What do you think is the most likely explanation for the Fermi paradox?

[Noclevername]

(1) I said if they were even vaguely like us. It's reasonable to expect this, because of the law of mediocrity.

We've found that our Solar System is atypical of planetary systems. Why would our biology not be as well?

Anyhow, if ET was commonplace, it would only take one out of many to spread through the galaxy.

And it might not be commonplace, I'm saying. Or it might be so different from us as to have no commonality of behavior or goals.

(2) Going by appearances this is about the one fact we have to work with. Yes human style civs seem to be vanishingly rare, so much so that we appear unique

We don't know that. We'd be undetectable from only a few light years away. There could be a million like us in our galaxy and they would be invisible from Earth.

But that's not enough, you can't just say ET is not observed because he does not exist. You have to say WHY ET does not exist.

On the contrary, in a big empty universe WE are the exception. Most of the Universe is inimical to life. It took a very special niche to make something like us, with liquid water, the right amount of energy, the right mix of chemicals, and stability over time.

And this is a big problem, because life started pretty quickly on Earth, and many argue that the evolutionary steps that lead to us are pretty much inevitable given enough time.

Logically, this does not follow. We have an example of one, with no way to calculate how often life occurs, or fails. And life does not just mean intelligent, starfaring life. Plenty of room for alternate lines of evolution that do not include brains like ours. We almost went extinct several times in our evolutionary history. Our survival itself appears to be very much a fluke.

[profloater]

Indeed we seem to have had many major events that are part of our evolution, the moon, the distance from the sun, the composition. the impacts, the volcanoes, the tectonic plates, the extinctions, but given billions of possible planets we might expect that to happen again. The lack of evidence is surely no surprise for the distances and times we now have in our cosmic model. Of course some people believe we have encountered aliens and we might have that in our distant past (2001 hypothesis?) but that comes down to a conspiracy theory. And talking of conspiracy theories, the lack of evidence? How can a person test that element? Billions of years is a really long time upon which to speculate, if we count in 10,000 years of our recorded history as an epoch, that's 100,000 epochs in one billion years. Synchronicity really seems unlikely between us and distant stars.

[Noclevername]

Billions of years is a really long time upon which to speculate, if we count in 10,000 years of our recorded history as an epoch, that's 100,000 epochs in one billion years. Synchronicity really seems unlikely between us and distant stars.

Right, see post #45.

[kzb]

We've found that our Solar System is atypical of planetary systems. Why would our biology not be as well? (1)



And it might not be commonplace, I'm saying (2). Or it might be so different from us as to have no commonality of behavior or goals (3).



We don't know that. We'd be undetectable from only a few light years away. There could be a million like us in our galaxy and they would be invisible from Earth (4).



On the contrary, in a big empty universe WE are the exception. Most of the Universe is inimical to life. It took a very special niche to make something like us, with liquid water, the right amount of energy, the right mix of chemicals, and stability over time. (5)



Logically, this does not follow. We have an example of one, with no way to calculate how often life occurs, or fails. And life does not just mean intelligent, starfaring life. Plenty of room for alternate lines of evolution that do not include brains like ours. We almost went extinct several times in our evolutionary history. Our survival itself appears to be very much a fluke. (6)

(1) The principle of mediocrity. Yes it might be wrong in this case but it is the only thing we have to go on.

(2) The evidence is that is certainly not commonplace. But you can't stop there. The question is why.

(3) See (1)

(4) It's exceedingly improbable there could be a million like us in the galaxy and none of them are advanced enough for interstellar travel. Many of them had 4 billion years on us. It's just inconceivable if you believe the galactic habitable zone started to exist when the mainstream theory says it did. Statistically the vast majority of that "million like us" are millions of years in advance of us.

(5) The problem is, given an Earth-like planet and billions of years, the evidence points to life and evolution being pretty much inevitable. Life started on Earth as soon as conditions became suitable.

(6) See (1)

[Noclevername]

1. The "principle" of mediocrity is a philosophy, not a physical law. It can certainly be wrong or misleading.

2. What evidence? Please present it.

3. See 1.

4. "Inconceivable" is a failure of imagination, not a valid point and certainly not a supported statistic.

5. Again, please show evidence.

6. See 1.

[mkline55]

My explanation is that there is no paradox. The reasons: Long term - I mean VERY long term - determination, organization, communication and dedication plus limited resources and time.

