# Extra Terrestrial Life **URL:** \ **Category:** Great Debates\ **Created:** [December 20, 2013, 10:47am UTC](https://boards.straightdope.com/t/extra-terrestrial-life/676811 "2013-12-20T10:47:34Z")\ **Posts on this page:** 12\ **Page:** 8
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [January 2, 2014, 8:59pm UTC](https://boards.straightdope.com/t/extra-terrestrial-life/676811/141 "2014-01-02T20:59:38Z")
> [@Learjeff](#): > > My guess is that this determination would require incredibly high precision measurements, since the layer of water over the crust could be terribly thin (as it is on Earth, and would be even if we had enough water to be a water world.) Some waterworlds might be more than 50% water, and should have detectably lower densities than the Earth. But there are probably many more where the water layer is less deep. There is probably a whole planetary zoo up there, of many different types of world that we have never seen, or even imagined, yet. I suspect, although I can’t be sure, that if we expect to find many Earth-clone worlds in the stellar neighbourhood, we will be disappointed - but if we are looking for planetary diversity our search will be rewarded. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [January 3, 2014, 1:51am UTC](https://boards.straightdope.com/t/extra-terrestrial-life/676811/142 "2014-01-03T01:51:34Z")
> [@eburacum45](#): > > Some waterworlds might be more than 50% water, and should have detectably lower densities than the Earth. But there are probably many more where the water layer is less deep. OK, I see: we couldn’t detect all waterworlds, but we could rule out the obvious ones. Thanks, ignorance fought! ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [January 3, 2014, 1:53am UTC](https://boards.straightdope.com/t/extra-terrestrial-life/676811/143 "2014-01-03T01:53:26Z")
> [@eburacum45](#): > > There is probably a whole planetary zoo up there, of many different types of world that we have never seen, or even imagined, yet. I suspect, although I can’t be sure, that if we expect to find many Earth-clone worlds in the stellar neighbourhood, we will be disappointed - but if we are looking for planetary diversity our search will be rewarded. There’s some pretty awesome diversity just in our own solar system. I would be surprised to find that we have most of the bases covered already! ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [January 3, 2014, 2:00am UTC](https://boards.straightdope.com/t/extra-terrestrial-life/676811/144 "2014-01-03T02:00:03Z")
> [@Evil\_Captor](#): > > I 1) The argument that we are unique in the universe is part of that old line of geocentrism that has changed repeatedly throughout the ages because it always gets proven wrong. > … > Geocentrism has a DISMAL track record, and the notion that we are the only intelligent life in the universe definitely fits in right along with the geocentrism. > > So I tend to doubt the notion that we are the only intelligent life in the universe because the argument that we are fits very comfortably with the geocentric ideas about Earth and its inhabitants, which have been proven completely wrong time and time again. Good point. However … > [@](#): > > This is probably just the latest iteration of geocentrism. This may follow for many people, but doesn’t apply to those of us who simply argue that you can’t assign a probability, or even make a reasonable ballpark estimate of the order of magnitude of the probability. I bet most of us, if we had to go on our hunches, would agree with you and guess that life probably exists elsewhere. That’s a far cry from stating that it’s definitely likely that there is life elsewhere. I think this is the only distinction we’re arguing here (amongst other interesting sidebars). ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [January 3, 2014, 3:34am UTC](https://boards.straightdope.com/t/extra-terrestrial-life/676811/145 "2014-01-03T03:34:19Z")
