Simulations Back Up Theory That Universe Is a Hologram 433
ananyo writes "A team of physicists has provided some of the clearest evidence yet that our Universe could be just one big projection. In 1997, theoretical physicist Juan Maldacena proposed that an audacious model of the Universe in which gravity arises from infinitesimally thin, vibrating strings could be reinterpreted in terms of well-established physics. The mathematically intricate world of strings, which exist in nine dimensions of space plus one of time, would be merely a hologram: the real action would play out in a simpler, flatter cosmos where there is no gravity. Maldacena's idea thrilled physicists because it offered a way to put the popular but still unproven theory of strings on solid footing — and because it solved apparent inconsistencies between quantum physics and Einstein's theory of gravity. It provided physicists with a mathematical Rosetta stone, a 'duality', that allowed them to translate back and forth between the two languages, and solve problems in one model that seemed intractable in the other and vice versa. But although the validity of Maldacena's ideas has pretty much been taken for granted ever since, a rigorous proof has been elusive. In two papers posted on the arXiv repository, Yoshifumi Hyakutake of Ibaraki University in Japan and his colleagues now provide, if not an actual proof, at least compelling evidence that Maldacena's conjecture is true."
On Other Dimensions (Score:5, Informative)
A lot of people might find this a little hokey, especially coming from the journal Nature. The biggest thing to overcome is science fictions deception of other dimensions. A dimension is just another direction. We know about the six directions we can currently move in (3 dimensions) plus time (which we always move forward through at a constant rate; you can slow down how fast you move through time relative to everything else, but it's not noticeable unless you can afford a very very fast vehicle). Here's a great explanation of extra dimensions:
http://www.phdcomics.com/tv/#010
The other "Things explained" videos are also really good for understanding more complex physics concepts.
Re:No idea what that means (Score:4, Informative)
They're talking about the AdS/CFT corresondence. (Score:5, Informative)
What this means (Score:5, Informative)
Someone clever was working out the maximum entropy of a black hole, and found that (unexpectedly) it was proportional to the surface area of the event horizon, not its volume. After some more thought, other clever people found that the full state of every particle that falls into a black hole remains encoded as oscillations and deformations of its surface area.
This leads to the realization that the despite the fact that a black hole's event horizon is seemingly much simpler than a full-dimensional portion of a universe, it's theoretically possible that it's just as rich a simulation. Perhaps the "real" representation of the universe is actually just a rippling membrane, and the 3D view we see around us is just an alternate interpretation. This is where the word "hologram" comes in - it's only an analogy (because flattish holograms seem to encode 3D data).
Now, the word "real" is misleading - neither representation is 'more true', it's just that the fewer-dimensional representation might be a lot simpler. A comparable situation is the way the earth goes around the sun, or the sun goes around the earth. A stationary sun makes models of the planetary orbits a heck of a lot simpler, but a stationary earth makes it a lot easier to give directions to your party.
All of this was theoretical until this recent finding. The researches created two mathematical models of the universe - one of them ten-dimensional (similar to some forms of modern theories of our universe, though the article points out their model was simpler). The other model was a one-dimensional universe filled with ideal springs. These models were identical, in the same way as the 3D universe and the event horizon - they're alternate ways of calculating the same thing.
The researchers discovered that simulations in both of these universe models have the same output - in other words, they do seem to be different ways of describing the same universe.
Re:so does this mean.... (Score:5, Informative)
Eleven vs Ten dimensions is at the heart of the "hologram" thing. The universe as a hologram (nothing at all to do with a simulation) is a metaphor for how the math worked out in a very surprising way from two different directions.
In the study of black holes, a block hole represents the maximum entropy is is possible to have in a given volume. That there is a maximum possible information needed to completely describe a volume of space. Surprisingly that limit grows with surface area, not volume. By analogy, this is like saying you could take a holographic recording of a volume at its surface, and completely reconstruct the volume from that data. But the "holographic universe" is just an analogy for the very odd result that all the information describing a volume of space "fits" in 2 dimensions. It's best not to read too much into that because the limit here is really quite high, the maximum possible information is on the order of the surface area of a sphere measured in plank-lengths - vastly more bits than is likely relevant to anything.
Inspired by this work, but in completely unrelated theory, it was found that the 11-diminsional quantum model can be completely captured in a 10-diminsional model that includes gravity. The presence of gravity in the universe "flattens" the state needed to describe it by one dimension. This was to me a much more interesting result that the black hole result (because the numbers there were so high it wasn't really a limit at all). Qualitatively all this is not that surprising in glorious hindsight, because gravity does limit the possible ways to arrange matter in the universe: black holes mean any arrangement with too much too close together collapses the information needed to describe it into just a few numbers. How that translates into needing 1 less dimension in quantum mechanics is far beyond me.
Re:They're talking about the AdS/CFT corresondence (Score:5, Informative)
Basically, there are two major concepts.
First, is duality. This is where two models can represent the same system (they are duals of each other). The thing with duality is that in many cases, a problem that is impossible to solve in one model may be trivially done in another. You may know the duality between time-domain and frequency-domain systems - a convolution in one is a multiplication in the other (which is handy for some really difficult convolutions).
The other concept is a hologram. Take a traditional hologram you can buy as a souvenir - it's just a flat piece of transparent material (glass or plastic), yet look through it and you see a 3D image hovering in space - projected if you will, in 3D. And it is 3D, because you can look around the object. Yet the object is stored on a 2D medium. (FYI - the same concept applies to holographic sights - the dot is projected on the target in 3D space). Holograms are useful because they can cast higher dimensional spaces into lower dimensional spaces, yet retain the original resolution and details of the higher dimensional space (or how they get a 3D projection on a 2D surface).
Holographic theory is one where our 3D world is actually on a 2D surface. Like a hologram.
Now, what the results are is that they found a set of dual systems that represent reality - between string theory and quantum mechanics using holographic theory. In other words, they could do a calculation using string theory and have the results line up with quantum mechanics (and holograms). By proving this, a difficult problem in quantum mechanics can be translated to string theory and be easily solved there, then the results translated back, which gives the same answer as if you did it the hard way.
Re:Does this Mean that String Theory... (Score:5, Informative)
My layman's understanding is that string theory is what you get when physicists try to compromise.
Problem is, we have two models of the universe. There's the model that describes gravity, and the model that describes everything else. Since these are mathematical models, it should be possible to have a single unified model that can describe both other models accurately under appropriate conditions, but the two models are different enough to make that difficult. Whatever that ultimate unified model is, it's probably something complex and hard to really understand fully.
That's string theory. It's a physical description of the math that makes the models make sense together. We don't really know how to prove it's right or wrong, because we can't observe it directly. Since its inception, the math has required a few logical leaps and assumptions that are not quite rigorously proven true... yet. Depending on which of those assumptions are accepted at any particular time, there are indeed several variations and possible implications that can be inferred. This doesn't necessarily mean the idea is invalid, but just that more mathematical work (such as in TFA) is needed before we can really say we know what's going on.
The terms "simulation" and "projection" are also used in an unusual sense here, as well. They refer to our observable universe being only the result of a system we can't observe directly, much like a projection on a screen or a simulation inside a computer. Ultimately, understanding the mechanism that's actually running the "simulation" could open the door to new phenomena in our universe that we haven't observed before.
Re:No idea what that means (Score:5, Informative)
Re:No idea what that means (Score:5, Informative)
Those two things are not mutually exclusive.
The first Matrix was damn good, the second one was cheesy, and the third one was just a big steaming pile. IMO.
Re:No idea what that means (Score:5, Informative)
They are brothers no more.