TECHNOLOGY: The future of computing depends on making it reversible.

[T]he most fundamental laws of physics are reversible, meaning that if you had complete knowledge of the state of a closed system at some time, you could always—at least in principle—run the laws of physics in reverse and determine the system’s exact state at any previous time.

To better see that, consider a game of billiards—an ideal one with no friction. If you were to make a movie of the balls bouncing off one another and the bumpers, the movie would look normal whether you ran it backward or forward: The collision physics would be the same, and you could work out the future configuration of the balls from their past configuration or vice versa equally easily.

The same fundamental reversibility holds for quantum-scale physics. As a consequence, you can’t have a situation in which two different detailed states of any physical system evolve into the exact same state at some later time, because that would make it impossible to determine the earlier state from the later one. In other words, at the lowest level in physics, information cannot be destroyed.

The reversibility of physics means that we can never truly erase information in a computer. Whenever we overwrite a bit of information with a new value, the previous information may be lost for all practical purposes, but it hasn’t really been physically destroyed. Instead it has been pushed out into the machine’s thermal environment, where it becomes entropy—in essence, randomized information—and manifests as heat.

A conventional computer is, essentially, an expensive electric heater that happens to perform a small amount of computation as a side effect.

So -- global warming, sorry, climate change is caused by cell phones?