Two fundamental concepts in physics, both of which explain the nature of the Universe in many ways, have been difficult to reconcile with each other. European researchers developed a mathematical approach to do so that has the potential to explain what came before the Big Bang.

According to Einstein’s (classical) theory of general relativity, space is a continuum. Regions of space can be subdivided into smaller and smaller volumes without end.

The fundamental idea of quantum mechanics is that physical quantities exist in discrete packets (quanta) rather than in a continuum. Further, these quanta and the physical phenomena related to them exist on an extremely small scale (Planck scale).

So far, the theories of quantum mechanics have failed to ‘quantise’ gravity. Loop quantum gravity (LQG) is an attempt to do so. It represents space as a net of quantised intersecting loops of excited gravitational fields called spin networks. This network viewed over time is called spin foam.

Not only does LQG provide a precise mathematical picture of space and time, it enables mathematical solutions to long-standing problems related to black holes and the Big Bang. Amazingly, LQG predicts that the Big Bang was actually a ‘Big Bounce’, not a singularity but a continuum, where the collapse of a previous universe spawned the creation of ours.

European researchers initiated the ‘Effective field theory for loop quantum gravity’ (EFTFORLQG) project to further develop this exciting candidate theory reconciling classical and quantum descriptions of the Universe.

Scientists focused on the background-independent structure of LQG which requires that the mathematics defining the system of spacetime be independent of any coordinate system or reference frame (background).

They applied both semi-classical approximations (Wentzel-Kramers-Brillouin approximations, WKBs) and effective field theory (sort of approximate gravitational field theory) techniques to analyze a classical geometry of space, study the dynamics of semi-classical states of spin foam and apply the mathematical formulations to astrophysical phenomena such as black holes.

Results produced by the EFTFORLQG project team exceeded expectations. Scientists truly contributed to establishing LQG as a major contender for describing the quantum picture of space and time compatible with general relativity with exciting implications for unravelling some of the major mysteries of the Universe.

**Explore further:**
Physicists propose test for loop quantum gravity

## Bewia

## vacuum-mechanics

By the way, it is interesting to note that nowadays we still do not understand the basic foundations of both theories, such as why and how electron could act as both wave and particle (in quantum mechanics), or how and why space-time could be curved (in general relativity). By consider these philosophical ideas (such as one below) parallel to mathematical approach may give the way to reconcile both theories.

http://www.vacuum...mid=4=en

## Parsec

Because the theory predicts on extremely fine space scales, gravity is repulsive. Think of a foam that is completely filled with matter. You cannot add more. So when space-time gets extremely compressed, the mathematics predicts that space-time would "bounce".

## Parsec

In terms of space-time curvature, that is both easy to visualize and easy to understand.

Meanwhile recent discoveries in how to combine the two theories (Quantum mechanics and general relativity) are showing that the so called intractable infinities caused by combining these theories are almost certainly a product of the math used, rather than being real.

## Deesky

The obvious (perhaps too obvious) question is, how is the universe going to achieve such states of compression (which sounds like the Big Crunch idea) when we see the opposite happening as Dark Energy is accelerating the expansion of space-time, leading perhaps to the Big Rip?

Also, how many times could this cycle repeat before the inevitable loss of energy after each iteration would halt the cycle?

I think LQG has a long way to go, even compared with string theory. For example, it cannot even reproduce the predictions made by the current standard model.

## Parsec

It almost certainly can't. And I agree with you about LQG.

## JIMBO

A quik scan of the arxiv under gr-qc reveals no such paper.

Suspect this is just filler. When will they stop doing this & allow their readers to follow up on the original research ??!!

## antialias_physorg

I'm not sure there would be an inevitable loss of energy. Why would energy conservation be violated?

The bounce is an interesting consequence of LQG, but it doesn't really solve the origin problem

(I'm very careful not to write 'first cause', here)

We really don't know if the universe has already gone through all the phase changes it is going to go through. There's nothing that says that ALL phase changes have to happen early on or at higher temperatures than the current CMB. There may be a phase change in the future that leads to eventual collapse.

## sanita

## JIMBO

## baudrunner

Crazy? How less so then LQG, or DE?

## antialias_physorg

Because DE and LQC have solid math behind them that matches with other observed phenomena. Your tripe does not. If you were to go through any math that would fit with your 'theory' then you'd see that it doesn't fit anything we currently observe.

Understand this: Unproven theory are not the same as made up theories. Serious unproven theories (like string theory, Brane theory, super symmetry, or LQG) have the math that fits with past observations. It is only when you make predictions from that math that you can find discrepancies betwen them. And it is exactly at that point where future experiments will separate the good from the bad.

Made up theories that some interent-poster pulled out of his rear are useless, as they neither fit past observation nor make testable predictions. They're just fairy tales.

## ewj

## ewj

## ewj

## antialias_physorg

I think you have a VASTLY oversimplified idea of what science is and how it works and how little scientists take pointers from fictional literature.

And yes: some people were 'made fun of' for their quirky theories which tured out to be true. But to turn that around and say that every quirky theory therefore has to be true is crazy in the extreme. For every theory that pans out there are literaly thousands that don't - and as long as a quirky theory makes no predictions different from the current best model it's useless.

Science is what works. Note the "what works" part. If your science doesn't work and holds no predictive value it's wankery.

## antialias_physorg

We have those. They're called scientists. Being a scientist is as much about being innovative as it is about being able to learn what has alread ben discovered and understand complex ideas.

But neither works without the other - and all these "arm-chair-theorists" ever do is jot down a brainfart and then think they have discovered the grand unified theory.

But when you look through history: those that REALLY came up with the groundbreaking changes were never arm-chair theorists. It was solid scientists, with a deep understanding of what was already learned, working hard and dilligently and putting it together in novel ways (E.g. relativity can be deduced from very simple principles with just two additional assumption: c is constant, and the principle of equivalence)

## neiorah

## Claudius

While I agree with you about arm-chair theorists, it seems to me that those "solid scientists" who come up with truly groundbreaking changes are often ridiculed for their work until later vindicated. From what I have observed, most "solid scientists" seem to lack imagination, work exclusively within the box, and the few that have imagination have an uphill fight to get their work accepted.

## casualjoe

The great discoveries in science have shown us that we are all studying the same thing.

## antialias_physorg

Then you should probably try to meet one in real life.

EVERY article here on physorg has (at least) one innovative idea behind it that, to date, non one on the planet has had. If you don't call that innovative, then what do you? And EVERY article here is the work of a group of 'solid scientists'.

If you work exclusively within the box then you're an engineer. (Not knocking engineers. They do also a LOT more for humanity than the armchair theorists)

Do revolutionary findings get questioned by other scientists? Yes.

Do they sometimes get fought? Yes.

Do they ever get ridiculed by other scientists? No.

Science is hard. Not every scientists understands what other scientists do immediately. I can't even read some papers in my own specialty straight away because sometimes I'm unfamiliar with the particular subset of math used. It's not surprising that revolutionary ideas take time to take root.

## CNA

## exequus