Fermi-Paradox (Arrghh!)

[Reaper]

After reading a whole bunch of literature regarding extraterrestrial civilizations and the Fermi Paradox, it has me wondering about a lot of things. Well, the first reaction is, what the hell?!

 

For one, it is reasonable to believe that there should be a huge number of advanced civilizations out there even if the Rare Earth hypothesis is true just simply because of the sheer size of the Universe.

 

But on the other hand, we have not have any success in making contact, or even detecting a single one, and there is no reliable evidence that some form of extraterrestrial intelligence has ever visited Earth.

 

It should be no surprise that SETI hasn't detected anything via radio and microwave frequencies because I read somewhere a while ago that our own civilization would not be detectable even from the Oort Cloud just simply because our sun would outshine it. The energy of our radio frequencies are just too low to be noticeable over large distances, and they would spread out. It's been proposed that interstellar communications would probably be through lasers because they won't spread out as much over huge distances, but unless one hits Earth, they won't be detected.

 

The one thing that really irritates me about it is the lack of adequate explanations for the Fermi paradox. Every hypothesis I've seen just doesn't seem to cut it. For one, astronomers have tried to make an equation for the probability of advanced civilizations, but I think that falls more under numerology than as an actual representation, simply because we have only one sample (us). And then other explanations ranging from self-destruction, culture, technology, etc. either contradict known laws of physics or just seem plain ludicrous. I say that they seem plain ludicrous, especially the self-destruction theory, because the sheer size of our own galaxy and even the number of possible solar systems (thanks to recent discoveries) seems to indicate that there should be enough civilizations out there that don't self destruct, even if the probability of such an event is high.

 

My personal take on it is that its a combination of technological issues, our lack of understanding of the Universe, and the vast distances that they are probably spread out over is the reason why we haven't detected anything.

 

For one, if we do indeed go out into the galaxy, given that it is impossible to travel faster than light, I would imagine that there would be major issues with communication, so eventually they would be completely cut off from their parent solar system. And then of course it's up to chance and evolution within their new home. Even if our species does spread out over the galaxy, a civilization such as portrayed in Star Wars and even Star Trek is probably impossible, and this would leave the possibility that there would be large areas within a given galaxy that are uninhabited by an intelligent civilization.

 

Also, there is the possibility that we may spread out into space, but probably evolve so that we live off of the material around, something akin to a sort of hunter-gatherer society, moving between star systems as opposed to making permanent settlements.

 

Or, since machine intelligence is evolving, ultimately the galaxy is inhabited by self-replicating machines. Such machines would not necessarily need planets to survive nor need to establish any kind of civilization.

 

This is just my take on it. I would be interested in hearing your ideas.

[Spyman]

A modern TV transmitter can put out as much as a megawatt of power. Its not very tightly focused, so even though much of the broadcast energy spills into space, its fairly weak by the time it reaches another star system. Consider one of our early TV programs just washing over a planet thats 50 light-years away. To detect the "carrier" signal from this broadcast in a few minutes time would require about 3,000 acres of rooftop antennas connected to a sensitive receiver. Thats a lot of antennas, and an unsightly concept. But its not hard to build, and the aliens could conceivably do it. If the extraterrestrials were unwise enough to actually want to see the program, then theyd need an antenna about 30,000 times greater in area (roughly the size of Colorado). Ambitious, but possible.

 

A rather easier task would be to detect our military radars. The bigger ones typically boast a megawatt of power, and are focused into beams that are a degree or two across. There are enough such radars that, at any given time, they cover a percent of the sky or so. The signal from the most powerful of these could be found at 50 light-years distance in a few minutes time with a receiving antenna 1,000 feet in diameter. Indeed, these military radars are the only signals routinely transmitted from Earth that are intense enough to be detectable at interstellar distances with setups equivalent to our own SETI experiments.

 

Bottom line? With radio technology slightly more advanced than our own, Homo sapiens is detectable out to a distance of roughly 50 light-years. Within that distance are about 5,000 stars, all of which have had the enviable pleasure of receiving terrestrial television. And each day, a fresh stellar system is exposed to signals from Earth.

http://www.space.com/searchforlife/seti_shostak_aliens_031023.html

 

A 'little' more distant than the Oort Cloud...

