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Quoted: I’m fixated on debunking any attempts to quantify it because that requires assumptions we don’t have data/information to make. View Quote A host of long dead philosophers and an army of dead and living physicists, astronomers and mathematicians, all who are lightyears smarter than you or I have long since debunked your positions as, well basic fallacies. But you keep on keeping on my friend! |
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Quoted: Aaaand... 6,000 years M I rite??? Yes... I'm sure that out of the number of stars in our observable universe, we're all alone. Because a loving, omnipotent God would piss around with all of that was ted space and creation. Like I'd pull out an extra-large pizza pan to eat my scrambled eggs from.x View Quote Huh? 6000 years to do what? |
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Quoted: I'm going to have to disagree with you on everything except your ultimate conclusion. We're just starting to get a handle on two factors of the equation, and we cannot be certain of our accuracy. However, at present it appears that about one-third of the stars have planets. The accuracy of this limited by our ability to observe both in distance, and resolution. We're also looking at the idea that only planets within the Goldilocks zone can support life. We've only ever seen life within that zone based on our sample size of one, and that has been defined as places that have liquid water. Of those exo-planets that have been discovered, they're assigning possibilities that they're in the Goldilocks zone based on star characteristics and planet distance from the star. Of course, our ability to define the Goldilocks zone is limited to our knowledge, so who knows how accurate it is. My point being that our ability to determine fp (the fraction of those stars that have planets) and ne (the average number of planets that can potentially support life per star that has planets) while admittedly limited is still better than a wild guess. All of that being said, anybody that answers the Drake equation is making a guess. View Quote Not just a guess, a wild-ass speculation based on no data whatsoever. As in 0. As in none. Nada. Zilch. Zippo. There might be life elsewhere. And there might not. Anything beyond that is void of logic. |
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Quoted: Sure. I estimate it's somewhere between zero and eighty-seven bazillion. Prove me wrong. The assumption that there have been any other civilizations, or any other life for that matter, seems faulty (or at least premature) to me. Everyone wants to throw around a bunch of huge numbers as though x-billion potentially-habitable planets is evidence of life, but it's not even evidence for the potential of life until we know where life came from here. View Quote Your logic is correct. I mean that. But right now it's 0 because there's no evidence whatsoever to support a theory of life beyond erf. I will give a free PMag to anyone and everyone who can show evidence to the contrary. |
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Quoted: I see that as galactically naive, given the size and age of the universe, along with the fact that we've become as advanced as we are in a very short time, relatively speaking. Not disrespecting you, and I understand that this is all just speculation. But it seems overwhelmingly obvious that we can't be the only intelligent life out there. The odds against it are too great - especially given the nature of organic chemistry, and the abundance of water. View Quote I didn't say that we are the only intelligent life. I said that based on the evidence at hand we are the only technologically advanced life within our current detection range. Which is quite vast. For all we know there could be life on the frozen moons of Jupiter or Saturn. But that life probably isn't going to make a radio or a rocket. Again, based on the evidence. It seems like most of the exoplanets. Or at least the ones we have discovered so far are very large. And life on those planets would be rather difficult. Life on those planets might have so much of a struggle simply surviving day to day life that creating advanced technologies just isn't in the cards for them. Could Aliens Build A Rocket To Escape A Super Earth? |
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Quoted: I see that as galactically naive, given the size and age of the universe, along with the fact that we've become as advanced as we are in a very short time, relatively speaking. Not disrespecting you, and I understand that this is all just speculation. But it seems overwhelmingly obvious that we can't be the only intelligent life out there. The odds against it are too great - especially given the nature of organic chemistry, and the abundance of water. View Quote Key word: speculation. You has it. Odds mean nothing when the only known instance of life = 1. |
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Quoted: It goes further than that. We find the fundamental building blocks of life all over the place... oxygen, nitrogen, carbon, sulfur, phosphorous etc... they are so common throughout the known universe that NASA recently found them in a star at the center of the Boötes constellation. Meteorites fall from the sky all the time, panspermia is a solid theory backed up by mounds of evidence. People who lash out at any idea we are not alone in the cosmos are just desperately trying to coverup their unwarranted fears. Mostly religious in nature. Funny how many demand absolute proof of life elsewhere before they will allow even others to discuss it, but most of them will accept unquestionably the existence of a supernatural god based on nothing more than a book written by men in the 1600's to control other men... View Quote I'm not basing my theory on anything but science. Or lack thereof. Prove me wrong. Provide your evidence. |
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Quoted: Your logic is correct. I mean that. But right now it's 0 because there's no evidence whatsoever to support a theory of life beyond erf. I will give a free PMag to anyone and everyone who can show evidence to the contrary. View Quote The sheer amount of stars kicking around out there makes it really hard to believe there isn't/wasn't/won't be life somewhere else. It's every bit as dumb as all of the astronomers - some still living - that assumed planets were rare. |
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If you put any stock into the infinite multiverse theory, then the answer is also infinite. An endless amount of civilizations have collapsed in an endless number of realities.
