The Delicate Balance of Nature

 Many Factors Combine to Allow Life on Earth

As we look at planet Earth and the factors that enabled us to be here, we quickly realize that our planet is very special. Here’s a short list: the long-term existence of a protective and oxygen-rich atmosphere; Earth’s axial tilt, stabilized by a single large moon; the ozone layer and the magnetic field, which jointly protect surface creatures from lethal cosmic radiation; plate tectonics, which regulates the levels of carbon dioxide and keeps the global temperature stable; the fact that our...

 Stable Orbits are Impossible in More Than Three Dimensions

If one assumes that a few hundred million years in stable orbit are necessary for planetary life to evolve, the number of space dimensions is also fixed by our existence. That is because, according to the laws of gravity, it is only in three dimensions that stable elliptical orbits are possible. Circular orbits are possible in other dimensions, but those, as Newton feared, are unstable. In any but three dimensions even a small disturbance, such as that produced by the pull of the other planet...

 The Precarious Laws of Nature

By examining the model universes we generate when the theories of physics are altered in certain ways, one can study the effect of changes to physical law in a methodical manner. It turns out that it is not only the strengths of the strong nuclear force and the electromagnetic force that are made to order for our existence. Most of the fundamental constants in our theories appear fine tuned in the sense that if they were altered by only modest amounts, the universe would be qualitatively diff...

 The Unique Properties of Ice

By the standard of other substances, the properties of ice are bizarre, yet ice is so perfectly suited to our purpose that if it didn't exist we should have to invent it. With few exceptions, the solid phase of matter is more dense than the liquid phase; water. alone among common substances, violates the rule. As water begins to cool, it first contracts and becomes more dense, in the typical way. But about four degrees above the freezing point, something peculiar happens. It ceases to contrac...