Testing for Vanishing Dimensions

A recent theory solves some problems in cosmology and particle physics by proposing that the early universe contained fewer spatial dimensions than the three we see today. In the 11 March Physical Review Letters, a team describes a specific test of the theory using LISA, a planned, space-based observatory for gravitational waves. The theorists say the waves can't exist in fewer than three dimensions, so above a certain frequency--representing the oldest waves--LISA should see no primordial waves. Although the theory is speculative, some researchers believe cosmic ray data has already shown hints of vanishing dimensions at high energies. The team says the new test would be more conclusive than previous results.