Cosmologists a step closer to understanding quantum gravity

January 23, 2017
Dr Vincent Vennin. Credit: University of Portsmouth

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 and cosmological structures that arise from .

"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

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Sonhouse
not rated yet Jan 30, 2017
That's the big story? where is the meat? What exactly are they saying here? They now understand quantum fluctuations now? What?
Seeker2
not rated yet Jan 30, 2017
"in the very early Universe where the expansion of space is driven by gravity"

I can see the expansion driven by cooling but gravity? I can believe gravity driven by expansion.
Da Schneib
not rated yet Jan 30, 2017
Excellent, the more we can constrain theories quantum gravity the closer we come to a good theory.

"in the very early Universe where the expansion of space is driven by gravity"

I can see the expansion driven by cooling but gravity? I can believe gravity driven by expansion.
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
not rated yet Jan 30, 2017
How do you expect to learn if you don't learn?
No expectations about learning whatsoever. Already know too much. Now let's figure out exactly what it means. OK?
Seeker2
not rated yet Jan 31, 2017
The inflaton-- which is high cosmological constant-- is gravity.

It's the cosmological constant term in the Einstein Field Equations, the one containing Λ.
I thought Λ=1. Did I get that wrong? Doesn't seem high. Anyway Λ is set to 1 in order to make the universe flat (actually symmetrical). Gravity has more to do with variations in this flatness. Anyway if there were no variations you would still need to make the universe flat in order to preserve its symmetry and assure conservation of energy. Inflation refers to spacetime, not matter. I would think inflation is still predicted by the field equations even if you set G=0 so there was no gravity. I think the value of G depends on spacetime density and varies - increases, to be exact, when you begin to leave galaxies and experience pure dark energy undiluted by matter. Just thinking.
Seeker2
not rated yet Jan 31, 2017
cont
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
not rated yet Jan 31, 2017
where is the meat?

In the arxiv link at the bottom of the article.
Seeker2
not rated yet Feb 01, 2017
"Quantum fluctuations during inflation are thought to be the origin of all structure in the Universe." According to the Science Channel there seems to be a special class of extremely large black holes. Suggesting these come from bubbles in the dark energy mostly before baryogenesis. They are empty of matter and dark energy and so support the full pressure of the dark energy at the time they were formed. Much greater than it would be today. Inside they would be pure zero point vacuum energy with no or very little matter or chemistry going on.
Seeker2
not rated yet Feb 01, 2017
cont
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
not rated yet Feb 01, 2017
Inside they would be pure zero point vacuum energy with no or very little matter or chemistry going on.
Lets make that pure vacuum with no zero point energy.

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