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filrabat
2006-May-28, 07:16 PM
This is Largely a continuation of this thread from last year (www.bautforum.com/showthread.php?t=18814). I decided upon a separate thread because I never saw a comprehensive explanation of why certain Drake Equation values had the values they did, of which my calculations are a variant. Furthermore, as alluded to in this post (www.bautforum.com/showthread.php?p=441892#post441892) on the same thread, Jared Diamond argues in his book [i]Guns, Germs, and Steel[/url] that a geography heavily influences which sections of a planet develop high technology the quickest. Having bought a copy of this book myself (not to mention possessing a lot of academic background in Geography) I can certainly vouch that Diamond's thesis is compelling, though provoking,and even mostly agreeabe IMO (even if not 100% convincing in all details). From here, it's easy for a geography minor (with considerable graduate level credit in geography as well) to see that the landform patterns of continents can determine how quickly it develops technology - certainly relevant for technically advanced alien life.

Further geographic aspects will be discussed on another thread, to be posted shortly. For now, I want to share my view of the factors influencing how amiable a solar system may be to life. The actual comprehensive calculation estimates will be in the next post

(STARS IN THE GALAXY- Estimates vary, but I will go with the highest figure I heard: 500 Billion ( Royal Greenwich Observatory (www.nmm.ac.uk/server/show/ConWebDoc.20495). I assume that includes everything from M-Class (Red Dwarfs) to Enormous O- Class Stars (very hot, very fast burning, Blue stars). Our sun is Class G.

Stars outside the core of the galaxy - I (?) We (?) could also be wrong, but I heard from an astronomy professor that this is about 2/3 of all stars.

Such Stars that are in the Galactic Habitable Zone - This is the zone of the galaxy where elements heavier than Helium tend to be most abundant. Iím not too sure about this, but arbitrarily, I will say itís about 10% of the Galactic Radius (i.e. the 10% of stars most likely to have planets that could harbor life given proper conditions)


Stars on the Main Sequence - These stars burn hydrogen for fuel - 85% of all such stars ( Wikipedia ( en.wikipedia.org/wiki/Stellar_classification)). Stars not on the main sequence are old giant stars that swallowed most of their inner solar system. (as our sun will do 5 billion years from now). Once a star leaves the main sequence, it will start burning Helium into Carbon and Oxygen. These reactions may last for any amount of time up to perhaps a few billion years at most, depending on the mass of the star. Our sun is forecast to be in a Helium-burning red giant for about a billion years, after which it will shed its atmosphere and become a white dwarf. For this reason, stars that have left the main sequence are not good candidates for life, even on the moons of its outer planets.

Stars that are Class G or K - The cooler and ďredderĒ the star, the longer it remains on the main sequence (barring the obvious exception of red giants). The previously-mentioned O-Class (very hot blue) stars will likely last only a few dozen million years, barely enough time for star dust to coalesce into planets. Furthermore, hotter stars emit enormous quantities of ionizing radiation (UV or higher). In fact, large stars tend to emit the bulk of their radiation in the UV band. Stars in classes B (a lower level blue-white) and A (white) suffer similarly, though to not to the extreme extent as O-class ones. Nevertheless, these stars will last only a few billion years at most. This may be long enough for simple life and perhaps even the simplest animal life to form, but not likely enough to allow technologically advanced life to arise (unless its evolution is incredibly quick). F-class (white) is likely to last from 4 to 6 billion years, certainly enough to give rise to complex life (perhaps even intelligent life). Unfortunately, in the Earth-term timeline at least, a white sun will start to leave the main sequence just when intelligence does arise. Timing truly is everything. So while itís certainly possible and even plausible for a white sun to have a technically advanced civilization, I donít find it particularly likely.

By contrast, the red dwarf (M-class) stars will be around for billions of years, much more than enough time for life to form. Furthermore, they do not emit as much ionizing radiation as even our own sun (G-Class), another factor favoring a life-friendly environment. Unfortunately, the cooler the star, the narrower its life zone. I personally interpret this fact to mean that a red starís HZ will be less likely to contain a planet of any sort, let alone one with other preconditions necessary for life to have a chance on it. Even if the red sunís HZ does have a planet with the appropriate gravity, atmospheric and other characteristics, odds are fairly high that the planet will suffer from ďrotation lockĒ (one face always facing the star). This means one side will be in eternal day or close to it (thus rendering it too hot) and one side will be in eternal night (rendering it too cold). However, there is still at least some chance other mitigating factors will come to play on such a planet (the hot spot over the planet may create atmospheric convection that creates winds, thus spreading heat more evenly over the planet). Obviously, a rotationally-locked planetís twilight zone could offer a happy medium in which life, and even intelligence can flourish in theory. However, as I will discuss later, such a planet will have a much more difficult time developing a sustainable high technology civilization, and even a high-end pre-industrial civilization.

For these reasons, I will cast my votes for G (yellow), K (orange), and low-level white stars as places favorable for advanced civilization to arise. If we include all G and K stars, plus about 1/3 of all F stars, these stars are about 22% of all stars in the galaxy ( Wikipedia ( en.wikipedia.org/wiki/Stellar_classification)). If M-class (red) stars - 78% of all stars - permit HZ planets without a rotation lock, then perhaps another 10 % of all stars (the hotter M-class ones) can be added to (though I admit this number is rather arbitrary). So we can say that as many as 33% of all stars could support a technical civilization, given other necessary planetary conditions listed above.

Such stars that are the appropriate age - If you are content with finding significant life in any form, you will likely find it around planets between two and five billion years old. This is certainly long enough for life to form an Oxygen atmosphere (strong evidence of life), though not necessarily sentient life. While I know of no proof that the following assumption is, in fact, true, for the sake of simplicity, I will assume that stars have formed at more or less equal rates over the course of at least the past 10 billion years. Within this assumption, it is relatively straight forward to calculate the expected proportion of stars that are between X and Y years old. This is done by dividing that starís present age by its expected life span (i.e. if we want to figure out what percentage of G2 class stars are between 2 and 5 billion years old, and we know such stars will likely last 10 billion years on the main sequence, then we can say that (5-2)/10 of all such stars are between 2 and 5 billion years old - or 30% of all G2 stars.

Such Stars That Are between 4.5 and 5.0 Billion Years Old - On the other hand, if you are interested only in life capable of extensive radio communication, then I believe you can use a variant of the above formula. For the sake of simplicity, allow me to use an Earth-Biased figure of 4.3 to 4.7 billion years old as the age of the stars we expect to find such worlds, regardless of spectral class (if you are dissatisfied with this bias, you can rework the formula using the target age you see fit). In this case (4.7 - 4.3)/10 equals 0.04. This means that within the appropriate target stars (low level F to high level M) we can plausibly claim that about 5% of all sun-like stars are in this age range. Admittedly, this is an earth-biased trait. We have no clue how quickly stars this age will give rise to technically advanced civilizations. We could have evolved ours slower than expected or more quickly. Thereís really no way to know at this time. Even so, 4.5 to 5.0 billion years does give us a proven time in which a planet COULD develop such a civilization. However, because the sun gradually swells and brightens as it gets older (I heard by about 1% every 100 million years), a life-bearing planet will likely undergo a ďheat deathĒ long before its star reaches the main sequence. Thus, I guesstimate that 5.5 billion years is usually the longest time frame in which a habitable planet could develop a civilization capable of radio communication. Even so, I will be conservative and stick with the 4.3 byo to 4.7 byo timeline and say that 4% of such stars are the optimal age to have a technical civilization, providing it has a continuously habitable planet.

