Venus and Creationism

[dgruss23]

Zathras wrote: With respect to the moon, I don't know what the answer would be. The most I can say on
that is that I cannot think of any reason why such an intervention would be necessary to
the Divine Plan.

It seems that this is the interesting distinction between the clockmaker view and the intervention view. I'm wondering why there is a need for such intervention when science offers a plausible explanation.

While I understand that some people's faith lead them that way, I'm not seeing why intervention on matters involving the physical processes that we've observed operating in the universe would ever be necessary. In particular I don't see why we would REPLACE a solid scientific explanation with a faith based untestable explanation.

[JS Princeton]

I guess what I'm asking is how can we scientifically demonstrate that those fluctuations could in fact happen at a point when the universe was not around to have any laws of physics? Isn't that a point where all we can really say is that the vacuum fluctuation "just was".

Depends who you ask. While one could say "just was." One could also say there was a further context or a self-creating context with closed time-like loops, etc. That's the issue: whenever someone claims to have arrived at an ab initio observation, there is always another interpretation that can prove them wrong. It's similar in type to the question of determinism and time travel (thought experiments alone cannot resolve the grandfather paradox).

[Zathras]

. . .
While I understand that some people's faith lead them that way, I'm not seeing why intervention on matters involving the physical processes that we've observed operating in the universe would ever be necessary. In particular I don't see why we would REPLACE a solid scientific explanation with a faith based untestable explanation.

Agreed. I have no idea why some go to such lengths. Even with the moon example, there is no reason that they could not be parallel descriptions.

[kilopi]

orchids(which need constant supervision)

You mean domesticated orchids?

[nebularain]

Neb, That's about the best analogy for the intervention position that I've seen! Thanks! So do you think the formation of the Moon was a case of intervention ... "fertilizing" if you will?

Cool! and you're welcome!

Formation of the Moon . . . . Well, all I can say is:
If it weren't for the formation of the Moon, would life on Earth as we know it exist?

(I know that is not a defininitive answer, but to be honest, that's the best I can understand it. I allow the reader to draw his/her own conclusions.) :wink:

Zathras - kind-of follows what G-K asked, but since you asked me -
Lots of flowers grow wild that humans have domesticated and cultivated to make them bigger and what-not. Orchids are one of those. There are wild orchids that grow just fine on their own, just like roses (yeah, there are wild roses!).

[DStahl]

Argh. Just lost a perfectly good post through my own thumbfingeredness.

Well, Zathras, it sounds like faith in God'god/gods is a purely subjective thing for you--I think you must assume that your interior perception is connected to Reality in some way. And I like to maintain that objective science similarly has to assume that our sensory perceptions are connected to Reality in some way. Neither assumption, in my book, is provable, and they are neither mutually exclusive nor mutually dependent. You can hold one, the other, both, or neither (though if you hold neither I am blasted and blamed if I can see any way to proceed.)

But what do you do when the two sources--subjective and objective--tell you contradictory things about Reality? That's the nub and the crux, to my mind. The best example I can think of is, sadly, not astronomical: Many Zen Buddhists believe that deep meditation connects them to an immanent cosmic unity of being, while neurophysiologists have found that deep meditation quiets the electrical activity in the area of the brain associated with a sense of self. Subjectively, mediyation validates a cosmic unity; objectively, meditation simply alters the activity of the brain.

I'm curious: If these two explanations were mutually exclusive (they're not, of course, but imagining that they were) then which would my fellow posters be most inclined to think was the truth of the matter?

(Dr. Phil, I PROMISE my next post on this thread will be astronomical through and through!)

[Zathras]

Argh. Just lost a perfectly good post through my own thumbfingeredness.

Well, Zathras, it sounds like faith in God'god/gods is a purely subjective thing for you--I think you must assume that your interior perception is connected to Reality in some way. And I like to maintain that objective science similarly has to assume that our sensory perceptions are connected to Reality in some way. Neither assumption, in my book, is provable, and they are neither mutually exclusive nor mutually dependent. You can hold one, the other, both, or neither (though if you hold neither I am blasted and blamed if I can see any way to proceed.)

Agreed.

But what do you do when the two sources--subjective and objective--tell you contradictory things about Reality? That's the nub and the crux, to my mind. The best example I can think of is, sadly, not astronomical: Many Zen Buddhists believe that deep meditation connects them to an immanent cosmic unity of being, while neurophysiologists have found that deep meditation quiets the electrical activity in the area of the brain associated with a sense of self. Subjectively, mediyation validates a cosmic unity; objectively, meditation simply alters the activity of the brain.

