Thursday, December 3, 2009

Anthropic Coincidence, Part 1 of 2

Or, Is the Universe Fine-Tuned for Life? (Yes)

This stuff fascinates me, both in its own right and for the theological implications.

The term, “anthropic coincidence,” as I’ve recently learned, has to do with whether or not the universe is fine-tuned for complex, intelligent life. If we consider the conditions that are physically necessary for there to be life as we know it, and if we find that their measurements must fall within an extremely small range of all possible values, then the universe can be said to be fine-tuned for life.

From one point of view (one atheists are fond of adopting), it is no coincidence at all if we find these improbable conditions having been met. We’re here, aren’t we? That proves all the conditions for complex, reason-endowed life have in fact been fulfilled. The chance is 100%, the very opposite of any coincidence. (In other words, this universe is NOT random at all! So the purpose of the argument is defeated.)

But that’s looking backward, after the fact. If we start at the very beginning of time and space and consider what might have been, if we consider all the (knowable) alternate conditions that in a random universe might just as easily have prevailed, such that we would not be here, then the chances of the right conditions all combining at the same time are vanishingly small.

Here are a few of those conditions, beginning with the universe itself, as a whole.

1.) The rate of expansion of the universe. If this rate were slightly faster, galaxies, stars and planets would not form; if slightly slower, the universe would collapse before any atoms formed.

2.) The expansion theories of the universe presuppose anthropic coincidences of their own, which I do not understand, but perhaps you do. One of these, for example, is that the “two components of the cosmological constant (bare lambda and quantum lambda) must cancel each other with an accuracy better than one part in 1050 in order for galaxies and planets to form.”

3.) There are four forces (gravity, electromagnetic, strong and weak) and two basic types of particles (bosons and fermions). Each of these must be in a very particular sort of balance with each of the others in order for there to be life. For example, the mass of an electron must be in a certain ratio to the mass of a proton: mm/mn ~ (1836)-1. This small value is a necessary condition of there being DNA molecules. Each of these necessary ratios ought properly to form its own entry on this list, but I do not understand them to list each one separately.

Not all galaxies are equally habitable, since habitability depends on a galaxy’s

4.) mass,

5.) type,

6.) age,

7.) allotment of heavy elements

8.) Even the relatively rare, large spiral galaxies like the Milky Way, which are likely optimal for life, probably contain only a few locations within a “Galactic Habitable Zone” compatible with complex life. Galaxies are filled with dangerous radiation hazards, and many regions are either so low in heavy elements as to prohibit terrestrial planets from forming, or so high that planetary systems will be hostile to life. A habitable planet must not be located near the center of the galaxy, nor far out in the spiral arms.

Within the right kind of galaxy, you need the right kind of solar system. First, you need the right kind of a star, like our Sun.

9.) The solar system must have only a single star.

10.) That star must be of moderate size. Stars more than about twice the mass of the sun do not last long enough for life to form on their planets. To give rise to life, a planet must not orbit a star that is too close to a cosmic explosion, like a supernova.

11.) The star must be of a stable, steady radiation output.

12.) The solar system must have just the correct distribution of large and medium sized planets to have swept clean most of the space through which Earth must travel. There are thus few asteroids anywhere near our path! Giant plantes like Jupiter and Saturn “catch” comets in their gravitational fields and keep these comets from targeting earth.

Then, within the right kind of solar system within the right kind of universe, you need the right kind of planet.

13.) The planet, to support life, must be far enough from massive planets that they do not continually divert asteroids to hit it or perturb its orbit strongly.

14.) Neighboring planets must have non-eccentric orbits, or they may collide with the otherwise habitable one.

15.) To be habitable, a planet must have a nearly circular orbit at a uniform distance from the sun. Our orbit through space, at 93 million miles from the Sun, departs from a true circle by only 3 percent. Were it as elliptical as is the orbit of Mars, the next planet out, we would alternate between baking when closer to the Sun and freezing when distant.

16.) The planet must be the right distance from the sun in order to preserve liquid water at the surface – if it’s too close, the water is burnt off in a runaway greenhouse effect, if it’s too far, the water is permanently frozen in a runaway glaciation

17.) Life needs a planet with just enough internal radioactivity to maintain a molten core. The molten core, I do not understand how, produces the magnetic shield around the planet that deflects an otherwise lethal dose of solar radiation.

18.) The planet’s internal heating must drive just enough volcanic activity release previously stored subterranean waters into the biosphere, making them available for life processes, but not so much volcanism as to shroud the planet in dust.

19.) The volcanic activity must be sufficient to provide a land mass.

20.) The planet must be terrestrial (non-gaseous). There must be enough useful room to forage, grow, molt and reproduce without excessive crowding right away.

21.) The core most also be molten to provide for plate tectonics. That is, large plates of the planet’s crust must float over the molten core and shift. This mixes up the chemicals that need to combine to support life. It also produces the volcanic activity.

22.) The planet must have enough light to support some sort of photosynthesis, either microbial-cell (paramecia) or plant-cell (from algae on up) based.

To stabilize the tilt of the planet’s rotation and contribute to the tides, a habitable planet requires a moon that is

23.) large enough to do the job and

24.) well-placed.

25.) A habitable planet requires an atmosphere.

It must be the right kind of atmosphere. The planet needs:

26.) Enough hydrocarbon compounds to form proteins, amino acids, RNA and DNA

27.) Enough phosphorous to form mitochondria, making metabolism possible

28.) Enough oxygen to support further metabolism (only bacteria can use other elements like sulfur as an oxidant)

29.) High abundance of other molecules that were precursors to organic molecules: Carbon, Nitrogen, Sulphur, Calcium, etc.

30.) Abundant H20: good solvent, stable over a wide temperature range and causes erosion of rock important in the atmospheric and aquatic accumulations of "heavy" molecules.

31.) The right amount of hydrogen. Its loss and subsequent accumulation of other atmospheric elements allowed the early reducing atmosphere under which life originated.

In Part 2, I intend to provide a second list of conditions necessary to support complex life (or even any life at all). Then I'll have a word to say about how all this relates to theology.

Further Reading

I took some of the items on this list from here and here and here. Two more lists are given here and here, with some overlapping among all these lists.


Anam Cara said...

If you have not seen the DVD The Priviledged Planet, I suggest you do.

It is available from netflix or amazon below: