What is Déjà vu? Have you ever heard of it before? Déjà vu is a French word and it means "already seen". It is actually a strong feeling or sensation about an event currently being experienced that it has been experienced in the past, it doesn’t have to do with whether it has truly occurred or not. Déjà vu is a phenomenon that we all have experienced, that strange feeling when you walk into a room or enter into a new situation and you say to yourself that I have been there before, you say that everything here is familiar. It turns out that we can actually induce forms of Déjà vu in subjects, in experiments.
So there is a theory that says the Déjà vu is simply a fragment of memories that we have stored in our brain, memories that can be recalled by entering into an environment that resembles to something that we have already experienced. So we don’t have to involve parallel universe, we don’t have to involve the multiverse in order to explain most of the Déjà vu. However, it does raise the other question. Is it ever possible on any level to possibly flip between different universes? And the answer is actually unclear. Some physicists believe that there really is a multiverse that exist even in a living room. We are waves, vibrating waves according to string theory. These waves vibrate and then split apart with time.
Think of a radio playing a frequency, that radio is actually tuned to one frequency, but the room in which the radio is contains all the frequencies of other channels. All the radio frequencies of different channels are vibrating in that room, but the radio is tuned to one frequency. In other words, when the two universes are in the phase, they are coherent and you can shuffle between the two universes, but when the times start to evolve these two universes start to vibrate at different frequencies and you can only play one frequency. They no longer interfere with each other, so question here is why your radio cannot listen to all the frequencies? And the answer is your radio cannot listen to all the frequencies because your radio is incoherent to others. Same thing in quantum physics is we consist of atoms and our atoms vibrate, but they no longer can vibrate in unison with the other universes. So Déjà vu is probably a fragment or a feeling in our brain related to previous situations. However, in quantum physics there are in a sense parallel universe surrounding us. Problem is we cannot get access to those parallel universes because we are no longer vibrating in a unison with them.