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Other Life in the Multiverse?

What conditions would you say are ‘congenial to life’? For physicist Robert Jaffe and colleagues at MIT, the phrase refers to places where stable forms of hydrogen, carbon and oxygen can exist. Jaffe explains why:

“If you don’t have a stable entity with the chemistry of hydrogen, you’re not going to have hydrocarbons, or complex carbohydrates, and you’re not going to have life. The same goes for carbon and oxygen. Beyond those three we felt the rest is detail.”

It’s an important issue in Jaffe’s work because he wants to see whether other universes could harbor life. We know that slight changes to the laws of physics would disrupt the evolution of the universe we live in. The strong nuclear force, for example, could have been just a bit stronger, or weaker, and stars would have been able to produce few of the elements needed to build planets. Remove the electromagnetic force and light would not exist, nor would atoms and chemical bonds.

Nudging Nature’s Parameters

Run through the constants of nature and you’ll find many that have to show precise values for life as we know it to have formed. Thus the idea that there may be not one but many universes, each with its own laws, and the thought that we happen to occupy a universe where the conditions that make life a possibility managed to fall into place.

Anthropic reasoning like this — things have to be this way because otherwise we couldn’t be here to think about all this — suggests that multitudes of universes exist, a multiverse in which almost all the universes would be devoid of life and, indeed, matter as we know it. Jaffe is interested in finding out whether universes with different physical laws might not be so inhospitable to life after all. His team focused on universes with nuclear and electromagnetic forces that allow atoms to exist. Another stipulation: Universes that allowed stable forms of hydrogen, carbon and oxygen.

Then it became a matter of playing with nature’s building blocks. Take quarks: In our universe, the ‘down’ quark is roughly twice as heavy as the ‘up’ quark, so that neutrons are 0.1 percent heavier than protons. Jaffe’s team lightened up the down quark so that protons were up to one percent heavier than neutrons. According to this modeling, hydrogen would no longer be stable, but the heavier isotopes deuterium and tritium would be. Carbon-14 could exist and so would a form of oxygen. It’s a different universe than ours, but the models say life could emerge in it.

Other quark variations, including one where the ‘up’ and ‘strange’ quarks have roughly the same mass, unlike in our universe, produced atomic nuclei made up of neutrons and a hyperon called the ‘sigma minus,’ which would replace protons. The fact that we have a reasonable understanding about quark interactions makes them useful for studies of this kind, but changing other physical laws is even trickier business.

Into a ‘Weakless’ Universe

Nonetheless, Lawrence Berkeley National Laboratory researchers have modeled universes that lack one of the four fundamental forces of ours. Without the weak force big bang nucleosynthesis — turning groups of four protons into helium 4 nuclei of two protons and two neutrons — would not have been possible. But when the team at LNBL removed the weak nuclear force in their models, they were able to tweak the other three forces to compensate. Stable elements could form in this universe as well.

Note what’s happening here. Rather than changing a single constant, the LBNL researchers tweaked several. After all, in a multiverse that can keep spewing out universe after universe, all combinations would seem to be possible and you can keep trying until you get it right. This Scientific American article by Alejandro Jenkins (MIT) and Gilad Perez (now at the Weizmann Institute) gets into the specifics:

In the weakless universe, the usual fusing of protons to form helium would be impossible, because it requires that two of the protons convert into neutrons. But other pathways could exist for the creation of the elements. For example, our universe contains overwhelmingly more matter than antimatter, but a small adjustment to the parameter that controls this asymmetry is enough to ensure that the big bang nucleosynthesis would leave behind a substantial amount of deuterium nuclei. Deuterium, also known as hydrogen 2, is the isotope of hydrogen whose nucleus contains a neutron in addition to the usual proton. Stars could then shine by fusing a proton and a deuterium nucleus to make a helium 3 (two protons and one neutron) nucleus.

But would these stars be anything like what we are familiar with? The article continues:

Such weakless stars would be colder and smaller than the stars in our own universe. According to computer simulations by astrophysicist Adam Burrows of Princeton University, they could burn for about seven billion years—about the current age of our sun—and radiate energy at a rate that would be a few percent of that of the sun.

A Strange But Living Universe

A strange place, this ‘weakless’ universe. Supernova explosions of the kind that synthesize and distribute heavy elements in our universe would not occur, at least not from the same causes, but a different kind of supernova caused by accretion rather than gravitational collapse would be possible, allowing elements to seed interstellar space. A planet like ours circling one of the weakless stars would need to be six times closer to the Sun to stay habitable. And check this out:

Weakless Earths would be significantly different from our own Earth in other ways. In our world, plate tectonics and volcanic activity are powered by the radioactive decay of uranium and thorium deep within Earth. Without these heavy elements, a typical weakless Earth might have a comparatively boring and featureless geology—except if gravitational processes provided an alternative source of heating, as happens on some moons of Saturn and Jupiter.

