Author Topic: General SETI Thread  (Read 34773 times)

Offline Dao Angkan

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Re: General SETI Thread
« Reply #120 on: 01/09/2018 08:39 PM »
Simple, single-celled life forms were the only life on Earth for 3.5 billion years. We don't know why life jumped from simple, single-celled forms to multiple-celled critters. The Cambrian explosion was sudden and there's not much evidence available that can clue us in to why it happened, though it's an area of intense research. It's entirely possible that a planet could be inhabited by bacteria for tens of billions of years without any more complex life forming, particularly because we don't yet understand how it happened here.

This is really debatable, some argue that cyanobacteria were multicellular 3.5Gya, others differentiate between those and "complex multicellular organisms" (roughly the timescale that you argue for). I think that one thing that most agree on is that "complex life" could not have evolved without prior "basic life" oxygenating the atmosphere over several billions of years.
« Last Edit: 01/09/2018 08:40 PM by Dao Angkan »

Offline QuantumG

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Re: General SETI Thread
« Reply #121 on: 01/09/2018 09:08 PM »
The argument that we can't generalize about life in the universe as we only have one data sample (life on Earth) is a good one.
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline whitelancer64

Re: General SETI Thread
« Reply #122 on: 01/09/2018 09:18 PM »
It's a lot like many physics problems. Assume a perfectly spherical mass of 1 kg on a perfectly flat, frictionless plane... now apply to real life situation.
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Offline Dao Angkan

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Re: General SETI Thread
« Reply #123 on: 01/09/2018 09:22 PM »
We don't need to generalise, we can restrict the question to "life as we know it". We know that "life as we know it" is possible, what we don't know is how likely it is (although how soon it happened on Earth suggests that it is quite likely, but maybe it takes so long for intelligence to evolve that only the planets that are lucky enough to evolve life quickly have enough time to evolve intelligence before the star dies).

It's quite possible that within many of our lifetimes that we will have a census of habitable zone terrestrial planet atmospheres. If we can detect O2 percentages in some atmospheres, then we can at least know that we're not unique (although we won't be able to prove that it was due to biological processes). Alternatively, we could find that no other planets have detectable levels of biomarkers, which would be an equally profound discovery.
« Last Edit: 01/09/2018 09:36 PM by Dao Angkan »

Offline Dao Angkan

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Re: General SETI Thread
« Reply #124 on: 01/09/2018 10:52 PM »
Now this is an intriguing theory.

Are Alien Civilizations Technologically Advanced?

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Based on our own experience, we expect that civilizations much older than ours will be scientifically savvy and hence technologically advanced. But it is also possible that a simpler lifestyle rather than scientific prosperity has dominated the political landscape on other planets, leading to old civilizations that are nevertheless technologically primitive.

https://blogs.scientificamerican.com/observations/are-alien-civilizations-technologically-advanced/#

From my reading, this suffers from the same flaw that hampers so many attempted answers to the Fermi paradox. Namely that while this theory might apply to some alien civilizations, you only need one civilization that is aggressively expansionist to populate the entire galaxy with Von Neuman probes or some such scenario.

The latter seems unlikely even for an advanced civilisation due to the vast distances involved.

Astronomically speaking it would take very little time for a space faring civilisation to colonise the whole galaxy. If a civilisation "just" colonises the nearest 100 stars, and only 1% of those does the same, then exponentially the entire Milky Way would be colonised in as little as hundreds of thousands of years, maybe more realistically in tens of millions of years. If we assume that Earth like planets first started to be formed 10Gya, then the galaxy should have been colonised many times over.

We could argue that interstellar travel isn't practicle, but most stars aren't that far from each other, at 10% lightspeed most systems' closest stars should be achievable in current human lifetimes.

