With all of the discoveries that have been made in the last ten years or so in the area of astronomy, I'm starting to shake my head a little when anyone suggests that Earth is the only place in the universe where life evolved. It's been a complete shift; where once it was illogical to believe in alien life, I think it's now completely illogical to disbelieve it in the face of the evidence.

When the first extrasolar planets were discovered in the early nineties, the researchers were reluctant to publish the results because they feared being labelled as UFO nuts. Now there are over 300 confirmed planets orbiting other stars, the variety and frequency of the discoveries increasing with each passing year.

Some of the more notable discoveries:

1) A solar system with planets the size of Jupiter in Saturn, in the same orbits, suggesting the likelihood of terrestrial planets in the same orbits as Mercury, Venus, Earth, and Mars.

2) An extrasolar planet with an atmosphere that was directly detected, and found to have methane, a key organic compound.

3) The Gilese system with two planets not much larger than Earth, one of which some argue could be habitable.

4) Water everywhere - Found on Mars. Found on Mercury. Confirmed on comets. Likely in ice form on asteroids and moons throughout the solar system.

5) Extreme bacteria - able to survive at extremely high and low pressures and temperatures. Found to thrive in zero-gravity. Suspected to be capable of surviving journey through space on meteroids from planet to planet.

What are your thoughts? Would you agree that it's becoming a bit unreasonable to argue against extraterrestrial life? And if there is life out there, why wouldn't it evolve intelligence, especially when there's countless billions of planets in the universe?

The reasoning behind your last sentence pretty much sums up my view. The idea that we could be the only life - and intelligent life - in such a vast universe is ludicrous, even leaving aside recent discoveries of extrasolar planets and extremophiles. While the chances of us ever encountering intelligent aliens is a valid topic of debate, I believe that the existence of such creatures is not.

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The main reason is that it's not a straight shot from bacteria to intelligent alien. There's probably been a billion species on this planet, yet only one "intelligent", i.e., technological species. So that makes the odds a billion to one. We're probably the only species within a billion light-years.

Only if there was only an average of one species per 418 billion cubic light years. But we know earth has many species so it may be possible that other planets also have many species.

And I don't think number of technological species divided by total number of species is a way to generate sensible proabilities. Otherwise someone in the United States might see that there are 300 million people in the US and only one president and conclude that the chance of another country having a president is one in 300 million.

I think it is pointless to speculate on how common (or uncommon) life is in the universe at this time. If we find direct evidence for ET life on other worlds, that will clear it up once and for all. And if we keep looking, and never find any direct evidence, we'll be able to say that (at least) life is very rare.

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Well, I do agree with you on one level, but on another level we haven't got the sort of evidence which proves that life exists anywhere else yet. Let's have a look at your list of data points with a critical eye to see if they do give any support to the idea that life is widespread. But that is no proof that there are any planets there- and if there are, they could be as inhospitable as Mercury, Venus, or the Moon. Just having a terrestrial planet doesn't imply that life can or will form there. Methane is also found on Titan, and in Jupiter's atmosphere, as well as on several other bodies in the solar system. However none of this methane requires life for its formation or existence, nor does it suggest that life will arise easily on those worlds.
Not habitable by humans, that is for sure; both worlds are hellish compared to our own planet. But it is just possible that extremophiles could live on one, or both worlds, if certain conditions are met. More about that later.
Water is one of the most common compounds in the Universe- but by itself it does not imply that life is common or even that life has arisen anywhere outside our planet.
Yes, the existence of such extreme life is very encouraging; I would like to think that this implies that life might be found on worlds which do not resemble the Earth very closely at all.

But the problem with the extremophiles that we know of from Earth is that they all derive from our own biosphere- presumably life emerged on our planet, once (at least), long ago, and diverged since that time to inhabit many environments. But we can't tell from that evidence just how likely, or unlikely, that original emergence was. It may be the case that the emergence of life on our planet was so unlikely that it has literally happened nowhere else in the visible universe; if so, the existence of myriads of terrestrial planets and environments which could conceivably support life does not prove the existence of life elsewhere.

To prove that life is widespread we have to actually find it- and that is something we can't do at the moment.

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Not directly, but it seems likely given the metallicity of the star involved. Regardless, direct detections have been made of a dozen or so terrestrial planets in varied orbits. The fact that they are there makes it a statistical certainty that there are terrestrial planets circling in the habitable zones of their stars.

And we've already found a ton of gas giants, some of which orbit in their star's habitable zone. It's entirely plausible that they have habitable moons.

I do not recognise this paradigm shift.