Chemistry, on the other hand, would be very similar to that of our world. One difference would be that the periodic table would stop at iron, except for extremely small traces of other elements. But this limitation should not prevent life-forms similar to the ones we know from evolving. Thus, even a universe with just three fundamental forces could be congenial to life.

Accounting for the Cosmological Constant

Still tantalizing is the cosmological constant, a measure of the amount of energy found in empty space. The discovery of the continuing acceleration of the universe’s expansion has brought ‘dark energy’ into the picture, implying a cosmological constant that is positive as well as minute, allowing the universe to form structure. It’s a constant that seems fine-tuned to a remarkable degree, and as the article notes, “…the methods our teams have applied to the weak nuclear force and to the masses of quarks seem to fail in this case, because it seems impossible to find congenial universes in which the cosmological constant is substantially larger than the value we observe. Within a multiverse, the vast majority of universes could have cosmological constants incompatible with the formation of any structure.”

All of this is almost joyously theoretical, basing itself on a theory of inflation that conceives of small pockets of spacetime that inflate so rapidly that it is impossible to travel between them. Inflation is highly regarded but not definitively understood, but different values for the constants of nature in the universes it produces seem like a reasonable conjecture. And the cosmological constant itself is an example of fine-tuning on such a scale that it may require the existence of a multiverse to give us a rational explanation for how we lucked into this one.


Comments on this entry are closed.

  • Eniac February 25, 2010, 10:58

    It does not make sense to speak of the “Existence” of other universes. We get heavily into semantics here. For one, the original meaning of “universe” is “that which contains everything”, so by definition there cannot be anything outside of the universe, nor can there be a plural.

    However, this does not undermine the anthropic principle. Indeed, it could be postulated that there is no reality beyond mathematics. Universes “exist” as mathematical possibilities, with ALL possible values of the parameters to the Theory of Everything. We ourselves only exist as constructs within one of those mathematical frameworks. We perceive those possibilities as real that contain us, so of course those must be the ones that allow our “existence”.

    Our asking the question “why is everything so fine-tuned to create us?” is like a prime number asking “Why do I not have any divisors other than 1 and myself?”

  • Blade O'Grass February 25, 2010, 12:35

    First there was nothing, and then it exploded.

    :/ … : )) … Ha!

    What do the folks here think of the like the idea of plasma cosmology or an electric universe? I found some interesting info. at:


    Fun stuff if you’re into alternate concepts…I also like the expanding Earth theory (no, I don’t think it’s holo…what do you think I am–some sort of wobblie-eyed nutter?).

  • Steve February 25, 2010, 12:59

    Eniac, “the universe” is often used in cosmology to refer to the observable universe, that 93 billion light year sphere we can detect. Phenomena like Dark Flow(1) strongly indicate that there’s more than we can see; indeed, expansion theory indicates there’s 10^23 to 10^26 more out there than we can see. Some cosmologists think that different conditions in the initial shape of the Big Bang could lead to different physical laws in the sections beyond our observation.

    (1) http://en.wikipedia.org/wiki/Dark_flow

  • NS February 25, 2010, 15:55

    There are a number of ways in which “different universes” may exist:


    Cosmologist Max Tegmark originated the classification discussed:


  • NS February 25, 2010, 16:29

    This downloadable paper by Tegmark (also linked from his site) looks like a good summary of his multiple universe ideas:


    Sorry for the hasty multiple posts…

  • Christopher L. Bennett February 25, 2010, 17:33

    What I want to know is: what would happen if people from our universe crossed over into one of these other continua like the “weakless” universe or the varied-quark universes? Would they be able to survive? Would the EM interactions between their own particles still have the values from our universe, or would they adopt the local values? And could their bodies — and consciousness — survive such a change in EM field strength? Or if they went into a universe with different quark types, would the “exotic” quarks making up their bodies remain stable or would they decay into something native to that universe?

    Naturally, my interest as a writer is in whether you could tell a story about people exploring an alien universe, or about beings from an alien universe coming here. Is such direct interaction possible, or would interaction be limited to some form of communication such as gravity waves?

  • David W February 25, 2010, 17:54

    You can go back to Hoyle on find tuning all well described by Barrow and Tipler on the 1986 in the Anthropic Cosmolgical Principle.
    Tipler has since gone on to Physics of Immortality and Physics of Christianity in which he proposed Baryonic annhilation for interstellar travel and consuming the Dark Energy.

    More on Robert Forward -Forward came up with a quantm aspect of consciousness at least 10 Years before Penrose and Hameroff

    Tipler has his critcs but he never proposes new physical laws and I dont recall Forward did either

  • David W February 25, 2010, 17:57

    Sorry it should be FINE tuning and IN ACP.
    Neither my me or my laptop have been working right recently

  • Athena Andreadis February 25, 2010, 23:48

    The weak anthropic principle is a tautology, and hence totally void as a predictive scientific tool. The strong anthropic principle is equivalent to theism.