 

 

Fermi realized that any civilization with a modest amount of rocket technology and an immodest amount of imperial incentive could rapidly colonize the entire Galaxy. Within ten million years, every star system could be brought under the wing of empire. Ten million years may sound long, but in fact it's quite short compared with the age of the Galaxy, which is roughly ten thousand million years. Colonization of the Milky Way should be a quick exercise.

http://www.space.com/searchforlife/shostak_paradox_011024.html

 

the Fermi Paradox, which assumes that if sophisticated societies are common, they should also be ubiquitous. Well, I just checked the parking lot outside the Institute, and I see no large animals with long, prehensile noses. The conclusion a la Fermi is that elephants don't exist on this Earth, right? After all, any putative pachyderms have had plenty of time to get to my office, even if only a few of them are so inclined.

 

To use the Fermi Paradox as a reason for the lack of a SETI signal is to make a very big extrapolation from a very local observation. Seems chancy to me.

The number of star systems we've carefully examined is only about a thousand. That's a trifling sample compared with the several hundred billion suns that stud the Milky Way, and of little statistical significance. It's comparable to initiating a quest for Americans who play the oboe, but considering the search meaningful after interrogating only two people.

http://www.space.com/searchforlife/seti_thursday_060720.html

 

Even if there are ten thousand transmitting societies nestled in the arms of the Milky Way, we might need to search millions of star systems before we find one. The actual number of star systems that radio SETI experiments have carefully examined is fewer than a thousand.

 

It's a simple truth, although one not universally acknowledged, that SETI is still in its early stages.

http://www.space.com/searchforlife/seti_shostak_surrender_070118.html

 

I agree with Shostak, we have to little statistical data to make any conclusions yet.

 

Even if the Milky Way should be teeming with technological advanced intelligent life searching for others, the vast distances and numerous stars, reduces the probability for them to find us and make contact, in the short timespan we have been around, to the chance of accidentally stumble on us by pure luck.

[JamesBrown]

I thought you guys might be interested in my thoughts on the subject.

-------------------------

After looking at the software and hardware requirements for my SETI station, and mulling over such technical questions as integration time constant and Doppler shift correction, I have come to the following epiphany:

 

I must look for the most obvious signal - and that is the signal that I would choose to send myself, if I had the money to do so. What that means (and it seems obvious once put on paper) is that:

 

I must look for myself

Any ETI that I might hope to detect must be more like myself than unlike me, in most basic ways. Not to put too fine a point on it, but, for example, I think this ET would think in the same time frame as we do. Not at the speed of a glacier or at the speed of bullet, but somewhere near our 'thinking speed'. This is necessary to make the signal recognizable to us when finally detected.

 

ET's physical makeup would have to be about the same as ours. Not as small as a bacterium or as large as one of the rolling hills I can see from my window, but somewhere in-between. This would give him the same type of control over his environment, and the same capability as I have to construct the needed transmitter, which could produce a signal which I can recognize. Not all ETI need be like me; only those who I have a realistic chance of detecting.

 

ETI's transmitter must be an RF signal generator. Some other, more exotic form of communication may well be in use, but since I can't construct a receiver to detect exotica, it's not worth considering. This leaves open optical SETI - but not for me. I know nothing about the optics required on that scale. As a microwaver, I'll stick to the area where I have a shot at SETI success.

 

The signal must be a deliberate beacon. That's the only type I and most other Argus stations would have a ghost of a chance of hearing. Leakage detection seems less likely, if only because of the transmit power requirements needed to show up on my system. Detecting planetary Radar also seems unlikely, because it seems that it would only be sent for short periods. Once a radar echo was recovered, the transmitter would most likely be turned off or pointed somewhere else. The modulation scheme needed for an effective Planetary Radar might also make it difficult to recognize on this end.

