Is there some scale (energy, length, and time) on which the linear superposition principle breaks down?

Is the quantum-classical "transition" a crossover or a phase transition?

What are the distinct signatures of quantum complexity?

Which interpretations of quantum theory are not experimentally falsifiable?

Are there any biological processes which require/involve quantum coherence beyond the nanometer length scale and picosecond time scale?

Are there any experiments which should cause one to abandon a philosophical position of critical realism?

Why doesn't the decoherence interpretation solve the quantum measurement "problem"?

In what sense can the classical world be considered to be an emergent phenomena?

Hopefully, I will write more about some of these soon. Comments and suggestions welcome.

Hi Ross,

ReplyDeleteI really like your blog as it plants the seeds of thoughts about areas of physics other than my own.

I would be interested to hear how you might test in the next decade the question "In what sense can the classical world be considered to be an emergent phenomena?". There are nice theories (such as linked to below) where it is shown how particles may emerge from lattice models. There are examples of quasi-particles 'emerging' in materials with gauge constraints in condensed matter now.

I would be interested in your thoughts on how the idea of an emergent universe could be tested though.

http://arXiv.org/abs/cond-mat/0404617

Bob

Hi Ross,

ReplyDeleteI vote for the emergence of the classical world as well. As you've mentioned elsewhere, emergence as a concept comes up in many different contexts. Whether or not string net condensation can explain electrons and photons, Wen's ideas along these lines are pretty exciting.

Maybe an order parameter type argument of quantum behaviour will be used to justify the phase transition picture between QM and CM?!

Anyway, that gets my vote, and it's very well suited to your particular field.

I can only ask the questions that I have... these may not be those asked by people that have had another 30 years or so to train.

ReplyDeleteMy reading on the thermodynamics of finite quantum systems suggests to me that the concept of "work" in such a system is not very well understood. In particular, Balian's statistical mechanics book "From Microphysics to Macrophysics Vol I" suggests that the concept of work has almost no meaning without invoking a Bohr-like idea of a "classical apparatus" on which the work can be exchanged.

My understanding is that work is to be interpreted as an adiabatic change in the eigenvalues of some effective hamiltonian describing the system - these eigenvalues are the "knobs" on a classical device. This suggests superselection is an important element of work transfer. Heat exchange, on the other hand, is manifested in a change in the eigenvalues of a density matrix, and in this case there doesn't seem to be any classical restriction: heat transfer to or from a system can change the density matrix of the system or its environment, and superselection doesn't seem like a necessary part of the description.

Is there any meaningful distinction between work and heat in quantum mechanics, or does this separation only make sense if the environment is classical?

Personally I would really like to see a good discussion of these ones:

ReplyDeleteWhy doesn't the decoherence interpretation solve the quantum measurement "problem"?

Which interpretations of quantum theory are not experimentally falsifiable?

Are there any biological processes which require/involve quantum coherence beyond the nanometer length scale and picosecond time scale?