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Quoted: Gravity dont exist... View Quote Tell that to anyone who has ever fallen down a mountain. I dare you. Gravity does exist. It's just the most poorly understood of the fundamental forces and perhaps there's a reason for that. If we had complete control of the 'force' of gravity... The scientific possibilities would extend far beyond fancy spaceships with antigravity drives and artificial gravity for the crew. |
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Quoted: The sheer amount of stars kicking around out there makes it really hard to believe there isn't/wasn't/won't be life somewhere else. It's every bit as dumb as all of the astronomers - some still living - that assumed planets were rare. View Quote The "sheer amount" of planets says nothing about life on them. Nothing. There might be life, there might not. Until some evidence comes along, I'm going with what we know, or have evidence to support. Which is 0. |
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Quoted: The "sheer amount" of planets says nothing about life on them. Nothing. There might be life, there might not. Until some evidence comes along, I'm going with what we know, or have evidence to support. Which is 0. View Quote View All Quotes View All Quotes Quoted: Quoted: The sheer amount of stars kicking around out there makes it really hard to believe there isn't/wasn't/won't be life somewhere else. It's every bit as dumb as all of the astronomers - some still living - that assumed planets were rare. The "sheer amount" of planets says nothing about life on them. Nothing. There might be life, there might not. Until some evidence comes along, I'm going with what we know, or have evidence to support. Which is 0. This guy gets it. Big numbers are neither evidence of life nor are they evidence for the POTENTIAL FOR THE EXISTENCE OF LIFE. Because we haven't defined the conditions necessary for the emergence of said life. We know what the conditions are NOW, and we know many of the conditions that existed before now. But we don't know WHAT WE DON'T KNOW with regard to the emergence (or manifestation) of life on THIS PLANET. So it is faulty to assume that just because there are big numbers out there, or that there are planets with conditions similar to the conditions on this planet, that those planets all possess the necessary conditions for life to exist. You are all guessing, and you are putting out a bunch of big numbers and complex theories to explain why your guess is more educated than someone else's guess. We currently have EVIDENCE for the existence of life on this planet right now and in the recent past. That's it. One instance, in the entire universe. When someone comes up with evidence of life anywhere else in the universe, it's going to be a big deal, and it won't come in the form of an equation. |
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Quoted: Quoted: And all of this has happened before, and will happen again. /media/mediaFiles/sharedAlbum/capReference-550.jpg A question no one bothers to answer about that series though. Why were the Cylons all stupidly insane? I mean, Brother Cavill's alleged plan was pure weapons grade stupidity. Dumb cunt couldn't even figure out that he had a programming lock preventing him or the other Cylons from killing the final five. Never mind the fact that even though the Cylons on the 'Real Earth' had a completely pure Cylon society that apparently went happily on its way for millennia until some dumb cunt there decided to make centurions and they all turned out to be suicidally insane as well. Like I keep saying. Bad writing. |
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Quoted: Not just a guess, a wild-ass speculation based on no data whatsoever. As in 0. As in none. Nada. Zilch. Zippo. There might be life elsewhere. And there might not. Anything beyond that is void of logic. View Quote View All Quotes View All Quotes Quoted: Quoted: I'm going to have to disagree with you on everything except your ultimate conclusion. We're just starting to get a handle on two factors of the equation, and we cannot be certain of our accuracy. However, at present it appears that about one-third of the stars have planets. The accuracy of this limited by our ability to observe both in distance, and resolution. We're also looking at the idea that only planets within the Goldilocks zone can support life. We've only ever seen life within that zone based on our sample size of one, and that has been defined as places that have liquid water. Of those exo-planets that have been discovered, they're assigning possibilities that they're in the Goldilocks zone based on star characteristics and planet distance from the star. Of course, our ability to define the Goldilocks zone is limited to our knowledge, so who knows how accurate it is. My point being that our ability to determine fp (the fraction of those stars that have planets) and ne (the average number of planets that can potentially support life per star that has planets) while admittedly limited is still better than a wild guess. All of that being said, anybody that answers the Drake equation is making a guess. Not just a guess, a wild-ass speculation based on no data whatsoever. As in 0. As in none. Nada. Zilch. Zippo. There might be life elsewhere. And there might not. Anything beyond that is void of logic. Except we do have data. It's an incomplete data set, and we cannot be certain of it's accuracy, but it does exist. Based on Earth, we know that life can exist under the circumstances present on Earth. That is data. We have observed other rocky planets in other star systems. Of the star systems that we can observe with the appropriate resolution to determine if there are planets in orbit, about one-third of them have planets. That is data. Of those planets, some of them (I don't know the percentage off hand) are within the Goldilocks Zone. That is to say that they are in a position that makes the potential for having liquid water a possibility. That is also data. Of those planets, some have also been observed to have atmospheres that include water vapor. That is data. So to posit that we have zero data is as asinine as saying we have the answer to the Drake Equation. |
