Can we go beyond a semiclassical description of cosmology?

Mark Van Raamsdonk (UBC)

CIFAR 2012

1/2

no

2/2

Should we care?

Yes:

Still some major theoretical issues that a semiclassical description can’t address:e.g.: • cosmological constant problem• validity of effective field theory• initial conditions/ likelihood of inflation

Can we come up with a consistent theoretical framework for cosmology (fully consistent theoretical mode including quantum gravity)?

Doesn’t string theory provide such a framework?

Nonperturbative description available only for special cases (e.g. asymptotically AdS):

AdS/CFT or gauge-theory / gravity duality

Cosmological spacetimes: typically have horizons

No single observer has access to full spacetime.

AdS analog: accelerating observers

Each observer has access to part of spacetime bounded by a horizon.

Each wedge: asymptotically AdS spacetime with boundary Hd

New description: Entangled state of two separate CFTs on Hd

-each side described by thermal density matrix-``Rindler” description of AdS

General story: certain patches of spacetime described by density matrices (mixed states).

Interesting feature: patches connected together by entanglement of non-perturbative degrees of freedom

e.g. : what happens if we disentangle two sides?

Emergence of spacetime ↔ quantum entanglement

Can we describe finite patches?

Want a density matrix that describes only the IR degrees of freedom (finitely many).

Such an object naturally associated with low-energy effective action.

Best guess for full description:

Regions inside horizons associated with density matrices describing finitely many degrees of freedom. Maybe no global description.

Entanglement between degrees of freedom for different patches carries information about how full spacetime is pieced together.

Requirement of nice global spacetime places constraints on what density matrices are allowed and how the various degrees of freedom are entangled.

Thanks!