Template:M intro design Nomological machine

Nomological machine
/ˈnɒməˈlɒʤɪkᵊl məˈʃiːn/ (n.)
A term coined by philosopher of science Nancy Cartwright two describe the limited conditions which must prevail for posited laws of science to work.

“It is a fixed (enough) arrangement of components, or factors, with stable (enough) capacities that in the right sort of stable (enough) environment will, with repeated operation, give rise to the kind of regular behavior that we represent in our scientific laws”

This is fancy way of saying it’s a model. So, for example, take Newton’s second law of motion, which describes the relationship between an object’s mass and the amount of force needed to accelerate it.

This is stated as F=ma which means the force (F) acting on an object is equal to the mass (m) of an object times its acceleration (a). This is an immutable law of physics which holds in all non-relativistic, non-quantum scales.

But the conditions in which it operates — zero friction, perfect elasticity, non-intertial frame of reference — circumstances which never exist in real life. So, a rolling ball with no force acting upon it will eventually stop. A crisp packet blowing across St. Mark’s square probably does still obey Newton’s laws of motion — once you have discounted all the contaminating effects of the real world, such as friction, convection and so on — but good luck calculating its trajectory using them in any case, so really it is impossible to know. We give Newton the benefit of a large and practically untestable doubt.

Cartwright’s point is that we are not justified in extrapolating laws that hold for nomological machines to the real world: it does not follow that the behaviour of apparatus in tightly-constrained, not-naturally occurring laboratory conditions give any great insight into the mechanics of a wind-blown crisp packet, or any of the other myriad quotidian physical effects we see and take for granted.