Describing the universe requires fewer dimensions than we might think. New calculations show that this may not just be a mathematical trick, but a fundamental feature of space itself.

At first glance, there is not the slightest doubt: to us, the universe looks three dimensional. But one of the most fruitful theories of theoretical physics in the last two decades is challenging this assumption. The "holographic principle" asserts that a mathematical description of the universe actually requires one fewer dimension than it seems. What we perceive as three dimensional may just be the image of two dimensional processes on a huge cosmic horizon.

Up until now, this principle has only been studied in exotic spaces with negative curvature. This is interesting from a theoretical point of view, but such spaces are quite different from the space in our own universe. Results obtained by scientists at TU Wien (Vienna) now suggest that the holographic principle even holds in a flat spacetime.

**The Holographic Principle**

Everybody knows holograms from credit cards or banknotes. They are two dimensional, but to us they appear three dimensional. Our universe could behave quite similarly: "In 1997, the physicist Juan Maldacena proposed the idea that there is a correspondence between gravitational theories in curved anti-de-sitter spaces on the one hand and quantum field theories in spaces with one fewer dimension on the other", says Daniel Grumiller (TU Wien).

Gravitational phenomena are described in a theory with three spatial dimensions, the behaviour of quantum particles is calculated in a theory with just two spatial dimensions - and the results of both calculations can be mapped onto each other. Such a correspondence is quite surprising. It is like finding out that equations from an astronomy textbook can also be used to repair a CD-player. But this method has proven to be very successful. More than ten thousand scientific papers about Maldacena's "AdS-CFT-correspondence" have been published to date.

**Correspondence Even in Flat Spaces**

For theoretical physics, this is extremely important, but it does not seem to have much to do with our own universe. Apparently, we do not live in such an anti-de-sitter-space. These spaces have quite peculiar properties. They are negatively curved, any object thrown away on a straight line will eventually return. "Our universe, in contrast, is quite flat - and on astronomic distances, it has positive curvature", says Daniel Grumiller.

However, Grumiller has suspected for quite some time that a correspondence principle could also hold true for our real universe. To test this hypothesis, gravitational theories have to be constructed, which do not require exotic anti-de-sitter spaces, but live in a flat space. For three years, he and his team at TU Wien (Vienna) have been working on that, in cooperation with the University of Edinburgh, Harvard, IISER Pune, the MIT and the University of Kyoto. Now Grumiller and colleagues from India and Japan have published an article in the journal *Physical Review Letters*, confirming the validity of the correspondence principle in a flat universe.

**Calculated Twice, Same Result**

"If quantum gravity in a flat space allows for a holographic description by a standard quantum theory, then there must by physical quantities, which can be calculated in both theories - and the results must agree", says Grumiller. Especially one key feature of quantum mechanics -quantum entanglement - has to appear in the gravitational theory.

When quantum particles are entangled, they cannot be described individually. They form a single quantum object, even if they are located far apart. There is a measure for the amount of entanglement in a quantum system, called "entropy of entanglement". Together with Arjun Bagchi, Rudranil Basu and Max Riegler, Daniel Grumiller managed to show that this entropy of entanglement takes the same value in flat quantum gravity and in a low dimension quantum field theory.

"This calculation affirms our assumption that the holographic principle can also be realized in flat spaces. It is evidence for the validity of this correspondence in our universe", says Max Riegler (TU Wien). "The fact that we can even talk about quantum information and entropy of entanglement in a theory of gravity is astounding in itself, and would hardly have been imaginable only a few years back. That we are now able to use this as a tool to test the validity of the holographic principle, and that this test works out, is quite remarkable", says Daniel Grumiller.

This however, does not yet prove that we are indeed living in a hologram - but apparently there is growing evidence for the validity of the correspondence principle in our own universe.

**Explore further:**
Who cares about the fourth dimension?

**More information:**
Entanglement Entropy in Galilean Conformal Field Theories and Flat Holography, *Phys. Rev. Lett*. 114, 111602 – Published 19 March 2015, dx.doi.org/10.1103/PhysRevLett.114.111602

## jalmy

## Tangent2

So they created a theory to make their hypothesis work in flat space-time and claimed this to be proof that the holographic principle works in flat spame-time. Now they have to prove that their gravity theory is correct for any of their efforts to pay off.