I'm curious: If these two explanations were mutually exclusive (they're not, of course, but imagining that they were) then which would my fellow posters be most inclined to think was the truth of the matter?

(Dr. Phil, I PROMISE my next post on this thread will be astronomical through and through!)

Right now, given the state of the particular science in question, I would throw my lot with religion. "area of the brain associated with a sense of self?" Scientists cannot even define "sense of self," let alone locate it. The science in question does nothing more than compare blood flow & electrical activity in the brain with and without the meditation. Of course there will be some changes. This expiriment actually was used the prove the converse--because there was a change in the body associated with meditation, they decided this was where the "sense of self" was. To go backwards is circular reasoning.

In the past, pyschologists conducted expiriments which allegedly proved that there was no such thing as consciousness. Should I defer to this? No, and I would be right, because consciousness is now a field of research for scientists.

[JS Princeton]

Formation of the Moon . . . . Well, all I can say is:
If it weren't for the formation of the Moon, would life on Earth as we know it exist?

Well, aside from the evolutionary benefits of tidal pools, the moon really doesn't affect the existence of life all that much.

[dgruss23]

Formation of the Moon . . . . Well, all I can say is:
If it weren't for the formation of the Moon, would life on Earth as we know it exist?

Well, aside from the evolutionary benefits of tidal pools, the moon really doesn't affect the existence of life all that much.

It is known that the Moon stabilizes the tilt of the Earth's rotation axis. Some have speculated that dramatic changes in the Earth's axial tilt would be possible without the Moon and thus the climate would be less stable which would have a significant impact for life on land:

http://adsabs.harvard.edu/cgi-bin/np...e5c03c80a28011

http://adsabs.harvard.edu/cgi-bin/np...e5c03c80a26338

See also pages 223-226 of Rare Earth by Ward and Brownlee.

[beskeptical]

Just how stable do you consider multiple ice ages, large impacts, super volcanic eruptions like Yellowstone and things like these?

Life has survived several mass extinctions without complete extinction. I will again say, here is another example where the 'Rare Earth' hypothesis may not be supported by the evidence.

[Klausnh]

I’ve just read this thread and find it fascinating.
Here’s my $.02.
My belief is that everything is connected through other dimensions and God is just a way our limited minds have to try to understand and explain that connection. To take the thread back to science, I think that 10 or 26 dimensional string theory will bring us closer to understanding what we now perceive as God and show us the connection. Once we understand the multidimensional universe, beginning and end will have no meaning and will not be necessary.
So I guess you could say I’m an atheist that doesn’t believe in a Supreme Being, but believes that God is everywhere and he is Us.

[DJ]

So I guess you could say I’m an atheist that doesn’t believe in a Supreme Being, but believes that God is everywhere and he is Us.

I don't think that makes you an athiest.

I feel so... validated

DJ

[NubiWan]

AACK!!! A den of raving Pantheists. :wink:

Just curious, does "god" have to be sentient?

[nebularain]

Well, aside from the evolutionary benefits of tidal pools, the moon really doesn't affect the existence of life all that much.

Huh? Where did that come from??? Everything I have heard suggests the formation of the Moon was an essential element for life on Earth coming to be as we know. Such as is described here .

For instance: The crust would have been thicker. Would there be plate tectonic activity with a thicker crust? Would there be plate tectonic activity without the Moon even? Do you mean this process of recycling the Earth's surface is not important to life on Earth as we know it?

The intertidal zones are essential habitats to many plants and animals that are significant to the food chain. Tides impact ocean currents and thus weather patterns. Do you mean that these factors are unimprotant to life as we know it?

Are you suggesting that everything that is important to life on Earth as we know it would be the same if there were no tides?

I defer to this web page and this web page for expansions on what I am referring to as well.

I am truly baffled. This is the first time I have ever heard a scientist/science enthusiast state or imply that we did not or do not need the Moon for our life and/or our survival.

:walking away and shaking my head:

[RickNZ]

I follow the scientific philosophy. If it cant be replicated, then discard it.

For example, that russian fellows result of two spinning super conductors altered gravity. Cant be replicated? Discard.

Now if the gates to heavens opened up and the hand of god exited baring angels to do good. Then well you cant argue with that can you?

Wether you believe in gods word or not, it doesnt matter because youll live the same life with the same benifits as your religious neighbour. You can both win lotto and get piles on that same day. Whats that you say? you cant enter heaven without following the faith?

