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Old 07-10-2016, 11:35 AM
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Is the Fermi Paradox becoming more acute?


Seth Shostak, Senior Astronomer and Director at the Center for SETI Research said in 1914: “”One in five stars has at least one planet where life might spring up. That’s a fantastically large percentage. That means in our galaxy there’s an order of tens of billions of Earth-like worlds.” He predicts that extraterrestrial life will have been discovered by 2040.

I think that if we haven’t discovered extraterrestrial life by 2040, chances are we never will.

About half a century ago physicist Enrico Fermi was surprised by the apparent contradiction between the lack of evidence and high probability estimates for the existence of extraterrestrial civilizations. Given the billions of stars in our galaxy and the billions of years since life could have thrived in so many places, the Milky Way should be bustling with alien activity. “Where is everybody?” Fermi asked.

“We still have plenty of time to discover alien civilizations,” optimists say.

Maybe. The problem is most of the action in the universe has already happened. The first generation of galaxies appeared when the universe was about 400 million years old. Early galaxies were only several thousand solar masses but they increased in size through successive merges until they were reached the size of up to billions of solar masses. Certain scientists (such as David Sobral) think that fifty percent of the stars ever created were already born nine billion years ago. For nine billion years the universe has been producing the other half. At the moment the rate of star formation has diminished dramatically – only a number equal to a twentieth of the total number of today’s existing stars could still be generated until the end of time.

Plus, the dark energy that makes up over 2/3 of the universe’s energy causes the universe to expand at an accelerating rate. It’s been quite a while since dark energy has superseded other forms of energy and galaxies themselves -- matter started to become quite dilute billions of years ago. Since the effect of dark energy increases as the space expands, one of its consequences is that new structures are less and less likely to form from now on. That is, gradually dark energy will become so strong that it will rip apart galaxies, stars and even atoms.

I think the heyday of extraterrestrial civilizations is now or has already passed. If we still want to discover them, we’d better hurry.
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Old 07-10-2016, 11:44 AM
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Just to head off some obvious jokes, I presume the OP means the Fermi Paradox.
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Old 07-10-2016, 11:56 AM
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Originally Posted by Wendell Wagner View Post
Just to head off some obvious jokes, I presume the OP means the Fermi Paradox.


You presume well.

I wonder if somebody could edit the title accordingly.
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Old 07-10-2016, 01:09 PM
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It's worse than you think.

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”One in five stars has at least one planet where life might spring up. That’s a fantastically large percentage. That means in our galaxy there’s an order of tens of billions of Earth-like worlds.”
"Life" doesn't necessarily mean life as we know it. We may not even recognize different life forms. And he's referring to planets where life MIGHT spring up, not that it necessarily will . . . or has. And none of this implies "Earth-like worlds."

But I agree, the Universe is probably teeming with life. If the chances of us discovering them by 2040 are remote, the chances of them discovering us (if they haven't already) are much, much greater.
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Old 07-10-2016, 01:20 PM
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"Life" doesn't necessarily mean life as we know it. We may not even recognize different life forms.
At least until it invades our space homes. "Honey, remember that funny rock I found? Did you move it?"

"No, dear."

"And I don't recall the floor being so slimy."

"Maybe if you washed it once in a while."
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Old 07-10-2016, 05:42 PM
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'By 2040, or we never will'?

Laughable. We will keep looking no matter what and we will just find it when we find it. If we ever do, then we will keep looking anyway.
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Old 07-10-2016, 05:51 PM
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We all take it for granted after having read and watched tons of sci-fi that we're going to figure out how to do FTL travel one day. It's just assumed that if there were advanced life in the universe, they'd be all over the place. But I think it's pretty likely that there is life out there, and we'll never meet it simply because of the distances involved.

People also overestimate our detection methods. They've bought into the meme that we'll be able to see everyone's radio and TV broadcasts. But those signals diminish with the cube of the distance. You'd need an antenna network bigger than the solar system to detect radio signals from more than a few light years away.

It seems to me the way we'll discover life will actually be pretty anticlimactic - we'll probably detect a world far away to which we apply some sort of spectroscopy and decide that the combination of elements in their atmosphere very probably indicates life, but not quite for sure.
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Old 07-10-2016, 07:25 PM
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I forget the name of the theory, but there is a theory that life couldn't arise for the first 9 billion years of the universe because stars had a different % of heavy metals in them, and as a result there were more gamma rays. So life couldn't develop because gamma rays were a bigger threat. However I don't know if this theory meant that intelligent life couldn't develop, or that all life would die. Also, in the 600 million years of multicellular life we have had 5 natural extinction events and life has always recovered and kept going. In fact one of the 5 major extinction events could've been due to a gamma ray.

Anyway, forget the name of the theory, but life seems to have arisen 4.1 billion years ago on earth, which is within a billion years of the time when gamma rays became less of a threat.

