The Fermi Paradox: where are they?

[lpetrich]

The lack of overt and widely-agreed-on evidence of extraterrestrial intelligent entities is a serious problem, when one considers how large and old our Universe is. This is the Fermi Paradox, after physicist Enrico Fermi allegedly once asking "Where is everybody?" or "Where are they?"

I've come across numerous proposed solutions, like what's listed in  Fermi Paradox, The Fermi Paradox , Expanded | Second Nexus, Possible Answers to the Fermi Paradox, and 11 of the Weirdest Solutions to the Fermi Paradox.

It might be that we are the only technological civilization in all of the Universe. We could be the first to emerge, or else our emergence is an extremely lucky accident that will never be repeated.

That can be the case if it takes too many lucky accidents to produce a civilization capable of interstellar communication or spaceflight. Drake's equation is a simplified version of what is necessary. Here is my estimate: Earthlike planets in dynamically stable orbits around Sunlike stars. Origin of life. Autotrophic metabolism, making all one's biological molecules from inorganic precursors. Photosynthesis. Oxygen release. Multicellularity, both plantlike and animallike. Living on land, both plants and animals. Social groups. Language. Manipulation and tool making. Sentience. Nerdiness, for lack of a better word. Agriculture. Abstract science. Industrialization. Radio. Computers. Avoiding self-destruction.

Another sort of lucky accident would be surviving some big natural disaster like a big asteroid impact or a nearby supernova. If such disasters are common, that could make it difficult to evolve much complexity.

This argument would also work if there are many ET civilizations, but they are all too far away for feasible communication or travel, like intergalactic distances.


If there are lots of ET civilizations, there are plenty of additional possibilities.

• Some of them like to destroy any others that they find, because they are competition or whatever.
• They want to hide from other civilizations.
• They do not have any interest in interstellar communication or travel.
• They are using some advanced technology that we do not know about.
• We are unable to recognize their messages or their artifacts.
• They broadcast only briefly. This can happen from their technology advancing.
• Everybody is listening, and nobody is transmitting.
• We have not searched enough, or with enough sensitivity.
• The Zoo Hypothesis: they know about us, but they avoid letting us know about them.
• "They are made of meat" -- incredulity at our nature.
• They prefer to live away from us, like in the outer parts of our Galaxy to avoid overheating.
• The Simulation Hypothesis: it includes no ET's.

Etc.

A lot to argue over, I'm sure.

 

[rousseau]

The solution might be a lot simpler than you think:

- the probability of a civilisation that can receive, and a civilisation that can transmit the exact same message, at the same time, might just be so astronomically low that it just cannot happen. Life has existed on earth for billions of years, but computer technology has existed for about a hundred. It's feasible that a similar civilisation existed a million years ago but no longer exists

- it's also possible that inter-stellar travel is just not possible due to bio-physical law. As humans we greatly tend to over-estimate our abilities, and our importance

 

[DBT]

Perhaps the trend is to upload one's consciousness into the virtual world of choice once it becomes technologically possible? Eliminate physical ailments and physical needs, live forever, be the God of your own world, play any role of your own choosing, etc.

 

[Underseer]

I like Bill Watterson's resolution to the Fermi paradox: "Perhaps the proof that intelligent life exists elsewhere is that none of it has tried to contact us."

 

[Underseer]

Anyway, we've only been listening for a few decades (how many depends on how you count it), so we would only be able to detect alien transmissions from within a sphere of tens of light years.

So at most, all we can say is that there are no alien civilizations transmitting radio waves that we can detect within a radius of a few tens of light years.

It's a bit early to talk about the Fermi paradox, if you ask me.

 

[rousseau]

As an aside, there's no need to contact other civilisations to know they're there. All we have to do is look in the mirror.

