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."

Comments

A unique situation?

[Hubbell]

Last I remembered there are hundreds of billions of stars in the universe, and thousands if not millions of galaxies out there. The situation earth was in is hardly unique in such a large set of data (can't think of a good way to put it, just woke up!). We've been hearing everytime they come up with a new reason for life forming 'omg guys, we are unique!' Sorry, but we are not unique in the fact that life is on the planet, it's a statistical(sp?) impossibility. We may be unique in our forms of life, aerobic respiration, and many other parts of our ecological systems may be utterly incompatible with alien life forms, more than likely they are incompatible, but by no means is the very fact that life exists here unique.

Re: A unique situation?

[Anonymous Coward]

Sorry, but we are not unique in the fact that life is on the planet, it's a statistical(sp?) impossibility.

Care to do the math for us here? Be sure to explain where you got all your "statistical" data. I'd like to see this P(x, y, z, ...) = 1 formula of yours.

Re: A unique situation?

[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 thing as a unique situation in that kind of context. That was the GP's point.

Re: A unique situation?

[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: A unique situation?

[WageDomain]

Lack of proof is not necessarily a proof of a lack. In other words, no one is saying they can prove it yet, but rather that it's so likely that it is most definitely true.

Re: A unique situation?

[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.

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.

Re:Probability theory

[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 or later we will find it.

Re:Probability theory

[Anonymous Coward]

I agree with you. Calling some physical process in the universe unique is sort of silly. There are probably millions of nebulae that humans would name "The Horsehead Nebula," and there are probably thousands of nebulae that humans would describe as "Natalie Portman Covered in Hot Grits Nebula." Assuming that the Milky Way Galaxy is unique in its radiation patterns 2 billion years ago is beyond pretentious.

Re:Probability theory

[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 definition of life created by the church.

Re:Probability theory

[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: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:Probability theory

[GrayCalx]

I do agree with you that simply because of the sheer number of possibilities where life could be existing that intelligence has arisen or will arise on some other planet at some point. Keep in mind though the universe is, what are they saying now, 13.7 billion years old. And Homo Sapiens have been around for... well lets say 200,000 years though its probably longer. Though you could argue intelligence wasn't seen until much later (or not even yet, nyuck nyuck). You're talking mere fractions of the entire lifespan of the universe. We'll die out at some point and the universe will continue on for much much longer, making our entire existence that much smaller of a fraction. Then as you point out too, add the whole distance thing to that small timeframe (of any species) problem and I find it hard to believe that any species will exist, evolve, master interstellar travel and just happen to coexist at the same time as another species (with any substantial intelligence) AND be able to actually locate them in the sea of nothingness.

Its great to dream about and makes fantastic sci-fi, but we'll be lucky if we find some relic of an ancient civilization... and thats probably the best we can hope for.

Re:Probability theory

[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:Probability theory

[Lord Lemur]

Well there are 2 issues with that.. 1. The F.R.W. (Fundmentalist Religious Wackos) will either say that god put them their to test their faith, or that on closer reading the Religious Text of their preferance actully mentions in passing something about other living things being made for mans benifit (Space Slavery here we come!), or it's just another struggle for the jewish people, (ie. Christians, Jews and Muslims) to prove they are the chosen people of god by being dumped on. Some how I think the Budhist and Hindu people would be ok with it in a metaphysical sence. 2. It Doesn't mater what the FRW would think about it because if we were discovered by other intellegent life we would die really fast. There is no evidence to support that a grouping of an intellegent species that is technologically and militarily superior from another grouping of an intellegent species, wouldn't subjegate or annialate them in all due haste. There is plenty of evidence to support it, however. IMHO I beleive they are out there, both intelllegent and not. I just hope that we either get the jump on them, or only ever observe them indirectly. -Lemur

Re:Probability theory

[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:Probability theory

[alexhard]

Humans seem to want to be perceived as being special

I think religion has played a big role in that, and it is probably one of our big faults..

In any case, Tyler Durden summed it up pretty well:

"Listen up magots, you are not special, you are not a beautiful or a unique snowflake, you are the same decaying organic matter as everything else."

Re:Probability theory

[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. Untill we have done real surveys at at least two other solar systems "similar" to our own, we have no reason beyond faith or wishful thinking to believe on thing or another.

Re:Probability theory

[Tjeerd]

It is even more interesting if you think about *when* these possible other civilizations have evolved. If they do already exist out there and they have the technology, we might expect them to give us a visit somewhere in the future (or perhaps they already did in the past)?

Re:Probability theory

[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:Probability theory

[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 Earth.

Re:Probability theory

[ceoyoyo]

Or interstellar travel and colonization is harder than we think.

Re:Probability theory

[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] to be a planet); so if the odds are 1 in Q where Q is the number of stars in the universe, there is still the chance that more than 1 stars rolled a natural 20 on their Chance for Life roll.

Layne

Re:Probability theory

[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 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. But then, everyone who is not a fundamentalist fanatic pretty much does their best to ignore them.

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.

Re:Probability theory

[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:Probability theory

[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 anthropic principle, so be it.

However, note that I'm not stating that the probability is 1 in NUMBER_OF_STARS, I'm asserting that it's absolutely impossible, at the moment, to say with certainty that it's not, and to pretend otherwise is a fallacy.

Re:Probability theory

[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:Probability theory

[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 relevant facts that we DO know.

Re:Probability theory

[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 your own planet before you get the urge to toss more colony ships out into the void (supported somewhat by patterns of colonization of Earth). 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.

Fermi's paradox does mean that long range faster than light travel is probably not going to happen in my lifetime though. :(

Re:Probability theory

[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:Probability theory

[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:Probability theory

[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

[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:Probability theory

[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:Probability theory

[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:Probability theory

[PhotoJim]

The difference here, of course, is that we have proven that pink unicorns (i.e. life in this case) already exist. The question is whether this is the only instance or not. That's completely different from asking the question where none have ever proven to exist at all.

