FQXi's 5th International Conference
If a Tree Falls: The Physics of What Happens and Who Is Listening

This conference will bring together leading researchers from across a wide range of fields within physics, including cosmology, astrophysics, philosophy of physics, complex systems, biophysics, neuroscience, computer science, and mathematics. Attendees will investigate the meaning of events in physics and “what happens”; the nature and role of observers; and how these two categories interact and overlap.

Questions include:

  • What is the nature of Events in Quantum Mechanics?
    • What, if anything, is an event in QM? Or do events only emerge from QM? If so, how?
    • Can events 'un-happen'? Under what circumstances?
    • Are events fundamental and primary, or are they emergent?
    • Are there useful alternatives to considering events as building-blocks of reality, such as relations, histories, processes, correlations, etc.?

  • What is the nature of Events in Special Relativity/General Relativity/Cosmology?
    • What is an event in relativity? Are events relative?
    • Are events more fundamental than spacetime?
    • What is the relationship between events and causality?
    • Are singularities like the Big Bang "events", or something else?

  • What is the nature of Events in Quantum Field Theory and Quantum Gravity?
    • How does a quantum event happen in spacetime? Are there new issues in understanding events that arise when moving from quantum mechanics to quantum field theory?
    • Do events have definite locations in space and time, or are they something else? Can we gain new insights into holographic approaches or AdS/CFT from an "events"-based perspective?
    • What does a particle detector actually detect – an event or something more complicated?

  • How do Events relate to the Nature of Time?
    • Is time an external ordering of events, or does time emerge from events?
    • How does the flow of time emerge from a sequence of events?
    • How do future events differ from past events?

  • What does being an observer mean?
    • What are the properties or attributes that a system must have in order to constitute an ‘observer’ in varying contexts? Possible properties could include:
      • An agent that can gather and process information, and act on the basis of the gathered information.
      • Some level of independence from what is being observed (how much independence is possible/necessary?)
      • Memory of past events, or external or internal states
      • An internal representation of the external environment
      • An internal representation of the observing agent itself
      • Inner awareness or qualia; the property of being a 'subject' rather than an 'object'
      • Consciousness of the type generally assumed to be enjoyed by higher life-forms with well-developed brains
      • Self-reflective, self-aware consciousness of the type enjoyed by humans

  • What sort of physical systems have the requisite properties for those systems to construe various types of observers? In a spectrum from most simple to most complex physical structures, which systems constitute observers?
    • How simple can an observer be? Do particles observe each other? Simple biochemical systems? Complex biochemical systems? Viruses? Bacteria?
    • Are there systems such as ecosystems, collections or societies of organisms, etc., that are not normally considered observers but should be, by some definitions?
    • There is a hierarchy of observations that occur in biological processes, at quantum, biomolecular, intracellular, and intercellular levels (e.g. in vision before information even reaches the brain). Should all of these entities be considered to be separate observers, and if so, are there general principles for describing their interactions?
    • How clearly must an observer be delineated from its environment, or from an object of observation, to be an observer? How much coupling with the environment is necessary for observation to occur?
    • Do complex information-processing systems such as AI (in principle if not in practice) constitute observers, and under what definitions? Might they do so in radically different ways than biological intelligences?
    • Detector technology has already expanded the range of what we humans can observe in many ways, including a vast range of electromagnetic wavelengths as well as new scales from microscopic to astronomical. There may also be qualitatively different sorts of observations that can be made than those we make. Are there/can there be observers that far transcend current human-level observers?
    • Do observers require a well-defined arrow of time? Can they exist in thermal equilibrium? (Some very simple biochemical systems regularly see entropy decrease; and ‘Boltzmann brains’ represent hypothetical observers that exist in equilibrium systems).
    • If consciousness (specifically, having a subjective experience) is a necessary condition for being an observer, then which physical systems are conscious? If complex information processing is required, then what principles must this information processing obey to give rise to consciousness? Can we probe this experimentally using neuroimaging?

  • Are there interesting questions, to which the answers depend upon how we think of observers?
    • Is a rigorous physics-based definition of an observer required to derive the emergence of a semiclassical world from quantum mechanics? From quantum gravity?
    • Is a satisfactory understanding of what an observer is required to solve the quantum factorization problem, i.e., the problem that there is nothing in the formulation of quantum field theory that explains how to factor Hilbert space into subsystems? It has been argued that decoherence alone cannot explain, for example, why we perceive the semiclassical world in terms of an a hierarchy of objects in real space as opposed to, say, in Fourier space or the eigenbasis of the full Hamiltonian.
    • There has been a discussion in the literature about how small in mass a 'Boltzmann’s brain' could be — under a certain set of assumptions and reasoning, this minimal mass could be crucial in determining whether certain cosmologies are viable.
    • There is a significant discussion in the literature of what 'reference class' (which in many cases amounts to what sort of observers) should be considered in making 'anthropic' arguments that include self-selection.
    • If some types of observer are imbued with moral value, it becomes important to know which types, and what systems are of that type. This has long been discussed in the ethics of animal and human rights, but could also in the future be applied to machine intelligence or synthetic life.
    • The (in)famous black hole information (and related 'firewall') paradox is intimately involved with what observers can have what information. How accurately must such observers be modeled?
    • How fallible are observers? Given that detecting events, then processing and storing them requires the 2nd law of thermodymanics, does there have to be some possibility of a mishap? Can we put strict bounds on this?