Such stars with planets. Recently, itís been found that stars whose metal content is at least one-third that of the sun are somewhat likely to develop planets. Of these stars, I calculate that about 8.4% of such stars are actually found to have planets ( exoplanets.org ( exoplanets.org/metalicity.html))

Such stars whose planets are in Sufficiently Stable and Circular Orbits -At the time of this post, the Extrasolar Planets Encyclopedia ( http://exoplanet.eu/catalog-all.php?&mode=5&more=yes) lists 193 surveyed star systems found to have planets as of the date of this post, 60 of them have eccentricities of 0.1 or less known to contain at least one planet. Of these the majority are in orbits that are highly eccentric by Earth standards, reminiscent of what we think of as cometary orbits. Moderate degrees of eccentricity within a habitable zone for a sun-like star (say, from 0.9 to 1.3 AU; 1 AU = Sun-Earth distance) does not necessarily preclude life from forming but it does makes its development more difficult due to a more extreme climatic regime. Therefore, I will say that life will function and prosper much more readily when the orbital eccentricity is 0.1 (i.e. the difference between apehelion and parahelion is only 10%. Earthís eccentricity is around 0.02).


Such stars with roughly earth-size planets. Here is where we really truly enter the realm of speculation. Thanks to the discovery of Jupiter-like worlds (ďgas giantsĒ) in numerous inner portions of planetary systems, this is not as straight forward as it once seemed to be. Here, we have to use our own solar system as a framework, however imperfect a model it may be. Currently, there are two worlds whose mass is between 0.5 and 10 Earth Masses (the current theoretical optimum size, gravity, etc for which lifeís development is favorable due to the ability to hold atmospheres, plate tectonics, magnetic fields, etc.): Earth and Venus. Too little mass and the planet wonít be able to keep its atmosphere (and inevitably liquid water) for longer than a few billion years; too much mass and odds are fairly good that itíll retain hydrogen and helium, thereby adding more mass to the planet that allows it to trap more H and He - thus starting a cycle that transforms the planet into a gas giant. Based roughly on our own solar system, I will be rather liberal allow for 3 such planets out of a total of 9 revolving around such stars mentioned. This means 33% of the planets are estimated to be between 0.5 and 10 Earth Masses.


Stars Within the Continuous Habitable Zone. Itís been found that stars tend to brighten with age, even when they are not on the main sequence. This means the stars Habitable Zone will move outward with time. Many strongly believe that Venus was once within our sunís HZ until the sunís increasing brightness rendered the planet too hot to retain liquid water (although the lack of plate tectonics certainly deprived the planet of a carbonate-silicate cycle that could have trapped CO2 in its rocks, as is the case here on Earth). Earth, being further away, was spared this fate (although some say that its early atmosphere of methane, CO2, and other gases kept the planet warm in an otherwise cold place to be in the young sun days). Mars itself might have had liquid water and a fairly thick atmosphere at one time, which would have effectively rendered it in the HZ. As far as I can tell, HZ boundaries seems rather Earth-centric, and so the boundaries can only exist in a semi-arbitrary sense. In this case, I will go out on a limb and say that 1.5 terrestrial planets of appropriate size are likely to be found in the Continuous HZ, or 50% of all planets.

Such Stars whose planets had A Major Collision That Formed A Moon - It seems that collisions between planet sized bodies may be fairly common in the early solar system. Earth moon was almost certainly formed from such a collision, while some say that the moon Charon resulted from a similar collision with Pluto. Neptuneís radical axial tilt may have been the result of such a collision, though I believe this explanation is rather weak. Nevertheless, it seems that at least one solid body in a young solar system will experience such a collision, and thus has a real possibility of gaining at least a small satellite. Therefore, I will say that one of every three terrestrial planets will undergo such a cataclysm.

I believe this factor is important for a number of reasons: (a) it forms a body that stabilizes a planetís axial tilt over time (b) it thins out the planetís crust, thus allowing for more active volcanism, plate tectonics, and other geological processes necessary to take much CO2 from the atmosphere AND form a two-tiered land mass of continental and oceanic landmasses. Although Venus almost certainly has volcanism, it seems to have no plate tectonics. It is strongly believed that Venus has a very thick lithosphere (surface) compared to the earth, which makes for a more rigid surface. This in turn severely limits, if not eliminates, the formation of plates. It also renders volcanism in scattered spots throughout the planet, rather than concentrated in certain areas near plate boundaries as on earth. A Space Daily article addressing this issue said that if all the water in Earthís oceans were deposited on Venus, then these oceans would cover 90% of the planetís surface. As we will see later, this seriously limits a planetís ability to develop a technical civilization, though I donít think it will too badly impede life itself.

filrabat
2006-May-28, 07:37 PM
5E+11 5E+11
0.666666667 3.33333E+11
0.1 33333333333
0.85 28333333333
0.333333333 9444444444
0.3 2833333333
0.084 238000000
0.552147239 131411042.9
0.333333333 43803680.98
0.5 21901840.49
0.333333333 7,300,613.497 planets containing ANY kind of life, intelligent or not

5E+11 5E+11
0.666666667 3.33333E+11
0.1 33333333333
0.85 28333333333
0.333333333 9444444444
0.04 377777777.8
0.084 31733333.33
0.552147239 17521472.39
0.333333333 5840490.798
0.5 2920245.399
0.333333333 973415.1329 "Jurassic" worlds or any other whose most intelligent species is sub-sentient

5E+11 5E+11
0.666666667 3.33333E+11
0.1 33333333333
0.85 28333333333
0.333333333 9444444444
0.0000005 4722.222222
0.084 396.6666667
0.552147239 219.0184049
0.333333333 73.00613497
0.5 36.50306748
0.333333333 12.16768916 planets whose most intelligent species is within (but not over) 5000 years of current Western World techonolgical development.

I will stop here, since any specuation about odds of survival of nuclear war or other disaster is highly speculative even for human beings themselves, let alone aliens. I only seek to provide an arguably plausible framework within which the alien intelligent life issue can be answered.

Conclusion: While I think life itself is fairly common throughout this galaxy, and is likely common even among fairly nearby stars, I believe that advanced technical civilizations are quite rare, though not unreasonable to believe in.

filrabat
2006-May-28, 07:39 PM
Last years long thread How Many Intelligent Civilizations are in This Galaxy? (www.bautforum.com/showthread.php?t=18814) provides many previous posts that are relevant.

eburacum45
2006-May-28, 08:23 PM
There are plenty of assumptions you have made which are arguable, and much fun can be had arguing the details; but the conclusion you have reached seems to me to be a non-sequitur.

You have made an estimate of ~ 12 worlds with 'planets whose most intelligent species is within (but not over) 5000 years of current Western World techonolgical development'.
From this you conclude that 'advanced technical civilizations are quite rare, though not unreasonable to believe in'.

Because you have not considered civilisations more than 5000 years old, you have introduced a limitation that may not apply. If the average age of a civilisation is a million years, that increases the number of civilisations to 2400, all other things being equal.

filrabat
2006-May-28, 08:53 PM
There are plenty of assumptions you have made which are arguable, and much fun can be had arguing the details; but the conclusion you have reached seems to me to be a non-sequitur.

You have made an estimate of ~ 12 worlds with 'planets whose most intelligent species is within (but not over) 5000 years of current Western World techonolgical development'.
From this you conclude that 'advanced technical civilizations are quite rare, though not unreasonable to believe in'.

Because you have not considered civilisations more than 5000 years old, you have introduced a limitation that may not apply. If the average age of a civilisation is a million years, that increases the number of civilisations to 2400, all other things being equal.