However, it would only take an alien civilization traveling at 10% the speed of light a million years to colonize the galaxy. That is a rounding error at the timeframes being discussed. We can probably achieve 10% the speed of light with nuclear pluse ships which were theoretically possible back in the 1950s.

I really don't know the answer.

Last edited by Wesley Clark; 07-10-2016 at 07:26 PM.
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Old 07-10-2016, 07:44 PM
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I forget the name of the theory, but there is a theory that life couldn't arise for the first 9 billion years of the universe because stars had a different % of heavy metals in them, and as a result there were more gamma rays. So life couldn't develop because gamma rays were a bigger threat. . . .
I'd never heard that one, but there is a similar argument that it required a few generations of stars, to cook up heavier elements, which are conducive to life, if not absolutely necessary. Chlorophyll has that odd Magnesium atom. Maybe plant life could have developed some other sunlight-gathering molecule, but good old chlorophyll is mighty important to life as we know it.

ETA: Okay, atomic number 12 isn't all that heavy. But, still, it wouldn't have been around before a generation of nucleosynthesis.

Last edited by Trinopus; 07-10-2016 at 07:45 PM.
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Old 07-10-2016, 08:24 PM
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I'd never heard that one, but there is a similar argument that it required a few generations of stars, to cook up heavier elements, which are conducive to life, if not absolutely necessary. Chlorophyll has that odd Magnesium atom. Maybe plant life could have developed some other sunlight-gathering molecule, but good old chlorophyll is mighty important to life as we know it.
Life as we know it existed quite happily without chlorophyll for 500 million years.
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Old 07-10-2016, 08:38 PM
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I think the putative notion that there must be extraterrestrial contact in order for life beyond Earth to exists, is a fallacy and one that's been perpetuated, exacerbated and, indeed, inculcated by [science fiction] entertainment media.

Firstly, who is to say how long a species survives for? Perhaps species die out before they can harness technologies that permit them to travel to other worlds (...even if such an endeavour was an explicit desire in the first place). A destiny that's been postulated for our own kind, by more than one luminary.

Secondly, who is to confirm that intergalactic space travel is even possible for flesh-based organisms? The assumption that "E.T.'s" are all flying about in cloaked U.F.O.'s, is predicated upon "Area-51" silliness and has scant scientific substrata, only rumination, to buttress it. Even getting to the mere neighbouring planet, in Mars, is a massive feat of preservation -- with ramshackle solutions posited of travellers requiring to be hid behind stowed cargo in order to avoid the potential deadly cosmic rays. Reaching literal galaxies, would likely require the realisation of "A.I." and what we now dub "machines", sent in place of our organic selves (...that, or some kind of 'cryo-storage' of the crew). Assuming that "A.I." would not expunge us altogether... or that we do not commune with it and are no longer "human", in the sense we consider ourselves now. But, I digress...

Lastly, why would a far-advanced species - which is a given presumption for interstellar space travel to be reconcilable without fanciful deus ex machina intervention - have any desire to commune with what would comparatively be akin to humans "communing" with insects? Sure -- they may want to "study" us and perhaps simple enact intergalactic diplomatic relations. However, travelling literal light years would not be some off-the-cuff pursuit they could undertake just to fill a couple of petri dishes and for a handshake -- of which, the former 'analysis' could surely be conducted remotely, given their implied, available technology.

Bonus rumination:
What if aliens are not corporeal 'beings'; rather, energy-based entities that we cannot directly contact? What if contact could only be enacted through other energy-harnessing conduits -- e.g., computers? (See: The Astronaut's Wife (1999))

In summation:
I believe this Protagoras’ bias - viewing the universe through an anthropoidal prism - is what leads us to the quandary of why we have yet to make contact with aliens; despite all our efforts and the mathematical proofs that seem to bear out the probability of 'contact' being quite high. If we step outside the square and consider the scenario from an alien species' angle, it's actually quite logical that we have not, and perhaps will not, 'meet' an E.T. outside of a moonshine-fuelled, Bible Belt hoedown.

Our "A.I." successors, on the other hand - if it comes to that - may have a better chance at bridging the aforementioned 'galaxy of gaps'. But by then, perhaps expansion theory would have the skies empty, with nothing to aim for anyway.
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Old 07-10-2016, 08:38 PM
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People also overestimate our detection methods. They've bought into the meme that we'll be able to see everyone's radio and TV broadcasts. But those signals diminish with the cube of the distance. You'd need an antenna network bigger than the solar system to detect radio signals from more than a few light years away.
If they even use that any more (or not yet).

Heck there is also the assumption that a species may exist (as itself or in closely incremental enough evolutionary steps as to maintain civilizational continuity) long enough before plain old extinction catches up with it as to make some sort of significant interstellar progress.

