Talk:Rare Earth hypothesis

Non neutral POV

All the arguments and explanations presented only with one point of view. That of our Earth.

If you have arguments and explanations from the perspective of another inhabited planet, I'm all ears. Marskell 09:18, 16 November 2005 (UTC)

Nice joke, but what he's saying is similar to the carbon chauvanism counterargument used to counter the Rare Earth hypothesis. We cannot simply assume without proof that carbon-based life is the only type of life possible. Ever seen the alternative biochemistry article? Andreus 18:46, 11 July 2006 (UTC)

Fantastic work here, guys. (Wayne Hardman)

I'm not clear how the issue of NPOV is relevant to this article. If this article is presenting the fundamentals of the Rare Earth hypothesis, which is a sensible hypothesis (id est, a hypothesis sensible people can get behind, though still allowing other sensible individuals to disagree with it), to claim it is "POV" is trivially true. The hypothesis by definition is proposing a specific point of view, just as, say, an article about the Democratic or Republican party would carry a "POV" simply by stating the guiding principles of those political parties. Thus to say that the article is POV is a meaningless attack. And in a subtle way, it is a disqualifier of the hypothesis itself.

As an aside, I've noticed that lately, an awful lot of articles are being labeled "POV" simply for acertaining facts—facts about people's opinions about specific subjects and topics. Question: If an article is explaining what a specific group of people think, how can it avoid being POV? Just a thought. --TallulahBelle 01:32, 19 August 2006 (UTC)

A problem I've had with this article is that it lists 'facts' supporting the hypothesis without adequately presenting other interpretations of the evidence. For instance, the section The galactic habitable zone states, The orbit of the Sun around the center of the Milky Way is almost perfectly circular, with a period of 226 Ma, one closely matching the rotational period of the galaxy. The Sun's orbit is so perfect that it has remained clear of the spiral arms of the Milky Way over its entire 4.6 Ga lifetime. I added one reference (there are many others available) that shows that other astonomers interpret observations to mean that the Solar system passes through spiral arms on a regular basis. -- Donald Albury^(Talk) 12:21, 19 August 2006 (UTC)

I read the book some years ago, and am looking for it now in order to tweak the article. Reading the article more carefully, the key assumption made by the Rare Earth hypothesis remains unstated, and that key assumption is that, since intelligent life takes billions of years to develop, such development can only be successful in environments (planets) that have remained very stable over those billions of years. That stability, the hypothesis goes on to say, is statistically very improbable.

I think the problem with the article as it stands now is that it is stating the Rare Earth hypothesis almost as if there had been a teleological determinism to the events described—that is, it is stating things as if some higher power had deliberately but subtly made the universe the way it is just so that we humans would develop.

But from what I recall, the hypothesis is statistical in its approach: It is basically saying that the planet we humans live on is the result of wildly improbable events that created a stable environment suitable to our brand of intelligent life. The hypothesis, from what I recall, wasn't saying that these wild improbabilities were the result of a higher power—it was saying that in a large enough statistical sampling, any odd-ball example can be found. The upshot is that, for the theory, life on Earth is the result of a combination of several statistical anomalies that in no way imply a higher power controlling or influencing events.

Over the weekend I'll reread the material I have and rewrite the article to remove that cloying feel the article currently has. As an aside, I find the theory in its distilled form fascinating. And it is the only hypothesis that satisfactorily answers the Fermi paradox, at least to me. --TallulahBelle 13:46, 19 August 2006 (UTC)

Whether the argument is teleological or statistical, there are many assumptions in the argument. When there are prominent published reliable sources that contradict or call into question the assumptions made in the argument, those other views must be included to achieve balance. Personally, I think that there are other possible explanations for the Fermi paradox that do not require Earth to be 'rare'. The only constraint that the Fermi paradox seems to impose is that technological civilizations engaging in interstellar exploration or travel or, pouring energy into space, are very rare at this time. One possibility is that a sufficiently advanced civilization won't waste energy by spewing it into space. I also think that there is considerable doubt whether Earth will ever send people or machines more than very short distances outside of the Solar System, and I would not be surprised if space exploration is eventually abandoned as too expensive. In any case, we need much more data before we can draw more than the shakiest of conclusions. -- Donald Albury^(Talk) 17:01, 19 August 2006 (UTC)

No, Ward and Brownlee make no mention of teleology. Guillermo Gonzalez, who worked with them and is quoted approvingly and at length in the book, does apparently make an "argument for God" in the Privileged Planet. W & B were apparently unaware he published intelligent design articles—the story is there in one of the reviews.