 

[lpetrich]

The solution might be a lot simpler than you think:

- the probability of a civilisation that can receive, and a civilisation that can transmit the exact same message, at the same time, might just be so astronomically low that it just cannot happen. Life has existed on earth for billions of years, but computer technology has existed for about a hundred. It's feasible that a similar civilisation existed a million years ago but no longer exists

Why does it have to be the exact same message? Do you mean sending a message that the would-be receiver can receive?

SETI mentions how digital transmissions may be more difficult to detect than analog ones from having less overall power and being more tightly beamed. There is also the problem of decoding such transmissions. They often have data compression and error-correcting coding and encryption in them, and without knowing the transmission protocols, one is stuck.

- it's also possible that inter-stellar travel is just not possible due to bio-physical law. As humans we greatly tend to over-estimate our abilities, and our importance

I would not dismiss it outright. But there are some severe problems with it. One can scrimp on rocket fuel by going very slowly, like a few km/s, but that means a very large travel time, and that is slower than the relative velocities of the nearby stars. One will need about 50 km/s to overcome the relative-velocity barrier, and that's much greater than what one can feasibly do with chemical reactions. The best readily-feasible chemical exhaust velocity is around 4.5 km/s, and that's from hydrogen-oxygen. Fluorine instead of oxygen can do a little better, but fluorine is toxic, corrosive, and rare. The actual velocity change or delta-V can be greater with a large-enough mass ratio, but it increases logarithmically:

v = v_e*log(m_i/m_f)

So one won't get much faster than a few times the exhaust velocity.

Perhaps the trend is to upload one's consciousness into the virtual world of choice once it becomes technologically possible? Eliminate physical ailments and physical needs, live forever, be the God of your own world, play any role of your own choosing, etc.

Yes, lack of interest.

I like Bill Watterson's resolution to the Fermi paradox: "Perhaps the proof that intelligent life exists elsewhere is that none of it has tried to contact us."

Yes, that we are too primitive to be considered worth contacting.

Anyway, we've only been listening for a few decades (how many depends on how you count it), so we would only be able to detect alien transmissions from within a sphere of tens of light years.

They could have been transmitting for much longer than we have been receiving, so one will be limited by signal strength.

One will need a planet-sized antenna to watch our TV shows across interstellar space, and that's for the closest stars. But one can detect the broadcasts' carrier waves much more easily, since they have much of the signal power in a very small bandwidth, about 0.1 Hz, instead of the full broadcast's 3 MHz or thereabouts.

 

[Loren Pechtel]

I have a big problem with most of the dodges of the Fermi Paradox.

Many of them make sense if interstellar travel is impossible. However, I do not find that credible.

The fusion version of Orion could push a craft to .01c and stop it at the other end. That's not feasible for humans now but I have a hard time believing that old age will not be conquered. Once it is no longer a generation mission eventually there will be those who want to undertake such a voyage. Manufacturing will have reached the point that a small starship can boostrap civilization.

Eventually enough people who want to push the horizons will get together and head for a nearby star and colonize it. So long as there is adequate matter around the star it doesn't need planets. The progress will be very slow, but that doesn't matter. Lets say it takes a thousand years of civilization before such a group forms. They spend 500 years in flight (a reasonable value for the closest stars.) That's 5ly in 1500y, or 1/300th of lightspeed. X the size of the galaxy means they'll have crossed it in 30My. Lets figure they didn't go straight and double that, still only 60My. That's not even 1% of the age of the universe.

Now, they might be deliberately choosing to avoid stars that have the potential for indigenous life but we should still see evidence of them about other stars. They don't need to be actively seeking communication for us to notice them.

All I can conclude is that we are alone in this galaxy. We know enough of the physical parameters to know that planets aren't the limiting factor. Looking at our own fossil record shows life arose basically as soon as it was able to, making that very unlikely to be the limiting factor.

Thus we are left with:

1) Multicellular life might be very hard. It took billions of years on Earth, perhaps we were just very lucky.

