The Case for a Creator (28 page)

THE HOSTILE WORLD OF M13

I granted the point that only certain kinds of planetary environments can play host to life. On the other hand, the universe is salted with trillions of stars, with countless terrestrial bodies undoubtedly revolving around them. Surely the mathematical odds favor many stars spawning Earth-like habitats—a point that argues against the idea that Earth is special and therefore designed.

But while my untrained eyes see each star as having equal potential to preside over a civilization-bearing solar system, I was soon to learn differently as I pursued questions concerning the conditions that are necessary for life to flourish.

I turned toward Gonzalez. “As we look out at the billions of stars that constitute our Milky Way galaxy,” I said, “can’t we logically assume that planets teeming with life are strewn all over the place?”

“No,” he said unequivocally, “that’s not a logical assumption based on the evidence. Along with Don Brownlee and Peter Ward of the University of Washington, I developed a concept called the Galactic Habitable Zone—that is, a zone in the galaxy where habitable planets might be possible. You see, you just can’t form a habitable planet anywhere; there’s a large number of threats to life as you go from place to place.”

My mind flashed back to when Drake and Sagan beamed their message to the large concentration of stars called globular cluster M13. Their theory was that by transmitting their greeting toward a place packed with stars, there would be a higher chance of detection by an intelligent civilization. When I asked Gonzalez what he thought of that experiment, his reply was immediately dismissive.

“The problem is that if the probability of life at any one star is zero, then the probability for all the stars remains zero,” he said.

“Zero?” I replied. “There are more than a quarter million stars in that globular cluster. Don’t you think
any
of them harbor planets with life?”

Gonzalez stood his ground. “A globular cluster is one of the worst places in the entire galaxy to expect any life,” he replied.

“Why?”

“Two reasons,” he said. “First, globular clusters are among the most ancient things in our galaxy. Since they’re extremely old, their stars have a very low abundance of heavy elements—carbon, nitrogen, oxygen, phosphorous, calcium, and so on. Instead, they’re made up almost entirely of hydrogen and helium. In contrast, Earth is composed of iron, oxygen, magnesium, and silicone. Next comes sulfur.

“You see, the Big Bang produced basically hydrogen and helium. That’s what the earliest stars were made of. The heavier elements were synthesized—cooked, if you will—in the interior of stars. Eventually, when these stars exploded as supernovae, these elements got expelled into the interstellar medium. They coalesced into other stars, where more heavy elements were cooked. Then they were expelled again and again, with stars subsequently containing ever-greater amounts of these ‘metals,’ or heavier elements.

“Now, you need these elements to eventually build terrestrial planets like Earth. Because the very old stars in globular clusters formed so early that they’re composed virtually exclusively of hydrogen and helium, they’re not going to have planets accompanying them. Maybe there will be dust, or grains, or boulders, but that’s about it. You’re not going to have Earth-size planets.

“The second problem is that globular clusters are so densely packed with stars that they wouldn’t allow for stable, circular orbits to exist around them. The gravitational pull of the stars would create elliptical orbits that would take a hypothetical planet into extremes of cold and heat, which would create a life-prohibitive situation.”

His assessment made sense, but it caused me to wonder why Sagan and Drake, both knowledgeable astronomers, would waste their time trying to communicate with the stars of M13. Gonzalez shook his head when I asked him about it.

“It’s really surprising that they would think there would be any chance of a civilization receiving their message in a globular cluster,” Gonzalez said. “They should have known better! Frankly, I think they were so deluded by their complete belief in the metaphysical Copernican Principle—that life was just going to be everywhere in the galaxy—that they overlooked the facts.”

LIVING IN THE SAFE ZONE

Gonzalez’s explanation made me wonder about the suitability of other places to harbor intelligent life. I knew that there are three basic types of galaxies in our universe. First, there are
spiral galaxies
like our own Milky Way. These are dominated by a central spherical bulge and a disk with “spiral arms” extending outward from the nucleus in a spiral pattern, resembling a celestial pinwheel. Second, there are
elliptical galaxies
, which are sort of egg-shaped. And, third, there are
irregular galaxies
, which appear disorganized and distorted. I asked Gonzalez to assess the life-bearing potential of each one.

