Milky Way Star Births May Have Influenced Life

eldavojohn writes "Space.com has an interesting article that speculates that the period when our galaxy was giving birth to stars resulted in huge fluctuations and impact on earth. From the article, 'Some 2.4 billion years ago when the Milky Way started upping its star production, cosmic rays — high-speed atomic particles — started pouring onto our planet, causing instability within the living. Populations of bacteria and algae repeatedly soared and crashed in the oceans.' Causes one to wonder what the probability for life arising on a planet is given that our own seemed to be in a very unique situation on many different counts."

Probability theory

[PhotoJim]

Even if the chances were one in a billion or one in a trillion, the sheer number of stars and planetary systems in the galaxy (and indeed the universe) make it entirely unlikely that there *isn't* life out there somewhere. Humans seem to want to be perceived as being special on both an individual and a collective level. We don't really want to accept being common or normal or average. There is life out there somewhere. We'll never find it because of the distances involved, but I am convinced it's there. I think we beat huge odds to get here, but there are still huge numbers of other civilizations that beat similar odds.

Insert God Jokes Here

[TubeSteak]

Humans seem to want to be perceived as being special on both an individual and a collective level. We don't really want to accept being common or normal or average.

As God once said to his pangalactic dominion: All Your Base Are Belong To Us.

Re:

[drinkypoo]

As God once said to his pangalactic dominion: All Your Base Are Belong To Us.

This was right after he stole the handle, preventing the train from stopping (though it might slow down.)

Re:

[Shakrai]

Humans seem to want to be perceived as being special on both an individual and a collective level

I don't see how Humans would cease to be special on a individual or collective level when we discover life outside of our own solar system.

There is life out there somewhere. We'll never find it because of the distances involved, but I am convinced it's there. I think we beat huge odds to get here, but there are still huge numbers of other civilizations that beat similar odds.

I'd like to think that sooner

Re:

[aliendisaster]

I don't see how Humans would cease to be special on a individual or collective level when we discover life outside of our own solar system.

Most people will agree that humans are still special even if we find an advanced civilization outside our solar system. However, the majority of Christians (and other religions) believe we were placed here by a supreme being in his likeness and the whole universe is ours and ours alone. The idea of another race of beings on another planet would basically shatter the

Re:Probability theory

[Shakrai]

Most people will agree that humans are still special even if we find an advanced civilization outside our solar system. However, the majority of Christians (and other religions) believe we were placed here by a supreme being in his likeness and the whole universe is ours and ours alone. The idea of another race of beings on another planet would basically shatter the definition of life created by the church.

I think that most Christians (and other religions) could accept the concept of life beyond Earth without having their faith completely shattered. Hell, the Catholic Church is more or less accepting of evolution as a concept (though "guided" by God as they say). The Fundies might have a problem with it, but then, what don't they have a problem with?

Re:

[drinkypoo]

the majority of Christians (and other religions) believe we were placed here by a supreme being in his likeness and the whole universe is ours and ours alone

I think that most Christians (and other religions) could accept the concept of life beyond Earth without having their faith completely shattered.

It's important to note that it doesn't say what God did on days eight through infinity. There's no reason he couldn't have made other planets, other peoples.

By the same token, the bible never even add

According to its kind

[tepples]

By the same token, the bible never even addresses the issue of evolution

The account of creation in Genesis leaves room for at least microevolution [wikipedia.org]: God created each plant and animal "after its kind", where "kind" translates a Hebrew word corresponding roughly to the taxonomic family [wikipedia.org].

Re:

[Scrameustache]

By the same token, the bible never even addresses the issue of evolution, so people who are using it as a basis for believing or not believing in evolution are a bunch of chumps.

What has been will be again,
what has been done will be done again;
there is nothing new under the sun.

Is there anything of which one can say,
"Look! This is something new"?
It was here already, long ago;
it was here before our time.

...just saying.

Re:

[julesh]

As I am fond of saying to various wingnuts, a god who can't set up evolution to achieve a desired end is not omnipotent.

An interesting argument a friend presented: the entire "Intelligent Design" movement is probably heretical, in some fashion. Because:

1. As you say, an omnipotent god could set up the universe so that evolution achieves his ends.
2. Intelligent Design argues that evolution does not work, that certain things have evolved that would not evolve without some kind of guiding assistance, becau

Evolution and G-d

[arete]

The worst of the fundies take a very old document from a time when metaphor was often used and interpret it both very literally AND very selectively. (eg gays are bad but wearing blended clothes is ok and they don't keep Kosher*. That's the same old testament! ) And they choose to very literally interpret the English translation, no matter what the original probably said. In a country which is really not that literate I can see how this happens - religion is about your pastor, not about the book.

