Do the authors of “Privileged Planet” fail to present quantifiable measures for habitability and measurability?
Yes – the measures aren’t quantifiable. However, does that mean they aren’t significant, or scientific? No. Let me give an example.
The Earth’s atmosphere is transparent in the “visible” part of the electromagnetic spectrum. This is a very narrow part of the EM spectrum, and it is only “visible” because that’s where our eyes happen to be sensitive. But the fact that our eyes are sensitive to light in this band doesn’t do justice to the significance of this narrow band of frequencies. Photons of this energy are “just right” in terms of molecular reactions – they are of a high enough frequency to lead to chemical reactions (in our retinas; in plants) but not so high that they will break up complex molecules (unlike ultraviolet). They are also at a frequency at which it is possible to recognise that there is a difference between different stars. These are key frequencies for observing the universe – though there is no guarantee that an atmosphere would be transparent at these frequencies – and they are key frequencies for habitability – for the presence of intelligent, complex species.
If we wanted to, we could quantify this sort of issue. We could ask how many of the planets that we know about have an atmosphere that is transparent to light with these frequencies. We could ask what combinations of gases allow for such a visible atmosphere. We could ask what range of surface temperatures of the stellar primary could allow for such an atmosphere to be present at the triple point of water. We could go on, and ask what proportion of planets have moons that are large enough to stabilise the angle of the planetary axis. How many planetary bodies allow total eclipses of the stellar primary? What proportion of interstellar space has sufficient density of elements to form planet systems ... but without such a great density as to obscure the rest of the galaxy and the universe.
But the thing is, even as we word this sort of question, we know that the reason that the theory isn’t quantifiable is not because the issues are vague and hand-waving, but because the earth is – to all intents and purposes – unique. The probability of finding another planet like earth, upon which life might appear, is incredibly small. And that is before you address the issue of how life itself might appear.
Do they rely on a single data point?
No. Although we only have one “earth-like” planet to look at, we can learn plenty about the rest of the universe by looking elsewhere, and also by deducing what other parts of the universe are like on the basis of our understanding of physics. So we know that the band of habitability within the solar system is small – and that the likelihood of complex life arising outside the galactic habitable zone within a spiral galaxy is small – and that gas giants close to the stellar primary (as interstellar observations have often revealed them) will destabilise planets further out, whereas further out gas giants (like Jupiter and Saturn) will protect against asteroid impact – and that non-spiral galaxies are much less likely to have stable planetary systems – and that the fine tuning of physical constants is such that they produce a physically and chemically complex universe – in addition to the traditional facts that a G2 type star is heavier than 90% of stars, but is large enough to have a significant circumstellar habitable zone, but not so large that it will exhaust its fuel in too short a time for evolution to occur, nor so large as to bombard its planetary system with too much high energy radiation. There may be only one Earth for us to look at, but we can see what the rest of the universe is like – and by looking at the rest of the universe, we can see how atypical the Earth is.
In essence, the process is the same as that followed by the SETI programme when looking for life elsewhere in the universe. It makes an assessment of how likely life is to be present in orbit around different stars. This is only based on our knowledge of one star system, and one form of life. Are their assumptions about where intelligent life might be found unreasonable? Well, I haven’t heard objections from the science community to this pursuit. In fact, Carl Sagan’s “Contact” was all about the programme. But of course, whereas SETI would (in effect) support the principle of mediocrity, PP opposes it. Whereas the SETI programme has been optimistic about the possibility of there being life elsewhere – because, according to the principle of mediocrity, there can’t be anything special about Earth (Sagan apparently thought there might be 100,000 intelligent forms of life just in this galaxy) – PP is pretty negative.
Is PP simply an extension of the Weak Anthropic Principle?
PvM suggests that Richards and Gonzalez’ belief in humans’ ability to observe is simply a product of what we happen to be able to observe – in other words, we don’t know that we have a “globally optimal” position to observe the universe.