## Torbjorn_Larsson_OM

@jalmy: No, it is a toy model because the 3 and 4 D cases are too hard as of yet. (Though they hoped that at least one side of their proof could be extended to higher dimensions.)

The way I think of AdS-CFT is that it generalizes the usual situation for differential equations to spacetime physics. Usually you can have the local diff eq and know that it applies in a region, and so deduce the global solution if you know the boundary conditions. But it applies for one field (say, thermal "field"), not the whole enchilada.

And here you have it constrain a duality. Like when you can look at either currents or voltages in a circuit, because they are dual to each other. But a deep duality.

## arom

By the way, it is interesting to note that nowadays we still could not visualize what the curvature of space is; Maybe understanding its physical could help solving the problem ….

http://www.vacuum...=7〈=en

## OdinsAcolyte

That just opens up all kinds of wild ideas in my strange little mind.

Wow.

What a Universe. A leaf...on a branch and we know not where the branch is...or the tree or the other leaves. I know. Silly. But it is certainly fun. I do not lay claim to the leaf idea. It is an old one.

## deleterjoe

## docile

Apr 27, 2015## SuperThunderRocketJockey

Have mercy on this smeghead, oh great Ace of Aces! You pass all astronavs in my heart, Big Man!

## jabailo

## Returners

Finite area? Infinite length?

## Whydening Gyre

## Professor Plum

## PhysicsMatter

Interesting take on theory v.s. reality I found at: https://questforn...-quanta/

## Soinium

## antialias_physorg

"Quantum tunneling of gravity"?

Throwing a couple of buzzwords together ain't science.

## zorro6204

## snd

--Tangent2

They didn't claim this to be proof of anything for "their efforts to pay out" (whatever that means?). Scientists working on theoretical physics usually do it out of enjoyment, not because they expect a "payout". And simply presenting research does not correspond to "claiming proof".

## Returners

Our computers are 3-dimensional space, even though circuitry is "2d" (actually fractal above 2d), so you can store a 2d space and the code in the 3d , then convert the 2d space to 3d, but this is only true because the computer is a 3d space to begin with.

A 3d space can contain a 2d space and it's laws, but a 2d space can't contain a 3d space and it's laws. That's nonsense. Especially if it's a vector space, because the 3rd dimension is continuous and infinite, so it can't just be "sliced up" like frames in the 2nd dimension and converted with some code.

I call BS on this version of the Holographic Universe concept.

## Uncle Ira

@ Whydening-Skippy. How you are too Cher? I'm still good. Don't mind Returnering-Skippy's weird questions non. He'll be back around with the weird answer to go with them soon enough.

## Uncle Ira

## Whydening Gyre

Hey, Ira. Good to see ya.

Actually, Returners has provided decent input in other threads. Just that ALL the prior comments seemed rather "convoluted" , thereby prompting my comment.

That seems to be the nature of these kind of articles, tho. The authors seem to think they are instilling some kind of deep thought process. they're working too hard to tickle the "imagination

bone".

I mean - what is it a "holograph" OF? Itself?

Of course, I could change my opinion after I meditated on the subject...

## TechnoCreed

This comment of yours is certainly the most sensible comment here so far. Although AA's comment was not bad, he should have generalized... sadly it was only aimed at the preceding comment.

Personally, I think it applies just as much to Sponge_Bob_Smarty_OM's comment. This guy, who seemingly writes cogent things, never comes back to defend his point when he is challenged; notice that in the future. That is why I am allowing myself to be condescending to him (I think he is scared to look bad).

## TechnoCreed

We are here to share ideas on science; those who use tricks to impress should be denounced. Torbjorg would probably be good to write sci-fi scripts in comic books. But, although he uses alot of 'advanced knowledge' he pulls answers out of a hat just like an illusionist and that pisses me off.

## TechnoCreed

https://www.youtu...l3Hfh9tY

## Protoplasmix

Seems that way when you don't understand the math/physics for it, and fail to appreciate what the "C" stands for in CFT.

## docile

Apr 28, 2015## TechnoCreed

Is that so docile puppy dog?