But not

Re:

[Scrameustache]

G-d

Why do you spell god that way?

Re:

[Trogre]

Perhaps they're Jewish. Their religion doesn't allow them to write a name for God on anything that may be destroyed (paper, pottery or a computer screen).

Re:

[arete]

I'm not actually Jewish, I just have Jewish friends. But that's the genesis for my spelling it that way, because it feels to me like respecting them and because it might start this discussion.

(To my knowledge it's probably actually fine for a non-Jew to write it out... my understanding is that conversion to Judaism is discouraged because according to Judaism if you're a non-Jew you basically just have to be a good person to go to heaven but if you're a Jew you need to also follow like 3000 laws. So conver

Re:

[arete]

Well, you seem to have been intent on interpreting everything I said backwards*. I agree with you that some of the words you put in my mouth are silly. You seem to be some kind of fundamentalist athiest - I can't talk about philosophy without you seeing everything in a black and white that makes me your enemy.

The very first paragraph was bible-specific, the rest was not. Honestly my whole post was about telling religious people evolution wasn't bad, not about telling evolutionists they need to join a rel

Re:

[FooAtWFU]

I think that most Christians (and other religions) could accept the concept of life beyond Earth without having their faith completely shattered. Hell, the Catholic Church is more or less accepting of evolution as a concept (though "guided" by God as they say).

Also, if you believe what you read in your Orson Scott Card novels (such as Speaker for the Dead), they'd also be among the first to go out and try to convert it. :P

Re:

[teslar]

Most people will agree that humans are still special even if we find an advanced civilization outside our solar system.

True. Especially to that advanced civilisation. Human meat will be a very special délicatesse indeed. :)

Re:

[kalirion]

I don't see how Humans would cease to be special on a individual or collective level when we discover life outside of our own solar system.

Why, the same way that the sanctity of marriage will be destroyed once gays can tie the knot. Don't you watch FOXNews?

Re:

[geoffspear]

And what if the chance is 1 in (insert number of stars in the Universe here) or less?

I just love when people try to use "probability theory" to argue for something when they can't possibly know the probabilities involved.

Re:

[joto]

And what if the chance is 1? So far, we have only briefly landed a few probes on the moon and mars. Certainly not enough to conclusively say that there is not life there.

Basically, we lack statisical data. When both "we are the only place in the universe with life", and "life is everywhere in the universe" is a reasonable position to have in a debate about the issue, the whole issue stops being science untill we gather more data. Three is more or less accepted as the minimum statistical significant number

Re:

[SQLGuru]

And just because the probability is 1 in X, doesn't mean that an event can't occur more than 1 times.

Proof:
The chance of a die landing on 3 for a given roll is 1 in 6. If I roll a die six times, how many times will it land on 3? On AVERAGE, 1, but for a specific set of 6 rolls, it could be as high as 6.

So, if the odds that life would develop around a star (not counting bodies orbiting that star -- I am reluctant to use the term planet because Pluto could house life and is not longer considered [by others]

Re:

[drinkypoo]

At the same time, there's no certainty that a set of twenty planets, each with a one in twenty chance of having life, will even contain one planet that has life. Most everything cuts at least two ways...

Re:

[ceoyoyo]

For the probability to be 1 in NUMBER_OF_STARS and for us to exist to wonder about it, you'd have to resort to the anthropic principle. Generally you try not to do that, so a simpler explanation is that we're not really all that unusual.

I really don't see why this hypothesis (star birth triggering life) would make it any less likely that life is common. It's not like star birth wasn't widespread throughout the galaxy, or that radiation from stars being born is restricted to tight beams that only shone on

Re:

[geoffspear]

Of course this hypothesis doesn't make it any less likely that life is common. It doesn't make it any more likely, either. However, until you have any actual evidence either way, it's unscientific for someone to say that the odds of life/intelligent life arising on a given planet are high enough that there must necessarily be such life on other planets. I generally try not to make up "facts" with no supporting evidence whatsoever, and then base "certain" belief in those facts. If that leads to the anthro

Re:

[ceoyoyo]

Of course you can't say for certain that the probability is not a particular value, just as you can't say for certain that it is a particular value. It's still an interesting discussion to have, though. So you can say "not enough information" and go away, or you can make some more or less reasonable assumptions and see where that leads you.