It's easy enough to draw out a plan that says each colony takes t1 amount of time to build n1 new colony ships and then it takes t2 amount of time to reach the next destination. Isn't that nice! But who says your 20th generation grandkids will care anything about your galaxy domination plan? What links each instance of civilization together over decades-long and centuries-long communication distances? It's like saying, "We're sending all of you families on this 200-year journey. Call this number when you get there for more instructions." "This number" will be long disconnected in 200 years. And if you did get a response? 8 years delay minimum. You can't really stay in constant contact. But lets say you allowed that anyway. Who wants to take their orders from those Earthers?

Now suppose you assume the ability to achieve 1% light speed. Great! But you really need to double that, because you'll probably want to slow down before you reach the target unless your goal is to just splash some bits of DNA around the next star. Your star ship has a major energy problem.

Suppose one complete colony ship arrives on a planet. It's something like Mars or Venus. No life. Very unfriendly atmosphere. No food. No oil fields. No coal. No wood to burn. No smelters. No industry. No surface water. Nothing. You will have to build all that. Even if you already had the technology, you lack the very basic infrastructure. The colony would spend its first decades just fighting to stay alive. Terra-forming could take several millennia if not tens of millennia or never. It would almost certainly not be building star ships for another 10000 years. Why build star ships until you've fully utilized the resources where you already are?

So there you are, 10,000 -100,000 years from now. You lost communication with home long, long ago and don't even know if they still exist. What's your plan? The original plan is a long-ago myth, and that's assuming everything went right. How's that galaxy domination coming along?

[cosmocrazy]

Well it certainly looks like it. But the question is why?

The only explanation that seems reasonable at the moment is that technological intelligence is/could be extremely rare because it takes just the right conditions, time and sequence of events for it to develop. When you you look at us here on Earth and you piece together everything that had to be, happen and at the right time for us to develop into technological intelligence, its quite amazing.

Maybe life is abundant throughout the universe, but we have an example here on Earth that, although life has been around for a couple of billion years or so only one species has developed with technological capabilities, us. Its quite plausible that even if we find life elsewhere technological life could be so rare it happens/ed only once.

[Jens]

The only explanation that seems reasonable at the moment is that technological intelligence is/could be extremely rare because it takes just the right conditions, time and sequence of events for it to develop. When you you look at us here on Earth and you piece together everything that had to be, happen and at the right time for us to develop into technological intelligence, its quite amazing.

I think that is one reasonable explanation. I do have another, which I may prefer, which requires a little bit of thinking that is different from how I think most people think. We have never gone to another star ourselves. Now, if we are basically at the pinnacle of technological achievement, i.e. if progress has more or less come to an end and we have made the important discoveries that can be made, then perhaps going to another star is just technologically impractical and so nobody does it. There may be things like Voyager floating around, but again, we didn't target any particular extrasolar planet because Voyager will be long dead by the time it reaches anything, and it would just seem like a rock, and would burn up in an atmosphere so it would not be detected. I realize that most people like to think that in a million years we will be incredibly advanced, but it is not a given. We have harnessed combustion, nuclear fission, and almost nuclear fusion, but there may be nothing beyond that.

[Noclevername]

I think that is one reasonable explanation. I do have another, which I may prefer, which requires a little bit of thinking that is different from how I think most people think. We have never gone to another star ourselves. Now, if we are basically at the pinnacle of technological achievement, i.e. if progress has more or less come to an end and we have made the important discoveries that can be made, then perhaps going to another star is just technologically impractical and so nobody does it. There may be things like Voyager floating around, but again, we didn't target any particular extrasolar planet because Voyager will be long dead by the time it reaches anything, and it would just seem like a rock, and would burn up in an atmosphere so it would not be detected. I realize that most people like to think that in a million years we will be incredibly advanced, but it is not a given. We have harnessed combustion, nuclear fission, and almost nuclear fusion, but there may be nothing beyond that.

I don't know of any evidence that supports the idea that we're out of ideas.

[Jens]

I don't know of any evidence that supports the idea that we're out of ideas.

Two things:

First, I never said I thought we had run out of ideas. I was not making such a sweeping statement. I only meant to say that whatever ideas we have, they might not be sufficient, because of limitations of the physical world, to allow us to make interstellar travel possible. Do you understand the difference?

And second, I never said I had evidence. Please do not twist what I said. I only meant to say that it is a possibility. Of course I recognize that there could be some force that we have not encountered yet, so please do not treat me like I'm too stupid to recognize that possibility. I am only saying that it is possible that it is too technically difficult; I am not asserting that it is.

[cosmocrazy]

Two things:

First, I never said I thought we had run out of ideas. I was not making such a sweeping statement. I only meant to say that whatever ideas we have, they might not be sufficient, because of limitations of the physical world, to allow us to make interstellar travel possible. Do you understand the difference?

