Diving into traversable wormholes

Transcription

1 Diving into traversable wormholes Douglas Stanford IAS July 5, 2017 Based on with Juan Maldacena and Zhenbin Yang, following up on by Ping Gao, Daniel Jafferis, and Aron Wall.

2 Wormholes can be made traversable by coupling the two sides. This provides a model for how information can escape BHs.

3 Wormholes can be made traversable by coupling the two sides. This provides a model for how information can escape BHs. Disclaimer: this is not useful for space travel.

4 Wormholes can be made traversable by coupling the two sides. This provides a model for how information can escape BHs. Disclaimer: this is not useful for space travel. Plan: The thermofield double Negative energy in QFT Making wormholes traversable A limited application to the BHIP

5 The thermofield double

6 L R

7 L R L R TFD = n e βen/2 E n L E n R [Israel,Maldacena] Non-traversability looks delicate from gravity side, robust from QM side...

8 L R L R φ R TFD = n e βen/2 E n L φ E n R

9 L R L R φ R TFD = n e βen/2 E n L φ E n R Non-traversability looks robust on QM side but delicate in gravity?

10 The perturbed thermofield double ΔX + ΔX + t w t w X + = G N P + = G N dx T > 0

11 The perturbed thermofield double ΔX + ΔX + t w t w X + = G N P + = G N dx T > 0 Averaged null energy condition (ANEC) makes non-traversability robust on gravity side too. [Morris,Thorne,Yurtsever] Recent ANEC proofs: [Faulkner,Leigh,Parrikar,Wang][Hartman,Kundu,Tajdini]

12 Correlations and chaos O L O R t w

13 Correlations and chaos O L O R t w O L O R TFD O L O R TFD = 1 G Ne 2π β tw +... Becomes small around the scrambling time t β 2π log 1 G N. [Hayden,Preskill][Sekino,Susskind][Shenker, DS][Kitaev][Maldacena,Shenker,DS]

14 Negative energy in QFT

15 S = 1 2 d 2 x( O) 2,

16 S = 1 2 d 2 x( O) 2, Ψ = e igo LO R 0. Ψ T 00 (x) Ψ = ig 0 [O L O R, T 00 (x)] Ψ + O(g 2 ). T dx = 0

17 S = 1 2 d 2 x( O) 2, Ψ = e igo LO R 0. Ψ T 00 (x) Ψ = ig 0 [O L O R, T 00 (x)] Ψ + O(g 2 ). T dx = 0

18 S = 1 2 d 2 x( O) 2, Ψ = e igo LO R 0. Ψ T 00 (x) Ψ = ig 0 [O L O R, T 00 (x)] Ψ + O(g 2 ). P + = T dx = 0

19 Can instead think of a history with time-dependent Hamiltonian: start with vacuum, then at t = 0 act with e igo LO R : P + = T dx < 0

20 Making wormholes traversable

21 Gao-Jafferis-Wall Start with TFD state where we have added a signal from R. Then at t = 0, apply e igo LO R ϕ L (t ) (more precise version: e i g K K j=1 O(j) L O(j) R ): OL(0) O R(0) ϕ R (t ) Wormhole becomes traversable.

22 Amplification by chaos Traversability happens when G N e 2π β t becomes order one, t t ϕ L (t ) t * OL(0) O R(0) t * ϕ R (t )

23 Is it surprising? ϕ L (t ) O OL(0) O R(0) ϕ R (t )

24 Teleportation interpretation

25 Teleportation interpretation Instead of applying e igo LO R, can measure O R, get result o R and then apply e igo Lo R on the L system. This has the same effect: ϕ L OL ΠOR ϕ R Comfortable quantum teleportation!

26 A limited application to the BHIP

27 Simplified gravity in AdS 2 Jackiw-Teitelboim gravity: S = 1 d 2 x g Φ (R + 2) + 2 G N G N bdry ΦK After integrating over Φ we set R + 2 = 0 so geometry is rigid AdS 2. Only degree of freedom is the location of the boundary. The dynamics for this is equivalent to a particle in an electric field in AdS 2.

28 The thermofield double TFD = uniformly accelerated R, L trajectories:

29 The thermofield double TFD = uniformly accelerated R, L trajectories:

30 The traversable wormhole protocol Acting with e igo LO R can be approximated by adding g O L O R to the potential energy. This is an attractive potential potential energy: separation between boundaries so turning it on briefly gives an impulsive force.

31 The traversable wormhole protocol

32 The traversable wormhole protocol

33 Review: Hayden-Preskill collapsing matter (1) A black hole forms from collapse. We wait until it evaporates halfway, becoming maximally entangled with its Hawking radiation.

34 Review: Hayden-Preskill Bob collapsing matter Alice (2) Alice throws a bit into the black hole.

35 Review: Hayden-Preskill Bob collapsing matter Alice (3) Bob grabs a couple more quanta after Alice s bit falls in. Feeding this plus the first half of the radiation into a quantum computer, he can decode Alice s bit!

36 Review: Hayden-Preskill Bob collapsing matter Alice (4) If he then jumps in with his copy, it looks like there is quantum cloning. :(

37 1st half of Hawking radiation / quantum computer black hole (1) Half evaporated black hole (R) is maximally entangled with radiation, which our quantum computer is storing as a simulated black hole (L).

38 (2) Alice throws bit into BH.

39 (3) Bob waits a while, then collects a few more quanta from R and acts on L with them. Wormhole becomes traversable and the bit propagates to Bob s computer.

40 What about cloning?

41 Bob doesn t extract the bit from the quantum computer. It reflects off the boundary.

42 Bob disconnects form the quantum computer and jumps into the black hole.

43 He finds the bit behind the horizon.

44 Alternatively, Bob can extract the bit from the quantum computer...

45 ... carry it over to the black hole...

46 ... and dive in with it. Now he is carrying a copy but there is no second copy behind the horizon.

47 How to apply this to general black holes? Where is the wormhole connecting the Hawking radiation to the interior? Better understanding of ER = EPR is needed. [Maldacena,Susskind]

48 Summary By coupling the two sides of the TFD wormhole together, we can create negative energy that makes the wormhole traversable. This gives a geometrical realization of the Hayden-Preskill protocol. It makes it clear that cloning is avoided because the operation of recovering the information removes it from the region behind the horizon. We don t know how to apply this to evaporating black holes but ER = EPR might help.

49 Happy Birthday Stephen!