Time as an emergent property of entanglement

Monday, 4 November 2013
The holy grail in Physics is to unify quantum theory with general relativity. But, as Wheeler-De Witt showed, the "problem of time" arises when doing so. The prediction of their equation is that nothing happens in the universe, which is contrary to our experience. 

Page and Wootters found that we can describe an evolving universe from the point of view of internal observers thanks to quantum entanglement, even having a static system for an outside observer. In their article, Moreva and co-authors have shown how this can be achieved experimentally, for a toy universe. In particular, they show how a static, entangled state of two photons can be seen as evolving by an observer that uses one of the two photons as a clock to gauge the time-evolution of the other photon. However, an external observer can show that the global entangled state does not evolve (arxiv.org/abs/1310.4691). 

So, to experience time, we have to be entangled with the rest of the universe. An outsider, a God-like observer wouldn't see a difference in the state of the universe, in order for both, quantum physics and relativity to be compatible. However, all that comprises the universe would see the evolution of time, as we can experience. 

So time has no meaning outside the universe, and it is embedded in the relationship between its elements. It is an exchange of information between the different parts which are interacting within it. Note that time is related to the second law of thermodynamics, to the probabilistic nature of our experience. Interactions, as always, make all the fun.

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