I pointed out that the probability is unlikely to be 1 in NUMBER_OF_STARS because that would make our own existence very unlikely. Our own existence is one of the rele

Re:

[bill_mcgonigle]

We'll never find it because of the distances involved, but I am convinced it's there.

This is the trickiest part - we should see abundant life just within the Milky Way, and given the distances involved most civilizations should spread out to all of its stars within a billion years or so. So, either we're first, or they're not saying "Hi" (who could blame them since we haven't either).

Re:

[ceoyoyo]

Or interstellar travel and colonization is harder than we think.

Re:

[bill_mcgonigle]

Or interstellar travel and colonization is harder than we think.

Could be - or we might have an unusually robust biology that can possibly travel to another solar system with just a mile-long ship's worth of supplies. That seems like we're calling ourselves special again, though, so the Zoo still makes some sense.

Re:

[ceoyoyo]

We have yet to travel to another habitable solar system....

Perhaps it takes an average of four billion years for a star of our generation to develop intelligent life (supported by observation), and then a few hundred thousand years for life to develop interstellar space travel (we're pretty close to that and we still don't have it), then maybe after you DO travel for centuries or millennia to the nearest habitable star maybe you want to stay put for another fifty thousand years and concentrate on filling up

Re:

[bill_mcgonigle]

Then you'd get a galaxy that won't be full for another billion years at least, assuming that everyone else is pretty much just like us.

Agreed. Isn't Earth a third-generation Milky Way star though? So there have been at least two go-arounds of this cycle so far. Unless we _need_ a third generation star with its heaviest elements for life to succeed, or perhaps for there to be enough nuclear fissible material to get technology moving. Clearly far more questions than answers with a sample size of 1.

Re:

[ceoyoyo]

It seems reasonable that advanced life is going to need a third generation star. Even if life doesn't need the heavy elements, technology probably does, and that puts a pretty severe limitation on how long life has had to colonize the universe.

Maybe when the aliens arrive (or better yet we go out and meet them) we'll be able to ask. In the meantime nothing to do but speculate.

Re:

[mgblst]

Or interstellar travel and colonization is harder than we think.
 
Or interstellar travel and colonization is as hard as we think, but harder than we would like to dream of.

Re:

[ceoyoyo]

Shush. I insist on thinking that we're the first and cleverest (though not by much) and that practical faster than light travel will be discovered in my lifetime, which will then be greatly extended so I can live as long as I want and enjoy exploring deep space.

Re:

[CODiNE]

That's called faith my friend. Remember that the burden of proof is on the one who claims pink unicorns, not the one who doubts them.

Re:

[kalirion]

There is life out there somewhere. We'll never find it because of the distances involved, but I am convinced it's there. I think we beat huge odds to get here, but there are still huge numbers of other civilizations that beat similar odds.

And with a huge enough number of civilizations, at least a few of them will beat the odds and discover ways to make the distances between us meaningless.

Re:Probability theory -- The Drake Equation

[DrJimbo]

The Drake Equation [wikipedia.org] Gives a probabilistic estimate of the number of civilization in the galaxy that we could expect to communicate with. The last factor in the equation, denoted by L, is the expected lifetime of a civilization that we could communicate with.

Some people speculate that the reason we have not had any results from SETI so far is because this last factor is extremely small: the time between when a civilization is able to communicate galactically and the time it discovers nuclear weapons and s

Wrong probabilities, dude

[fm6]

We'll never find it because of the distances involved...

Never? Do you have any idea how long "never" is?

That's a favorite quip of mine, which I stole from a camera commercial circa 1980. But in this case you really don't know how long "never" is. The universe is big not just in space but in time. If the human race lasts long enough, there will be plenty of time to search out the galaxy. Say it takes us 10,000 years to colonize the nearest star system. (If we can survive that long without destroying ourse

A long time ago

[franksands]

2.4 billion years ago, cosmic rays travelled through space to create this first post.

Re: A long time ago

[Black Parrot]

> 2.4 billion years ago, cosmic rays travelled through space to create this first post.

Are more on their way for the dupe?

A long time ago, Joni Mitchel sang We are stardust

[Morgaine]

Woodstock was in 1969, and the idea that essentially all life is recycled through supernova explosions was already established strongly enough in popular culture for it to appear in Joni Mitchel's wonderful Woodstock [lyricsfreak.com] lyrics:


We are stardust
Billion year old carbon
We are golden


Although we know quite a bit more now than then, TFA is recycling really old news. :-)

Not too much different from other changes

[Josh Lindenmuth]

In general, any period of time where there is massive stress on a population would likely see rapid evolutionary changes. Whether it's volcanos, or asteroids hitting the planets, an ice age, or interstellar radiation, the effect is basically the same - an initial decimation of existing populations with amazing biodiversification thereafter.

