It's a set of equations that explains all particles and forces in the universe allowing
us to understand just about every phenomenon past and present. I'm talking of course about
the mythical theory of everything. Mythical because it has eluded scientists for decades.
But there is a theory on the horizon that appears to be the missing link that explains
not only the fabric of time and space, but also one of the biggest mysteries of existence.
And that is what came before the big bang.
What is it and what does it have to say about existence, that's coming up right now.
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 I showed in a previous
video that this model is flawed because it does not explain gravity. Gravity can currently
only be modeled using Einstein's general theory of relativity. 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. The core mathematics of LQG are super complicated, but I'm giong to simplify
it as much as I can. According to Einstein, gravity is not a force, it is a geometric
property of space time itself.
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. Space
time is similarly not smooth at the smallest scale according to LQG.
Now 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 like your clothing or your television.
So this means that distance has a minimum quantity about equivalent to the plank length
or 10 to the -33 cm. Volume has a minimum value of ten to the negative ninetynice centimeters
cubed. below which it can not go.
Now This is super tiny. To give you an idea of the smallness of the scales we are talking
about, 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.
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? Well, you can't really visualize
it but conceptually, the clue is in the name loop quantum. Space time is actually made
up of finite 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. The loops in between the nodes
represent two dimensional areas. And large quantities of these loops and nodes are called
spin networks. Space is defined by the geometry of the spin network. 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 seconds. Every
location in the spin network where a quantum move takes place, time has ticked once.
How to particles traverse this quantized space?
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 spin network is unimaginably large. If we could draw a detailed picture of the spin
network of our universe, it would consist of approximately ten to the one eighty four
nodes.
The exciting thing about QLG 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 something called
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 just about anything else over the past
100 years.