I have been interested in astronomy since 1974, and back then, the attitude seemed to be that whereas alien life seemed very likely, given the size and variety of the universe, there was no evidence that it actually had arisen anywhere other than on Earth.

34 years on, the attitude seems to be exactly the same.

The details have changed, of course. Prior to 1976, when the Vikings landed, it was a real possibility that there would be life forms on Mars that resembled jellyfish, burrowing into the soil to reach the ice. We've lost that, of course, but we gained Europa with its possible ocean. Years ago, we had no idea if other stars had planets, but we assumed they probably did, and if they did, they would be arranged pretty much the same as our solar system. Now we know that there are planets around other stars, but their arrangements are bizarre compared to our own.

And so on.

On the one hand, it becomes extremely unlikely that Earth is the only planet with life; on the other hand, we're not making the discoveries we expect to make.

As others have said, we can only make a sensible judgement when we have actual evidence of other life.

Incidentally, I don't think anybody gets called a crackpot simply for believing there might be life out there. It's only those who claim to have met it that do.

Its an interesting question as asked by Drunk Vegan because the oddest aspect about life in the cosmos, is why do we seem to have a default built-in logic on the matter which assumes we could not possibly be alone within this immense universe? I have this "gut instinct" feeling that there must be other biology in the universe. I know that sounds pretty unscientific but could that logic not have a perfectly rational explanation? Perhaps we've picked up evolutionary logic based on natural/physical imperatives such as the conservation of energy. For instance, we look out at the cosmos and might naturally think: what a huge waste of matter and energy unless there is biology to observe/define it. If we have the concept deeply imbedded on our psyche it perhaps would be a natural conclusion to make.

For me the thought that we are some unique fluke within the whole universe, never to occur again even in the form of bacteria, is quite disturbing. We cannot possibly be the only observers of this massive beautiful universe - That would be like a universal killing joke.

Once we have the ability to recognize the gases and atmospheres of planets the size of Earth, the question will be answered. How far are we from having that technology? 5 years right?

Farther beyond that, the definition for the Goldilocks Zone may include areas on planets or moons with active cores far away from their sun and deep within their surface (IE Europa). And if Earth's own weather system is capable of bitterly cold ice ages and sweltering heat ages, what are the most extreme conditions on planets like Venus and Mars? Is Venus or Mars capable of having a low or high enough temperature and pressure to develop and maintain simple life? Would a slow orbiting moon of a "hot-jupiter" be able to properly distribute heat throughout the moon in a stable way? Exciting questions and answers.

Exactly. We have insufficient information at this time to determine how likely life is and how common the conditions that would lead to it are in the universe. Once we move out into a significant number of other systems we'll have enough information to make an informed guess.

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If a gas giant is too close to the primary star, it is unlikely to have moons, because it will have a smaller Hill Sphere- that is the location where the planet's gravity is dominant. So I'd not go looking for too many habitable moons of hot jupiters.

However a moon of a gas giant in the habitable zone, oe even a little way outside it, is a reasonable proposition; if a moon of a giant is not heated enough by the local star, it might be heated by tidal heating just enough to make it habitable.

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Is it illogical not to believe in something you have no evidence for? No, it's perfectly logical. How is it logical to believe that since life evolved on one world, then the universe must be full of it? Assumptions, and theories, nothing more.

I'd like to believe in E.T., but as evidence is, there's no basis for my believe other than pure fantasy.

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I don't think it is or ever was illogical to believe in the existence of alien life. As one astronomer (sorry, can't remember his name) said on an episode of "The Universe," "absence of evidence does not equal evidence of absence."

Given the vast number of stars in each galaxy and the vast number of galaxies, it seems highly unlikely that life evolved in only one place in the entire universe. When I was a child, the idea of other stars having planets was often looked upon as fantasy. Yet it seemed logical that if the sun is an average yellow dwarf star, and it has a planetary system, the chances are that such systems are common to many stars. Back then, I had many a debate with people about this, which is why I was absolutely thrilled with the first discoveries of exoplanets. We're at a point now where we're finding out there is far more diversity in the universe than we could have ever imagined.

It's possible that life may be out there and that we will never find it. First, the majority of life forms, if they exist, are likely to be non-intelligent, probably microbial types. Then there is the issue of the vast distances between star systems, which could easily lead to a situation where there are scattered worlds harboring intelligent life, but those worlds are so many light years away from one another that none is ever aware of or able to communicate with any others. Our sun is in a pretty isolated area, with the nearest star system being four light years away. If we don't find evidence for extra-terrestrial life, it may very well be because the sheer distances between us and other worlds harboring such life makes it impossible, at least with current technology.