 

I would set my beacon up in the waterhole to maximize its chances of discovery. I would want to be heard, and that is the most obvious place to start. The hydrogen line is at 1420 MHz and the hydroxyl line at 1662 MHZ. I would transmit at exactly 1/2 way between the two at 1541 MHz. (One could also make a case for the geometric mean of the hydrogen and hydroxyl lines, which is 1536 MHz. But we're splitting hairs here.) I would expect ETI to similarly transmit somewhere near the middle of the waterhole, if he wants me to detect him. Unfortunately, my Project Argus system (receiver and filter) can't tune this frequency, but if I were to make changes to my system, that is where I would choose to monitor.

 

An ideal interstellar beacon should be narrow band to concentrate the transmit power, and to make it distinguishable from natural sources. It must be directed at our star. This is necessary to conserve power, and to make possible reception over huge distances. So a directed beacon is what I am looking for. I can see ETI pointing such a beacon at each candidate star, one at a time, sending the beacon for some length of time, and then moving to the next star.

 

The above targeted beacon strategy implies that earth rotation Doppler compensation is a minimum requirement of our Project Argus receiving stations, if only to exclude local signals. Correcting for the Doppler shift due to our travel around the sun is also a requirement. I have the earth rotation Doppler chirp running now - the other compensation is an unknown quantity to me at this point, but something which Project Argus participants should be working on.

 

My hypothetical interstellar beacon would be locked onto each star for about a year at a time. We may have missed ETI's signal already, and may have to wait another 300 million years for it to show up again. Or, it may be starting tomorrow. Since we just don't know, we may as well assume that it starts tomorrow.

 

If I were sending a beacon, its transmitter frequency would be Doppler-adjusted to the Galactic center of rest. Since the purpose of a beacon is to be seen against a background of other signals, this would make it clear to anyone receiving it that it was an intentional signal. Again, I have no idea how to design this correction into my receiver chirp. If it's small (less than about 0.01 Hz/sec), no matter where I point my antenna I can't use it anyway, because my 10Hz/Bin resolution and planned 30-minute integration time constant make such small Doppler rates moot. If the compensation for the Galactic center of rest is a sizeable fraction of a Hz per second, I'd better figure out how to implement it!

 

My beacon would be a CW signal on/off modulated in a regular way. I might send morse code in a repetitive pattern, and I would send it at a speed slow enough to allow integration of each character, but not so slow as to allow the signal to drift across many bins during a given key-down period.

 

If I concentrate on looking for myself, I may well miss signals sent by those not like me. But I know that creatures who think like me exist (if only by Earth's own example.) Designing our search around those not like us involves pure speculation, and may reduce our chances for SETI success.

-----------

Regards.. Jim (http://www.SETI.Net)

[Reaper]

I thought you guys might be interested in my thoughts on the subject.

-------------------------

After looking at the software and hardware requirements for my SETI station, and mulling over such technical questions as integration time constant and Doppler shift correction, I have come to the following epiphany:

 

I must look for the most obvious signal - and that is the signal that I would choose to send myself, if I had the money to do so. What that means (and it seems obvious once put on paper) is that:

 

I must look for myself

Any ETI that I might hope to detect must be more like myself than unlike me, in most basic ways. Not to put too fine a point on it, but, for example, I think this ET would think in the same time frame as we do. Not at the speed of a glacier or at the speed of bullet, but somewhere near our 'thinking speed'. This is necessary to make the signal recognizable to us when finally detected.

 

ET's physical makeup would have to be about the same as ours. Not as small as a bacterium or as large as one of the rolling hills I can see from my window, but somewhere in-between. This would give him the same type of control over his environment, and the same capability as I have to construct the needed transmitter, which could produce a signal which I can recognize. Not all ETI need be like me; only those who I have a realistic chance of detecting.

 

ETI's transmitter must be an RF signal generator. Some other, more exotic form of communication may well be in use, but since I can't construct a receiver to detect exotica, it's not worth considering. This leaves open optical SETI - but not for me. I know nothing about the optics required on that scale. As a microwaver, I'll stick to the area where I have a shot at SETI success.

