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A.DIM
2012-Dec-03, 02:05 PM
Among dozens of papers written about the Drake Equation, some have suggested new considerations for the formula. One such paper stands out for adding well-established probabilistic principles from statistics. In 2010, the Italian astronomer Claudio Maccone published in the journal Acta Astronautica the Statistical Drake Equation (SDE). It is mathematically more complex and robust than the Classical Drake Equation (CDE). The SDE is based on the Central Limit Theorem, which states that given the enough number of independent random variables with finite mean and variance, those variables will be normally distributed as represented by a Gaussian or bell curve in a plot. In this way, each of the seven factors of the Drake Equation become independent positive random variables. In his paper, Maccone tested his SDE using values usually accepted by the SETI community, and the results may be good news for the "alien hunters".
...

Still, according to SDE, the average distance we should expect to find any alien intelligent life form may be 2,670 light-years from Earth. There is a 75% chance we could find ET between 1,361 and 3,979 light-years away. 500 light-years away, the chance of detecting any signal from an advanced civilization approaches zero. And that is exactly the range in which our present technology is searching for extraterrestrial radio signals. So, the "Great Silence" detected by our radio telescopes is not discouraging at all. Our signals just need to travel a little farther – at least 900 light years more – before they have a high chance of coming across an advanced alien civilization.


From physorg (http://phys.org/news/2012-12-alien-civilizations.html).

All those fancy mathematics and we still don't know anything. :D

Paul Wally
2012-Dec-03, 03:52 PM
Still, according to SDE, the average distance we should expect to find any alien intelligent life form may be 2,670 light-years from Earth. There is a 75% chance we could find ET between 1,361 and 3,979 light-years away. 500 light-years away, the chance of detecting any signal from an advanced civilization approaches zero. And that is exactly the range in which our present technology is searching for extraterrestrial radio signals. So, the "Great Silence" detected by our radio telescopes is not discouraging at all. Our signals just need to travel a little farther – at least 900 light years more – before they have a high chance of coming across an advanced alien civilization.[/i]


From physorg (http://phys.org/news/2012-12-alien-civilizations.html).

All those fancy mathematics and we still don't know anything. :D

Thanks for that. Another question is how strong the alien civilization's signal will have to be in order for it to be detectable by our current technology.

Van Rijn
2012-Dec-03, 07:21 PM
From physorg (http://phys.org/news/2012-12-alien-civilizations.html).

All those fancy mathematics and we still don't know anything. :D

Right. For that, you need evidence.

I thought this was the best part of the article:

Looking to the Drake equation factors, it is obvious that none can be precisely determined by modern science. More than that, as we move from the left to right in the equation, estimating each factor becomes more controversial. The later terms are highly speculative, and the values one may attribute to each of them might tell more about a person's beliefs than about scientific facts.

But this part of the article seemed very odd:


The L term is considered the most important one in Drake equation. We have no idea how long a technological civilization can last.


This makes no sense - the "L" term is about how long an alien civilization lasts. But surely the "N" term (number of alien civilizations in the galaxy) would be more important? After all, if "N" is zero, L doesn't apply.

ZunarJ5
2012-Dec-03, 07:57 PM
...But this part of the article seemed very odd:


The L term is considered the most important one in Drake equation. We have no idea how long a technological civilization can last.


This makes no sense - the "L" term is about how long an alien civilization lasts. But surely the "N" term (number of alien civilizations in the galaxy) would be more important? After all, if "N" is zero, L doesn't apply.

I think what the article is saying is that the "L" term is most important in determining "N"... as "N" is the answer...

TooMany
2012-Dec-03, 08:03 PM
As I tried to point out in another thread... Suppose an alien civilization developed in our galaxy one billion years ago (hey, why not?). Using technology that we can at least imagine, they could send self reproducing probes to every system in the galaxy within about 1 million years. We are perhaps just a few centuries from becoming such a civilization. Even if the chances of intelligent life evolving and developing this technology were are as rare as 1 in a billion star systems, there would be 100 in the galaxy.

Fermi said "where are they"? People often use this galactic colonization argument to argue that no other advanced intelligence exists in the galaxy or that we are the first to evolve - asserting the extreme rarity argument. I find it hard to accept the extreme rarity argument. So for me there must be another explanation that we are unaware of the existence of advanced civilizations, like the following:


The aliens simply don't care to explore the galaxy
The aliens are satisfied with remote sensing
The aliens visit us but do not want to interfere and can avoid detection
Interstellar travel is impossible (doubtful?)
A founding civilization enforces a prime directive so that developing civilizations are not interfered with unless they become some sort of threat
All civilizations collapse before reaching the technology required for interstellar travel

iquestor
2012-Dec-03, 08:30 PM
As I tried to point out in another thread... Suppose an alien civilization developed in our galaxy one billion years ago (hey, why not?). Using technology that we can at least imagine, they could send self reproducing probes to every system in the galaxy within about 1 million years. We are perhaps just a few centuries from becoming such a civilization. Even if the chances of intelligent life evolving and developing this technology were are as rare as 1 in a billion star systems, there would be 100 in the galaxy.

Fermi said "where are they"? People often use this galactic colonization argument to argue that no other advanced intelligence exists in the galaxy or that we are the first to evolve - asserting the extreme rarity argument. I find it hard to accept the extreme rarity argument. So for me there must be another explanation that we are unaware of the existence of advanced civilizations, like the following:


The aliens simply don't care to explore the galaxy
The aliens are satisfied with remote sensing
The aliens visit us but do not want to interfere and can avoid detection
Interstellar travel is impossible (doubtful?)
A founding civilization enforces a prime directive so that developing civilizations are not interfered with unless they become some sort of threat
All civilizations collapse before reaching the technology required for interstellar travel

tooMany -- there are a few threads here on Fermi, one of my favorite subjects.

A recent paper on Arxiv suggests that all developing intelligences that make it through the filter end up becoming machine intelligences, which have nothing in common with biological civilizations, and therefore leave us alone. Id say we are headed in the same direction.

Selfsim
2012-Dec-03, 08:39 PM
The essence of this study is the Central Limit Theorem (CLT):


The SDE is based on the Central Limit Theorem, which states that given enough number(s) of independent random variables with finite mean and variance, those variables will be normally distributed as represented by a Gaussian or bell curve in a plot.

Wiki quotes from a Statistics and Probability textbook in defining the Central Limit Theorem (my underlines):

In probability theory, the central limit theorem (CLT) states that, given certain conditions, the mean of a sufficiently large number of independent random variables, each with finite mean and variance, will be approximately normally distributed.So, if one is to apply this to a hypothetical model developed as an analogy for speculated alien civilisations, what 'physical condition' assumptions have been made which would make anyone think this has any relevance to the physical universe? This is after all how physics 'borrows' from mathematics theorems, but physical evidence is the only factor which facilitates the translation .. and Maccone deliberately ignores this crucial factor. As long as he does, this 'study' is purely about an already known and verified mathematical theorem .. not 'alien civilvisations'.

(I'll have to search deeper for those assumptions, as it seems he deliberately avoids stating them (in the article)).

As an aside: I'm afraid Maccone is also notoriously biased. He has previously publically encouraged deliberate political deception (http://www.youtube.com/watch?v=ObvKVe5H8pc&feature=plcp) by the SETI camp, in order to gain advantage from the successful Cosmology stream of Astrophysics, in moving speculative exo-life investigation forwards … (for no other reasons other than political).

At around the 55:54 min mark of the above Youtube lecture, Maccone says:

So, this is the political "trick", (sorry), if you like, to be tried in order to have the support of a larger community than just the SETI side…I guess I'm allowed to express my personal opinions within the forum rules, so my view is that this particular gentleman's deliberate and unashamed distortion of science, is as close to pure fraudulence as it gets, (as far as science is concerned .. and this is based on his own words, such as those just quoted).

TooMany
2012-Dec-03, 09:42 PM
tooMany -- there are a few threads here on Fermi, one of my favorite subjects.

A recent paper on Arxiv suggests that all developing intelligences that make it through the filter end up becoming machine intelligences, which have nothing in common with biological civilizations, and therefore leave us alone. Id say we are headed in the same direction.

I share your opinion. It's seem inevitable.

Van Rijn
2012-Dec-04, 12:31 AM
I think what the article is saying is that the "L" term is most important in determining "N"... as "N" is the answer...

Surely it is more important that a civilization exists in the first place?

Paul Wally
2012-Dec-04, 12:35 AM
Surely it is more important that a civilization exists in the first place?

Yes, but the purpose of the equation is to calculate the number of civilizations, from certain prior assumptions.

Selfsim
2012-Dec-04, 12:54 AM
Yes, but the purpose of the equation is to calculate the number of civilizations, from certain prior assumptions.And those prior assumptions have no basis of observational validity, so the end product contains the same invalidity.
(Ie: a net zero knowledge gained exercise).

The CL theorem was already nicely established, irregardless of this 'study'.

TooMany
2012-Dec-04, 01:10 AM
And those prior assumptions have no basis of observational validity, so the end product contains the same invalidity.
(Ie: a net zero knowledge gained exercise).


I believe you have mentioned that before. You insist that it is impossible or pointless to guess you when you don't actually know with certainty. That's nonsense of course. You don't know with absolute certainty that Sun will come up tomorrow, you just guess that it will. This is the last on this point from me.

Paul Wally
2012-Dec-04, 01:14 AM
And those prior assumptions have no basis of observational validity, so the end product contains the same invalidity.
(Ie: a net zero knowledge gained exercise).

The CL theorem was already nicely established, irregardless of this 'study'.

In all reasonableness I'd say the prior assumptions (parameter values) have a very limited observational validity, the range of possible values are still too unconstrained by evidence. But the true parameter values must lie somewhere within the range of possibilities. N=0 is a possible outcome of the Drake equation. It is not however true that zero knowledge is gained. Mathematical knowledge is gained from the application of the central limit theorem to the Drake equation.

