Is the island universe model consistent with observations?

We study the island universe model, in which initially the universe is in a cosmological constant sea, then the local quantum fluctuations violating the null energy condition create the islands of matter, some of which might correspond to our observable universe. We examine the possibility that the island universe model is regarded as an alternative scenario of the origin of observable universe.

Figure 1

The sketch of evolution of local $\ln (1/ah)$ with respect to the scale factor $\ln a$, in which the shadow region denotes the NEC violating fluctuation and the gray lines denote the evolution of primordial perturbation modes. The perturbation modes exit the Hubble horizon during the NEC violating fluctuation and then re-enter the horizon during the radiation/matter domination at late time.

Figure 2

The Penrose diagram of creation and evolution of island universe, in which the event horizon of $\Lambda$ sea and the evolution of Hubble scale have been marked, and the gray line denotes the evolution of primordial perturbation modes. The region between black dashed lines denotes the NEC violating fluctuation. The dashed line of $t=0$ is the thermalization surface, after which the NEC violating fluctuation is over, the local island universe starts the FRW evolution, and with the lapsing of time finally will return to the blue $\Lambda$ sea again.