It should be noted that the earliest homo sapiens are thought to be 300,000 years old, theoretically we could colonise the entire galaxy in less time than we took to invent the microprocessor.
« Last Edit: 01/09/2018 11:02 PM by Dao Angkan »

Offline Star One

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Re: General SETI Thread
« Reply #125 on: 01/10/2018 07:23 PM »
SETI project homes in on strange ‘fast radio bursts’

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Another possibility, though remote, is that the FRB is a high-powered signal from an advanced civilization. Hence the interest of Breakthrough Listen, which looks for signs of intelligent life in the universe, funded by $100 million over 10 years from internet investor Yuri Milner.

“Although it’s extremely unlikely that pulses we have detected from FRB 121102 were transmitted by ETs, we would like to test various ET hypotheses for the FRB type transient signals in general,” Gajjar said.

Breakthrough Listen has to date recorded data from a dozen FRBs, including FRB 121102, and plans eventually to sample all 30-some known sources of fast radio bursts.

“We want a complete sample so that we can conduct our standard SETI analysis in search of modulation patterns or narrow-band signals – any kind of information-bearing signal emitted from their direction that we don’t expect from nature,” he said.

http://news.berkeley.edu/2018/01/10/seti-project-homes-in-on-strange-fast-radio-bursts/

Offline missinglink

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Re: General SETI Thread
« Reply #126 on: 01/11/2018 10:22 PM »
but it’s too late, we’ve already sent out our calling card. Hitler at the 1936 Olympics is already out there. A timestamp of our own history.
That seems unlikely to me. Signal strength is so low to begin with and diminishes rapidly due to the inverse-square law, the signal becomes lost in noise not long after leaving the solar system.

Of course, the reverse is true as well. From Wikipedia's article on SETI:

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For SERENDIP and most other SETI projects to detect a signal from an extraterrestrial civilization, the civilization would have to be beaming a powerful signal directly at us.

The image this calls to mind is that of a soap bubble. You can touch it while it is expanding and moving, but only for a short time, then it pops (similar to EM radiation becoming too weak to detect).

Admittedly, the Intro to CONTACT (the movie starring Jodie Foster) showing successive broadcast signals going out into deep space was very cool  8)

Offline M.E.T.

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Re: General SETI Thread
« Reply #127 on: 01/12/2018 05:44 AM »
but it’s too late, we’ve already sent out our calling card. Hitler at the 1936 Olympics is already out there. A timestamp of our own history.
That seems unlikely to me. Signal strength is so low to begin with and diminishes rapidly due to the inverse-square law, the signal becomes lost in noise not long after leaving the solar system.

Of course, the reverse is true as well. From Wikipedia's article on SETI:

Quote
For SERENDIP and most other SETI projects to detect a signal from an extraterrestrial civilization, the civilization would have to be beaming a powerful signal directly at us.

The image this calls to mind is that of a soap bubble. You can touch it while it is expanding and moving, but only for a short time, then it pops (similar to EM radiation becoming too weak to detect).

Admittedly, the Intro to CONTACT (the movie starring Jodie Foster) showing successive broadcast signals going out into deep space was very cool  8)

That's why I don't see the lack of radio signals as an issue as far as the Fermi Paradox is concerned. It is quite plausible that most general signals originate from too far away too reach us, and that no one feels it is worth the effort to send a high powered beam directly to us, in the hope of hearing back in a few thousand years.

The lack of physical evidence of ET intelligence, such as Von Neuman probes, distant megastructures etc. is what seems like a stronger argument to me. We might receive a signal from another star one day, but I don't see the lack of such a signal as a problem.

Offline Johnnyhinbos

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Offline Star One

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General SETI Thread
« Reply #129 on: 01/16/2018 07:19 PM »
Persuasive article by Jason Wright arguing that SETI should be part of NASA’s astrobiology strategy. With in my view some well deserved criticism of NASA in the astrobiology arena.

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What follows is my submission to the National Academies of Sciences, Engineering, and Medicine ad hoc Committee on Astrobiology Science Strategy for Life in the Universe, 2018. It is available as a PDF here.