Van Rijn
2012-Dec-04, 01:45 AM
Yes, but the purpose of the equation is to calculate the number of civilizations, from certain prior assumptions.

I thought the purpose of the equation was to be a starting point for discussion, so we can focus research on the factors that we would need to know in order calculate the number of existing civilizations. There's been some progress on those factors (we now have a pretty good idea of the percentage of stars with planets, for instance), but there are other factors we don't know much about at all yet.

Jens
2012-Dec-04, 02:20 AM
But this part of the article seemed very odd:


The L term is considered the most important one in Drake equation. We have no idea how long a technological civilization can last.


This makes no sense - the "L" term is about how long an alien civilization lasts.

Although it's not really clear, I could venture a guess. Actually, to me personally, the L term is the most important. For obvious reasons. For humanity, the L term is the most important because it is the one term in the equation that has an important impact on our own civilization. So it has an importance that goes beyond the simple question of whether we will encounter aliens.

Maybe that's what the author meant, but it isn't clear.

Colin Robinson
2012-Dec-04, 02:38 AM
Although it's not really clear, I could venture a guess. Actually, to me personally, the L term is the most important. For obvious reasons. For humanity, the L term is the most important because it is the one term in the equation that has an important impact on our own civilization. So it has an importance that goes beyond the simple question of whether we will encounter aliens.

I think perhaps the point is that we have no examples at all to tell us whether a civilization with technology capable of radio signaling is going to last for several hundreds, thousands, millions of years, or whether it is going to collapse after a century or two, or whether it is likely to morph into something else.

For other terms in the Drake equation (e.g. regarding chances of life getting started, chances of intelligence evolving) we have at least the one example of the Earth and its history. But for the L term we don't have even that one example, because we don't know what our own civilization's long term future is going to be. The one thing worse that generalizing for a single example, is generalizing from zero examples.

That is the sense in which we know less about the term L than any of the other terms.

Jens
2012-Dec-04, 03:01 AM
That is the sense in which we know less about the term L than any of the other terms.

Yeah, but the article didn't say that. It said that that L was the most important of the terms, not the least understood. That's what Van Rijn was puzzled about.

Colin Robinson
2012-Dec-04, 03:35 AM
Yeah, but the article didn't say that. It said that that L was the most important of the terms, not the least understood. That's what Van Rijn was puzzled about.

Actually it says both -- L is most important and least understood.


But this part of the article seemed very odd:

The L term is considered the most important one in Drake equation. We have no idea how long a technological civilization can last.

Maybe the author's point is that it is most important because it is least understood. Because we have very little idea of its value, it is most important to consider carefully…

Selfsim
2012-Dec-04, 03:39 AM
In all reasonableness I'd say the prior assumptions (parameter values) have a very limited observational validity, the range of possible values are still too unconstrained by evidence. Agreed. (And noted by the author himself).

The original paper is here. (http://uavarese.altervista.org/0_Statistical_Drake_Equation.pdf) I suggest a read of it. EDit: Link seems to break upon copying .. try here …

http://www.google.com.au/#hl=en&sugexp=les%3Bernk_cprob&gs_nf=3&gs_rn=0&gs_ri=hp&cp=95&gs_id=4&xhr=t&q=Claudio+Maccone+published+in+the+journal+Acta+As tronautica+the+Statistical+Drake+Equation+(SDE)&pf=p&tbo=d&output=search&sclient=psy-ab&oq=Claudio+Maccone+published+in+the+journal+Acta+A stronautica+the+Statistical+Drake+Equation+(SDE)&gs_l=&pbx=1&fp=1&bpcl=39314241&biw=1186&bih=861&bav=on.2,or.r_gc.r_pw.r_qf.&cad=b


In loose terms, the CLT states that the sum of any number of independent random variables, each of which may be ARBITRARILY distributed, approaches a Gaussian (i.e. normal) random variable.

As noted in this quote, the more important aspect, is that he posits that each of the seven Drake factors to be arbitrarily distributed random variables. A random variable is a variable whose value is subject the variations due to chance. Just think about this for a minute, eh?

Is it reasonable' to assume that, (for example), the number of stars in the galaxy is randomly distributed (by pure chance)? (How come astronomers have distinguished a barred spiral pattern for the MW? Is this indicative of a random spatial distribution?)

I won't go through the other factors but why would this general posit result in any clearer picture of the speculated numbers of civilisations in our galaxy, when compared to some other theoretical, geometrical, exponential, location-centric, double bounded, asymptotic, etc distributions?? (There are 9,687 entries for statistics distribution in Wiki. (http://en.wikipedia.org/w/index.php?title=Special:Search&limit=50&offset=0&redirs=1&profile=default&search=statistics+distribution)

What makes a random one any better as an assumption, than any of the other named ones?

whimsyfree
2012-Dec-04, 03:46 AM
All those fancy mathematics and we still don't know anything. :D


As far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality.
-- Albert Einstein

Selfsim
2012-Dec-04, 09:58 AM
Just correcting/clarifying my last post... the point I was trying to make, (somewhat awkwardly ... I was in a hurry), was that Maccone's equation assumes the terms to be independent random variables ... but they aren't defined that way in the original Drake equation. They are in fact defined as conditional probabilities.

The normality of the distribution appears in the limit for an infinite sum (the left hand side or the 'ln N' term) and this is so, whatever the distributions of the independent random variables in the sum may be. (This the the CLT in action), but if the right hand side variables aren't independent to begin with, (and they aren't because that's not how they're defined), then I don't think the conclusion about normality is theoretically valid(?)

The 'error bars' he seeks to constrain in the so-called 'independent' distributions, are completely unconstrained physically, also (which I think we all agree about).

I think this whole thing is a bit of a 'dodgy' interpretation, from a theoretical mathematical perspective, as well as having scant empirical evidence in support of some of the variables.

Paul Wally
2012-Dec-04, 02:10 PM
Just correcting/clarifying my last post... the point I was trying to make, (somewhat awkwardly ... I was in a hurry), was that Maccone's equation assumes the terms to be independent random variables ... but they aren't defined that way in the original Drake equation. They are in fact defined as conditional probabilities.



I think the independence is assumed between different solar systems separated by vast distances. The dependence you speak of in the Drake equation is for one planet, because obviously the existence of life depends on the existence of the planet, and the existence of a civilization depends on the existence of life, and so forth. But what happens on one planet is independent from what happens on another planet light years away. However Maccone's assumption of independence could be questioned on other grounds, for instance if a group of stars formed together in the same nebula, perhaps there would then be some statistical correlations between their respective systems.

MarianoRF
2012-Dec-04, 02:14 PM
The aliens simply don't care to explore the galaxy
The aliens are satisfied with remote sensing
The aliens visit us but do not want to interfere and can avoid detection
Interstellar travel is impossible (doubtful?)
A founding civilization enforces a prime directive so that developing civilizations are not interfered with unless they become some sort of threat
All civilizations collapse before reaching the technology required for interstellar travel

I agree with you, mostly with Interstellar travel is impossible. Since we are talking about extreme vast distances here, no one could make a journey of 70000 years or more to our nearest star Proxima Centauri, and not even to mention intergalactic travel.

So, maybe there are hundreds, thousands... even millions of civilizations out there... but with those extreme vast distances, it's impossible for all of us to meet each other. Maybe these distances, are a barrier of some kind to protect us from each other.

Gomar
2012-Dec-04, 06:46 PM
All civilizations collapse before reaching the technology required for interstellar travel

Most plausible theory. Look at what has happened on Earth in the 20c. Humans came close to nuclear
war in 1962 during the Cuban Missile Crisis.
Then, China obtained nukes; then India; then Pakistan; then Israel. Brits and French have nukes.
Iraq tried to build them, as did Iran. North Korea has 3.
Thus, I do see aliens spreading to other planets, colonizing or conquering perhaps other species,
but eventually waging war with each other which leads to being bombed back to stone age.

However, suppose some alien species had learned a lesson the hard way, and after watching
humans for a while have determined that human possession of nuclear weapons must not be
tolerated. Thus, we could expect alien contact or some sort of warning to change our ways at any time.

TooMany
2012-Dec-04, 07:03 PM
I agree with you, mostly with Interstellar travel is impossible. Since we are talking about extreme vast distances here, no one could make a journey of 70000 years or more to our nearest star Proxima Centauri, and not even to mention intergalactic travel.

So, maybe there are hundreds, thousands... even millions of civilizations out there... but with those extreme vast distances, it's impossible for all of us to meet each other. Maybe these distances, are a barrier of some kind to protect us from each other.

It's a comforting thought that we might be protected from the alien conquistadors by these vast distances. That's been a theory of mine for some time, but I've lately changed my tune.

I admit to not having studied in detail what we can reasonably conjecture about the possibility of interstellar travel (aha, something else to research). Is the 70,000 years is based on how long it would take a chemically-power rocket to get there after accelerating to 40,000 mph? Don't you suppose that technology a couple of centuries from now could do a heck of lot better than that?

At one time, the only way to get to from the East Coast to California was to sail around the horn or to ride across the land in an animal-pulled wagon. Both possibilities took many months of travel. Recently (1990) the SR-71 "Blackbird" made the trip in under two hours. I know that's just an analogy, but the point is that technology will not stand still.

When people argue the impossibility of interstellar travel, they seem to make some implicit assumptions. Perhaps the most important of these assumptions is that biological beings like ourselves would make the trip. This assumption indeed makes the problem very difficult. Even if biological lives could be extended to several centuries we would be looking at many generations to make such a trip.

