# Holographic principle where it stops and why

I just read "Black hole wars" by L. Susskind. Essentially he claims that a boundary contains all the information about the volume it encompasses. He proclaims this the holographic principle (HP).

My questions in regard to the holographic principle are:

1) Does the volume (3D) still exists or everything is 2D which for us (humans) appear as 3D (spatial dimensions only) ? Or is it just clever reductionism that 3D is real but we can described it with information on the boundary (like the entropy of a black hole).

2) If the holographic principle is a general law of nature, how about scaling. If I have a disk (2D) can I describe it with a line (1D) ? Where it stops ? Singularity ?

3) How the HP fits with 9 spatial dimensions in the M-theory (the author proudly claims that the string theory nicely proofs the HP) ?

4) Why the time is untouched by the holographic principle ?

Thanks !

2. The most famous example of holography actually holds when the volume is 4d, and the surface is 3d. There are various other examples in other dimensions, such as when the volume is 2d and the surface is 1d (named AdS$_2/$CFT$_1$). I think there are not known examples when the volume is 1d, so that the surface had to be a point (zero dimensional).