No, it doesn't necessarily mean that large objects such as the universe, or large macroscopic objects such as a Tesla Semi Truck or a cat have a single wave function.
What you described is an extrapolation of the laws of quantum mechanics to very large systems, which is called the "Copenhagen view" of quantum mechanics, which actually only a minority of quantum physicists support (!):
The "Copenhagen view" has a number of problems:
- Who are the "observers" that "measure" and cause the collapse of a wave function?
- Who were the "observers" one microsecond after the Big Bang? The universe couldn't have expanded without the wave function collapsing.
- Who are the "observers" inside a black hole?
- Is Schrödinger's cat dead or alive before we open the box?
So there are other, scientifically rigorous explanations for the "observer problem":
- that there's a dampening of quantum fields with larger objects,
- that there's a "many worlds" multiverse,
- or super-determinism,
- or a simulation universe,
- or "objective collapse" where larger quantum systems automatically collapse their wave functions,
- etc.
We simply don't know (yet) whether large, complex wave functions exist, we don't know which of the variants above actually exist - but we
do know that the Copenhagen view is not universally accepted!
BTW., some of these are falsifiable, with viable experiments proposed that would test whether very large quantum system have wave or particle behavior.
(Anyway, this comment is OT and not OT at once, until a moderator measures it: the "TMC uncertainty principle".)
I am aware of these issues. Nonetheless, your claim is a little misleading re Copenhagen. It still holds 42% consensus (below 50%, so not a majority, but still the largest held view, with the next largest being 24%). From the article you cited:
"The Copenhagen interpretation still reigns supreme here, especially if we lump it together with intellectual offsprings such as information-based interpretations and the Quantum Bayesian inter- pretation."
Also, the Copenhagen interpretation doesn't really bare on macroscopic systems, rather it has to do with interpreting any quantum system, whether micro or macro. From
Copenhagen interpretation - Wikipedia:
"According to the Copenhagen interpretation, physical systems generally do not have definite properties prior to being measured, and quantum mechanics can only predict the probability distribution of a given measurement's possible results. The act of measurement affects the system, causing the set of probabilities to reduce to only one of the possible values immediately after the measurement. This feature is known as
wave function collapse."
Of course, you can debate whether the Copenhagen interpretation applies to very large objects, i.e., Schrodinger cat.
Look, utlimately, we cannot say for sure whether QM (quantum mechanics) is a final theory. We, for example, know that Einstein's theory of gravity is not, since it cannot describe quantum systems. And QM may likewise be impacted as it tries to deal with gravity (it currently cannot). But current consensus is that QM is fundamentally correct and applies to all physical systems, regardless of whatever interpretation you may have, Copenhagen or otherwise. Different interpretations, such as many worlds, super-determinism, etc. does not mean that the system is not described by the mathematical laws of quantum mechanics (wavefunction, matrix mechanics, etc.). Rather, it is a question of how you interpret the mathematics.
(Agree this is OT. My background is physics, and I'm quite familiar with the nuances of various quantum interpretations and its impact on reality and philosophy. What I was talking about was the consensus view. If you really want to have a discussion of physics, philosophy, and reality, we can. I can talk all day about Bell's inequality, whether objects really exist, and what quantum mechanics really means.)