 

The signal must be a deliberate beacon. That's the only type I and most other Argus stations would have a ghost of a chance of hearing. Leakage detection seems less likely, if only because of the transmit power requirements needed to show up on my system. Detecting planetary Radar also seems unlikely, because it seems that it would only be sent for short periods. Once a radar echo was recovered, the transmitter would most likely be turned off or pointed somewhere else. The modulation scheme needed for an effective Planetary Radar might also make it difficult to recognize on this end.

 

I would set my beacon up in the waterhole to maximize its chances of discovery. I would want to be heard, and that is the most obvious place to start. The hydrogen line is at 1420 MHz and the hydroxyl line at 1662 MHZ. I would transmit at exactly 1/2 way between the two at 1541 MHz. (One could also make a case for the geometric mean of the hydrogen and hydroxyl lines, which is 1536 MHz. But we're splitting hairs here.) I would expect ETI to similarly transmit somewhere near the middle of the waterhole, if he wants me to detect him. Unfortunately, my Project Argus system (receiver and filter) can't tune this frequency, but if I were to make changes to my system, that is where I would choose to monitor.

 

An ideal interstellar beacon should be narrow band to concentrate the transmit power, and to make it distinguishable from natural sources. It must be directed at our star. This is necessary to conserve power, and to make possible reception over huge distances. So a directed beacon is what I am looking for. I can see ETI pointing such a beacon at each candidate star, one at a time, sending the beacon for some length of time, and then moving to the next star.

 

The above targeted beacon strategy implies that earth rotation Doppler compensation is a minimum requirement of our Project Argus receiving stations, if only to exclude local signals. Correcting for the Doppler shift due to our travel around the sun is also a requirement. I have the earth rotation Doppler chirp running now - the other compensation is an unknown quantity to me at this point, but something which Project Argus participants should be working on.

 

My hypothetical interstellar beacon would be locked onto each star for about a year at a time. We may have missed ETI's signal already, and may have to wait another 300 million years for it to show up again. Or, it may be starting tomorrow. Since we just don't know, we may as well assume that it starts tomorrow.

 

If I were sending a beacon, its transmitter frequency would be Doppler-adjusted to the Galactic center of rest. Since the purpose of a beacon is to be seen against a background of other signals, this would make it clear to anyone receiving it that it was an intentional signal. Again, I have no idea how to design this correction into my receiver chirp. If it's small (less than about 0.01 Hz/sec), no matter where I point my antenna I can't use it anyway, because my 10Hz/Bin resolution and planned 30-minute integration time constant make such small Doppler rates moot. If the compensation for the Galactic center of rest is a sizeable fraction of a Hz per second, I'd better figure out how to implement it!

 

My beacon would be a CW signal on/off modulated in a regular way. I might send morse code in a repetitive pattern, and I would send it at a speed slow enough to allow integration of each character, but not so slow as to allow the signal to drift across many bins during a given key-down period.

 

If I concentrate on looking for myself, I may well miss signals sent by those not like me. But I know that creatures who think like me exist (if only by Earth's own example.) Designing our search around those not like us involves pure speculation, and may reduce our chances for SETI success.

-----------

Regards.. Jim (www.SETI.Net)

 

 

That's great, but not really the point of this thread. The point is that we haven't found anything, and I'm wondering why. And secondly, humans did not initially make a radio so that they could contact ET. We are only doing that very recently, and even then its pointed at stars that may not have ET listening to our part of the Universe.

 

 

I agree with Shostak' date=' we have to little statistical data to make any conclusions yet.

 

Even if the Milky Way should be teeming with technological advanced intelligent life searching for others, the vast distances and numerous stars, reduces the probability for them to find us and make contact, in the short timespan we have been around, to the chance of accidentally stumble on us by pure luck.

[/quote']

 

That's what I have thought, but the bigger mystery then is why we haven't apparently been visited by any sort of extraterrestrial life yet. The galaxy is estimated to be about 10 billion years old, and there is ample time for intelligent life to evolve in some fashion, and even enough some civilization to get far enough in tech to be able to colonize the entire galaxy. It has been estimated that even if FTL is impossible, some form of intelligent life should have been able to colonize a galaxy this size within a few million years.