In any case, I don't think the problem here is an implied teleology, but simply that the article has been presenting the book's arguments without qualification as Dalbury is suggesting. Rare Earth is fascinating, but they consistently cherrypick arguments that support their position and present overly definitive statements as to what planets/systems/galactic regions cannot support life. To some degree the book is a polemic. The anon who was editing this, however, would simply take "A cannot B" and repeat it here without qualification. I tried to remove this pattern in the first few sections but, as often happens, left it for some other wiki-work because the page is so damn long. This, BTW, is why the balance tag is there, and I don't think it should be removed yet—the page needs to be carefully scoured. If and when you have a go at this, it would be nice if you could shave off ten K. Marskell 17:15, 19 August 2006 (UTC)

I disagree strongly that the article is POV-tainted. (a) it's obviously describing a theory which of necessity involves describing the arguments for that theory, and (b) contrary viewpoints are presented. This is an excellent example of a well-researched thourough article. I petition the Wikipedia Gods to remove the POV tag. Jberkus 20:12, 8 October 2006 (UTC)

Done. BTW, the second paragraph vectors people to the opposite, the principle of mediocrity. I think that takes in the larger scale NPOV problem. And let's face it, we just don't have the observations to say how rare the earth is yet so it's got to be opinion if you are going to have an article at all. Keith Henson 00:18, 25 October 2006 (UTC)

Fact check.

Someone needs to fact check this as the "99% of stars are red dwarves" statistic conflicts with at least two other Wikipedia pages. 'fraid I don't have time or expertise tho.

There appear to be a lot of other facts in here that need checking too, or at least proper qualification of how certain they are. Despite recent advances we still know very little about what it takes for a planet to become Earthlike, stating that there must be this or that condition is probably inappropriate. Bryan 04:55, 23 Mar 2005 (UTC)

But surely the assumption that a whole series of improbable events are required to create an Earth-like planet is a premise of the Rare Earth hypothesis. Once you qualify this by saying these events are not necessarily so improbable, and may not all be required anyway, then you have created a different hypothesis - something like the Not Quite So Rare Earth hypothesis, perhaps. Having said that, the point that the Rare Earth hypothesis is based on assumptions rather than known facts should probably be stated more clearly in the intro. Gandalf61 20:25, Mar 23, 2005 (UTC)

I think it must be mentioned that the planet itself must have oceans in which life will be created. Because life can emerge only in liquids but not in gas (because molecules interact with each other pritty rearly) or hard state (because molecules do not interact at all). Also the planet must have a magnetic field to repel the radiation. See Mars for a good example - it has no magnetic field and the atmosphere and (eventualy) any water is blown off by the solar wind making it a desert planet.

Interaction with other bodies???

I don't deny that an impact with Earth probably occured, but I don't think that it is necessary for plate techtonics. In Earth's beginning the interior is very hot, and heat from the core began pushing it's way to the surface as a mantle plume. The plumes would form numerous volcanoes and hot spots (like Yellowstone) that would begin to seperate the crust with three huge cracks, or rifts, at 120° (the Red Sea, Arabian Sea, and the East Africa Rift System are examples of three rifts). As the crust began to push against itself, it would eventully begin to fold and split with one side going below the other forming many subduction zones. Volcaninc arcs would begin forming on the overlying basin. As the thicker volcanoes on a subducting plate approaced the subduction zone it would be accreted to the overlying plate and a new trench would begin forming on the other side of the volcano. This method of accretion formed the cratons of the continents.