Re:Not too much different from other changes

[Konster]

So....what's going to happen after Bush is out of office?

100 Billion

[Gotung]

To borrow a theme from Carl Sagan.
Estimations are that there are 100 Billion stars in our galaxy. Thats:

100,000,000,000 -- Let's say 1 in ten of those are in a good region of the galaxy (not a bunch of cataclysmic crap going on)
Thats: 10,000,000,000 -- Let's say 1 in ten of those have planets.
Thats: 1,000,000,000 -- Let's say 1 in ten of those have a planet in the stars habitable zone
Thats: 100,000,000 -- Lets say 1 in ten of those have adequate amounts of water
Thats: 10,000,000 -- Lets say on 1 in ten of those simple life arises.
Thats: 1,000,000 -- Lets say on 1 in ten of those complex life develops.
Thats: 100,000 -- Lets say on 1 in ten of those intelligent life develops.
Thats: 10,000 -- Lets say on 1 in ten of those advanced civilization pops up.
Thats: 1000

10,000,000 planets that foster life, and 1000 advanced civilizations.

I think the chances are pretty good. :P

Fermi Paradox

[benhocking]

Let's say 1 in 10 of those decide to start colonizing other star systems with generational ships. Where are they? [wikipedia.org]

Re:

[Shakrai]

They missed WW2 [wikipedia.org] and are waiting for WW3 before they decide to invade and conquer us ;) They'll be bi-pedal, ginger addicts and won't understand our desire for sex.

You missed World War III

[tepples]

They missed WW2 and are waiting for WW3 before they decide to invade and conquer us

World War III was the Cold War, which started in Korea, spread to Vietnam, and ended with the breakup of the Soviet Union. We're in World War IV [wikipedia.org] now, the war on militant Islam.

Re:

[PFI_Optix]

100 advanced civilizations in the galaxy, evenly distributed and travelling at sub-light speeds, would have very little chance of ever encountering one another. That's roughly 2 billion stars and 78,500,000 square light years of the galaxy (and that's only two-dimensional). If my math is right, 100 civilizations would be separated from each other by an average of 10,000 light years (plus some on the Z axis).

For us to even detect an undirected signal--as in, not particularly meant for us--at 10,000 lightyear

Until you consider exponential growth

[benhocking]

Read the link in my GP post about the Fermi Paradox. It explains that once a civilization develops that starts colonizing other worlds, it will tend to generate two (or more) other inhabited planets. This will then lead to 4, 8, 16, until after 40 such doublings you have over a trillion inhabited planets (i.e., about 10 for every star in the Milky Way). Obviously there will be limiting factors (such as the number of inhabitable planets), but you'd think that eventually (i.e., in less than a few million year

Re:

[ceoyoyo]

There's a serious limit on that rate that you've ignored. Only the surface of the colonization sphere will be likely to send out new ships so you won't have exponential growth.

Re:

[khallow]

But how fast does that surface propagate? If it's 0.1 C then that's roughly a million years. 0.01C would be 10 million years, and 0.001 C would be 100 million years. Stars move on the order of that speed relative to the local neighborhood and it should be possible using gravity assists alone for a vehicle to achieve 0.001 C speeds. In comparison, the Voyager spacecraft (1 and 2), using mostly gravity assists, are travelling around 10^-4 C (which would take around a billion years to cover the galaxy).

Re:

[ceoyoyo]

If you're talking about a colonization surface, it spreads much slower than the ship speed. There's colonization to do, which takes a long time. Suppose you can travel at 0.01c. It takes you on average 700 years to get to the nearest star (average star spacing in the galaxy). How long does it take to build up a colony capable of, and wishing to, launch a colony ship? It's on it's own, with a necessarily VERY small seed population. The colony is only going to WANT to keep colonizing when they become a

Re:

[khallow]

The thing is, you can do a little better than 0.0007 c just by sporadically launching to a nearby system whenever one comes close. The relative motion of stars in the galaxy is surprisingly fast. And what's to keep ships from traveling further than just the nearest star system? Especially if they have a good idea what's out there from probes? 100 light years would take 10,000 years to cross, for example. And suddenly you're talking 0.005 c for the colonization front propagation speed. That's only 20 million

Re:

[ceoyoyo]

I'm making a lot of assumptions, but I think they're a reasonable answer to the Fermi Paradox.

