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Posts Tagged ‘Rare earth’

Countering this potentially theistic trend that Brownlee had placed on the table with his Rare Earth, Stephen Hawking made the desperate gambit of suggesting that there might be an infinite (really infinite, or just virtually infinite?) number of “bangs” – some Big Bangs, some Little Bangs, and just this one that we inhabit being the fortuitous size that allowed human life. In an infinite time, all possibilities can be tried. His reasoning was based on some physical considerations that are beyond the scope of this discussion; you can read about the Copenhagen Interpretation. But fundamentally, there were unrecognized philosophical issues behind this bid, as Jaki points out in his Is There a Universe? Hawking, like Hoyle before him, needed matter to arise mathematically from nothing – in this case from the probability that was believed to govern electrons. That probability could generate matter was a passing odd position; nevertheless Hawking has a vast following, and, in truth, God does not force our hands — or our minds. Belief, atheistic or not, has a certain latitude for choice; the evidence is never absolute because men and their information are never absolute. Hawking had made the case for an accidental universe: Yes, our universe is finite, but it is set within an infinite cosmic foam of other universes. It’s just the one that works for us.

But there was more evidence coming in.

The next salvo in the battle for a genuinely finite universe was the book Privileged Planet, by Guillermo Gonzalez. He and several colleagues have gathered evidence that the earth is not only uniquely fitted for life, which it would have to be or we wouldn’t be talking about it, but also uniquely fitted for discovery, which is not necessary to life, even to intelligent life. Interestingly, however, they discovered that the same conditions that are essential to life area also the conditions for discovery.

For example, our Earth is the only place in the solar system from which the Sun is fully eclipsed by another body (our Moon) so that the corona is visible. This fact has been very important in the study of stars – the Sun is so bright, and the stars are so dim, that both are very difficult to study. The corona of the sun, the beautiful display that is visible for just a few minutes during a total eclipse, gives lots of information, which was otherwise unavailable until the launching of artificial satellites. It is essential to universe discovery.

At the same time, the Moon is essential to life because it stabilizes the rotation of Earth, without which the seasons would vary too strongly and life would not be possible.

That the same planet suited to life should also be suited to discovery of the nature of the stars, and therefore of the universe, deeply disturbs the accidentalist case. It makes the universe look like a home.

(The next post will be the end of the talk.)

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How likely intelligence?

Carl Sagan, the great scientific pagan of the mid-20th century, estimated that there must be at least 10,000 inhabited planets per galaxy. It would be ridiculous to think we had the universe to ourselves. He was very famous, and the number was repeated again and again.

Still — no sign of anyone else.

In 1965, Penzias & Wilson found the radio signal that Gamov had said would vindicate LeMaitre’s Big Bang and lock physics into a finite universe. The universe was not eternal; it had an age, and in consequence of its age, it had a finite dimension, somewhere between 1024 and 1027th meters. We had a universe size at last. Not perfectly definite, but fairly so. Not infinite. Not even as much as 30 billion light years in diameter. Probably 13 or 14 billion light years radius.

1027 * 1024 * 1021 galaxy size * 1018 * 1015 *

1012 * 109 sun size * 106 * 103 * 100 =1 people size

10-3 * 106 * 10-9 molecules * 10-12 * 10-15

Just at the turn of the century, Robert Jastrow of NASA wrote a book called God and the Astronomers, in which he acknowledged that this discovery had forced him to abandon a lifetime of atheism, and he invited his Catholic subordinate, John O’Keefe, to write an Afterword. O’Keefe had several interesting things to say, including a suggestion on how to approach the relative likelihood of other intelligent life. It could be very simple. If there were, say, 23 independent conditions for the development of intelligent life, and if each one had a 10% chance of turning up near a given star, then the chance of developing life in the universe would be 1/1023rd. That is about the number of stars in the universe. If the conditions were more likely, then we should continue to look around; if less, we’re probably alone.

This was much better than just by saying, “Gee, it’s awful big for just one human race.” Math is always nice; you can get somewhere.

In the 1990’s Ward and Brownlee came along with a book, Rare Earth, which listed all the known conditions for life, including very unexpected conditions such as tectonic plate motions. Many of the conditions were much less than 10% likely and they concluded that, yes, we might be the only ones.

