Conservation Of Information?

[koganbot]

Posting again on a subject I don't understand and never will: what physicists mean by "information." My brain balks at mathematical symbols, but I'm good at concepts; so my guess is that if some articulate physicist were to wander by, he or she could explain "conservation of information" in a way that doesn't totally leave me at sea. Wikipedia hasn

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The world of ordinary experience is a hologram

[koganbot]

A month ago I made it back to the library and copied these down from Susskind and from Carroll. Unfortunately there are gaps in my notes.

From Leonard Susskind's The Black Hole War, p. 298:

The three-dimensional world of ordinary experience - the universe filled with galaxies, stars, planets, houses, boulders, and people - is a hologram, an image of reality coded on a two-dimensional surface. This new law of physics, known as the Holographic Principle, asserts that everything inside a region of space can be described by bits of information restricted to the boundary.
On page 411, Susskind says that this boundary is "only an imaginary mathematical surface with no real substance." So anything can enter or leave. But we can think of something called "anti de Sitter space" in which the angles in triangles add up to less than 180 degrees. He describes it as like the reverse of a Mercator projection: anything close to the boundary gets smaller, infinitely small, without crossing the boundary. So in effect the boundary is impenetrable. "Everything inside a box with impenetrable walls can be described by bits of information stored in pixels on the walls."

Then (pp 416-417) he goes into the work of Juan Maldacena. This is where my notes are incomplete. But Maldacena showed that a world with four dimensions (three dimensions of space and one dimension of time) without gravity can alternately be described (is "dual" to) (is mathematically equivalent to, I assume) a world with five dimensions (four of space and one of time) with gravity, if the space in this [4 + 1]-dimensional world is an anti de Sitter space. Paraphrasing Susskind:

growing and shrinking [in size] in the [3 + 1] half of the duality is exactly the same as moving back and forth along the [fourth] direction in the other half of the duality.