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Quoted: Except we do have data. It's an incomplete data set, and we cannot be certain of it's accuracy, but it does exist. Based on Earth, we know that life can exist under the circumstances present on Earth. That is data. We have observed other rocky planets in other star systems. Of the star systems that we can observe with the appropriate resolution to determine if there are planets in orbit, about one-third of them have planets. That is data. Of those planets, some of them (I don't know the percentage off hand) are within the Goldilocks Zone. That is to say that they are in a position that makes the potential for having liquid water a possibility. That is also data. Of those planets, some have also been observed to have atmospheres that include water vapor. That is data. So to posit that we have zero data is as asinine as saying we have the answer to the Drake Equation. View Quote Wrong. The "data" you're referring to is the number of planets that might support life. We all agree those exist. What you and all others fail to grasp is that there is no data whatsoever to suggest there is actual life on those planets. None. Zilch. Provide evidence of life. Free PMag. Easy, right? |
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Quoted: This guy gets it. Big numbers are neither evidence of life nor are they evidence for the POTENTIAL FOR THE EXISTENCE OF LIFE. Because we haven't defined the conditions necessary for the emergence of said life. We know what the conditions are NOW, and we know many of the conditions that existed before now. But we don't know WHAT WE DON'T KNOW with regard to the emergence (or manifestation) of life on THIS PLANET. So it is faulty to assume that just because there are big numbers out there, or that there are planets with conditions similar to the conditions on this planet, that those planets all possess the necessary conditions for life to exist. You are all guessing, and you are putting out a bunch of big numbers and complex theories to explain why your guess is more educated than someone else's guess. We currently have EVIDENCE for the existence of life on this planet right now and in the recent past. That's it. One instance, in the entire universe. When someone comes up with evidence of life anywhere else in the universe, it's going to be a big deal, and it won't come in the form of an equation. View Quote Correct! I should give you the PMag for simply being not dense. But I won't because that's not the challenge. |
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Quoted: Except we do have data. It's an incomplete data set, and we cannot be certain of it's accuracy, but it does exist. Based on Earth, we know that life can exist under the circumstances present on Earth. That is data. We have observed other rocky planets in other star systems. Of the star systems that we can observe with the appropriate resolution to determine if there are planets in orbit, about one-third of them have planets. That is data. Of those planets, some of them (I don't know the percentage off hand) are within the Goldilocks Zone. That is to say that they are in a position that makes the potential for having liquid water a possibility. That is also data. Of those planets, some have also been observed to have atmospheres that include water vapor. That is data. So to posit that we have zero data is as asinine as saying we have the answer to the Drake Equation. View Quote Battlestar Galactica reboot yet again. They were stumbling around the Galaxy looking for planets which would sustain human life that weren't rendered uninhabitable by nuclear war on an absurd scale. They found one and a half. Earth and New Caprica. The Algae planet doesn't really count for me because it's star was right on the ragged edge of supernova and it being a TV drama. Did supernova, wiping out the Algae planet. Life on New Caprica was marginal. Yes there is water out there, yes there is oxygen, carbon, nitrogen. All the building blocks. But the life on those worlds, if it exists will most likely be like it was on New Caprica. Marginal. Once you are technologically advanced enough to build ships and O'neil cylinders you don't have to worry about that. You can park your habitats close to a star and have all the energy you could ever want or need. But you have to get to the point where you can build those habitats in the first place! That is no small thing. As I keep saying, it took awhile for us to get to here and we are a bit of a ways away from creating sustainable space stations. |