Personally, I share Jetlack's sentiment. The idea that one planet revolving around one star is a fluke in the entire universe seems downright illogical.

Extremely unlikely, sure, but why "cannot possibly"? It sounds more religious than scientific.

Hi Paul,

I'd say its more of a gut instinct based on logic; though i can understand how it comes across like a religious belief. If we can agree that a naturalistic logic exists in the universe such as cause and effect; then i think we can argue that there is genuine logic involved in this unshakeable faith that there is other life in the cosmos. For instance:

1) Primitive life appears to have taken hold on earth very soon after its initial formation. If what happened on earth is such a fluke why did it happen so quickly? As far as I know the earliest confirmed signs of life/fossils are from about 3.75 billion years ago. However recently they found some diamonds with carbon signatures which if biogenic would take us to 4.25 billion years ago. Even if for argument purposes we agree on 4 billion years that is pretty fast for something which could be a unique fluke in the universe.

2) The various physical constants of our universe which have been shown to be ridiculously tuned to encourage the developement of life. Since these constants appear throughout the visible universe it is logical to assume that life has similar chances elsewhere in the cosmos.

3) Quantum Mechanics. Okay this is arguable since there is still no solution to the "measurement problem" but I prefer the "observer collapses superposition/wave" interpretation. I dont buy the "many-worlds/decoherence" interpretation which ejects the need for an observer. I know its the "shut up and calculate" consensus but that does not make it correct - just easier to deal with from a philosophical perspective. (see point 4 for my reasoning)

4) Nature's conservation of energy. If the observer collapses superposition/wave" interpretation is right then it would be logical to assume that this universe would not exist in a defined state without observers. Since without observers there is no need for matter and energy to be defined. Why would nature waste so much energy if there is no requirement for its definition? Surely all the matter in our universe would stay in its undefined quantum superposition state if there is no observer/s. (I know this is speculative and many phycists are uncomfortable with that interpretation but its as valid as any of the other QM interpretations - until proven otherwise)

5) If we are totally alone and the above is all bull and we really are some super-duper fluke then it gives more credence to the idea that we are special and of divine inspiration - which i find very hard to believe. It would make us the centre of the universe. Unlikely i think.

Of course I could be totally wrong

To this I'd add that we do not yet know enough about planet formation in terms of how common or rare terrestrial planets are in our galaxy, (based on our beginning assumption that life could likely form on a terrestrial or ocean world.)

We have some actual observations of forming solar systems and have detected a growing list of extra-solar planets. We've also made intelligent conjectures on planet formation based on observations. However, we still do not know how many Earthlike planets there could be in the Milky Way. We also don't fully understand the natural processes that lead to such planet formation in terms of how common terrestrial and Earthlike planets form. As more observations are made, and as more terrestrial worlds are detected, we might eventually have a bigger picture of the processes in nature that lead to probably life on other worlds.

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Hi DV (can I call you that?).

I wouldn't term it illogical at all; rare earth hypothesis seems logically conceived, given what evidence there is, no?
Neither do I perceive a "complete shift" in the mindset. A "plurality of worlds" perspective, an outgrowth of the copernican revolution, has for long been considered logical, several centuries or more in fact. One could go further and find in various ancient philosophies an acceptance that the universe is abundantly inhabited, that there have been "those from heaven to earth came."

...snip...

What is intelligence though?
Looking at earth's biosphere from afar humankind might well appear to be a virus rather than intelligence. Is our kind of intelligence "natural?" Who knows? I personally think it likely to have arisen before but how frequently I could not say.

And I don't agree it's becoming unreasonable to argue against the ETH when we've but a single example; instead, I'd say it's becoming a less tenable viewpoint.

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Is this actually true? Did someone mention this in their memoirs? Or in a public interview? How long did it delay publication?

I'm still shaking my head over that gut instinct based on logic--what's that?

Anyway, sure, I have pretty good faith that the sun will rise tomorrow--but that's happened before. I really don't have any confirmed instances of alian sightings, yet.

I disagree.
I think without having left the planet we've acquired enough info to make informed guesses. Speculation is necessary, not pointless.
We know our sun is but a star amongst innumerable stars while we are finding with great rapidity planets which are likely amongst innumerable planets. The discovery of exoplanets was confirmation of informed guesses. I suspect our guesses about earthlike planets and conditions will soon be confirmed as detection methods and technology improve.
We know the universe's most abundant elements are those with which Life is made. If chemistry and physics, as we understand them, are correct an informed guess would be that similar ingredients in similar conditions produce similar results. I don't think it will be necessary to visit a significant number of systems before we determine this to be the case.

