### Grokking Gravity

After remembering my dreams in the bath the other morning, I puzzled some more about gravity, wondering “where is the equal and opposite reaction to the force of gravity?”

Looking at gravity from Einstein’s point of view, that it is a curving of spacetime, allowed me to wonder if there shouldn’t be a corresponding negative curving of spacetime to have the momentum equations balance (conserving momentum)? Even though we don’t see this negative curvature locally, if it could only show up by wrapping around the universe from another “edge”, it would nicely explain dark energy (and scale properly if dark matter were included).

Imagine my surprise and delight when, the next morning, one of my daughters’ Facebook page had a link to a new mathematical description and further development of my insight. I have long subscribed to the notion that the conversation of a time is what stimulates, usually several people at once, to similar discoveries. Although I am pleased to imagine I’m tuned in enough to the conversation about the nature of the universe to have this glimmer of insight, I cannot really take any credit for it. Newton said it well to Hooke: “If I have seen further it is by standing on the shoulders of giants”.

Wang and Ma, the mathematicians who published the new version of gravity last week, say it also explains dark matter and dark energy. From the ScienceDaily article:

The researchers postulate that the energy-momentum tensor of normal matter is no longer conserved and that new gravitational field equations follow from Einstein’s principles of equivalence and general relativity, and the principle of Lagrangian dynamics, just as Einstein derived his field equations. Wang said the new equations were the unique outcome of the non-conservation of the energy-momentum tensor of normal matter.

Other questions remain to be understood by me, like if acceleration and gravity are indistinguishable as Einstein said, why doesn’t the whole cylinder above a rocket ship get sucked up into the curvature into which the rocket is “falling”?

This entire line of inquiry started with my attempting to understand classical (not quantum) spin, like doesn’t a spinning thing experience constant acceleration? My researches have developed a timeline of when we learned about spinning things, while wondering why the bicycle wasn’t invented thousands of years earlier.