You'd tend to try and reach the nearest habitable system to establish a colony. You COULD go further, but you probably wouldn't, if your goal was colonization. Even reaching the nearest habitable star going so slowly would probably be a big stretch. How many resources does it take to build a starship that can reach a significant fraction of light speed AND maintain generations of its occupants for centuries or m

Re:

[julesh]

How long does it take to build up a colony capable of, and wishing to, launch a colony ship? It's on it's own, with a necessarily VERY small seed population. The colony is only going to WANT to keep colonizing when they become a mature, stable population -- when they're finished with the thorough colonization of their own planet. Maybe 10,000 years?

I think that's a substantial overestimate. It took a lot less than 500 years for European colonists to the Americas and Australia to reach a mature level of civ

Re:

[ceoyoyo]

Your colony won't experience exponential growth though. And I'm not sure how you can compare colonists to the Americas and Australia with interstellar travelers since we still haven't gotten to the point where we're overly interested in poking around in space, never mind outfitting a generation ship.

You won't have a bunch of colonists who swarm over a planet, develop it, then decide to go on to the next one. We're talking about multi-generations and a LONG time. If they're anything like us their coloniza

Re:

[Scrameustache]

eventually (i.e., in less than a few million years), they'd find Earth - we wouldn't need to find them.

And we're to assume that once they found us, they'd say hi?

Sure, in the same way we said "hi"...

[benhocking]

Sure, in the same way we said "hi" to the inhabitants that we found when we decided to colonize America... :P

(Actually, I can't really say I have any expectations one way or the other.)

Re:

[Scrameustache]

I can't really say I have any expectations one way or the other.

Me neither, I just think it's silly to assume no one's out there because they aren't waving at us.
I think the hypothetical Aliens might have watched monty python's "How not to be seen" and learned a lot from it.

Re:

[Woldry]

You mean they'll give us space syphilis?

Re:

[PFI_Optix]

As has already been said, it would be an exercise in futility for planets inside the sphere of colonization to spread; growth would not be exponential as you predict.

What's more, it stands to reason that civilizations will not grow indefinitely. There are any number of things that could halt the spread of a civilization. Then of course there's the possibility of war: for all we know there is a massive war raging on the other side of the galaxy right now that has halted expansion for our space-faring neighbo

Millions of years

[benhocking]

It could take millions of years from the beginning of colonization before a civilization stumbled across us. There may be ships on the way here now; why should we assume that there has been intelligent life in the galaxy for millions of years when our own planet has supported for so short a time?

Actually, that is what I believe I said initially. It could take millions of years. However, what are the odds that in the X billion years the Milky Way has been around, all of the (highly) advanced civilization

Re:

[joto]

10,000 lightyears? Assuming each civilization spreads out in every direction, then they only need, say 50,000 years to meet at the middle, if they spread out at 10% of the speed of light. I think it's safe to say they will meet.

You don't need to start worrying about being able to "detect signals" when they land in your front yard, or you in theirs!

Re:

[bill_mcgonigle]

Wikipedia doesn't list this possibility: they're waiting for us to mature enough to not be afraid to say, "hello". And sticking your head out the window one every decade or so isn't the same as putting out the Welcome mat.

Re:

[Gulthek]

Got news for ya. We are as "mature" as we're going to get. That's it. We're human and we are who we are.

It's not like the world is gradually approaching a state of more perfect being; we're just retelling the same stories again and again in different settings and different people.

If you have an example of how any human civilization is or was ever progressing into maturity I'd love to read about it.

Re:

[bill_mcgonigle]

If you have an example of how any human civilization is or was ever progressing into maturity I'd love to read about it.

Few people still believe that rats are created from piles of rags in barns. They used to a few hundred years ago.

Science continues to have a major influence on peoples' beliefs. It's not a stretch to say those humans educated in the ways of science have a significantly differently belief structure than those who aren't.

The percentages of people educated in science are increasing in most

Re:

[joto]

Why wouldn't they give us anal probes?

When we contact wild animals, we usually end up doing one of the following

1. Exterminating them
2. Hunting them
3. Domesticating them
4. Marking them with metal rings and/or small radio transmitters
5. Just watching/photographing them

If anything, we should expect our encounter with a more advanced alien species to be taking one of the above-mentioned forms. Most likely they have encountered thousands of other civilizations, whereas it's our first. Our enthusiasm/fear/whatever

Re:

[bill_mcgonigle]

I expect there to be little chance they are interested in just talking with us, respecting us, exchanging technology, etc. Certainly we don't do that ourselves when we encounter new species on earth.