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Quoted: Battlestar Galactica reboot yet again. They were stumbling around the Galaxy looking for worlds which would sustain human life that weren't rendered uninhabitable by nuclear war on an absurd scale. They found one and a half. Earth and New Caprica. Life on New Caprica was marginal. Yes there is water out there, yes there is oxygen, carbon, nitrogen. All the building blocks. But the life on those worlds, if it exists will most likely be like it was on New Caprica. Marginal. Once you are technologically advanced enough to build ships and O'neil cylinders you don't have to worry about that. You can park your habitats close to a star and have all the energy you could ever want or need. But you have to get to the point where you can build those habitats in the first place! That is no small thing. As I keep saying, it took awhile for us to get to here and we are a bit of a ways away from creating sustainable space stations. View Quote I'll go you one further. There is no data to suggest even the existence of simple, single-celled organisms elsewhere in the universe. None. Zilch. Nada. |
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Quoted: Wrong. The "data" you're referring to is the number of planets that might support life. We all agree those exist. What you and all others fail to grasp is that there is no data whatsoever to suggest there is actual life on those planets. None. Zilch. Provide evidence of life. Free PMag. Easy, right? View Quote View All Quotes View All Quotes Quoted: Quoted: Except we do have data. It's an incomplete data set, and we cannot be certain of it's accuracy, but it does exist. Based on Earth, we know that life can exist under the circumstances present on Earth. That is data. We have observed other rocky planets in other star systems. Of the star systems that we can observe with the appropriate resolution to determine if there are planets in orbit, about one-third of them have planets. That is data. Of those planets, some of them (I don't know the percentage off hand) are within the Goldilocks Zone. That is to say that they are in a position that makes the potential for having liquid water a possibility. That is also data. Of those planets, some have also been observed to have atmospheres that include water vapor. That is data. So to posit that we have zero data is as asinine as saying we have the answer to the Drake Equation. Wrong. The "data" you're referring to is the number of planets that might support life. We all agree those exist. What you and all others fail to grasp is that there is no data whatsoever to suggest there is actual life on those planets. None. Zilch. Provide evidence of life. Free PMag. Easy, right? As I was explaining before your attempt to derail the conversation, we do have data which informs the Drake Equation, but not enough to answer it. |
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Quoted: I'll go you one further. There is no data to suggest even the existence of simple, single-celled organisms elsewhere in the universe. None. Zilch. Nada. View Quote Not yet. I'm cautiously optimistic that we might find something like that on Jupiters moons. Or perhaps on Pluto. If we find incontrovertibly alien life. Even if it is just single celled organisms it will be a momentous day. I believe that if we ever send probes and ships to other stars that we might find something. But yeah, as you said. No hard evidence yet. |
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Quoted: As I was explaining before your attempt to derail the conversation, we do have data which informs the Drake Equation, but not enough to answer it. View Quote As I have been explaining before you didn't understand basic logic, there is no evidence whatsoever to support the theory of advanced life elsewhere. If there was, you'd provide it. That's the OP topic. Please re-read it and try to keep up. The Drake Equation doesn't even qualify as a "theory". Why? Because theories can be tested. The Drake Equation cannot even be tested. It fails at a basic level to be relevant to the the scientific method. Do I have to describe "scientific method" for you, too? |
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Quoted: Not yet. I'm cautiously optimistic that we might find something like that on Jupiters moons. Or perhaps on Pluto. If we find incontrovertibly alien life. Even if it is just single celled organisms it will be a momentous day. I believe that if we ever send probes and ships to other stars that we might find something. But yeah, as you said. No hard evidence yet. View Quote There isn't even "soft" evidence. None. But I'm open to changing my mind. That's because I'm a good scientist. |
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Quoted: Infinite amount View Quote People should really become more familiar with words like infinity before they start bandying them about. Exponential Growth and its Philosophical Implications |
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Quoted: Gravity is not a dimension, it's a force. And a poorly understood one, at that. View Quote Quoted: Tell that to anyone who has ever fallen down a mountain. I dare you. Gravity does exist. It's just the most poorly understood of the fundamental forces and perhaps there's a reason for that. If we had complete control of the 'force' of gravity... The scientific possibilities would extend far beyond fancy spaceships with antigravity drives and artificial gravity for the crew. View Quote I say it’s magic... |
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There's a very good book , Rare Earth, that follows the evolution of the planet from dust to primitive life.