If you want a good example, boil a soup of some kind (or anything else that would form a lot of bubbles) and watch how the heated bubbles will be grouped together between the rising "hot spots" of the liquid. BRO_co03 23:43, Mar 30, 2005 (UTC)

This is not an assertion on our part, but rather we assert that the authors of the hypothesis assert it. I don't doubt your objection has been raised elsewhere — you might want to add something about it to the criticism section if you can find an authoritative source about it (otherwise I'm afraid it's only original research). Deco 03:34, 31 Mar 2005 (UTC)

Correction Made

I have changed 99% to 70% for the percentage of Red Dwarfs while noting 5% for G stars. See for instance:

[1], 3.3 or [2]

I have never heard the 99% figure. Dwarfs period, perhaps (the sun is technically a dwarf, after all, just not a red one :)? Marskell 15:29, 11 Apr 2005 (UTC)

I changed it to 90%, based on the Spectral classification article. But maybe this is wrong too. Ben Standeven 03:23, 16 Jun 2005 (UTC)

Looks like 70% are M class and 20% are K class. Of course, the article doesn't mention the dwarf/giant divide, which is also significant. Ben Standeven 15:14, 19 September 2006 (UTC)

Position of our Solar System in the Milky Way

I was taught that our sun is in fact located in the spiral arms of the Milky Way. This page says the Sun would have to be located outside of the spiral arms to avoid events that would destroy life on Earth.

I don't have a reference handy, but my understanding is that spiral arms are not permanent structures, but rather density waves, so that stars move in and out of spiral arms. -- Donald Albury^(Talk) 10:52, 20 July 2006 (UTC)

Here's a site stating the 'density wave' theory for 'Grand Design' spiral galaxies. And this page says that the sun does indeed pass through spiral arms on a regular basis. -- Donald Albury^(Talk) 11:15, 20 July 2006 (UTC)

What's being done here

The new greatly expanded article is presenting too many statements of fact rather than qualified arguments (it's also rather verbose). Small example: "The central star cannot be a multiple star system, for which the stability of planetary orbits is problematic". We have no business saying it "cannot be". See the binary star heading on Planetary habitability.

That said, a great deal of work has gone into this (by an anon I think). I feel we just need to step back and examine the language we are employing. Marskell 11:27, 26 June 2006 (UTC)

"The central star cannot be a multiple star system, for which the stability of planetary orbits is problematic" describes standard thinking in astrobiology since the 1960s. Moreover, the sentence asserts that planets that are part of multiple star systems are less likely to support complex life, not that complex life is impossible on such planets.

Repeat

Anon, you there? The work effort is great, but the language in this article is exceptionally problematic. After the intro, essentially everything is presented as a statement of fact. Another example: "Complex life requires water in the liquid state." Period. We have not business writing sentences like this. We don't know what complex life requires because we only have one example of it. That's the central fact of this entire field, for the lay person and scientist alike. This article is advocating, not describing, a position. Marskell 21:26, 9 July 2006 (UTC)

I agree. Serious accuracy/POV problems. The anon is probably not coming back soon. Please be bold and fix it. Deco 01:53, 10 July 2006 (UTC)

"Complex life requires water in the liquid state." is intended to describe Ward and Brownlee's thinking and should be read in that spirit. No one can pretend that that sentence is a statement of fact. It would be hopelessly tedious and pedantic to preface every statement with "Ward and Brownlee state that...", "...believe that...", "contend that...", and so on.

The intent of this entry is not to describe the universe and its history, but to summarize the book Rare Earth, noting concurring academic voices and giving due deference to critical ones.