Within just the next thirty years we're going to have the technology to do a completely non-invasive high-resolution full-body scan and sequence/simulation of DNA for any creature on earth, making the 'chop up the critters' approach unnecessary.

Even if you argue that technology is still a hundred years off, we'r

Re:

[joto]

Within just the next thirty years we're going to have the technology to do a completely non-invasive high-resolution full-body scan and sequence/simulation of DNA for any creature on earth, making the 'chop up the critters' approach unnecessary.

So how are you going to find out the migratory patterns of deep-sea squids unless you probe them? You certainly can't find out by doing a full-body scan. And I have great trouble to imagine what other ways can exist to do it in the future. Most likely, we will impr

Re:

[bill_mcgonigle]

So how are you going to find out the migratory patterns of deep-sea squids unless you probe them?

If you want to study migration patterns you have to leave them in-situ. Also, one has trouble asking a squid about its migration patterns.

Organism analysis is a far way off.

The sequencing part is effectively done. We can do a complete sequence for under $10K now. The simulation part is still too demanding of computer time but computers will be a million times faster than they are today in 30 years. Simulati

Re:

[ceoyoyo]

So which part of the world is as mature as it's going to get? Much of the world's population still hasn't really experienced the industrial revolution. If you were an alien making (peaceful) first contact would you rather talk to a planet full of people who are looking outward to realize their potential or one that is busy trying to feed itself?

Re:

[Scrameustache]

Got news for ya. We are as "mature" as we're going to get. That's it. We're human and we are who we are.
It's not like the world is gradually approaching a state of more perfect being; we're just retelling the same stories again and again in different settings and different people. If you have an example of how any human civilization is or was ever progressing into maturity I'd love to read about it.

In the beginning, a nation warring with another nation would raze the land, rape the women to death, and bring home a few slaves.
Then Zarathustra came along, and with him his civilisation learned that it could leave the conquered nations alive and well, even build roads up to them and tax them.

A few thousand years later, the descended civilisations no longer even hold slaves.

Some societies now take care of their sick and wounded. Just a hundred years ago people were left to fend for themselves, or to rely o

No other galaxies required

[benhocking]

According to the GGP post (to which I had responded) there should be 1,000 advanced civilizations in our galaxy. If only 1 of those had developed a desire and the ability to colonize nearby star systems (e.g., alpha centauri for us) a million years or so ago and then kept spreading out from there, they should be here by now. Again, see the link on the Fermi Paradox that I mentioned in the GP post.

I'm not claiming there's no life elsewhere, or even intelligent life, but the Fermi Paradox does put suggest s

Meeting in the context of loyal subjects

[benhocking]

However, if even one alien civilization exists that has the ability and desire to colonize nearby star systems, than one would expect that after a hundred million years or so (at modest speeds), they will have colonized every habitable star system, including ours (assuming that our star system is habitable for them, of course). The fact that we haven't been colonized by aliens tells us something about what's not out there. Perhaps there is an organized community of ET's that have a prime directive type of r

But you're ignoring exponential growth

[benhocking]

See my previous discussion about that. Simply put, once an alien race has the ability to colonize other worlds, those worlds will also colonize other worlds, and you end up with exponential growth. Even with fairly pessimistic (or optimistic - depending on whether you want to be colonized by alien races, I guess) assumptions, they'd find Earth within 100 million years after they began their colonization efforts.

Re:100 Billion

[CmdrGravy]

The trouble is that the Universe is maybe 17 Billion years old and although we have no figures on the length of time you can expect an intelligent species to survive for it's probably a small fraction of 17 Billion. It's likely that intelligent species will not have the capability for space travel or inter-stellar communication for their entire existence which cuts the percentage down further.

The rate at which a species can expand through the galaxy is likely to be quite an awful lot slower than the maximum speed of whatever craft they have developed so for us to ever be aware of anyone else in the Universe we'd have to have arrived in a similar time frame and be very close to them spacially. It's possible there may be a fantastic co-incidence and a probe or exploration vehicle come across us but really the universe is so huge both us and them would need huge blocks of inhabited space which would at some point need to intersect.

Re:

[Ginger Unicorn]

But only three of those probabilities have to be 1 in 100 for you to end with 1 advanced civilisation. From whose ass does he pull the 1 in 10 probabilities for everything?

Dont get me wrong, i'm entirely open to evidence either way and would be excited by a convincing reason to think there are other intelligent lifeforms, and for all i know such an explanation exists. This isnt one of them though.

