I’ve said before that we have pretty good evidence for off-Earth bacteria life, suggesting that such life is common in the nearby universe. However, bacterial life might be common, yet complex multi-cellular life very rare. Here’s a plausible detailed theory about why:
If this analysis is correct, the likelihood of life on Mars now is pretty high. Mars has had a habitable zone for 4.5 billion years. If there is a 10% chance of life developing every 200 million years (the way it did on Earth), then the likelihood of life on Mars is about 1- (1-0.1)^(4.5/0.2) = 90%.
You, however, claimed that it was a "plausible" explanation for complex life being "very rare." If such endosymbiosis happens multiple times (and perhaps even more often in lineages that have since gone extinct, perhaps losing to the ancestors of today's eukaryotes) then the base rate for mitochondria formation looks much too high to explain very much of the Great Filter.
He didn't claim that was the only embedding. A fuller quote is:"These huge genomes provided the genetic raw material that led to the evolution of complex life. Mitochondria did not prescribe complexity, but they permitted it. It's hard to imagine any other way of getting around the energy problem - and we know it happened just once on Earth because all eukaryotes descend from a common ancestor."
We can make estimates about how easy it is for life to evolve by looking at how long it took for life to evolve on Earth.
Prokaryotes evolved just about as soon as the Earth cooled below the boiling point, a few hundred million years. Eukaryotes evolved just about as soon as the Earth had an atmosphere containing more than a few percent O2. If we consider the appearance of life to be stochastic and depend upon the volume of suitable habitat and the length of time that the habitat exists.
For an Earth surface area times a biosphere depth (couple km) and 0.2 billion years, even if we assign a 10% likelihood, the chances of life emerging on another planet in 2 billion years becomes quite high (1- (1-0.1)^10 = ~65%). If this calculation is correct, then the likelihood of bacterial life on Mars is pretty high. There is still a very large habitable zone on Mars, beneath the surface where it is warm enough for liquid water to circulate but not so hot that proteins can't form. The volume of habitable zone on Mars might even be larger than the volume on Earth because Mars is cooler. Mars cooled faster, and probably did not experience the kind of complete melting that happened during moon formation.
Eukarites developed on Earth so we know that it's not impossible, however improbable.
Planets are not rare. The building blocks of life are not rare. They've had billions of years to interact and evolve.
It seems unimaginably unlikely that any naturally occurring mix of chemicals and conditions occurred exactly once on exactly one planet over the life of the universe. (Hey! If I stop here, I could be a creationist!)
I'm not saying it's common - I'm saying a Eukarite barrier is unlikely to be the reason we haven't heard from aliens. It's far more likely that mass extinction events and the vast distances involved have made it physically impossible or at least very difficult for aliens to contact us.
We are still using chemical rockets, even though we already know how to make vastly more powerful nuclear rockets.
This claim is too bold.NASA conducted preliminary experiments on nuclear rockets, then politicians lost interest and the project was abandoned. Initial results were encouraging, but this still remains a speculative and largely unproven technology.
Sailboats were the "mature" ocean travel tech for a long time, until they weren't and vastly more powerful motor-tech came a long.
Yes, but this required harnessing a new energy source. Maybe they'll invent a fusion-antimatter-green rocks engine in the future, but I'm not holding my breath.
You just seem to have a provincial belief that we are near the peak tech. level for space travel.
Calling a belief "provincial" doesn't diminish its likelihood.
And yes, future probes will be vastly faster. We currently aren't even using the fission rockets engines we already know how to build.
According to Wikipedia ( http://en.wikipedia.org/wik... ) the nuclear rocket design NASA was working on was expected to yield relatively moderate (same order of magnitude) performance improvements with respect to the Saturn V.
V V: We are still using chemical rockets, even though we already know how to make vastly more powerful nuclear rockets. We've plateaued where we are in space travel for the time being, but that is not unusual even when there is great progress to be made. Sailboats were the "mature" ocean travel tech for a long time, until they weren't and vastly more powerful motor-tech came a long.
You just seem to have a provincial belief that we are near the peak tech. level for space travel. There is no real justification for this. And yes, future probes will be vastly faster. We currently aren't even using the fission rockets engines we already know how to build.
reproducing probes powered by nuclear engines should definitely be viable.
That's dubious. A probe would need to function continuously for thousands of years during the transit between one star and another, periodically performing course correction (hence expending energy and reaction mass), in an environment with cosmic rays and ablative interstellar dust.While most stars are hypothesised to have planets, they might not have easly retrievable uranium and thorium.
Even our feeble technology circa the 1970s was able to build the voyager probe currently on the edge of the solar system.
The Voyager 1 will stop working in a few years or decades at most, then it will just drift away. It's not going anywhere.