However, this fails to deal with the fact that as far as physics is concerned, the belief of science is that things are – in large measure – pretty well tied up now. The principle forces that shape the universe – the electroweak force, the strong nuclear force, gravity – and the fundamental particles that constitute the mass-energy of the universe, and the fundamental physical constants, are well mapped. There may be surprises – there almost certainly will be, in fact – but science has a pretty good understanding of how most of the 15 thousand million lightyear radius of space in which we find ourselves behaves. And the environments in which any of the rest of the explanations are likely to be hiding (dark matter, for example) are not likely to be environments in which complex, intelligent life might evolve.
PvM hypothesises a Planet X on which relativity hasn’t been discovered, and argues that we may continue to be in the dark (figuratively) concerning some other “obvious” scientific idea. That may be the case. However, as far as physics is concerned, the laws that we already know describe the behaviour of the universe to many decimal places (perhaps darwinian biologists find it hard to believe that such a level of confidence is possible concerning scientific processes!). So given our confidence in our understanding of the universe, whilst technically the argument appears to be irrefutable, in practice it looks less solid.
Can the Privileged Planet hypothesis be falsified?
PvM argues no. He says:
The following statement by the authors
Finally, we don’t argue that Earth is unique. Discovering another planet around another star in the Galaxy would be quite compatible with our hypothesis, so long as that planet is genuinely Earth-like. Finding a fundamentally different planet with (native) complex life on it, in contrast, would contradict our argument that the conditions for life and scientific discovery correlate in the universe.
makes even less sense. Why would finding a ‘non earth like planet’ with complex life contradict their claim of correlation. Since such a planet would show another datapoint in favor of a correlation between life and scientific discovery.
He seems to have misunderstood what Gonzalez and Richards are getting at. The hypothesis is something like: “There is a correlation between habitability and measurability, which indicates intelligent design.” So the falsification they offer is intelligent, complex life being found on a planet that is not earth-like – that is, although suited for habitation (evidently, if life is found there), not suited for observing the universe.
However, I think the hypothesis is strong enough to go further. As a stronger falsification, let me offer: is it possible to conceive of an environment that might exist anywhere in the universe that would have the same levels of habitability (suitable for a complex biosphere, including intelligent, complex life) and observability (that in the space of let’s say 4000 years, an intelligent organism might go from having no knowledge of technology to having a full understanding of the structure of the universe). In other words, don’t even try and beat it – don’t worry about looking for a better environment. Just try and find an environment that is as good.
And that’s where my strongest theological objection to the Privileged Planet can be found. By insisting that the earth is privileged based on some mathematical arguments, the authors miss the obvious, the earth is privileged because that’s where we are living. To suggest that a Creator would create a universe with countless planets and consider only one to be privileged requires a knowledge and understanding of said Creator, beyond our realm of knowledge. In fact, it shows a certain level of hubris.
Now this is the real crunch, and it comes to the real heart of the opposition to the book from people whose science in theory oughtn’t to be connected. Because, if it is the case that Earth is privileged, as the authors suggest, then we are no longer in the realms of Intelligent Design in the abstract sense. We don’t just “happen to be here”, with some intelligent agent out there of provenance unknown throwing teasing bits and pieces in our direction. All of a sudden, if the hypothesis is true, we – the people who are able to observe the universe, on this privileged planet – represent the focus of the universe. All of a sudden, there is a link between science and theology – our ability to know about the universe, and our significance as an organism.
Although this may come as a surprise to PvM, theologically it is not unreasonable to suggest precisely what he suggests. Are the authors being anthropocentric? Not from a Christian point of view – not if Christianity is true. From this perspective, humans were created by an infinite-personal God to be stewards of the universe. The claim of the Bible is that we can learn about God from the created universe – theologically, this is known as “general revelation” - so in Christian terms, we shouldn’t be surprised if that turns out to be the case.
Of course, this is so far removed from the principles of mediocrity and darwinism as to completely blow them out of the water, if it is true. If you have never thought it before, it is profoundly shocking to think that a God might have created a whole universe with human beings at the focus of it. But that’s where the evidence leads – to pick up an ID buzzphrase. Maybe the real surprise then, given this challenge to the naturalism that darwinism is built on, is that PP hasn’t incurred even stronger opposition.