2) Survival of the biosphere for long enough might be very hard. We are lucky in this regard, the odds say we should have been hit by a cosmic reset button by now. Note, also, that even without a reset button we just squeaked in under the wire. More than 99% of the available time for intelligence to arise has already passed, soon global warming will render Earth unsuitable for slow-evolving creatures.

3) Intelligence may be destructive.

Note that it would be very hard for intelligence to do itself in once it's spread to the stars.

Some combination of these factors almost certainly is a billions-to-one longshot. Are we the survivors of such odds, or is the limit ahead of us? Unfortunately, the latter is by far the most likely option.

Note that there is a variation on #3--the lotus eater path. Perhaps we abandon reality for more entertaining virtual words rather than actually be destroyed.

 

[beero1000]

I have a big problem with most of the dodges of the Fermi Paradox.

Many of them make sense if interstellar travel is impossible. However, I do not find that credible.

The fusion version of Orion could push a craft to .01c and stop it at the other end. That's not feasible for humans now but I have a hard time believing that old age will not be conquered. Once it is no longer a generation mission eventually there will be those who want to undertake such a voyage. Manufacturing will have reached the point that a small starship can boostrap civilization.

Eventually enough people who want to push the horizons will get together and head for a nearby star and colonize it. So long as there is adequate matter around the star it doesn't need planets. The progress will be very slow, but that doesn't matter. Lets say it takes a thousand years of civilization before such a group forms. They spend 500 years in flight (a reasonable value for the closest stars.) That's 5ly in 1500y, or 1/300th of lightspeed. X the size of the galaxy means they'll have crossed it in 30My. Lets figure they didn't go straight and double that, still only 60My. That's not even 1% of the age of the universe.

Now, they might be deliberately choosing to avoid stars that have the potential for indigenous life but we should still see evidence of them about other stars. They don't need to be actively seeking communication for us to notice them.

All I can conclude is that we are alone in this galaxy. We know enough of the physical parameters to know that planets aren't the limiting factor. Looking at our own fossil record shows life arose basically as soon as it was able to, making that very unlikely to be the limiting factor.

Thus we are left with:

1) Multicellular life might be very hard. It took billions of years on Earth, perhaps we were just very lucky.

2) Survival of the biosphere for long enough might be very hard. We are lucky in this regard, the odds say we should have been hit by a cosmic reset button by now. Note, also, that even without a reset button we just squeaked in under the wire. More than 99% of the available time for intelligence to arise has already passed, soon global warming will render Earth unsuitable for slow-evolving creatures.

3) Intelligence may be destructive.

Note that it would be very hard for intelligence to do itself in once it's spread to the stars.

Some combination of these factors almost certainly is a billions-to-one longshot. Are we the survivors of such odds, or is the limit ahead of us? Unfortunately, the latter is by far the most likely option.

Note that there is a variation on #3--the lotus eater path. Perhaps we abandon reality for more entertaining virtual words rather than actually be destroyed.

You're missing a major aspect of expansion - it's almost certainly breadth-first, not depth-first. Civilizations would probably expand in a sphere around the home star, and be much more likely to travel to nearby stars instead of just heading out by hopping farther and farther. To cover a significant portion of the ~100 billion stars in the milky way would take many times the age of the universe, even accounting for the potential effects of parallelization.

 

[rousseau]

Probability of detecting intelligent life off the top of my head:

- probability that intelligent life with transmission technology exists in both point A and point B
*
- probability that intelligent life with transmission technology exists in both point A and point B at the same time
*
- probability that these two civilisations have the technology to talk to each other
*
- probability that they're transmitting a signal that will reach and be detected by the other civilisation

All of these variables individually seem to have astronomically low probabilities, so when you combine them all, we're talking a situation that might only happen a small number of times in the life-time of the universe. It's possible that it *has* happened, just not to us.

If anyone has a solid critique against this logic, I'd love to hear it.

 

[rousseau]

I have a big problem with most of the dodges of the Fermi Paradox.

Many of them make sense if interstellar travel is impossible. However, I do not find that credible.