    Hoyle also believed in a steady-state universe, and in the notion that bacteria arose spontaneously in the interstellar medium. He cut his science to fit his religious views.

    As for Penrose and Hameroff’s quantum theory of consciousness, it’s too silly to even discuss. Quantum decoherence sets it at much smaller scales than those of the cell or its molecular components.

  • Eniac February 26, 2010, 0:02

    Cosmologist Max Tegmark originated the classification discussed

    I guess that means I’m with Tegmark, then.

    This is pretty much want I wanted to say, only said much better:


    I don’t think we need all of those other bubbles and dimensions and stuff, Tegmark’s level IV by itself covers everything, literally. What remains now is to finally find this particular TOE that we owe our existence to.

  • ramkumar February 26, 2010, 2:12

    lee smolin promulagated a theory of natural selection amoung multiverses.
    the universe that will have life forms will be the ones with best DNA .That will be the ones with correct six fundamental costants.Anthropic principle is valid .A small value change in strong neuclear force would have resulted in a universe only with hydrogen and no heavier elements …yet there might be lot of failed Big bangs …lot of universes were hydogen has not concentrated to form stars.

  • Athena Andreadis February 26, 2010, 11:16

    Define “best DNA”, Ramkumar.

  • Athena Andreadis February 26, 2010, 11:54

    The anthropic principle, like its “rare earth” extension, is circular. In science, theories cannot be identical to their predictions, nor can their predictions be trivial. The anthropic principle and the rare earth theory is neither hypothetical nor predictive. They’re merely descriptive. Calculating probabilities after the fact is equivalent to placing a bet after the race has been run. It is also not a coincidence that most adherents of the anthropic principle are religious, and several of them are unabashed creationists.

  • Eniac February 26, 2010, 15:43

    It is true that the anthropic principle is not predictive, which is why it is not called a theory. It falls into the category of unprovable interpretations that are the subject of philosophy. It does, though, neatly explain away the “coincidence” and “fine-tuning” that is often misused by those same religious and creationist types Athena is referring to.

    I would not call it circular, though. The usual meaning of circular in reasoning is that you assume the thing you want to prove. The anthropic principle does not do any such thing, precisely because it is neither hypothetical nor predictive.

    The rare Earth hypothesis, on the other hand, is a real hypothesis. It could easily be falsified by finding ubiquitous life, and evidence for it can be accumulated through continued fruitless search. I would not lump it with the anthropic principle. There is a relationship, however: The anthropic principle makes the Rare Earth hypothesis much easier to accept, since it addresses the discomfort about the “coincidence” associated with it.

  • Ron S February 26, 2010, 17:01

    Eniac: “The rare Earth hypothesis, on the other hand, is a real hypothesis.”

    Depends what you mean by this. Since Earth and all of its attributes, including us, comes about by natural causes, there must be some prior probability for Earth being as it is (and, importantly, a pdf for a spectrum of similar and interesting planets). We do not know the probability (or pdf), except that it is greater than zero. Assume some value for this probability. If you do, I can tell you the probability of two or more planets. It isn’t much lower than it is for Earth (that is, one or more such planets).

    One of the difficulties about discussing Rare Earth is that there is a diversity of assumptions about quantifying ‘rare’. Often I hear folks declare Rare Earth to mean there can only be one. This is nonsense, as I outlined above. It’s important to quantify ‘rare’ in a discussion about Rare Earth.

  • Athena Andreadis February 26, 2010, 17:20

    Rare Earth hypothesis: though bacterial life may be common in the universe, terrestrial intelligence is unique. Prediction: upon examining other planets, we’ll find that bacterial life is common, and intelligence absent.

    I don’t know how anyone else defines circular, but this meets my criteria. For more, here’s my review of Rare Earth, whose skewed presentation I found highly suspicious before I knew that the creationist Guillermo Gonzalez was a major consultant to the book’s author: http://www.setileague.org/reviews/rarearth.htm

  • Terraformer (a.k.a Tobias Holbrook) February 26, 2010, 18:30

    “Rare Earth hypothesis: though bacterial life may be common in the universe, terrestrial intelligence is unique. Prediction: upon examining other planets, we’ll find that bacterial life is common, and intelligence absent.”
    How is it circular for a hypothesis to predic what it, well, predicts? The hypothesis: bacterial life common, advcanced life not. That’s the same as predicting bacterial life common, advance life not so. It’s not circular reasoning. If I have a hypothesis that, for example, release of a certain chemical into the water supply will result in mass death, and it is found that when that chemical is released into the water supply, a lot of people die, I haven’t used circular reasoning.