Metallicity problem

To be honest, I am unconvinced by the "stars-with-low-metallicity-cannot-support-terrestrial-planets" argument. Take a look at Tau Ceti which has anything from 70% to 22% the metallicity of Sol yet astronomers have found ammounts of asteroidal/comet-like material exceeding Sol's nearly tenfold. They say this makes it very likely that the star supports terrestrial planets. Of course, having that many asteroids and comets would be adverse to life in other ways but consider that a star possibly having only a fifth of the Sun's metallicity has that much solid, asteroidal matter around it - I think that's bound to cause some doubt in the theorems surrounding metallicity and its relation to terrestrial planet formation. Consider the Zeta Reticuli binary system, for instance - both stars of which are believe to have 60-70% of Sol's metallicity - they were ruled out of the HabCat project because of this, I belive. Evidence garnered from Tau Ceti could suggest terrestrial planet formation around Zeta Reticuli might be more likely than we think.

There are other serious issues that I have with the Rare Earth hypothesis, such as its carbon chauvanism.

I hold no brief for the "stars-with-low-metallicity-cannot-support-terrestrial-planets" position. While it is standard in the contemporary literature, Rare Earth included, it could well be mistaken and I am happy to acknowledge that. Truly low metallicity, by the way, is not 20% or 50% of Sol, but more like <10% or even <1%. And it appears that there are many galaxies, and many parts of the Milky Way, whose metallicity is a tenth or even a hundredth of that of Sol. The purpose of this entry is, again, not to describe the "truth" about the universe, but to summarize the book Rare Earth and its critics.

I would welcome someone adding 200-500 words to this entry describing the "carbon chauvinism" position.

Abundance of asteroids, comets and dust around Tau Ceti does not imply there are any terrestrial planets around it. Look at our asteroid belt: there's much dust there, but no planet. Moreover, all these asteroids combined would be less even than our Moon. And this is why there is an asteroid belt instead of planet - there is not enough material to coalesce into a single planet. The same situation may be around Tau Ceti - there is much dust there, but only because actually there is not enough to create planets. If planets were formed, they would coalesce most of the dust, and we would see much less dust there. Grzes 13:22, 27 September 2006 (UTC)

so that the star will only gradually, if at all, drift into a spiral.

It seems counterintuitive to the point being made to not have made this edit. I hope someone will confirm.

This site indicates that the solar system passes through a spiral arm about every 100 million years. -- Donald Albury^(Talk) 11:10, 20 July 2006 (UTC)

So our solar system has a less than optimal galactic orbit, but one that has not proved catastrophic.

I would say the Sun has a typical orbit for stars in spiral galaxies outside of the central core. Stars close to the core move faster than the spiral arms. Orbital speed decreases with distance from the core, so stars furthar out move more slowly between spiral arms, until at some radius from the core, the orbital speeds of stars approximately match the speed of the spiral arms. Even further out, the orbital speed of stars is less than that of the spiral arms, and you could say that the spiral arms catch up with stars and pass around them. As the extra mass in spiral arms tends to pull stars towards it both when the star is approaching and when it is receding, stars spend more time in spiral arms than would seem the case just looking at the width and spacing of spiral arms. All in all, I would say there is nothing special about the Sun's orbit in the Galaxy, and if staying out of spiral arms is optimal, there are very few stars that qualify, and the Sun isn't one of them. -- Donald Albury^(Talk) 14:59, 20 July 2006 (UTC)

n sub e

The article says:

• $n_{e}$ is the average number of planets in a star's habitable zone. This zone is fairly narrow, because constrained by the requirement that the average planetary temperature be consistent with water remaining liquid throughout the time required for complex life to evolve. Thus $n_{e}$ = 1 is a likely upper bound.

