When soup is heated, it starts to boil. When time and space are heated, an expanding universe can emerge, without requiring anything like a "Big Bang". This phase transition between a boring empty space and an expanding universe containing mass has now been mathematically described by a research team at the Vienna University of Technology, together with colleagues from Harvard, the MIT and Edinburgh. The idea behind this result is a remarkable connection between quantum field theory and Einstein's theory of relativity.

**A Cookbook for Spacetime**

Everybody knows of the transitions between liquid, solid and gaseous phases. But also time and space can undergo a phase transition, as the physicists Steven Hawking and Don Page pointed out in 1983. They calculated that empty space can turn into a black hole at a specific temperature.

Can a similar process create a whole expanding universe such as ours? Daniel Grumiller from the Vienna University of Technology looked into this, together with colleagues from the USA and Great Britain. Their calculations show that there is indeed a critical temperature at which an empty, flat spacetime turns into an expanding universe with mass. "The empty spacetime starts to boil, little bubbles form, one of which expands and eventually takes up all of spacetime", explains Grumiller.

For this to be possible, the universe has to rotate – so the recipe for creating the universe is "apply heat and stir". However, the required rotation can be arbitrarily small. In a first step, a spacetime with only two spatial dimensions was considered. "But there is no reason why the same should not be true for a universe with three spatial dimensions", says Grumiller.

**Looking for the Structure of the Universe**

Our own universe does not seem to have come into existence this way. The phase-transition model is not meant to replace the theory of the Big Bang. "Today, cosmologists know a lot about the early universe – we are not challenging their findings. But we are interested in the question, which phase transitions are possible for time and space and how the mathematical structure of spacetime can be described" says Grumiller.

The new theory is the logical next step after the so called "AdS-CFT correspondence", a conjecture put forward in 1997, which has strongly influenced fundamental physics research ever since. It describes a peculiar connection between theories of gravity and quantum field theories – two areas which, at first glance, do not have much in common. In certain limiting cases, according to AdS-CFT correspondence, statements from quantum field theories can be translated into statements concerning gravitational theories and vice versa. This is almost as surprising as the idea of making statements about a stone falling to the ground by actually calculating the temperature of a hot gas. Two completely different areas are being connected – but it works.

In this kind of correspondence, the quantum field theory is always described in one fewer dimension than the gravitational theory. This is called "holographic principle". Similar to a two dimensional hologram which can depict a three dimensional object, a quantum field theory with two spatial dimensions can describe a physical situation in three spatial dimensions.

**A Correspondence Principle for Flat Spacetimes**

To do this, the gravitational calculations usually have to be done in an exotic kind of geometry – in so-called "Anti-de-Sitter-spaces", which are quite different from the flat geometry we are used to. However, it has been suspected for a while, that there may be a similar version of the "holographic principle" for flat spacetimes. But for a long time there haven't been any models showing this.

Last year, Daniel Grumiller and colleagues established such a model (in two spatial dimensions, for simplicity). This led to the current question; phase transitions in quantum field theories are well known. But for symmetry reasons this would mean that gravitational theories should exhibit phase transitions too.

"At first, this was a mystery for us", says Daniel Grumiller. "This would mean a phase transition between an empty spacetime and an expanding universe. To us, this sounded extremely implausible." But the calculations showed exactly that. "We are only beginning to understand these remarkable correspondence relations", says Daniel Grumiller. Which new ideas about our own universe can be derived from this, is hard to say – only spacetime will tell.

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

**More information:**
"Cosmic evolution from phase transition of 3-dimensional flat space." Arjun Bagchi, Stephane Detournay, Daniel Grumiller, Joan Simon. *Phys. Rev. Lett.* 111, 181301 (2013) arXiv:1305.2919. arxiv.org/abs/arXiv:1305.2919

See also: A. Bagchi, S. Detournay and D. Grumiller, Phys. Rev. Lett. 109, 151301 (2012) arxiv.org/abs/arXiv:1208.1658

## verkle

Some things don't have to be complicated.

## Zephir_fan

Dec 10, 2013## Tacso

## megmaltese

Waves keep bouncing thanks to the internal pressure of the Universe.

Our perception of time is the slow loss of internal pressure in the Universe.

## Egleton

I guess they mean the activity of the virtual particles.But that still does not get me very far because the total energy is conserved. (Zero)

Or is it?

I can see one sacred cow headed for the slaughterhouse.

Well done the reporter- you made a stout effort at explaining an esoteric subject.

## Egleton

## DonGateley

## animah

The average temperature of space is 2.7 Kelvin, look up CMBR on Wikipedia.

## snoosebaum

## orti

## loneislander

Also, for those who utterly pan this kind of work, I promise you that the moment you lower the internal rhetoric of your conclusions (you can still blab out loud, but start thinking for yourself...hesaidhopingtonotoffendbutneedingtobeclear) and put some of that energy to understanding what ~just the main-stream~ physicists are saying these days, it will enrichen your life in beautiful ways. And, you'll not longer be afraid of the dark -- that goes early.

## 11791

Dec 11, 2013## nowhere

From the article:

## JIMBO

## taka

That is light inside space. Not empty space.

## 11791

Dec 15, 2013## antialias_physorg

There's several ways to define a temperature (also note that an absolute vacuum is only a theoretical construct)

The temperature here is what a black body would settle at if left in outer space (i.e. what temperature it would radiate if it, on average, radiated as much energy as it would receive.) That temperature would be the current temperature of the CMB

The temperature of the CMB does not originate from the current 'vacuum' or its virtual particles (if it were then the universe would be heating up all the time as you'd be pumping net energy into it). That temperature is the afterglow of the big bang spread through an expanding spacetime (i.e. red shifted).

## antialias_physorg

That's the question then, isn't it?. It can rotate if the universe is embedded in a larger structure (branes), as passing other universes can have an effect there and impart net (local) spin to a region.

However this directly leads to the question how all the other branes got to be there. if by the same mechanism then we need to think about how rotation is not conserved in this larger system...

... because if it is then we'd be back to square one: where does the rotation come from to craete the first brane?.

Unless we can have a phase transition there as well where two parts split off - each with a net rotation but the sum of which is always zero.

## rsklyar

Their plagiaristic compilation titled Macroporous nanowire nanoelectronic scaffolds for synthetic tissues (DOI: 10.1038/NMAT3404) and Outside Looking In: Nanotube Transistor Intracellular Sensors (dx.doi.org/10.1021/nl301623p) was funded by NIH Director's Pioneer Award (1DP1OD003900) and a McKnight Foundation Technol Innovations in Neurosc Award, also a Biotechnology Research Endowment from the Dept. of Anesthesiology at Children's Hospital Boston and NIH grants GM073626, DE01-3023/6516