The closest thing we have to an all-encompassing framework that explains all particles and forces is represented by the Standard Model of particle physics. But this model is flawed because it does not explain gravity.A theory of everything has to be able to reconcile quantum mechanics with the general theory of relativity.
This reconciliation appears to be possible with a theory called “Loop Quantum Gravity” — or LQG. What is it?
The theory of LQG attempts to show that this geometric fabric of space-time is not continuous as Einstein presumed, but is itself quantum, made up of discrete quanta.
This is akin to the clothes or sweater you might be wearing right now. Even though it looks smooth from far away, if you looked at it closely, you would see threads, nodes and loops woven together. These are the quanta or bits that your clothing is made of.
This is different than every other theory including string theory. Because even in string theory, space is the background or the canvas, on which strings vibrate.
In LQG this space-time background is itself quantized . So this means that distance has a minimum quantity about equivalent to the plank length or 10 to the -33 cm. Similarly, area has a minimum value of 10 to the -66 cm squared, and volume has a minimum value of 10 to the -99 cm cubed – below which it cannot go.
This is super tiny. LQG says that there are about 10 to the 99 quanta of volume in every cubic centimeter of space. This quantum of volume is so tiny that there are more such quanta in a cubic centimeter than there are cubic centimeters in the entire visible universe — (10 to the 85)
And Time itself has a minimum quantity as well which is 10 to the -43 seconds or close to plank time. And what do these space-time quanta look like? They are like loops.
The nodes that intersect is where the quanta volumes of space reside. It has a volume that is a multiple of the plank volume 10 to the -99 cubic centimeters. The loops in between the nodes represent 2 dimensional areas. And large quantities of these loops and nodes are called “spin networks.” — because their properties are related to particle qualities called spins.
And Time is defined by the moves that rearrange this spin network.
The spin network, when combined with these quantum movements of time, is called a spin foam.
Time does not flow like a river in the spin foam, it ticks like a digital clock. And each such quantum tick or movement of the spin network is 1 X 10 to the -43 second. Every location in the spin network where a quantum move takes place, time has ticked once.
When mass and energy are added to this spin foam, the shape of the volumes of the spin network is distorted. This distorts space and time, because any movement of these quanta also affects the time quanta. Time is essentially movement of these volume quanta.
And this distortion of space and time is what we perceive as gravity.
The exciting thing about LQG is that it appears to explain some of cosmology’s greatest questions, like, what came before the big bang. According to LQG the big bang could not have started with a singularity which would have been infinitesimally small, and of infinite density…because there is a limit to how small space can become, 10 to the -99 cubic centimeters.
This is the smallest volume of space according to LQG. This also implies a maximum energy density that this minimum volume of space could have had. And once that maximum energy density was reached, it would have repelled any additional energy added to it — like a sponge that gets saturated with water, will repel any additional water.
So LQG predicts that the universe did not start with a big bang, but with a big bounce. The universe was big at one time. It then contracted. It bounced and then exploded from this bounce.
So prior to what we call the big bang, the universe was in a contracting phase of a prior universe. And when it reached a minimum plank volume, all additional energy bounced off and created what looks to us like a big bang.
So LQG has a lot going for it. Is it the theory of everything? No, not quite yet, because it needs to be confirmed with observation. And, its mathematics needs to be further developed to make dark energy and dark matter emerge. But, in my view, Loop Quantum Gravity has brought us closer to a theory of everything than anything else over the past 100 years.
Citations:
http://universe-review.ca/R01-07-quantumfoam.htm
https://www.edge.org/conversation/lee_smolin-loop-quantum-gravity-lee-smolin
http://www.phys.lsu.edu/faculty/pullin/sciam.pdf
http://www.einstein-online.info/elementary/quantum/loops.html
http://igpg.gravity.psu.edu/people/Ashtekar/articles/rovelli03.pdf
https://commons.wikimedia.org/wiki/File:Loop_quantum_gravity.jpg
http://inspirehep.net/record/882216/plots
https://www.pbs.org/wgbh/nova/article/big-bounce/