The fusion version of Orion could push a craft to .01c and stop it at the other end. That's not feasible for humans now but I have a hard time believing that old age will not be conquered. Once it is no longer a generation mission eventually there will be those who want to undertake such a voyage. Manufacturing will have reached the point that a small starship can boostrap civilization.

Eventually enough people who want to push the horizons will get together and head for a nearby star and colonize it. So long as there is adequate matter around the star it doesn't need planets. The progress will be very slow, but that doesn't matter. Lets say it takes a thousand years of civilization before such a group forms. They spend 500 years in flight (a reasonable value for the closest stars.) That's 5ly in 1500y, or 1/300th of lightspeed. X the size of the galaxy means they'll have crossed it in 30My. Lets figure they didn't go straight and double that, still only 60My. That's not even 1% of the age of the universe.

Now, they might be deliberately choosing to avoid stars that have the potential for indigenous life but we should still see evidence of them about other stars. They don't need to be actively seeking communication for us to notice them.

All I can conclude is that we are alone in this galaxy. We know enough of the physical parameters to know that planets aren't the limiting factor. Looking at our own fossil record shows life arose basically as soon as it was able to, making that very unlikely to be the limiting factor.

Thus we are left with:

1) Multicellular life might be very hard. It took billions of years on Earth, perhaps we were just very lucky.

2) Survival of the biosphere for long enough might be very hard. We are lucky in this regard, the odds say we should have been hit by a cosmic reset button by now. Note, also, that even without a reset button we just squeaked in under the wire. More than 99% of the available time for intelligence to arise has already passed, soon global warming will render Earth unsuitable for slow-evolving creatures.

3) Intelligence may be destructive.

Note that it would be very hard for intelligence to do itself in once it's spread to the stars.

Some combination of these factors almost certainly is a billions-to-one longshot. Are we the survivors of such odds, or is the limit ahead of us? Unfortunately, the latter is by far the most likely option.

Note that there is a variation on #3--the lotus eater path. Perhaps we abandon reality for more entertaining virtual words rather than actually be destroyed.

As in you think people will live for a very long time?

 

[Loren Pechtel]

You're missing a major aspect of expansion - it's almost certainly breadth-first, not depth-first. Civilizations would probably expand in a sphere around the home star, and be much more likely to travel to nearby stars instead of just heading out by hopping farther and farther. To cover a significant portion of the ~100 billion stars in the milky way would take many times the age of the universe, even accounting for the potential effects of parallelization.

I don't think either is really the right model. You're assuming all the expansion is from the homeworld, something I do not expect to happen. Rather, once a system is fully inhabited it can also be the origin of another group heading out. That group will look around for the closest available star--but the ones close to the already inhabited worlds will probably already be taken. Thus I expect most ships to be heading pretty much outward.

 

[Loren Pechtel]

I have a big problem with most of the dodges of the Fermi Paradox.

Many of them make sense if interstellar travel is impossible. However, I do not find that credible.

The fusion version of Orion could push a craft to .01c and stop it at the other end. That's not feasible for humans now but I have a hard time believing that old age will not be conquered. Once it is no longer a generation mission eventually there will be those who want to undertake such a voyage. Manufacturing will have reached the point that a small starship can boostrap civilization.

Eventually enough people who want to push the horizons will get together and head for a nearby star and colonize it. So long as there is adequate matter around the star it doesn't need planets. The progress will be very slow, but that doesn't matter. Lets say it takes a thousand years of civilization before such a group forms. They spend 500 years in flight (a reasonable value for the closest stars.) That's 5ly in 1500y, or 1/300th of lightspeed. X the size of the galaxy means they'll have crossed it in 30My. Lets figure they didn't go straight and double that, still only 60My. That's not even 1% of the age of the universe.

Now, they might be deliberately choosing to avoid stars that have the potential for indigenous life but we should still see evidence of them about other stars. They don't need to be actively seeking communication for us to notice them.