> [@Evil\_Captor](#): > > One, the lack of evidence of intelligent life elsewhere. Surely some portion of intelligent life would use the radio band of the spectrum to communicate, just as we do. If intelligent life has evolved repeatedly on other worlds, why aren’t we awash in messages they’ve sent out over time? Just as our radio and TV broadcasts are now travelling to the stars at the speed of light, why shouldn’t theirs? Why are we not awash in alien TV series and talk radio programs? If not awash, why have there been absolutely no detectable alien emissions on any of the bandwidths SETI has scanned? This is very straightforward. Take the most powerful laser we have, with a pinpoint aperture. Aim it carefully at the nearest candidate system, Alpha Centauri A, a yellow dwarf similar to the one nearby and give it a blast. By the time this very coherent beam of light reaches that system, it will be well over a billion miles across, just due to beam spread. And that is not accounting for 4+ lightyears of fluff between here and there, which contribute to beam scatter. Not much to detect, even if you are looking really, really hard. And that is just a nearby star. Run a program called “[Celestia](http://sourceforge.net/projects/celestia/?source=directory)”, line it up on the sun and move away until the sun is no longer visible. I lost sight of it after just 58ly, much closer than I would ever realistically expect to find another inhabited system. That is the most powerful beacon in our system, and it becomes background noise in less than 20pc. As sophisticated as our search hardware is, the distances over which it is trying to scan are just beyond comprehension. We will simply not find EM evidence of distant civilizations because there is no way such weak signals would carry far enough. There is just too much background noise. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [January 5, 2014, 7:30pm UTC](https://boards.straightdope.com/t/extra-terrestrial-life/676811/146 "2014-01-05T19:30:57Z")
> [@Learjeff](#): > > There might be life that’s not even based in chemistry. Perhaps Jupiter’s Red Spot is an intelligent storm. Goodness knows what might go on inside a star. Of course, I’m being facetious here: I think the likelihood of those two is too small to move the most sensitive needle. My point is simply that there’s a lot more in the universe than chemistry, though it does seem to be the biggie from where we sit. It seems rather difficult to come up with a specific definition of “life” that is sufficiently broad to cover all the bases yet narrow enough to be useful. I would suggest the following constraints: [ul] [li]it should be a natural process (but, then, what is not a natural process?)[/li][li]it should have a distinct boundary with respect to its environment[/li][li]it should consume available natural resources, affect their composition, and expel waste (metabolism)[/li][li]it should have a replication mechanism[/li][li]it should have the potential for mortality[/li][/ul] By this measure, the Red Spot does not constitute life because it lacks a distinct boundary from its environment (it is just a reconfiguration of the stuff around it) and it has no metabolism (anything that enters it also later leaves essentially unaltered). Yet, this definition, being satisfactory to describe an oak, is not sufficient to exclude stars. They consume available resources (the nebulous media from which they form), they metabolize those resources into something else, they are distinct from their environment, they eventually die, and some of them beget new stars (which is true of life as we know it: not all living thing do, or even can, reproduce). If we mandate some sort of aggregate structure (like cells), stars appear to be defenestrated, but OTOH, we are not entirely certain what all goes on inside them. Galaxies are generally thought to have a “goldilocks” region, simplistically portrayed as an annulus that excludes the outer reaches (inappropriate balance of elements) and the bulge (too much radiation and violence). But that relies on life being in a form we can [del]eat[/del] recognize. Perhaps life could involve a process that thrives on or even requires large amounts of ionizing radiation. It would obviously be pretty hard to study or interact with, but those beings would find our form of life similarly difficult to imagine or study. If life is a wide enough category as to possibly be beyond what we can definitively discover, much less study or have encounters with, does the whole thing become a matter of, “hmm, that’s interesting, let’s look for something more familiar”? ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [January 5, 2014, 9:03pm UTC](https://boards.straightdope.com/t/extra-terrestrial-life/676811/147 "2014-01-05T21:03:29Z")