## Whydening Gyre

All these acronyms... What does the "C" stand for? As long as your at it, how bout "F" and"T", too?

## richardwenzel987

## Protoplasmix

Conformal Field Theory. Also helpful to know about Conformal mapping, and considering the significance of the work showing the correspondence principle is valid in flat spacetime, it couldn't hurt to wrap your mind around the representation of an infinite amount of asymptotically flat spacetime in a 2d diagram of finite size, i.e., a Penrose diagram :)

## Whydening Gyre

Will do a little "delving" into it...

## TechnoCreed

4.2/5 for such an idiotic comment... AdS-CFT Is the concordance between anti-deSitter ( A mathematical model of space of n dimensions with a NEGATIVE cosmological constant ) and CFT ( A 2D Lorentzian scale invariant space ) it comes out from string theory and it synthesize our mathematical knowledge of black holes (from event horizon and beyond) ONLY. Do we need to 'make the inroad on Ads-CFT' as you said? NO, IT IS A GIVEN. It came about when physics theorists were looking for an answer to the 'information paradox'. Of course the Holy Grail of string theorist would be to link GR with QFT but this paper is NOT about GR at all.

Cont.

## TechnoCreed

Cont.

## TechnoCreed

NO. It is ONLY about a 2D flat space holographic model. HOLOGROPHY = 2D.

Cont.

## TechnoCreed

Cont.

## TechnoCreed

Cont.

## TechnoCreed

## bbbbwindows

Time began..."boot up"

Dark matter...no particles ever detected, null processing

Planck length/time...pixels

Malleable time..only in a virtual reality

Curved space...only in a 3d processing network

Max speed....C is the fastest transmission rate (pixels/second)

Double slit...set of reboots explains quantum waves and quantum collapse

Electron tunneling..quantum world is real, physical world is it's product

Quantum entanglement...code reallocation ignores distance

Anti-matter...reverse processing, anti-time only in a virtual reality

Randomness...client-server acts to which we are not privy

The fact that "physical reality' is mostly empty space and all matter is basically pure energy is the reason this hypothesis is most attractive.

As time goes on we will see that everything, even gravity is an electromagnetic entity. The underlying 2D electric field of limitless possibilities is the "real" universe.

## bbbbwindows

## EWH

Finding intersections, unions and other operations between the different objects is much easier using this scheme. The 2D euclidean CGA is equivalent to the Minkowski space of relativity, that is, with a (+++-) signature. The 3D CGA is equivalent to adding an additional dimension of the same sign as the spatial dimensions to represent "proper time" (++++-).

## EWH

Despite this explaination being nearly incomprehensible, CGA is not hard to use practically. The free program "GAViewer" and its tutorials are actually quite intuitive - any one interested in getting a shortcut to understanding a type of math used to describe all areas of physics including quantum mechanics and relativity should try it out.

## robandlezlye

--Returners

...what about a Fourier Transform? -- the 'code' is in your brain.

## gkam

There are some politicians and televangelists I can see completely through.

## Protoplasmix

## MRBlizzard

http://arxiv.org/abs/1410.4089

## viko_mx

## Whydening Gyre

No. The Universe IS the teddy bear.

WE are located in the belly...

## jsdarkdestruction

Interestingly enough that idea and the existence of a god have the same amount of evidence for them. None. Yet both are technically possible.

## viko_mx

However I have more confidence in the theory of Big Teddy than the theory of big bang.

## FainAvis

## TechnoCreed

## bbbbwindows

## bbbbwindows

## OdinsAcolyte

It would depend upon the point of reference...

## malapropism

Hey, don't denigrate Dr Who.

## Mayday

## Mike_Massen

Whereas big bang theory has support of physics/maths independent of any singular idea as a claim in a book but, based on foundation of Physics & Maths is attainable without ANY expectation of claims/faith in a book which are ALL untestable. ie ALL religions are based on claims which CANNOT ever be tested, the claimed deity is ALWAYS silent !

Why is that viko_mx ? why are ALL deities silent, is it somehow consistent with them ONLY being claim ?

Just like your 'big teddy' manufactured from the ideas of men, some sincere, some insecure & all ego based !