Re:Probability theory

[noigmn]

I agree. Our view of what causes life is very limited so far. We don't know much at all.

So far we are on the way to modelling one type of lifeform, which is Earth based carbon lifeforms. We are getting better knowledge of how they evolved, we have ideas about how life on Earth started, but that is about it.

In terms of studying other planets in detail we have done a localised study of Mars from ground level and landed a lander on Titan. Beyond our solar system we know very little about other planets. We can estimate their mass and guess what elements they are made from, and guess how warm they are from their distance from the star, the rest is speculation.

Going by what we know the probability can be argued to be high because the only planet we've studied is covered in advanced lifeforms. Though the opposite can be argued by saying we see it because we exist on the planet where it worked.

In terms of religion I think it comes down to would God be enough of a prick to put it all out there and put nothing in it. To let us see all this stuff and never reach it. And every time in the past that we have answered this question with yes, it has just slowed progress for a while until we found we were wrong.

Re:Probability theory

[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, because they are too unlikely to occur by chance, and selection does not assist in their production due to local maxima issues. These things are interpreted as evidence of the work of an intelligent designer (i.e., God).
3. This can be rephrased: "Evolution is broken, so God has to intervene to fix it now and then"
4. This implies that evolution, an aspect of God's design of the universe, is imperfect. An omnipotent god could have made it perfect, so God is not omnipotent. This contradicts the standard doctrines of most faiths.

The argument isn't perfect; it fails to address the issue that God could intentionally have created a broken form of evolution. Why He would have done that is a mystery, although as we know, "God Moves In Mysterious Ways", or so they keep telling me. But it means that IDers are relying in their arguments on God doing something that seems, under intelligent examination, to be irrational at best. That's not a good place to be arguing from.

Re:Probability theory

[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:Probability theory

[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.

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?

Re: A long time ago

[franksands]

Actually, the dupes are echoes from the first message, but the time gap between them is so large that they are interpreted as different messages...

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?

1 in a billion?

[Gr8Apes]

Well, with billions upon billions upon billions of stars out there, even a 1 in a billion chance will result in billions of chances... so I'd hazard a guess that the odds are pretty good. Now, what are the odds that 2 sentient races will arise within the same time span and actually meet? Not so good - there's that speed of light problem we still have to solve.

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

Re:100 Billion

[tom17]

And taking it the other way... Hundreds of billions of galaxies.

"Space is big, really big"

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:100 Billion

[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 interesting.

Re:100 Billion

[DarkOmen1stmi]

I think from any type of scientific study the chances of life are far more then 1 in 10. Fix your numbers and I 'might' consider it.

Re:100 Billion

[Anonymous Coward]

The 1/10 assumption is pretty big. On what is that assumption based?
Change that to 1/25, and suddenly we barely exist statistically.
Change that to 1/2500, and suddenly we do not exist statistically.
But we, indeed, do exist.
To be fair, it should be understood that those are only notional numbers. The liklihood is that the numbers are higher all around.

Re:100 Billion

[Thraxen]

Fair enough... but keep in mind that that little mathmatical excercise was based on the stars in ONE galaxy (our own). Now take into account that there are an estimated 200+ BILLION galaxies in the universe. Suddenly those percentages starting going back up.

Re:100 Billion

[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:100 Billion

[Anonymous Coward]

Say at each step the odds is 1/1000. I don't think that's unreasonable. Then, your reasoning says that your reasoning has a very little chance of being from an advanced civilization.

This this sheer speculation and let's talk about emperical facts. No one has found aliens.

Re:100 Billion

[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:100 Billion

[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 likely it is that any kind of complex life forms from simple life, or intelligent life forms from complex life, simply because we've only had our own planet to study, and we're the only intelligent life on it.

And then there's the problem of coexistance. If advanced civilizations live only on average for a million years (still ~100 times longer than us, depending on your definition of 'advanced'), than the probability that two such civilizations would overlap is extremely tiny. Remember, our earth is over 4.5 billion years old, and life giving stars have been around for even longer.

Personally, I think the chances of finding other life in the galaxy are very low.

Re:100 Billion

[davido42]

and billions of chances to win win win the lottery!
http://www.bitworksmusic.com/

Re:100 Billion

[VanessaE]

He pulled those numbers out of Carl Sagan's ass, like he said!

Re:100 Billion

[Ginger Unicorn]

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

Re:100 Billion

[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:100 Billion

[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:100 Billion

[gcanyon]

Please:

Start with 100 Billion stars in our galaxy:

100,000,000,000 -- Let's say 1 in 100 of those are in a good region of the galaxy (not a bunch of cataclysmic crap going on)
Thats: 1,000,000,000 -- Let's say 1 in 100 of those have planets.
Thats: 10,000,000 -- Let's say 1 in 100 of those have a planet in the stars habitable zone
Thats: 100,000 -- Let's say 1 in 100 of those have adequate amounts of water
Thats: 1,000 -- Let's say on 1 in 100 of those simple life arises.
Thats: 10 -- Let's say on 1 in 100 of those complex life develops.
Thats: 0.1 -- Let's say on 1 in 100 of those intelligent life develops.
Thats: 0.001 -- Let's say on 1 in 100 of those advanced civilization pops up.
Thats: 0.00001

10 planets that foster life per galaxy,
and 1 in 100,000 galaxies like ours that develop a single advanced civilization.

Gee, my wild assumptions lead to a very different conclusion than your wild assumptions. I say we're damn lucky we live in a galaxy that developed an advanced civilization, rather than one of the 99,999 that didn't ;-)

For further reading on how rare we might be (and some slightly less wild assumptions):
http://en.wikipedia.org/wiki/Rare_Earth_hypothesis

I knew it!

