Until the End of Time: Mind, Matter, and Our Search for Meaning in an Evolving Universe

by Brian Greene

While entropy and the second law enjoy a great many cultural references, public nods to the first law of thermodynamics are less common. Yet to fully grasp the second law it’s good to grasp the first law first. As it turns out, the first law is widely known too, but under an alias. It’s the law of energy conservation. Whatever energy you have at the beginning of a process is the same energy you’ll have at the end of the process. You must be fastidious in your energy accounting, including all forms into which an initial cache of energy may have transformed, such as kinetic energy (energy of motion), or potential energy (stored energy, as in a stretched spring), or radiation (energy carried by fields, like the electromagnetic or gravitational fields), or heat (the random jittery motion of molecules and atoms). But if you keep track carefully, the first law of thermodynamics ensures that the energy balance sheet will balance.