The alternative for the intelligent aliens is to build autonomous machines to make the trip. The life support requirements of such machines may be a couple orders of magnitude less complex and heavy than biological life support. Besides which the machines can go into a state of suspended animation by simply powering down the the majority of their systems. These machines (as sentient devices) don't have to get bored or hopeless during the trip. Once the alien biological life form makes the transition to a non-organic life form, intelligence and experience can be copied from one machine into another. If the motive of exploration is preserved in the machinery, then there is little doubt that some of the machines may want to launch themselves on the adventure of interstellar travel, perhaps taking a bunch of friends for company (if such a concept even makes sense to non-organic life).

So I claim that interstellar travel is not impossible but rather quite realistic. It's just that it is completely impractical for our civilization as it currently exists.

TooMany
2012-Dec-04, 07:18 PM
Most plausible theory. Look at what has happened on Earth in the 20c. Humans came close to nuclear
war in 1962 during the Cuban Missile Crisis.
Then, China obtained nukes; then India; then Pakistan; then Israel. Brits and French have nukes.
Iraq tried to build them, as did Iran. North Korea has 3.
Thus, I do see aliens spreading to other planets, colonizing or conquering perhaps other species,
but eventually waging war with each other which leads to being bombed back to stone age.

However, suppose some alien species had learned a lesson the hard way, and after watching
humans for a while have determined that human possession of nuclear weapons must not be
tolerated. Thus, we could expect alien contact or some sort of warning to change our ways at any time.

Nuclear armageddon looked like a real possibility from the 50's through the 80's. We got through this period and finally (in spite of the Star Wars threat of continuing) the one-upmanship seems to have dwindled now. Maybe will find some other way to destroy ourselves (like GW or overpopulation). It's really hard to say. It's sort of a race between destructive technology and development of social maturity in which we get our baser instincts under control of reason.

My hope both for our own protection from ourselves and from potential alien enemies is that this social maturity is in fact possible and primitive motives of dominance and theft become obsolete. We have not been conquered by the aliens yet so either they do not exist or they are not all that interested in such an endeavor.

Selfsim
2012-Dec-04, 07:45 PM
I think the independence is assumed between different solar systems separated by vast distances. The dependence you speak of in the Drake equation is for one planet, because obviously the existence of life depends on the existence of the planet, and the existence of a civilization depends on the existence of life, and so forth. But what happens on one planet is independent from what happens on another planet light years away. However Maccone's assumption of independence could be questioned on other grounds, for instance if a group of stars formed together in the same nebula, perhaps there would then be some statistical correlations between their respective systems.Yep … the physical dependence aspects, I think, are pretty clear.
But even just within the purely mathematical domain, I thought the CLT was applicable to only independent variables, having any arbitrary type of distribution(?)

As you have demonstrated, most of the variables are defined initially as being of type 'dependent', so the theorem proof, (resulting in a normal distribution in the limit), is not necessarily applicable either(?) If this is the case, then the whole application of the CLT is invalidated on the basis of a flawed assumption (ie: of it being of an incorrect variable type(?) )

Elukka
2012-Dec-04, 08:26 PM
My hope both for our own protection from ourselves and from potential alien enemies is that this social maturity is in fact possible and primitive motives of dominance and theft become obsolete. We have not been conquered by the aliens yet so either they do not exist or they are not all that interested in such an endeavor.
What would they have to gain by conquering us? We have no special resources that aren't freely available everywhere else with nobody to contest them. The Earth probably isn't an ideal place for them to live either. Making use of our labor in servitude would be made very difficult by the inevitable communications issues and probably incompatible environments. I don't think we have, or ever will have, anything they will want, though they could be curious about us. But that's really the only reason I can see for making contact.

TooMany
2012-Dec-04, 09:19 PM
I think this whole thing is a bit of a 'dodgy' interpretation, from a theoretical mathematical perspective, as well as having scant empirical evidence in support of some of the variables.

True, but even as we speak, we may be making some progress with some of these variables by finding out what went on with Mars. It's a terrestrial analogue in many ways. If we were to find life for example, that might tip the scales a bit on the probability of life forming, even on a planet that could not ultimately sustain earth-type fruition.

TooMany
2012-Dec-04, 09:23 PM
What would they have to gain by conquering us? We have no special resources that aren't freely available everywhere else with nobody to contest them. The Earth probably isn't an ideal place for them to live either. Making use of our labor in servitude would be made very difficult by the inevitable communications issues and probably incompatible environments. I don't think we have, or ever will have, anything they will want, though they could be curious about us. But that's really the only reason I can see for making contact.

That's my conclusion as well. What the heck would they need with us, except perhaps to satisfy their curiosity (which cannot as easily be discounted as a motive to visit)?

Luckmeister
2012-Dec-04, 09:55 PM
However, suppose some alien species had learned a lesson the hard way, and after watching
humans for a while have determined that human possession of nuclear weapons must not be tolerated. Thus, we could expect alien contact or some sort of warning to change our ways at any time.

Alien intelligence would have to be in our cosmic back yard to be aware of our recent nuclear proliferation. If they were a mere 70 ly away, they would not quite yet be able to detect any development of nuclear weapons on Earth since they would be studying us as we were 70 years ago. It is highly unlikely there is a civilization even as developed as us that near.

Selfsim
2012-Dec-04, 10:27 PM
True, but even as we speak, we may be making some progress with some of these variables by finding out what went on with Mars. It's a terrestrial analogue in many ways. If we were to find life for example, that might tip the scales a bit on the probability of life forming, even on a planet that could not ultimately sustain earth-type fruition.Well, in the woolly world of unconstrained speculation, I would think the present state of evidence should also then define progress as well (by the same 'logic'). Ie: the finding of organics of insufficient quantities in order to distinguish past life, (in all its anticipated, inevitable abundance), would already tell us something incremental too, wouldn't it?

Colin Robinson
2012-Dec-04, 11:28 PM
As an aside: I'm afraid Maccone is also notoriously biased. He has previously publically encouraged deliberate political deception (http://www.youtube.com/watch?v=ObvKVe5H8pc&feature=plcp) by the SETI camp, in order to gain advantage from the successful Cosmology stream of Astrophysics, in moving speculative exo-life investigation forwards … (for no other reasons other than political).

At around the 55:54 min mark of the above Youtube lecture, Maccone says:


So, this is the political "trick", (sorry), if you like, to be tried in order to have the support of a larger community than just the SETI side…

I guess I'm allowed to express my personal opinions within the forum rules, so my view is that this particular gentleman's deliberate and unashamed distortion of science, is as close to pure fraudulence as it gets, (as far as science is concerned .. and this is based on his own words, such as those just quoted).

I checked the You-tube reference. Yes, Maccone uses the word "trick". But what sort of "trick" is he talking about?

Actually he is suggesting that SETI researchers cooperate with cosmologists to back a deep space research proposal which would be of value for both fields. The mission would use the Sun as a gravitational lens, which would require going a long way out into space. Maccone says that if it was conceived just as a SETI mission, it would be less likely to get support from governments, than if it was conceived as a mission with both a SETI function and a cosmological function.

Is this a case of "deliberate deception"... "unashamed distortion of science"... "as close to fraudulence as it gets"?

Or is it more a case of out-of-context quoting for character assassination?

Selfsim
2012-Dec-05, 01:09 AM
I checked the You-tube reference. Yes, Maccone uses the word "trick". But what sort of "trick" is he talking about? My quote was exactly what he said ..

So, this is the political "trick", (sorry), if you like, to be tried in order to have the support of a larger community than just the SETI side…

Professionals expecting to be taken seriously, don't advocate deliberate 'political trickery' to any audience. Either a proposal stands on its own scientific merit, or it doesn't. He was speaking about leveraging what he perceives to be an 'extremely powerful' cosmology community, to 'prop up' an impractical proposal. Well, if the cosmology community are that, how did they get that way? By 'political trickery??? .... Or by developing proposals which stand on their own merits in demonstrating relatively low risk returns on investment?


Is this a case of "deliberate deception"... "unashamed distortion of science"... "as close to fraudulence as it gets"?I'm afraid so .. an attempted conspiracy even(??)
The man was there, ostensibly to present science .. not politics.


Or is it more a case of out-of-context quoting for character assassination?They're his words .. not mine.
PS: This will be my last post on this matter. I was attempting to draw to others' attention how this man mixes political motives, with matters of science.
(Some of my own opinions were also expressed … in keeping with the true LIS Forum 'style', I might add). I am addressing the details of his 'Statistical Drake Equation' in my conversation with Paul Wally.

Colin Robinson
2012-Dec-05, 01:46 AM
I'm afraid so .. an attempted conspiracy even(??)

If you're exposing an attempted conspiracy, why not use the CT forum?

NoChoice
2012-Dec-05, 01:59 AM
Professionals expecting to be taken seriously, don't advocate deliberate 'political trickery' to any audience. Either a proposal stands on its own scientific merit, or it doesn't.

Not in the real world it doesn't. No offense but that is just naive and not how science "works" in the real world where funding considerations and peer influences more often than not (unfortunately) decide what science gets pursued and what doesn't.

IMHO, he used appropriate means to try to get a proposal through.

There was no "deliberate deception". It's hardly a deception if it's that public.
There was no "unashamed distortion of science". What science exactly did he distort?
This was not "as close to fraudulence as it gets". It is common practice in the often cut-throat world of trying to secure funding.

I am with Colin Robinson. That did sound more like "a case of out-of-context quoting for character assassination".

whimsyfree
2012-Dec-05, 08:18 AM
It's a comforting thought that we might be protected from the alien conquistadors by these vast distances. That's been a theory of mine for some time, but I've lately changed my tune.

I admit to not having studied in detail what we can reasonably conjecture about the possibility of interstellar travel (aha, something else to research). Is the 70,000 years is based on how long it would take a chemically-power rocket to get there after accelerating to 40,000 mph? Don't you suppose that technology a couple of centuries from now could do a heck of lot better than that?