  • Doug M. February 26, 2010, 19:29

    “The anthropic principle, like its “rare earth” extension, is circular. In science, theories cannot be identical to their predictions, nor can their predictions be trivial.”

    The anthropic principle has one firm, falsifiable prediction under its belt. Only one, but it was a doozy: Fred Hoyle, carbon resonance, and the triple-alpha process. Trivial, this was not.

    Attacks on this one tend not to be “it wasn’t a prediction” — because it most certainly was — but “it wasn’t really the anthropic principle”. Specifically, Hoyle may have put it in terms of “we’re here”, but what he really meant was, “carbon is here”.

    Perhaps; it’s a continuing argument. But any condemnation of the anthropic principle has to at least touch on this episode in passing.

    Doug M.

  • amphiox February 26, 2010, 20:34

    It’s important to quantify ‘rare’ in a discussion about Rare Earth.

    It is also important to quantify ‘Earth’.

  • Eniac February 26, 2010, 20:52

    Rare Earth hypothesis: though bacterial life may be common in the universe, terrestrial intelligence is unique. Prediction: upon examining other planets, we’ll find that bacterial life is common, and intelligence absent.

    I don’t know how anyone else defines circular, but this meets my criteria.

    How exactly is this circular? I do not know your criteria for circular, but to me the above sounds like a straightforward testable hypothesis.

  • drpayton February 27, 2010, 0:24

    The idea of multiple universes is an interesting idea though I really invisioned it differently. More like massive galaxies of galaxies…or universe sized supernovas feeding other universe systems. Universes could be in huge systems that interact with eachother… Some of the galaxies in our “universe” could have come from another “universe” the way I conceptualize it multiverse could exist but the same laws govern it all. Just a thought don’t know if it is even possible.

  • Ron S February 27, 2010, 1:13

    Me: It’s important to quantify ‘rare’ in a discussion about Rare Earth.
    amphiox: It is also important to quantify ‘Earth’.

    Yes, as I elaborated upon in the paragraph prior to the one you quoted me from. Plug in whatever “attributes” you believe are important (I saw no reason to be specific in a description of a general statistical argument) and the algorithm I (concisely) specified will apply.

  • drpayton February 27, 2010, 2:44

    Anthropic?… We aren’t able to see the reality of the universe because we are on the inside looking out… If the cells in our body were sentient would they be able to conceptualize the fact that they were part of a larger organism, especially if they couldn’t see the group as a whole? It makes most of what we see conjecture at best because we have no true frame of reference. We can create theory after theory but until we find a true constant (light?) then the questions answered will simply be followed by more questions… But at least we are here to ask them. Ftl will happen because we have imagined it. There are others because we are here. We will meet them because we want to. I am therefore I think!………. Athena I don’t know the math of it but it seems that the rare earth theory has arose from people who are tired of thinking about it… How rare is anything in the observable universe? How rare are spiral galaxies? How rare is liquid water? I think from the surface u are probably right, the rare earth theory is probably derived by someone who wants it to be true and a theist is someone who would most want that to be true. However the same could be said of an atheist who didn’t want the rare earth theory to be true. Thing is, millions of intelligent civilizations across infinite space doesn’t disprove the existence of architecture. Nor does the fact that we have seen no signs of life other than our earth prove the presence of architecture. ” In science, theories cannot be identical to their predictions, nor can their predictions be trivial” How very true and obviously universal. A theory proven true is not affected by the beliefs of the mind that concieved the idea. I’ve read several things that have been written here and I noticed that belief in a deity seems to automatically disprove an idea or theory and it occured to me that bias is not part of the scientific process as it was taught to me in highschool lol. In fact I think that religion helps ease the paradox of self awareness. If nothing else it could be one of the things necassary for the survival of an evolving species such as ourselves. One thing that I do know for sure is that tolerance a factor that must be in place if we as a species ever expect to become a spacefaring lot. Without tolerance we will never so much as colonize our own solar system! It is the proliferation of team work that the Tau Zero Foundation is built upon and the common goal is to come together regardless of creed and reach for our place in time and space.

  • Eniac February 27, 2010, 11:38


    Depends what you mean by this. Since Earth and all of its attributes, including us, comes about by natural causes, there must be some prior probability for Earth being as it is (and, importantly, a pdf for a spectrum of similar and interesting planets). We do not know the probability (or pdf), except that it is greater than zero. Assume some value for this probability. If you do, I can tell you the probability of two or more planets. It isn’t much lower than it is for Earth (that is, one or more such planets).

    You can turn this around. If you give me the number of stars in the observable universe, I will give you a pdf that will comfortably predict 1 Earth over 2 or more with a large margin. This works with any definition of “Earth” and any definition of “large margin”.