“Certainly, our type of galaxy optimizes habitability, because it provides safe zones,” he said, his tone professorial. “And Earth happens to be located in a safe area, which is why life has been able to flourish here.

“You see, galaxies have varying degrees of star formation, where interstellar gases coalesce to form stars, star clusters, and massive stars that blow up as supernovae. Places with active star formation are very dangerous, because that’s where you have supernovae exploding at a fairly high rate. In our galaxy, those dangerous places are primarily in the spiral arms, where there are also hazardous giant molecular clouds. Fortunately, though, we happen to be situated safely between the Sagittarius and Perseus spiral arms.

“Also, we’re very far from the nucleus of the galaxy, which is also a dangerous place. We now know that there’s a massive black hole at the center of our galaxy. In fact, the Hubble space telescope has found that nearly every large nearby galaxy has a giant black hole at its nucleus. And believe me—these are dangerous things!

“Most black holes, at any given time, are inactive. But whenever anything gets near or falls into one, it gets torn up by the strong tidal forces. Lots of high energy is released—gamma rays, X-rays, particle radiation—and anything in the inner region of the galaxy would be subjected to high radiation levels. That’s very dangerous for life forms. The center of the galaxy is also dangerous because there are more supernovae exploding in that region.

“One more thing: the composition of a spiral galaxy changes as you go out from the center. The abundance of heavy elements is greater towards the center, because that’s where star formation has been more vigorous over the history of the galaxy. So it has been able to cook the hydrogen and helium into heavy elements more quickly, whereas in the outer disk of the galaxy, star formation has been going on more slowly over the years and so the abundance of heavy elements isn’t quite as high. Consequently, the outer regions of the disk are less likely to have Earth-type planets.

“Now, put all of this together—the inner region of the galaxy is much more dangerous from radiation and other threats; the outer part of the galaxy isn’t going to be able to form Earth-like planets because the heavy elements are not abundant enough; and I haven’t even mentioned how the thin disk of our galaxy helps our sun stay in its desirable circular orbit. A very eccentric orbit could cause it to cross spiral arms and visit the dangerous inner regions of the galaxy, but being circular it remains in the safe zone.

“All of this,” he said, his voice sounding a bit triumphant, “works together to create a narrow safe zone where life-sustaining planets are possible.”

SCANNING THE STARS FOR LIFE

Suddenly, the Earth was sounding pretty special, nestled as it is in a sliver of space that gives it safe haven from the otherwise menacing conditions of the Milky Way. But what about other types of galaxies? Might they also provide threat-free neighborhoods for life-populated planets?

“What about elliptical galaxies?” I asked Gonzalez. “Do they have the potential to harbor life?”

“Elliptical galaxies look amorphous and are sort of egg-shaped, with stars having very random orbits, like bees swarming a beehive,” he explained. “The problem for life in these galaxies is that the stars visit every region, which means they’ll occasionally visit the dangerous, dense inner regions, where a black hole may be active. In any event, you’re less likely to find Earth-like planets in elliptical galaxies because most of them lack the heavy elements needed to form them.”

This was an important point, because I knew that most galaxies fall into the elliptical category.

“Most elliptical galaxies are less massive and luminous than our galaxy,” Gonzalez continued. “Our galaxy is on the top one or two percent of the most massive and luminous. The bigger the galaxy, the more heavy elements it can have, because its stronger gravity can attract more hydrogen and helium and cycle them to build heavy elements. In the low-mass galaxies, which make up the vast majority, you can have whole galaxies without a single Earth-like planet. They just don’t have enough of the heavy elements to construct Earths. Just like a globular cluster—you can have a whole globular cluster with hundreds of thousands of stars, and yet there won’t be a single Earth.

“If you look at the deepest pictures ever taken by the Hubble Space Telescope, they show literally thousands of galaxies when the universe was really young. People have commented, ‘Wow, look at all those galaxies! I wonder how many civilizations there are looking back at us?’ In that picture, I’d say zero. Thousands and thousands and thousands of galaxies—but zero Earths, because the heavier elements haven’t built up enough yet.”