And second, I never said I had evidence. Please do not twist what I said. I only meant to say that it is a possibility. Of course I recognize that there could be some force that we have not encountered yet, so please do not treat me like I'm too stupid to recognize that possibility. I am only saying that it is possible that it is too technically difficult; I am not asserting that it is.

I think this is probably the main stumbling block (my bold) unless we/ET somehow develops/discovers technology that enables practical, low risk, fast interstellar travel then we are as good as cut off from any other extra solar planetary system especially beyond our local region. Other than waiting long periods of time to exchange information by radio we are presently stuffed.

Its a bit like being stuck on a tiny island in the middle of a vast ocean thousands of miles away from any other known land, with just a flimsy dingy and a tennis racket as a paddle, with faint smoke signals as the only means of communication, that may or may not be detected if there just happens to be somebody out there looking in the right direction and identifying the signal as unusual enough to investigate it.

[Roger E. Moore]

...unless we/ET somehow develops/discovers technology that enables practical, low risk, fast interstellar travel then we are as good as cut off from any other extra solar planetary system especially beyond our local region.

The stunning increase in technology and scientific methods being applied to astronomy in general is, to my thinking, allowing us increasing knowledge of star systems over tremendous distances. It is almost, but not quite, like going there ourselves.

Earlier I entertained the idea that actual discovery of and communication with aliens could be far more difficult than we realize, not to mention whether we are able to recognize the aliens as intelligent at all (at first). We do not know anything about the actual life span of civilizations, how high-tech cultures develop, etc. It's a blank. I hear from people who think we'll be immortal and turn into little gods, but that remains to be seen.

[Ross 54]

There are apparently about 40 billion potentially habitable planets in our galaxy. If only one in a million of those is actually host to a civilization, that means 40,000 such civilizations in the Milky Way. It doesn't seem too much to hope that a fair number of these civilizations are our contemporaries, are interested in communicating with other life in the galaxy, and have enough in common with us to make for mutual recognition, and allow some level of understanding to develop between us.

[kzb]

1. The "principle" of mediocrity is a philosophy, not a physical law. It can certainly be wrong or misleading.

2. What evidence? Please present it.

3. See 1.

4. "Inconceivable" is a failure of imagination, not a valid point and certainly not a supported statistic.

5. Again, please show evidence.

6. See 1.

1) I agree but in the absence of anything else it's all we have to go on. It's reasonable to think we are not complete outliers. The chances are, we are near the average, not miles away from it.

2) The evidence is we do not observe any signs of ET. No artefacts in the geological record, no calling cards left on the moon, no communication even though they must know we are here.

3) See (1)

4) You might not like the word inconceivable, but it is a valid point and it is very much a supported statistic. Out of one million intelligent races in the galaxy, the probability that we are the first in a simplistic view would be one in a million. But it's worse than that because we know (or think we know) that the galaxy has been habitable for about 8 billion years. The first civilisations should've been around about 4 billion years ago. The average civilisation in the MW is one billion years old. Those are the valid statistics and its not imagination.

5) The only example known is the Earth itself. Life started as soon as possible. That supports the idea that it is pretty inevitable. This is the only evidence available at present time, so we have to go with the principle of mediocrity. It might be wrong in this instance but it's all we've got.

6) See (1)

[kzb]

Here are two theories which seem to have current traction:

(1) The Great Filter occurs between prokaryotic life and eukaryotic life.

This was given as the reason by no less than Brian Cox on his TV programme. In support is the observation that prokaryotic life started on Earth pretty much immediately. It was about 3 billion years after that eukaryotes appeared, the long delay being due to the low probability of the symbiotic events needed to bring it about. According to this theory, prokaryotic life will be commonplace in the universe but complex life extremely rare.

(2) The idea that the galaxy first became habitable 8 billion years ago is wrong. It was much later.

This has got called the "phase change" for some reason. The idea is that GRBs and supernovae had a higher frequency in the past. It is only comparatively recently that the GRB frequency has declined to the point that Earth-like planets are left alone for long enough to evolve intelligent life. According to this theory, ET did not first evolve billions of years ago, and has not had time to colonise the galaxy as assumed in the Fermi paradox. This theory on the face of it fits the bill but there are still problems.

[Colin Robinson]

My explanation is that there is no paradox. The reasons: Long term - I mean VERY long term - determination, organization, communication and dedication plus limited resources and time.

