timescales in the proposal. This is efficient for what the paper is about: A solution to the sun's gradual evolution towards a red giant. So long timescale is not a problem, since we have 1B year before the sun becomes too hot for where we are today, and 5B years before being engulfed by it. Space sunshades works well to reduce incoming radiations by a few % (e.g. for current climate change problem), it won't work so well when the earth will be within the sun's corona.

LorenPechtel 5y ago
No--we have nowhere near a billion years. It's roughly a billion until all life is wiped from the planet, but it will be uninhabitable for humans *long* before that point. We have only 50 million years before Earth's ability to adapt to solar warming pegs and the temperature starts crawling up--and note that even that will not be good for an awful lot of plant life because of low CO2 levels. Earth needs to start it's retreat before then.
- nextaccountic 5y ago
  > We have only 50 million years before Earth's ability to adapt to solar warming pegs and the temperature starts crawling up This sounds like an oddly small estimate. Life has been around 3.5 billions of years and has passed through multiple extinction events. It would be a puzzling coincidence that human civilization appears and then we have only some tens of million years to avert catastrophe.
  - kadoban 5y ago
    Doesn't necessarily sound like a bad estimate just based on approximate frequency of other extinction events. What they're describing doesn't necessarily sound like the end of life on Earth, only the end of life as we know it. I'm not following what the mechanism is supposed to be though.
    - LorenPechtel 5y ago
      Mechanism: To keep the Earth cool the greenhouse effect needs to be turned down. That happens by CO2 being absorbed by water and turning into limestone. This is countered by limestone weathering and limestone getting sucked into volcanoes.
  - LorenPechtel 5y ago
    Over the eons the sun has grown warmer and Earth's CO2 levels have dropped, keeping the overall temperature pretty much stable. (There have been fluctuations in both directions that were major extinction events, though.) Warming increases the rate CO2 gets converted into limestone, thus lowering the temperature. 50 million years is when that pegs and the mercury starts rising. As for it being a puzzling coincidence--it might not be a coincidence at all. Think of the Fermi Paradox--where are the aliens? These days the astronomers tell us planets are very common. A look at the emergence of life on Earth says it happened about as fast as possible. Why are we alone? Enter the Great Filter hypothesis--*something* stops species from colonizing the galaxy. Looking at what has happened on Earth there are only three likely candidates: 1) The jump to multicellular life. It took billions of years. One data point isn't enough to determine an average but we can see it's not something that happens easily. 2) The emergence of intelligence. Same situation, again. 3) The lifespan of intelligent civilizations. The odds of successfully crossing these three hurdles must be billions to one. Either intelligent races destroy themselves before reaching the stars or the billions to one odds are in the first two hurdles. The most favorable interpretation for humanity is that the average time to cross those hurdles is well beyond the couple of billion years it took Earth, most planets fail to produce intelligence before their ecosystem gets fried or smacked with something substantially larger than the dinosaur killer. If this is the answer it's no surprise we squeaked in just under the wire. And if that's not the answer humanity isn't going to be around for too much longer.

LorenPechtel 5y ago

No--we have nowhere near a billion years. It's roughly a billion until all life is wiped from the planet, but it will be uninhabitable for humans *long* before that point. We have only 50 million years before Earth's ability to adapt to solar warming pegs and the temperature starts crawling up--and note that even that will not be good for an awful lot of plant life because of low CO2 levels. Earth needs to start it's retreat before then.

nextaccountic 5y ago
> We have only 50 million years before Earth's ability to adapt to solar warming pegs and the temperature starts crawling up This sounds like an oddly small estimate. Life has been around 3.5 billions of years and has passed through multiple extinction events. It would be a puzzling coincidence that human civilization appears and then we have only some tens of million years to avert catastrophe.
- kadoban 5y ago
  Doesn't necessarily sound like a bad estimate just based on approximate frequency of other extinction events. What they're describing doesn't necessarily sound like the end of life on Earth, only the end of life as we know it. I'm not following what the mechanism is supposed to be though.
  - LorenPechtel 5y ago
    Mechanism: To keep the Earth cool the greenhouse effect needs to be turned down. That happens by CO2 being absorbed by water and turning into limestone. This is countered by limestone weathering and limestone getting sucked into volcanoes.
- LorenPechtel 5y ago
  Over the eons the sun has grown warmer and Earth's CO2 levels have dropped, keeping the overall temperature pretty much stable. (There have been fluctuations in both directions that were major extinction events, though.) Warming increases the rate CO2 gets converted into limestone, thus lowering the temperature. 50 million years is when that pegs and the mercury starts rising. As for it being a puzzling coincidence--it might not be a coincidence at all. Think of the Fermi Paradox--where are the aliens? These days the astronomers tell us planets are very common. A look at the emergence of life on Earth says it happened about as fast as possible. Why are we alone? Enter the Great Filter hypothesis--*something* stops species from colonizing the galaxy. Looking at what has happened on Earth there are only three likely candidates: 1) The jump to multicellular life. It took billions of years. One data point isn't enough to determine an average but we can see it's not something that happens easily. 2) The emergence of intelligence. Same situation, again. 3) The lifespan of intelligent civilizations. The odds of successfully crossing these three hurdles must be billions to one. Either intelligent races destroy themselves before reaching the stars or the billions to one odds are in the first two hurdles. The most favorable interpretation for humanity is that the average time to cross those hurdles is well beyond the couple of billion years it took Earth, most planets fail to produce intelligence before their ecosystem gets fried or smacked with something substantially larger than the dinosaur killer. If this is the answer it's no surprise we squeaked in just under the wire. And if that's not the answer humanity isn't going to be around for too much longer.