One of nature’s venerable constants – gravity – may not be the same for every type of particle in the universe, suggest new calculations.

The gravitational constant (G) first estimated by Isaac Newton and also known as Newton’s constant, describes the strength of the gravitational pull that bodies exert on each other. For particles – protons, neutrons and electrons – this relates to their mass. In the case of light – photons – it relates to energy.

In conventional models, the constant is the same for both particles of matter and photons of light. But John Barrow of Cambridge University, UK, and Robert Scherrer of Vanderbilt University in Nashville, Tennessee, US, wondered what would happen if it were different for matter and light.

“The original motivation was to test this idea and rule it out or restrict it somehow,” Scherrer told New Scientist. But the pair was surprised to see that changing the gravitational constant in computer models had no discernable impact on the development of the early universe. The models used protons and neutrons for matter.

If photons wielded a smaller value of G than do the protons and neutrons, their model could explain why helium appears to be less abundant in the early universe than theoretically predicted.

More here.