[el_womble]

Astrologists were right all along!

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:Insert God Jokes Here

[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.)

Fermi Paradox

[benhocking]

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

Re:Fermi Paradox

[Shakrai]

They missed WW2 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.

Re:Fermi Paradox

[Thraxen]

Oh, yeah? Let's say we decide to start colonizing other galaxies. Oh wait... we can't! Traveling hundreds or thousands of light years is not an easy task. We can't even get to the next closest star in our own galaxy. Whose to say there aren't other civilizations in the same boat as us? Also, say there are indeed civilizations that can travel between galaxies. Given that there may be as many as 200 billion galaxies they may have simply not arriveed here yet.

Re:Fermi Paradox

[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 lightyears would be quite a feat. I seriously doubt that out of the 200,000,000,000 stars in the galaxy, anyone pointed a transmitter at our little planet at just the right time for us to pick up a clear signal. THAT is where the odds are truly astronomical.

Re:Fermi Paradox

[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:Fermi Paradox

[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:Fermi Paradox

[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 cultures (not the US, sadly). Those with a good education are less likely to believe that aliens will come to earth to eat us and give us anal probes if we light up a beacon for them to see.

Re:Fermi Paradox

[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:Fermi Paradox

[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 is not going to be matched by theirs, who will view us as just another threat/resource/study-object to be oblitered/taken-advantage-of/studied.

Unless they are "virgins" themselves, having met few or no other alien civilization(s), 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.

Re:Fermi Paradox

[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:Fermi Paradox

[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're still much further from interplanetary travel than organism analysis. To assume that the 'visitors' will have a comparable level of technology to us is erroneous.

Re:Fermi Paradox

[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 improve our wild-animal-probing technology to the point where we can monitor even more (heart-rate, body-chemistry, thoughts, etc...), rather than make probes old-fashioned.

Even if you argue that technology is still a hundred years off, we're still much further from interplanetary travel than organism analysis. To assume that the 'visitors' will have a comparable level of technology to us is erroneous.

We have already travelled to the moon. Travelling to mars is a political/economical problem, not a technological problem. Interplanetary travel is expensive, but not impossible. Interstellar travel is a bit harder, since we do not have the technology to build generational ships yet, but the voyager probe keeps on floating out there...

Organism analysis is a far way off. Look at modern psychology/psychiatry. Look at anything they teaches at the university if you study social science. Just like we can't predict the failure of communism from looking at DNA of humans, there's plenty of reason to assume the aliens want to give us anal probes.

Re:Fermi Paradox

[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. Simulating DNA transcription isn't going to be a problem.

Look at modern psychology/psychiatry. Look at anything they teaches at the university if you study social science. Just like we can't predict the failure of communism from looking at DNA of humans, there's plenty of reason to assume the aliens want to give us anal probes.

It's true, the study of the mind is currently beyond our means. But why would one assume that an ET's technology would have the same limitations? If you can simulate a human brain you only need to build The Matrix to simulate a society. And if the ET's want to study our behavior in situ it's going to be much much harder if we all have gigantic mechanical antennas sticking out or pants seats.

Re:Fermi Paradox

[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 on the few kind souls who dedicated their lives to taking care of others selflessly.

It's happening. Slowly... over thousands of years, but it's happening.

Re:Fermi Paradox

[PhotoJim]

We can't see half of our own galaxy (the galaxy centre gets in the way). Goodness, there are galaxies in orbit around the Milky Way that we have just discovered in the last few years. To discover another civilization, we need to exist when they do, within sight (or at least with the ability to hear each other on radio), and actually be looking at the right time. It took me five years to meet my best friend's roommate, so the fact that these civilizations exist is only the beginning.

Re:Fermi Paradox

[Anonymous Coward]

I say that they have already visted Earth, and such a long time ago they where seen as gods, not only that, but the god of islrael is a extraterrestrial (and as evidence, i point you to their holy books (old testimate in christians bible), it seems as tho god isent the only god, but says that he is the god that helped people, this would mean that god cant be almighty, but instead, is mearly advanced, very advanced really. The second peice of evidence, is mosis, and gods landing on the mountian. Why would a mountian burn? what kind of god that "loves" everything say that whoever goes on the mountian will die, even animals that couldent know better? The awnser, is that god has no control (further proof of mearly being a advanced being) over things on Earth, and that, his landing wasent from "heaven" but from space, god is a alien and landed in a spacecraft, and the landing is what caused the mountian to burn.

Also, there are drawings over in america (south, i think) from long ago that depict their gods flying what appears to be spacecraft, or some form of flying devices that use rockets, as well as pictures of those gods in what appears to be spacesuits.

For some reason tho, it seems alien contact has gone down, prehaps its because of our militaries? Or the aliens could have had wars with eachother, and we are now in space controlled by aliens that try to keep lower profiles, or, god is still looking after us, and is about to come back like it said it would, and all the other aliens are to scared to challenge this.

Re:Fermi Paradox

[Pfhreak]

If you factor together all of Gotung's "1 in tens", you end up with 1 advanced civilation per 100 million stars. Using 63 stars within 5 parsecs as the model, 100 million stars would fill a sphere with radius of 580 parsecs (1,900 lightyears). Which means the closed advanced civilation is some 2,000 lightyears away.

That's a lot of generations, especially considering that they're probably not going to send a ship on a straight-shot to us, they're going to be expanding in all directions as fast as their colonization needs require. Considering that there'd be 1,000--100,000 colony worlds along the way (low number assuming they only colonize planets with at least simple life, high number assumes they have good terraforming technology and can change all of the planets in some star's HZ to suit their needs), and they're expanding at below the speed of light (I assume from them using generational ships, and there's no hard scientific evidence that superluminal travel is possible), they've got plenty of growing room, and wouldn't be in a hurry to sink the resources into starting a new colony unless it was necessary. In other words: slow expansion rate.