This is a problematic paragraph for two reasons. (1) The time required for complex life to evolve is already covered in $f_{l}$. and (2) $n_{e}$ cannot have an upper bound of 1 since in our own solar system, there are two planets in the habitalbe zone: Earth and the Moon. Aelffin 22:45, 13 August 2006 (UTC)

Nice point. And double planets probably are not rare either, as we have a second pair in the Solar system, Pluto and Charon (unless, that is, you don't accept Pluto as a planet). Now, let's find some sources that make those points. :) -- Donald Albury^(Talk) 09:21, 14 August 2006 (UTC)

Can you provide a reference that states that the moon is a planet? And no, Pluto is not a planet  ;-) - SigmaEpsilon → ΣΕ 20:11, 31 August 2006 (UTC)

Well, Pluto was a planet when I posted my comment. :-) Also note that the first proposal, which was rejected in favor of the one that reduced Pluto to a dwarf planet, would have made Charon a planet. As for the Moon being a planet, see Double planet, Welcome to the double planet at the European Space Agency, and here, an argument that the Earth-Moon system will eventually become a double planet. :-) -- Donald Albury 23:53, 31 August 2006 (UTC)

After reading all three articles, I still come to the conclusion that Earth and the moon are not a double-planet system.

• The double planet article specifically states that scientific consensus is against considering the moon part of a double-planet system; especially considering the IAU's recent decision.
• The ESA article only mentions "double planet" once, and has no scientific basis for that claim.
• The last link you give is just one person's (your?) letter to the IAU

- SigmaEpsilon → ΣΕ 01:27, 1 September 2006 (UTC)

Not my letter, and I guess my smileys were not prominent enough. In any case, 'double-planet' has been used many times to describe the Earth-Moon system (just Google for it), even if it is not scientifically valid, and the letter merely points out that the Earth-Moon system will eventually evolve to the point where it does meet the IAU definition of a double planet. -- Donald Albury 08:56, 1 September 2006 (UTC)

Perhaps in a few billion years we can reconsider the Rare Earth Hypothesis, but for now $n_{e}\leq 1$ is still not contradicted by our solar system. As far as this section of the talkpage is concerned, RE is valid. - SigmaEpsilon → ΣΕ 10:27, 1 September 2006 (UTC)

Rotation?

The giant impact theory hypothesizes that the Moon results from the impact of a Mars-sized body with the very young Earth. This giant impact also gave the Earth its axis tilt and velocity of rotation (Taylor 1998). Rapid rotation reduces the daily variation in temperature and makes photosynthesis viable.

Question: Why is the Earth's rotational speed attributed to the impact? Mars has a rotational speed very similar to Earth's without any evidence of a massive impact in the past. If the impact is what gave Earth its relatively rapid spin, what gave Mars its? Nik42 05:22, 18 August 2006 (UTC)

The Earth's rotation was much faster in the past (10-hour day?), and the Moon was much closer. Tidal friction has both slowed the Earth's rotation and pushed the Moon's orbit out. The close similarity of Earth's present rotational speed to that of Mars is a temporary (on a geological time scale) phenomenon. However, you are right, the impact theory does not explain why Mars rotates in just over 24 hours while Venus rotates in just over 243 days. Either other processes can give a planet a relatively fast rotation, or Mars also suffered an unidentified major impact, which implies that such impacts are not rare. -- Donald Albury^(Talk) 23:14, 18 August 2006 (UTC)

Stellar Flares In Red Dwarfs

The page in the section discussing the problems with red dwarfs, fails to mention the fact that many if not most of them periodically undergo stellar flares, where they emit out hundreds of thousands of times more x-rays than they normally do. Such flares would bake any planet close enough to the star to support life. I don't know if this was mentioned in the book, but it's an additional factor.

Correct me if I'm wrong.

Under "Rare Earth Equation" :

"And if any factor is near zero, so is the product of all factors."

This is not true. With the extremely high orders of magnitude in the calculation, a near zero factor does not imply a near zero product. For example: 1 x 10³⁰ * .000000000000000000000001 = 1 000 000 —The preceding unsigned comment was added by Stottpie (talk • contribs) 01:43, 8 December 2006 (UTC).

So what is consensus?

We can speculate all we want, but what is current scientific consensus as to the validity of the Rare Earth hypothesis? More generally, what is the most probable scientific resolution to the Fermi paradox? Neither article answers any questions about consensus, compared to an article like intelligent design which mentions in the first paragraph what the consensus is. 76.19.173.43 23:38, 1 January 2007 (UTC)