The Foundational Questions
The following is a selection of foundational questions that were raised at the Iceland conference in 2007 and triggered spirited debate.
The following is a selection of foundational questions that were raised at the Iceland conference in 2007 and triggered spirited debate.

Are there reasons to believe that standard QM is insufficient?
 Can quantum mechanics be falsified? In other words, when experiments agree with QM, what other consistent theories do they rule out?
 Can we devise further interesting tests of quantum mechanics by embedding it in a larger parametrized theory?
 Is it possible to characterize/parametrize the complete set of hidden variable theories? Local and nonlocal ones?
 Are there interesting incompatibilities between some versions of quantum theory and (special) relativity?

Can we apply QM to the entire universe?
 Are some QM interpretations worthless for cosmology, or are they all suitable in some way?
 is the Universe like any closed system, or might it have qualitative differences (e.g. being spatially infinite)?

What is quantum physics fundamentally about?
 About reality?
 About information?
 About something else?
 What is the real role of the observer?

How much information is really there in a quantum state?
 Does a qubit have 1 bit, or 2 bits, or infinitely many?
 Is it a cheat to say that QM, with qubits, really turns the information content finite, when the description of a qubit requires two real numbers?
 If we consider an entangled state of N qubits, is the amount of information exponential or polynomial in N?

Can one define probabilities in an eternally inflating spacetime?
 If two sets are countably infinite (or in general have the same cardinality), is there a meaningful way in which they can be said to have different sizes?
 Do measures exist which are sensible and avoid both the 'youngness' and 'oldness' (Boltzmann's Brain) paradoxes?
 Is counting observers inherently problematic because it gives rise, e.g. to the Doomsday, Boltzmann's Brain, and Simulation paradoxes?

On what side of the borderline between science and philosophy are parallel universes?
 In what senses are the inflationary many universes equivalent to or different from the Everett manyworlds?
 What, if any, observational signatures might exist of other inflationary universes?
 in manyworld QM, what does it mean for the other worlds to be 'real'? What does it mean for one world to be, e.g., 1% as real as another, or that the ratio depends on the basis employed?
 Can we consistently employ the Copernican/Mediocrity principle (frequentist statistics over observers) and also accept manyworlds QM?

What is dark energy?
 Are we in a true vacuum or false vacuum?
 Are early inflation and late inflation (dark energy) related?

Should we expect the "constants of nature" to be constant?
 Are observable changes in fundamental parameters ruled out by nearconstancy of vacuum energy?
 If fundamental constants oscillate, how well can we constrain this?
 How exactly do fundamental constants couple to vacuum transition in something like the stringtheory landscape?

Why did our universe begin in a lowentropy state?
 Are the relations between all of the 'arrows of time' understood?
 What role, if any, does the vacuum energy play in cosmic initial conditions?
 What is the nature of time in quantum physics?
 To what extent can quantum physics retrodict earlier states?
 Can one define Boltzmann entropy in quantum mechanics?

Is there any hope of experimentally testing quantum gravity?
 Are there fundamental limits to experimentally determining the theory of quantum gravity (e.g. scattering highenergy particle may just form black holes)?
 Can we devise a gedanken experiment to interfere different causal structures?

What will the ultimate theory (or at least the next one) be like?
 Will it actually use the current form of QM?
 Will we construct it by starting with a classical theory and quantizing it?
 Will it involve tensor category theory?
 As we go up in energy, should we expect to find more or less degrees of freedom?
 Will the next/final theory be simple or complicated?
 Beautiful or ugly?
 Funny or boring?
 What does it mean to understand something? Does ability to compute all answers mean that we really understand something? Or are 'emergent' phenomena just a real (and call for just as much explanation) as the processes underlying them?

Is nature fundamentally analog or digital (continuous or discrete)?  Is that a wellposed question?
 Is there a continuum between discreteness and continuity?
 Are there experiments in physics that really require one or the other?

Is nature completely mathematical?
 If not, what would the extra ingredient(s) be?
 Is 'being observed' in QM such a nonmathematical property?

Do any of our capabilities and experiences inform us that we are not in a computer simulation?
 is there a Measure catastrophe (the Simulation argument)?
 Does Penrose's argument have anything to say? Is there a variant that might?
 Can subjectivity exist in a simulation (the Hard AI problem)?

Can temporal duration or 'now' have meaning in a simulation?