**Langrangians**

'PERHAPS EVERY PHYSICAL PHENOMENON OCCURS IN REACTION TO MEASUREMENT - that the measurement acts as a kind of catalyst for the effect.'

Where do the laws of physics come from? Take quantum theory, over the last century it has passed every test, some predictions vindicated to 10 decimal places, yet no physicist thinks he knows where the laws of quantum theory comes from. "All the equations are just mathematical lash-ups, made out of bits and pieces from other parts of physics whose main justification is that they seem to work."

Ronald Fisher in the 1920s defined Fisher information, the equation which captures how much information you can squeeze out of a physical system. There is a limit to the amount of information due to the inherent errors - random disorder, jitters.

Frieden has discovered great similarities between Heinzberg's uncertainty principle and Fisher Information. "Since Heinzberg's principle is so basic, it occurred to me perhaps every physical phenomenon occurs in reaction to a measurement - that measurement acts as a kind of catalyst for the effect - the possibility that physical laws occur as answers to questions.

Digging into this possibility, Frieden found other mathematical 'coincidence.' Whenever he did calculations using the fisher information the final results were differential equations, formulae showing how the rate of change of a certain quantity changes under outside influences. Virtually all of physics can be expressed in terms of differential equations.

The ubiquity of these types of equation is intimately linked to one of the most profound mysteries in science: despite the vast range of phenomena covered by the fundamental laws of physics, all of those laws can be made to drop out of mathematical objects known as Lagrangians. And nobody knows why.

Lagrangians are made up of the difference between two quantities, which together form an action. For reasons totally unknown, this quantity stays as small as possible under all circumstances. This curiosity, known as the principle of least action, is reflected in the fact the fundamental laws of physics are differential equations, since that's what you need to minimise this action.