    Such a pdf will, of course, predict 0 Earths at an even much higher probability, that is until you add in the observation that there is at least one Earth. The posterior probability after this observation will then predict one Earth, exactly, with a very high margin. This is a Bayesian version of the rare Earth hypothesis, and it makes it somewhat plausible, without, of course, proving it.

  • duffer February 28, 2010, 19:42

    …many that have to show precise values for life as we know it to have formed. Thus the idea that there may be not one but many universes, each with its own laws…

    Why “thus”? Why does anthropic reasoning “suggest” the existence of multiverses? Such notions are only demanded if the design (capitalised or not, as you prefer) hypothesis is a priori excluded.

    It is not obvious to me why the idea of multiverses populating a fundamental physical parameter space of truly supra-astronomical dimensions (in every sense) is more implausible, or more scientific, than that of a designed universe. And it does seem it’s got to be either one or the other.

    And before you start, I’m no young-Earth creationist or even intelligent design believer in the biologically micromanaging sense (though the question of exactly how life got started remains a gaping hole in our understanding that shows no sign of being filled any time soon, and IMHO receives far too little attention). I would answer to ‘theistic evolutionist’.

  • duffer February 28, 2010, 19:45

    Oops. For ‘more implausible’, please read ‘less implausible’.

  • Ron S February 28, 2010, 22:22


    I’m not even sure where to begin, but I’ll try. I apologize if I’m being overly brief, but I don’t want to write too much right now.

    First, you can invent any pdf you like, *if* you can justify the choice.

    Second, something that I was carefully trying to avoid doing, seems to be something you have done, which is to be a bit careless in choice of Bayesian versus frequency analysis in separate parts of the process. If I misunderstood you, I’ll apologize in advance. The thing is, you claim a pdf based on a frequency, then jump into a Bayesian analysis by taking this as a prior or a posterior probability, depending on Earth’s inclusion in the sample. This is making my head hurt.

    While I didn’t get into it (figuring that no one would much care) I was keeping to a strictly frequency analysis. This should have been clear when I stated, “there must be some prior probability for Earth being as it is…Assume some value for this probability.” This is non-Bayesian. I did this deliberately for the purpose of painting a specific scenario where I assume that the probability of a population of planets exhibits one or more attributes that the Earth exhibits (for example, presence of life) and proposed to then calculate relative probabilities between one-or-more and two-or-more planets of that class. My base case was general natural law, not one based on empirical evidence such as “Earth exists, so there is at least one planet of this class.” If your intent is to calculate an estimator based on the empirical evidence, Earth is a significant item and Bayesian analysis is the proper choice. But that isn’t what I was doing!

    Briefly, the program I was describing assumed a probability of a planet exhibiting attributes (as I said, it is unknown but p>0) and then doing that relative comparison. To select a pdf (from an infinity of choices) I assumed statistical independence and a fixed observation point (present era). A good first-order choice is a cumulative Poisson since I want to calculate the more useful and interesting n >=k, rather than n=k. Then I compare the cases of k=1 and k=2. If you do this for an EV (expected value)=1 or, equivalently, that p=0.0025, representing that Earth is the only planet among ~400 planets and exoplanets known to exhibit life), then for k=1, P~=0.632, and for k=2, P=~0.264, and there is a 99% probability that the actual number is between 0 and ~3.57.

    Again, all I was trying to demonstrate is that Rare Earth arguments simply can’t be used to say that you can have exactly one planet (Earth) with the claimed attribute (e.g. life) yet also claim that the probability for more is vanishingly small in comparison. To do so would require special pleading, such as some version of the Anthropic Principle.

  • Ronald March 1, 2010, 6:49

    I tend to agree with Athena.

    The circularity of the Rare Earth hypothesis is not so much in the prediction of the prevalence of microbial life and rarity of complex life (which can indeed be tested, at least theoretically), but in the fact that is is based on non-subjective and biassed premises.
    The idea is based on the premises: conditions must be very similar to earthlike conditions for complex life –> these very earthlike conditions are very rare –> complex life is very rare.
    Earth was the starting point of the analysis, in stead of more objective parameters, logically leading to the conclusion that (exactly) this must be exceedingly rare.
    It is similar to a person living alone on a lonely island, stating that, because his little island and he himself are so unique, there cannot be other islands and other beings anywhere else.

    This isn’t scientific analysis, it’s just chauvinism.
    Any scientific analysis should not take one complete end result (earth as we know it) as a starting point and norm, but rather all the essential component parameters. And might then come to the conclusion, for instance, that a slightly cooler (i.e. more orange) sunlike star (such as G5/G6) is in fact more optimal for life-giving conditions and that we are actually very lucky to be here with such marginal conditions ;-)

  • Eniac March 1, 2010, 16:28


    I do think we agree on pretty much everything, I was simply pointing out that the prior probability for 1 Earth could easily have an expectation value of 10^-10, rather than your EV=1. I believe both are equally unjustified choices.

