Do we live on the skin of a bubble in an extra dimension?
Researchers at Uppsala University in Sweden have developed an interesting model of the universe. They describe and support their idea in a paper that uses the principles of string theory (according to which all matter is made up of tiny, vibrating strings) and simultaneously incorporates the phenomenon of dark energy (which is considered as a possible cause for the expansion of the cosmos).
According to their model, our universe is being carried along on the skin of a kind of bubble that is expanding in another dimension. Space and the bubble are far from the same thing; effectively we are merely passengers on the skin of a balloon. The balloon, the bubble, is here a five-dimensional anti-de Sitter space, that is, a spacetime with a negative cosmological constant. On the surface of its skin (a spherical brane), the researchers show, life appears to be playing out as we know it, in four dimensions and with the known laws of gravity. This is all just an appearance, because this is only how the universe looks to us poor four-dimensional observers who cannot see or measure the massless, five-dimensional gravitons that move effortlessly between the dimensions.
All matter of the cosmos produced in this model would then consist of the ends of strings that extend from our universe into the extra dimension. All of us, and any form of matter, would thus be like puppets guided by strings stretching out from this extra dimension.
In their paper, the researchers also show that such bubbles could be the result of some special cases of string theory. Our universe would also not necessarily be the only such bubble; numerous other bubbles could exist in the extra dimension.
The original physics-speak in the abstract makes this all sound even more complicated: “we propose an embedding of positive energy Friedmann-Lemaître-Robertson-Walker cosmology within string theory. Our proposal involves confining 4D gravity on a brane which mediates the decay from a nonsupersymmetric five-dimensional anti-de Sitter false vacuum to a true vacuum. In this way, it is natural for a 4D observer to experience an effective positive cosmological constant coupled to matter and radiation.”