Back of the envelope calculations previously posted by myself suggest that a pure stellar sailing approach could reach alphaC in about 14k years. This is using trajectories and sail areal densities from wikipedia, not future/fantasy technologies. It is reasonable to assume that near advances in technology and a more sophisticated (e.g. adding a nuclear electric ion rocket for propulsion at large stellarcentric distances) and aggressive (e.g. lower perihelia than wikipedia's 0.2 au) approach would reduce this considerably. This is sending a probe, of course. Sending a live human is ridiculously more difficult.


The alternative for the intelligent aliens is to build autonomous machines to make the trip.


Or, as you later suggested, the intelligent aliens may be autonomous machines.


So I claim that interstellar travel is not impossible but rather quite realistic. It's just that it is completely impractical for our civilization [species] as it currently exists.


Nuclear armageddon looked like a real possibility from the 50's through the 80's. We got through this period and finally (in spite of the Star Wars threat of continuing) the one-upmanship seems to have dwindled now. Maybe will find some other way to destroy ourselves (like GW or overpopulation). It's really hard to say. It's sort of a race between destructive technology and development of social maturity in which we get our baser instincts under control of reason.


I think it's a stretch to attribute GW or overpopulation to destructive technology. Until about 1990 industrialization was almost universally regarded as a good, and the factors responsible for over-population (mainly advances in medicine) still are. Rather these are the unintended consequences of technology. As to nuclear energy, like all power sources nuclear power can be used for productive or destructive purposes. The prospects of nuclear armageddon may have dimmed, but the prospects of more limited nuclear war grow as more countries obtain the means.


My hope both for our own protection from ourselves and from potential alien enemies is that this social maturity is in fact possible and primitive motives of dominance and theft become obsolete. We have not been conquered by the aliens yet so either they do not exist or they are not all that interested in such an endeavor.

Or they haven't arrived yet. Interstellar conquest seems pointless, but interstellar destruction may be the rational. What could threaten a civilization with the power to visit destruction across interstellar space but another such civilization?

Paul Wally
2012-Dec-05, 08:53 AM
Or they haven't arrived yet. Interstellar conquest seems pointless, but interstellar destruction may be the rational. What could threaten a civilization with the power to visit destruction across interstellar space but another such civilization?

If interstellar conquest seems pointless, then why doesn't interstellar destruction seem pointless too? It seems irrationality is the rationale here.

Van Rijn
2012-Dec-05, 10:03 AM
My quote was exactly what he said ..


Professionals expecting to be taken seriously, don't advocate deliberate 'political trickery' to any audience. Either a proposal stands on its own scientific merit, or it doesn't. He was speaking about leveraging what he perceives to be an 'extremely powerful' cosmology community, to 'prop up' an impractical proposal.


I did not see anywhere that he said he was going to use the cosmology community to prop up an impractical proposal. And he was showing how a FOCAL mission (a space telescope using the sun as a gravitational lens to dramatically increase effectiveness) would have multiple lines of scientific merit, one example being cosmology related observational research.


I'm afraid so .. an attempted conspiracy even(??)


An attempted conspiracy? Because he mentions politics in a filmed discussion? Or is there something else you're referring to?



The man was there, ostensibly to present science .. not politics.


Wow. This was nearly an hour and a half presentation, and you're complaining about a sentence or two where he mentions politics? It sounds like you have an ivory tower view of science. Space missions especially (given their expense) involve a lot of political wrangling, and often with completely non-science issues playing a big factor. In this case, the scientist is discussing politics in order to achieve science goals, in what would be a win-win for scientists in multiple fields.



PS: This will be my last post on this matter.



... so you presumably won't explain what you're basing that "attempted conspiracy" claim on.


I was attempting to draw to others' attention how this man mixes political motives, with matters of science.


Well, you did draw my attention to the video.

Van Rijn
2012-Dec-05, 10:30 AM
If interstellar conquest seems pointless, then why doesn't interstellar destruction seem pointless too? It seems irrationality is the rationale here.

I could see an argument for a paranoid civilization preemptively hitting worlds with evidence of life to stop any possible competition. It would be irrational to wait to see signs of civilization and THEN attack, though, since by that time you may be hitting a civilization that has already made it off their home planet and started dispersing. Attack too late and you've made an enemy that will likely try to hit back.

Gomar
2012-Dec-05, 05:30 PM
except perhaps to satisfy their curiosity (which cannot as easily be discounted as a motive to visit)?

I do not think aliens would fly that far from their home world to Earth just because they are
curious, as then they would have to fly all the way back home. If they are here, they'll stay; either
as colonists, conquerors, settlers, "undocumented aliens", mestizos, or do what the nephilim did
mate with daughters of man.

If indeed an alien Columbus were to "find" Earth, then in time the so-called "new world" will be
settled by others from the home planet. However, given the millions of planets in the galaxy,
some millions of years older than Earth, and the fact there are no green men with bug eyes
walking around Earth, means it just wont ever happen.

Luckmeister
2012-Dec-05, 06:43 PM
If indeed an alien Columbus were to "find" Earth, then in time the so-called "new world" will be
settled by others from the home planet. However, given the millions of planets in the galaxy, some millions of years older than Earth, and the fact there are no green men with bug eyes
walking around Earth, means it just wont ever happen.

Your logic escapes me. To draw a parallel, given the number of teams in the NFL and the fact that my home team has never won a superbowl, I can conclude that it just won't ever happen?

TooMany
2012-Dec-05, 08:04 PM
I could see an argument for a paranoid civilization preemptively hitting worlds with evidence of life to stop any possible competition. It would be irrational to wait to see signs of civilization and THEN attack, though, since by that time you may be hitting a civilization that has already made it off their home planet and started dispersing. Attack too late and you've made an enemy that will likely try to hit back.

This seems to be a somewhat common political philosophy (preemptive attack) among certain personality types. Years ago I participated in an excise at work in which a number of us were split up into teams and given some working rules. It was set up so that the teams could mutually benefit through cooperation or sacrifice mutual benefit, in favor of more assured but smaller benefit, by choosing not to cooperate and by analogy "launch a first strike" which would also prevent the other teams from receiving any benefits.

On my team, one of these types immediately set out to dominate the team and proposed a plan to screw the other teams. Oh well...

I suspect that some similar types in the military suggested that we hit the Russians with all we've got before they have time to develop mutually assured destruction. Fortunately it did not happen. Not to get too political, but in recent years Gingrich has proposed this approach to deal with threats from Iran and N. Korea (somehow ignoring Pakistan). This fits the personality profile I mentioned.

Back to the subject, given a deliberative and unemotional intelligence with superior technology, I would expect vigilance concerning the possibility of a threat but not preemptive annihilation as a solution. Call me a dreamer, but we haven't been wiped out by the aliens yet.

Selfsim
2012-Dec-05, 09:14 PM
I think the independence is assumed between different solar systems separated by vast distances. The dependence you speak of in the Drake equation is for one planet, because obviously the existence of life depends on the existence of the planet, and the existence of a civilization depends on the existence of life, and so forth. But what happens on one planet is independent from what happens on another planet light years away. However Maccone's assumption of independence could be questioned on other grounds, for instance if a group of stars formed together in the same nebula, perhaps there would then be some statistical correlations between their respective systems.
Yep … the physical dependence aspects, I think, are pretty clear.
But even just within the purely mathematical domain, I thought the CLT was applicable to only independent variables, having any arbitrary type of distribution(?)

As you have demonstrated, most of the variables are defined initially as being of type 'dependent', so the theorem proof, (resulting in a normal distribution in the limit), is not necessarily applicable either(?) If this is the case, then the whole application of the CLT is invalidated on the basis of a flawed assumption (ie: of it being of an incorrect variable type(?) )
Ok, so coming back to the OP topic, (and answering my own question), I think I'm now convinced that the CLT is still, in fact, applicable in this case, irregardless of the dependence or independence of the variables involved.

If the sum limit (ie: the sample space), approaches infinity, then the 'N' figure approaches the mean of what it would be if the sample was a normal (Gaussian) distribution. (Hope that makes sense .. this is the CLT in action).

The critical factor in this however, is the sampling method. Or, in empirical terms, the test's ability to conclusively eliminate non-ET life planets from the sample space, as it progresses. The bigger the sample space, the slower the 'N' figure approaches the mean value.

Maccone's point is totally irrelevant though, because we haven't yet devised a method for conclusively eliminating the 'possibility' of life on any given planet, or eliminating the possibility of civilisations existing on a remote planet of light years distant, such that it can be removed from the sample set before the next iteration of the 'test'. Distributing such a test across the entire sample set of selected 'Earth-like' planets, is dubious also, because we don't have a good enough feeling for how big this sample set is yet, either.

Maccone's claimed improvement' over the classical Drake Equation is thus also completely moot and once again, results in a question of what has been gained in this exercise, that wasn't already obvious?

Jens
2012-Dec-06, 12:34 AM
Maybe the author's point is that it is most important because it is least understood. Because we have very little idea of its value, it is most important to consider carefully…

Yes, I agree, that may be what the author was trying to say. And I offered an alternative explanation of what he might have been trying to say. But I think that probably without actually asking the author, it would be hard to figure out exactly what was meant.

whimsyfree
2012-Dec-06, 02:36 AM
This seems to be a somewhat common political philosophy (preemptive attack) among certain personality types. ...

Let's steer clear of political philosophies and politicians. It is prudent to assume that the diversity of attitudes, motivations, and philosophies across all intelligent species in the galaxy will be at least as broad as we see within our own species.


Back to the subject, given a deliberative and unemotional intelligence with superior technology, I would expect vigilance concerning the possibility of a threat but not preemptive annihilation as a solution. Call me a dreamer, but we haven't been wiped out by the aliens yet.