The problem with the Fermi Paradox is that even if you assume optimistic conditions that would allow for thousands of advanced civilizations, there's still an awfully big haystack to search in if you're specifically looking for an alien civilization, and you're probably not going to be putting that much energy into it, since you'll probably be putting all that technology to other uses. The sheer resources required just to build a powerful enough radio transmitter to reach every star within a couple thousand lightyears (the minimum distance to the nearest neighbor giving these optimistic conditions) is staggering, not to mention that the civilization would have to be willing to sink maintenance costs into that sucker for a good 4,000 years before a responce could be expected.

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.

Re:Non-unique

[Anonymous Coward]

Just to make this clear, Earth is unique among all the planets we know simply because we can't detect Earth-like planets around other stars.

We really don't know how common planets like Earth are, but if you're interested in finding out be sure to write to your politicians and ask them to fund the planet-finding telescopes and spacecraft that are in the pipeline :)

Re:Non-unique

[Anonymous Coward]

Earth is the only earth like planet we have discovered so far because we do not have the technology to detect other earth like planets. We will have the ability to detect earth sized and earth like planets in 10 to 15 years. Then we shall see how good our chances are.

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 fluctuating wildly.

In short, I'm sceptical.

Re:Distance?

[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.

Re:Distance?

[602]

Cosmic ray particles get trapped in the galaxy's magnetic field and fly around and around for typically 15 million years or so before they arrive at earth. They generally retain their energy (some particles arriving at earth are within in part in 10^-22 of the speed of light). So really, distance isn't a factor. Only the very fastest particles emitted by supernovae, a minute fraction, travel in anything close to a straight line to be subject to a 1/r^2 law.

Source: "A Thin Cosmic Rain" by Friedlander

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 some interesting limitations to what we should assume.

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 years), they'd find Earth - we wouldn't need to find them.

Re:Until you consider exponential growth

[alexhard]

One of the most interesting answers to the Fermi paradox IMO is that civilisations can't survive long enough to spread out...looking at humans, I'd say there's a pretty good chance that's true..

Re:Until you consider exponential growth

[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:Until you consider exponential growth

[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:Until you consider exponential growth

[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?

Re:Until you consider exponential growth

[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 mature, stable population -- when they're finished with the thorough colonization of their own planet. Maybe 10,000 years? So now your propagation speed is somewhere around 10,700 / 7 light years... about 0.0007c, max. Probably that 10,000 years is on the low side... colonies would fail or experience serious setbacks. If your planet wasn't perfectly habitable it would take you a lot longer to fill it up. Interstellar colonization is probably a lot harder than the best case. So now you're talking about time to fill the galaxy that's getting up towards less than an order of magnitude less than the age of the Earth. There are good reasons to suspect that most life won't be able to live on planets older than Earth, and much younger planets won't have had time to develop life. It's unlikely we're the first intelligent species, but it's not nearly as unlikely that we're within a few hundred million years of the first.

Now, if you're talking about probes, I don't see a civilization trying to send probes to every single star. They'd send out a few and then turn their energies to colonization. Even if a probe DID visit the solar system, if it chose not to announce itself then we'd probably never know it had been here.

Re:Until you consider exponential growth

[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 years to move 100,000 light years.

OTOH, overall it's a good point though. My take is 0.01 c is pretty fast for interstellar travel. And nobody smart would announce their first visit to an unknown race unless they couldn't hide it.

Re:Until you consider exponential growth

[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 millenia? Maybe generational ships don't work so well because their occupants tend to become agoraphobic and just put their ships into orbit around the nearest UNINHABITABLE star they can find.

Your point about using your solar system as a starship is a good idea. You still have to make the hop to the star at closest approach though, and just riding your star around will tend to limit you to stars around it's orbit.

You may well be right -- the speed of colonization might be quite fast. You don't have to make any unreasonable assumptions to slow it down quite a bit though. And a few more assumptions, such as life taking a while to get up to interstellar travel intelligence and technological societies requiring the metals of a third generation solar system and Fermi's paradox goes away.

Re:Until you consider exponential growth

[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 civilisation. Admittedly, they had larger numbers and assistance that interstellar colonists would lack, but still I doubt we're talking enough influence to make an order of magnitude difference.

Assuming that a population will take an active interest in colonization and will have the resources to pursue it when it reaches 1,000,000,000 and the population growth rate is e (just for convenience's sake... it seems a reasonable guess for an expanding colony) you only need 16 generations from a seed colony of 100 individuals. My guess is 500-1,000 years would be enough.

Re:Until you consider exponential growth

[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 neighbors.

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?

Re:Until you consider exponential growth

[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 colonization patterns will be similar. Spread out, build, stagnate, spread out. How long did it take before European civilization got interested in spreading out to the Americas? They had the technology, and it's a far smaller undertaking. Interstellar settlers would have to not only fill up their new planet, but then fill up their solar system and develop considerable space infrastructure before they could even think about building a ship that's going to keep a seed colony worth of them alive for a thousand years of travel.

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.

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:Rare Earth ? Think again...

[Woldry]

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

Re:Rare Earth ? Think again...

[Purity Of Essence]

It is, however, natural that some people think that Earth is unique, as it is the only living planet we know of.

It is, however, natural that some people thing that Earth is not unique, as we have found intelligent life on every planet we have personally explored.

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 waves would probably be detectable across an even larger area.

Now, assuming this is true of other races in the galaxy (obviously a shaky assumption, but any life will have a drive to grow and expand, so not so awful), 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.

So, either we are in roughly the same boat as any other sentient species out there, or else post- or pre-date them. It seems unlikely at this point for us to run into a galactic empire or the like, without some major breakthroughs in physics that explain why SETI etc. haven't noticed anything.