Dont you dare extort me! Ill not be swayed by fear of the unknown like some weak minded cretin!

[DStahl]

Bad errors on my part--should have Googled first. The meditation studies showed increased activity in the frontal lobes (reasonable, given that this style of meditation requires paying attention) and decreased activity in the parietal region:

"The second image shows that there is decreased activity in the parietal lobe. This area of the brain is responsible for giving us a sense of our orientation in space and time. We hypothesized that blocking all sensory and cognitive input into this area during meditation results in the sense of no space and no time which is so often described in meditation." (reference here)

So my statement about "sense of self" was darned inaccurate.

----

On to astronomy! In a column written for Analog magazine, science fiction writer John Cramer writes about Gabriele Veneziano's super-string, M-theory speculation about the genesis of the big bang:

"Veneziano's starting point is the so-called 'scale-factor duality' of superstring theory, a symmetry in the time domain. If one knows the behavior of a system for positive times, its behavior at negative times can be predicted. He applies this duality to the universe before and after the Big Bang, reflecting the universe in the duality mirror to examine its condition before the Big Bang."

"The universe behind the mirror looks very different from ours. It starts as a nearly empty, cold, flat space. It is very simple, lacking in structure, and describable by a minimal set of parameters, but it is dynamically unstable. A small patch of this simple universe fluctuates slightly, and that patch begins to expand exponentially. As it approaches t=0 (the Big Bang) from the back side this pre-universe has a rapidly increasing Hubble parameter (or expansion rate). It squeezes through t=0 point with a maximum expansion rate, emerging as the small, hot, dense system, the Big Bang from which our universe evolved."

A more complete but still general-audience article on Veneziano's theory is on the Cern Courier website. Another is on the New Scientist website, here.

Veneziano's speculation seems to remove a need for a First Term or Prime Mover by raising the possibility that the universe is infinite into the past as well as into the future.

[DJ]

Veneziano's speculation seems to remove a need for a First Term or Prime Mover by raising the possibility that the universe is infinite into the past as well as into the future.

Think: bigger

DJ

[beskeptical]

Veneziano's speculation seems to remove a need for a First Term or Prime Mover by raising the possibility that the universe is infinite into the past as well as into the future.

Think: bigger

DJ

I'm pleased to see there are others who think the idea that we 'will never know' (in this case before the BB), is a statement that may end up being retracted and probably isn't wise to state.

I think it makes more sense that the Universe is part of something that was always here and always will be. But when I start thinking about that my mind starts thinking: nahhhh, there's no way we are even here now. :P

[kilopi]

Are you suggesting that everything that is important to life on Earth as we know it would be the same if there were no tides

There would still be solar tides. Without the moon, the solar tide would be about as strong as the neap tides are now (the tides at first and third quarter moon).

As to whether the crust would be thicker, I'm not convinced that that would be the case. The thick part of Earth's crust has been built up over the years, and it's getting bigger. Apparently, all it takes is to start from a molten state, at one time.

[cable]

creation:

all of you talking about creation without giving a definition.
a man creates with his hands, eg. a sculptor creates a statue.
seem you are attributing to God, this sort of creation. in doing so you are projecting human behaviour on God.
ie. you are making unproven xtrapolation.

think about creation of the universe,as another sort of creation where ther's no creator at all.
strange ?? not at all.
consider the chicken/egg problem. the solution could be neither an egg nor a chicken. somehing else.
strange ?? not at all.
"causality", "not physical", "creation" ... are aspects of how our brain works.
and our brain has it's limits.

miracles:

those miracles in the Bible, were written LOOOONG time after they occurred.
why no miracles nowadays ??
if God exists, then he may show us some of them. some suggestions to stay in astronomy:
- black sun in no eclypse conditions.
- earth stops spinng.
- show us the hidden face of the moon, etc .....

centuries ago, meteorological casulaties were thought to be holy punishment, attesting the presnce of God.
trouble is they hit BOTH believers and unbelievers, undistinctively. a holy injustice !!!!
to strenghthen their belief ?? yeaaaaaaaaah !!!

God controls/knows about everything ???
why don't he make some adjustments from time to time in solar system ?
why he didn't put the moon, closer to earth to help Apollo 11. or put it far away, out of reach ??
why he didn't stop wars ??

my opinion:
a God with no evidence of his presence, could equally mean no God at all.

[dgruss23]

Just how stable do you consider multiple ice ages, large impacts, super volcanic eruptions like Yellowstone and things like these?