    If you then admit the existing evidence of at least one Earth, and reconcile that with the prior (Baysian or not), you get the prediction that there is exactly one Earth. Or, more precisely, the chance of getting two is about 1 in 10^10

    You are right about the special pleading, too, and this is exactly why the rare Earth hypothesis only becomes plausible in combination with the anthropic principle, which I thought I had made clear.

    Think of it as a strict probability problem, solidly frequentist: The universe is made of 1000 dice (stars) and each has a chance of 1:1,000,000 (Drake equation) of coming up “Earth”. You then keep drawing universes by throwing the dice. After throwing a billion times, you will have, on average, 1 million cases of 1 Earth, 1,000 cases of 2 Earths, 1 case of three Earth’s, and no cases of more. We can find ourselves in any one of the 1,001,001 universes with at least one Earth in it, but you can see that in the overwhelming number of cases there will be only one.

    If you are one that thinks that the universe was given only a single chance, you would find the 1:1,000,000 chance implausible, because it would make your own existence very improbable. If on the other hand, you adhere to the Many-worlds, Universal Ensemble, or Anthropic Principle school of thought, you would have no problem with it, and might in fact find a small probability very plausible, given all the factors that have to come together just right.

  • Eniac March 1, 2010, 16:40


    Hypotheses are frequently based on subjective and biased premises, even some that turn out to be true. Neither that, nor chauvinism, however, have a lot to do with circular, so I am still baffled by the “circular” characterization.

    That said, I am myself not a fan of the Rare Earth hypothesis and hope that it will be falsified soon.

  • Ronald March 1, 2010, 18:15

    Of course I meant non-objective (i.e. subjective) premises in my previous post.

  • Athena Andreadis March 1, 2010, 18:32

    Hypothesis: Earth is rare or unique.
    Prediction: Earth is rare or unique.

    Hypothesis: Parameters are such that this universe contains humans.
    Prediction: Different parameters would result in this universe not containing humans.

    The predictions are trivial and/or identical to the hypotheses. The reasoning is circular (tautological, if you like more polysyllables) and descriptive, not predictive. Furthermore, the anthropic principle blithely ignores the fact that all our knowledge is based on a single sample, as well as the role of chance into specific outcomes — the Yucatán asteroid is a prominent example. Of course there won’t be any humans anywhere else. But there may be a plethora of Others, up to and including advanced sentience.

    Such “hypotheses” would get their originators zero papers or grants in the peer-reviewed domain. Popular books, well, there the level of science can vary from high to basement. I discuss the anthropic principle and the rare earth “theory” in one of my reviews. Ward and Brownlee’s book in particular was full of errors across all the domains it chose to investigate. For example, they state that Mars and Venus are orbit-locked, in their hurry to make earth unique (there are plenty of other howlers, but they’re more specialized).

  • Administrator March 1, 2010, 19:20

    Athena wrote:

    Ward and Brownlee’s book in particular was full of errors across all the domains it chose to investigate. For example, they state that Mars and Venus are orbit-locked, in their hurry to make earth unique (there are plenty of other howlers, but they’re more specialized).

    Are you sure about this, Athena? I’ve got Rare Earth in digital format and running a search on both Mars and Venus doesn’t turn anything up about orbital locking. Maybe you’re thinking of a different book?

  • Athena Andreadis March 1, 2010, 20:10

    No, Paul. I’m thinking of Rare Earth. I reviewed the first edition. It is possible that they changed it, if they edited the book in subsequent versions. I certainly would have done so in their place.

  • Ron S March 1, 2010, 21:22


    I think you’re right that we’re nearly agreed. The one difference, which you seem to have correctly described, is that you are sampling universes and I am sampling within one universe. Which one you choose very much depends on the hypothesis you’re exploring.

  • Eniac March 1, 2010, 22:53

    Athena: I do not think your characterization of the rare Earth hypothesis is fair. It is like saying “Hypothesis: the Earth moves”, prediction: the Earth moves”, to mock Galileo. You would ignore that the hypothesis was motivated by observations, and the predictions can be much more concrete. The same goes for Rare Earth, it is motivated by a book full of more or less reasonable observations, and predictions can be more concrete, e.g. “SETI will be unsuccessful”.

    The anthropic principle is indeed a tautology, if you look at it solely as “if things were different, things would be different.” However, once you get into how different exactly things would be (would there be life, would there be intelligence), it becomes far from trivial. And the tautology itself works just fine as a philosophical principle, taking care of the “fine-tuning” which would be surprising (or require design) otherwise. At least, as a tautology, you do not have to worry about whether it is true or not…

    I like this collection of the different theories, quoted from http://en.wikipedia.org/wiki/Anthropic_principle (and I subscribe to #3, more or less):

    Paul Davies’s book The Goldilocks Enigma (2006) reviews the current state of the fine tuning debate in detail, and concludes by enumerating the following responses to that debate:

    1. The absurd universe

    Our universe just happens to be the way it is.

