Quantum past, present and future

carlo rovelli vancouver 2017 loop , Many directions of investigation string , Hořava–Lifshitz theory, , Vastly different numbers of researchers involved asymptotic safety, AdS-CFT-like dualities A few offer rather complete , tentative of quantum gravity causal set theory, , Most are highly incomplete emergent gravity, non-commutative geometry, Several are related, boundaries are fluid group theory, Penrose nonlinear quantum dynamics causal dynamical triangulations, Several are only vaguely connected to the actual problem of quantum gravity shape dynamics, ’t Hooft theory non-quantization of geometry Many offer useful insights … loop quantum causal dynamical gravity triangulations

asymptotic Hořava–Lifshitz safety group field AdS-CFT theory dualities

twistor theory shape dynamics causal set supergravity theory Penrose nonlinear quantum dynamics non-commutative geometry Violation of QM non-quantized geometry entropic ’t Hooft emergent gravity theory gravity Several are related

Herman Verlinde at LOOP17 in Warsaw No major physical assumptions over GR&QM

No infinity in the small loop quantum causal dynamical Infinity gravity triangulations in the small

Supersymmetry string High dimensions theory Strings Lorentz Violation asymptotic Hořava–Lifshitz safety group field AdS-CFT theory dualities

twistor theory Mostly still shape dynamics causal set classical supergravity theory Penrose nonlinear quantum dynamics non-commutative geometry Violation of QM non-quantized geometry entropic ’t Hooft emergent gravity theory gravity Discriminatory questions:

Is Lorentz symmetry violated at the Planck scale or not? Are there supersymmetric particles or not? Is violated in the presence of gravity or not? Are there physical degrees of freedom at any arbitrary small scale or not? Is geometry discrete i the small?

Lorentz violations Infinite d.o.f. QM violations Geometry is discrete? at Planck scale at Planck scale

Strings No No Yes No No

Loops No No No No Yes

Hojava Lifshitz Yes Yes No No No

Asymptotic safety No Yes No No No

Nonlinear quantum No Yes No Yes No dynamics

Your favorite … … … … … We do have existing and possibly developing empirical evidence Empirical evidence: 1: Lorentz invariance

Violation of Lorentz invariance → Renormalizability Observation has already ruled out theories

S. Liberati, Class. Quant. Grav. 30, 133001 (2013)

Lorentz violating solutions of QG are under empirical stress Is Lorentz invariance compatible with discreteness ?

Yes!

Classical discreteness breaks Lorentz invariance. Quantum discreteness does not !

Cfr rotational invariance: If a classical vector component can take only discrete values only, then SO(3) is broken. But if quantum vector can have discrete eigenvalues in a SO(3) invariant theory L L(β)

Lorentz invariance and quantum discreteness are compatible

=> Geometry is Empirical evidence: 2: Supersymmetry

Once again, no sign of supersymmetry

Solution of QG using supersymmetry are under empirical stress A point about philosophy of science:

- Popper’s falsification: theories are either “OK” or “proved wrong”. - Bayesian “confirmation”: we have “degrees of confidence” in theories; these are are lowered, of enhanced, by empirical (dis-)confirmation.

Karl Popper Bruno De Finetti

Not seeing a giraffe in the forests of Canada during a hike, does not prove that there are no giraffes in the forests of Canada A point about philosophy of science:

- Popper’s falsification: theories are either “OK” or “proved wrong”. - Bayesian “confirmation”: we have “degrees of confidence” in theories; these are are lowered, of enhanced, by empirical (dis-)confirmation.

Karl Popper Bruno De Finetti

Not seeing a giraffe in the forests of Canada during a hike, does not prove that there are no giraffes in the forests of Canada

But if for thirty years nobody sees a giraffe…

And we have now heard that supersymmetry is “going to be seen soon” for more than thirty years…. Empirical evidence: 3: Lab experiments

Analog systems Test the consequences of an assumption. Not the assumption themselves.

Planck scale effects NOT predicted by most QG theories in the lab

Violations of QM suggested by QG

Quantum property Can falsify the hypothesis that the of the metric gravitational field is classical. Is the metric a Can falsify the hypothesis that the quantum entity? gravitational field is classical.

S Bose, A Mazumdar, GW Morley, H Ulbricht, M Toroš, M Paternostro, A Geraci, P Barker, MS Kim, G Milburn: A Entanglement Witness for Quantum Gravity, 2017. C Marletto, V Vedral: An entanglement-based test of quantum gravity using two massive particles, 2017. Empirical evidence: 4: The Sky

a) Early Universe: “Quantum

b) Black holes: Disruption of the photon ring

Planck Stars A: In the early universe, quantum gravity effects cannot be disregarded These leave traces in the current universe. Few degrees of freedom. Gravity is quantum, is dynamical Schrödinger equation → Wheeler de Witt equation Absence of a preferred time variable.