 

My reasoning is, like yours, distance issues, but I feel that the explanation has something missing in it. I'm guessing it has much more to do than just sheer distance though.

[JamesBrown]

That's great, but not really the point of this thread. The point is that we haven't found anything, and I'm wondering why. And secondly, humans did not initially make a radio so that they could contact ET. We are only doing that very recently, and even then its pointed at stars that may not have ET listening to our part of the Universe.

.

Lockheed - The point is that there is no use in looking for anything OTHER than ourselves. There is no way we would recognize anything else. Radio or Optical astronomy are the only tools we have.

[Reaper]

Lockheed - The point is that there is no use in looking for anything OTHER than ourselves. There is no way we would recognize anything else. Radio or Optical astronomy are the only tools we have.

 

I understood what you said, but what I am wondering is why we haven't detected anything yet. Or more importantly, why Earth hasn't been visited given the age of our galaxy and the apparent likelihood of intelligent life.

 

If some ET has sent a signal to our star and is moving from star to star, then we really have a small window of time to actually detect it. What is even worse is that it would only take up a very small fraction of our sky (think less than a degree).

 

I like the article that Spyman has displayed, which suggest that it might be easier to detect signals comparable to that used by the military, some of which are listed here. Of course, there is a chance that ET might use different frequencies, but its a shot, given that signals with this purpose will probably be frequent enough to allow a good chance of detection.

[JohnB]

Or more importantly, why Earth hasn't been visited given the age of our galaxy and the apparent likelihood of intelligent life.

Can you prove that statement? Earth may have been visited thousands of times during it's history but unless it happened within reach of a record keeping society in the last thousand years or so, we would never know.

 

As to why we haven't found anyone yet. Space is very, very big. If there were 10,000 civilizations transmitting strongly enough for us to hear and they have been doing so for 1,000 years but the nearest one is 1500 light years away, (not far on Galactic distances) it would still be 500 years before we would hear them.

 

A mighty civilization may have arisen on a planet around Alpha Centauri only to be wiped out by disease in the Earth year 1940. The last of their signals pass Earth in 1944, but no-one is listening.

 

Or an ancient and wise society evolved around Sirius, surviving for a billion years, yet was destroyed by the "Great Collapsing Hrung Disaster". An offshoot of which hit Earth around 65 million years ago, ending some rather promising lines of reptillian evolution.

 

The Galaxy is very, very big and has been around for a long, long time. To detect someone they must be tranmitting from a place and time so that their signals pass Earth during the last 50 years while our radio telescopes are pointing in the right direction.

 

Be patient.

[Widdekind]

In the spirit of Stephen Webb's book, If the Universe Is Teeming with Aliens ... Where Is Everybody?: Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life, this author offers:

 

 

Solution 51 -- Aliens are Predators

 

According to Webb (p.113),

One reason why ETCs

[Extra-Terrestrial Civilizations]

might choose to keep quiet is

fear

. When an ETC broadcasts to space, it reveals its location, and perhaps level of technology. Any neighbors who are listening may be

aggressive

...

Perhaps caution is a general trait among advanced intelligences

.

I offer that this is due to Natural Selection -- the Milky Way Galaxy is populated by an advanced Predatory Civilization, that has already annihilated -- to wit, "predated" -- all the unwary intelligences in our Galaxy.

 

Indeed, Webb proposes basically this hypothesis, but uses the word "Berserker" instead of "Predator" (p. 112). By but replacing these two words, in Webb's proposal, we have that:

ETCs have either been prevented from arising by

[Predators]

, wiped out by

[Predators]

, or else are keeping quiet for fear of attracting

[Predators]

... So, why have

[Predators]

silenced all other

Civilizations

, but left us alone? We could argue that

[Predators]

destroy only

Technological Life-forms

, and need a "trigger" -- presumably the detection of

Radio Waves

-- before they begin to work.

Note that yet another of Webb's proposals is called "They are here, and are meddling in Human affairs". This "Berserker-Predator" hypothesis succinctly sets a pre-Industrial Glass Ceiling upon emerging Civilizations, neatly explaining the apparent lack of the same in our skies.