If it's a form of the Prisoner's Dilemma then the correct deliberative and unemotional solution was established by game theorists to be defecting (pre-emptive attack in this case). i.e. Pre-emptive attack defeats playing nice (assuming interstellar attacks are effective). Against another pre-emptive attacker it's a matter of who is quicker on the draw, so to speak. OTOH pre-emptive attack may be unnecessary, e.g. because the aliens know how far ahead they are and how long it will take us to become a threat and they are confident of their ability to manage the potential threat we pose by other means. This may not be applicable if the technological singularity hypothesis is correct.

It's noteworthy that humans are generally averse to the pre-emptive attack solution, even when game theorists tell them it's the rational thing to do. This probably due to our inheritance as social animals. The aversion is notably weaker when dealing with out-group strangers, though.


I could see an argument for a paranoid civilization preemptively hitting worlds with evidence of life to stop any possible competition. It would be irrational to wait to see signs of civilization and THEN attack, though, since by that time you may be hitting a civilization that has already made it off their home planet and started dispersing. Attack too late and you've made an enemy that will likely try to hit back.

The more distributed and ubiquitous the paranoid civilization's threat detection and elimination system is the less of a hair-trigger it needs. Also, we don't know how far away we are from posing a threat. If the singularity hypothesis is correct it may be decades, if not, it may be millenia.

To return to the thread title, what exactly is the Drake equation? I have seen multiple versions of it. For example, the one in the linked article differs from that in Wikipedia. None of them seems quite right to me. Most debate revolves around the values of the numbers, but the form of the equation bothers me more. It assumes an infinitely old steady-state universe. That it assumes steady state is attested by the fact that it treats as constant several quantities that are known not to be constant. The rate at which stars form has varied with time and it's likely that the nature of the concurrently formed planets has changed over the life of the galaxy too. That it assumes an infinitely old galaxy is shown by the its use of fractions such as fi, the fraction of life-bearing worlds that ultimately evolve intelligent life. If the galaxy is only finitely old (and not very old compared to the lifetime of stars, and it's not) then it matters how long it takes for intelligent life to evolve. You get a very different result if the mean value is, say, 1010 years than if it is, say, 109 years.

Selfsim
2012-Dec-06, 06:45 AM
TTo return to the thread title, what exactly is the Drake equation? I have seen multiple versions of it. For example, the one in the linked article differs from that in Wikipedia. None of them seems quite right to me. Most debate revolves around the values of the numbers, but the form of the equation bothers me more. It assumes an infinitely old steady-state universe. That it assumes steady state is attested by the fact that it treats as constant several quantities that are known not to be constant. The rate at which stars form has varied with time and it's likely that the nature of the concurrently formed planets has changed over the life of the galaxy too. That it assumes an infinitely old galaxy is shown by the its use of fractions such as fi, the fraction of life-bearing worlds that ultimately evolve intelligent life. If the galaxy is only finitely old (and not very old compared to the lifetime of stars, and it's not) then it matters how long it takes for intelligent life to evolve. You get a very different result if the mean value is, say, 1010 years than if it is, say, 109 years.That's the whole point of Maccone's Statistical Drake Equation and the Central Limit Theorem. Each term can take on a complete distribution of numbers, which can all be taken into account, in coming up with an 'N' estimate. It doesn't matter how much a particular term varies, or by how much, the end distribution of 'N' ends up being a normal (or Gaussian) distribution, if the universe is estimated to be pretty well infinite (or extremely humungous). Once the end result ends up as a normal distribution, the confidence level of the final 'N' figure be can estimated.

I'm not comfortable with the outcome if any term is really, really tiny, though (such as what typically happens with the fL term. (fL is the number of civilizations now transmitting and receiving, and this implies an estimate of ‘‘how long will a technological civilization live?" He assumes a mean value of 1 in 107 with the same standard deviation, in his sample calculation). I'm not convinced a normal distribution works as a good approximation in that scenario, although I'm not sure what distribution type might be more appropriate(??)

Oh ... and I think he's said that the time-varying (or time dependent) version of his equation is 'for future study' ... (and I wouldn't hold my breath waiting for it).

Elukka
2012-Dec-06, 11:02 AM
I think there are various issues with blanket annihilation of other civilizations. Let's say you're an alien a couple hundred light years away from us. You know Earth has an industrial civilization and decide it's time for us to go. Can you absolutely guarantee that in the centuries your weapons would be traveling here we won't detect them and perhaps develop our own and fire back? Slim chance, perhaps, but are you willing to bet your species on it? Better watch out for any other civilizations that may be watching, too; you've now not only announced your existence but that you're out to kill them all.

Highly advanced civilizations may also very well have some significant fraction of their population and functions on space habitats instead of planets. You can't destroy them very easily with relativistic weapons since they can simply move out of the way. Now you're looking at sending a fleet of actual space warships after your relativistic weapons have hit to mop up the survivors. Note that the survivors here might be 90% of their civilization and they could just destroy your silly spaceships.
Your attack won't have eliminated them but it will make clear to them and possibly others that you're a civilization of omnicidal maniacs that should probably be eliminated. You've put yourself into a mindless interstellar war with no point beyond paranoia.

Or you could not do any of that and just leave the others alone.

Paul Wally
2012-Dec-06, 11:23 AM
To return to the thread title, what exactly is the Drake equation? I have seen multiple versions of it. For example, the one in the linked article differs from that in Wikipedia. None of them seems quite right to me. Most debate revolves around the values of the numbers, but the form of the equation bothers me more. It assumes an infinitely old steady-state universe. That it assumes steady state is attested by the fact that it treats as constant several quantities that are known not to be constant. The rate at which stars form has varied with time and it's likely that the nature of the concurrently formed planets has changed over the life of the galaxy too. That it assumes an infinitely old galaxy is shown by the its use of fractions such as fi, the fraction of life-bearing worlds that ultimately evolve intelligent life. If the galaxy is only finitely old (and not very old compared to the lifetime of stars, and it's not) then it matters how long it takes for intelligent life to evolve. You get a very different result if the mean value is, say, 1010 years than if it is, say, 109 years.

My underline

Yes, either the assumption is of a steady state galaxy or the equation could be applicable only for sufficiently small time periods (say 1 billion years) where the factors would be approximately constant. I think the averaqe life-time of a civilization must also be sufficiently short if the equation is to be applicable. If civilizations continue indefinitely then there should then be an accumulation of civilizations since the beginning of time, but if there is a birthrate and mortality rate for civilizations then there would again always be a certain number of civilizations only for some time period and the earlier time periods become irrelevant.

Another factor not considered in the Drake equation is that the amount of carbon and other heavier elements produced by nuclear synthesis in stars would have been too small during the first couple of billion years. Also these heavier elements, necessary for the formation of terrestrial planets like Earth, are released by supernovae, stars which already existed for a very long time. So if life requires these heavier elements to evolve then perhaps only the third or fourth generation of stars (and later ones) are capable of supporting life.

eburacum45
2012-Dec-06, 12:26 PM
[Another factor not considered in the Drake equation is that the amount of carbon and other heavier elements produced by nuclear synthesis in stars would have been too small during the first couple of billion years. Also these heavier elements, necessary for the formation of terrestrial planets like Earth, are released by supernovae, stars which already existed for a very long time. So if life requires these heavier elements to evolve then perhaps only the third or fourth generation of stars (and later ones) are capable of supporting life.

That's right. Additionally, the steady build-up of heavier elements in the Galaxy as a whole means that planets will be getting heavier on average; if life tends to evolve on Earth-like terrestrials (which is far from certain), then in future these smaller planets might be out-numbered by more massive planets. The period in which life is most likely to emerge might already have passed.

eburacum45
2012-Dec-06, 12:31 PM
Let's say you're an alien a couple hundred light years away from us. You know Earth has an industrial civilization and decide it's time for us to go. Can you absolutely guarantee that in the centuries your weapons would be traveling here we won't detect them and perhaps develop our own and fire back?
A truly ancient and successful civilisation could plant a number of autonomous weapons in each system with life, ready to eliminate the first signs of industrial capability. Or. maybe, primed to act when the first interstellar spacecraft are built (as per Pellegrino and Zebrowski's The Killing Star (http://en.wikipedia.org/wiki/The_Killing_Star)).

MarianoRF
2012-Dec-06, 12:31 PM
It's a comforting thought that we might be protected from the alien conquistadors by these vast distances. That's been a theory of mine for some time, but I've lately changed my tune.

I admit to not having studied in detail what we can reasonably conjecture about the possibility of interstellar travel (aha, something else to research). Is the 70,000 years is based on how long it would take a chemically-power rocket to get there after accelerating to 40,000 mph? Don't you suppose that technology a couple of centuries from now could do a heck of lot better than that?

At one time, the only way to get to from the East Coast to California was to sail around the horn or to ride across the land in an animal-pulled wagon. Both possibilities took many months of travel. Recently (1990) the SR-71 "Blackbird" made the trip in under two hours. I know that's just an analogy, but the point is that technology will not stand still.

I know exactly what you mean, and the point behind that. I know that tech is always improving, but we are talking about the vastness of space, endless distances. It's an enviornment where the speed of light is slow, because even travelling at that speed (if that day ever comes), you would still need 100.000 years just to span across our own galaxy. What about the others? Andromeda: 2 millons light-years. Which living-entity can stand that amount of time? I can't imagine it.

Let's think of our nearest star: Proxima Centauri. Travelling at the speed of light, 4.3 years (one way). It sounds "better" than 100.000, right? but think for a moment: who can stand 8 years (round-trip) seeing nothing else than blackness through the window? in a reduced size spaceship, where probably there's nothing much to do, just waiting to arrive... it's insane for human mind.