Technology centuries hence will certainly be able to reach other star systems with some form of reproducing entity.
Technology is not magic.A few centuries from now, they will possibly have discovered the "theory of everything", and solved various current open problems, but with high probability, most of their physics, in particular the physics relevant to space travel, will be pretty much the same as our physics.
Our space technology quickly reached maturity in just a few decades, how much room for improvement might there be? We don't expect future probes to be orders of magnitude faster or more energy efficient than the current ones.
There might be significant improvements in automation technology, but in a barren, hostile environment with extremely diluited resources, even being super-smart and flexible isn't going to help you very much.
It so happens that the way human brain works, the correctness requires more scepticism (especially towards one's own conclusions), not less, but the rationalism is the belief in the greater power of reason than customarily assumed, and calls for less scepticism towards 'reason'; the reason unfortunately being largely subjective in any topics that are too big to be tractable. Consequently the tendency towards such failure mode.
When you read atrociously bad biological article and it asserts that something only happens once, you can't subject this to scrutiny unless you already know it happened more than once; internally you can't evaluate it's validity, but it feels intuitively that you can as you often evaluate validity of less bad articles that very rarely get their assertions wrong, and which can be evaluated on the purely logical merits alone, without having to put the assertions to scrutiny.
Interstellar travel is certainly not technologically impossible. It is extremely unlikely to be viable for complex organisms a la "Star Trek", but reproducing probes powered by nuclear engines should definitely be viable. Even our feeble technology circa the 1970s was able to build the voyager probe currently on the edge of the solar system. Technology centuries hence will certainly be able to reach other star systems with some form of reproducing entity.
> It took us billions of years to get where we are today. Given the length of this time frame and the number of planets in the universe, you would expect that our improbable eukaryotic fluke to happen over and over and over again.
Complex life is in fact highly probable. Once the environment at a particular level is filled, the only way, in a real sense, is "up," as in up in complexity. Evolution drives complexity.
We have good reasons to hypothesise that interstellar travel is essentially technologically impossible, or at least uneconomical, for pretty much any type of civilization we can imagine.So we don't expect direct contact.
Remote detection is impossible with our current detection technology, unless the aliens happened to be on a close star (something we can already rule out, IIUC) or used a technology that radiated many orders of magnitude more power than ours. Similarly, aliens with a detection technology similar to ours, wouldn't be able to detect us.
Detection technology can improve with time, but there are physical limits.
If this analysis is correct, the likelihood of life on Mars now is pretty high. Mars has had a habitable zone for 4.5 billion years. If there is a 10% chance of life developing every 200 million years (the way it did on Earth), then the likelihood of life on Mars is about 1- (1-0.1)^(4.5/0.2) = 90%.
It seems to be a certain sort of embedding that he claims is rare. This isn't my theory it is his - read him for more details.
You, however, claimed that it was a "plausible" explanation for complex life being "very rare." If such endosymbiosis happens multiple times (and perhaps even more often in lineages that have since gone extinct, perhaps losing to the ancestors of today's eukaryotes) then the base rate for mitochondria formation looks much too high to explain very much of the Great Filter.
I read the article itself, and found it reasonable. As TGGP indicates, the wikipedia article contains no substantive criticisms.
He didn't claim that was the only embedding. A fuller quote is:"These huge genomes provided the genetic raw material that led to the evolution of complex life. Mitochondria did not prescribe complexity, but they permitted it. It's hard to imagine any other way of getting around the energy problem - and we know it happened just once on Earth because all eukaryotes descend from a common ancestor."
We can make estimates about how easy it is for life to evolve by looking at how long it took for life to evolve on Earth.
Prokaryotes evolved just about as soon as the Earth cooled below the boiling point, a few hundred million years. Eukaryotes evolved just about as soon as the Earth had an atmosphere containing more than a few percent O2. If we consider the appearance of life to be stochastic and depend upon the volume of suitable habitat and the length of time that the habitat exists.
For an Earth surface area times a biosphere depth (couple km) and 0.2 billion years, even if we assign a 10% likelihood, the chances of life emerging on another planet in 2 billion years becomes quite high (1- (1-0.1)^10 = ~65%). If this calculation is correct, then the likelihood of bacterial life on Mars is pretty high. There is still a very large habitable zone on Mars, beneath the surface where it is warm enough for liquid water to circulate but not so hot that proteins can't form. The volume of habitable zone on Mars might even be larger than the volume on Earth because Mars is cooler. Mars cooled faster, and probably did not experience the kind of complete melting that happened during moon formation.
Eukarites developed on Earth so we know that it's not impossible, however improbable.
Planets are not rare. The building blocks of life are not rare. They've had billions of years to interact and evolve.
It seems unimaginably unlikely that any naturally occurring mix of chemicals and conditions occurred exactly once on exactly one planet over the life of the universe. (Hey! If I stop here, I could be a creationist!)
