"Deterministic underlying theories for QM are possible. They are still difficult to construct, but simple "toy models" are possible. These models are not good enough to replace today's existing quantum theories."

"... trying to solve a paradox will lead to new kinds of understanding. And I think that the problem of subjecting black holes to quantum mechanics is a fundamental paradox of the same nature, and the same depth, and the same importance as the paradox that Max Planck was studying at the beginning of the twentieth century."

"When investigating theories at the tiniest conceivable scales in nature, almost all researchers today revert to the quantum language, accepting the verdict from the Copenhagen doctrine that the only way to describe what is going on will always involve states in HIlbert space, controlled by operator equations."

"In practice, quantum mechanics merely gives predictions with probabilities attached. This should be considered as a normal and quite acceptable feature of predictions made by science: different possible outcomes with different probabilities. In the world that is familiar to us, we always have such a situation when we make predictions. Thus the question remains: What is the reality described by quantum theories? I claim that we can attribute the fact that our predictions come with probability distributions to the fact that not all relevant data for the predictions are known to us, in particular important features of the initial state."

"The usual no-go theorems telling us that hidden variables are irreconcilable with locality, appear to start with fairly conventional pictures of particle systems, detectors, space and time. Usually, it is taken for granted that events at one place in the universe can be described independently from what happens elsewhere. Perhaps one has to search for descriptions where the situation is more complex. Maybe, it needs not be half as complex as superstring theory itself. The conventional Copenhagen interpretation of quantum mechanics suffices to answer all practical questions concerning conventional experiments with quantum mechanics, and the outcome of experiments such as that of Aspect et al can be precisely predicted by conventional quantum mechanics. This is used by some to state that no additional interpretation prescriptions for quantum mechanics are necessary. Yet we insist that the axioms for any "complete" quantum theory for the entire cosmos would present us with as yet unresolved paradoxes."

"Quantum mechanics as it stands would be perfect if we didn't have the quantum-gravity issue and a few other very deep fundamental problems."

"On your way towards becoming a bad theoretician, take your own immature theory, stop checking it for mistakes, don't listen to colleagues who do spot weaknesses, and start admiring your own infallible intelligence."

"If you really want to contribute to our theoretical understanding of physical laws — and it is an exciting experience if you succeed! — there are many things you need to know. First of all, be serious about it!"

"The reader may ask why in this book string theory and supersymmetry have not been discussed. ... The fact is that this book is about physics and this implies that the theoretical ideas discussed must be supported by experimental facts. Neither supersymmetry and string theory satisfy this criterion. They are figments of the theoretical mind."

"Great physics does not automatically imply complicated mathematics!"

"We understand many things about particles and their interactions, but this and other mysteries make it very clear that we are nowhere close to a full understanding."

"Mathematical physics is in the first place physics and it could not exist without experimental investigations."