Life in the universe.

cepheid

Ryan_m_b,

I don't claim to know what abiogenesis is, but regarding your point that maybe Earth was "extremely lucky". Okay, let's quantify that. How much of a statistical fluke was the development of life? Are we talking 1 in a million? One in a billion? Given that probability, but given also the vastness of the cosmos, how many instances of life arising does that lead to? I cannot help but think that the answer is always going to be: "a lot."

Regarding, I think it was Nabeshin who mentioned that all the parameters of the Drake equation are well-defined, we just don't know their values. Aren't actually being a little too restrictive in our thinking here? I'm no biologist, but if there's one thing that life on Earth has taught me, it's that it is resilient and that it can thrive even in what we think of as the most extreme of conditions. Who says that extraterrestrial life will need liquid water, or will need to live in a habitable zone where it is not too hot or cold, or that it will find somewhat high levels of radiation to be detrimental? What seems unlikely to me is that life arising elsewhere independently would have a similar biochemistry to our own, as opposed to something truly alien

Travis_King

My $0.02 for the current discussion:

1. The Drake equation is interesting in that it describes parameters for determining the probability of other life, but it is useless whether or not the parameters are well defined. If you are missing even one of the values, the equation becomes meaningless. So the fact that really most of the parameters have values which are unknown or unknowable really just makes it a fun thought experiment.

2. Good point, but then we have no business discussing the probability of such life, as we have no experience with what it could be, the likelihood of it being true, etc. It's a nice thing to speculate on, but there are far too many unknowns to make any reasonable judgements on the matter, let alone conclusions.

cepheid

I think your first point illustrates that your second point applies equally well to "familiar" life as it does to weird life. Even if we set defined criteria for the existence of life -- criteria that have a known geocentric bias, we *still* can't say anything meaningful (ie quantitative) about the abundance of such life in the galaxy or the universe as a whole. It was not my intention to. My only point was to say that there seems to be a good logical argument for being optimistic that life in some form exists elsewhere, and that it is plentiful.

Ryan_m_b

It is the study of how life originates. As I said we don't yet have a comprehensive theory of abiogenesis but there are some very interesting areas of research.
You seem to have missed the point, that and you seem to think I can't do basic maths. Of course if the chances of a star having a planet with life were 1 in 1 million or 1 in 1 billion the universe would be teeming with life. But we have no idea what that probability really is, without a good understanding of how life evolves and under what circumstances it is (un)likely to and the distribution of conditions that would lead to a planet of that nature forming it's all just guess work.

Yes it could be 1 in 1 million, it could also be 1 in 10²³. We just don't know.

Travis_King

Agreed.

This, however, I disagree with. It does not follow from what we've said that life is plentiful. There is a good argument that there is other "living" stuff out there, but we can't make any meaningful statements about the likelihood, let alone the abundance, of it.

DaveC426913

My bet is that the evolution curve between no life and primitive life is shallower than the evolutionary curve between primitive life and complex life.

i.e. I think that the basic replication of life happens "relatively" frequent in the galaxy where conditions are right, but that the vast bulk of them never evolved past the unicellular level.

Depending on how you interpret the timeline, life began relatively quickly (only a few 100My) after the crust cooled enough to allow it. By comparison, the the step from unicellular life to multi-cellular life took as much as a Gy.

I suspect that life forms but that systems aren't stable enough over huge expanses of time to allow more complex life.

Furthermore, I suspect that, when we go looking over the next millenia, we will encounter thousands of planets with microbial life before we come across one with anything as complex as a plant. And hundreds of those until we come across something as complex as a mammal. and so on...

Kind of depressing when you look at intelligent life as being at the end of a very long tail.

Ryan_m_b

IIRC this is because it took billions of years to do alter the environment (e.g free oxygen) to a level where more complex life was possible. Not that I disagree with anything else you say, it's certainly a possibility.

Chronos

Even a planet identical to earth in every respect would be an unlikely host for beings such as ourselves [sentient intelligence]. The development of intelligent life is precariously dependent on an unlikely sequence of events and blind luck. In my estimation, dinosaurs would still be the dominant life form on many such planets. I would hazard to guess intelligent life is exceedingly rare in the universe at any particular point in the history of the universe. I would not at all be surprised if we are one of the few, if not sole example of sentient intelligence in this galaxy at this particular time.

Eric333

Just to clarify, are you saying "galaxy" or Universe? I think you make a good argument either way mind you.

cepheid

I don't understand this, because it seems like you are just making a whole series of assertions that you think are obvious, but what you say is not at all obvious to me, and there is nothing to back any of them up. Could you maybe elaborate on what you think the unlikely sequence of events and blind luck was that led to the development of Homo sapiens, and why it is, in your estimation, so improbable, even given nearly identical conditions on some other planet?

DaveC426913

Perhaps so but that doesn't mean they wouldn't be intelligent.


http://www.daviddarling.info/encyclo...aurintell.html

Chronos

Yes, galaxy. 1 such planet per 100 billion or so star systems may seem optimistic, but, appears reasonable. Of course that implies there may be 100 billion or so intelligent civilizations scattered throughout the universe.

Chronos

Like the drake equation, this is merely an unsubstantiated guess. The unlikely sequence of events would be the evolutionary chain leading to homo sapiens. Blind luck was the series of catastrophic events that enabled the process without causing extinction of a link in our ancestral chain. As I recall the Toba supervolcano nearly wiped out the human race a mere 75,000 years ago.

ImaLooser

I think you are completely right. I don't see how there is anything terrifically special about our Solar System. I don't see why there can't be jillions of earth-like planets.

I also don't see why there can't be forms of life very different from ours that have nothing to do with atoms. In fact since atoms are quite rare in this Universe I would think non-atomic life would be much more common.

DaveC426913

I am astonished to discover my ignorance. I have never heard of this Toba eruption or the bottleneck in the human race.

ImaLooser

I have been to Lake Toba. Very big.

Chronos

I have way too much free time since I retired.