# How can cosmology help create or shape a theory of quantum gravity?

What quantum gravity experiments do we currently have?

Both black hole experiments and cosmological observations fit the bill.

It is important to distinguish doing quantum field theory in curved background and quantum gravity?

Probably, the only probe penetrating the wall of microwave background radiation are gravitational waves.

Another idea are studies of event horizons (EHT) of super-massive black holes. Are there firewalls?

Precession of star’s orbits seem to deviate from classical GR predictions.

What happens at the horizon? GR has nothing to say. The paradoxes arise when taking quantum effects into account.

Some comments about probing low vs high curvature regimes. To measure quantum gravity, one needs small black holes since they have higher curvatures.

It would be interesting to work out experimental predictions of the firewall proposal. Can we actually observe firewalls?

Is there any hope of measuring quantum effects?

Probably not. Better hope for measuring deviations from GR at the classical level.

What does it mean to view the whole universe as a black hole?

It relates to the idea of the “Big Bounce”, which states that our universe arose from a previous gravitational collapse, and thus can be viewed as a white hole.

How do you reconcile the observations that the Big Bang is an event, whereas a black hole singularity is a one-dimensional line of events.

Cosmology may be the way to probe experimentally the theory of quantum gravity.

Understanding for example how the universe emerged from the singularity or the big bang, it may inspire ideas for quantum gravity and string theory.

Cosmology can help constrain QG models, hopefully we can get a nice concentrated constrained group of theories.

We have a low-energy theory of quantum gravity.  For instance, we can use it to model some BICEP-type results.

Curvature as the delimiter.

Cosmological correlations as scattering-amplitude-like probe on QG.

Mercury perhilion shift in GR was an afterthought used to check, while in QM it was the messy experimental details that led us.  Which way will it be for QG?

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