Does Intelligent Extraterrestrial Life Exist?

[Dr Mindbender]

The universe isn't infinite.

yes it is.

Read brief history of time.

[Stranger Than Paradise]

We can not of course say either way whether extraterrestrial life exists. I believe it does. It seems completely illogical to me that we are the only intelligent life in the universe.

[Bud Struggle]

yes it is.

Read brief history of time.

The universe is a big place, maybe even the biggest.--Kurt Vonnegut

[Demogorgon]

It isn't something we are likely to ever know, but given the size of the Universe it would seem pretty exceptional if we dwell on the only planet with life on it. Indeed if life is that rare, it would actually follow that it would likely be divinely created. Not believing in God, I must conclude that life is something that simply emerged from "primordial soup" under certain conditions and that in the extraordinary scope of the Universe it must have happened more than once. So I reckon life probably does exist elsewhere.

Do I think we will ever encounter it? No.

[ÑóẊîöʼn]

It's happened at least once, so it can happen again. Although going by the evidence there's certainly no sign of any intelligent life in our galactic neighbourhood.

But non-intelligent life? I reckon that will turn out to be pretty common.

[FreeFocus]

The sheer vastness of the universe lends credence to the possibility. Personally, there's no doubt in my mind, although we don't have any evidence for it at the moment.

[Rosa Lichtenstein]

Yes, but I am only visiting...

[Kronos]

[Kwisatz Haderach]

I voted no. Intelligent extraterrestrial life may exist in other galaxies, but the chances of it existing in the Milky Way are slim to none.

The existence of a technological civilization on a planet around a star should be blatantly obvious to anyone looking at that star. Even our own civilization, which is extremely young by cosmic standards and hasn't even reached the Kardashev I level yet, would be impossible to miss when looking at the Sun. Thanks to us and our telecommunications, the Earth (or, to any distant observer, the Sun) is unnaturally and inexplicably bright in the radio spectrum. If we pointed our primitive radiotelescopes at any star with a planet bearing a civilization like our own, we would detect it immediately. A more advanced civilization should be even easier to detect.

The fact that we have detected nothing strongly suggests that other technological civilizations do not exist.

The universe still has a long life ahead of it, so we may not be the last technological civilization. But I think we are the first.

[Manifesto]

The odds of Earth being the only planet with life is unlikely since there is a 1 out of 10,000 (I think thats right) chance that there is another planet like Earth that can support life.

[Manifesto]

So the odds of other life is likely.

[Kwisatz Haderach]

Other life, maybe... but other intelligent life? That's a different question.

[Lynx]

The existence of a technological civilization on a planet around a star should be blatantly obvious to anyone looking at that star. Even our own civilization, which is extremely young by cosmic standards and hasn't even reached the Kardashev I level yet, would be impossible to miss when looking at the Sun. Thanks to us and our telecommunications, the Earth (or, to any distant observer, the Sun) is unnaturally and inexplicably bright in the radio spectrum. If we pointed our primitive radiotelescopes at any star with a planet bearing a civilization like our own, we would detect it immediately. A more advanced civilization should be even easier to detect.

Among other considerations, being visible in the radio spectrum may be but a temporary stage:

The greatest problem is the sheer size of the radio search needed to look for signals, the limited amount of resources committed to SETI, and the sensitivity of modern instruments. SETI estimates, for instance, that with a radio telescope as sensitive as the Arecibo Observatory, Earth's television and radio broadcasts would only be detectable at distances up to 0.3 light years.[49] Clearly detecting an Earth type civilization at great distances is difficult. A signal is much easier to detect if the signal energy is focused in either a narrow range of frequencies (Narrowband transmissions), and/or directed at a specific part of the sky. Such signals can be detected at ranges of hundreds to tens of thousands of light-years distance.[50] However this means that detectors must be listening to an appropriate range of frequencies, and be in that region of space to which the beam is being sent. Many SETI searches, starting with the venerable Project Cyclops, go so far as to assume that extraterrestrial civilizations will be broadcasting a deliberate signal (like the Arecibo message), in order to be found.

Thus to detect alien civilizations through their radio emissions, Earth observers either need more sensitive instruments or must hope for fortuitous circumstances: that the broadband radio emissions of alien radio technology are much stronger than our own; that one of SETI's programs is listening to the correct frequencies from the right regions of space; or that aliens are sending focused transmissions such as the Arecibo message in our general direction.

Civilizations only broadcast detectable radio signals for a brief period of time

It may be that alien civilizations are detectable through their radio emissions for only a short time, reducing the likelihood of spotting them. There are two possibilities in this regard: civilizations outgrow radio through technological advance or, conversely, resource depletion cuts short the time in which a species broadcasts.

The first idea, that civilizations advance beyond radio, is based in part on the "fiber optic objection": the use of high power radio with low-to-medium gain (i.e., non-directional) antennas for long-distance transmission is wasteful of spectrum, yet this "waste" is precisely what makes these systems conspicuous at interstellar distances. Humans are moving to directional or guided transmission channels such as electrical cables, optical fibers, narrow-beam microwave and lasers, and conventional radio with non-directional antennas is increasingly reserved for low-power, short-range applications such as cell phones and Wi-Fi networks. These signals are far less detectable from space. Analog television, developed in the mid-twentieth century, contains strong carriers to aid reception and demodulation. Carriers are spectral lines that are very easily detected yet do not convey any information beyond their highly artificial nature. Nearly every SETI project is looking for carriers for just this reason, and UHF TV carriers are currently the most conspicuous and artificial signals from Earth that could be detected at interstellar distances. But advances in technology are replacing analog TV with digital television which uses spectrum more efficiently precisely by eliminating or reducing components such as carriers that make them so conspicuous. Using our own experience as an example, we could set the date of radio-visibility for Earth as December 12, 1901, when Guglielmo Marconi sent radio signals from Cornwall, England, to Newfoundland, Canada.[51]. Visibility is now ending, or at least becoming orders of magnitude more difficult, as analog TV is being phased out. And so, if our experience is typical, a civilization remains radio-visible for approximately a hundred years. So a civilization may have been very visible from 1325 to 1483, but we were just not listening at that time. This is essentially the solution, "Everyone is listening, no one is sending."

Source article

[ÑóẊîöʼn]

Also, even if technological civilisations leak radio signals into space for appreciable amounts of time, the inverse-square law means that such signals will degrade into the general background noise a short distance (in galactic terms) from the source. A focused signal would increase the range at which it could be detected, but would also reduce the area covered.

Another thing to remember is that transmitting signals omnidirectionally is an incredibly wasteful way of communicating between planets and stars - an interplanetary or interstellar civilisation would use focused signals such as large laser arrays to transmit information in as efficient a manner as possible. Such methods of communication greatly reduce the chances of us picking up a stray signal. Even if such civilisations are constructing dyson swarms to power such powerful communications arrays, there are anywhere between 200 and 400 billion stars in the Milky Way, most of them red dwarfs or main sequence stars which are perfectly capable of producing life. We haven't looked too closely at most of them. People underestimate just how mind-meltingly huge our galaxy is, let alone the entire visible universe.