Please also see Jill Tarter’s companion white paper here.

http://sites.psu.edu/astrowright/2018/01/16/seti-is-part-of-astrobiology/
« Last Edit: 01/16/2018 07:28 PM by Star One »

Offline moreno7798

Re: General SETI Thread
« Reply #130 on: 01/16/2018 10:57 PM »
My bet is that to the universe earth is basically a niche extremophile environment. Think about it, a planet living very close to a hot star. So hot that biology becomes liquid. Water may be one of the most dangerous poisonous liquids in the universe but hey we're made of it so that's what we think life is composed of.

The vast majority of the universe may sees us as the extremophiles of the universe. That is because the vast majority of the universe probably lives in in much colder and darker environments where energy is not derived from heat and Photosynthesis is not a thing. Any aliens living in those environments are probably not sending signals to planets close to stars. They could be looking in the space between the stars. The perception of where life in the universe may lie is relative to your perception of what life may be. They probably consider anything that close to a star to be devoid of life. That could be a possible solution to the Fermi Paradox.

Online RotoSequence

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Re: General SETI Thread
« Reply #131 on: 01/17/2018 12:12 AM »
My bet is that to the universe earth is basically a niche extremophile environment. Think about it, a planet living very close to a hot star. So hot that biology becomes liquid. Water may be one of the most dangerous poisonous liquids in the universe but hey we're made of it so that's what we think life is composed of.

The vast majority of the universe may sees us as the extremophiles of the universe. That is because the vast majority of the universe probably lives in in much colder and darker environments where energy is not derived from heat and Photosynthesis is not a thing. Any aliens living in those environments are probably not sending signals to planets close to stars. They could be looking in the space between the stars. The perception of where life in the universe may lie is relative to your perception of what life may be. They probably consider anything that close to a star to be devoid of life. That could be a possible solution to the Fermi Paradox.

It's a fun idea for sci-fi authors, but interesting chemistry with common elements seems to prefer Room Temperature.  ;)

Offline Welsh Dragon

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Re: General SETI Thread
« Reply #132 on: 01/17/2018 07:55 AM »
<snip>. Water may be one of the most dangerous poisonous liquids in the universe but hey we're made of it so that's what we think life is composed of. </snip>
Oxygen is the poison, not water.

Online Bynaus

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Re: General SETI Thread
« Reply #133 on: 01/17/2018 08:32 AM »
Quote
The perception of where life in the universe may lie is relative to your perception of what life may be.

Maybe - but the argument of mediocrity (we are much more likely to be typical, rather than atypical) would suggest that this is a low-probability suggestion.
More thoughts: www.final-frontier.ch (in German)

Online RotoSequence

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Re: General SETI Thread
« Reply #134 on: 01/17/2018 08:46 AM »
Quote
The perception of where life in the universe may lie is relative to your perception of what life may be.

Maybe - but the argument of mediocrity (we are much more likely to be typical, rather than atypical) would suggest that this is a low-probability suggestion.

The Kepler dataset shows that The Solar System has an uncommon arrangement of planets compared to most stars. The odds may be long, but sometimes you hit the jackpot, and space gives you trillions of chances to try your odds.

Offline jebbo

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Re: General SETI Thread
« Reply #135 on: 01/17/2018 09:18 AM »
The Kepler dataset shows that The Solar System has an uncommon arrangement of planets compared to most stars. The odds may be long, but sometimes you hit the jackpot, and space gives you trillions of chances to try your odds.

We're not really that sure of the occurrence rates of systems like ours yet as it is very hard to detect systems with a similar architecture to ours (and not just for Kepler).  Yes, they seem to be rarer, but how rare is unknown. Essentially all current detection methods are biased towards larger planets on shorter period orbits. So the catalogues are strongly biased towards compact systems & hot Jupiters ...

However, RV searches have yielded a number of Jupiter analogues - but this requires >10 years of data, so the number of systems is limited. 

We'll have a better idea (at least for Jupiter-analogue occurrence rates) in a few years when the Gaia planet catalogue is released as astrometry is biased towards finding planets on wider orbits (from memory, Jupiter distance is about the optimum).

--- Tony

Online Bynaus

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Re: General SETI Thread
« Reply #136 on: 01/17/2018 10:00 AM »
Quote
The perception of where life in the universe may lie is relative to your perception of what life may be.