It details the various obstacles that occurred to the formation of life, from million year long asteroid bombardments to various toxic events like volcanic acid rains. It's a sobering assessment of the chain of causality that led to the brief intermission that we're currently enjoying. It also discusses extremophiles, the critters in the deep ocean that thrive in the vents on the floor that allow hot gases to emerge. It's the most hostile environment possible, yet life is there. Highly recommended. |
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Quoted: Quoted: Gravity is not a dimension, it's a force. And a poorly understood one, at that. Quoted: Tell that to anyone who has ever fallen down a mountain. I dare you. Gravity does exist. It's just the most poorly understood of the fundamental forces and perhaps there's a reason for that. If we had complete control of the 'force' of gravity... The scientific possibilities would extend far beyond fancy spaceships with antigravity drives and artificial gravity for the crew. I say it’s magic... it's a product of time dilation, *yawn*... next |
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Quoted: There's a very good book , Rare Earth, that follows the evolution of the planet from dust to primitive life. It details the various obstacles that occurred to the formation of life, from million year long asteroid bombardments to various toxic events like volcanic acid rains. It's a sobering assessment of the chain of causality that led to the brief intermission that we're currently enjoying. It also discusses extremophiles, the critters in the deep ocean that thrive in the vents on the floor that allow hot gases to emerge. It's the most hostile environment possible, yet life is there. Highly recommended. View Quote Your description is spot-on. It is remarkable that life on erf exists at all. A miracle, you might say. And add to that the apparent violation of the Laws of Thermodynamics, specifically the Second Law. It says that closed systems move toward more disorder. Life, by definition, is toward more order, not less. And considering that life on earth is several billion years old, the Second Law has been apparently violated for billions of years. This is simply not possible without an "input" from outside the system. So, a logical conclusion would be that the Laws of Thermodynamics are incorrect, or there has been an input of energy from outside the system to create more order - namely, life - not less. This is a good argument for a Creator. Not proof, surely, but a good argument. |
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Quoted: Seems that scientists make educated guesses all the time. Has anyone ever figured it out? If not the Universe how about just our galaxy? View Quote Not been figured out positively no. That is why it is called a Paradox. |
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Quoted: There's a very good book , Rare Earth, that follows the evolution of the planet from dust to primitive life. It details the various obstacles that occurred to the formation of life, from million year long asteroid bombardments to various toxic events like volcanic acid rains. It's a sobering assessment of the chain of causality that led to the brief intermission that we're currently enjoying. It also discusses extremophiles, the critters in the deep ocean that thrive in the vents on the floor that allow hot gases to emerge. It's the most hostile environment possible, yet life is there. Highly recommended. View Quote Thanks for that recommendation. I read Sagan's Cosmos last year and found myself reading the chapters that dealt with the origins of organic life on Earth several damn times. |
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Quoted: As I have been explaining before you didn't understand basic logic, there is no evidence whatsoever to support the theory of advanced life elsewhere. If there was, you'd provide it. That's the OP topic. Please re-read it and try to keep up. The Drake Equation doesn't even qualify as a "theory". Why? Because theories can be tested. The Drake Equation cannot even be tested. It fails at a basic level to be relevant to the the scientific method. Do I have to describe "scientific method" for you, too? View Quote View All Quotes View All Quotes Quoted: Quoted: As I was explaining before your attempt to derail the conversation, we do have data which informs the Drake Equation, but not enough to answer it. As I have been explaining before you didn't understand basic logic, there is no evidence whatsoever to support the theory of advanced life elsewhere. If there was, you'd provide it. That's the OP topic. Please re-read it and try to keep up. The Drake Equation doesn't even qualify as a "theory". Why? Because theories can be tested. The Drake Equation cannot even be tested. It fails at a basic level to be relevant to the the scientific method. Do I have to describe "scientific method" for you, too? Either you're incapable of following a conversation, or your goal is to end any conversation about a topic which challenges your faith. In either event, I am uninterested in your ad hominem bait. Have a nice day. |
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There is absolutely no way to know. You can guess at it all you want, but it's meaningless.