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"Men occasionally stumble over the truth, but most pick themselves up and hurry off as if nothing had happened." - Churchill

"I'm still shaking my head over that gut instinct based on logic--what's that?"

Is it not possible some gut instincts are based on a conscious or even subconscious form of logic? For instance in the same way that we can walk around with irrational beliefs which might impair our gut instincts. I'm not saying they are always correct, but perhaps they are being driven by logical or at other times illogical conclusions.

What interests me is if any human logic can have originated through evolutionary experience via DNA, or is logic purely a product of human development. Animals appear to understand a certain basic logic as in cause and effect; and i just wonder how much they know but aren't telling us

I have pretty good gut instincts about logic

But then, I step back and walk through the logic. As long as we have the time, and we seem to to here at BAUT, let's walk through the logic. I don't see that happening.

This is highly flawed logic.

It is tantamount to saying:"In last week's marathon race of 10,000 runners, there was only one winner, therefore the chances of the race having a winner at all is 1 in 10,000. It was really lucky someone won!

(In fact: the chance of there being a winner in a marathon are 1:1.)

I have religous reasons to think trillions of ET planets, and off Earth habitats with ET that look like us humans, but may be quite different in other respects.
My science side says we don't know, but at least a few sentient planets are likely. Neil

We don't even know how common Earth-like planets are at this point, mostly because we can't even detect them with present technology. How are we possibly going to detect the presence of life at a few light-years distance unless it's because they contact us with radio signals?
We can theorize that they might be there, but it's only an informed guess if we have some actual data to work with - examination of other systems at close range with probes, presumably. And to confirm the presence of life will probably involve landings.

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Does anybody else know anything about this?

Was this a real concern? or was it a joke by somebody?

Well I'm all for that I think there are logical reasons for expecting life to occur elsewhere in the universe, and i've posted some of those arguments above. Of course i admit that some of my argument is biased; particularly the QM interpretation in regards to observers role in our universe. But there is plenty of other logic which does not rely on arguable interpretations.

Does life play a significant role reducing entropy in the universe? Or does it increase it somehow? I only ask because it if reduces it then that is a pretty logical reason for life to exist. Isnt it?

Interestingly that relationship between biology and inanimate matter from a "entropy" perspective, sort of mirrors the observer to observered relationship in certain QM interpretations. One is reducing entropy through macro-scale ordering and the other version is defining matter from a superposition (high entropy).

In both cases, biology could be said to have a vital role reducing entropy and defining matter.

I wonder if there is a sliding evolutionary scale of how life has effected the entropy in its surrounding environment. For instance does life increasingly reduce entropy as it evolves?

Feel free, everyone has been for years.

I think when we do find extraterrestrial intelligence we may not recognize it. I'd argue that there are different kinds of intelligence and being able to communicate with humans shouldn't be considered a prerequisite. For all we know dolphins are highly intelligent and communicate complex ideas with one another, but since it's impossible for us to speak with them we'll never really know.

They quoted one of the researchers about it in an article about the discovery. It seems goofy to me but I can understand their concern given the previous false positives (e.g. Barnard's Star). A wrong assertion that there were planets could have ruined their careers, and given the attitudes at the times, made people think they were seeing things in an attempt to find "little green men."

For me the reverse is true. My gut tells me there is life out there, and logic supports that assertion based on mounting evidence.

Not true. We can "sniff" the atmospheres of other worlds with spectrography, telling us the exact composition of gases present. We've already done this with a couple of worlds orbiting other stars. And we * can * detect an Earth-sized planet with current technology. It could happen tomorrow if someone got lucky with a nearby star viewed with microlensing and catching an Earth-sized planet transiting its star.

Coincidentally, it's precisely these types of discoveries that allow us to get data on the atmosphere of these worlds.

With an extreme stroke of luck, sometime this year a team could discover and Earth-sized planet and find out the exact composition of its atmosphere.

If the ratios of gases in the atmosphere are "unnatural" - such as they would be if someone looked at Earth, then bingo, we've found alien life without the need for space travel or radio signals.

We'd never know if they're intelligent without travelling there or communicating, but we'd know there was life there.

With, as you say, an extreme case of luck. But we can't detect them directly at this point - only with an occlusion of something we can detect.

Spectography has been used on large gas giant-type planets from long distances, would we be able to use them on an earth-sized world we can't see except for its effects on it's parent star?

And atmospheric spectrography won't confirm the presence of life in any case - only the elements that will make it possible or may be its result. It could be a strong case, but we wouldn't have confirmation until we went and looked.

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