Cosmologists trying to understand how to unite the two pillars of modern science – quantum physics and gravity – have found a new way to make robust predictions about the effect of quantum fluctuations on primordial density waves, ripples in the fabric of space and time.

Researchers from the University of Portsmouth have revealed quantum imprints left on cosmological structures in the very early Universe and shed light on what we may expect from a full quantum theory of gravity.

Dr Vincent Vennin, from the Institute of Cosmology and Gravitation said: "We haven't solved quantum gravity but we've learnt a little more about how it would work.

"Physicists do not yet know how to combine theories of gravity and the quantum world. Yet both play a crucial role in the very early Universe where the expansion of space is driven by gravity and cosmological structures that arise from quantum fluctuations.

"Quantum fluctuations during inflation are thought to be the origin of all structure in the Universe. Structures we see today such as galaxies, stars, planets and people can be traced back to these primordial fluctuations."

The paper is co-authored by Professor David Wands and Dr Hooshyar Assadullahi. It was published today in the *Physical Review Letters*.

**Explore further:**
Violations of energy conservation in the early universe may explain dark energy

**More information:**
Critical Number of Fields in Stochastic Inflation. 2017 Jan. 20, *Physical Review Letters* [journals.aps.org/prl/abstract/ … ysRevLett.118.031301 , arxiv.org/abs/1604.06017

## Sonhouse

## Seeker2

I can see the expansion driven by cooling but gravity? I can believe gravity driven by expansion.

## Da Schneib

The inflaton-- which is high cosmological constant-- is gravity.

It's the cosmological constant term in the Einstein Field Equations, the one containing Λ.

You have been told this multiple times before. How do you expect to learn if you don't learn?

Just askin'.

## Seeker2

## Seeker2

## Seeker2

Actually I understand universes are created all the time but if they don't have the correct energy input they violate conservation and don't persist long enough for time to kick in along with the associated conservation laws.

## antialias_physorg

In the arxiv link at the bottom of the article.

## Seeker2

## Seeker2

As opposed to more normal sized black holes formed from matter which displaces the dark energy. So there could be some chemistry going on since the force of gravity near the center of these black holes is nearly zero. The stories about singularities at these centers may fit the Einstein field equations but I don't think they would be very helpful with any theory of quantum gravity.

## Seeker2