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The estimate is 36 civilizations (capable of communication) per galaxy.
The estimated number of galaxies in this universe is 2 trillion... |
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Quoted: People should really become more familiar with words like infinity before they start bandying them about. https://www.youtube.com/watch?v=Vqc1M1agKgA View Quote Lol. Video doesn't mean shit. Disprove an infinite universe. You can't. |
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Quoted: The estimate is 36 civilizations (capable of communication) per galaxy. The estimated number of galaxies in this universe is 2 trillion... View Quote "Estimate" based on what? The Drake Equation? LOL. The DE isn't even a theory, that's how irrelevant it is at predicting life elsewhere. How convenient that people who tout the DE believe in something that cannot be tested. Once again, my mind is open to life elsewhere, provided there is some evidence for it. In fact, I'd love to see it. |
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Quoted: I know the exact number: 0. We are the first and only and there's not a single scrap of evidence to the contrary. The Drake Equation is an imaginary construct. There is no proof it even comes close to the truth. It's called an "equation" because it doesn't even rate the moniker "theory", much less a "law". View Quote We have a sample size of one. We have no evidence one way or the other if there are more or not. Being as we have already come across possible signs of life on other planets in this very solar system...the odds are against you. Nick |
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Quoted: As stated, the number is zero, with the knowledge we have at the moment. It would be odd to find beings that resemble us. We are bipods on a planet with most lifeforms having 4 or more appendages View Quote Looks like we also have 4 appendages. Am I mathing wrong? Nick |
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Quoted: We have a sample size of one. We have no evidence one way or the other if there are more or not. Being as we have already come across possible signs of life on other planets in this very solar system...the odds are against you. Nick View Quote Let me re-phrase: AS OF NOW I know for a fact the number is 0 for life elsewhere. None. Zilch. Nada. We have no evidence whatsoever of "possible" signs of life elsewhere. Here is your opportunity to provide it or retract/rephrase your statement. |
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Quoted: Let me re-phrase: AS OF NOW I know for a fact the number is 0 for life elsewhere. None. Zilch. Nada. We have no evidence whatsoever of "possible" signs of life elsewhere. Here is your opportunity to provide it or retract/rephrase your statement. View Quote As far as signs of life possible elsewhere, I would suggest you read up the Viking lander experiments and their results, the Martian meteorite found in Antarctica, and the recent detection of phosgene in Venus's atmosphere. Nick |
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Sean Carroll: Is There Intelligent Life Out There in the Universe? | AI Podcast Clips |
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Quoted: The Drake equation is a thing. View Quote The Drake Equation is a joke. It makes assumptions based upon conjecture not fact. Putting aside it is not based on real data it is out dated to say the least. Since it was created we have learned a tremendous amount more about how unique earth is. In the book Rare Earth there is a more up to date equation: https://en.wikipedia.org/wiki/Rare_Earth_hypothesis The following discussion is adapted from Cramer.