On 2014-01-11 19:37, James Propp wrote:

Has anyone ever proposed in the Annals of Improbable Research or a similar venue that, in addition to undergoing periodic reversals of its magnetic field, Earth is also subject to occasional short-lasting reversals of its gravitational field?

Botannical evidence: gosper.org/IMG_0323.JPG

Such a phenomenon would handily explain selective extinction of megafauna: a mouse could survive an upward fall for five seconds followed by a downward fall for five seconds followed by an extreme deceleration, but a mastodon would not fare as well. :-)

Jim Propp

Maybe it was a gravity wave from a thud like the following, or maybe the following already happened. -------- Original Message -------- Subject: [math-fun] Humongous Thud coming Date: 2015-01-07 12:57 From: Warren D Smith <warren.wds@gmail.com> To: math-fun@mailman.xmission.com Reply-To: math-fun <math-fun@mailman.xmission.com> http://www.nytimes.com/2015/01/08/science/in-a-far-off-galaxy-2-black-holes-... https://www.caltech.edu/news/unusual-light-signal-yields-clues-about-elusive... Matthew J. Graham, S. G. Djorgovski, Daniel Stern, Eilat Glikman, Andrew J. Drake, Ashish A. Mahabal, Ciro Donalek, Steve Larson, Eric Christensen: A possible close supermassive black-hole binary in a quasar with optical periodicity, NATURE Wednesday 7 January 2015 http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14143.html If they are right, then two supermassive black holes are in an orbit the size of the solar system, and are going to merge soon (within 1 million years) due to loss of energy from gravity waves it is radiating. The resulting thud is going to be far bigger than anything humanity has ever observed. Matthew J. Graham, S. G. Djorgovski, Daniel Stern, Eilat Glikman, Andrew J. Drake, Ashish A. Mahabal, Ciro Donalek, Steve Larson, Eric Christensen, DOI:10.1038/nature14143