Otherworldly life

General physics and astronomy discussions not directly related to Celestia
Malenfant
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Post #21by Malenfant » 21.10.2005, 00:54

WildMoon wrote:Hunter Parasite's right. We only know what life on one planet needs to survive, defined as the Goldilocks Conditions. Maybe hte Goldilocks Conditions for one planet are different than those of another planet.

A planet doesn't have to be exactly earthlike. There could be life in Europa's oceans for example, similar to that found around hydrothermal vents on Earth. But again, there have to be key ingredients - organic compounds, an energy source etc for them to be present at all.

And also, ya'll've said that in certain conditions only single-celled life would exist and that all multicelled life would die. How do you know that multicelled life would not be able to adapt so it can survive on another planet? If single celled life could exist there, why can't it evolve and be a multicellular organism yet still be able to survive?

Nobody said it can't. But there's a world of difference between a eucaryote microbe and a dinosaur or an insect. As I said, it took us three billion years or so to get from microbe to invertebrate.

Also, who's to say that life can't maybe be in the form of energy? Ghosts are nuthin' but energy. And some ghosts seem to even be sentient (watch Ghost Hunters - they actually go about trying to disprove ghosts and have alot of equipment that'll detect weird things that have been known to happen around ghosts. They also don't go around like other ghosts groups and say everywhere they go is haunted). So why can't there be life in the form of energy too?


Now you're off in cloud-cuckoo-land. Energy based life is entirely in the realms of science fiction. And furthermore, there is as yet no definitive proof that ghosts even exist, let alone what they are composed of if they do. This is not the realm of science - it may be at some point in the future if they are shown to be actually real (and that itself would be a major scientific revolution), but certainly right now it isn't.


Honestly, I can see why people like Fridger give up on this forum. This is supposed to be about science and reality, and yet people are going on about wishful thinking and what you see on TV. A little critical thinking and more scientific knowledge would go a long way before posting here.

Dollan
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Post #22by Dollan » 21.10.2005, 02:14

Malenfant wrote:A planet doesn't have to be exactly earthlike. There could be life in Europa's oceans for example, similar to that found around hydrothermal vents on Earth. But again, there have to be key ingredients - organic compounds, an energy source etc for them to be present at all.

At many points throughout Earth's history, it has not been very Earth-like. There is a huge range of global environments, never mind small-scale environments, that can host life.

The problem is, we don't have any kind of representative sample of multicellular life, aside from Earth, that can effectively demonstrate where or how well such life could survive. There are more than likely environments that would be actively inhospitable to Earth-life, despite apparent "shirt-sleeve" habitats, which support diverse biomes.

Of course, we may never know this, or at least not for quite some time....

Now you're off in cloud-cuckoo-land. Energy based life is entirely in the realms of science fiction. And furthermore, there is as yet no definitive proof that ghosts even exist, let alone what they are composed of if they do. This is not the realm of science - it may be at some point in the future if they are shown to be actually real (and that itself would be a major scientific revolution), but certainly right now it isn't.

Gotta agree here. When you start using paranormal examples to further some sort of scientific discussion, the only thing you do is utterly destroy your credibility.

Honestly, I can see why people like Fridger give up on this forum. This is supposed to be about science and reality, and yet people are going on about wishful thinking and what you see on TV. A little critical thinking and more scientific knowledge would go a long way before posting here.


Here I gotta disagree. Half of what is produced for Celestia is unrealistic. Big deal. It's *fun*. unless you're talking about keeping a specific *thread* scientific and realistic, I for one would find Celestia a shadow of itself if folks didn't put out some of the more outrageous items that they do. Cham's fantasy models, with the temples... love 'em!

...John...
"To make an apple pie from scratch, you must first create the universe..."
--Carl Sagan

Malenfant
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Post #23by Malenfant » 21.10.2005, 04:19

Dollan wrote:
Honestly, I can see why people like Fridger give up on this forum. This is supposed to be about science and reality, and yet people are going on about wishful thinking and what you see on TV. A little critical thinking and more scientific knowledge would go a long way before posting here.

Here I gotta disagree. Half of what is produced for Celestia is unrealistic. Big deal. It's *fun*. unless you're talking about keeping a specific *thread* scientific and realistic, I for one would find Celestia a shadow of itself if folks didn't put out some of the more outrageous items that they do. Cham's fantasy models, with the temples... love 'em!

...John...


Yes, but that's entirely different. I'm not complaining about the addons that people do, it's the questions that get asked here that are the problem sometimes.

This forum is supposed to be here to ask about and comment on physics and astronomy, but some threads (like this) have veered into navel-gazing, unanswerable metaphysics and wishful thinking. It's supposed to be about asking questions about the universe - to expand your knowledge about what you see in Celestia and to listen to and learn from people who know the answers. Not a place for people who have very little knowledge of the subject to declare how they think the universe should work.

