Theory of everything (for some universes) ... ... most likely not ours ... so far

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Every condensed matter system itself can be viewed as a model universe. Most of those model universes are very different from our universe. The issue here is to design a condensed matter system that resemble our universe.
The first rule of game is that only local bosonic models with finite cut-off are allowed in the design.

  1. Emergence of helicity +/- 2 modes (gravitons) from qubit models (pdf)
    Zheng-Cheng Gu and Xiao-Gang Wen
    arXiv:0907.1203, Nuclear Physics B online
  3. A lattice bosonic model as a quantum theory of gravity (pdf)
    Zheng-Cheng Gu and Xiao-Gang Wen
    • Constructed a quantum spin model on a lattice which gives rise to emergent gravitons (linearized quantum gravity).
  5. Photons and electrons as emergent phenomena (pdf)
    Michael A. Levin and Xiao-Gang Wen
    Rev. Mod. Phys. 77, 871-879 (2005), cond-mat/0407140
    • String-net condensation provides a way to unify light and electrons.
      Rejected by Science :-(
  7. String-net condensation: A physical mechanism for topological phases (pdf)
    Michael Levin and Xiao-Gang Wen
    Phys. Rev. B71, 045110 (2005). cond-mat/0404617
    • Pointed out that all the gauge theories and doubled Chern-Simons theories as well as all statistics (Fermi, fractional, and non-Abelian statistics) can be realized in lattice spin models through different string-net condensations.
  9. Quantum order from string-net condensations and origin of light and massless fermions (pdf)
    Xiao-Gang Wen
    Phys. Rev. D68, 024501 (2003). hep-th/0302201
    • Quantum ordered states that produce and protect massless gauge bosons and massless fermions are string-net condensed states.
    • Different string-net condensations are not characterized by symmetries, but by projective symmetry group (PSG). PSG describes the symmetry in the hopping Hamiltonian for the end points of condensed strings.
    • PSG protects masslessness of Dirac fermions. PSG leads to an emergent chiral symmetry.
    • Constructed an local boson model on cubic lattice that has emergent QED and QCD.
  11. Fermions, strings, and gauge fields in lattice spin models (pdf)
    Michael Levin and Xiao-Gang Wen
    Phys. Rev. B67, 245316 (2003). cond-mat/0302460
    • Pointed out that fermions can emerge in local bosonic models as ends of open strings.
    • The string picture for fermions works in any dimensions, which is more general than the flux-binding picture in 2D.
    • Pointed out that emergent fermions always carry gauge charges.
  13. Artificial light and quantum order in systems of screened dipoles (pdf)
    Xiao-Gang Wen
    Phys. Rev. B68, 115413 (2003). cond-mat/0210040
    • Constructed realistic screened dipole systems in 2D and 3D that contain artificial photon as their low energy collective excitations.
    • Find that U(1) gauge bosons are collective motions condensed string-nets.
    • According to the string-net picture, we can answer the following three questions about light:
      What is light?
      Light is a fluctuation of closed strings of arbitrary sizes.
      Where light comes from?
      Light comes from the collective motions of ``things'' that fill our vacuum. (Note that our vacuum is not empty. It is filled with ``things'' that form the space-time.)
      Why light exists?
      Light exists because our vacuum is a quantum liquid of string-nets.
      Rejected by Nature :-(
  15. Origin of Light (pdf)
    Origin of Gauge Bosons from Strong Quantum Correlations
    Xiao-Gang Wen
    Phys. Rev. Lett. 88 11602 (2002) hep-th/0109120
    • Proposed that light and fermions originate from a certain "pattern" of quantum entanglement in a many-boson system. The "pattern" of quantum entanglement is called quantum order.
    • Proposed that gaplessness of photons and fermions is protected by the quantum order.
    • Constructed a spin model (which can sit on your palm) that reproduces a complete 1+3D QED (a cosmos with light, electrons, protons, atoms, ...).
      Rejected by Science :-(
      At the PRL editor's request, the published version got a new and longer title.

    An artistic summary of the result:
    The following picture

    has mountain, lake, trees, snow,... ..., and light.

    If we look closer, we see

    atoms, electrons, protons, and photons.

    If we look even closer (I mean really really close), we see ... ...

    boring spins on a lattice.

    How can a simple boring spin system produce such a nice scenery?
    The answer is "more is different". When many quantum spins interact with each other, the spins can get organized (or entangled). The pattern of organization is called quantum order. It is this pattern (ie the quantum order) of spins that makes wonders. The twists and defects in the pattern correspond to "elementary" particles. In this way, quantum order produces electrons, photons, atoms, ... ..., and the beautiful scenery.


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