I don't care

um... what? Reading the synopsis of the book in @marmot84's comment I noted;

"Stephen Hawking claimed that anything sucked in a black hole was lost forever"

and

"a new paradigm that argues the world--this catalog, your home, your breakfast, you--is actually a hologram projected from the edges of space."

Which have nothing to do with each other!

Having not read it I cannot speak to the book beyond that, but unless there are scientifically peer reviewed articles cited in the book I feel it might be pseudo-science.

I do agree that "3d volume that we take for granted can be represented by a 2d enclosure surrounding it" no question that good math can lead to some answers that clash with common sense (Gabriel's Horn is a good and very simple one where you can fill a container with paint but you can't paint its outside surface).

Math alone proves nothing it is cold hard experimentation that wins out over mathematical models, which granted pave the way, or well several ways but we need to weed out the virtual from the solid.

I know Hawking also postulated, as his Ph.D. Thesis(maybe, it is one of his for sure) that particles near the event horizon which 'decay' from the fabric of the universe, i.e. the void of nothingness, into a particle and anti-particle pair which away from the event horizon will cancel each other out in a matter of time on the scale of Planck time (10^-44 seconds) I believe.

However, at the event horizon of a Black Hole one falls in thus leaving the other to be what we will call Hawking Radiation if it is ever detected. I don't think that's realistic considering it's a 50/50 shot of which one falls in so then another particle pair near the first will have the same chance and like annihilate the first but I have no evidence of model to support that, it is conjecture.

Then there is also the consideration of energy siphoned from a black hole from the gases that obtain enough angular velocity before entering the event horizon to escape the gravitation force of the black hole, the energy is derived from the black hole's own gravity which means it also loses mass (E^2 = (mc^2)^2+(pc)^2 ; full form of Einstein's equation since the matter is in motion and not at rest) which could mean that over time even a black hole evaporates through loss of gravitational energy.

That's only the piece regarding black holes, if we get into the expansion of space from cosmology that there is space beyond the visible universe then we're talking too much to cover here easily. First one must understand that space itself can expand faster than light but nothing in space can.

Ok beyond that science, you're asking; is the universe open(flat) or closed(which could allow for a hologram hypothetically). Measurements of the visible universe and the cosmic background radiation lean toward an open(flat) universe. Though I'm not sure how a saddle universe was ruled out, perhaps it wasn't given the saddle is a deviant of an open plane...

Personally I see the universe as a finite cluster of matter and energy is expanding into an infinitely open void where time, space and matter have no meaning...

I find a holographic universe hard to grasp, bazinga!

The holographic theory has been compelling for me.

The Holographic principle is, in my opinion a done deal. That doesn't mean that the universe is a hologram, but rather that the 3d volume that we take for granted can be represented by a 2d enclosure surrounding it.

If you are interested in the physics and the mathematical details I strongly recommend Leonard Suskin's book: Black Hole Wars - My battle with Steven Hawking to make The world safe for quantum mechanics.

[amazon.com]