    2. The unique universe

    There is a deep underlying unity in physics which necessitates the universe being the way it is. Some Theory of Everything will explain why the various features of the Universe must have exactly the values that we see.

    3. The multiverse

    Multiple Universes exist, having all possible combinations of characteristics, and we inevitably find ourselves within a Universe that allows us to exist.

    4. Creationism

    A creator designed the Universe with the purpose of supporting complexity and the emergence of Intelligence.

    5. The life principle

    There is an underlying principle that constrains the universe to evolve towards life and mind.

    6. The self-explaining universe

    A closed explanatory or causal loop: “perhaps only universes with a capacity for consciousness can exist.” This is Wheeler’s Participatory Anthropic Principle (PAP).

    7. The fake universe

    We live inside a virtual reality simulation.

  • Administrator March 2, 2010, 11:29

    Athena wrote:

    No, Paul. I’m thinking of Rare Earth. I reviewed the first edition. It is possible that they changed it, if they edited the book in subsequent versions. I certainly would have done so in their place.

    Interesting! The text was evidently changed after the first edition, and Athena checked on this later and sent me the original text, which clearly showed the statement that Venus and Mercury were tidally locked to the Sun. I now wonder what other changes might have occurred between editions.

  • Athena Andreadis March 2, 2010, 11:51

    Paul, thank you for posting the note. I, too, wonder how many things they changed, after they received an avalanche of criticism for their sloppiness and for unquestioningly incorporating the “facts” fed to them by Guillermo Gonzalez, a well-known creationist whose views determined his scientific conclusions. Of course, if they changed all the errors of the first edition (the discussion of plate tectonics, the real number of genes in the human genome, etc) that would weaken their thesis significantly.

    If anyone is interested in finding out how biased and cherry-picked the “facts” are in Rare Earth, read David Darling’s Life Everywhere: The Maverick Science of Astrobiology.

    Eniac, the rare earth hypothesis, at least as presented in the Ward & Brownlee book (and in a later Scientific American article about habitable zones, co-authored by one of the authors and Gonzalez, as well as in Gonzalez’ The Privileged Planet) does not make predictions other than to repeatedly state that all the conditions that shaped earth must bring us to the unavoidable conclusion that only earth can harbor complex life — particularly sentient highly technological life like humans.

    This conclusion is 1) trivial, since nobody argues that humans could arise elsewhere, or even on earth if circumstances were even slightly different, 2) biased, since it privileges the specific circumstances of earth for no particular reason except that we happen to be here and 3) statistically invalid, since it bases sweeping conclusions on a single sample. The authors do not allow anything that would disagree with their thesis to rear its ugly head; they present incorrect supporting “facts” or violently shoehorn data into Procrustean beds to support their “theory”. Both Rare Earth and The Privileged Planet are rather obvious vehicles for intelligent design — the first unconsciously so (at least so the authors say); the latter very much on purpose.

  • Eniac March 2, 2010, 13:18

    Maybe they took Athena’s review to heart and fixed all of the whoppers she found. Talk about whitewashing a rotten fence…

  • Athena Andreadis March 2, 2010, 14:21

    Whitewashing a rotten fence… I love the concept and image! *still laughing*

  • Eniac March 2, 2010, 19:40

    I got into trouble for my principled defense of a concept I don’t believe in and the name of which has previously been sullied beyond rescue in a book I have not read. I must try to do better. :-)

  • drpayton March 4, 2010, 0:30

    How many systems have we found planets in? I apologize in advance if that information has already been posted… But if it was say 10000 then that’s 1 in 25…and that’s just the ones we are capable of seeing in those systems… So how could the rare earth theory even be plausible? We have viewed a very minuscule part of our near space and have found planet after planet. Intelligent life is likely more rare than “basic” life, but even if u look at humans ourselves we are all very different. Take for instance allergies. Not only do we adapt but we adapt differently, and some cannot adapt at all though they are human. I can eat shell fish… Others it kills. A smoker lives to be 90 a non- smoker dies of lung cancer. People live in jungles, on islands, in mountains, and on oceans…(We even have intelligent life other than us in the oceans) this says volumes about how diverse life is and how intelligence and adaptability has happened in billions and billions of ways right here on our own planet . I am not an astrobiologist (what exactly do they study lol) or even an amateur astronomer, but common sense says that there are others out there… wondering the same things we are. The amount of planets we have found in such a short time is not coincidence it is simply because there are just so many of them out there. It is just a matter of time before we find a blue jewel in the sky! Not to say that a planet exactly like ours is the only kind that could have life, just that we can go there and look around without life support lol. Would an experiment that involved sending cultures of extremophiles to venus be a good study of the diverse atmospheres life could exist in? Look I’m just a regular guy and there is obviously nothing technical about what I am saying and I really have nothing to base my opinions on but looking at our own planet and all the different types of life I have to paraphrase Jody Foster in Contact ” if we are the only ones then that’s an awful waste of space”

  • Eniac March 5, 2010, 2:37

    It used to be people said planets are rare. Now we know better, they aren’t. However, there are many factors in that Drake equation, many of which we know nothing about. Just because some of them turn out to be nice and large does not mean they all are. There may be one or two that we know little about that are extremely small.

