Lisa Randall and Raman Sundrum propose an alternative to compactification in higher-dimensional theories, demonstrating that four non-compact dimensions can exist without contradicting experimental gravity. Their model involves a single 3-brane embedded in a five-dimensional bulk spacetime, where gravity is effectively four-dimensional due to the localization of the graviton in the extra dimension. The theory avoids the need for a gap in the Kaluza-Klein spectrum, allowing for a continuous spectrum of modes. The effective four-dimensional Planck scale is determined by the higher-dimensional curvature rather than the size of the extra dimension. The graviton is a bound state localized near the brane, while other KK modes have weak coupling to low-energy states on the brane. The theory reproduces Newtonian gravity and general relativity with high precision, even in the limit of an infinite extra dimension. The model also addresses the cosmological constant problem and provides a framework for understanding gravitational interactions in a non-compact extra dimension. The results suggest that a consistent four-dimensional theory of gravity can exist without compactification, offering a novel alternative to traditional compactification schemes. The theory is consistent with current experimental constraints and provides a viable framework for studying gravity in higher dimensions.Lisa Randall and Raman Sundrum propose an alternative to compactification in higher-dimensional theories, demonstrating that four non-compact dimensions can exist without contradicting experimental gravity. Their model involves a single 3-brane embedded in a five-dimensional bulk spacetime, where gravity is effectively four-dimensional due to the localization of the graviton in the extra dimension. The theory avoids the need for a gap in the Kaluza-Klein spectrum, allowing for a continuous spectrum of modes. The effective four-dimensional Planck scale is determined by the higher-dimensional curvature rather than the size of the extra dimension. The graviton is a bound state localized near the brane, while other KK modes have weak coupling to low-energy states on the brane. The theory reproduces Newtonian gravity and general relativity with high precision, even in the limit of an infinite extra dimension. The model also addresses the cosmological constant problem and provides a framework for understanding gravitational interactions in a non-compact extra dimension. The results suggest that a consistent four-dimensional theory of gravity can exist without compactification, offering a novel alternative to traditional compactification schemes. The theory is consistent with current experimental constraints and provides a viable framework for studying gravity in higher dimensions.