  in physics, randallâsundrum models (also called 5-dimensional warped geometry theory) imagines that the real world is a higher-dimensional universe described by warped geometry. more concretely, our universe is a five-dimensional anti-de sitter space and the elementary particles except for the graviton are localized on a (3&nbsp;+&nbsp;1)-dimensional brane or branes. the models were proposed in 1999 by lisa randall and raman sundrum because they were dissatisfied with the universal extra-dimensional models then in vogue. such models require two fine tunings; one for the value of the bulk cosmological constant and the other for the brane tensions. later, while studying rs models in the context of the  anti-de sitter / conformal field theory (ads/cft) correspondence, they showed how it can be dual to technicolor models. there are two popular models. the first, called rs1, has a finite size for the extra dimension with two branes, one at each end. the second, rs2, is similar to the first, but one brane has been placed infinitely far away, so that there is only one brane left in the model. ==overview== the model is a braneworld theory developed while trying to solve the hierarchy problem of the standard model. it involves a finite five-dimensional bulk that is extremely warped and contains two branes: the planckbrane (where gravity is a relatively strong force; also called "gravitybrane") and the tevbrane (our home with the standard model particles; also called "weakbrane"). in this model, the two branes are separated in the not-necessarily large fifth dimension by approximately 16 units (the units based on the brane and bulk energies). the planckbrane has positive brane energy, and the tevbrane has negative brane energy. these energies are the cause of the extremely warped spacetime. ==graviton probability function== in this warped spacetime that is only warped along the fifth dimension, the graviton's probability function is extremely high at the planckbrane, but it drops exponentially as it moves closer towards the tevbrane. in this, gravity would be much weaker on the tevbrane than on the planckbrane. ==growing, shrinking, and changing weight: solving the hierarchy problem== also in this model, any object moving from the planckbrane to the tevbrane in the bulk would be growing, becoming lighter, and moving more slowly through time. distance and time expand near the tevbrane, and mass and energy shrink near it. this creates an alternate explanation of gravity's weakness in the tevbrane: everything is lighter. an interesting part of this is that the hie
Particle_physics Physical_cosmology String_theory