A teacher said to her class, "God so loved the earth, that He put the earth just right from the sun." As a child of six, I was shocked by the simplicity and power of this argument. If God had put Earth too far from the Sun. then the oceans would have frozen. If He had put Earth too close, then the oceans would have boiled off. To her, this meant that not only did God exist, but that He was also benevolent, so loving Earth that He put it just right from the Sun. It made a deep impact on me.
Today, scientists say that Earth lives in the "Goldilocks zone" from the Sun, just far enough so that liquid water; the "universal solvent." can exist to create the chemicals of life. If Earth were farther from the Sun, it might become like Mars, a "frozen desert." Where temperatures have created a harsh, barren surface where water and even carbon dioxide are often frozen solid. Even beneath the soil of Mars one finds permafrost, a permanent layer of frozen water.
If Earth were closer to the Sun, then it might become more like the planet Venus, which is nearly identical to Earth in size but is known as the "greenhouse planet." Because Venus is so close to the Sun, and its atmosphere is made of carbon dioxide, the energy of sunlight is captured by Venus, sending temperatures soaring to 900 degrees Fahrenheit. Because of this, Venus is the hottest planet, on average, in the solar system. With rains of sulfuric acid, atmospheric pressures a hundred times greater than those found on Earth, and scorching temperatures, Venus is perhaps the most hellish planet in the solar system, largely because it is closer to the Sun than is Earth.
Analyzing my second grade teacher's argument, scientists would say that her statement is an example of the anthropic principle, which states that the laws of nature are arranged so that life and consciousness are possible. Whether these laws are arranged by some greater design or by accident has been the subject of much debate, especially in recent years, because of the overwhelming number of "accidents" or coincidences that have been found which make life and consciousness possible. To some, this is evidence of a deity who has deliberately arranged the laws of nature to make life, and us, possible. But to other scientists, it means we are the by-products of a series of lucky accidents. Or perhaps, if one believes the ramifications of inflation and M-theory, there is a multiverse of universes.
To appreciate the complexity of these arguments, consider first the coincidences that make life on Earth possible. We live not just within the Goldilocks zone of the Sun, we also live within a series of other Goldilocks zones. For example, our Moon is just the right size to stabilize Earth's orbit. If the Moon were much smaller, even tiny perturbations in Earth's spin would slowly accumulate over hundreds of millions of years, causing Earth to wobble disastrously and creating drastic changes in the climate so as to make life impossible.
Computer programs show that without a large Moon (about a third the size of Earth), Earth's axis might have shifted by as much as 90 degrees over a period of many millions of years. Since scientists believe the creation of DNA required hundreds of millions of years of climactic stability, an Earth that periodically tips on its axis would create catastrophic changes in the weather, making the creation of DNA impossible. Fortunately, our Moon is "just right" in size to stabilize the orbit of Earth, so that such a disaster will not happen. (The moons of Mars are not large enough to stabilize its spin. As a result, Mars is slowly beginning to enter another era of instability. In the past, astronomers believe, Mars might have wobbled on its axis by as much as 45 degrees.)
Due to small tidal forces, the Moon is also moving away from Earth at the rate of about 4 centimetres per year; in about 2 billion years, it will be too far to stabilize Earth's spin. This could be disastrous for life on Earth. Billions of years from now, not only will the night sky be moonless, we might see an entirely different set of constellations, as Earth tumbles in its orbit. The weather on Earth will become unrecognizable, making life impossible. Geologist Peter Ward and astronomer Donald Brownlee of the University of Washington write, "Without the Moon there would be no moonbeams, no month, no lunacy, no Apollo program, less poetry, and a world where every night was dark and gloomy. Without the Moon it is also likely that no birds, redwoods, whales, trilobite, or other advanced life would ever grace the earth."
Similarly, computer models of our solar system show that the presence of the planet Jupiter in our solar system is a fortuitous one for life on Earth, because its immense gravity helps to fling asteroids into outer space. It took almost a billion years, during the "age of meteors," which extended from 3.5 billion to 4.5 billion years ago, to "clean out" our solar system of the debris of asteroids and comets left over from its creation. If Jupiter were much smaller and its gravity much weaker, then our solar system would still be full of asteroids, making life on Earth impossible, as asteroids plunged into our oceans and destroyed life. Hence, Jupiter, too, is just the right size. We also live in the Goldilocks zone of planetary masses. If Earth were a bit smaller, its gravity would be so weak that it could not keep its oxygen. If it were too large, it would retain many of its primordial, poisonous gases, making life impossible. Earth has "just the right" weight to keep an atmospheric composition beneficial to life.
We also live in the Goldilocks zone of permissible planetary orbits. Remarkably, the orbits of the other planets, except for Pluto, 244 Michio Kaku are all nearly circular, meaning that planetary impacts are quite rare in the solar system. This means that Earth won't come close to any gas giants, whose gravity could easily disrupt Earth's orbit. This is again good for life, which requires hundreds of millions of years of stability.
Likewise, Earth also exists within the Goldilocks zone of the Milky Way galaxy, about two-thirds of the way from the centre. If the solar system were too close to the galactic centre, where a black hole lurks, the radiation field would be so intense that life would be impossible. And if the solar system were too far away, there would not be enough higher elements to create the necessary elements of life.
Scientists can provide scores of examples where Earth lies within myriad Goldilocks zones. Astronomers Ward and Brownlee argue that we live within so many narrow bands or Goldilocks zones that perhaps intelligent life on earth is unique to the galaxy, maybe even to the universe. They recite a remarkable list of ways that Earth has "just the right" amount of oceans, plate tectonics, oxygen content, heat content, tilt of its axis, and so on to create intelligent life. If Earth were outside just one these very narrow bands, we would not be here to discuss the question.
Was Earth placed in the middle of all these Goldilocks zones because God loved it? Perhaps. We can, however, arrive at a conclusion that does not rely on a deity. Perhaps there are millions of dead planets in space that are too close to their suns, whose moons are too small, whose Jupiters are too small, or that are too close to their galactic centre. The existence of Goldilocks zones with respect to Earth does not necessarily mean that God has bestowed a special blessing on us; it might simply be a coincidence, one rare example among millions of dead planets in space that lie outside Goldilocks zones.
.