Re:The same time span

[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 difficult to detect. Our transmissions look more and more like noise, heavily compressed digital data. Instead of AM and FM, we increasingly use more obscure technologies, even multiband. And we use lower power in our transmissions. Add a few thousand years to that, and I doubt we would be able to detect ourselves.

Also, radio is a pretty recent invention. It's not something humanity has depended upon for millenia. If we are still using radio in 5000 years, you might have a point. As of now, I don't think it's completely unthinkable that we will invent something better. Perhaps as a result of finally finding a grand unified theory in physics, or something else way longer down the road. Remember, the perspectives we are talking about in cosmic scale is billions of years. Here we keep complaining that progress in AI, fusion, string theory, etc is slow because nothing has happened in 50 years.

So, either we are in roughly the same boat as any other sentient species out there, or else post- or pre-date them.

That, at least, is for sure!

Re:The same time span

[Talinth]

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

Also, humans didn't invent radio, we simply discovered it.

Re:The same time span

[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 it by statistical techniques, and signal strength too low to find it that way...

Also, humans didn't invent radio, we simply discovered it.

Radio transmitters and receivers is certainly something we invented, not something we "discovered". We didn't go around in the forest and suddenly found a two-way CB-radio. Radio waves is a different matter, but I was talking about radio as used in human communication here, not the phenomenon of low-frequency electromagnetic waves. You should work on you ability to interpret things in context.

Re:The same time span

[Gr8Apes]

We invented radio. We discovered that part of the EM spectrum that comprises radio waves.

As for radio transmissions, they're intended for a rather small area of receivership. Move out a few million light years and with the strength diminishing as the square of distance, that signal is going to be miniscule if you can even detect it against the background radiation. (That's not to mention that someone would have to be out there to detect it, which implies faster than light travel, but let's not let physics bother us...)

Right now - we have at least a 134 light year diameter sphere of radio transimissions that theoretically could be detected, with generic noise (ie, not structured broadcasts) forming a larger sphere roughly 185 light years in diameter. That's still much smaller than the Milky Way. If we were to move away from broadcast to wired signals within 15 years, we could conceivably have a spherical band 200 light years across that would theoretically be detectable. You'd have to be within that shell to detect it, and on the scope of the cosmos, that's infinitesimally small.

Re:The same time span

[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:The same time span

[Gr8Apes]

yes, but what if they've moved on to a new communications medium and that bubble is only a couple of hundred years wide? Once that band passes you, you cannot detect those emissions anymore.

Then consider that we're still discovering things like quasars, which emit incredible amounts of radiation in continuous pulses, and the detection of alien emissions makes finding a needle in all the hay ever grown look simple.

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 everyone who's religious is like that. It's perfectly reasonable to think that G-d guided each step of evolution - evolution isn't incompatible with G-d at all. But I think this doesn't give your G-d enough credit...

Which do you think shows more omnipotence: Building a car that G-d has to tuneup every 100 miles, or building a car that drives forever and constantly improves itself on the fly to be better for existing road conditions.

Evolution does not logically require a god. But to me the wonderful elegance of evolution - and indeed of most science once humankind actually understands the topic fairly well - is closer to be proof OF G-d than a refutation of him/her.

My personal feeling is that if someone can't understand how I can have this position (even if they disagree), they need to take more math and science classes.

Computers are really built on just a couple SIMPLE elements - transitors. But millions of these SAME elements working together in a particular way gives us the computer I'm typing this on, Google, and Wikipedia. There is a wonderful elegance to this extreme complexity being built from the extreme simplicity of the evolutionary process.

Alchemy was really hard. With chemistry we can do much more... and we realize that all things we're familiar with are made up only of protons, neutrons and electrons. (and those of quarks - and yes there are less-common particles and radiation)

When you get down to basics, there's only a very few times numbers we need that aren't integers... All around, it's extremely elegant.

*and Kosher food is often healthier than "normal" food, in the same general way that Organic is - there are rules about icky things you aren't allowed to do prepping them.

Re:Evolution and G-d

[Scrameustache]

G-d

Why do you spell god that way?

Re:Evolution and G-d

[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:Evolution and G-d

[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 converting does NOT get you access to heaven, it actually makes it HARDER to get to heaven. So broadly speaking converting people isn't really a nice thing to do to them. I'm guessing this is one of those differential laws. )

Re:Evolution and G-d

[xTantrum]

But not everyone who's religious is like that. It's perfectly reasonable to think that G-d guided each step of evolution - evolution isn't incompatible with G-d at all. But I think this doesn't give your G-d enough credit...

maybe they aren't mutually exclusive, but a bible that starts off "let us make man in our own image..." and without adequate explanation of this trinity or however many 'god' there were and then through the rest of the penteuch doesn't give adequate explanations of this, doesn't encourage belief from me. How many are you?

Evolution does not logically require a god. But to me the wonderful elegance of evolution - and indeed of most science once humankind actually understands the topic fairly well - is closer to be proof OF G-d than a refutation of him/her.

expalain. IMHO opinion its more proof of the FSM.

My personal feeling is that if someone can't understand how I can have this position (even if they disagree), they need to take more math and science classes.

pleaseeeeee.... i'll give you that through the renaissance and a while after, due to the social times in those days and the rise and fight between the church and state many scientist were belivers in god. newton, c.s lewis etc. but in all probability if you ask most scientist today you would get more agnostics than believers. Because of the seemingly complicated and elegant structure of the universe it would be nice to think some higher entity put it all together, but the fact is the universe has had billions of years to get it right and is continuing its process of evolution. Even in Chaos there is order. don't try to put something there to make yourself feel better.