Richards interrupted to say, “Of course, we’re not looking at these galaxies as they exist now; we’re looking back in time, say, nine billion years ago. It’s possible that some of those galaxies are now at the state where the Milky Way is. We don’t know for sure.”

“But,” added Gonzalez, “this was back when it was much more dangerous, because it’s the era of quasars, supernovae going off, and black holes. Even if you had a few regions in the galaxy where there were sufficient heavy elements to build Earths, they would have been so irradiated that life wouldn’t be possible.”

With elliptical galaxies being unlikely sites for budding civilizations, I turned to the last category of galaxy, called irregulars. “What’s their potential for life?” I asked.

“Like the ellipticals, they also don’t provide a safe harbor. In fact, they’re worse. They’re distorted and ripped apart, with supernovae going off throughout their volume. There are no safe places where there are fewer supernovae exploding, like we have between our spiral arms.

“In fact, astronomers keep finding new threats to life. For example, we’re learning more about gamma ray bursts, which are more powerful than a supernova. If one of these goes off near you, the lights go out. So the probability for there being civilizations elsewhere actually keeps declining as we learn about the new threats that we didn’t know about before.”

“What’s your opinion, then, about where Earth is located in the universe?” I asked.

“In terms of habitability, I think we are in the best possible place,” Gonzalez said. “That’s because our location provides enough building blocks to yield an Earth, while providing a low level of threats to life. I really can’t come up with an example of another place in the galaxy that is as friendly to life as our location. Sometimes people claim you can be in any part of any galaxy. Well, I’ve studied other regions—spiral arms, galactic centers, globular clusters, edge of disks—and no matter where it is, it’s worse for life. I can’t think of any better place than where we are.”

“That’s ironic,” I said. “It’s the reverse of the Copernican Principle.”

Richards agreed. “The propaganda of the Copernican Principle has been that the long march of science has shown how common and ordinary our situation is. But the trend is in the opposite direction. The more you pile on the threats we’re discovering in most places in the universe, and you contrast that with the many ways we’re in a cocoon of safety, the more our situation appears special.”

“The most famous example is our own solar system,” Gonzalez said. “At one time or another, scientists have speculated that there are civilizations on just about every body in our solar system—the moon, Mars, Jupiter.

“Percival Lowell built his own observatory in Arizona to find these civilizations on Mars. He actually quoted Copernicus to justify his belief that we can’t be the only civilization. Now they’ve backtracked to the point of saying, well, maybe there’s some very simple slime mold beneath the surface of Mars or Europa. And even that is extremely questionable. That’s how far back they’ve had to retreat.”

“Very often,” observed Richards, “the Copernican Principle describes properties that don’t matter. Who really cares whether we’re in the physical center of the galaxy? It’s irrelevant! What really matters is being in the place that’s most conducive to life. And that’s exactly where Earth finds itself.”

PLANETS CIRCLING OTHER STARS

Within the last few years, astronomers finally have been able to discover planets orbiting other stars—a major confirmation of what was once merely widespread speculation. “Doesn’t this confirm that there’s nothing particularly out of the ordinary about our nine-planet system?” I asked.

“I’ll concede,” said Gonzalez, “that it demonstrates our solar system is not unique when it comes to having planets circling a star. But prior to the detection of the first planet orbiting another sun-like star in 1995, the expectation was that astronomers would find giant gas planets in large circular orbits, much like Jupiter. Jupiter orbits the sun in twelve years in a nearly circular orbit, far out from the terrestrial planets—Mercury, Venus, Earth, and Mars.

“However, we’re finding that the planets circling other stars are quite different from Jupiter. They orbit over a full range of distances, from just a tiny fraction of an Astronomical Unit—which is the distance between the Earth and the sun—out to several Astronomical Units. Most of their orbits are highly elliptical; very few are circular. These strongly non-circular orbits utterly surprised astronomers. Because they strongly subscribed to the Copernican Principle, they had expected that other planetary systems would be just like ours. And that expectation was basically dashed.”