All I can conclude is that we are alone in this galaxy. We know enough of the physical parameters to know that planets aren't the limiting factor. Looking at our own fossil record shows life arose basically as soon as it was able to, making that very unlikely to be the limiting factor.

Thus we are left with:

1) Multicellular life might be very hard. It took billions of years on Earth, perhaps we were just very lucky.

2) Survival of the biosphere for long enough might be very hard. We are lucky in this regard, the odds say we should have been hit by a cosmic reset button by now. Note, also, that even without a reset button we just squeaked in under the wire. More than 99% of the available time for intelligence to arise has already passed, soon global warming will render Earth unsuitable for slow-evolving creatures.

3) Intelligence may be destructive.

Note that it would be very hard for intelligence to do itself in once it's spread to the stars.

Some combination of these factors almost certainly is a billions-to-one longshot. Are we the survivors of such odds, or is the limit ahead of us? Unfortunately, the latter is by far the most likely option.

Note that there is a variation on #3--the lotus eater path. Perhaps we abandon reality for more entertaining virtual words rather than actually be destroyed.

As in you think people will live for a very long time?

I have no idea how long we would survive if we basically retreated to virtual worlds. Reproduction would likely severely suffer, we might die out from a simple failure to reproduce.

 

[beero1000]

You're missing a major aspect of expansion - it's almost certainly breadth-first, not depth-first. Civilizations would probably expand in a sphere around the home star, and be much more likely to travel to nearby stars instead of just heading out by hopping farther and farther. To cover a significant portion of the ~100 billion stars in the milky way would take many times the age of the universe, even accounting for the potential effects of parallelization.

I don't think either is really the right model. You're assuming all the expansion is from the homeworld, something I do not expect to happen. Rather, once a system is fully inhabited it can also be the origin of another group heading out. That group will look around for the closest available star--but the ones close to the already inhabited worlds will probably already be taken. Thus I expect most ships to be heading pretty much outward.

You missed my point. First, I'm not assuming all of the expansion is from the home world, rather at a uniform rate from every inhabited world. Second, that process would expand radially from the homeworld non-linearly - by necessity, we should expect about 7 times as many planets that are 100-200 light years away as there are 0-100 light years away, and so on.

 

[rjh01]

Apart from extreme difficulty in transporting anything form one star to another there is also the issue of radio transmissions. Most of these we broadcast would be very hard to detect more than a few light years away.

 

[Malintent]

before we understood how birds glide, it was thought that human flight was physically impossible. There would be no way to operate the massive wings needed to "beat them into the air"... until we learned about air pressure changes in wind across an airfoil.

Before we understood the nature of fluid dynamics in transonic flight, the "sound barrier" could not be broken. It was thought physically impossible to exceed the speed of sound in a body of air, due to what appeared to be a reversal of the laws of physics at those pressure gradients.

One can go on and on about all the things thought "physically impossible"... and eventually be thought the fool.

It is still impossible to flap our arms and fly. That has not changed. The way we worked around the limitation to use the natural laws to our advantage in that case is not much different than how we WILL break the "light speed barrier"... if not by demonstrating there is no such barrier, then by working around the barrier in a novel way.. like not by accelerating, but by taking a shortcut 'around' space-time..

 

[lpetrich]

If every colonized planet sends out colony spaceships to its uncolonized neighbors, then the colonized region will grow at a steady rate:
(neighbor distance) / (colonization time)

where (colonization time) = (travel time) + (colony-development time) where the latter is the time between arrival of a colony ship and the development of the colony to the point where it can send out colony ships.

From stars' velocities relative to their local average, one would need at least 50 km/s, and that is 50 parsecs per million years, or 1 parsec per 20,000 years.

The nearest stars are a few parsecs away:  List of nearest stars and brown dwarfs (56 stars, all closer than 5 parsecs),  List of nearest bright stars (out to 15 parsecs). So I'll use an average travel distance of about 10 parsecs. That means traveling for about 200,000 years.

