Dude! Hologram!

Ever since Stephen Hawking got involved, black holes have been weird. Janna Levin didn't talk about Cauchy horizons; but she did bring up what Pournelle had reported 45 years ago. Stuff about us being a hologram.

I think what this means is that, with the information beamed into a black hole from without, anyone on the inside can see a 2-dimensional video of the universe outside. As noted space and time don't quite work the same from inside the Event Horizon. The black hole can be described in two dimensions; it is, from our perspective, just a shell, maybe with spin (mass corresponds to volume, so I guess - just radius and oblateness?). A 3-D object that can be described, without a frame-of-reference, in only two dimensions is holographic.

When you take this up to four dimensions and try to describe them in three, congratulations, you're Grisha Perelman.

An aside to those who assume black holes are spheres: well, according to relativity, sure, but quantum theory adds some provisos to that. These lads over in Stack Exchange compare Schwarzchild to Kerr. Kerr's holes spin, rather should spin since we've not seen it, so shall be oblate. I forgot above to mention some Kerr holes, already theoretical, may have charge too so are "Kerr Newman". Thus, the three hairs of the otherwise famously bald black hole - and we observe only the first, the mass (a couple years ago we dramatically saw the disc of M87's).

We think we live in three dimensions in which case we are projecting ourselves upon black holes' monitor screens. But, some say, we might actually be playing out our lives inside a black hole and projecting ourselves upon the space of the universe. We'd just need to change our coördinate systems.

Again, Dude! Hologram! is a mathematical / theological question, not a question of physics. Worse, if the holographic-principle math makes a physicist's job harder and gives nothing back, we have not gained anything; much like how Einstein does not help us build rockets in a Keplerian system. Discovering Kerr and Newman properties for a black hole, by contrast, is a question of physics. I should start there.

How to observe Kerr and then Newman, oblateness and then charge? Gravity waves would help, for which we use "interferometer" detectors. The in'ferometers we got are good enough to detect a hole grabbing (much) more mass; but they are not rated for telling much about the holes beyond mass. We need better ones which means, bigger ones.

WORMHOLE 4/18/23: Ryan Bilotta. I'm not following the logic myself, but maybe you can.