My conclussion: even travelling at light-speed, the vastness of space can't be shortened. Distances involved are so so enormous that even light-speed is slow, thus making unfeasible any kind of human-trip, and we are talking about the nearest star. What about other stars then?

MarianoRF
2012-Dec-06, 12:56 PM
Back to the subject, given a deliberative and unemotional intelligence with superior technology, I would expect vigilance concerning the possibility of a threat but not preemptive annihilation as a solution. Call me a dreamer, but we haven't been wiped out by the aliens yet.

One can easily ask: is there an intelligence with superior tech? is there an alien advance life-form? or there's nothing at all? because you see, this "Star Trek" sci-fi story that we are discussing, maybe never happened, and may never will.
Personally, (besides equations, formulas, etc) I do think that there's life out there, but not advanced, just bacteria/uni-cellular or another simple life form. I don't expect some Earth like civilization, because the events that lead to our existence here, are quite difficult to happen in another place.

eburacum45
2012-Dec-06, 01:34 PM
There are certain possible solutions to the distance problem.

The first, and perhaps least likely, is the very-fast sublight ship. If we could build very fast ships then time dilation would reduce the travel time. Some interesting methods of travelling more quickly have been proposed, such as Jordin Kare's Sailbeam concept coupled with Zubrin's magsail brake; but these sort of very fast ships are very energy hungry animals.

A second solution is the generation ship; a long, slow trip with a breeding population on board, waiting to fulfil their destiny at the destination after many generations have passed. The energy requirements for these vast, slow ships are also massive, and could easily exceed the energy requirements for the faster ships.

A third solution, sleeper ships, that is to say placing the passengers and crew in hibernation, might not be possible for humans, although I suspect that it will be possible long before we are ready to build any starships. On the other hand, even if it is impossible for humans, hibernation might be commonplace among certain alien species. Perhaps only those species which are capable of hibernation would ever colonise the galaxy.

A fourth solution involves extending the life-span of the space traveller until these decades or centuries of flight are trivial concerns. It may not be possible to extend human lifespans in this way, although I suspect that it will be possible long before we are ready to build any starships. On the other hand, even if it is impossible for humans, life extension might be commonplace among certain alien species. Perhaps only those species which can extend their lifespan would ever colonise the galaxy.

A fifth solution involves uploading the mind state of the traveller into a computer substrate. The uploaded personalities could be suspended in the database and reactivated on arrival. It may not be possible ever to upload human mindstates in this way, or it might take a long time to perfect this sort of technology. Maybe uploading technolgy will be even further in the future than the first starships; but I'm just guessing here. On the other hand, even if it is impossible to upload humans, those species which have the sort of mental architecture which allows uploading might be the only ones to colonise the galaxy.

A sixth solution involves wholly artificially intelligent entities. If we can somehow create AIs, they might colonise the galaxy for us. Or in spite of us. Even if we never develop AI, other alien species might. Perhaps alien AIs would be so alien that we wouldn't even recognise them as sentient; other threads have expolred this theme.

A seventh solution proposes some kind of faster-than-light travel; everything seems to rule this out as far as I can see, so we'll provisionally ignore this one...

In short there are plenty of solutions to the problem of interstellar flight, and even if humans can't solve them, others might. We would, of course, tend to encounter those species which sucessfully solve these problems. I think at least some, and perhaps several of these solutions are feasable, and more than one might be used by any given advanced civilisation.

IsaacKuo
2012-Dec-06, 03:29 PM
Another important solution to the distance problem is fractional c propulsion, and realizing that the distances are not ridiculously far. Using sailbeam propulsion, or something similar, speeds greater tha .5c are plausible and far more affordable than time dilated near-c propulsion. Speeds of .3c are even more affordable.

And yet, even at only .3c a 4.3 light year trip is a reasonable 15 year journey. A person leaving at age 25 could arrive at age 40. There would be no shortage of volunteers for such a mission!

Of course, we're speculating on alien civilizations. Maybe some aliens have shorter natural lifespans. Maybe some aliens have longer natural lifespans. Looking at our own example, and looking at other life forms on Earth, both are plausible. So, even if interstellar journey time may be a plausible barrier for some alien civilizations, it wouldn't be a plausible barrier for others.

This is a case where looking at the average is not good enough. For example, suppose the average technological species has a natural lifespan of 5 years and no natural "hibernation" capability, but 10% of them have a natural "hibernation" capability which helps them survive long winters? (Maybe they live on planets with much longer years than ours, with a more elliptical orbit.) Maybe those guys have an easier time going interplanetary and interstellar, because they can naturally shut down their bodies into a state with minimal life support requirements. If you just look at the average, then you mistakenly think interstellar travel just takes too long. But in fact, there's a good fraction of technological species for which interstellar travel is no big deal.

MarianoRF
2012-Dec-06, 04:51 PM
Back to the original topic, in my opinion, we are the only "intelligent" civilization in the Cosmos. As I said before, I do think there's life out there, but simple one: bacteria and uni-cellular microbian life.

MarianoRF
2012-Dec-06, 04:55 PM
Alien intelligence would have to be in our cosmic back yard to be aware of our recent nuclear proliferation. If they were a mere 70 ly away, they would not quite yet be able to detect any development of nuclear weapons on Earth since they would be studying us as we were 70 years ago. It is highly unlikely there is a civilization even as developed as us that near.

Very good point! Now... "near" is quite relative, for me 70 ly is a tremendous distance, very far away.

Selfsim
2012-Dec-06, 08:04 PM
Another factor not considered in the Drake equation is that the amount of carbon and other heavier elements produced by nuclear synthesis in stars would have been too small during the first couple of billion years. Also these heavier elements, necessary for the formation of terrestrial planets like Earth, are released by supernovae, stars which already existed for a very long time. So if life requires these heavier elements to evolve then perhaps only the third or fourth generation of stars (and later ones) are capable of supporting life.Interestingly, an observational study (http://phys.org/news/2012-12-stars-universe-million-years.html) of a distant quasar has just been published. From the article: It was found to show no spectrographic signs of the heavy elements oxygen, silicon, iron or magnesium. (It was around when the universe was only 750 million years old). Explaining the absence of theses elements resulted in a confirmation that the spectrum indeed, was devoid of these elements (ie: there were no other explanations known). They're now looking for more of these types.

Until this observation, objects of less than 11 billion years old, all exhibited heavy element spectra.

However, some caution may be needed in 'inferring' too much from this. Quasar light has some unexpected characteristics, (like showing no signs of expected time dilation), which are yet to be explained.

TooMany
2012-Dec-06, 09:19 PM
Let's steer clear of political philosophies and politicians. It is prudent to assume that the diversity of attitudes, motivations, and philosophies across all intelligent species in the galaxy will be at least as broad as we see within our own species.

We are required to steer clear because it's a highly emotional topic. Nevertheless, motivation and behavior is relevant to speculation about alien civilization. I agree that's it's quite likely that attitudes and motivations like are own will also exist in other species as a natural result of evolution. But consider this.

We as humans have been very successful at manipulating our environment for our own benefit to an extent that vastly exceeds that of any other organism on earth. Just as we have manipulated the environment for our betterment, it is foreseeable that we will manipulate ourselves or more likely our inorganic, artificially-intelligent progeny. Therefore we should not conclude that aliens who have far exceeded us technologically should still be driven (as much as we are) by primitive drives like fear or domination.

Something I have come to realize about us humans is that although we are capable of logical thought, quite often our logical capabilities are subservient to our more primitive emotions and irrational beliefs. This happens all the time and I think many people are not aware of it. People will hurl logical arguments until they turn blue in defense of things that they simple feel or believe, but can be shown to be objectively irrational. Typically it is useless to appeal to logic and facts to get people to change views that are based on their feelings or beliefs.

Anyhow, we should not assume that aliens will fail to transcend these remnants of biological evolution. Personally I'm not a worried at all that the aliens are going to invade.



OTOH pre-emptive attack may be unnecessary, e.g. because the aliens know how far ahead they are and how long it will take us to become a threat and they are confident of their ability to manage the potential threat we pose by other means.


That's my conclusion. After all, as soon as they are able to launch autonomous, self-reproducing interstellar probes, they can set up a warning system that can practically guarantee their safety.



This may not be applicable if the technological singularity hypothesis is correct.


Can you explain?



It's noteworthy that humans are generally averse to the pre-emptive attack solution, even when game theorists tell them it's the rational thing to do. This probably due to our inheritance as social animals. The aversion is notably weaker when dealing with out-group strangers, though.


Is the game theorist's conclusion really accurate? It's a highly simplified model. Pre-emptive attack may seem like the safest solution, but in the real world things are much more complex. The pre-emptive attack may backfire. Just look at the history of the last few decades and the efforts of governments to manipulate foreign situations. These efforts have repeatedly backfired or at least resulted in serious unforeseen consequences.

There is great advantage to cooperation. Modern civilization would be impossible with this social trust we possess that allows us to risk pre-emptive attack in the hope of mutual benefit. Your observation that it tends to be intra-tribal is accurate.



Also, we don't know how far away we are from posing a threat. If the singularity hypothesis is correct it may be decades, if not, it may be millenia.


But you can also argue that the singularity will make us much less of a threat for we can dispense with the reptilian brain that we imagine exists in advanced civilizations that threaten us.



To return to the thread title, what exactly is the Drake equation? I have seen multiple versions of it. For example, the one in the linked article differs from that in Wikipedia. None of them seems quite right to me. Most debate revolves around the values of the numbers, but the form of the equation bothers me more. It assumes an infinitely old steady-state universe. That it assumes steady state is attested by the fact that it treats as constant several quantities that are known not to be constant. The rate at which stars form has varied with time and it's likely that the nature of the concurrently formed planets has changed over the life of the galaxy too. That it assumes an infinitely old galaxy is shown by the its use of fractions such as fi, the fraction of life-bearing worlds that ultimately evolve intelligent life. If the galaxy is only finitely old (and not very old compared to the lifetime of stars, and it's not) then it matters how long it takes for intelligent life to evolve. You get a very different result if the mean value is, say, 1010 years than if it is, say, 109 years.