This time seems like plenty of time to found a colony and build it up to the point where it can easily send out more colony ships. So I'll take that time as much less.

Thus, there is a wave of advance of colonization at about 50 km/s or 50 parsecs per million years. The distance to our Galaxy's center is about 8 kiloparsecs, and its radius about 15 - 25 kpc. So it would take about 160 million years to spread to the center, and about 500 - 700 million years to spread to the farthest outer rim.

This is still younger than our Galaxy.

 

[Bomb#20]

Eventually enough people who want to push the horizons will get together and head for a nearby star and colonize it. So long as there is adequate matter around the star it doesn't need planets. The progress will be very slow, but that doesn't matter. Lets say it takes a thousand years of civilization before such a group forms. They spend 500 years in flight (a reasonable value for the closest stars.) That's 5ly in 1500y, or 1/300th of lightspeed. X the size of the galaxy means they'll have crossed it in 30My. Lets figure they didn't go straight and double that, still only 60My. That's not even 1% of the age of the universe.

Now, they might be deliberately choosing to avoid stars that have the potential for indigenous life but we should still see evidence of them about other stars. They don't need to be actively seeking communication for us to notice them.

All I can conclude is that we are alone in this galaxy...

You appear to be assuming that building a starship will eventually be so cheap that a small group of disaffected people looking to start over without their government will be able to afford to pay for one, as if they were Voortrekkers building covered wagons. If we assume instead that a starship is always going to be a massive undertaking that requires the commitment of a national or planetary government, then the calculation needs to take into account whether the government has a good reason for deploying a large fraction of its available resources for many years. It seems to me the only nation-scale problem for which a starship is likely to become a practical solution is extinction insurance. But once a species has expanded to a half a dozen planets spread over ten or twenty light-years, it will as you say be very hard for intelligence to do itself in. Natural disasters, likewise. So what motive is there for further expansion, that would be convincing to rational politicians?

 

[Loren Pechtel]

I don't think either is really the right model. You're assuming all the expansion is from the homeworld, something I do not expect to happen. Rather, once a system is fully inhabited it can also be the origin of another group heading out. That group will look around for the closest available star--but the ones close to the already inhabited worlds will probably already be taken. Thus I expect most ships to be heading pretty much outward.

You missed my point. First, I'm not assuming all of the expansion is from the home world, rather at a uniform rate from every inhabited world. Second, that process would expand radially from the homeworld non-linearly - by necessity, we should expect about 7 times as many planets that are 100-200 light years away as there are 0-100 light years away, and so on.

Note that at a uniform rate from inhabited worlds ends up being a sphere expanding outward at the expansion rate--which is what I modeled.

If they are making 100ly jumps then the expansion goes even faster than I was envisioning--I was figuring all hops were to nearby stars.

 

[Loren Pechtel]

Before we understood the nature of fluid dynamics in transonic flight, the "sound barrier" could not be broken. It was thought physically impossible to exceed the speed of sound in a body of air, due to what appeared to be a reversal of the laws of physics at those pressure gradients.

No, that was just a case of idiots. Bullets are supersonic. Cracked whips are supersonic.

The issue was whether people could survive such a flight.

It is still impossible to flap our arms and fly. That has not changed. The way we worked around the limitation to use the natural laws to our advantage in that case is not much different than how we WILL break the "light speed barrier"... if not by demonstrating there is no such barrier, then by working around the barrier in a novel way.. like not by accelerating, but by taking a shortcut 'around' space-time..

The problem is that there might not be any such shortcut.

While the laws of physics do not preclude there being some way of FTL, neither do they indicate any way that FTL could work. Note, also, that wormholes and warp drives cause some very nasty time travel issues. (However, time travel issues do not mean all forms of FTL are out of the question. A FTL system that forces a reference frame avoids the problem and is not inherently incompatible with relativity. Einstein showed we do not need a reference frame for evaluating physics in our universe but that does not mean there might not be a reference frame present in a hyperdrive.)