There has been liquid water on the Earth throughout all of those events. In a broad habitability sense that is what is required for a "stable climate". If the planet completely froze then we lose the complex ecosystems. If the oceans boil away then we lose the complex ecosystems.

My perspective on this topic is that you have a stable planet as long as long term complex ecosystems can survive. What the articles I cited above suggest is that it is possible that without our large Moon, the swings in the tilt of our rotational axis would be too extreme to allow for a stable enough climate to support complex ecosystems.

Life has survived several mass extinctions without complete extinction. I will again say, here is another example where the 'Rare Earth' hypothesis may not be supported by the evidence.

Mass extinctions are not that important to this question. The Earth recovered every time there was a mass extinction precisely because we have a long term stable planetary climate that has allowed water to exist in all three phases.

The key question is what are the characteristics needed to maintain that long term stable climate. In my view that is what matters. According to the recent science you need plate tectonics, you need the large moon, you need Jupiter and Saturn out there shielding us from asteroid impacts because the simulations suggest that the Earth would get pelted with one of those mass extinction events about every 100,000 years instead of every ~ 100,000,000 years. Since the geologic evidence indicates it takes the Earth millions of years to recover the full diversity from these impacts, this would create havoc on evolution. But Jupiter can't be too close or it will prevent the planetesimals from building up a large enough Earth. Although I saw some debate about this on another thread, there is a case that red dwarfs which make up ~70% of the population may not be good life supporting stars because the habitable zone is too close and the planet would be tidally locked. Multiple star systems (~2/3 of stars) are also generally thought to be poor environments because of questions about orbital parameters for planets in such systems.

Now I'm not denying that these factors may be overly restrictive, but from what the current science suggests there is little reason to believe that we live in a galaxy with abundant civilizations. I certainly expect there is other intelligent life out there ... but the science suggests that it is a pretty rare event - which was the point of the Rare Earth book.

[russ_watters]

Just how stable do you consider multiple ice ages, large impacts, super volcanic eruptions like Yellowstone and things like these?

There has been liquid water on the Earth throughout all of those events. In a broad habitability sense that is what is required for a "stable climate".

In the past few billion years the climate hasn't deviated by more than about 10C from the average. Thats pretty stable.

[JS Princeton]

Huh? Where did that come from??? Everything I have heard suggests the formation of the Moon was an essential element for life on Earth coming to be as we know. Such as is described here .

You'll note, neb, that the moon only INFLUENCES life but life does not REQUIRE the moon. If the moon were to suddenly disappear, we would keep on living, evolution would keep on happening, and things would go on. They might be different in some ways, but there's no disastorous effects to be expected.

For instance: The crust would have been thicker. Would there be plate tectonic activity with a thicker crust?

Tectonic activity is somewhat interesting, but it is not clear that life requires tectonic activity to exist. In fact, life doesn't as far as I can tell.

Would there be plate tectonic activity without the Moon even? Do you mean this process of recycling the Earth's surface is not important to life on Earth as we know it?

It may influence life, but life does not require it, no.

The intertidal zones are essential habitats to many plants and animals that are significant to the food chain. Tides impact ocean currents and thus weather patterns. Do you mean that these factors are unimprotant to life as we know it?

kilopi pointed out that tides would still occur, and also the existential importance is different from effectual importance.

Are you suggesting that everything that is important to life on Earth as we know it would be the same if there were no tides?

Everything that is required for life to exist would still be around if the moon disappeared.

I defer to this web page and this web page for expansions on what I am referring to as well.

I don't know who wrote the first page, but it's basically wrong. I can't find any analysis that shows that their statement of "The Moon, our home planet's only natural satellite, was formed soon after the formation of the Earth and has been essential for the development of life on Earth." It may have INFLUENCED development, but it's far from essential.

The second page doesn't contradict my thesis. Here's what it has to say:

The Moon also plays a continuing role. Its driving of the tidal rhythm is important for coastal organisms, and has in fact slowed the Earth's rotation (at least from a value near 18 hours). Its tidal influence may also help stabilize the orientation of the Earth's axis, preventing the kinds of wild climate variations over geological time that Mars seems to be subject to.

This is all better, but again, it doesn't say A THING about whether life requires the moon. Indeed, it seems from careful consideration that life doesn't require the moon at all. More than that, I think their final statement is a bit off. There have been major climactic swings on Earth as well over a geologic time (they're called ice ages). Perhaps there might be something to the argument, but life can survive through catastrophes quite well, thank you. It does not require the moon.