Computers are really built on just a couple SIMPLE elements - transitors. But millions of these SAME elements working together in a particular way gives us the computer I'm typing this on, Google, and Wikipedia. There is a wonderful elegance to this extreme complexity being built from the extreme simplicity of the evolutionary process

I understand what your trying to say so i won't be a pedant and attack the part that transistors are a technology we rarely if do use still. i'll agree that it is elegant in the design of the computer, but its not really that simple. sure its pushing bits around memory, but the manipulation of flip flops and gates can get a little complicated to have it do the desired results. the abstraction of simple base2 and utilising its twos compliments not to mention the protocols, the DOM and networking hierarchy - all of these and more compounded, make what looks easy in theory still a complicated process. I'm pretty sure you couldn't build a modern day computer in your basement - from scratch. whats that old saying? "everything works in theory....in practice...."

Alchemy was really hard. With chemistry we can do much more... and we realize that all things we're familiar with are made up only of protons, neutrons and electrons.

I always smile when i hear ppl say things like these. even as scientist we tend to think we've reached the pinnacle of understanding and can usally go no further in understanding and implementing certain things. However the operative words that should be used to preface your statement here are as far as we know... i wish i could be alive years from now when we laugh at ourselves for our limited understanding of certain concepts. There are way too many sub-atomic particles we have no clue about or whether they can be subsituted for similiar ones we used today or have ideas about. what if there is a sub atomic paricle more efficient that the electron?

(and those of quarks - and yes there are less-common particles and radiation)

at least you acknowledged it.

When you get down to basics, there's only a very few times numbers we need that aren't integers... All around, it's extre

Re:Evolution and G-d

[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 religion. I'm not sure where you got that second idea because I sure wasn't trying to make that point, and wouldn't.

First off, what I actually said was "...evolution... is closer to be proof OF G-d than a refutation of him/her" I did NOT say that it DID prove there was a G-d, did make me believe in him/her, that I did believe in a god or (especially) that it encouraged belief in the Bible - which is NOT synonymous with believing in a god!

I'm not trying to weigh in one way or the other on a proof of a god, which is by its nature impossible to prove. _ALL_ I said was that I thought evolution was usually grouped on the wrong side of a debate about divinity.

Similarly, I did NOT say that most scientists believed in a god** I also said "if someone can't understand how I can have this position (even if they disagree)" That last part, which you quoted, should've told you something. Whether they believe in it or not, I'd be willing to bet those scientists can UNDERSTAND the point I'm trying to make.

While your post doesn't seem to be a good example, it is quite possible to understand something without agreeing with it. Scientists do it all the time.

computers: I by no means am trying to reduce the value of the countless years of hard work to make modern computers. I'm merely trying to say that most of that work is in making arrangements of a relatively small number of components - that you can _make_ complexity from simplicity. I never meant that the arrangement was easy.

quarks: I completely agree that we aren't at any pinnacle of science. I purposefully chose a less than current "psuedopinnacle" so that point would be clearer. I know what a quark is, I used to work at FermiLab.

I personally think there's some suggestion in the math that quarks will eventually be broken apart farther. I certainly wasn't trying to claim that protons were unbreakable. What I WAS trying to claim goes like this: Chemistry with ~100 elements is much simpler than alchemy with a zillion materials. Chemistry with protons, neutrons, and electrons is simpler than that... And with EM, those alone DO make up all the stuff we "usually" encounter in the sense of people interacting with materials in a conscious sense.

The history of science doesn't suggest to me that we're going to find out that protons don't exist, even if we may learn much more about them and may learn about other weird particles we didn't know existed.

Numbers: I never said irrational numbers weren't USEFUL, or that we might not use any variety of numbers in performing calculations. What I said was that at the most basic physical level we only needed a few numbers that weren't integers***. But I can explain more:

If we were calculating how long it was going to take light to cross some distance, we'd probably use "c" - the speed of light. This number is very important in many calculations, but it's not philosophically important, because it has units, so this number is different depending on the units. With the right units, this value would be 1. This number is only important within the context we happened to chose for meter and second. It turns out that if you combine important physical equations you can do so in such a way that the units cancel. If you do this you either get an integer or not. But if not, it's one or a combination of a very few numbers.****

pi and e are _math_ constants. They can be derived purely from math. pi can be derived as long as you assume flat plane

Re:Evolution and G-d

[Scrameustache]

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).
 
  Interresting, except that god isn't a name, it's a title.
The name's Yaveh, god is his description. So it doesn't make any kind of sense.

It's like saying G-d created M-n in his image.

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, like those in the Drake equation or Sagan's discussions, may be plausible, but since they're not factual we can argue about them forever.

What we do know is that life arose on Earth very quickly after the initial heavy bombardment slowed down. Very quickly means a few hundred million years. That's fast enough to mean that life probably arose several times, each time getting wiped out in a new wave of bombardments, until the meteor strikes finally weren't big enough to liquefy the whole surface of Earth. Or until life was widespread enough that devastating half the Earth wasn't enough to kill it. Here again, we have no proof that repeated chemical evolution of life happened, but the speed with which it did happen, at least once, implies that it's not a particularly iffy process.

The lack of a second data point is why solar system exploration is so hugely important. Mars had a few hundred million years with liquid water. If there is evidence of fossil bacteria from that time, it'll mean there is life everywhere in the universe where there is water. I can't imagine anything more significant than that. And if exploration of, say, Europa, also turns up bacteria, well, then it'll be all over except the shouting. NASA, ESA, Japan, _everybody_ needs to hurry up and send those critical missions out there so that we have our answers, and this forum can sink it's teeth into them!

Re:Zwiebelemärit Spiel!

[Sneakernets]

On the other hand, Trolls were influenced by black holes.

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: God created each plant and animal "after its kind", where "kind" translates a Hebrew word corresponding roughly to the taxonomic family.

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 simple life", and I'll have exactly as much evidence to support my position as you do to support yours - which is to say, none.

