From Derek Hacking, Ely, Cambridgeshire, UK
I have long wondered whether antimatter would have the same effect on the curvature of space as normal matter, and was delighted to see that this is going to be tested in the next couple of years (7 January, p 28). In the unlikely event that it does turn out that antimatter has a negative gravitational mass, I wonder what this would say about dark matter.
Cold dark matter is now central to our understanding of the evolution of the universe. It provides the scaffolding for the aggregation of normal matter and the formation of galaxies and stars. Could there be cold dark antimatter with a negative gravitational mass? Could aggregations of this explain the normal matter voids that seem to be associated with dark energy, invoked to explain the accelerating expansion of the universe? In other words, could dark energy be explained by cold dark antimatter?
The editor writes:
• Such a scenario would work if dark antimatter does not gravitationally attract normal antimatter: normal antimatter gives out light just like matter does, and so would not appear to be a void.