Plus there is the possibility that that civilizations with both actual interstellar potential AND the interest in doing it are not too common on either value, and combined even rarer, and that on top of it either they don't last or can't maintain effort as long as it takes or would at some point just stop because, well, they had enough (as suggested in a different thread). We like to think that all it takes is just one with enough drive to do it. Well, maybe we're wrong.

My purely speculative instinct is that even in the best of cases a vast majority of civilizations come and go without ever making contact, or even finding compelling evidence of life beyond their own stellar system. Nothing to be depressed about in that -- there's 7 billion people on Earth and are we going to say every one of them who did not become Bill Gates or Pope Francis or Kenneth Branagh or Narendra Modi was a failure?
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Old 07-10-2016, 09:06 PM
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Life as we know it existed quite happily without chlorophyll for 500 million years.
For certain definitions of "as we know it." Life as I know it exists in a very rich ecological environment, made up a a web of thousands of species. Early life, B.C. (before chlorophyll) was bacterial soup and algae mats.

(Even that is kind of impressive. Any form of self-organizing life -- throwing energy into the face of entropy -- is remarkably cool.)
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Old 07-10-2016, 09:11 PM
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I forget the name of the theory, but there is a theory that life couldn't arise for the first 9 billion years of the universe because stars had a different % of heavy metals in them, and as a result there were more gamma rays. So life couldn't develop because gamma rays were a bigger threat.
http://io9.gizmodo.com/is-it-time-to...rse-1654960619

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But here's where it gets interesting: The frequency of GRBs were greater in the past owing to lower levels of metallicity in the galaxy. Metal-rich galaxies (i.e. those with significant accumulations of elements other than hydrogen and helium) feature less gamma-ray bursts. Thus, as our galaxy becomes richer in metals, the frequency of GRBs decreases. What this means is that prior to recent times (and by recent we're talking the past 5 billion years or so), GRB extinction events were quite common. And in fact, some scientists suspect that the Earth was struck by a GRB many billions of years ago. Piran and Jimenez figure that these events were frequent and disbursed enough across the Milky Way to serve as constant evolutionary reset buttons, sending habitable planets back to the microbial dark ages before complex life and intelligence had a chance to develop further. Fascinatingly, before about 5 billion years ago, GRBs were so common that life would have struggled to maintain a presence anywhere in the cosmos (yes, the entire cosmos).

This would suggest, in the words of Annis, "the Galaxy is currently undergoing a phase transition between an equilibrium state devoid of intelligent life to a different equilibrium state where it is full of intelligent life."

Humanity, therefore, may not be alone, but one of many intelligent civilizations emerging at roughly the same time.
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Old 07-10-2016, 09:28 PM
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Here is a good article from Wait but Why about the fermi paradox.

http://waitbutwhy.com/2014/05/fermi-paradox.html

This is good too.

https://www.youtube.com/watch?v=sNhhvQGsMEc

Last edited by Wesley Clark; 07-10-2016 at 09:30 PM.
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Old 07-11-2016, 01:35 AM
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it would only take an alien civilization traveling at 10% the speed of light a million years to colonize the galaxy..
Why would they want to colonize the galaxy?
To spread out that far, you have to make a lot of babies.
But we now know that people don't like to make babies.
Every country on earth (with first-world technology and lifestyle) is declining in population, as new births are below replacement level.

So, based on the only scientific evidence we have (i.e. ourselves) we have proof that when an intellligent species becomes advanced, it stops breeding.

Fermi's parodox is solved.
The aliens are sitting at home quite comfortably, with their door closed.
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Old 07-11-2016, 01:49 AM
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People also overestimate our detection methods. They've bought into the meme that we'll be able to see everyone's radio and TV broadcasts. But those signals diminish with the cube of the distance. You'd need an antenna network bigger than the solar system to detect radio signals from more than a few light years away.
There are a few more issues with that theory. As technology advances, data compression improves. When you compress data, you mostly do it by removing redundancy and patterns. Any pattern can be exploited to shrink the data by simply defining the pattern, where it appears, and maybe how that instance deviates from the norm. You end up with, what looks like, random noise.

Also, as technology advances, the efficiency of the system improves. Why beam signals strong enough to go into space if you can use more, local transmitters or directional transmissions or less lossy transmission mediums?

So, you quickly end up with a situation where there are no significant signals going into space, the ones that are look like random background noise, and they are falling off at a cubic rate.
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Old 07-11-2016, 02:12 AM
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What if aliens are not corporeal 'beings'; rather, energy-based entities that we cannot directly contact? What if contact could only be enacted through other energy-harnessing conduits -- e.g., computers? (See: The Astronaut's Wife (1999))
'Beings composed of pure energy' is a popular and fun SF trope, but has anyone ever come up with a remotely plausible framework for how that would work?

