Is our Universe a hologram?

I can't give a good answer but I did find the documentary and out of curiosity, watched some of it, skipped forward and found the hologram section you're talking about, it's at the end about 1:18:40 in. (I'm not going to post a link to the video cause I'm not sure it's correctly copyrighted by those who are showing it)

The video itself isn't bad, but it's basically a science channel level program, which is written to appeal to viewers and explanations are often over-simplified. This video in particular seemed to try to cover so much ground that it explains very little. But on the positive side, they have Brian Greene and Leonard Susskind discussing the hologram idea and those guys are both real physicists who've talked about this before. I don't think it's a main stream idea, just an idea that a few people like.

Here's a magazine article on the subject and an excerpt from Brian Greene's book.

and Here's Leonard Susskind giving a talk on the subject at Stanford, not at a class, more of a lecture cause he mentions that not everyone in attendance might be a physicist, but I've since watched his lecture and he makes a few of these points more clear, at least to me.

And Here's a question and answer on a similar subject. There's also no shortage of articles that can be found on the Holographic principal or the "universe is a hologram", though I think the first is a better set of words to search and the 2nd might lead you to some sub-par articles.

Philip Gibbs - inactive's answer (also in the link above) on what the Holographic Principal implies is better than anything I could say about it, so I'd start there.

As a rule, it's a good idea to post links and if the video is 2 hours long, the specific time as well. YouTube links can also be removed so they're not ideal.

Edit to answer questions.

Had to think about this one a bit, and sometimes trying to answer "why" is opening a can of worms, but . . . here I go.

Why do they think that it is our Universe that is the Holograph?

I'm not a fan of the theory myself and I'd guess that not all physicists agree with it either. One big problem with the theory is that it can't be proven, which really makes it more of a guess based off a mathematical model and not a good theory. One definition of a good theory is one that can be tested. If it can't be tested true or false, it's really more of an idea.

As for why Brian Greene likes the theory, you might need to ask him or search his interviews, but maybe he likes it so can sell books - I don't know. Maybe he likes the idea of the Universe being a Hologram. He's obviously a pretty smart guy. You don't get a PHD in physics and get recognition and invited to ted talks and all that by being dumb, but smart guys are wrong all the time when it comes to new theories. There's no evidence that this theory is true.

Now, I should point out that the Holographic principal as it applies to black holes and the information paradox, all that stuff is good and valid theoretical physics rooted in ideas we understand such as entropy and time dilation and red-shift. The Holographic principal seems a very reasonably deduced feature of black holes that also, cleverly answers the information paradox, but whether it can be extrapolated to apply to the entire universe is a whole different ball game and to me, it's basically a guess. Not much more.

Why couldn't our Universe be reality and a Holograph exists of it
somewhere else?

Well, I could say "you're right", but the truth is, you're just flipping around the question. The more relevant questions are whether the theory is true at all, and as I said above (and Susskind said in his video), whether it can be tested. Susskind's video is really quite good though he starts slowly, but if you're really interested in this it's worth watching.

What makes them think that this is the Holograph instead of the
reality?

One thing about Physics to keep in mind. It's often surprised us. Physics has given us answers that physicists didn't expect many many times, perhaps more than any other field of study. Physics is probably more likely to yank the rug of reality out from under us than any other field and with that in mind, it's not a subject to study if you want to feel secure in what you believe and know. In the days after Newton, Physicists were very confident in what they knew and felt that nothing very new was out there, though the constant speed of light was a puzzle they'd not expected.

Then Einstein came along and pretty much threw everybody's understanding out the window when he started to figure things out and not long after that, the quantum physicists came up with ideas that made Einstein's head spin and to which he directly disagreed. After that the big bang was unexpected, background radiation was unexpected. Dark matter was unexpected (except for maybe Fritz Zwicky) and dark energy was quite the surprise when it was discovered.

Being regularly surprised, of-course, doesn't make the hologram theory any more true or false, cause nobody knows, but good physicists these days try to keep an open mind to mathematically valid new ideas.

• my 2 cents as a hobbyist. Hope that wasn't too long and off the point, and please, take what I say with a grain of salt. I'm not an expert.