I grant that it is a non-sequitor on its face, particularly regarding civilizations whose technology is ahead of current Earth-standard; most of all, those who are 1 million years ahead of us.

Perhaps it has to do with the meaning of "rare", which I admit is quite open-ended. Since I didn't bother to define it, I won't quibble too much about whose idea of "rare" ought to be accepted. Assuming you are correct, 2400 civilizations is quite a lot, though by my simplistic calculations still fairly far from Earth (about 941 LY)*.

If "rare" is defined as "not likely to make contact of any sort", then you probably have the stronger case, particularly with a million-year time frame (although I follow Carl Sagan in saying that a civilization a million years ahead of us is likely to be as much beyond us as we are beyond a macaque. Would we even recognize such a civilization. But that's just a minor quibble, and I don't want to pull the rug out from anyone.).

On the other hand if "rare" means "not likely to be spotted among stars that are less than 12th magnitude in Earth's sky", then "rare" could quite possibly still apply.

But at this point, I'm close to breaking my promise not to quibble. So I'll allow you your well-made point

HenrikOlsen
2006-May-28, 09:07 PM
Answering just the question asked in the subject of this thread, the answer is a clear and simple 0.

A planet that is contained in a star is not inhabitable (and will very soon cease to be a planet at all). :)

kmarinas86
2006-May-28, 09:10 PM
What if one of the intelligent species colonizes 3 planets and 9 moons, that would be 12 worlds just by itself. If we count Russia's Venera, the Mars spacecrafts, and the Huygens mission, we have 3 planets and 2 moons, 5 worlds for Humanity alone!

Open you mind! Our current evolution is a catalyst for interplanetary base establishment. Some day, we will have "base that are belong to us" - hehe. Evolution is a primitive step, with AI, we can invent a faster process which only takes thousands of years. It's a new frontier.

http://www.google.com/search?hl=en&q=maxis+spore

eburacum45
2006-May-28, 10:06 PM
One of the factors in your calculation which strikes me as a little dubious is the proportion of G class and K class stars. If you accept the high estimate of the number of stars in the galaxy (500 billion) you should realise that the high estimates almost certainly include many more very small red dwarfs. The estimate of the population of red dwarfs is increasing all the time, as more and more tiny dwarfs are found.

If the high estimate of 500 billion stars includes the very small stars which are now being discovered, then the proportion of red dwarfs is likely to be quite a bit higher than 78%, and the proportion of Sun-like stars is therefore likely to be quite a bit lower.

eburacum45
2006-May-28, 10:18 PM
On the other hand, the concept of the galactic habitable zone is a little flawed, in my opinion. Rather than a fixed zone which contains the most likely stars to have habitable planets, it is more likely to be a moving zone whch changes location over time.

See this simulation of the development of the GHZ over time. The green zone moves outwards, and will continue to do so in the future allowing a much wider habitable region covering much of the galaxy.
http://astronomy.swin.edu.au/GHZ/GHZmovie.html

filrabat
2006-May-28, 11:27 PM
This thread I started in "General Science" deals with how a planet's geography man influence its ability to develop high techonolgy http://www.bautforum.com/showthread.php?t=42025 (pardon the self-link, but its best to keep this limit this thread to astronomical aspects)

filrabat
2006-May-29, 12:02 AM
Henrik,
You caught me fair and square - though you quibble too much

kmarinas
What if one of the intelligent species colonizes 3 planets and 9 moons, that would be 12 worlds just by itself. If we count Russia's Venera, the Mars spacecrafts, and the Huygens mission, we have 3 planets and 2 moons, 5 worlds for Humanity alone!

I was actually speaking of planets where life evolved without artificial intervention to the extent our science can know, not any colonized worlds themselves within that solar system. Personally, I find it very unlikely that two planets in a solar system can evolve life independently, which was my point. On other matters, I will not deal with sentient intervention in life's development on other planets in the system because those other planets are unlikely to have evolved life and sustained it to the point where it developed radio technology. However, I grant that even extrasolar worlds might have some colonies, though I think that would be for species far older and far more technologically advanced that we are (which feeds into eburacum's point).

eburacum
The G & K class percentages (plus other stars): It's obvious that adjusting my estimates down from 33% to even an extreme of 8.25% will still mean 600 such worlds based on your description of potential civs of up to 1 million years old (and a "fourth-ing" of every other conclusion, for that matter).

The Galactic HZ: TY for your movie link, cool and quite instructive. Although you are skeptical of the GHZ, allow me to expand it to include "all past and present locations of the GHZ". Multiplying that by 4 will do one of two things

(a) assuming the 33% figure mentioned above, roughly triple the number of planets we describe (triple because the inner regions of the galaxy will have smaller 3-D volume for their 10% circular band around the core. or
(b) assuming the 8.25% figure, it brings us to 3/4 of our original figures for the number of inhabited worlds of some form.

The 500 billion figure: given the math calculations, you can probably predict how assuming even a rather low-ball figure of 200 million would affect our figures.

Bottom Line: No matter how you slice it, if a civilization has a good chance of surviving its raucous warline adolescence and other disasters - it has a good chance of being a million year old civilization. There could well be hundreds or even thousands of such intelligences in this galaxy. On the other hand, as I said, would we even recognize such a civilization so far ahead of us (and likely almost god-like, barring some unforeseen major physics or technological bottleneck barring advancement to almost-god status).

Even so, this is ultimately beside the point. The point is the estimated ACTUAL number of civs, regardless of how easily we would recognize them.

GOURDHEAD
2006-May-29, 12:52 PM
Is it worth considering starless planets in independent "orbits" within and without the galaxy that are from 0.5 to 20 times the mass of Jupiter and have moons the size of Venus including gravitationally driven plate tectonics. Habitable zones may come in many variations and evolution is an engine capable of powering factories with many outputs.

It's quite likely that within 1000 years we will have spread over a 100 light year radius in our section of the MW and will be detectable by sentients 1000 light years away who won't be able to tell whether we are indigenous to the planet on which we were detected or transplanted from somewhere else. The same holds for us detecting a similar spread of other sentients.

Unless the Europans stop us.

folkhemmet
2006-May-29, 09:51 PM
Modern data from a number of planned space science missions should greatly aid in answering the question, "how many stars have habitable planets?" This October the CNES COROT mission will launch, and it will be capable of determining what fraction of stars have very large terrestrial planets. Next in line (2008), assuming it does not fall to the appalling science budget ax, is the Kepler mission. The Kepler mission will tell us what fraction of stars (spectral type M-F), single and mulitple, have terrestrial planets. We should know this stuff by 2015. People have been wondering about this for ages. Exciting times. In the meantime, microlensing planet searches are already telling us the following:

