Researchers suggest that one of nature’s venerable constants — gravity (G) — may not be the same for every type of particle in the universe.

Calculations by John Barrow of Cambridge University and Robert Scherrer of Vanderbilt University suggest that G could have been smaller for photons than for other particles in the early universe.

The work might explain the lower abundance of helium seen, because the expansion of the early universe and its energy density are dependent on G.