If it were backed up with some evidence to suggest each of those probabilities, then it would be interesti

Re:

[Princeofcups]

> If it were backed up with some evidence to suggest
> each of those probabilities, then it would be
> interesting.

The numbers are used to show that it is *reasonable* to think that there is intelligent life besides us in the galaxy. It's not meant to be any kind of proof.

jfs

Re:

[Ginger Unicorn]

of course if 1 in 10 is a really conservative estimate in each case, then it would make some sense, but there is nothing to suggest these are. they just seem to be arbitrary. how does he know its isnt 1 in 100 for three of these things? (perhaps he has reasons, but they arent self-evident, and need presenting to make this mean anything at all)

Re:

[fonetik]

"But only three of those probabilities have to be 1 in 100 for you to end with 1 advanced civilisation. From whose ass does he pull the 1 in 10 probabilities for everything?"

Yes, but if you consider that there are roughly 140 billion visible galaxies in the universe, and typical galaxies contain ten million to one trillion stars, you can easily overcome even the 1/100 odds.

Not that it really matters, with the distances involved we'll be swallowed by the sun before most of them could hear us say "Hello".

Re:

[Ginger Unicorn]

yeah, i dont disagree the amount of stars in the universe make it very unlikely we are the only advanced life, i was just pointing out that carl sagan's example doesn't mean anything if it's just plugged full of arbitrary numbers.

Re:

[Ginger Unicorn]

i mean who's ass did carl sagan pull them from ;)

Re:

[shma]

The problem is that there's no reason one of your 'one in ten' couldn't be '1 in a billion', in which case, you only have a one in a million chance of developing an advanced civilization per galaxy. For starters, there's no reason to believe that 10% of planets in stars habitable zones will have an adequate amount of water. In fact, we don't even know what a reasonable estimate of an adequate amount of water IS (certainly nothing more specific than "no more than what we have"). We have no way of knowing how

So, in other words...

[sean.peters]

... you just made up 10 numbers and multiplied them together. To say: "out of 10,000,000 candidates, let's say 1 in 10 develops simple life" or "out of 1,000,000 planets with simple life, 1 in 10 develops complex life" is to beg the question. We have no evidence whatsover of how likely it is that planets with the "right" conditions develop life. In fact, we have a sample size of exactly one. I can say "only 1 out of every 100 trillion planets with the "right" conditions (whatever they are) will develop simp

I knew it!

[el_womble]

Astrologists were right all along!

Non-unique

[AJWM]

'Some 2.4 billion years ago when the Milky Way started upping its star production, cosmic rays -- high-speed atomic particles -- started pouring onto our planet [...]' Causes one to wonder what the probability for life arising on a planet is given that our own seemed to be in a very unique situation on many different counts."

While Earth does seem to be unique amongst the hundred or so planets that we're aware of, the above circumstance is not one of the reasons. Those cosmic rays would have been pouring onto every planet in the galaxy, or at least this corner of it. If that cosmic ray flux did have an effect on jump starting the primitive life that was around at the time, it may have done so on tens of thousands of planets.

It may also have wiped out the local equivalent of the dinosaurs - or even intelligent species - on some other planets.

Distance?

[aproposofwhat]

It's a nice theory and all that, and yes, from the analogy of a cloud chamber I can see how cosmic rays can seed clouds, but...

All these stars were a long, long way away.

The amount of radiation (any sort) falling on a body decreases in an inverse square manner, so I doubt that even in the maddest periods of star formation there would have been more than a tiny effect on our atmosphere, especially compared with the effects of a cosmic ray emmitter only 8 light-minutes away that may also have been fluctuati

Re:

[fred fleenblat]

Not only that, but life on earth in that time frame was all in the ocean, which cosmic rays don't penetrate very far.

Rare Earth ? Think again...

[wikinerd]

what the probability for life arising on a planet is given that our own seemed to be in a very unique situation on many different counts

The probability of life appearing on a planet may be high, and our planet's situation may not be as unique as you think. I study Planetary Science at the Open University (UK) and the fact that they decided to couple lessons about the search for life in the, primarily geology-themed, planetology course has to say a lot about what scientists think of the Rare Earth Hypothesis [wikipedia.org].

It is, however, natural that some people think that Earth is unique, as it is the only living planet we know of. Sure, your first lemonade was unique, your first PC was unique, and your first GNU/Linux distro was also unique.

