

Ask HN: I am trying to understand Holographic universe, can anyone help?  - pavs

I have read Wikipedia/blog, watched lecture video explaining what Holographic principle is and every time I think I have an idea what they are talking about; only to find out that I have absolutely no idea what the hell they are talking about.<p>For instance, what does this even mean?<p><i>"In a larger and more speculative sense, the theory suggests that the entire universe can be seen as a two-dimensional information structure "painted" on the cosmological horizon, such that the three dimensions we observe are only an effective description at macroscopic scales and at low energies."</i><p>My non-science friend told me that his understanding is that our universe is just an event horizon of a black hole. We are all just information, nothing more, nothing less.<p>Mind. Fucked.<p>Just a gentle reminder before anyone starts yapping:<p>From http://ycombinator.com/newsguidelines.html<p>On-Topic: Anything that good hackers would find interesting. That includes more than hacking and startups. If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity.
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SandB0x
How much mathematics and physics do you know? If you want to _understand_ an
advanced area of theoretical physics, a few paragraphs on a discussion site
isn't really going to help. You need a substantial amount of background
knowledge.

If I wanted to understand this topic, I would be re-learning statistical
physics, quantum mechanics and cosmology, and probably a bunch of other
courses. It would probably take a good year.

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mian2zi3
> For instance, what does this even mean?

I'm not a physicist. Here is my lay understanding of the holographic
principle. Let's think of a physical theory (that attempts to describe the
universe) as space of states together with a "time evolution operator" that
says how states move around in the state space as time goes forward.

Now, one such theory might be, say, the location and velocity of matter in
3-dimensional space as the state space, together with the laws of Newtonian
mechanics. Another theory is given by particles on a 2-dimensional film
together with the laws of fluid mechanics.

Now, how are we to decided when two theories A and B are the same? Basically,
we need to identify the states of A with the states of B, such that the
identification respects the time evolution operator. (Mathematically, this is
an isomorphism of theories.) The holographic principle says basically there
are isomorphic 2- and 3-dimensional physical theories.