Energy doesn't tend to interact with other energy directly, and energy doesn't tend to stay in one place without dissipating or dispersing.

Never mind a sentient being. How can you make any complex system out of pure energy?
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Old 07-11-2016, 07:44 AM
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chappachula writes:

> Every country on earth (with first-world technology and lifestyle) is declining in
> population, as new births are below replacement level.

This is exaggerated and speculative. Most of the world is somewhere close to replacement level, a little above or a little below. The big drop in fertility rates has really gone on only since the mid-twentieth century. To predict that this means that human beings will quit breeding and die out is pushing it. Most trends don't last forever:

https://en.wikipedia.org/wiki/List_o...fertility_rate

https://en.wikipedia.org/wiki/Total_fertility_rate
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Old 07-11-2016, 09:22 AM
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If FTL travel is possible ... where are all the tourists?

I think the most likely thing we'll find out there that presumes to be biological in origin will be an atmosphere with a profound amount of O2, something we'll detect when we can image the spectrum of these atmospheres ... and that technology is a ways off still.
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Old 07-11-2016, 09:31 AM
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We all take it for granted after having read and watched tons of sci-fi that we're going to figure out how to do FTL travel one day. It's just assumed that if there were advanced life in the universe, they'd be all over the place. But I think it's pretty likely that there is life out there, and we'll never meet it simply because of the distances involved.

People also overestimate our detection methods. They've bought into the meme that we'll be able to see everyone's radio and TV broadcasts. But those signals diminish with the cube of the distance. You'd need an antenna network bigger than the solar system to detect radio signals from more than a few light years away.

It seems to me the way we'll discover life will actually be pretty anticlimactic - we'll probably detect a world far away to which we apply some sort of spectroscopy and decide that the combination of elements in their atmosphere very probably indicates life, but not quite for sure.
Pretty much my line of thinking. I once joked that the search for intelligent life will be concluded when we do some spectroscopy using more advanced techniques and find evidence of smog and hydrocarbons in the atmosphere.
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Old 07-11-2016, 10:00 AM
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The least probable thing about Star Trek wasn't any of the technology, except perhaps transporters, but the fact that you had multiple alien species, and us too, existing in a state of rough technological parity. Unlikely in the extreme. So any existing alien species are either so far ahead of us that they'd be here visiting us (presuming that they're the traveling sort), or so far behind us that they're undetectable with our existing capabilities.

Gerard O'Neill once posited the existence of a species he called the "Primans", the first emergent technologically adept intelligence. He postulated that they would eventually create self-replicating probes that would expand out from their parent solar system but would, and fairly quickly as the universe reckons these things, be in place orbiting every star in the galaxy. Maybe the Primans are out there, maybe they're us.

Is there a case to be made for Earth being the home of the first technologically adept intelligence? Maybe there is. There is another theory, and I'm uncertain as to whom to credit for it, that Earth gained an evolutionary advantage due to the nearby presence of a really big moon, relative to the size of it's primary. That the moon, through tidal actions, "stirred the pot", in the primordial seas, resulting in earlier combinations of materials that brought about in life.
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Old 07-11-2016, 10:22 AM
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The issue with the Fermi Paradox is that there's so many assumptions baked into it that it's impossible to even begin to know which one is incorrect and by how much. Chances are many of the assumptions are off, and some probably by a lot. As some pointed out, we have a sample size of one for what life looks like, it's possible it might have arisen in ways very different from ours to the point that we'd have difficulty recognizing it as life. Or maybe just because it's common on Earth doesn't mean that there isn't some odd cosmic coincidence of factors that make our form of life fairly easy to arise and evolve on Earth but difficult or impossible outside that narrow window of precise factors. It's also possible that life might even be fairly common, but intelligent life, the type that could actually create technology to communicate or travel across interstellar space is extremely rare. After all, we're not even sure exactly what factors were involved in why human brain size changed so drastically compared to our ape cousins.

Or maybe there are other intelligent species comparable to ours, but various other factors just never got them to develop advanced technology, perhaps cultural or religious or economic or ecological reasons. Or maybe they did, but they chose not to leave their planet. Or maybe they died out before they could from changes in climate or impacts or star variances; Earth has been remarkably stable in that regard. Or maybe their technology wiped them out.

Or maybe they're out there and we just haven't run into them yet. After all, our earliest radio signals are on the order of a century old, which means they've only traveled as far as about one tenth of one percent of the distance across our own galaxy. Or maybe they just have no interest in communicating with us any more than we do with random wildlife we pass by, they just see us as primitive. Or, perhaps as part of that primitiveness and some idea along the lines of the Prime Directive from Star Trek, they're not interfering with our progress. Or maybe they've seen us and find our culture repulsive for some reason. Or maybe they've TRIED to communicate with us and we weren't able to realize it, either because our technology isn't advanced enough or we just weren't clever enough to decode it.