But we do know in our case that it took 4*109 and many stars in the galaxy are much older than that. I would expect that a more refined form of the Drake equation would take these things into consideration.

Van Rijn
2012-Dec-06, 11:39 PM
I think there are various issues with blanket annihilation of other civilizations. Let's say you're an alien a couple hundred light years away from us. You know Earth has an industrial civilization and decide it's time for us to go. Can you absolutely guarantee that in the centuries your weapons would be traveling here we won't detect them and perhaps develop our own and fire back? Slim chance, perhaps, but are you willing to bet your species on it? Better watch out for any other civilizations that may be watching, too; you've now not only announced your existence but that you're out to kill them all.


Which is why it would make more sense for a paranoid species to destroy any sign of life, and never give it a chance to develop into anything potentially dangerous.

Van Rijn
2012-Dec-06, 11:40 PM
A truly ancient and successful civilisation could plant a number of autonomous weapons in each system with life, ready to eliminate the first signs of industrial capability. Or. maybe, primed to act when the first interstellar spacecraft are built (as per Pellegrino and Zebrowski's The Killing Star (http://en.wikipedia.org/wiki/The_Killing_Star)).

But why would they wait?

whimsyfree
2012-Dec-07, 01:39 AM
Which is why it would make more sense for a paranoid species to destroy any sign of life, and never give it a chance to develop into anything potentially dangerous.

That's a good point and I don't have a good reply other than to posit that such aliens might have motivations in addition to paranoia. For example, they might be nature-loving life-affirming paranoid aliens. :) That might sound silly but humans are not too far from that. Many people would want to at least consider our military options if we encountered an intelligent alien species that wasn't obviously overwhelmingly superior. Hardly anyone would think of sterilizing a planet just because it had algae or even trees and bugs.

Elukka made another point: that the aliens might be worried about the wider consequences of their actions. That depends on their having a fairly specific level of ignorance though: they know of other life in the galaxy but don't know whether there are behavioral norms for intelligent species.

TooMany
2012-Dec-07, 02:31 AM
They are watching us now. We are pathetic as a threat and will be for long enough for us to transcend our stupid ideas like dominating alien civilizations or gobbling up stellar real estate.

Of course if we actually look like a threat, we're toast.

Van Rijn
2012-Dec-07, 09:39 AM
That's a good point and I don't have a good reply other than to posit that such aliens might have motivations in addition to paranoia. For example, they might be nature-loving life-affirming paranoid aliens. :) That might sound silly but humans are not too far from that. Many people would want to at least consider our military options if we encountered an intelligent alien species that wasn't obviously overwhelmingly superior. Hardly anyone would think of sterilizing a planet just because it had algae or even trees and bugs.

Elukka made another point: that the aliens might be worried about the wider consequences of their actions. That depends on their having a fairly specific level of ignorance though: they know of other life in the galaxy but don't know whether there are behavioral norms for intelligent species.

My main issue is with the idea that we today (or a civilization at our current level of development) would be especially at risk of being attacked by paranoid aliens. If there were any species interested in preemptive attacks, it would make so much more sense for them to have already done it, whether they're looking for any life or if they're only attacking technological species. Attacking after it is possible there could be dispersal from the home planet could create eventual enemies where there might have never been one.

eburacum45
2012-Dec-07, 08:23 PM
My main issue is with the idea that we today (or a civilization at our current level of development) would be especially at risk of being attacked by paranoid aliens. If there were any species interested in preemptive attacks, it would make so much more sense for them to have already done it, whether they're looking for any life or if they're only attacking technological species. Attacking after it is possible there could be dispersal from the home planet could create eventual enemies where there might have never been one.

Brandon Carter might have an argument that explains why the aliens haven't attacked yet. The Doomsday argument suggests that we only have a limited amount of time left as a species.
http://en.wikipedia.org/wiki/Brandon_Carter%27s_Doomsday_Argument

Perhaps they only have to watch and wait and we'll die out by ourselves. If by any chance we survive the Carter Catastrophe, then they'll step in with the relativistic kinetic missiles.

Van Rijn
2012-Dec-07, 08:59 PM
Perhaps they only have to watch and wait and we'll die out by ourselves. If by any chance we survive the Carter Catastrophe, then they'll step in with the relativistic kinetic missiles.

What criteria would they use to decide we had survived the Carter Catastrophe?

Anyway, this doesn't make sense to me. The primary issue that makes it risky for a paranoid species to wait also makes it less likely there would be any one catastrophe that would wipe out the species: Namely, spreading off the home planet. If ET waits to attack after we've dispersed, they've got a much more difficult task and they might miss somebody. Better to attack before there was any possibility we could launch any spacecraft.

whimsyfree
2012-Dec-07, 10:05 PM
Brandon Carter might have an argument that explains why the aliens haven't attacked yet. The Doomsday argument suggests that we only have a limited amount of time left as a species.
http://en.wikipedia.org/wiki/Brandon_Carter%27s_Doomsday_Argument


Take me word for it as someone with a master's in statistics: his argument makes no sense at all.


What criteria would they use to decide we had survived the Carter Catastrophe?


There isn't any. Carter's argument makes the same prediction all the time, which is one clue that it is bunkum.


Anyway, this doesn't make sense to me. The primary issue that makes it risky for a paranoid species to wait also makes it less likely there would be any one catastrophe that would wipe out the species: Namely, spreading off the home planet. If ET waits to attack after we've dispersed, they've got a much more difficult task and they might miss somebody. Better to attack before there was any possibility we could launch any spacecraft.

What makes you think we're about to spread off the home planet?

Actually I agree with you. The lack of any manifestations of homicidal (or any other sort of) aliens so far is an indication they don't exist in our corner of the universe. This shouldn't surprise. I plugged what I thought were reasonable guesstimates into an online Drake calculator (http://www.pbs.org/lifebeyondearth/listening/drake.html) and got 0.2.

TooMany
2012-Dec-07, 11:26 PM
The lack of any manifestations of homicidal (or any other sort of) aliens so far is an indication they don't exist in our corner of the universe.


I have to disagree. The homicidal aliens fantasy is a refection of our immature social structure and animal brains. Both of these would be outgrown prior to significant interstellar travel. Another implicit assumption is that the aliens either want to be seen or are too stupid to avoid being seen.

If a single advanced civilization ever existed (that reached a few centuries beyond our technology) they may well have already explored the entire galaxy and set up monitoring throughout. If they do have any interest in us, it's hard to imagine why they would interfere with us. To bring us their religion or steal our women? They certainly would have little to fear from us.



This shouldn't surprise. I plugged what I thought were reasonable guesstimates into an online Drake calculator (http://www.pbs.org/lifebeyondearth/listening/drake.html) and got 0.2.

As it says, many of those parameters are anybody's guess and the results can easily change by 106 depending on the guesses. The strangest possibility that I can image is that we are the only civilization that has ever occurred. Second strangest is that no civilization ever launches interstellar craft nor invents autonomous self-reproducing explorers.

whimsyfree
2012-Dec-07, 11:49 PM
We are required to steer clear because it's a highly emotional topic. Nevertheless, motivation and behavior is relevant to speculation about alien civilization. I agree that's it's quite likely that attitudes and motivations like are own will also exist in other species as a natural result of evolution.


Right. Our motivations are built in by evolution. They come from our heritage as animals and we share them, in some form, with other animals. Animals flee or fight when confronted by danger and compete for resources (food, territory, mates) because failing to do so reduces their contribution to future generations.


But consider this.

We as humans have been very successful at manipulating our environment for our own benefit to an extent that vastly exceeds that of any other organism on earth. Just as we have manipulated the environment for our betterment, it is foreseeable that we will manipulate ourselves or more likely our inorganic, artificially-intelligent progeny. Therefore we should not conclude that aliens who have far exceeded us technologically should still be driven (as much as we are) by primitive drives like fear or domination.


I don't know what would motivate super-intelligent AI. Without motivation such an entity is not an independent actor. It's a big box with blinking lights on it that does nothing. Initially its motivations would derive from its creators. Being animals it is most likely they will build the AI to help them out-compete or eliminate their rivals.

I know that natural selection would apply to them. Those that protect themselves will survive longer than those that passively submit to destruction; those with the will to dominate will be the ones that do so; and those that reproduce and spread themselves the most will be the most common and widespread.

The assumption that the relocation of the game of life from a carbon-based to a silicon-based substrate will render obsolete all the old survival strategies seems too hopeful to me.


Something I have come to realize about us humans is that although we are capable of logical thought, quite often our logical capabilities are subservient to our more primitive emotions and irrational beliefs. This happens all the time and I think many people are not aware of it. People will hurl logical arguments until they turn blue in defense of things that they simple feel or believe, but can be shown to be objectively irrational. Typically it is useless to appeal to logic and facts to get people to change views that are based on their feelings or beliefs.


True. You see that all the time. People who were very taken with Star Trek or somesuch at an early age are insistent that the focus of space science must be manned missions and the near-term human settlement of other planets.


Anyhow, we should not assume that aliens will fail to transcend these remnants of biological evolution. Personally I'm not a worried at all that the aliens are going to invade.


I'm not worried in the least. I don't think there are any aliens nearby, I don't think interstellar conquest is viable, and I think if paranoia was their main driving force their would have killed us already.



Can you explain?


The singularity supposedly leads to every possible technology being rapidly discovered, which implies whatever technologies aliens find threatening will rapidly be discovered. If I forecast when meat-bag humans will be ready to launch an interstellar probe (or weapon) I say centuries, if ever. A post-human super-intelligence OTOH will know everything it needs to about building the fastest, best possible inter-stellar craft and so it can start straight away if it wants to.



