1. Weak Points of Quantum Mechanics. 

Even though quantum mechanics provides accurate agreement with so many observations, and even though it agrees with our everyday observations, it still has weak points.

(1) It gives no understanding of why the probability law holds.

(2) It treats all versions of reality equally, so it does not explain why we perceive a particular version (IIIA3, subsection 12).

(3) Even though it tells us observers cannot disagree (IIIA3, subsection 10), it doesn’t adequately explain why we are each consciously aware of the same version of reality.

(4) Quantum mechanics has the undesirable feature that the past is unstable (IIIA3, subsection 13).

Because of these weak points—and also because it has not always been appreciated just how well quantum mechanics explains the particlelike nature of the physical world—there have been a number of attempts to modify or amend the theory of quantum mechanics.

2. Attempts to Modify Quantum Mechanics. 

Objective Reality Models.  There have been two types of attempts to modify quantum mechanics that interest us here.  The first is to suppose that, in addition to the wave function, there is something else, such as particles, that physically exists.  This something else is to objectively exist in the sense that, at each instant, it must give a single version of reality, unlike the wave function with its many versions. 

The most well-developed model of a reality with both waves and particles is the Bohm model ("model" is a word often used for a trial theory).  We will show in section IIIB2  ,  however, that the Bohm model makes two assumptions which disqualify it as a valid theory of particles underlying quantum mechanics.

Then in section section IIIB3 , we give three general arguments, one experimental and two theoretical, against anything besides the wave function existing.

Collapse Models.  The other primary attempt to deal with the weaknesses of quantum mechanics is to suppose that, for some reason, the many branches (versions of reality) of the wave function collapse down to just one branch.  We will argue in sections IIIB4 and IIIB5 that these attempts also face severe problems.

3. Extremely Difficult to Amend Quantum Mechanics.

The net result is that it looks nearly impossible to modify or amend quantum mechanics.  Thus how we are to deal with the weaknesses of quantum mechanics is currently an open question.  We present a possible answer in section IIIE.