Re:

[Woldry]

So you're saying that all these unique things are the same? ;-)

Don't have the data (yet) on likelihood of life

[quixote9]

Hard radiation to generate mutations can't be a limiting factor because it's not in short supply in the universe. Without Earth's magnetic blanket, we'd be getting so much, even without major galactic star formation, the trick would be staying alive rather than generating enough mutations to do anything interesting.

The probability of life arising is much more difficult to pin down. Right now, we have one data point: Earth. Kind of hard to extrapolate any sort of line from that. Invented probabilities,

The scientist not the popular science mag

[mattr]

Honestly, independent bloggers and popular science sites may be a great way to quickly hear news, but Slashdot ought to be more focused on the technical details and the scientists figuring them out. That used to be what Slashdot was anyway.

Okay, here is the link [www.dsri.dk] to
Henrik Svensmark, Danish Space Research Institute and his papes on
Cosmic rays and Earth's Cloud Cover. He is quoted in the story.

I am providing this in self defense since I prefer to discuss intelligently with people who do not need that popular s

Re:

[mattr]

I see, thank you! I will try to learn some more about supernovae and galactic evolution in the future. I see there is apparently a supernova every 50 years or so but also there is a 500 Myear cycle of mass at the center of the Milky Way reaching critical mass and producing supernovae at about 1 per year. (Our next one is in 300My). Which is perhaps why the paper only goes back 200My... before that being chaos?

Link to abstract

[mattr]

This is my second post to this thread. Here is a link to the paper mentioned in the article. It is not on Svesnmark's site I think. Also it is not the latest issue of Astronomische Nachrichten (Astronomical Notes), which is Dec. 2006. Actually he wrote two articles that seem to be the focus of the Space.com article, and both articles are published in AN's Nov. 2006 issue.

It seems we get clobbered when we pass through spiral arms, last time maybe 31 million years ago. So the idea of a static neighborhood tha

The same time span

[246o1]

Assuming, since there is no evidence in any other direction (we are the only current data point), that life3 on other planets would look like us, there are the issues of timing, on a cosmic scale, and growth across stars. I am convinced that, given just a thousand years or more from now, human beings will start their first interstellar colonies, barring global disasters. With exponential growth, it would probably take a few dozen million years for us to take up a huge part of the galaxy, and our radio wav

Re:

[joto]

the complete lack of evidence that other races exist means that no other intelligent races arose significantly before us (in cosmic time), or else any that did wiped themselves out as far as we can tell, either through no longer using electromagnetic waves of any kind (making their stray radiation invisible to us), killing themselves off, or something else.

I wouldn't call stop using electromagnetic waves as killing yourself off. Besides, even on earth, our radio transmissions becomes more and more difficu

Re:

[joto]

If we got to a point where we couldn't detect our own radio transmitions, then what would be the point of broadcasting them?

Well, what I meant was that it's likely that our present technology wouldn't able to detect a transmission sent with technology from a few thousand years in the future.

Of course, the interpretation you gave isn't impossible either. You have to know what to listen for, because the search space is too vast to simply find it by searching, signals too similar to random noise to find i

Re:

[246o1]

My point was that if any race a million or two years more advanced than us exists, there would be a million or two light-year bubble of space which could detect their radio emissions. This only applies, however, if these theoretical aliens have to deal with our current understanding of physics for communications. Our current potential to be noticed is very small, but our potential to notice people is not limited by our short history, only by our current technology and the history of any aliens out there.

Re:

[XenoRyet]

I'll throw a few numbers out there, though there is too little exact data to do a rigorous statistical calculation.

First, the average galaxy has 10 million to 1 trillion stars in it. Second, there are on the order of 100 trillion galaxies in the observable universe. That leads to, roughly, 10^18 to 10^23 stars in the observable universe. Add to that that the observable universe is likely only have as big as the probable lower bound for the size of the total universe. There just simply isn't any such thin

Re:

[drinkypoo]

There just simply isn't any such thing as a unique situation in that kind of context.

Show me evidence that there is life on other planets, and I will agree. Until then I will maintain that we don't know WTF is out there.

Right now our sample set says that life exists in one out of one solar system we have examined.

Statistics tells us that is not enough of a base to draw conclusions from.

I will avoid doing so.

Re:

[drinkypoo]

The point is that we have no idea how likely it actually is. For all we know, Earth is home to something special that makes it the only place life can exist. Maybe the mathematical constants we take for granted are different in differently-shaped galaxies or something. The only thing I'm [fairly] sure of is that no one alive today will ever know because we're not likely to get FTL travel any time soon.