    The origin of life is a candidate. We know in principle how it might have occurred, but we certainly do not know enough to put a number on the probability. Once you have life, evolution is a powerful force pushing for higher complexity, but before that, the anthropic principle is really all we’ve got. So, it could be that the reason the universe is as large as it is, is that it needs to be this large to produce us. If that was true, there might be only us, or at most a handful of others, in the entire universe.

  • Athena Andreadis March 5, 2010, 12:40

    Eniac, in a word, no. We don’t just have the anthropic principle; we also have the mediocrity principle. In any case, both are philosophy (and philisophy lite at that) rather than science — the former more so than the latter. If you start asking how complex non-terrestrial life is, how far from here it is, how similar it is to us — those are not yes or no questions. But if you ask “Is there life in the universe beyond earth?” I guarantee you the answer is yes.

  • Eniac March 7, 2010, 18:07

    What I meant is the anthropic principle is the only answer we have for the fine tuning problem. Why do all the physical constants conspire to allow complexity to exist in the universe? The mediocrity principle does not answer that, does it?

  • Ron S March 7, 2010, 22:08

    The anthropic principle doesn’t really tell us much, and may not even be acceptable (falsifiable) as a scientific theory:

    My own admittedly not-deeply-thought-through view is that it is barely one ladder rung above goddidit (god of the gaps), since if the universe is truly fine tuned to permit our existence then we still have the question of how it happened or how it occurred. The anthropic principle is not an answer.

    Related to the above-referenced debate between Smolin and Susskind, there is Smolin’s own hypothesis/theory of how this universe came to be as it is:

    I’ve read Smolin’s book and, while I find it intriguing, I remain unconvinced. This isn’t a easy problem and so may remain unresolved for a long, long time.

  • Administrator March 8, 2010, 9:43

    Ron, we should also mention Sean Carroll’s recently published From Eternity to Here: The Quest for the Ultimate Theory of Time (Dutton), which I’ve just finished. Carroll walks through the numerous current theories about the multiverse and the problem of entropy and time’s arrow. And of course, you’re right — we’re nowhere near resolving these matters, and Carroll speaks of many of these notions not as ‘theories’ but as ‘predictions.’

  • Eniac March 8, 2010, 10:32


    I think we all agree that the anthropic principle is not a falsifiable theory. Some see it as a tautology, which would make it a trivial, self-evident truth. Whatever it is called, I find it useful in that it really does explain why physical laws are as they are, to me it removes the “Gee, isn’t that a terrible coincidence” surprise you otherwise have to deal with when pondering cosmology.

    To me, Smolin’s “fecund universes” theory sounds like an awkward substitute for the anthropic principle, where the concept of irrelevance (what good is a cosmos that does not contain us) is replaced by some kind of actual “death” or lack of “reproduction”.

    The most convincing argument I have heard on these philosophical issues is the “type IV multiverse” of Tegmark, which, IIUC, says that there is no such thing as reality, except for that of mathematics, and that therefore there is no one privileged Theory of Everything (TOE), all possible mathematical constructs are equally valid. The one governing “our” universe (in line with the anthropic principle) is one which allows sufficiently complex solutions to describe us and everything we see. Even within one TEO, there is nothing to privilege our particular solution with respect to other ones (in which things would have gone slightly or terribly different), except for our point of view. There might be others like us in some other solution of the same TOE (or in some other TEO) who would be wondering the same thing.

    What I like about this particular interpretation is that it cleans up all the various “paradoxa” we get in quantum mechanics, quite neatly, in line with the many-worlds interpretation originating with Everett and Wheeler.

    I feel, but have no proof, that following this logic (and with some kind of maximum entropy arguments), the “reality” we find ourselves in will most likely be tuned just enough to produce us, but not (wastefully) be tuned even better such that there are numerous other intelligent species around. This would be a shame, but it would neatly explain the Fermi paradox. And, it would be better than some of the other solutions to the Fermi paradox, especially those postulating our imminent extinction. At least this one would leave us unencumbered to go out and claim the universe for ourselves.

    The other view would be that any tuning precise enough to produce us would automatically also produce many others, but I cannot quite see the inevitability of that.