Wheeler wouldn't have made the claim that he understood the underlying reality- he had strong OPINIONS and opinions based on a lot of brilliant work- but still just opinions, I doubt even the most egotistical of the founders of QM would have made that claim ... and if they did they would be in the delusional camp... But I doubt any of the greats even deluded themselves that they understood it. By 'understanding' I mean understanding what QM is saying about the true nature of the underlying reality. When I was a grad student I spoke with another grad student about our QM coursework, and I was blown away at how the mathematics of it seemed almost intuitive to him, and how he grasped the calculations at a gut level, as if it was just hardwired into his brain... some people through chance or through intense hard work are wired differently in just the right way.... but he didn't understand what QM meant about the reality of the universe.

It is not clear that the human mind is capable of 'understanding' QM. There are those people that are gifted and grasp the mathematics at a fundamental level, and some of them have insights into how it works and make incredible leaps in the theory... but QM, like some other areas of physics is a set of rules and implications FAR beyond what our primate brains evolved with. The best minds intimately know the mathematics and what its telling us- the rules of QM were not come up with by some brilliant guy having a flash of inspiration and suddenly understanding the true nature of reality. No, the entire scientific world was dragged into QM- with many people, including Einstein kicking and screaming about how at least some of the interpretations of what the math is telling us must be fundamentally flawed.

None of the greats denied that that the theory works- it is spectacularly good at explaining and predicting the results of experiment- as a tool it is as effective as it gets. It describes reality - it has implications that are so alien and counter-intuitive to our minds, but as weird as those implications are, they are undeniably true...

But what does it all MEAN? What does it say about the true nature of reality? Fuck if I know... No one knows for sure, plenty of people have ideas, and interpretations- most of which are unprovable. I am listening to a book on QM by Sean Caroll called 'The many hidden worlds of Quantum Mechanics'- he is a proponent of the 'Many Worlds' interpretation of QM (an interpretation first espoused by Hugh Everett, a student of Wheeler's by the way) . In this interpretation ALL quantum possibilities are equally real. Schroedinger's cat doesn't become alive or dead when you open the box, instead there is a multitude of universes where it alive and a multitude where its dead- all equally real, unable to be seen by the others, (making it terribly hard to falsify the supposition). It can, and has been, said that the Many Worlds interpretation is a FAR more 'natural' interpretation than the Copenhagen Convention that observation collapses the wavefunction. There really is no real mathematical justification for that interpretation- again, I am not an expert, but it was sort of just decreed that this was a comfortable way of sidestepping the philosophical questions we had no way of answering. (again, just my opinion informed by people that ARE experts)

Once we try to go beyond the math and try to understand the meaning we start to enter the realm of philosophy, not testable science. At least not testable yet.

Take the following analogy-
Imagine taking a sophisticated solar powered calculator back to the 1600's and giving it to Newton... after a brief tutorial you show him that it can do complex calculations that would be almost impossible to do in that age. It can even do the calculus that he helped invent, it speeds up his research greatly, and every time he tries to catch it giving an incorrect answer he is forced to admit it is correct... it even gives him glimpses at complex math he has not even dreamed of... Everyone eventually has to admit that the calculator gives the correct answer- they eventually are simply forced to admit that it is correct, even if it gives answers that are counter to their own intuition. Wise scientists of the era would admit that there might be cases where it gives incorrect answers, but if that is the case then the calculations are so complicated or alien to them that they have no way to check it... yet.

None of the greatest minds of the age could possibly explain how the calculator works... the reality behind it, the microscopic circuits carrying electrons might as well be angels and demons for all they know. All they know is its a powerful tool that- as far as they are capable of testing it- is ALWAYS right.

Having the calculator greatly accelerates their understanding of physics, and MAYBE eventually they will use it to help develop the physics that explains how it works and build more like it... but by the 1700's if a student asks 'But how does this device do all these things? What is the reality inside the box?' The teacher may say 'at this point, there is no way to know- it just works, shut up and use it to get answers'.

In many ways that is where we are with QM- through decades of theory and experiment we have to accept it works astoundingly well, even when it reveals weird answers like entanglement, the uncertainty principle, tunnelling, etc... answers that are completely counter to our day to day experience, our intuition that has evolved over millions of years.

Maybe someday the use of QM will help reveal the underlying reality... and we will understand why the calculator gives the answers it does- what makes it work... but right now we are still in the 'shut up and use it to calculate' phase.

There was- and still is- much debate about how to interpret what the facts mean... I (I am NOT an expert at all in QM) and actual experts feel that the Copenhagen convention (the idea of observation causing the wavefunction to collapse) is a bullshit way of shutting up the debate, an idea shoehorned into the physics simply because its the least disturbing or alien of all the other mathematically viable interpretations. It is NOT a natural interpretation of what QM is saying, it raises more philosophical questions that are swept under the rug such as "WHAT exactly qualifies as an observer and an observation", "Isn't it equally valid to say that when the observation is made, what really happens is that the observer becomes entangled with what is being observed", "In reality there is not a wavefunction for a single particle, isn't it more correct to say there is a single wavefunction for the entire universe?"

I can't say definitively that there is no God, but I am pretty damn certain that if there is, its nothing like the God described in the bible- in much the same way I don't know what the correct interpretation of QM is, but I am pretty damn certain the Copenhagen convention with the collapse of the wavefunction isn't close to reality.

But don't take my word on this- I studied QM and did the math well enough to get through grad school- experts that have far more experience and insight have come to the same conclusion. They have all sorts of alternatives to the Copenhagen convention... but for now they just have personal philosophies- any interpretation consistent with the math and experimental data is just as good as any other until we find a way to prove or falsify them.

What we DO know is that as weird as QM is, it indicates an underlying reality that is far weirder- perhaps one the human mind cannot fully grasp.

Classical mechanics 'makes sense' to us because it operates on a scale we witness every day... it was good enough for primates living in this world to survive and flourish. Knowing that there were electrons and protons, or that these particles were also waves wouldn't have done a damn to help our ancestors to not be eaten by a sabretooth tiger... so its actually pretty amazing our brains- pretty much unchanged over the past 20,000 years- have figured things out to this point... at what point will our brains simply be unable to grasp the tools we have discovered, let alone understand the reality of how they work?

Intelligence helps, so does hard work- and sometimes it also takes luck, or having some crazy quirk in the way you personally look at things. Education is critical, but it does NOT have to be a formal one- Faraday had little in the way of formal education... yet he laid the groundwork for much of the modern age... Technically, I am a high-school drop-out.

The most important thing I have learned is to find people smarter than you in a given area and try and absorb what they know. I learned a lot in my graduate courses, but it was WORKING with smarter people that really led me to understand things. The education just let me speak the same language so I could learn from them.

There is no reason to be bothered or regret, instead just feel the awe of knowing that the underlying nature of reality is currently so weird and awesome that countless billions of primates have not figured it out yet... but if we don't kill ourselves off we might...or perhaps it will be a never-ending journey...but we have, after all, come quite a far way from rubbing sticks together to get fire.