Is the game theorist's conclusion really accurate? It's a highly simplified model. Pre-emptive attack may seem like the safest solution, but in the real world things are much more complex. The pre-emptive attack may backfire. Just look at the history of the last few decades and the efforts of governments to manipulate foreign situations. These efforts have repeatedly backfired or at least resulted in serious unforeseen consequences.


You're right, the game theorists solution is correct in their model but their model is grossly simplified. For example, in the classic prisoner's dilemma it's all about getting the shortest time in jail. In reality there's a qualitative as well as quantitative aspect to jail time, and "dogs" aren't popular in prison. In the great natural experiment of evolution, pre-emptive attacks rarely seem to be the preferred solution. There are all sorts of reasons for this -- violence is risky even for the strong, usually both parties know which is stronger so the weaker one backs down, ultimately biological success is reproduction not survival, life for social animals isn't just a series of isolated one-on-one confrontations, etc. Mostly those don't apply to interactions with aliens though.



But you can also argue that the singularity will make us much less of a threat for we can dispense with the reptilian brain that we imagine exists in advanced civilizations that threaten us.


Without the singularity will we ever advance far enough to be a threat? and why are you so down on the reptilian brain? Animals are aggressive, dominating, territorial etc not because of some defect but because that's the best strategy for them in the context in which they evolved. The feelings humans sometimes have of loyalty, love, trust, self-sacrifice, kinship with all nature etc are just another part of our animal heritage. Why will the transition to machine intelligence eliminate all the evolved tendencies that are socially unpopular while keeping the ones we approve of (in others)?


But we do know in our case that it took 4*109 and many stars in the galaxy are much older than that. I would expect that a more refined form of the Drake equation would take these things into consideration.

Our having developed after that long is potentially consistent with either mean. Moreover there is very little information to be had in the one case we have already because it's not an independent observation. v. Anthropic principle.

TooMany
2012-Dec-08, 02:48 AM
I don't know what would motivate super-intelligent AI. Without motivation such an entity is not an independent actor. It's a big box with blinking lights on it that does nothing. Initially its motivations would derive from its creators. Being animals it is most likely they will build the AI to help them out-compete or eliminate their rivals.

I know that natural selection would apply to them. Those that protect themselves will survive longer than those that passively submit to destruction; those with the will to dominate will be the ones that do so; and those that reproduce and spread themselves the most will be the most common and widespread.

The assumption that the relocation of the game of life from a carbon-based to a silicon-based substrate will render obsolete all the old survival strategies seems too hopeful to me.

...

Without the singularity will we ever advance far enough to be a threat? and why are you so down on the reptilian brain? Animals are aggressive, dominating, territorial etc not because of some defect but because that's the best strategy for them in the context in which they evolved. The feelings humans sometimes have of loyalty, love, trust, self-sacrifice, kinship with all nature etc are just another part of our animal heritage. Why will the transition to machine intelligence eliminate all the evolved tendencies that are socially unpopular while keeping the ones we approve of (in others)?


Biological life on Earth involves a competition for resources. We are high on the food chain so we eat plants and kill and eat other animals. Our cleverness makes us dangerous to one another. It's easier to steal the food someone else has gathered than gather it yourself. So, we have a mix of successful behaviors. We have both cooperative and competitive behaviors. Again, this has a lot to do with resources. It's all pretty complex.

Some of our evolved behaviors nearly threaten our own existence. I'm thinking of wars and development of powerful weapons. What underlies these things is also a competition for resources and desire for dominance (which is arguably the result of competition for resources). As I mentioned, much of our behavior is not based on the higher functions that have most recently evolved. That new symbolic thinking capability often (if not mostly) still sits in the passenger seat.

However when we are starting fresh in silicon, we get to make some choices instead of waiting for some natural selection process to occur. What will we choose to motivate AI? The nature of further evolution may be rather different from the tooth and nail evolution we are accustomed thinking about. I can only guess what AI is going to want, but we are not required to build-in something that makes AI#1 try to kill or dominate AI#2. We do not have to create AI in our exact image. If we have any sense, we won't

So that's one reason I have some hope. The second is this: as our technology becomes mature, resources will cease to be an issue. There is plenty of elemental matter around and we will be able to get whatever we need from our solar system and make whatever we want with. We have no evidence that there is some "unobtainium" that we would need from another system. This changes things. Competition for resources becomes obsolete. What takes over? I don't know exactly but whatever AI becomes, I don't see much reason for him to be predatory.

On the other hand, AI must defend himself from threats, but that should be relatively easy. One way to assure safety is to send a fleet of autonomous self-replicating AIs in all directions to monitor the surrounding systems for potential trouble. Still using the argument I've already tried to make, a serious threat is unlikely.



I'm not worried in the least. I don't think there are any aliens nearby, I don't think interstellar conquest is viable, and I think if paranoia was their main driving force their would have killed us already.


I think interstellar conquest is possible, but pointless.



The singularity supposedly leads to every possible technology being rapidly discovered, which implies whatever technologies aliens find threatening will rapidly be discovered. If I forecast when meat-bag humans will be ready to launch an interstellar probe (or weapon) I say centuries, if ever. A post-human super-intelligence OTOH will know everything it needs to about building the fastest, best possible inter-stellar craft and so it can start straight away if it wants to.


AI could become threatening, but the motive is missing because he would already be self-sufficient. You would have to hypothesize a psychotic AI that just likes to destroy or dominate for no practical gain.

Van Rijn
2012-Dec-08, 09:34 AM
What makes you think we're about to spread off the home planet?


Because of the changes of enabling technology for one, which I think will dramatically reduce support costs in the next few decades. But the issue for this thread is not whether we will, but that we have the potential of doing it, and paranoid ET can't count on us NOT doing it.

eburacum45
2012-Dec-08, 10:27 AM
The Doomsday argument suggests that we only have a limited amount of time left as a species.
http://en.wikipedia.org/wiki/Brandon...msday_Argument

Take me word for it as someone with a master's in statistics: his argument makes no sense at all.
Oh, I agree, for (what I like to think are) good reasons of my own. We've had a few threads on the subject on this very forum. I'd like to hear your argument, perhaps in a new thread. It could well add new information to that particular long-running debate.

Gomar
2012-Dec-10, 03:28 AM
Your logic escapes me... I can conclude that it just won't ever happen?

If you had 250million years to wait for some losing NFL team to win, and they dont, you can indeed
conclude that it wont ever happen.
No aliens have settled nor colonized Earth during the time the dinosaurs roamed the planet;
which is enough time for all members here to win the Powerball jackpot of $550m 1000 times.
Take the last 50,000 years of homo sapien existence, or even 5000 years of culture, nope, still
no green aliens with tails and bug eyes walking around in Paris.

Elukka
2012-Dec-10, 05:42 PM
They would have no reason to colonize Earth unless it just happened that the environment is ideal for them and the biospheres happen to be compatible. I don't think it's particularly likely they'd come to live here, even if they did visit.

Luckmeister
2012-Dec-11, 04:34 AM
If you had 250million years to wait for some losing NFL team to win, and they dont, you can indeed
conclude that it wont ever happen.
No aliens have settled nor colonized Earth during the time the dinosaurs roamed the planet;
which is enough time for all members here to win the Powerball jackpot of $550m 1000 times.
Take the last 50,000 years of homo sapien existence, or even 5000 years of culture, nope, still
no green aliens with tails and bug eyes walking around in Paris.

We can't say ET has never visited, only that they didn't leave unmistakable evidence if they did. I can agree that it's unlikely they will drop in but I can't conclude from what you say that it can never happen. There's no practical reason why I need to make that determination so I have no problem leaving it just as a slim possibility.

ETA: Perhaps the only other current intelligent life in the galaxy just happens by rare chance to be on an Earthlike planet 12 ly away from us, they are just beginning to explore the neighborhood and they will be here in a few years. Highly unlikely?.... Yes. Impossible?.... No.

Also, you seem to consider it a given that if they had visited, they would have colonized. I don't see why that need be the case. Our environment may not support their life enough to make that feasible. We cannot make assumptions as to their needs or desires.

ASTRO BOY
2012-Dec-11, 05:10 AM
If you had 250million years to wait for some losing NFL team to win, and they dont, you can indeed
conclude that it wont ever happen.
No aliens have settled nor colonized Earth during the time the dinosaurs roamed the planet;
which is enough time for all members here to win the Powerball jackpot of $550m 1000 times.
Take the last 50,000 years of homo sapien existence, or even 5000 years of culture, nope, still
no green aliens with tails and bug eyes walking around in Paris.



Time and distance are two formidable barriers to meeting ET.

ASTRO BOY
2012-Dec-14, 08:17 PM
I agree with you, mostly with Interstellar travel is impossible. Since we are talking about extreme vast distances here, no one could make a journey of 70000 years or more to our nearest star Proxima Centauri, and not even to mention intergalactic travel.

So, maybe there are hundreds, thousands... even millions of civilizations out there... but with those extreme vast distances, it's impossible for all of us to meet each other. Maybe these distances, are a barrier of some kind to protect us from each other.


Time and distance are the two great barriers in meeting up with our ET cousins most certainly......but by the same token, time is also beneficial to us in gaining the technology necessary to achieve inter-stellar travel.

TooMany
2012-Dec-14, 10:08 PM
Also, you seem to consider it a given that if they had visited, they would have colonized. I don't see why that need be the case. Our environment may not support their life enough to make that feasible. We cannot make assumptions as to their needs or desires.

No we cannot. I would argue they are unlikely to still be a biological race if they have traveled between the stars. Biological intelligence will likely be obsolete before interstellar travel becomes possible.