The sense of human specialness was again on the march. It deepened as further consideration of the Big Bang – the explosion at the origin of the universe – showed that it had to have been incredibly specific in order to work – too intense and the universe would have blown to dust without forming stars, planets, or people – too slight and matter would have been recaptured by gravity before it had time to form stars, planets, or people. It was very, very special. The sort of exactitude its numbers required went to 51 decimal places, which is about what it would take to locate your nose within the solar system — the entire system, out to the furthest comets.

It began to look as if the intelligent radio signal had indeed been found, right there in the Big Bang, and it meant that our one intelligent companion was the creator.

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Even those pagans who don’t engage the fantasy of multiple universes are prone to imagine many “earths” at least. Most famously, Carl Sagan quoted an equation (doesn’t that sound objective and irrefutable: an equation!) according to which one should expect to find around 10,000 planets like earth – and therefore harboring intelligent life – in any galaxy such as the Milky Way. Many like him expected to find other intelligent life in short order. This was the 1980’s, and it was based on the Drake equation of the 1960’s.

We have not yet (in 2010) found intelligent life, and the search has been quite sophisticated.

What could be the problem?

In 1978, shortly before Sagan’s utterance, a different expectation was expressed in a small book called God and the Astronomers, by Robert Jastrow. It was part of a 30-page afterword written by John O’Keefe who had worked for Jastrow at NASA, and who was well-known as a believer, as a Catholic in fact. When Jastrow came to write out his new-found perception of the existence of God, he invited O’Keefe to add an essay, and it included a simple suggestion: O’Keefe said that if you thought of as few as 22 independent conditions for human life, and if each of them had about one chance in ten of turning up on a randomly chosen planet, then the chance of all of them turning up at once on a single planet would be 1022nd power, which is about one chance among all the stars of the universe.

The Afterword is a very interesting 30 pages, well worth reading in full, but here, from page 143, is the quotation I refer to:

For my part, I am not so sure that intelligent life exists on other planets. The basic argument for this view is that each star offers life an opportunity, and there are 1022 (ten thousand million, million, million) stars and planets in the observable universe. Even if the chance of life evolving is as small as, say, one in a million, still there must be millions upon millions of inhabited planets in the Universe.

Suppose, however, that twenty-two separate conditions must be met for intelligent life: the star must be single; it must produce visible and ultra-violet light; its planet must have an atmosphere that transmits light but not X-rays or extreme ultraviolet; there must be liquid water; there must be carbon; the star must live a long time; its output of energy must not vary rapidly; the planet must be in a suitable zone of distance from its star; it must have land as well as water; it must not suffer excessive and prolonged bombardment by meteorites; and so on.

These conditions would not be satisfied on every planet in the Universe. If each were satisfied on only one planet in ten, which is not an unreasonable estimate, then if the requirements are really separate, the chance of finding a planet with all 22 conditions satisfied simultaneously would be one tenth multiplied by itself twenty-two times, or 1/1022. This means only one planet in the Universe is likely to bear intelligent life. We know of one – the earth – but it is not certain that there are many others, and perhaps there are no others.

John O’Keefe, 1978

An interesting challenge…

Ward and Brownlee came along several years later (in 2003) with a fascinating book called Rare Earth, in which they showed that the series of requirements for intelligent life was probably considerably more extensive than Sagan had considered, and we might very well be the only intelligent life in the Milky Way, or even in the universe, just considering the problem statistically – how many stars, how likely that one would have planets the right size, the right distance, with water, with plate tectonics, without supernova interference during the development of life, and so forth. It was a direct response to Sagan and to the Drake equation. Brownlee was a friend of John O’Keefe and may well have been aware of his suggestion. In any case, Rare Earth is a very interesting read, and spells out some of the things O’Keefe mentioned as well as others that are quite unexpected. (Who thinks plate tectonics is essential to life?) I never counted exactly how many conditions are listed but several of them required planetary conditions that are much rarer than 10% of what’s out there. Here are some excerpts.

The following year, yet another book appeared: The Privileged Planet, by Guillermo Gonzalez (as well as a companion DVD by John Rhys-Davies) in which the theme of Earth’s uniqueness was taken still further. Gonzales stated that Earth was not only uniquely placed for the emergence of human life, but also uniquely placed for the study of the universe. For example, it is so placed that our moon perfectly eclipses our sun, enabling certain observations (in the corona) that would not be possible from any other vantage point in our solar system and would be rare in any case. This takes the concept of design one step farther – the universe was designed to give us life – and our universe home was designed to serve our curiosity!

Awesome!

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