Consider, a civilization similar enough to us biologically and culturally and technologically that we could theoretically communicate, and they could even be less than 100 light years away, and we'd still have not had enough time for them to have received a signal from us, if they could even detect it against all the background radiation, and and even send a simple "hi" back to us.


Really, I think probablistically, if we exist, even if it's a ridiculously rare event, as unimaginably large as the universe is, it's almost a certainty that other life, even intelligent life exists, it's just impossible to really guess whether life is common enough that we should expect millions or billions in our own galaxy and it's odd that we haven't run into any of them yet, or if it's so rare that we may never encounter them even if we do develop FTL technology and explore our own and adjacent galaxies.
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Old 07-11-2016, 11:18 AM
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When he expressed his perplexity at the lack of observed alien activity, Fermi did not mean to doubt the existence of alien life or civilizations, but to suggest there's something wrong with our approach to the issue.

I don't want to beat about the bush.

If we put our faith aside and look at the facts, what do we have?
1. A 15-billion-old homogeneous universe, where nature follows its course.
2. The nearing end of star formation & galaxy regeneration.
3. Dark energy thinning out the remaining structures & eventually destroying them.
4. Intelligent life on Milky Way’s Earth, a small planet in a peripheral solar system.
5. Absence of alien contact.
6. No evidence of extraterrestrial life.

What can we infer?
1. There must be alien life somewhere else in the universe.
2. There must be alien civilizations contemporary to our own (and there might have been others in the past).
3. Chances of future alien life and especially of future alien civilizations are decreasing dramatically.
4. Life in the universe is typically assimilated by the general context of natural phenomena and fails to stand out.
5. Intelligent life fails to control large-scale environments, such as solar systems, galaxies and so on.
6. Life will be almost impossible to find and there will be no alien contact.
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Old 07-11-2016, 12:35 PM
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When he expressed his perplexity at the lack of observed alien activity, Fermi did not mean to doubt the existence of alien life or civilizations, but to suggest there's something wrong with our approach to the issue.

I don't want to beat about the bush.

If we put our faith aside and look at the facts, what do we have?
1. A 15-billion-old homogeneous universe, where nature follows its course.
In what way was it homogeneous? The Universe has already proceeded through many different stages, with different areas being in different states.

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2. The nearing end of star formation & galaxy regeneration.
Star formation will continue for about 100 trillion years. We are currently near the very beginning of the 'Stelliferous' area. We are nowhere near the end.

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3. Dark energy thinning out the remaining structures & eventually destroying them.
The major effect of expansion from our perspective will be that somewhere between 100 billion and 1 trillion years from now, we will no longer be able to interact with anything in the universe outside of our local group of galaxies. But these are effects so incredibly far into the future that they are essentially irrelevant to any discussion of the Fermi Paradox.

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4. Intelligent life on Milky Way’s Earth, a small planet in a peripheral solar system.
5. Absence of alien contact.
6. No evidence of extraterrestrial life.

What can we infer?
1. There must be alien life somewhere else in the universe.
Nothing you've stated requires this.

Quote:
2. There must be alien civilizations contemporary to our own (and there might have been others in the past).
Again, you're making a claim that is exactly what the Fermi paradox is calling into question.

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3. Chances of future alien life and especially of future alien civilizations are decreasing dramatically.
Only if your curve stretches out over 100 trillion years. For any reasonable timeframe relevant to human existence, we can treat the universe as static and un-evolving.

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4. Life in the universe is typically assimilated by the general context of natural phenomena and fails to stand out.
Sounds like a flowery way of saying, "there's a lot of noise, which makes it hard to discover tiny signals."

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5. Intelligent life fails to control large-scale environments, such as solar systems, galaxies and so on.
Are you assuming that we should have already spotted civilizations capable of controlling their solar system environment?

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6. Life will be almost impossible to find and there will be no alien contact.
I'm not sure where this conclusion comes from. Nothing you've stated leads to this.

The fact is that the time we have actually spent looking for alien civilisations is just a blink of an eye on the time scale of the universe. The number of star systems we have examined is a tiny fraction of a tiny fraction of our own galaxy, and our examination of them consists of views of small portions of their visible light spectrum. It is way, WAY too early to make any declarations about the likelihood of extraterrestrial life or our likelihood of finding them.
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Old 07-11-2016, 12:47 PM
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We still have not ruled out the existence of life within our own solar system. Seems a wee bit early to giving up on the entire galaxy, much less the universe.

Last edited by John Mace; 07-11-2016 at 12:47 PM.
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Old 07-11-2016, 01:08 PM
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One conclusion that seems to jump out of the facts as we know them today is that there will never, ever be FTL travel. All the evidence we have suggests that the universe is essentially infinite in size. The part that we can see, our 'light bubble' is an infinitesimal part of the entire universe.