Speculating about how many planets contain advanced civiliations, while entertaining, is pointless without any evidence one way or the other.

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 now, the war on militant Islam.

Re:You missed World War III

[Anonymous Coward]

You totally missed the point dude.

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

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

[Woldry]

You mean they'll give us space syphilis?

Probability is not numeric guessing

[Anonymous Coward]

Most of the posts talking about the probability of extraterrestrial life are rehashes of the nefarious Drake equation. Except for an estimate of the number of stars in the universe (acurate to maybe a couple of orders of magnitude), all of the other "statistics" are pulled straight out of the place Dr Drake's proctologist knows so well.

We have ONE DATA POINT folks. That means no statistics, no probabilities, and no meaningful conjecture. You may hope there is life in space, but to assert it's certitude is pure wishful thinking.

One planet, multiple data points

[geek2k5]

When you get down to it, our one planet provides multiple data points on how life arises /or survives. We have the carbon based life that depends upon photosynthesis and its byproducts as one example. Until recently as far as human history is concerned, we got most of what we needed from plants and the animals that consumed them. Then there are the ecologies found in the oceans, those that rely upon hydrogen sulfide and the black smokers. While still carbon based, they do not use photosynthesis as the energy collection mechanism. I read a recent article about how some scientists have found bacteria that use radioactive decay as an energy source. These were found deep in the Earth, in places that people didn't expect to find life. The fact that we have found these variations, and others, on this planet tells us that we really need to look in a lot more places off planet to find life. Our current photographs, atmospheric probes and surface scrapings of places outside Earth are trivial compared to what they should be. Still, we do need to make sure that our extra terrestrial explorations don't bring back something that causes problems. Our knowledge of the biological sciences is far from complete, though it is getting more in depth every day.

Re:One planet, multiple data points

[Anonymous Coward]

Sorry one data point. Life arose once on Earth, and adapted to many environments. I hope we're not resurrecting the spontaneous generation theory again.

Re:One planet, multiple data points

[quixote9]

As Anonymous Coward also says, all that variation in metabolisms may still go back to a single development of life on this planet. On the other hand, it may not. We don't know for a fact that some of the weirder metabolisms didn't originate independently. The DNA, cell membranes, etc., all share the same principles, but at this point we don't know if that's because they're related or whether it's because that's the only way life does evolve. We could be looking at three, four?, ten?, parallel and independent originations and never know it. If we find bacteria on other planets or moons, and they're equally similar, then we'll have a new issue: some people will say life was transported there from Earth and that accounts for the similarity. And it might. Unless off-Earth life is obviously different, we're going to have to figure out how to distinguish convergence from real relatedness. As I said, I, for one, wish they'd hurry up and give us that problem to solve!

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 rule, but in order for that to work it means that every alien civilization would have to agree to that rule, or that at least the most powerful one is enforcing that rule. And, of course, perhaps there are no other civilizations out there with the ability to colonize other star systems. However, I'd also like to point out that once an alien civilization starts colonizing other star systems, the odds of that civilization becoming extinct are reduced dramatically.

Re:Meeting in the context of loyal subjects

[noigmn]

There are 6 billion people on earth at the moment. There is around 400 billion stars in our galaxy. I'm guessing exploration would be quite dangerous and not really something you would be doing while bringing up chldren. Or something everyone would want to do. So the question of whether a group could have enough population growth under exploration circumstances to colonise that many planets is probably also one to ask. Obviously they would be better off if one in a million could house life. But if the probability is high, they wouldn't spread as far as you think. Just because of the sheer man power needed to colonise and the basic reluctance to move that the average intelligent lifeform on Earth seems to have. Who says that at that stage cable TV wouldn't be so good that the other colonies wouldnt leave the couch.

Re:Probability theory -- The Drake Equation

[DrJimbo]

The Drake Equation 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 self annihilates is so small that even though there are potentially millions of civilizations in our galaxy, the chances of two them being able to communicate is extremely small due to their short life spans.

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 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. :-)

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 ourselves, mere interstellar travel is nothing!) Then suppose it takes another 10,000 years for the two inhabited systems to colonize two others, and you have 4 inhabited star systems. Iterate a mere 47 times, and real-estate prices skyrocket (forgive the pun) because 2^47 is about 140 billion — and there's only about 100 billion stars in our galaxy.

So, if humanity survives a mere 470,000 years, and there are any other civilizations in our galaxy, we'll have met them. And half a million years is nothing on a cosmic scale.

And that, alas, is the big argument for there not being any ETs. If it takes less than a million years to go from flint axes to colonizing an entire galaxy, how come nobody's done it? Yeah yeah, some of them will have destroyed themselves, some will have evolved into something we wouldn't even recognize, and some just don't like to travel. But obviously there's a small chance of avoiding such hazards. So in a galaxy with billions of stars that is 11 billion years old, there's no explaining why nobody else has had their million-year spree yet. Unless there is nobody else.

And please don't tell me I'm being anthrocentric. I've been reading science fiction since before we landed on the moon. I want to share water with the ancient Martians and discuss philosophy with the Venusian Dragons. It kills me that there's this big universe out there and there's nobody home!

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.

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 civilizations that are out there arose within the same 10-100 million year time span that we did? So, the best guess is that, for whatever reason, there are no aliens in the process of colonizing the Milky Way. I guess we'll have to be first. :)

As for (prolonged) interstellar war, I would rate that as very unlikely. Whenever two civilizations meet, one is very likely to be far more advanced - even if they share a common "parent" civilization. Also, without superluminal speeds (which this discussion has assumed is unlikely), such a war becomes impractical for other reasons as well.