And again, it seems to me that HP is really coming into it with the wrong attitude IMO. Like his other thread, he seems to be coming up with rebuttals for scientific explanations just to keep his wishful thinking alive. I'm all for teaching people about science but really, the people who don't know about the subject should accept what people more knowledgeable than they are have to say about it. If not, then it's just an exercise in frustration. The universe does not work the way you want it to work. Accept that and we might be getting somewhere.

This isn't a forum about philosophy or metaphysics or "wouldn't it be cool if..." or anything else that isn't scientific. I suspect that Fridger gave up on it because more of these threads have been popping up lately.

Dollan
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Post #24by Dollan » 21.10.2005, 06:02

Malenfant wrote:Yes, but that's entirely different. I'm not complaining about the addons that people do, it's the questions that get asked here that are the problem sometimes.

Then it is the task of those who know better to educate those asking the questions, not to berate them for not knowing enough. Granted, there are times that it goes way out there, such as the ghost thing (I'll admit, that one had me chuckling), but you're going to have to accept that not everyone has a grasp on science. Derisive comments will do little to educate people. I've always had a simple rule in my classes. "There are no stupid questions. There are, however, stupid answers."

This forum is supposed to be here to ask about and comment on physics and astronomy, but some threads (like this) have veered into navel-gazing, unanswerable metaphysics and wishful thinking. It's supposed to be about asking questions about the universe - to expand your knowledge about what you see in Celestia and to listen to and learn from people who know the answers. Not a place for people who have very little knowledge of the subject to declare how they think the universe should work.

As far as I can tell, this has happened very few times. The over all quality of knowledge displayed in the archives would be adequate for what people sometimes try to accomplish here, and many times the level of knowledge is impressive. Don't use a few people to quantify the whole. It's not fair, nor is it proper.

And again, it seems to me that HP is really coming into it with the wrong attitude IMO. Like his other thread, he seems to be coming up with rebuttals for scientific explanations just to keep his wishful thinking alive. I'm all for teaching people about science but really, the people who don't know about the subject should accept what people more knowledgeable than they are have to say about it. If not, then it's just an exercise in frustration. The universe does not work the way you want it to work. Accept that and we might be getting somewhere.

So that's one person. Why suddenly paint the whole forum as a lost cause? Seems a little short sighted.

This isn't a forum about philosophy or metaphysics or "wouldn't it be cool if..." or anything else that isn't scientific. I suspect that Fridger gave up on it because more of these threads have been popping up lately.


Really? I was under the impression, in my time here, that it was also a forum for "What if...", to be followed by "Because" or "Because nots", as well as items of a more scientific nature.

Look, I understand your frustration. I experience it all the time when dealing with paleontology. But I've learned that dismissing people in this manner simply creates bad feelings, and perpetuates the other's lack of knowledge while enforcing a lack of desire to learn. And that is never good.

...John...
"To make an apple pie from scratch, you must first create the universe..."
--Carl Sagan

Malenfant
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Post #25by Malenfant » 21.10.2005, 07:30

Well take this thread - its starts with a question about peoples' opinions about something that we don't even know exists. Nobody can answer it with any real data. A scientific response just gets "well, I think you could have it with [insert wacky element here] instead".

HP's other thread about 'theories about how the universe began' was similar. He wasn't asking anything scientific, he was asking for opinions about something which we have a pretty good handle on anyway.

This kind of thing to me serves no educational purpose. Stick it in purgatory or something as off topic conversation if you just want peoples' opinions about subjects and want to treat them equally (since nobody knows any better than anyone else really). But if it's actual data that you want - something that we DO know about - then it should be here I think.

(I guess it doesn't help that it's the question I hate most as someone who knows astronomy. First thing anyone says when I mention that is "oh, do you think there's aliens up there?" - drives me nuts. I guess it's like asking someone who studies sharks if they're all like the one in Jaws...)

eburacum45
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Post #26by eburacum45 » 21.10.2005, 11:33

I think there is a lot more to this question than just polling people's opinions; there is a large body of work out there on the subject of astrobiology, and it is becoming more systematic all the time. Thanks to the catalogue of extrasolar planets now available it is possible to put some real data behind these speculations.
It is something that I. for one, have been thinking about all my life; I really wanted to do astrobiology at college, but it wasn't available- in fact I studied environmental science, always with an eye towards the conditions on other worlds. In fact I went to the same uni as David Darling, who has become something of a specialist in this field- he left the same year I went there, so we never met.
So astrobiology is certainly speculative, but there is a certain amount of data available which can be used to form opinions. This amount of data can only increase.
If you want to speculate about intelligent and/or civilised life in the universe the field of study becomes much wider, and perhaps more interesting, but also more open. You need to know a little about anthropology, and world history, and the science behind the development f sentience. For instance take Wildmoon's question;
Why does life out there have to be either highly advanced or microbial to everyone? Why not neanderthals? Why not people as advanced as us? Why not civilizations similar to the Greeks, and the Romans, and the Egyptians?

is a fascinating question, and some rough estimates can be made of these chances.