The thing about infinities is that anything that has a probability > 0 must be certain. So not only must there be other planets with life, there must be an infinite number of them. If FTL travel exists, then this becomes a serious problem for the Fermi Paradox. But if FTL travel is impossible, we are insulated from the infinite universe by our 'light bubble'. And furthermore, we are isolated from other civilizations that developed in our own light bubble but which developed insterstellar travel too late to allow them to get to us. So for example, if some civilization has developed Von Neumann replicating probes that travel at the speed of light 2 billion years ago, they could only conceivably reach our galaxy if the ET galaxy is less than 2 billion light years away. If we assume that the early universe was unsuitable for life for, say the first 5 billion years, and if it takes 4 billion years for intelligent life to arise, then we could theoretically only ever have contact with a civilization less than 4 billion light years from us.

To make the problem even more tractable, we can ignore other galaxies as we don't have the ability to spot life in another galaxy unless it's a Kardachev Type III civilization. We've scanned for these in the nearest globular clusters and galaxies, and found no evidence for them. But they are highly speculative anyway. For any other civilization type, our only hope for detection is within our own galaxy. And realistically, probably only the part of our galaxy nearest us and not obscured by the galactic center.

Narrowing down the problem even more, with our current technology we might be able to detect life spectroscopically or by direct detection of large structures like Dyson Spheres out to perhaps 5000 light years. That gets us down to about 600 million stars, of which only a fraction are 'G' type stars. Of those, we have only looked at a tiny fraction of them - about 70,000 stars with Kepler, for example. And, we're just starting to develop the capability to look at the atmosphere's of planets spectroscopically.

I believe this is the region that Seth Shostak is talking about when he says he thinks it's likely that we will discover life by 2040. It's in this time period that new space and ground-based telecopes will be able to identify planets and their atmospheric signatures at that scale.

Traditional SETI has been focused on picking up radio signals. This is a much more dicey proposition, as no reasonable radio signals could be picked up unless the stars are very close. SETI has only scanned a few thousand systems, so it's not that surprising that nothing has been found.
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Old 07-11-2016, 02:55 PM
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Why would they want to colonize the galaxy?
To spread out that far, you have to make a lot of babies.
But we now know that people don't like to make babies.
Every country on earth (with first-world technology and lifestyle) is declining in population, as new births are below replacement level.

So, based on the only scientific evidence we have (i.e. ourselves) we have proof that when an intellligent species becomes advanced, it stops breeding.

Fermi's parodox is solved.
The aliens are sitting at home quite comfortably, with their door closed.
They might stop breeding, but Von Neumann machines aren't just about breeding. Self-replicating probes would be an obvious solution to any species that is even half as curious as human beings. If it ever becomes remotely possible, I suspect humans will try sending probes to other galaxies even if millions of years have to pass before any data is returned.

But even more important that that: all you need is one species that does want to keep breeding. As long as we're playing with percentages, you can plug in a factor for that as well and still come up with a number that suggests the galaxy should be overrun by now, even at sub light speeds and even if most species have no interest in doing.
  #29  
Old 07-11-2016, 04:04 PM
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UY Scuti writes:

> . . . A 15-billion-old homogeneous universe . . .

13.8 billion.
  #30  
Old 07-11-2016, 04:47 PM
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If FTL travel is possible ... where are all the tourists?

I think the most likely thing we'll find out there that presumes to be biological in origin will be an atmosphere with a profound amount of O2, something we'll detect when we can image the spectrum of these atmospheres ... and that technology is a ways off still.
Where are the tourists? Same place as the tourists going to Egypt - we're too violent to want to visit.

O2 will indicate the presence of life. Once we find pollution in an atmosphere we'll know that we've found intelligent life. And I agree finding intelligent life that way is much more likely than by them dropping in.
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Old 07-11-2016, 10:57 PM
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The issue with the Fermi Paradox is that there's so many assumptions baked into it that it's impossible to even begin to know which one is incorrect and by how much. Chances are many of the assumptions are off, and some probably by a lot.
I think many in this thread have misunderstood the Fermi Paradox.
It's not saying "Assuming aliens are humanoid, communicate using radio waves, and exploit FTL...".
It makes no such assumptions.