Also, I'm not sure why colonies wouldn't grow inside the sphere of influence, or why it matters too much. For the first part, assume that the more desirable planets are colonized first, where desirability is a mixture of closeness to where you are as well as the amount of "alienforming" that would be required to make the planet habitable. Some planets would be initially skipped, but then returned to. Secondly, I'll agree that the sphere growth is a limiting factor on reaching us. However, if the sphere is growing approximately uniformly (also being limited on "top" and "bottom" of the galaxy), then the alien species in question will reach us as if they were traveling in an almost straight line towards us, with stops for colonization along the way, of course.

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 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 science website (which is fine on its own) to provide a link to every darned word in the article. I think it is up to the Editors to do this sort of thing to promote some you know, talk about science and technology around here.

Anyway they also link to the Fermi paradox about where are they (the aliens). But I saw it just after reading about how vortices are thought to push dolphins forward and solve Gray's paradox about how they swim so fast. It is nice how paradoxes have ways of getting resolved over time. Oh, that's alright then.

Okay, I didn't like the term cosmic rays.. Wikipedia says it covers lots of things including the helium nuclei that remained in my head. Which is a lot more than just the gamma rays from Supernovae that I thought caused extinction events.

Anyway, as some posters mention it seems likely that lots of life in the galaxy must have died back or been sterilized in high radiation eras and what we need now is some kind of chronological and spatial map of what regions were affected to that degree and when. If our local neighbors failed to survive such radiation, then our biological histories are all of approximately the same age. Perhaps having deep oceans or thick ice sheets, would have something to do with preserving that too.

Now my guess has always been that even so, the geographic scale of time we are talking about, and the comparatively very rapid industrialization and advancement of a planet once the biology reaches a critical stage (perhaps a certain number of organisims at near human level?), meant that even so it most certain that civilizations hundreds of thousands or millions of years more advanced than us must exist. My picture was always that supernovae were the killer but we had been lucky... and we need to continue to be lucky until we can spread out and shield ourselves or move to safer places for the long term.

But now, it might mean that a relatively short window of time has been available to all planets in this local region to develop life. It is not clear how many times we failed or whether other planets would have to go through all the stages we did. It seems logical to have the planetary chemistry alterations in order like we had, with vegetation, and big plant eaters. Maybe the meteor that killed them was not the only problem? Anyway it took this long to get where we are. It is possible our type of chemistry is the only one that works, since the world we have obviously came from a darwinian evolution it would appear to be a result of very high probability.

So now I am looking on the web to see if there is information about just how long the part of the galaxy we know anything about could have survived biologically intact to the present day, how far back does the current window go, and how long are windows on average. It also seems that we should look for signals from areas that got hit with high radiation far away but maybe had time to beam something at us from the other side of the galaxy - to us who would evolve in the next window... Anyway it would be interesting (if we had the data which I guess we don't maybe) to be able to plot a 4D map of garden regions that did not get totally ionized and disrupted, and to see where in our neighborhood is the oldest such area.

Re:The scientist not the popular science mag

[Anonymous Coward]

A spatial map wouldn't do as much good as you think. The spiral arms of the galaxy are dynamic features, not static ones. Our solar system has passed in and out of all the arms many times. It wouldn't be useless, but for any given system of interest, it's orbit around the galactic core would have to be determined before the map would be useful.

Re:The scientist not the popular science mag

[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 that I mentioned in the other post is too simplistic since we appear to be moving faster than the spiral arms (else how could we cross) at any rate, even without the full papers he claims an extraordinary link to the the fossil record, using 3 Gyear fossil record and 200Myear galactic data. Obviously the key is to staying out of the arms so maybe this should be used to tune Seti searches?

http://www3.interscience.wiley.com/cgi-bin/abstrac t/113391302/ABSTRACT
http://www3.interscience.wiley.com/cgi-bin/abstrac t/113391301/ABSTRACT

The full text PDFs are not accessible to guests. Anyone have copies?

Here are the two abstracts.

Cosmic rays and the biosphere over 4 billion years
H. Svensmark
Center for Sun-Climate Research, Danish National Space Center, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
email: H. Svensmark (hsv@spacecenter.dk)

Keywords
Cosmic Rays Climate Biosphere

Abstract
Variations in the flux of cosmic rays (CR) at Earth during the last 4.6 billion years are constructed from information about the star formation rate in the Milky Way and the evolution of the solar activity. The constructed CR signal is compared with variations in the Earths biological productivity as recorded in the isotope 13C, which spans more than 3 billion years. CR and fluctuations in biological productivity show a remarkable correlation and indicate that the evolution of climate and the biosphere on the Earth is closely linked to the evolution of the Milky Way. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Received: 28 May 2006; Accepted: 14 June 2006

Digital Object Identifier (DOI)

10.1002/asna.200610651 About DOI

Imprint of Galactic dynamics on Earth's climate
H. Svensmark
Center for Sun Climate Research, Danish National Space Center, Juliane Marie Vej 30, 2100 Copenhagen Ø, Denmark
email: H. Svensmark (hsv@spacecenter.dk)

Keywords
Galaxy: kinematics and dynamics Earth

Abstract
A connection between climate and the Solar system's motion perpendicular to the Galactic plane during the last 200 Myr years is studied. An imprint of galactic dynamics is found in a long-term record of the Earth's climate that is consistent with variations in the Solar system oscillation around the Galactic midplane. From small modulations in the oscillation frequency of Earth's climate the following features of the Galaxy along the Solar circle can be determined: 1) the mass distribution, 2) the timing of two spiral arm crossings (31 Myr and 142 Myr) 3) Spiral arm/interarm density ratio ( arm/ interarm 1.5-1.8), and finally, using current knowledge of spiral arm positions, a pattern speed of P = 13.6 ± 1.4 km s-1 kpc-1 is determined. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Received: 28 May 2006; Accepted: 26 June 2006

Digital Object Identifier (DOI)

10.1002/asna.200610650 About DOI