Sun-like stars have a wide range of ages, and few re exactly as old as our own Sun; this suggests that life bearing planets ill have a wide range of ages too, and will be encountered in a range of stages of development. We have the example of our own world to guess what those stages might be.
Since the expected lifespan of the Earth is about nine billion years we can estimate the chances of our encountering a similar world amongst the subset of Earth-like terrestrial planets with life.
For a couple of billion years the Earth had almost no life, and had a reducing atmosphere. We are likely to find quite a few of those. Next the development of photosynthesis led to a cyclic alternation between oxygen rich and oxygen poor conditions, caused by the fact that oxygen was toxic to the very organisms which produced it; this period, during which the Banded Iron formations were laid down, lasted a little less than a billion years. Once oxygen tolerant organisms developed the atmosphere became increasingly oxygen rich; a slow process, as the crust hungrily absorbed much of the free oxygen.
This state lasted more than a billion years until the Cambrian period, when multicellular life developed. This latest phase, an Earth with a complex multicellular biosphere, has lasted half a billion years- about 0.6% of the Earth's entire history so far. But we can expect this rich biosphere to persist for perhaps another billion years or longer, until the Sun warms up and causes the Earth to develop a wet greenhouse climate. So, barring accidents the period with a complex biosphere could be the longest of all the Earth's stages.
Any random Earth-like planet we meet might have as much as a 30% chance of having a complex biosphere (I am only considering worlds orbiting G-class stars for the moment, by the way). The last three billion years of the Earth's existence will be increasingly inhospitable, but life may adapt to these conditions; we must expect to find many such marginal worlds.

Now what are the chances of encountering a semi-intelligent species like the Neanderthals, or a pre-industrial civilisation like the Egyptians?

The Neanderthals as a species only existed for a million years or so; if Homo sapiens sapiens had not wiped them out they might have survived for longer. An average species lasts about two and a half million years; but to be generous we could allow them to last as long as the other semi-intelligent inhabitants of our planet- the dolphins. Around thirty million years or so. Given a random earthlike world with a randomly chosen stage of development, we might expect to find such a semi-intelligent species on [30 million divided by 9 billion] = one third of a per cent of all such worlds.
Pre industrial civilisations are even more rare; the earliest cities re dated to around ten thousand years ago, so a pre-industrial civilisation might last ten thousand years before becoming industralised; the chances of encountering such a preindustrial state might be [10,000 divided by 9 billion] = 0.0001% of all worlds.

It seems possible that such preindustrial societies will be very rare..

eburacum45
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Post #27by eburacum45 » 21.10.2005, 11:50

Having said that, the chances of meeting a semisentient species might be increased if they last considerably longer than the dolphins have so far.

Similarly a preindustrial society might remain static for millions of years, especially if the conditions for survival are good; there might be no incentive to improve the level of technology if a stable, reasonably comfortable lifestyle can be acheived with low technology.
Or a civilisation might revert to preindustrialism folowing a collapse of the technlogical infrastructure (perhaps when fossil fuels run out- this might be our fate). Or the psychology of an alien race might mitigate against inquisitiveness and technological advancement for some reason.

I did not yet consider the possibility of life around stars different to our own; if life is possible arount orange or red dwarfs then the biosphere might persist for many more billions of years in some cases. This might allow the development of many more instances of semisentient life, and perhaps also many more chances for the development of pre-industrial society; but the pre-industrial phase will be in many cases a short precursor to the development of a highly advanced technological society.

How long such a high tech society could persist is a matter for speculation once again; but if you expect them to be short-duration phenomena then you have to give reasons for their final disappearance. Do they all die out through warfare or ennui? How long does this take? A truly advanced civilisation could utilise all the energy from its local star; this should allow them to persist for billions of years. This would put advanced civilisation in the ?€?very probable?€™ bracket, perhaps several percent of all Earth-like worlds.
If that is a plausible estimate, it begs the question posed by Fermi-

Where are they?

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Hunter Parasite
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Post #28by Hunter Parasite » 26.10.2005, 00:06

This should shows that there most likely is life in the universe; intelligent or not. http://planetquest.jpl.nasa.gov/AlienSafari_508.html

Dollan
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Post #29by Dollan » 26.10.2005, 14:09

In the end, the question of any form of life out there, right now, is going to be based on what amounts to an educated guess, extrapolated from any number of variables, the answer to almost everyone of which will involve a lot of guess work in its own right.

