What is Loop Quantum Gravity?

Loop quantum gravity is a competitor to String theory, mostly because it treats space as if it comes in chucks. Quantum physics says that everything is quantified, which means that it has discrete values. This works for most of the things in physics but not gravity.

General relativity says that space-time is a dynamic entity, not a fixed framework. String theory, on the other hand, is based on a fixed framework. In other words, it's background dependent.

Loop quantum gravity has to be background independent. It takes the smooth fabric of space-time and looks at it as being composed of smaller fibers woven together. This is where the loop concept comes from. In Loop theory space is a field not a bunch of points, and the field lines don't have to be straight. In fact, they're woven together by looping around and through each other. Loop theory calls this a spin network of space bundles or atoms of space.

The problem with this idea is how to depict individual particles. Looping these space bundles into braids solved this problem. Each particle can be shown as a specific braid. As you might guess all of this is based on theoretical math.

The gravity prediction in Loop Quantum theory comes from the concept that one of these looped braids predicts a graviton, the theoretical particle that carries gravity, and this matches Einstein's relativity predictions about gravity.

So, what's wrong with this theory? Well, for one it's the fact that you can't take a quantized space and extract a smooth space-time out of it. The spin-network idea cannot incorporate time. In other words, this is a work in process.

Thanks for reading.