The definition of life [has been discussed before.](http://boards.straightdope.com/sdmb/showthread.php?t=694884) [Schrödinger’s _What is Life?_ (32 pages)](http://whatislife.stanford.edu/LoCo_files/What-is-Life.pdf) is worth reading; it makes several important points. I hope someone else will post a good synopsis; I’ll just note here that he concludes that redundant ensembles of complex molecules are the right scale. IMO, a #1 requirement for “_life_” is that _it create order_, i.e. manufacture negative entropy. The 2nd Law of Thermodynamics then implies that waste entropy will be created; that must be carried away by some “conveyer belt” apparatus. (The lowest-level “conveyer” is water in the well known implementation of life). Creating _much_ order, requires consuming _much_ energy. Need for _persistence_ may dictate some form of replication, perhaps supplemented by repair, etc. This leaves five key requirements: [ul] [li] Consume energy[/li][li] Create order[/li][li] Dispose of waste[/li][li] Replicate[/li][/ul] The five most common _ **non-inert** _ elements in the Universe are Hydrogen, Oxygen, Nitrogen, Carbon, Silicon. The top two here form water, a rather magical solvent. The top four are the main constituents in all organic compounds. I’ll ask experts whether the chemical richness of fifth-place Silicon can compete with Carbon’s. One way to come up with a “living” creature _not_ based on molecules is via (magnetic?) crystals, perhaps obtaining the high energy needed to support high-tempo life via incoming lightning bolts. An even less likely proposal is replicating storm systems, e.g. in ocean or atmosphere. Perhaps a powerful and stable community can be designed, _but how would it have evolved?_ (Does anyone have a cite for the plausibility of lifeless waterworlds with atmospheric oxygen? Oxygen does react with hydrogen, ammonia and many other molecules.) ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [January 5, 2014, 9:28pm UTC](https://boards.straightdope.com/t/extra-terrestrial-life/676811/148 "2014-01-05T21:28:36Z")
> [@septimus](#): > > (Does anyone have a cite for the plausibility of lifeless waterworlds with atmospheric oxygen? Oxygen does react with hydrogen, ammonia and many other molecules.) Certainly. Leger et al 2003 > **[A New Family of Planets ? "Ocean Planets"](http://arxiv.org/abs/astro-ph/0308324)** > > A new family of planets is considered which is between rochy terrestrial planets and gaseous giant ones: "Ocean-Planets". We present the possible formation, composition and internal models of these putative planets, including that of their ocean, as... > [@](#): > > As in Earth-like planets, photodissociation of H2O can produce abiotic O2. This gas can accumulate, the more as the removing processes present on Earth, oxidation of rocks by soil weathering and oxidation of volcanic gases, are not expected on an Ocean-Planet. Consequently, the presence of O2 is not a reliable biosignature Hydrogen will combine readily with O2, so on worlds where gravity is high and Jeans escape is difficult then abiotic O2 will be insignificant. Where the escape velocity is low enough, H2 will escape before the O2 can recombine. Ammonia is a reasonable option, but doesn’t occur frequently in the inner system. It is very rare compared to water in warmer regions, and on a waterworld will probably occur in solution if at all. ---
**Author:** ![Stringbean](https://avatars.discourse-cdn.com/v4/letter/s/d6d6ee/32.png) [@Stringbean](https://boards.straightdope.com/u/Stringbean)\ **Post date:** [January 6, 2014, 9:02pm UTC](https://boards.straightdope.com/t/extra-terrestrial-life/676811/149 "2014-01-06T21:02:46Z")
I anyone is interested Stephen Hawking had an episode of his series Into The Universe dedicated to the possibilities of extra-terrestrial life. He covers some of the more radical possibilities too. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [January 6, 2014, 9:57pm UTC](https://boards.straightdope.com/t/extra-terrestrial-life/676811/150 "2014-01-06T21:57:04Z")
> [@For You](#): > > By this measure, the Red Spot does not constitute life because it lacks a distinct boundary from its environment (it is just a reconfiguration of the stuff around it) and it has no metabolism (anything that enters it also later leaves essentially unaltered). And yet, if it sent us a message saying “Hi, how’s the weather?” would it not be life? (Good post overall, btw .. thanks.) My definition for life is simpler than a list of characteristics, though I’ll admit it has its weaknesses: Life is that which evolves itself Most of the entries in lists of what life requires are probably valid, though I don’t know whether I agree with the boundary part. (I think of a colony of bees as the organism, more than the individual bee. I was delighted to read Goedel Escher & Bach to find that Hofstadter agreed with me, to some extent.) Beside the point, though. In any case there’s definitely a difference between life and intelligence, but I would call any naturally occurring intelligence “life” and expect it would have to have arisen from “that which evolves itself”. > [@septimus](#): > > The definition of life [has been discussed before.](http://boards.straightdope.com/sdmb/showthread.php?t=694884) > [Schrödinger’s _What is Life?