I am truly baffled. This is the first time I have ever heard a scientist/science enthusiast state or imply that we did not or do not need the Moon for our life and/or our survival.

:walking away and shaking my head:

Well, I certainly am not alone in this. The question comes up a lot in hypotheticals "what if the moon weren't around". The answer is, things would be different, but they wouldn't prevent life from doing it's thing.

[JS Princeton]

There has been liquid water on the Earth throughout all of those events. In a broad habitability sense that is what is required for a "stable climate". If the planet completely froze then we lose the complex ecosystems. If the oceans boil away then we lose the complex ecosystems.

The rumors for the difficulties of keeping liquid water are greatly exaggerated. Comets have liquid water, Europa has liquid water, and there is probably liquid water of some sort on Mars from time to time. In effect, this argument has been shown to be not a valid one for proving a unique Earth.

My perspective on this topic is that you have a stable planet as long as long term complex ecosystems can survive. What the articles I cited above suggest is that it is possible that without our large Moon, the swings in the tilt of our rotational axis would be too extreme to allow for a stable enough climate to support complex ecosystems.

The key here is that it is "possible", not that it should happen. The fact is, this is just convenient theorizing and not rigorous. And the effects they outline do not seem to be different in type from the climactic changes already seen. I don't see how they are different.

For instance, the thesis that Mars would somehow be more stable climatically and more favorable to life with a large moon doesn't seem to be supported by any papers I can find. Perhaps you can point me to one?

More than this, once we get into the Eukaryotic details of life we run the risk of falling prey to the adaptation versus requirement fallacy. If life adapts to a stable Earth that does not mean it requires a stable Earth provided for by the moon. I definitely think that there would be differences in the ecosystem without the moon. I don't think the argument has been convincingly made that no ecosystem is possible without a moon.

Mass extinctions are not that important to this question. The Earth recovered every time there was a mass extinction precisely because we have a long term stable planetary climate that has allowed water to exist in all three phases.

That, again, is jumping to conclusions. An equally likely explanation is that Earth's ecosystems recovered in such a way that it was adapted to the stable planetary climate.

The key question is what are the characteristics needed to maintain that long term stable climate. In my view that is what matters.

But you have failed to demonstrate this is the case. The problem is, you have only one data point and we KNOW life adapts evolutionarily to its environment so that single data point has a clear sampling bias. That's pretty shoddy evidence to build a case on.

According to the recent science you need plate tectonics, you need the large moon, you need Jupiter and Saturn out there shielding us from asteroid impacts because the simulations suggest that the Earth would get pelted with one of those mass extinction events about every 100,000 years instead of every ~ 100,000,000 years.

Actually, Jupiter shielding theory, while popularly put in many textbooks, has been criticized heartily as of late. It's not clear that the analysis still stands. Do an adsabs search and you'll see what I mean. The "rare Earth" hypothesis doesn't seem to be that rigorous when it comes to simple biology. What we do have is an Earth that we're adapted to living on, so if you look at the requirement for US to live here you find that there's a lot of "coincidences". But these coincidences are just (if not more) likely to be the result of biological adaptation and not requisite for development of life in general.

Since the geologic evidence indicates it takes the Earth millions of years to recover the full diversity from these impacts, this would create havoc on evolution.

This is incorrect. The vast majority of life on Earth doesn't care at all about mass extinctions. It is only our highly adapted crown eukaryotes that have a difficult time. The more hearty bacteria and archea don't care about mass extinctions at all.

But Jupiter can't be too close or it will prevent the planetesimals from building up a large enough Earth.

This only says that we are likely to live in a solar system with a well-placed Jupiter. Since Jupiters are fairly common, it seems, there's nothing to say that we're special.

Although I saw some debate about this on another thread, there is a case that red dwarfs which make up ~70% of the population may not be good life supporting stars because the habitable zone is too close and the planet would be tidally locked. Multiple star systems (~2/3 of stars) are also generally thought to be poor environments because of questions about orbital parameters for planets in such systems.

That still leaves a whole lot of stars where things are possible. More than that, there are questions as to whether the assumptions that went into how life couldn't be maintained in multiple star systems or in red dwarfs are correct or not. I'm inclined to err on the conservative side because we are finding life EVERYWHERE we look on Earth.

Now I'm not denying that these factors may be overly restrictive, but from what the current science suggests there is little reason to believe that we live in a galaxy with abundant civilizations.

That may be true, but that's not the issue at hand. Neb insinuated that the moon was a requisite for life. I think there's ample evidence to say this is Bad Astronomy.