Microlens OGLE-2005-BLG-169 Implies Cool Neptune-Like Planets are Common

B. S. Gaudi1, A. Gould2, A. Udalski3, D. An2, D. Bennett4, A. Zhou5, S. Dong2, N. J. Rattenbury6, P. C. Yock7, I. A. Bond8, G. W. Christie9, K. Horne10, J. Anderson11, K. Z. Stanek2, MicroFUN Collaboration, OGLE Collaboration, RobotNet Collaboration
1Harvard-Smithsonian, CfA, 2Ohio State, 3Warsaw University, Poland, 4Notre Dame, 5Missouri State University, 6Jodrell Bank, United Kingdom, 7University of Auckland, New Zealand, 8Massey, New Zealand, 9Auckland Observatory, New Zealand, 10St. Andrews, United Kingdom, 11Rice.
Presentation Number: 9.03
We report the detection a Neptune mass-ratio (q~8e-5) planetary companion to the lens star in the extremely high-magnification (A~800) microlensing event OGLE-2005-BLG-169. If the parent is a main-sequence star, it has mass M~0.5 M⊙ implying a planet mass of ~13 M⊕ and projected separation of ~2.7 AU. When intensely monitored over their peak, high-magnification events similar to OGLE-2005-BLG-169 have nearly complete sensitivity to Neptune mass-ratio planets with projected separations of 0.6 to 1.6 Einstein radii, corresponding to 1.6--4.3 AU in the present case. Only two other such events were monitored well enough to detect Neptunes, and so this detection by itself suggests that Neptune mass-ratio planets are common. Moreover, another Neptune was recently discovered at a similar distance from its parent star in a low-magnification event, which are more common but are individually much less sensitive to planets. Combining the two
detections yields 90% upper and lower frequency limits f=0.37+0.30-0.21 over just 0.4 decades of planet-star separation. Analogs of OGLE-2005-BLG-169Lb orbiting nearby stars would be difficult to detect by other methods of planet detection, including radial velocities, transits, or astrometry.

dgavin
2006-May-30, 02:41 PM
Actually I don't think surviving war like stages is the deciding factor of what civilizations moves onward or not as is the civilization impact on thier own environment.

I'd break it down like this.

Per 100 Industrial/Post Industrial Civilizations.

Wiped out due to planatary or solar catastophy 1
Wiped out due to nulclear or biological wars 5
Wiped out due to contact with bateria from other planets in thier own solar system 10
Wiped out due to natural evolotionary changes 3
Wiped out due to planatary mismanagement of climate changes 35.

Leaving 46 of 100 potentials that could have reached instersteler travel.

Of those

Choose to revert to a simpler life 20 (abandons most technology)
That commit some from of mass suicide because of beliefs 5
Choose to not become space farring outside thier own solar system
10

So around 11 out of 100 would make it to instersellar travel stage.

So where are we?

Just begining on our way to being wiped out due to planatary mismanagement of climate changes, IMHO

Trantor
2006-May-30, 08:56 PM
A very intelligent and thought provoking thread. Just my opinion, but I would be surprised if there were more than a couple of dozen technological civilizations at any given time in our galaxy. Thank You for the interesting read.

filrabat
2006-May-30, 10:05 PM
GOURDHEAD
Is it worth considering starless planets in independent "orbits" within and without the galaxy that are from 0.5 to 20 times the mass of Jupiter and have moons the size of Venus including gravitationally driven plate tectonics. Habitable zones may come in many variations and evolution is an engine capable of powering factories with many outputs.

This certainly is a possibility for sub-sentient life, and perhaps for low to mid complexity multi-cellular self-propelling life (animal by definition, Iíd think). I was actually thinking of surface-dwelling life when I drew up this list, but since I didnít explicitly say so, Iíll have to allow you that point. Everyoneís heard about how Europa is a promising place, so I wonít elaborate on it.

On the other hand, I think that any moon close enough to such a gas giant to induce plate tectnoics would generate enormous ocean tides - to the point where it would really stir up the amino acids and other building blocks to the point that the organic soup canít concentrate in one spot. Perhaps thereís some spot well inland that could serve as a tidal pool, but itís difficult for me to see how any self-replicating system can survive for long in such an environment.


dgavin
Per 100 Industrial/Post Industrial Civilizations.

Wiped out due to planatary or solar catastophy 1
Wiped out due to nulclear or biological wars 5
Wiped out due to contact with bateria from other planets in thier own solar system 10
Wiped out due to natural evolotionary changes 3
Wiped out due to planatary mismanagement of climate changes 35.


Planetary Catastrophe: I think this is somewhat measurable, albeit barely so because we have only one solar system of which we have detailed knowledge thereof. Even so, Iíd think it possible to construct some probability of wipe-out based on some probable maximum time span between hits from asteroids >1000 meters wide (or whichever other figure you care to use). Still, keep in mind this factor is only relevant for societies with pre 21st century space technology/engineering, and maybe even pre 2050 CE space tech/engineering too (more advanced civs would find it fairly easy to prevent a collision in some way)

On all others, the only one I disagree with is the third one (space bacteria): Firstly, I think any expedition to a sister planet in a solar system will take strong precautions to prevent this (this is beside the fact that the rest of the solar system is likely to be incredibly hostile to life in any conceivable form [Carbon-water, Carbon-ammonia, Silicon-X, or any other combo you can likely think of]).

Even if a ďbad bugĒ is present and does make it back to the home planet and does cause a horrid epidemic, itís still going to be very hard to wipe out an entire species - although I can see how a particularly virulent bug might wipe out a civilization. We have the Native Americans as an example particularly the Aztecs and Incas. Their civ was wiped out in great part by diseases, yet the ethnic groups themselves survived.

Result: It may be trivial to say so, but I have to go with 55 out of 100. Certainly itís not enough to substantially alter the calculations.
Leaving 46 of 100 potentials that could have reached instersteler travel.


dgavin

Of those

Choose to revert to a simpler life 20 (abandons most technology)
That commit some from of mass suicide because of beliefs 5
Choose to not become space farring outside thier own solar system
10

So around 11 out of 100 would make it to instersellar travel stage.

My instinct tells me that only 2 or 3 would abandon technology. Even if 1/100 keep that technology, thatís still a pretty substantial core to maintain it (I think a nation of 63 Million people could adequately sustain a technology even without much help from the rest of the world, if only because their technology gives them superiority over other peoples and hence can easily take those important resources that enable space exploration if they wanted them badly enough). Ditto for mass suicides, except I would choose an even lower figure, given that only the most fanatical will choose to commit suicide for their beliefs, or even say their race should cease to exist altogether (remember that 1 out of 1,000 exception). So I would say ďpractically zeroĒ in this case

However, I grant the cessation of extrasolar exploration is quite plausible, to the point where I say you underestimated this figure (Iíd go with 20, given the extraordinary expenses, distances, time and resources to sustain an extrasolar exploration effort - let alone colonization).

dgavin
Based on my figure, Iíd say 55-2-0-20= 31 civilizations might get into space
So where are we?

Just begining on our way to being wiped out due to planatary mismanagement of climate changes, IMHO

filrabat
That I do find disturbing plausible, though by no means strikingly high in probability. There's still plenty of hope

To Folkhemmet
Thanks for the information, folk. Iím sure we will be a lot closer to finding out in a little more than 10 years. This will truly be an exciting time - ever closer to a definitive answer to that centuries, if not millennia, old question.

To Trevor
Glad to be of service <grins>. Thatís what BAUT is for. Of course all these numbers are little better than speculative, but they are an honest attempt to form a sound framework (though as you can see, itís still far from complete acceptance as truth).

filrabat
2006-May-31, 11:43 AM
I MISattributed the following remark to dgavin
dgavin
Based on my figure, Iíd say 55-2-0-20= 31 civilizations might get into space
So where are we?

Just begining on our way to being wiped out due to planatary mismanagement of climate changes, IMHO

That remark was actually made by me. Dgavin actually made the following estimate

So around 11 out of 100 would make it to instersellar travel stage.

My apologies to dgavin

Cookie
2006-May-31, 12:49 PM
How Many Stars Might Contain Inhabited Planets?
When I first read that topic, "Zero" came to mind.

I then thought that maybe you were asking about the material ejected from a supernova that may someday form into a planet.

Curious, I opened the thread and started reading.

That's when I was hit with all of that math.