Until we actually get out there and can do some hands on surveys (even if those hands are via robotic probes), the answer is going to be nothing but a guess.

...John...
"To make an apple pie from scratch, you must first create the universe..."
--Carl Sagan

bdm
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Post #30by bdm » 27.10.2005, 01:09

eburacum45 wrote:This state lasted more than a billion years until the Cambrian period, when multicellular life developed. This latest phase, an Earth with a complex multicellular biosphere, has lasted half a billion years- about 0.6% of the Earth's entire history so far.

Two small corrections here:
1. The first known multicellular life developed during the Ediacaran (Vendian) period, not the Cambrian period.
2. This period was c.600 m years ago and the age of the Earth is 4,600 m years. 6/46 is about 13%, not 0.6%.

The essential point is correct - the Earth has had microbial life for most of its history.

Based on this, the most likely form of life that we will encounter on other worlds if we physically explored those worlds would be microbial. If we discovered life through SETI research, it would be technological. The difference here is a selection effect: microbes would find it very difficult to build a working radio transmitter. Therefore, the nature of the life we discover elsewhere would depend heavily on the methods we employ to search for that life.

One small point regarding intelligent life - in all the universe, some planet has to be first to develop it. What if it happened to be the Earth? (I assume here that the Earth has intelligent life.)

Malenfant
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Post #31by Malenfant » 27.10.2005, 05:41

bdm wrote:1. The first known multicellular life developed during the Ediacaran (Vendian) period, not the Cambrian period.


http://news.bbc.co.uk/2/hi/science/nature/3721481.stm

Huh. Must have missed that announcement... so they basically renamed made a new Period out of what was the lower Cambrian? (I thought the (old) Cambrian went back to about 650 Ma)

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Post #32by Michael Kilderry » 27.10.2005, 10:01

I think the Vendian occurs towards the end of the Precambrian, not in the Cambrian period.
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Juan Marino
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Post #33by Juan Marino » 27.10.2005, 19:53

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Malenfant
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Post #34by Malenfant » 27.10.2005, 21:28

Juan Marino wrote:
Malenfant wrote:I'd also ask you what evidence there is that the universe is infinite - or at least, that the amount of stars and matterin the universe is infitite. There's a hell of a lot of them sure, but that's not the same as infinite. AFAIK there's no evidence that the big bang released an infinite amount of energy, so there is no evidence that an infinite amount of matter from which to form stars coalesced from that.

The true definition of the infinite is the point. The infinite doesn??t have dimensions just as the singularity of black holes. And the universe is not a singularity!!


That's a meaningless statement that has nothing to do with what I said. It's also incorrect - an infinite space most certainly does have dimensions, just like a finite space would - an infinite space would just have no boundaries.

Whether the universe is or isn't a singularity is irrelevant.

Juan Marino
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Post #35by Juan Marino » 27.10.2005, 21:46

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Malenfant
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Post #36by Malenfant » 27.10.2005, 22:38

Juan Marino wrote:
an infinite matter or energy most certainly does have dimensions.

......NOOOO!!!

I never said that at all. We're talking about space, not matter or energy.
An infinite space doesn't even necessarily have to contain an infinite amount of matter or energy in it.


infinite matter or energy = singularity

only space = mind illusion
matter-space-matter = true


Yet more meaningless, irrelevant statements. This is a physics and astronomy board, please keep your pseudoscience away from it.

Juan Marino
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Post #37by Juan Marino » 27.10.2005, 23:10

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Smacklug
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Post #38by Smacklug » 07.11.2005, 00:29

Oh god it's like some unholy book of pseudoscience and physics combined got blown up. 8O

Malenfant
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Post #39by Malenfant » 07.11.2005, 00:42

Juan Marino wrote:pseudoscience????

Yes. You're babbling about mind and space and matter and illusion. You're making statements without evidence. That's pseudoscience.


Nothing said there supports your claims.

Malefant wrote:This is your chief problem, you dissociates the space of the matter.
The size of the space is according to the degree of dispersion of the matter, and matter is finite.


No, that's YOUR "chief problem" - you're associating the size of the universe with the amount of matter in it. The distribution of matter might affect theshape of the universe - that is, whether it's open, closed, or 'flat', but these have nothing to do with how big the universe actually is.

bdm
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Post #40by bdm » 07.11.2005, 01:48

Michael Kilderry wrote:I think the Vendian occurs towards the end of the Precambrian, not in the Cambrian period.

That is correct (although "Ediacaran" is the correct name for this period by international agreement). The Precambrian has been divided into ten new periods and the Ediacaran period is the most recent.

It was an interesting period, when killer mattresses swarmed the oceans and microbes lived in fear.


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