Now go, write it before them in a table, and note it in a book, that it may be for the time to come for ever and ever... Isaiah 30:8
".....textbooks say that the general theory reduces to special relativity
when you go far—ideally, infinitely far—from a planet, star, or other
gravitating body. Way out there, gravity fades to nothingness, and the
usually floppy spacetime continuum should harden into a rigid framework.
Because gravity diminishes with distance, planets and stars are nearly
independent of one another, and what happens in our solar system depends
very little on the rest of the 
galaxy.....Compère of the Université Libre de Bruxelles, in Belgium, likens the
structure of the “flat spacetime” that special relativity describes to a
crystal. It has only a limited degree of symmetry, he explains: It
looks the same if you take three steps to the right (a shift in
position, known as a “translation”) or board a train moving at a
constant velocity, for example.
Yet on close examination, Bondi and his colleagues discovered that, even
when they zeroed out gravity, spacetime stayed floppy rather than
becoming rigidly flat. In other words, even where there is no gravity,
there is still gravity; a residue always remains. Distant planets and
stars are not independent of one another after all. The textbook
picture, then, is wrong, but there was no intuitive way to understand
why, or what it means in practice. “General relativity did not end up
being the same thing as special relativity even at very, very long
distances,” Strominger says.
At those distances, what remains are not just the symmetries of special
relativity, but an infinite number of other symmetries called
supertranslations. These are angle-dependent translations that relate
points infinitely far from a gravitating body. This profusion of
symmetries, known as the BMS group, gives empty spacetime an enormous
latent complexity. Put simply, there are infinitely many ways for
spacetime to be empty. “The literature is just replete with errors, because the proper context was not understood,” Strominger says.
A supertranslation, he says, adds soft particles to spacetime.
----Nonetheless, physicists are on the hunt for evidence of an 
observable
“memory effect” left behind by gravity that could soon be picked up in a
lab. In the 1970s, Soviet physicists Yakov Zel’dovich and Alexander
Polnarev suggested that gravitational waves would not only cause a
fleeting oscillation in a detector, such as those famously picked up by
the mirrors of the LIGO system, but they would also leave a permanent
shift. “The mirrors wiggle and, after the wave passes, they don’t return
to their original position,” Strominger says.
Strominger suggested that the vacuum of general relativity may provide a memory matrix that preserves this information in the universe." Nautilus