Seriously though, I find this topic interesting.

Unfortunately, I am only knowledgeable enough to nitpick a little grammar.
=b

filrabat
2006-Jun-01, 03:26 AM
First Henrik, now Cookie <groans!>

Ok, peeps, who would be the moderator in charge of this thread? I need to request him or her to slightly adjust the thread title.

SactoGuy88
2006-Jun-04, 01:35 PM
Hopefully, by 2016-2020 the Terrestrial Planet Finder (TPF) project will finally give the answers we all want--where there are rocky crust planets orbiting around G to K class stars within 200-300 light years of Earth. If we find such planets then the chances of finding life there could be quite good, especially if the TPF detectors discover an atmosphere with water vapor as a large component of the atmospheric gases.

antoniseb
2006-Jun-04, 02:49 PM
who would be the moderator in charge of this thread? I need to request him or her to slightly adjust the thread title.
Any moderator can change the thread title. Outside special case situations mostly in the ATM section threads don't have specific moderators.

antoniseb
2006-Jun-04, 03:55 PM
Hopefully, by 2016-2020 the Terrestrial Planet Finder (TPF) project will finally give the answers we all want--where there are rocky crust planets orbiting around G to K class stars within 200-300 light years of Earth. If we find such planets then the chances of finding life there could be quite good, especially if the TPF detectors discover an atmosphere with water vapor as a large component of the atmospheric gases.

The TPF mission will survey enough stars that we should be able to get a good statsitical sample to be able to estimate the number of Earth-sized planets in habitable zone orbits in the galaxy. I don't think that it will be able to tell us very much about the chemistry of the planet's surfaces, and even atmospheres will be questionable. Prior to having probes enter the atmospheres of Mars, Venus, and Titan, we only had rough guesses about the composition of their atmospheres. This, inspite of having good very clear views of these bright nearby objects.

Dave Mitsky
2006-Jun-05, 06:03 AM
First Henrik, now Cookie <groans!>

Ok, peeps, who would be the moderator in charge of this thread? I need to request him or her to slightly adjust the thread title.

How would you like it to read?

Dave Mitsky

filrabat
2006-Jun-07, 12:32 AM
How would you like it to read?

Dave Mitsky

Philip: How Many Star Systems Might Contain Inhabited Planets?

Thank You, Anton and Dave.

filrabat
2006-Jun-07, 12:48 AM
The TPF mission will survey enough stars that we should be able to get a good statsitical sample to be able to estimate the number of Earth-sized planets in habitable zone orbits in the galaxy.

I suppose the total number of stars (orbited by inhabited planets or not) would be anywhere from several hundred to a few thousand. Do you have a more specific estimate available?


I don't think that it will be able to tell us very much about the chemistry of the planet's surfaces, and even atmospheres will be questionable. Prior to having probes enter the atmospheres of Mars, Venus, and Titan, we only had rough guesses about the composition of their atmospheres. This, inspite of having good very clear views of these bright nearby objects.

I can vaguely conceive how our spectography might be skewed (especially for degrees in liberal arts & business, but not science :P ).

Is there something about the visible light and other EM bands that makes it prone to distortion between the other planet's atmosphere and our own insturments? That's the only think I (again, a NONscience-degreed person) could think of. BTW, feel free to go a notch or two higher than your basic layman's explanation, as I think I can handle it (I may eat crow after saying this, but I'll give it a try)

thothicabob
2007-Aug-10, 05:10 AM
I'm almost tempted to jump in here, but due to the huge subjectivity involved, I won't get too far. I'd just suggest that I would bet heavily against there being two or more contemporary reflective, technological species in a given galaxy at any given time, and I'd also likely take a bet against there being ANY most of the time in any given galaxy.

While I DO believe life can and will arise anywhere the conditions allow and given enough time, the obstacles, trials and tribulations, and associated gyrations it needs to survive AND evolve to anywhere near the level we have are huge. Given, evolutionary life allows, even implies a great flexibility and adaptability in surviving many situations, given the time scales involved some - and I suggest not infrequently (with regards to the overall history of a planet) - are just so significant in effect that missing all possible problems en route to intelligence implies a great deal of plain dumb luck. I believe WE are very, very lucky indeed...so far (knock wood).

Oh, and one little 'quibble' - 'sub-sentient'? 'sentient' means capable of 'sensing' - a fish is sentient. Is it self-aware? Only very dimly. Intelligent? Only to a limited degree and in specific contexts (eg. intelligent enough to flee from predators (regardless of whether or not that ability is hardwired - it's a behaviour pattern that makes sense. Otherwise, why call software "intelligent" that conducts automated functions that involve much simpler behaviour and less complex action than a fish recognizing and fleeing a predator?)). There's a continuum here, in my view, from the simplest to the most complex, with no specific 'borders' apart from a few stages equivalent to 'phase transitions' in the context of cognition and such higher functions, and even those are a bit 'fuzzy' (not absolute). Technology is one such 'phase transition', I think, in the expression of intellect in biological life.

Jerry
2007-Aug-10, 05:42 AM
When I first read that topic, "Zero" came to mind.
=b

Well there is at least one...last time I checked.

m1omg
2007-Aug-10, 09:50 AM
Why high tech civilisation must have problems on tidelocked planets.
Read The Neaderthal Parallax, what descibes Homo neanderthalis civilisation in the paralell Earth and it's contact with humanity.
Neaderthals (barast in ther language) were having a low population ( about 150 million people) peaceful and nature friendly civilisation without agriculture or any kind of "religion", but knowing genetics,solar power, ecological cars, airplanes, quantum computers...before us, mainly because they never bothered with such things as going to the moon or war and concentrated themselves to solving crime problems and maintaining a stable hunter gatherer hi tech low population peaceful civilisation (they never ran out of food because they did not killed all the megafauna and many other animals so there is enough food for anyone unlike us).
That might be the humanity's life if we did not utilised violence as a mean to solve problems from the prehistorical times...
No, folks, (fanatical) religion and violence are not things required to have a civilization, but they are things that are destroying it!
The neaderthal parralax style civilisation will probably last much more than our megalomaniac warry because there will be never threats of nuclear war or famine and other nasty things charasterical for overpopulated agressive human civilisation.
If anyone want lament, please first read the first book from the trilogy; Hominids, and see that it will work perfectly, but we are just plain stupid.

thothicabob
2007-Aug-10, 03:44 PM
It's pretty hard to make any extrapolations based on fiction, m1omg - everything that happens in it 'happens' because the author decrees it to be so, not because it could or can happen in reality, and despite any reasons why it couldn't.

I agree 'religion' isn't required for a civilization, but SOME sort of social entity that can enforce cooperative/moral behaviour is if there is to be any hope of large-scale civilization (and hence technology); otherwise, the species would be reduced to being influenced by and making decisions based on what's good for me and mine - something that is anyway a problem for US still, but somewhat mitigated by law and social pressures such as those imposed by religious entities, and were generally behind whatever laws were in place and enforced early in our history.

A further note regarding the idea of 'contemporary' civilizations in a galaxy: a given galaxy COULD give rise to 1000 technology species during the course of it's history, or more, but even being generous and giving them a 10,000 year window of BEING technological, the odds of any two of them being co-temporal AND within some reasonable distance of each other, I'd think, would be very long. Even with the assumption that if life formed on one planet in a given region of a galaxy, then another one nearby could, 10,000 years is quite a close match that I doubt it could happen in reality.