_ (32 pages)](http://whatislife.stanford.edu/LoCo_files/What-is-Life.pdf) is worth reading; it makes several important points. I hope someone else will post a good synopsis; I’ll just note here that he concludes that redundant ensembles of complex molecules are the right scale. > > IMO, a #1 requirement for “_life_” is that _it create order_, i.e. manufacture negative entropy. The 2nd Law of Thermodynamics then implies that waste entropy will be created; that must be carried away by some “conveyer belt” apparatus. (The lowest-level “conveyer” is water in the well known implementation of life). Creating _much_ order, requires consuming _much_ energy. Need for _persistence_ may dictate some form of replication, perhaps supplemented by repair, etc. This leaves five key requirements: > > [ul] > [li] Consume energy[/li][li] Create order[/li][li] Dispose of waste[/li][li] Replicate[/li][/ul] Yeah, I can’t imagine life that doesn’t do those things. Nor can I imagine how ‘storm life’ could have arisen, evolved, or even persist. We’re having a hard enough time coming up with ideas how the life we know so much about arose! All this aside, I’m still curious about the requirements life imposes on its substrate. What kinds of parts and principles are necessary to create life? Or even an automaton, for that matter. Schrodinger’s list is definitely a subset. I look forward to reading the paper; thanks for posting! ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [January 6, 2014, 9:59pm UTC](https://boards.straightdope.com/t/extra-terrestrial-life/676811/151 "2014-01-06T21:59:45Z")
[quote=“For You, post:146, topic:676811”] [li]it should be a natural process (but, then, what is not a natural process?)[/li][/QUOTE] I think that caveat is just to exclude stuff invented by humans, which might meet the criteria, but which we would not call life. It raises the question of at what point could stuff we create take on a “life” of its own, but for current practical purposes I’m OK with it. ---
**Author:** ![tullsterx](https://avatars.discourse-cdn.com/v4/letter/t/e9bcb4/32.png) [@tullsterx](https://boards.straightdope.com/u/tullsterx)\ **Post date:** [January 9, 2014, 1:38pm UTC](https://boards.straightdope.com/t/extra-terrestrial-life/676811/152 "2014-01-09T13:38:17Z")
> [@Sam\_Stone](#): > > We know that there are billions of planets of roughly Earth-size, orbiting in roughly Earth-like orbits around sun-like stars. > > The history of astronomy is a history of us learning that we are less special with each discovery we make. There doesn’t appear to be anything unusual about Earth in terms of the ability of life to form. > > What we don’t know is how likely intelligent, tool-using civilization is. After all, Earth is full of successful animals that did not evolve high intelligence. We don’t really know how much of an outlier we are. > > Also, we don’t know the odds of the chain of life existing for for the billions of years required to evolve intelligence. Between star output variation, gamma-ray bursts, supernovas, collisions with other bodies, planetary disasters like megavolcanoes or runaway greenhouses, it may be fantastically unlikely for planets to have a biosphere that survives long enough to evolve intelligent life. > > My personal opinion is that life is ubiquitous throughout the universe, but intelligent civilizations with the technology required to contact us may be incredibly rare. In fact, we might be the only ones in our galaxy, or at least in our neighborhood of the galaxy. I agree with this, but think it’s a little too optimistic. One factor that many don’t give enough weight to is TIME. Human civilization has only been around a very brief time on a cosmic scale. So, there may have been other life/intelligent life, but it may be dust by now; or we may be dust before intelligent life develops elsewhere. Space is big, but so is Time, and it’s totally unclear how long we’re going to be around. [Previous page](https://boards.straightdope.com/t/extra-terrestrial-life/676811.md?page=7)