In article <771609e1-0092-40c9...@googlegroups.com
> The following quote is from a sciam article titled "Black Hole
> Computers" by Seth Lloyd and Y. Jack Ng (April 1, 2007). They
> are referring to satellites measuring any region with radius R
> and certain ultimate limits to the possible accuracy which can be
> obtained by even the most advanced civilization imaginable; lp
> is the Planck length:
The article (from 2012) is freely available; Google finds it quickly.
In general, it is concerned with the fascinating union of
thermodynamics, general relativity, and quantum theory in relation to
the information content of black holes. In particular, it looks at
limits on information processing in the universe. About 20 years ago
(building on earlier work), Freeman Dyson (and Lawrence Krauss, in a
sort of debate) did some work on this (but more in the context of
> I don't have a concrete grasp of their conclusions-- Are they
> saying, as an example, if we had a system (equivalent to a
> cosmic tape measure), any attempt to measure the entire
> universe would never have an average accuracy finer than
> ~ 10^-15 meter?
> Also, the fact of this "fineness" accuracy,
> 10^-15 meters, re: the "measure of the universe", being
> roughly the radius of a proton, is fairly astonishing.
Do you mean the size or the coincidence (if it is one)? The interesting
thing is that, if true, their idea might be proved relatively soon.
> Also, what
> do Lloyd and Ng mean when they say that below that minimum
> (fineness) scale, spacetime geometry has no meaning?
They essentially mean that it can't be measured. Whether that means
that it doesn't exist is at least a philosophical question.
> this actually conform with the notion of spacetime being
> an emergent phenomenon outside of certain defined limits?
The two concepts are probably related, though perhaps not too closely.