GOURDHEAD
2007-Aug-11, 01:41 PM
Even with the assumption that if life formed on one planet in a given region of a galaxy, then another one nearby could, 10,000 years is quite a close match that I doubt it could happen in reality. Whether or not one chooses to call them "separate technical civilizations", many separate and diverging technical civilizations could proceed from the aboriginal "founder" and populate their section of the MW with a large number of technically competent civilizations. Also, as technical competence increases, so will the longevity of the species that practices it.

The germ of an idea that promotes humans as an aboriginal founder civilization can be found at http: www redcolony com wiki index php?title=Portal:Gourdheadian_Approach

thothicabob
2007-Aug-11, 03:16 PM
There are still the technical problems to overcome. Sure, if you are not looking for a coherent, centrally (or even distributively) controlled 'empire' or some such thing, it is possible that a technological race could send out seeder ships, or even colony ships that may colonize a few planets in the neighborhood...but it still is a huge stretch. Read "Rendevous with Rama" by Clarke for a pretty good treatment on that subject.

Personally, I think any "real" spacefaring intellect will be electronic/artificial intelligence; the biological stage of evolution (with regards to intelligence) will wind up being just one step up the ladder. Even a trip to any nearby stars will be a hugely daunting and time consuming project for a biology-based entity to consider, even assuming we could muster the required economic resources and social stability and maturity needed, neither of which are a given, judging by our current situation.

TaylorS
2007-Aug-12, 09:57 PM
I do there are other civilizations in the galaxy, though there aren't many of them, I'll guess that there are between 5 and 20.

thothicabob
2007-Aug-13, 12:49 AM
Contemporary with us - and within some reasonabe range of equivalance technologically or socially?

Personally, I'd be stunned if that were the case. On what do you base it?

Champion_Munch
2007-Aug-13, 01:22 AM
Far too many unknowns - if you change just one of the estimations by a small amount you end up with wildly different results. Also the Earth-bias is too strong, there is absolutely no way you can assume other civilisations will have evolved anything like ours, or what conditions they have evolved in.

With each new discovery in the universe our concept of what "conditions" under which intelligent life can arise will no doubt expand much further than what we can currently imagine.

with regards

thothicabob
2007-Sep-22, 07:07 AM
Far too many unknowns - if you change just one of the estimations by a small amount you end up with wildly different results. Also the Earth-bias is too strong, there is absolutely no way you can assume other civilisations will have evolved anything like ours, or what conditions they have evolved in.

With each new discovery in the universe our concept of what "conditions" under which intelligent life can arise will no doubt expand much further than what we can currently imagine.

with regards

That's likely true and I won't disagree, but there are some things needed for the evolution of complex life-like entities that we can define, and then further refine if needed. some are:

Time - evolution of complex structures like life take time - lots of it. getting it to the point of intelligent life takes still more. life on earth spent at least 2 billion years before multicelled life evolved. from there, another 500m years until "complex" life forms evolved such as arthropods and other such creatures...and so on.

Environmental Variation/Complexity - there needs to be something the induce changes and fitness selection pressures to push evolution along. a very simple, unchanging environment will not get one very far. that said, in some cases (at least) the existence of life alone can have a significant effect on some environments creating a feedback loop. But this is not likely true of ALL environments in which some basic form of life could get started (under the oceans of Europa, say); some environments would place severe constraints on the degree of "dynamicity" possible due to temperature, radiation, constituents (water, chemicals (organic and inorganic), gases, other liquids, etc.), etc.

Stability - this tied to time and to some degree offset by the above - you need to have some consistency in the evironment for long enough to allow and keep things going.

About 90 percent of the stars in our galaxy - of whatever class - are located in conditions where the above requirements are not and cannot be met - too close to the galactic core and there is just too much going on to allow life to happen; planetary orbits disrupted by passing stars, lots of sources of radiation, etc. Many stars even in the arms are located in or near highly ionized nebulae or gas clouds - a sterlizers of planets. And so on and so forth - all these things have to be considered before you then calculate how many possible planets could evolve life, and from them, intelligent/technological life.

My guess is that there is currently one intelligent technological species in our galaxy. There could be one more, but I doubt we'll ever meet them. I'd be willing to bet a pretty penny that there may well have been a few tens over the course of our galaxy's history, but likely not the entire farm. And I also think that our galaxy could go long periods without any technological species active within it at all (though I'll still wager that 'life' in all it's various forms/levels is quite common throughout it at all times). I'd also go so far as to say that I'd think our galaxy, while possibly typical of its type in this way, still is possibly one of the more life-friendly galaxies (perhaps top 20 percent?) in the universe. How do I know? Just a hunch...I'd also be willing to bet I'm not far off, though, either.

Wanna bet? ;o)

Of course, there could be the electronic/AI-based heirs of some of these civilizations floating around - and if anything, I'd bet that's what we'd run into.


bidi-bidi-beep

filrabat
2007-Sep-22, 07:15 AM
Speaking as the thread-starter,


Far too many unknowns - if you change just one of the estimations by a small amount you end up with wildly different results.

You're perfectly correct about this. This is more of an intellectual exercise, even if tempered with reasonable scientific data.


Also the Earth-bias is too strong, there is absolutely no way you can assume other civilisations will have evolved anything like ours, or what conditions they have evolved in.With each new discovery in the universe our concept of what "conditions" under which intelligent life can arise will no doubt expand much further than what we can currently imagine.


On the other hand, "earth-bias" is a matter of degree. I decisively agree that a humanoid civilization is so unlikely that it barely deserves discussion. On the other hand focusing on "Carbon-water based" is not quite as Earth-centric -- MANY possibilities come from this broad life-type alone. I implicitly stuck with this type because carbon forms much longer chains than other atoms (even silicon), and because water is an extremely common solvent. Carbon-ammonia, IMO the most likely alternate biochemistry, is quite speculative even if it does turn out to be a common life-type. Therefore, bringing in Carbon-ammonia would bring in another tangent that would muddy the issue. That kind of life needs another set of calculations entirely.

Having said that, I pretty much impled that my calculations were Earth-bias on a number of points. It's only because I believe in sticking closely to what we know rather than stacking hypothesis on top of hypothesis. Yes, there is plenty of room for alternatives, but without setting SOME limits you open the possibility of effectively asking your audience to believe in magic.

thothicabob
2007-Sep-24, 06:53 AM
Speaking as the thread-starter,



You're perfectly correct about this. This is more of an intellectual exercise, even if tempered with reasonable scientific data.



On the other hand, "earth-bias" is a matter of degree. I decisively agree that a humanoid civilization is so unlikely that it barely deserves discussion. On the other hand focusing on "Carbon-water based" is not quite as Earth-centric -- MANY possibilities come from this broad life-type alone. I implicitly stuck with this type because carbon forms much longer chains than other atoms (even silicon), and because water is an extremely common solvent. Carbon-ammonia, IMO the most likely alternate biochemistry, is quite speculative even if it does turn out to be a common life-type. Therefore, bringing in Carbon-ammonia would bring in another tangent that would muddy the issue. That kind of life needs another set of calculations entirely.

Having said that, I pretty much impled that my calculations were Earth-bias on a number of points. It's only because I believe in sticking closely to what we know rather than stacking hypothesis on top of hypothesis. Yes, there is plenty of room for alternatives, but without setting SOME limits you open the possibility of effectively asking your audience to believe in magic.

I agree that 'earth bias' or 'anthropocentrism' needs to be kept in check; that said, we shouldn't stray further from it than necessary. there are perhaps some good lessons to be drawn from how life here evolved, too...

for example, one of the things to be considered is the development of technology. Despite a FAR longer history, and - arguably - diversity, life in the sea has never developed very far up the intelligence chain (whales moved BACK into the water; their anscestors didn't evolve in it), and apart from some minimal tool-making behavious on the part of octopuses, there's never been any indication that any technology could get going in the sea.

