The largely successful interpretation of explaining our experiences of the world, collapses.

 known as the “collapse interpretation” because it supposes that an observer external to a system causes the system, upon observation, to collapse from a quantum mechanical state to a state in which the elements of the system appear to have a determinate value for the property measured. Although this interpretation is largely successful at explaining our experiences of the world, 

The standard interpretation also tells us that if we do not observe quantum particles, then that collapse will not happen and they will remain in their superpositions.

The difference in these empirical results is captured in two of the laws that are part of the theory of quantum mechanics:

1. When no measurement, or other observation, is made of a system, then that system evolves in a deterministic and linear fashion.
2. When a measurement, or other observation, is made of a system, then that system instantaneously and non-deterministically collapses into a definite value for the property being measured.

In the standard interpretation, the second law accounts for the fact that when we measure any property of an object, it has a definite value.

One difficulty with no-collapse theories is making sense of how it is that we seem to have determinate measurement records for quantum particles even though those particles do not have a determinate value for the property measured, since they never collapse out of their superpositions

Everett’s pure wave mechanics suggests that there is generally no determinate fact about the everyday properties of the objects in our world, since the equations that are supposed to describe such properties are such that they describe superpositions of those properties. Rather, Everett takes there to be only “relative states” and thus “relative properties” of quantum systems

To see what he means by “relative states” and “relative properties,” consider the following. When we want to learn the value of a property for some system, we measure for that property.  But Everett treats measuring devices just as he would any other system with which the object system interacts, and so the measuring device will become correlated with the system that it is measuring.  In order to learn anything about one subsystem, even the reading on a measuring device, one must make reference to the complement of the subsystem . . . There is no longer any independent system state or observer state, although the two have become correlated in a one-one manner (Everett 1957b: 144, 146).

Everett explains “correlation” this way: “If one makes the statement that two variables, X and Y, are correlated, what is basically meant is that one learns something about one variable when he is told the value of the other” (Everett 2012: 61; this definition also shows up in Everett 1973: 17). Even in this case, it only “seems” as if nothing can be settled because of this correlation between an object system and a measuring device.  In fact, one can settle matters with the use of relative states: