What does quantum gravity look like at or beyond the Planck scale?

Question

I am reading an article called The fundamental nature of space and time by Gerard 't Hooft. On page 3 he writes the following:

Physically, however, the perturbative approach fails. The difficulty is not the fact that the finite parts of the counter terms can be freely chosen. The difficulty is a combination of two features: (i) perturbation expansion does not converge, and (ii) the expansion parameter becomes large if center-of-mass energies reach beyond the Planck value. The latter situation is very reminiscent of the old weak interaction theory where a quartic interaction was assumed among the fermionic fields. This Fermi theory was also “non-renormalizable”.

In the Fermi theory, this problem was solved: the theory was replaced by a Yang-Mills theory with Brout-Englert-Higgs mechanism. This was not just ‘a way to deal with the infinities’, it was actually an answer to an absolutely crucial question: what happens at small distance scales?. At small distance scales, we do not have quartic interactions among fermionic fields, we have a local gauge theory instead. This is actually also the superior way to phrase the problem of quantum gravity: What happens at, or beyond, the Planck scale?

My Question

Can someone explain in relatively laymens terms what we think happens with quantum gravity at or beyond the Planck scale?

I am not a layman persay but I am not at 't Hooft's level either. Something hitting an audience in between would be great.

Answer 1

It is the refusal to accept the possibility that the speed of gravity exceeds the speed of light. Planck constant was derived from the speed of light. It is the smallest amount of energy exchange between electrons and charges.

In the case of gravity, the exchange of energy is not to move electrons to higher orbitals but to move mass or the entire nucleus if not the quarks themselves to a new position in space.

Light speed energy exchange fir gravity wont suffice. Such speed is too slow and would cause an abberation. A faster speed and much smaller discrete energy constant is a logical necessity for gravity to work. We also have to consider that the energy exchange is not a constant velocity just like for light but a constant accelaration. Afterall, gravity is an accelarating contraction of space.