I think it's not unreasonable, therefore, to consider the environment and what impact that would have on the development of higher technology. it seems to me that many of the more exotic chemistries proposed for life would also involve pretty volatile environments; how far could technology be taken in them?

and further, what impact does the ability to develop technology have on the impact of a species survival fitness and later evolution? in our case, admittedly a fairly limited sample (but a sample nonetheless), it's been a significant boost; our evolution has been fairly rapid since australopithecines began whacking their prey - and each other - with sticks, and their descendents began using fire...

So, while earth-bias IS something to avoid, our evolution and development is also something to perhaps draw lessons from, as well.

Ronald Brak
2007-Sep-24, 09:16 AM
It has been suggested that radiation makes much of the galaxy uninhabitable. This seems quite odd as in some areas on earth people are naturally exposed to over 100 times normal background radiation without significant health effects. Also bacteria and animal experiments show life has a signifcant ability to adapt to higher radiation levels. On top of all that radiation from space is greatly affected by the strength of a planet's magnetic field and the thickness of its atmosphere (or ice crust).

thothicabob
2007-Sep-24, 03:32 PM
It has been suggested that radiation makes much of the galaxy uninhabitable. This seems quite odd as in some areas on earth people are naturally exposed to over 100 times normal background radiation without significant health effects. Also bacteria and animal experiments show life has a signifcant ability to adapt to higher radiation levels. On top of all that radiation from space is greatly affected by the strength of a planet's magnetic field and the thickness of its atmosphere (or ice crust).

Well, 'normal' background radiation on earth is significantly lower on earth than what it would be if we were located close to the galactic core or within a nebula; i'm not sure HOW much of that a magnetic field would stop, but i'm pretty sure it wouldn't be enough. The make-up of our atmosphere also has an effect on reducing the amount of radiation that reaches the surface. even a supernova explosion within a few hundred ly from earth can have a significant effect (the impending impact of the Eta Carinae explosion will at least cause damage to space-borne electronics, and if it had been oriented so that it was 'aimed' at earth a bit more directly, our ozone layer could have been removed, allowing enough radiation to reach earth to seriously affect life on the surface - and that's 8000 ly away. of course, it is also an unusually large SN; but even much more modest explosions closer would have (and have had) an effect).

Any while it's true that some bacteria are radiation-tolerant to some degree, the issue of greatly increased mutation rates would play hell with evolution; by far most mutations are NOT beneficial - most are either have no real effect and many are outright fatal to the organism expressing mutated genes. very few actually improve an organism's fitness, and this effect is further multiplied as you increase the structural complexity of the organism involved. i supposed it is possible that complex creatures in such an environment could evolve some degree radiation tolerance, but i think there are probably upper limits even to that and those are likely not really far beyond ours in absolute terms.

We've evolved in a relatively quiet environment around a relatively stable star. We've been lucky. That said, life on earth is thought to have been negatively affected by such things as distant supernova explosions and transits through gaseous nebula, with some extinction events attributed to, or at least 'enhanced' by, them.

Ronald Brak
2007-Sep-24, 04:16 PM
Well, 'normal' background radiation on earth is significantly lower on earth than what it would be if we were located close to the galactic core or within a nebula; i'm not sure HOW much of that a magnetic field would stop, but i'm pretty sure it wouldn't be enough.

Well humans in Ramsar in Iran seem to be able to handle background radiation a hundred times higher than normal so it appears likely that we could also handle much higher amounts of radiation from space without difficulty. Very roughly, the lack of ill effects on people living in high radiation areas on earth suggests we could take at least 200 times as much radiation from space as we currently receive.



Any while it's true that some bacteria are radiation-tolerant to some degree, the issue of greatly increased mutation rates would play hell with evolution;...

Mutation rates aren't caused by radiation, although radiation can certainly cause mutations. DNA is not very stable room temperature is enough to cause mutations and is under constant repair. Mutation rates are basically determined by how much effort is put into preventing mutations.

Then we have to consider that we don't know what sort of planets are suitable for technologically advanced life to develop on. Perhaps life is common on earth sized Europa type planets under ice crusts many kilometers thick. And we can be certain that alien life won't use DNA identical to our own, so it's not really possible to discuss how radiation will affect their mutation rates.

thothicabob
2007-Sep-24, 05:36 PM
Well humans in Ramsar in Iran seem to be able to handle background radiation a hundred times higher than normal so it appears likely that we could also handle much higher amounts of radiation from space without difficulty. Very roughly, the lack of ill effects on people living in high radiation areas on earth suggests we could take at least 200 times as much radiation from space as we currently receive.

Well, i will need to check studies, if any are available, before accepting such a statement at face value; i do know that 'normal' background radiation levels on earth, however, is very low, so 100x increase may not be all that significant and what you're saying could be true. i'd also like check to be sure that negligible 'ill effects' from that (to include increased birth defects, cancer rates, etc.) degree of radiation is also a valid claim. one case in point where background radiation IS a significant cause of mutations is Chernobyl. I don't have handy the radiation levels, however, so i can't make many statements there except that that radiation is from only one small fission reactor; i'd expect radiation from cosmic sources to be orders of magnitude more intense in certain environments/locations in the galaxy.

i also believe that the levels of radiation being described in other environments (galactic core region (say inner 1/3 to 1/2) and nebula is on the order of several hundreds to many thousands (or millions) of times higher. if it were 'around 100 times earth's' then perhaps things would be fine. again, a relative measure vs earth's vs. absolute values in the amount of radiation are different things. while it may seem that 100 times earth's rate is 'high', if earth's rate is VERY low, then even 100 or 1000 times may not really mean much in absolute terms.



Mutation rates aren't caused by radiation, although radiation can certainly cause mutations. DNA is not very stable room temperature is enough to cause mutations and is under constant repair. Mutation rates are basically determined by how much effort is put into preventing mutations.

Radiation can cause mutations, but doesn't affect mutation rates? i'd think anything that causes mutations is a part of the 'cause' of the mutation rate, and an increase in mutations from a given cause would be considered as to causing an increase in that mutuation rate, no?



Then we have to consider that we don't know what sort of planets are suitable for technologically advanced life to develop on. Perhaps life is common on earth sized Europa type planets under ice crusts many kilometers thick. And we can be certain that alien life won't use DNA identical to our own, so it's not really possible to discuss how radiation will affect their mutation rates.

Well, i agree with you that life could be common on europa - and i hope it is...it would be exciting! but i also am a bit doubtful, for various reasons. but even if it is there, how diverse can it be, and how advanced? the two are related and the environment will place limits on both. and even if - somehow - intelligent life were to evolve in an environment similar to europa, what sort of technology could it possibly produce? would it even be aware of the rest of the universe? would it be even equipped to gain that knowledge? without fire, how could such technologies such as metallurgy or electronics be developed very far?

sure, it is possible to fall back on the 'we cannot know' argument, and for some things, i would have to say you'd be right; nature has a way of being very ingenious and life being very adaptive. that said, there are some things we can take fairly far with logic/reason alone, and we shouldn't let our ignorance of some things block such reasoning provided it's based on empirical evidence, understanding of nature, and logic, but rather should only temper it through being aware of the nature/implications of possibly unanticipated issues.

Ronald Brak
2007-Sep-25, 03:24 AM
Radiation can cause mutations, but doesn't affect mutation rates? i'd think anything that causes mutations is a part of the 'cause' of the mutation rate, and an increase in mutations from a given cause would be considered as to causing an increase in that mutuation rate, no?

