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Lisa Randall co-developed a geometric approach to the hierarchy problem with Raman Sundrum. Their Randall–Sundrum model uses a slice of five-dimensional Anti-de Sitter spacetime; its varying spacetime metric converts a fundamental large scale into a much smaller scale on the brane containing Standard Model fields. The mechanism relies on warping rather than an enormous compactification volume. It illustrates how assumptions about inaccessible spatial geometry can imply measurable particle excitations.^[ref]

Raman Sundrum and Lisa Randall proposed the Randall–Sundrum model to address the hierarchy problem. A warped spacetime metric produces an exponential relation between physical scales on two branes, even with only one compact additional spatial direction. In their 1999 construction, the Standard Model fields occupy one brane. The proposal makes the geometry of spacetime part of the explanation for a large separation of energy scales, with characteristic massive spin-two excitations as possible tests.^[ref]