Templeton-Cambridge Journalism Fellowships in Science & Religion

My hiking companion and I have lost our way on this damp late-summer morning. We're on a treeless, mist-shrouded hilltop in Snowdonia National Park, 1,000 feet or so above the Irish Sea along the coast of northern Wales. The bleating of sheep drifts up from the slopes below, muffled by fog that hides the lay of the land. We're trying to reach a village called -- by those able to pronounce its name -- Abergynolwyn, which lies in a nearby valley. But with the murk, we can't find the way down. Sir John Houghton pulls a topographic map and a compass from his backpack. After a few moments of thought he says, "We want to head north. That should take us downhill." So we follow a sheep trail, and a bit later I watch Houghton, who is 76, nimbly hoist himself over a chest-high wire fence.

Charting a path through difficult terrain is nothing new for Houghton, who may be the most important scientist you've never heard of. From 1988 until his semi-retirement in 2002, he was one of the leaders of the Intergovernmental Panel on Climate Change (IPCC), a body created by the United Nations 20 years ago to study global warming. As cochairman of the IPCC's scientific working group, Houghton had to coordinate the efforts -- and cope with the egos -- of more than 2,000 scientists from dozens of countries. Against all odds, the IPCC, which could have been a fractious and unwieldy nternational boondoggle, produced a series of authoritative and scientifically rigorous reports firmly establishing the magnitude of the threat posed by climate change. Largely because of the efforts of Houghton's group, the IPCC shared the 2007 Nobel Peace Prize with Al

A sublime cosmic mystery unfolds on a mild summer afternoon in Palo Alto, California, where I've come to talk with the visionary physicist Andrei Linde. The day seems ordinary enough. Cyclists maneuver through traffic, and orange poppies bloom on dry brown hills near Linde's office on the Stanford University campus. But everything here, right down to the photons lighting the scene after an eight-minute jaunt from the sun, bears witness to an extraordinary fact about the universe: Its basic properties are uncannily suited for life. Tweak the laws of physics in just about any way and–in this universe, anyway–life as we know it would not exist.

Consider just two possible changes. Atoms consist of protons, neutrons, and electrons. If those protons were just 0.2 percent more massive than they actually are, they would be unstable and would decay into simpler particles. Atoms wouldn't exist; neither would we. If gravity were slightly more powerful, the consequences would be nearly as grave. A beefed-up gravitational force would compress stars more tightly, making them smaller, hotter, and denser. Rather than surviving for billions of years, stars would burn through their fuel in a few million years, sputtering out long before life had a chance to evolve. There are many such examples of the universe's life-friendly properties–so many, in fact, that physicists can't dismiss them all as mere accidents.

"We have a lot of really, really strange coincidences, and all of these coincidences are such that they make life possible," Linde says.