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Comment by TwoFactor | Hacker News Reader

It's interesting that to a layman this seems like almost the exact opposite of what string theory proposes dimensionally. Holographic universe theory is stating there are effectively less dimensions, while string theory shows there could be significantly more.

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This is the first time I've read anything about Holographic universe theory and I really don't understand anything about it yet. But, does this mean we were the ones living in a 2-dimensional "flatland" the whole time?

So the earth is flat - told you so :-)

I think it means the max amount of information in the observable universe is bounded by the amount of information that could fit on the 2D surface of a spherical event horizon of a black hole of the same size.

That was the origin of the theory, but from what I understand it's been developed beyond that point.

Is there a why? I got curious.

If you take all the mass and energy of the observable universe and throw it into a black hole, its event horizon would expand and encode all the information you put into it. Information can't be destroyed so that's why it is encoded in the event horizon. The diameter of the event horizon would also be much smaller than the diameter of the observable universe, because there's a lot of empty space in the universe, and we don't see everything collapsing inwards due to too much mass. So if you had an event horizon with the diameter of the observable universe, it would encode a lot more information than what's in our observable universe. Note I'm just a layman here and I could be interpreting it incorrectly.

One way to think about is what goes on in a video game - you see characters on screen, but in the computer you actually have some data-structures describing them.

So a Player data-structure maps to a Player on screen, in the same way that some configuration of qubits on the surface of the universe corresponds to some thing from the "bulk" that we see.

Does that mean there are more low-level 2-D laws of physics that give rise to the observable laws of physics? If yes, would we be able to access them?

I'm not sure you're a 'layman' if you understand string theory.

But a layman might conflate two things that they do not understand.

Knowing that string theory requires 11 dimensions doesn't mean one understands it. And even string theorists aren't sure which version of the theory represents everyday reality, and the number of candidates is quite beyond imagining. Finally, to date there aren't any reliable empirical tests to place string theory on a firm scientific foundation.

In the long term string theory may contribute more to mathematics than to physics.

I thought that in order for a holographic universe to exist, then the universe needs to have a non-flat e.g. slightly-curved spacetime; in order to "close the boundary", so to speak.

But my understanding is that so far all our evidence shows that spacetime is flat?

i.e. we spacetime needs to be an Anti-de Sitter space. https://en.wikipedia.org/wiki/Anti-de_Sitter_space But I didn't think many actually think we live in an ADS universe?

Also relevant to string theory, https://en.wikipedia.org/wiki/AdS/CFT_correspondence

Couldn't the amount of curve within our observable universe be less than the margin of error in our methods of observation?

Of course.. big hologram though!

That's an interesting observation! Perhaps next we are going to learn that everything is - as the Buddhists keep teaching - indeed "one". I am saying this only half-jokingly. One thing you can derive from the statement that everything is one is that everything we can think of also includes what we would call the opposite of what we're thinking of . And thus it would be correct to say that the universe has many dimensions but it is also true that it has very few dimensions. This surely sounds somewhat anti-intellectual but it'll be fascinating to see if science will ever be able to come up with something more meaningful, i.e. something which is less contradicting.

You mean spatial dimensions. But space and time appear to be derivative notions anyway.

What really matters is the space of independent parameters (or, if truly independent parameters do not exist, then the truly fundamental ones). That would be really nice to figure out one day.

The holographic universe theory is derived from string theory. Specifically ADS/CFT correspondence:

https://en.wikipedia.org/wiki/AdS/CFT_correspondence

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