I certainly expect there is other intelligent life out there ... but the science suggests that it is a pretty rare event - which was the point of the Rare Earth book.

It may be rare, but the conspiracy of rarity isn't well documented as you describe it. Even if life is rare, the restrictive nature of whether crown Eukaryotes develop is probably due more to the fact that life ADAPTED to these conditions in our solar system rather than the solar system as it is set up is the way life deterministically REQUIRES the set-up to look like.

[JS Princeton]

In the past few billion years the climate hasn't deviated by more than about 10C from the average. Thats pretty stable.

Most planets in our solar system are very similar to us in that respect.

[nukular]

Correct me if I am wrong,

but with tectonic activity one typically has vulcanism which seems have to played an important role in the development of the atmosphere. Along with the magnetic field of the Earth is essential to preventing us from being bombarded by cosmic rays. As for semantics, the discovery of black smokers and the organisms surviving off of them demonstrates that "life" is somewhat ambiguous term.

As a side question, does Mars have a magnetic field? I thought I heard once that its magnetic field is extremely weak, which to me means colonizing Mars is a somewhat strange proposal because the atmosphere is surely not going to filter out all those nice cosmic rays.

[DStahl]

DJ: "Think: bigger"

Me: "What's the point?"

[DJ]

Correct me if I am wrong,

but with tectonic activity one typically has vulcanism which seems have to played an important role in the development of the atmosphere. Along with the magnetic field of the Earth is essential to preventing us from being bombarded by cosmic rays. As for semantics, the discovery of black smokers and the organisms surviving off of them demonstrates that "life" is somewhat ambiguous term.

As a side question, does Mars have a magnetic field? I thought I heard once that its magnetic field is extremely weak, which to me means colonizing Mars is a somewhat strange proposal because the atmosphere is surely not going to filter out all those nice cosmic rays.

http://science.nasa.gov/headlines/y2001/ast01may_1.htm
http://mars.jpl.nasa.gov/odyssey/technology/marie.html
http://marie.jsc.nasa.gov/Results.html

According to NASA, Mars does not have a magnetic field, and cosmic rays are definitely going to be a problem.

DJ

[DJ]

DJ: "Think: bigger"

Me: "What's the point?"

My Pithy Answer: Then why study anything at all? Why care that water boils at ~212F as long as you eventually figure out that when you put it on fire long enough, it boils and you can cook with it? Science didn't discover cooking.

My non-Pithy Answer: It's a valid question. The only answer I can come up with is: in order to discover it, you must think it.

Though the mental gymnastics you perform may seem arbitrary and completely unprovable, you just never know. Also, I find it keeps things in perspective down here on the ground. I try to never lose sight of exactly how big it really is.

DJ

[dgruss23]

dgruss23 wrote:

There has been liquid water on the Earth throughout all of those events. In a broad habitability sense that is what is required for a "stable climate". If the planet completely froze then we lose the complex ecosystems. If the oceans boil away then we lose the complex ecosystems.

JS – Thanks for the comments. Good Stuff. Before I respond let me make sure that you understand what I mean when I’m talking about “life” and “complex ecosystems”. I’m not advocating any formal definition here, but what I’m talking about is not bacterial or microbial life but multicellular life. Since the issue centers around other intelligent life I would hope we could agree that the complex ecosystems needed to sustain such life must include producers, consumers, preferably a terrestrial environment for reasons I’ll save for later if that is a point of debate, and some form of liquid for life chemistry. When I’m talking about frequency I’m not even placing a restriction that the planet must have intelligent life – only that it would have an environment capable of supporting an intelligent, technological species should one evolve. I also want to apologize to everybody that decides to read this because between JS’ comments and two sets of my comments this response is ridiculously long.

JS wrote: The rumors for the difficulties of keeping liquid water are greatly exaggerated. Comets have liquid water, Europa has liquid water, and there is probably liquid water of some sort on Mars from time to time. In effect, this argument has been shown to be not a valid one for proving a unique Earth.

I never said unique Earth. As I’ve tried to be clear about I’m talking about the evidence that is suggestive of planets like ours not being very common – rare. Now rare might mean different things to different people since this whole topic is very speculative. Lets just say that I’ve read nothing that leads me to believe there is a great chance of more than 100 technological civilizations being out there in our galaxy right now. But I understand that new developments could change that. So to help with numbers I’m going to say that if there is anything less than 100 civilizations out there, then that is compatible with my concept of “rare” given the galaxy has hundreds of billions of stars.