Maybe - but the argument of mediocrity (we are much more likely to be typical, rather than atypical) would suggest that this is a low-probability suggestion.

The Kepler dataset shows that The Solar System has an uncommon arrangement of planets compared to most stars. The odds may be long, but sometimes you hit the jackpot, and space gives you trillions of chances to try your odds.

But most of the times, you don't hit the jackpot. So the proposal of having hit it (without knowing) must be characterized as a low-probability proposition. This is all I am saying.

For the Kepler system, as jebbo just mentioned, its not yet fully clear what this means. But on top of that, there might be an anthropic bias involved (of which we are not yet aware), so that compact systems might be less habitable. There is a similar situation with the Sun not being an M-dwarf although the latter being very common: you could explain this by "luck", but perhaps M-dwarfs are just not as habitable as G-dwarfs.
More thoughts: www.final-frontier.ch (in German)

Offline M.E.T.

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Re: General SETI Thread
« Reply #137 on: 01/17/2018 10:04 AM »
Can someone help me to understand some of the parameters of the Mediocrity Principle. Because to me it seems you need to massage these parameters rather creatively to get to some kind of Mediocrity assumption.

For example, in our own solar system, we are the only one of eight planets that has intelligent life, most likely the only one out of eight that has any complex life, and as far as we know, the only one with even simple life.

So clearly, we aren't mediocre within the population of our Solar System. We are quite unique.

Next, our Sun, based on some cursory Googling, appears to be of a type (G-type main sequence), that only represents 5% or so of all observable stars in the Universe. So once again, we can't really say that sun-like stars are mediocre, if they only represent one in twenty stars out there.

Obviously this list can go on, for example the relative size and influence of our Moon would appear not to be mediocre at all, etc. etc.

My point being, under what parameters do we feel that our planet should be considered "Mediocre"? Or is it based more on a philosophical principle, rather than any kind of physical evidence?
« Last Edit: 01/17/2018 10:07 AM by M.E.T. »

Offline Alpha_Centauri

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Re: General SETI Thread
« Reply #138 on: 01/17/2018 10:27 AM »
You weren't claiming that the Earth or the Solar System were rare, you were claiming that life such as ours is extreme compared to life elsewhere in the universe.  Those are two different arguments.

Simple probability dictates that it is unlikely by chance to happen to find yourself a member of an extreme group, just as it is unlikely to pick out the one red ball in a bag of 9 other black balls, so the default (though not necessarily correct) assumption is that we are unlikely to be that unusual in the context of other life.  This of course is rather negated if we are the first example of sentient life so the bag is low on balls.

This is a separate question to the rarity of the conditions in which we formed.  Think of it like this, you have 5 oases in a 1000 sq km desert.  The chances that the first oasis you come across hosts very different life to that in the other four is low, but this has no relation to the rarity of the conditions (an oasis in the desert) that allows any of these ecosystems to develop.

« Last Edit: 01/17/2018 10:36 AM by Alpha_Centauri »

Offline M.E.T.

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Re: General SETI Thread
« Reply #139 on: 01/17/2018 10:31 AM »
You weren't claiming that the Earth or the Solar System were rare, you were claiming that life such as ours is extreme compared to life elsewhere in the universe.  Those are two different arguments.

Simple probability dictates that it is unlikely by chance to happen to find yourself a member of an extreme group, just as it is unlikely to pick out the one red ball in a bag of 9 other black balls, so the default (though not necessarily correct) assumption is that we are unlikely to be that unusual in the context of other life.  This of course is rather negated if we are the first example of sentient life so the bag is low on balls.

This is a separate question to the rarity of the conditions in which we formed.  Think of it like this, you have 5 oases in a 1000 sq km desert.  The chances that the first oasis you come across is hosts radically different life to that in the other four is low, but this has no relation to the rarity of the conditions (an oasis in the desert) that allows any of these ecosystems to develop.

Sorry, I thought the whole point of the Mediocrity Principle is that neither the Earth nor the fact that it has life on it is particularly special.

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