[55] The Rare Earth equation is Ward and Brownlee's riposte to the Drake equation. It calculates N {\displaystyle N} N, the number of Earth-like planets in the Milky Way having complex life forms, as: where: N* is the number of stars in the Milky Way. This number is not well-estimated, because the Milky Way's mass is not well estimated, with little information about the number of small stars. N* is at least 100 billion, and may be as high as 500 billion, if there are many low visibility stars. n e {\displaystyle n_{e}} n_{e} is the average number of planets in a star's habitable zone. This zone is fairly narrow, because constrained by the requirement that the average planetary temperature be consistent with water remaining liquid throughout the time required for complex life to evolve. Thus n e {\displaystyle n_{e}} n_{e}=1 is a likely upper bound. We assume N * · n e = 5 · 10 11 {\displaystyle N^{*}\cdot n_{e}=5\cdot 10^{11}} {\displaystyle N^{*}\cdot n_{e}=5\cdot 10^{11}}. The Rare Earth hypothesis can then be viewed as asserting that the product of the other nine Rare Earth equation factors listed below, which are all fractions, is no greater than 10-10 and could plausibly be as small as 10-12. In the latter case, N {\displaystyle N} N could be as small as 0 or 1. Ward and Brownlee do not actually calculate the value of N {\displaystyle N} N, because the numerical values of quite a few of the factors below can only be conjectured. They cannot be estimated simply because we have but one data point: the Earth, a rocky planet orbiting a G2 star in a quiet suburb of a large barred spiral galaxy, and the home of the only intelligent species we know; namely, ourselves. f g {\displaystyle f_{g}} f_g is the fraction of stars in the galactic habitable zone (Ward, Brownlee, and Gonzalez estimate this factor as 0.1[6]). f p {\displaystyle f_{p}} f_{p} is the fraction of stars in the Milky Way with planets. f p m {\displaystyle f_{pm}} f_{pm} is the fraction of planets that are rocky ("metallic") rather than gaseous. f i {\displaystyle f_{i}} f_{i} is the fraction of habitable planets where microbial life arises. Ward and Brownlee believe this fraction is unlikely to be small. f c {\displaystyle f_{c}} f_{c} is the fraction of planets where complex life evolves. For 80% of the time since microbial life first appeared on the Earth, there was only bacterial life. Hence Ward and Brownlee argue that this fraction may be small. f l {\displaystyle f_{l}} f_{l} is the fraction of the total lifespan of a planet during which complex life is present. Complex life cannot endure indefinitely, because the energy put out by the sort of star that allows complex life to emerge gradually rises, and the central star eventually becomes a red giant, engulfing all planets in the planetary habitable zone. Also, given enough time, a catastrophic extinction of all complex life becomes ever more likely. f m {\displaystyle f_{m}} f_{m} is the fraction of habitable planets with a large moon. If the giant impact theory of the Moon's origin is correct, this fraction is small. f j {\displaystyle f_{j}} f_{j} is the fraction of planetary systems with large Jovian planets. This fraction could be large. f m e {\displaystyle f_{me}} f_{me} is the fraction of planets with a sufficiently low number of extinction events. Ward and Brownlee argue that the low number of such events the Earth has experienced since the Cambrian explosion may be unusual, in which case this fraction would be small. The Rare Earth equation, unlike the Drake equation, does not factor the probability that complex life evolves into intelligent life that discovers technology. Barrow and Tipler[57] review the consensus among such biologists that the evolutionary path from primitive Cambrian chordates, e.g., Pikaia to Homo sapiens, was a highly improbable event. For example, the large brains of humans have marked adaptive disadvantages, requiring as they do an expensive metabolism, a long gestation period, and a childhood lasting more than 25% of the average total life span. Other improbable features of humans include: Being one of a handful of extant bipedal land (non-avian) vertebrate. Combined with an unusual eye–hand coordination, this permits dextrous manipulations of the physical environment with the hands; A vocal apparatus far more expressive[citation needed] than that of any other mammal, enabling speech. Speech makes it possible for humans to interact cooperatively, to share knowledge, and to acquire a culture; The capability of formulating abstractions to a degree permitting the invention of mathematics, and the discovery of science and technology. Only recently did humans acquire anything like their current scientific and technological sophistication. |
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