As for Mars and Europa - Sure they may have water, but I’m not seeing the complex terrestrial ecosystems. Why not? Mars is too small and Europa is too cold. Without an ice crust, there would be no oceans on Europa.

dgruss wrote:

My perspective on this topic is that you have a stable planet as long as long term complex ecosystems can survive. What the articles I cited above suggest is that it is possible that without our large Moon, the swings in the tilt of our rotational axis would be too extreme to allow for a stable enough climate to support complex ecosystems.

JS wrote: The key here is that it is "possible", not that it should happen. The fact is, this is just convenient theorizing and not rigorous. And the effects they outline do not seem to be different in type from the climactic changes already seen. I don't see how they are different.

They suggest that the Earth’s rotation axis could vary as much as 90 degrees. I think that would be quite a bit different than the climate we have since an Earth tilted at 90 deg. Would have quite the different seasonal pattern (See Neil F. Comins book “What if the Moon Didn’t Exist” for a description of what the Earth might be like if it was tilted like Uranus.

JS wrote: For instance, the thesis that Mars would somehow be more stable climatically and more favorable to life with a large moon doesn't seem to be supported by any papers I can find. Perhaps you can point me to one?

Why would we make that comparison when Mars is clearly uninhabitable (again complex ecosystems) due to its small size. Now if Mars was the size of Earth that would be a neat comparison.

JS wrote: More than this, once we get into the Eukaryotic details of life we run the risk of falling prey to the adaptation versus requirement fallacy. If life adapts to a stable Earth that does not mean it requires a stable Earth provided for by the moon. I definitely think that there would be differences in the ecosystem without the moon. I don't think the argument has been convincingly made that no ecosystem is possible without a moon.

I agree with this entirely- and I'm not basing my points upon individual adaptations. I never said there would be no ecosystem without the Moon. Again what I’m pointing out is that complex ecosystems might be more difficult without the Moon. Sure the idea has not been proven, but it has not been disproven either. The computer models at least back up the possibility.

dgruss wrote:
Mass extinctions are not that important to this question. The Earth recovered every time there was a mass extinction precisely because we have a long term stable planetary climate that has allowed water to exist in all three phases.

JS wrote: That, again, is jumping to conclusions. An equally likely explanation is that Earth's ecosystems recovered in such a way that it was adapted to the stable planetary climate.

You’ll need to clarify here. I’m not sure exactly how your response is a response to what I said.

dgruss wrote:

The key question is what are the characteristics needed to maintain that long term stable climate. In my view that is what matters.

JS wrote: But you have failed to demonstrate this is the case. The problem is, you have only one data point and we KNOW life adapts evolutionarily to its environment so that single data point has a clear sampling bias. That's pretty shoddy evidence to build a case on.

I disagree that we only have one data point. Mercury, Venus, the Moon, Mars, Pluto, the Moons of the outer planets are all data points. None of these objects have complex ecosystems and none of these objects has all of the same physical/geological features that the Earth has. They share some in common, but they don’t have all. If planetary size and plate tectonics were not important then why doesn’t Mars still have liquid water? Are there any other hypotheses out there as to why Mars lost its surface water? Isn’t the prevailing view that it did not have the plate tectonics needed to maintain its atmosphere? That said, I’ll agree that when we finally discover more complex ecosystems on other worlds, we’ll have a better basis for drawing conclusions. But nonetheless, the lessons we draw from the Earth offer a scientifically viable set of possible requirements.

dgruss wrote:
According to the recent science you need plate tectonics, you need the large moon, you need Jupiter and Saturn out there shielding us from asteroid impacts because the simulations suggest that the Earth would get pelted with one of those mass extinction events about every 100,000 years instead of every ~ 100,000,000 years.

JS wrote: Actually, Jupiter shielding theory, while popularly put in many textbooks, has been criticized heartily as of late. It's not clear that the analysis still stands. Do an adsabs search and you'll see what I mean.

Thanks for the tip on that. I’ll check it out.

JS wrote: The "rare Earth" hypothesis doesn't seem to be that rigorous when it comes to simple biology. What we do have is an Earth that we're adapted to living on, so if you look at the requirement for US to live here you find that there's a lot of "coincidences". But these coincidences are just (if not more) likely to be the result of biological adaptation and not requisite for development of life in general.

