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The existence of light a massless U(1) gauge boson is one of the unresolved mysteries in nature. We propose that light is originated from certain quantum orders in our vacuum. We construct quantum spin models on lattice to demonstrate that some quantum orders can give rise to light without breaking any symmetries and without any fine-tuning. Through our models, we show that the existence of light can simply be a phenomenon of quantum coherence in a system with many degrees of freedom. Massless gauge fluctuations appear commonly and naturally in strongly correlated quantum systems which originally contain no gauge fields.
Xiao-Gang Wen (Wed,) studied this question.