1. In the 2-slit experiment, particles are shot through 2 narrow slits, and their arrival registered on a screen.
2. If detectors are attached to the slits, to determine which particle went through which slit, the pattern formed on the screen is a pair of Gaussians, as if the particles were bullets being shot through a pair of windows.
3. Otherwise, the pattern is an “interference pattern’, as if the particles traveled through the slits as a single object, such as a body of water through a pair of sluice gates.
4. This means that, in the absence of detectors, particles behave like waves, and that their position, after the firing of the gun, and before their arrival is resisted on the screen, is best described as a ‘superposition’ of waves.
5. But this does not mean that unmeasured objects generally are in a superposition of contradictory states.
6. Nor does it mean that the world breaks into contradictory branches whenever a measurement is made.
7. What it means is that the non-contradictory classical world, in which things are either in one state or another, and not both, involves a balance that arises from imbalances; more particularly, it means that the classical world in which things are either in one state or another, and not both, is best described as a balanced superposition of waves.
8. In a 2-slit experiment in which their are no-detectors, the balance is tipped in one way, and the best way to describe the position of a particle is with an unbalanced superposition.
9. Attaching detectors restores that balance, and now the best way to describe the position of a particle is with a balanced superposition.
10. But classical objects, such as cats, are always in balanced superpositions, and so there is no question a cat is for example is either alive or dead, and not both, whether it is being measured or not.
11. Nor is there any question a cat exists in a single and continuous world, both before and after any measurement.
12. Key mathematical notion required to solve this problem: the distinction between balanced (classical) and unbalanced (non-classical) superpositions.
13. When there is a balance of unbalanced (non-classical) superpositions, we get a balanced (classical) superposition.
14. When no such balance exists, we do not.