I said radiation does not determine mutation rates. I didn't say it does not affect mutation rates. For one thing radiation from space is a very minor cause of mutation on earth. Also when mutation rates increase for whatever reason this promotes the spread of allele sets that can faithfully replicate so there is negative feedback occuring. Going downhill can certainly affect the speed of your car, but the rate at which your car travels is determined by your foot on the accelerator/brake.

Just how radiation will affect the mutation rate of aliens, we can't say.

My basic point is that life on earth, including us, can survive a lot more radiation from space than we currently do so we shouldn't dismiss the possibility of earthlike life in areas with only a few hundred times more radiation than in our area.

thothicabob
2007-Sep-25, 05:20 AM
I said radiation does not determine mutation rates. I didn't say it does not affect mutation rates. For one thing radiation from space is a very minor cause of mutation on earth. Also when mutation rates increase for whatever reason this promotes the spread of allele sets that can faithfully replicate so there is negative feedback occuring. Going downhill can certainly affect the speed of your car, but the rate at which your car travels is determined by your foot on the accelerator/brake.

Just how radiation will affect the mutation rate of aliens, we can't say.

My basic point is that life on earth, including us, can survive a lot more radiation from space than we currently do so we shouldn't dismiss the possibility of earthlike life in areas with only a few hundred times more radiation than in our area.

I'll give you that, however very relucantly; i think that it's unlikely that schemes that bypass the laws of physics and the effects of radiation on complex molecules could be evolved that would allow a sufficient balance of stability AND variation to allow for evolution of complex organisms, however i'll admit it's possible i could be in error here.

in any case, i think that the radiation levels of any planet of stars in the inhospitiable areas - such as the galactic core region (where the majority of stars are) and nebular regions (where another good batch of them are) - are much higher than a few hundred times that of earth. i'd need to double-check that, however that's my recollection.

the main thrust of my argument is that i think estimates of there being numerous contempory technological/intelligent races extant in a given galaxy at one time are highly optimistic; there could be some galaxies here or there where that is the case; the universe is a big place and there are a LOT of galaxies, so there is bound to be some degree of variation, but i would be willing to bet that, on average, 1 per given galaxy at any one time would still be a fortunate, but possible and reasonable, estimate. that's not to say that life is NOT much more common - I'd also bet in favor of that being the case - but life has many gradients, and i suspect the more complex the life you're looking for, the rarer it will be at an almost exponential rate going up the scale of complexity.

Ronald Brak
2007-Sep-25, 05:56 AM
I'll give you that, however very relucantly; i think that it's unlikely that schemes that bypass the laws of physics and the effects of radiation on complex molecules could be evolved that would allow a sufficient balance of stability AND variation to allow for evolution of complex organisms, however i'll admit it's possible i could be in error here.

No one is suggesting a bypass of the laws of physics and the effects of radiation on complex molecules. If you expose something to enough radiation it will get fried. But for earth creatures variation is free. Nothing needs to be done to induce variability in DNA. As I mentioned before, room temperature is sufficient. What organisms do work at is stability and over time mutations will tend to approach an equilbrium level if mutagens are increased or decreased.

thothicabob
2007-Sep-25, 06:55 AM
No one is suggesting a bypass of the laws of physics and the effects of radiation on complex molecules. If you expose something to enough radiation it will get fried. But for earth creatures variation is free. Nothing needs to be done to induce variability in DNA. As I mentioned before, room temperature is sufficient. What organisms do work at is stability and over time mutations will tend to approach an equilbrium level if mutagens are increased or decreased.

Sure, I don't disagree there in principle. But there are limits, and the necessary balance must be achieved within them, i think. if the rate of mutation is too high (eg. many parts of the genetic molecule undergoing numerous/frequent random changes/damage), it would seem to be impossible for a sufficiently stable/coherent/consistent mechanism of heredity to be created by any molecular construct to deal with that problem; it itself would have to evolve numerous redundancies, i'd think, and that in itself would, in turn, be quite inefficient and introduce it's own problems. but then, i'm no biochemist or physicist - just a layman sufficiently informed to be interested enough in such things so as to enjoy discussing/arguing/exploring such things (politely, I hope), but sufficiently insufficiently educated to be much more than dangerous...and lucky once in a while in his guesses. ;o)

filrabat
2007-Sep-25, 03:18 PM
Re: Technology Development.

I reread my "foundation" posts and found a potential source of confusion. If you're not confused yet, simply take this as a clarification. I said at the end of the calculation post.

""12.16768916 planets whose most intelligent species is within (but not over) 5000 years of current Western World techonolgical development.""

Though I also said one possible definition of advanced civilization was "one capable of extensive radio communication"

Making the admittedly doubtful assumption that life forms develop technology at the same rate we do (or at least that we humans are at or near the average rate of advance of all the universe's species)...that means the next most advanced society has technology about 5000/12 years behind ours - the same as 1590 CE Western Europe (i.e. late preindustrial economy, scientific revolution barely getting off the ground, cannons and muskets the most fearsome military technology, etc.).

On the other hand, as ebarachum (sp?), one of the eariest commenters said, that doesn't take into account species with technologies MORE advanced than ours (thus making the least advanced trans-present-human technology about early 25th century Earth). An early 25th century earth equivalent technology is still likely to be at least 90 degrees around the galaxy from us, possibly exactly 180 degrees (i.e. right behind the glactic core). So if any civilization IS closer to us, it's likely to be SO much more advanced than us that we might not even recognize them as an advanced species.

Re: Technology of aliens in other environments. I direct you to 3rdVogon's post from several years back, as I fully agree with him regarding developing technology on land vs in the water

http://www.bautforum.com/life-space/26104-life-if-found-what-will-their-language-2.html#post523305
Re: Habitat Desirable -- Though ebecharum (sp?) disagrees, I think life is most likely in the galactic habitable zone, though he does bring up interesting points I didn't think about.

All in all, great discussion you two have going there.

diamondberyllium
2007-Dec-25, 01:29 AM
There are too many unknowns and speculations. Human beings become arrogant to the point of their ignorance and have a habit of making up pet theories and parading their assumptions with dubious mathematical extrapolations to excuse all the knowledge they don't have. For all you know 90 percent of the galaxy may be inhabitable, with scattered hot radiation areas, and life throughout the universe is probably as abundant as it is on earth, but it's certain earth astronomers don't have the ability to measure the reality one way or the other, so they have to go into more and more fanciful mathematics based on assumptions and extrapolations. The "big bang theory" is the most laughable concoction yet. It's hard to imagine grown adults basing all their calculations on that fairy tale. When new data arrives that contradicts the "big boing", the gnomes rush in to discredit it or frantically adjust the data to protect their favorite pet theory. The only real proof is to go there and make the physical measurements, but earth denizens will never make it past the primitive stage of rocket technology. They are too busy killing each other off or destroying earth's four billion year evolved fragile and beautiful web of life. It would take extraordinary cooperation and social organization and a height of ethics that humankind doesn't have to make this trip to the stars. In a way it's a good thing that humans have a tendency to self-destruct and that other planets will not be contanimated by them.

Kaptain K
2007-Dec-25, 01:46 AM
Wow! You certainly took your "vinegar pill" today! :eek:
As for:

The "big bang theory" is the most laughable concoction yet, it's hard to imagine grown adults basing all their assumptions on that fairy tale.
Come up with an explanation that better fits the data and astrophysicists will drop the big bang like a hot potato.