It's easy enough to draw out a plan that says each colony takes t1 amount of time to build n1 new colony ships and then it takes t2 amount of time to reach the next destination. Isn't that nice! But who says your 20th generation grandkids will care anything about your galaxy domination plan? What links each instance of civilization together over decades-long and centuries-long communication distances? It's like saying, "We're sending all of you families on this 200-year journey. Call this number when you get there for more instructions." "This number" will be long disconnected in 200 years. And if you did get a response? 8 years delay minimum. You can't really stay in constant contact. But lets say you allowed that anyway. Who wants to take their orders from those Earthers?

Now suppose you assume the ability to achieve 1% light speed. Great! But you really need to double that, because you'll probably want to slow down before you reach the target unless your goal is to just splash some bits of DNA around the next star. Your star ship has a major energy problem.

Suppose one complete colony ship arrives on a planet. It's something like Mars or Venus. No life. Very unfriendly atmosphere. No food. No oil fields. No coal. No wood to burn. No smelters. No industry. No surface water. Nothing. You will have to build all that. Even if you already had the technology, you lack the very basic infrastructure. The colony would spend its first decades just fighting to stay alive. Terra-forming could take several millennia if not tens of millennia or never. It would almost certainly not be building star ships for another 10000 years. Why build star ships until you've fully utilized the resources where you already are?

So there you are, 10,000 -100,000 years from now. You lost communication with home long, long ago and don't even know if they still exist. What's your plan? The original plan is a long-ago myth, and that's assuming everything went right. How's that galaxy domination coming along?

Well said.

And even if the original coloniser planet has retained its wish to dominate the galaxy, detects that the 1st wave of colonists have abandoned that great project, and decides to put the plan back on track by sending out a 2nd wave of colonists in another star ship, there's a further snag... The descendants of the 1st wave may tell the newcomers: "Sorry strangers, but this star system is taken... You'll have to turn round and go back home."

That's part of the argument for Geoffrey Landis' percolation theory, which concludes that interstellar colonisation, even if feasible, may be a slow, patchy process, with big tracts of space remaining uncolonised over geological time.

[Noclevername]

1) I agree but in the absence of anything else it's all we have to go on. It's reasonable to think we are not complete outliers. The chances are, we are near the average, not miles away from it.

2) The evidence is we do not observe any signs of ET. No artefacts in the geological record, no calling cards left on the moon, no communication even though they must know we are here.

3) See (1)

4) You might not like the word inconceivable, but it is a valid point and it is very much a supported statistic. Out of one million intelligent races in the galaxy, the probability that we are the first in a simplistic view would be one in a million. But it's worse than that because we know (or think we know) that the galaxy has been habitable for about 8 billion years. The first civilisations should've been around about 4 billion years ago. The average civilisation in the MW is one billion years old. Those are the valid statistics and its not imagination.

5) The only example known is the Earth itself. Life started as soon as possible. That supports the idea that it is pretty inevitable. This is the only evidence available at present time, so we have to go with the principle of mediocrity. It might be wrong in this instance but it's all we've got.

6) See (1)

...


I yield the floor. No way I can argue on the basis of musts and should haves. You have fun now.

[SkepticJ]

“In the absence of evidence one way or another, it’s reasonable to conclude that most people will have four hundred million dollars.” - Lottery Winner assuming that they’re typical, in accordance with the principle of mediocrity.

[Colin Robinson]

“In the absence of evidence one way or another, it’s reasonable to conclude that most people will have four hundred million dollars.” - Lottery Winner assuming that they’re typical, in accordance with the principle of mediocrity.

What sort of lottery winner would have an “absence of evidence one way or another”?

Why do you think abiogenesis and/or evolution are comparable to a lottery?

[swampyankee]

There's all sorts of possible answers to the Fermi paradox, all of which have roughly equal evidence to support them.

• We're in some sort of nature preserve. Not a few SF authors, such as Brin, based fairly successful series on this concept.
• There are no technological aliens
• They're on the other side of the galaxy, and haven't yet gotten here
• They're here, but we don't notice
• We're unique
• There were technological aliens, but we missed them.
• Everyone is stupid and wipes themselves out at some time
• We're close to the realizable limits on space travel. Interstellar travel and communication is not feasible on a significant scale, even if it's physically possible. Gram scale star wisps are as good as it can get.

I think the easiest one for now is that the spread is not 0.1% of c, but orders of magnitude lower.

[SkepticJ]

What sort of lottery winner would have an “absence of evidence one way or another”?

Why do you think abiogenesis and/or evolution are comparable to a lottery?

One that’s confined to their house and yard out in a rural area, and that hypothesizes as to why no one ever comes to visit them?

Because evolution is a mindless process, it doesn’t have to make creatures remotely like us. It mostly doesn’t.

[Colin Robinson]

One that’s confined to their house and yard out in a rural area, and that hypothesizes as to why no one ever comes to visit them?