All it's saying, is that on the basis of what we know, it seems strange we have not detected any evidence of extraterrestrial life. We can speculate on why that is, and that's largely the point.

e.g. Maybe aliens have visited us but they are so advanced they can do so without us even realizing? Fermi's paradox does not declare such speculation wrong, but we have no data to support such an idea at this time. Hence the paradox -- and speculation -- continues.
  #32  
Old 07-12-2016, 12:04 AM
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Von Neumann machines ... Self-replicating probes would be an obvious solution
Even if you create a few billion machines and send them all over the universe, how would we detect them?
I assume each probe would be the size of one of our satellites, or maybe the size of the space station. (or maybe the size of a monolith, like in the movie )
It could come visiting, take some pictures, and keep on going, and we'd never know.
It could fly by the earth along with the millions of asteroids which we can't detect. (or don't bother detecting?.)
  #33  
Old 07-12-2016, 12:51 AM
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Even if you create a few billion machines and send them all over the universe, how would we detect them? . . .
If they're self-replicating machines, then one copy could remain here, monitoring events. When it detects signs of intelligent life, it would make another copy to send back home to report the news.

If it wants to make contact, we'd know!
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Old 07-12-2016, 01:08 AM
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When it detects signs of intelligent life, it would make another copy to send back home to report the news.
If it wants to make contact, we'd know!
Ahh...but what if:
After monitoring us for a couple million years, it detects something interesting, and reports back to ask for further instructions....only to get no answer, because its home civilization no longer exists ?
We'd never know we've been spotted!





(hmmm.....has anybody ever written a sci-fi story like this? )
  #35  
Old 07-12-2016, 01:20 AM
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Two necessarily speculative points:
1) As far as we know, we are the only species in billions of years of life on Earth that is capable of advanced civilization. Life in the universe may be common but intelligent life may be much rarer.

2) Advanced industrial civilization may not be stable because it tends to create technologies which threaten itself. We have already created one such technology, nuclear weapons, and have experienced at least one close shave during the Cuban missile crisis. In a few decades we may face another existential threat with climate change and there could be yet others with biological weapons and out-of-control AI. These threats don't have to complete destroy the species, just destroy the kind of advanced civilization which can travel and communicate through space. For all we know, the universe may be full of post-apocalyptic societies which are really hard to detect.
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Old 07-12-2016, 03:29 AM
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Two necessarily speculative points:
1) As far as we know, we are the only species in billions of years of life on Earth that is capable of advanced civilization. Life in the universe may be common but intelligent life may be much rarer.
If intelligent life persists once it has emerged, then it could be just as common as non-intelligent life. Multicellular life emerged about 0.5 gigayears ago; our civilisation is only ten thousand years old, but if it persists for a gigayear, then the duration of intelligence on our planet would be twice as long as that of non-intelligent life.

Quote:
2) Advanced industrial civilization may not be stable because it tends to create technologies which threaten itself. We have already created one such technology, nuclear weapons, and have experienced at least one close shave during the Cuban missile crisis. In a few decades we may face another existential threat with climate change and there could be yet others with biological weapons and out-of-control AI. These threats don't have to complete destroy the species, just destroy the kind of advanced civilization which can travel and communicate through space. For all we know, the universe may be full of post-apocalyptic societies which are really hard to detect.
This may be true of intelligent species which closely resemble humans in development, but if life turns out to be very diverse in our universe, we can't assume that their civilisation would follow a similar path. What crises would be faced by a civilisation made up of intelligent sea-snakes, or slime-molds, or bacterial mats? What climate changes would occur on a planet with supercritical water for an atmosphere? What weapons would a race of intelligent computers be vulnerable to?

Last edited by eburacum45; 07-12-2016 at 03:29 AM.
  #37  
Old 07-12-2016, 03:52 AM
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1) As far as we know, we are the only species in billions of years of life on Earth that is capable of advanced civilization. Life in the universe may be common but intelligent life may be much rarer.
Any sentient species would likely find itself in the same position (with maybe one or two very closely related subspecies).
A sentient species is unlikely to be among the simpler, earlier species to arise and a sentient species' learning and exchange of ideas is almost-certainly going to be orders of magnitude faster than slower-than-trial-and-error natural selection (so in the time it takes sentient species #2 to evolve, #1 is probably already exploring the galaxy).

2) Advanced industrial civilization may not be stable because it tends to create technologies which threaten itself.
[snip]
These threats don't have to complete destroy the species, just destroy the kind of advanced civilization which can travel and communicate through space. For all we know, the universe may be full of post-apocalyptic societies which are really hard to detect.[/QUOTE]

I think it would have to be 100% destruction, because post-apocalyptic scenarios are unlikely to be stable.
With the recent memory of technology, millions of artifacts lying around, and recalling how fast humans can multiply if we want to, I think we would likely be back to skyscrapers and iPhones in virtually no time at all.
Certainly not the timescales required for it to make a noticeable difference to the fermi paradox.
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Old 07-12-2016, 04:21 AM
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Obviously it would depend on the nature of the apocalypse. In the event of a major nuclear war you would not only have the initial destruction but the subsequent climate change which would probably lead to a collapse of the world food supply and probably most governments. After that there would probably be brutal wars around world for the limited resources that are still available. There is no telling what the ideologies of the survivors would be. I would guess many of them would be extreme religious cults along with brutal military dictatorships neither of which may have much of an interest in reviving industrial progress which could undermine their power. Even if they did, much of the world would be uninhabitable and you couldn't simple revive the very complex and interconnected economic system we have today.
  #39  
Old 07-12-2016, 08:58 AM
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If FTL travel is possible ... where are all the tourists?
Idunno. Checking out more interesting locales, maybe.
  #40  
Old 07-12-2016, 09:00 AM
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Ahh...but what if:
After monitoring us for a couple million years, it detects something interesting, and reports back to ask for further instructions....only to get no answer, because its home civilization no longer exists ?
We'd never know we've been spotted!