I'm not saying it's common - I'm saying a Eukarite barrier is unlikely to be the reason we haven't heard from aliens. It's far more likely that mass extinction events and the vast distances involved have made it physically impossible or at least very difficult for aliens to contact us.
We are still using chemical rockets, even though we already know how to make vastly more powerful nuclear rockets.
This claim is too bold.NASA conducted preliminary experiments on nuclear rockets, then politicians lost interest and the project was abandoned. Initial results were encouraging, but this still remains a speculative and largely unproven technology.
Sailboats were the "mature" ocean travel tech for a long time, until they weren't and vastly more powerful motor-tech came a long.
Yes, but this required harnessing a new energy source. Maybe they'll invent a fusion-antimatter-green rocks engine in the future, but I'm not holding my breath.
You just seem to have a provincial belief that we are near the peak tech. level for space travel.
Calling a belief "provincial" doesn't diminish its likelihood.
And yes, future probes will be vastly faster. We currently aren't even using the fission rockets engines we already know how to build.
According to Wikipedia ( http://en.wikipedia.org/wik... ) the nuclear rocket design NASA was working on was expected to yield relatively moderate (same order of magnitude) performance improvements with respect to the Saturn V.
V V: We are still using chemical rockets, even though we already know how to make vastly more powerful nuclear rockets. We've plateaued where we are in space travel for the time being, but that is not unusual even when there is great progress to be made. Sailboats were the "mature" ocean travel tech for a long time, until they weren't and vastly more powerful motor-tech came a long.
You just seem to have a provincial belief that we are near the peak tech. level for space travel. There is no real justification for this. And yes, future probes will be vastly faster. We currently aren't even using the fission rockets engines we already know how to build.
reproducing probes powered by nuclear engines should definitely be viable.
That's dubious. A probe would need to function continuously for thousands of years during the transit between one star and another, periodically performing course correction (hence expending energy and reaction mass), in an environment with cosmic rays and ablative interstellar dust.While most stars are hypothesised to have planets, they might not have easly retrievable uranium and thorium.
Even our feeble technology circa the 1970s was able to build the voyager probe currently on the edge of the solar system.
The Voyager 1 will stop working in a few years or decades at most, then it will just drift away. It's not going anywhere.
Technology centuries hence will certainly be able to reach other star systems with some form of reproducing entity.
Technology is not magic.A few centuries from now, they will possibly have discovered the "theory of everything", and solved various current open problems, but with high probability, most of their physics, in particular the physics relevant to space travel, will be pretty much the same as our physics.
Our space technology quickly reached maturity in just a few decades, how much room for improvement might there be? We don't expect future probes to be orders of magnitude faster or more energy efficient than the current ones.
There might be significant improvements in automation technology, but in a barren, hostile environment with extremely diluited resources, even being super-smart and flexible isn't going to help you very much.
It so happens that the way human brain works, the correctness requires more scepticism (especially towards one's own conclusions), not less, but the rationalism is the belief in the greater power of reason than customarily assumed, and calls for less scepticism towards 'reason'; the reason unfortunately being largely subjective in any topics that are too big to be tractable. Consequently the tendency towards such failure mode.
When you read atrociously bad biological article and it asserts that something only happens once, you can't subject this to scrutiny unless you already know it happened more than once; internally you can't evaluate it's validity, but it feels intuitively that you can as you often evaluate validity of less bad articles that very rarely get their assertions wrong, and which can be evaluated on the purely logical merits alone, without having to put the assertions to scrutiny.
Interstellar travel is certainly not technologically impossible. It is extremely unlikely to be viable for complex organisms a la "Star Trek", but reproducing probes powered by nuclear engines should definitely be viable. Even our feeble technology circa the 1970s was able to build the voyager probe currently on the edge of the solar system. Technology centuries hence will certainly be able to reach other star systems with some form of reproducing entity.
That's nonsensical.
> It took us billions of years to get where we are today. Given the length of this time frame and the number of planets in the universe, you would expect that our improbable eukaryotic fluke to happen over and over and over again.
Nope, does not follow.
Complex life is in fact highly probable. Once the environment at a particular level is filled, the only way, in a real sense, is "up," as in up in complexity. Evolution drives complexity.
We have good reasons to hypothesise that interstellar travel is essentially technologically impossible, or at least uneconomical, for pretty much any type of civilization we can imagine.So we don't expect direct contact.
Remote detection is impossible with our current detection technology, unless the aliens happened to be on a close star (something we can already rule out, IIUC) or used a technology that radiated many orders of magnitude more power than ours. Similarly, aliens with a detection technology similar to ours, wouldn't be able to detect us.
Detection technology can improve with time, but there are physical limits.