Because evolution is a mindless process, it doesn’t have to make creatures remotely like us. It mostly doesn’t.

Evolution has produced quite a range of creatures whose brains are bigger and more capable than those of their ancestors. We discussed a few of them in the thread Evolution of Intelligence: a comparison. Are all these critters lottery winners?

[Noclevername]

Evolution has produced quite a range of creatures whose brains are bigger and more capable than those of their ancestors. We discussed a few of them in the thread Evolution of Intelligence: a comparison. Are all these critters lottery winners?

You missed the context of the comment, I think. It was a response to kzb's assertion about mediocrity.

[kzb]

“In the absence of evidence one way or another, it’s reasonable to conclude that most people will have four hundred million dollars.” - Lottery Winner assuming that they’re typical, in accordance with the principle of mediocrity.

But it's all we have to go on.
If you say humans on Earth are a one in a trillion outlier then there is no paradox. There is no ETI, agreed.

[kzb]

There's all sorts of possible answers to the Fermi paradox, all of which have roughly equal evidence to support them.

• We're in some sort of nature preserve. Not a few SF authors, such as Brin, based fairly successful series on this concept.
• There are no technological aliens
• They're on the other side of the galaxy, and haven't yet gotten here
• They're here, but we don't notice
• We're unique
• There were technological aliens, but we missed them.
• Everyone is stupid and wipes themselves out at some time
• We're close to the realizable limits on space travel. Interstellar travel and communication is not feasible on a significant scale, even if it's physically possible. Gram scale star wisps are as good as it can get.

I think the easiest one for now is that the spread is not 0.1% of c, but orders of magnitude lower.

What about artificial intelligences?

[kzb]

You missed the context of the comment, I think. It was a response to kzb's assertion about mediocrity.

But the principle of mediocrity does support the evolution of intelligence. As does the fossil record.

[Noclevername]

But the principle of mediocrity does support the evolution of intelligence. As does the fossil record.

No. You cannot generalize based on an example of one. Period!

[Ross 54]

The generalization here is one based on repeated instances, where human beings imagined themselves uniquely situated in the the universe, only to find, when more knowledge was available, that this was not the case. From this it seems wise to have reservations about any claim about our special status.

In very ancient times, various nations tended to see themselves at the center of a flat world, with other nations surrounding them.

When the world was finally seen as a sphere, with a surface having no center, this world of ours was imagined to be at the center of the universe, with the planets, Sun and stars circling about it.

After it was realized that the Sun was the center of our solar system, it was often thought that planets circling other stars were very rare, and that our system of planets was the result of a freakish near-collision between the Sun and another star.

When the disk-like shape of our galaxy began to be understood, it was frequently assumed that we were at its center. Later, the tendency was to see out galaxy as unique in space, with the nature of other galaxies not understood.

All of these human conceits have come to nought, swept away by newer, better knowledge. Let us not assume, again, that our knowledge is now complete, and that intelligent life is somehow reserved for our one little planet, or that it is as unusual as planets orbiting other stars were once mistakenly believed to be.

[Noclevername]

The generalization here is one based on repeated instances, where human beings imagined themselves uniquely situated in the the universe, only to find, when more knowledge was available, that this was not the case. From this it seems wise to have reservations about any claim about our special status.

In very ancient times, various nations tended to see themselves at the center of a flat world, with other nations surrounding them.

When the world was finally seen as a sphere, with a surface having no center, this world of ours was imagined to be at the center of the universe, with the planets, Sun and stars circling about it.

After it was realized that the Sun was the center of our solar system, it was often thought that planets circling other stars were very rare, and that our system of planets was the result of a freakish near-collision between the Sun and another star.

When the disk-like shape of our galaxy began to be understood, it was frequently assumed that we were at its center. Later, the tendency was to see out galaxy as unique in space, with the nature of other galaxies not understood.

All of these human conceits have come to nought, swept away by newer, better knowledge. Let us not assume, again, that our knowledge is now complete, and that intelligent life is somehow reserved for our one little planet, or that it is as unusual as planets orbiting other stars were once mistakenly believed to be.

We are atypical in many ways. Let us also not assume that we are "normal" in a Universe that appears to have no such category. Infinite diversity in infinite combinations.

[Noclevername]

But the principle of mediocrity does support the evolution of intelligence. As does the fossil record.

Evolution Does Not Work That Way. It is all ad hoc, based on whatever random mutations pop up first that manage to continue to reproduce themselves. It's Rube Goldberg.

Case in point, Earth life has evolved billions of very successful solutions to survival that do not include any form of brain.