(hmmm.....has anybody ever written a sci-fi story like this? )
Kinda-sorta.

See Red Dwarf.
  #41  
Old 07-12-2016, 09:35 AM
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....radio and TV broadcasts. But those signals diminish with the cube of the distance. You'd need an antenna network bigger than the solar system to detect radio signals from more than a few light years away....
According to Dr. H. Paul Shuch who is an expert on this area, our current technology could detect earth-like TV and radio leakage signals from an extra-solar planet 1,000 light years away:

http://www.setileague.org/askdr/howfar.htm
  #42  
Old 07-12-2016, 11:43 AM
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It is entirely possible that technologically advanced species exist on other planets and already have visited us. And decided we just ain't ready yet.
  #43  
Old 07-12-2016, 12:03 PM
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And decided we just ain't ready yet.
What, we need to be fattened up?
  #44  
Old 07-12-2016, 12:08 PM
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Yea, and we'll be soon ready.
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Old 07-12-2016, 12:27 PM
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Even if you create a few billion machines and send them all over the universe, how would we detect them?
I assume each probe would be the size of one of our satellites, or maybe the size of the space station. (or maybe the size of a monolith, like in the movie )
It could come visiting, take some pictures, and keep on going, and we'd never know.
It could fly by the earth along with the millions of asteroids which we can't detect. (or don't bother detecting?.)
There are a lot of possibilities. It is certainly possible that someone like this is in orbit right now, but invisible to our sensors.

However, when it only takes one aggressive/expansionist species a few million years to span the galaxy, I would still interpret the lack of evidence for intelligent species to mean that there just aren't very many. (Especially so when natural selection favors aggressive expansionist species to such a large degree. That should be true on any planet.)
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Old 07-12-2016, 01:43 PM
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According to Dr. H. Paul Shuch who is an expert on this area, our current technology could detect earth-like TV and radio leakage signals from an extra-solar planet 1,000 light years away:

http://www.setileague.org/askdr/howfar.htm
He doesn't specify what kind of man-made radiation he is talking about, but probably the most detectable emissions would be various kinds of radar, especially the tight-beam radar that is used to map asteroids. Of course this sort of radiation is very directional, so you'd have to get lucky. Another highly directional emission would of course be deliberate messages aimed at likely candidates; I don't know if any alien species would be daft enough to do this, however.
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Old 07-12-2016, 01:48 PM
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Even if you create a few billion machines and send them all over the universe, how would we detect them?
I assume each probe would be the size of one of our satellites, or maybe the size of the space station.
The payload might be the size of the spacestation, but the rocket would probably be a lot larger. To get between the stars, a self-repping system might need to use very large, and very bright, rockets. We might detect such rockets at significant distances, especially if there are lots of them.
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Old 07-12-2016, 02:09 PM
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Bonus rumination:
What if aliens are not corporeal 'beings'; rather, energy-based entities that we cannot directly contact? What if contact could only be enacted through other energy-harnessing conduits -- e.g., computers? (See: The Astronaut's Wife (1999))
"Energy based beings" are a staple of sci-fi, but what does that even mean?
  #49  
Old 07-12-2016, 02:32 PM
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The payload might be the size of the spacestation, but the rocket would probably be a lot larger. To get between the stars, a self-repping system might need to use very large, and very bright, rockets. We might detect such rockets at significant distances, especially if there are lots of them.
I was going to post an analysis like this on why I suspect we'd be able to see alien probes - heat signatures, if nothing else, because getting rid of waste heat is not easy for a spaceship - but there's so much we don't know about what is possible. Anything we can theorize from current knowledge is very likely to be detectable by our current technology.

Still... I do acknowledge the possibility that HP Lovecraft was right and we're continually surrounded by fourth-dimensional Cthulhu-spawn.
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Old 07-12-2016, 03:01 PM
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A very good book on the subject: Webb, Stephen (2015). If the Universe Is Teeming with Aliens... Where Is Everybody? Seventy five Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life (2nd ed.). Copernicus Books. ISBN 978-3-319-13235-8. (I only have the 2002 edition which only contained 50 solutions.)
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