Every species is adapted to its conditions. But that doesn’t make it all coincidences. We can be pretty sure that if the Earth was the size of Mars we wouldn’t be here debating this. We can be pretty sure that if our planet had no terrestrial environments we wouldn’t be here debating this. We can be sure that if the planet was completely frozen over we wouldn’t be here debating this. So any features of our planet that make a terrestrial environment with liquid water possible must be evaluated as possible requirements for complex ecosystems. Why would those requirements change for other solar systems. Its not about the adaptations of specific species its about setting up a functional planet.

dgruss wrote:
Since the geologic evidence indicates it takes the Earth millions of years to recover the full diversity from these impacts, this would create havoc on evolution.

This is incorrect. The vast majority of life on Earth doesn't care at all about mass extinctions. It is only our highly adapted crown eukaryotes that have a difficult time. The more hearty bacteria and archea don't care about mass extinctions at all.

I'm well aware of the microbial world. Since I’ve explained above that I’m talking about complex ecosystems with animals/plants, I’ll stand behind the evidence that geologists have uncovered about recovery from mass extinctions … and the animals/plants are part of the full diversity.

dgruss wrote:
But Jupiter can't be too close or it will prevent the planetesimals from building up a large enough Earth.

JS wrote: This only says that we are likely to live in a solar system with a well-placed Jupiter. Since Jupiters are fairly common, it seems, there's nothing to say that we're special.

The second part of that sentence is not yet demonstrated. Yes they’ve found lots of Jupiters. But they’re much bigger in many cases and much closer to their stars in almost all cases. I remember we discussed this before and its definitely relevant here. First, I know that there is a bias in the sample of extrasolar planets. But the detection techniques allow us to identify solar systems similar to ours (the gas giants that is). And yet there are no solar systems at all like ours. But why not? We have detected Jupiters at 3-5 AU distances, but we also find Jupiters much closer in those same systems and much more massive - both factors that would affect terrestrial planets. So there isn’t a strong case that the set-up of our solar system is a common set-up - even though the detection techniques are good enough to find such systems. Thus we don’t need to find the Earth like planets to begin to see hints that they might not be very common.

dgruss wrote:
Although I saw some debate about this on another thread, there is a case that red dwarfs which make up ~70% of the population may not be good life supporting stars because the habitable zone is too close and the planet would be tidally locked. Multiple star systems (~2/3 of stars) are also generally thought to be poor environments because of questions about orbital parameters for planets in such systems.

JS wrote: That still leaves a whole lot of stars where things are possible. More than that, there are questions as to whether the assumptions that went into how life couldn't be maintained in multiple star systems or in red dwarfs are correct or not. I'm inclined to err on the conservative side because we are finding life EVERYWHERE we look on Earth.

I’m not surprised we find life everywhere on Earth. The planet is habitable after all. But if a planet isn’t suited to evolve life in the first place then it doesn’t really matter how comparable some environments on those planets might be to extreme Earth environments. My feeling is that if the conditions are right, life will very likely evolve. I’m just not convinced that it is easy to get all the right conditions.

dgruss wrote:

Now I'm not denying that these factors may be overly restrictive, but from what the current science suggests there is little reason to believe that we live in a galaxy with abundant civilizations.

JS wrote: That may be true, but that's not the issue at hand. Neb insinuated that the moon was a requisite for life. I think there's ample evidence to say this is Bad Astronomy.

It depends upon what you mean. Without the Moon the planet might still have bacterial life. I’d say the odd aren’t too bad there, but I’d also say that the odds of complex ecosystems would go down quite a bit … as long as they are in fact correct about the axial tilt stability. If that’s wrong then sure the Moon has much less relevance.

dgruss wrote:
I certainly expect there is other intelligent life out there ... but the science suggests that it is a pretty rare event - which was the point of the Rare Earth book.

JS wrote: It may be rare, but the conspiracy of rarity isn't well documented as you describe it. Even if life is rare, the restrictive nature of whether crown Eukaryotes develop is probably due more to the fact that life ADAPTED to these conditions in our solar system rather than the solar system as it is set up is the way life deterministically REQUIRES the set-up to look like.

What conspiracy of rarity? This is not a plot against life here. You either have suitable conditions or you don’t. Nor is the possible rarity as poorly documented as you suggest.

Again with regard to adaptation – I have no problems with Natural Selections sculpting all sorts of organisms in all sorts of strange environments. The rare Earth arguments are really about two questions. 1. What is needed for life to be able to form on a planet? 2. What is needed for life to be able to evolve complex ecosystems? - Keeping in mind that that is the relevant question if we’re talking about the odds of finding other civilizations. Earth in fact shows us that bacteria hang on where complex ecosystems will not.

Thanks JS! This is a good discussion.