Quantum Cosmology H: How to understand quantum theory of “the whole”. All degrees of freedom of the Universe. Absence of external observer? The problems raised by this would exist also if relativistic gravity did not exist.

Quantum Cosmology A is a totally different problem from Quantum Cosmology H Large activity to describe the physics of the very early universe, and find traces in the CMB

Notice: this is all physics of few degrees of freedom!

Great effort to find testable consequences of the theories in course b) Black holes Small effects pile up over time

- Wide quantum fluctuations of the metric Giddings

- Boson condensate of low energy Dvali

- Fluctuations of the causal structure allowing to decay Haggard, Barrau, Vidotto, CR - Wide quantum fluctuations of the metric

Theoretical reason: to bring information out of the hole

Observable consequence: Event Horizon Telescope

Possibly visible distortion of the photon ring

Imaging an Event Horizon: Mitigation of Scattering toward Sagittarius A* Fish et al 2014 - Fluctuations of the causal structure allowing black hole to decay

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5EJYCT\UEJKNF 3WCPVWOTGIKQP 5EJYCT\UEJKNF

/KPMQYUMK Exploding holes /KPMQYUMK

3WCPVWOTGIKQP 5EJYCT\UEJKNF

/KPMQYUMK Exploding holes At MG2 and in a paper ’79-’81 Frolov, Vilkovinski ‘79

Sean A. Hayward in ’06

Stephen, t’Hooft, Whithing ‘93 Valeri Frolov

In ’05 Ashtekar, Bojowald ’05

[see M. Smerlak’s talk]

Grigori A. Vilkovisky (left) Modesto ‘06 In ’93

Hayward ’06 Cristopher R. Stephens

Martin Bojowald

2 Hajicek Kieffer ’01

1 Gerard ’t Hooft

region 3 Haggard, Rovelli ’15

Bernard F. Whiting

Figure 2: for the gravitational collapse inside the event horizon (Region 1 and region 2) and outside the event horizon (Region3).

Solving the constraints equations (9) we obtain the known results for the classical dust matter gravi- tational collapse [8].

2GravitationalcollapseinAshtekarvariables

In this section we study the gravitational collapse in Ashtekar variables [12]. In particular we will express the Hamiltonian constraint inside and outside the matter and the constraints P1 and P2 in terms of the symmetric reduced Ashtekar connection [13], [14].

2.1 Ashtekar variables In LQG the fundamental variables are the Ashtekar variables:theyconsistofanSU(2) connection i a Aa and the electric field Ei ,wherea, b, c, =1, 2, 3aretensorialindicesonthespatialsectionand ··· a i, j, k, =1, 2, 3areindicesinthesu(2) algebra. The density weighted triad Ei is related to the ···i a 1 abc j k i j triad ea by the relation Ei = 2 ϵ ϵijk eb ec .Themetricisrelatedtothetriadbyqab = ea eb δij . Equivalently, ab a b ij det(q) q = Ei Ej δ . (10)

! i a The rest of the relation between the variables (Aa,Ei )andtheADMvariables(qab,Kab)isgivenby

i i b ij Aa = Γa + γ KabEj δ (11)

i where γ is the Immirzi parameter and Γa is the spin connection of the triad, namely the solution of i i j k Cartan’s equation: ∂[aeb] + ϵjk Γ[aeb] =0. The action is

1 3 a a i S = dt d x 2Tr(E A˙ a) N N a N i , (12) κγ Σ − − H − H − G " " # $ where N a is the shift vector, N is the lapse function and N i is the Lagrange multiplier for the Gauss a a i a constraint i.WehaveintroducedalsothenotationE[1] = E ∂a = Ei τ ∂a and A[1] = Aadx = i i a G A τ dx .Thefunctions , a and i are respectively the Hamiltonian, diffeomorphism and Gauss a H H G

4 /KPMQYUMK

3WCPVWOTGIKQP 5EJYCT\UEJKNF

/KPMQYUMK A technical result in classical GR:

The following metric is an exact vacuum solution, of the Einstein equations outside a finite spacetime region (grey), plus an ingoing and outgoing null shell, I The metric is determined by two constants:

ds2 = F (u, v)dudv + r2(u, v)(d✓2 + sin2✓d2) III II v u F (u ,v )=1,r(u ,v )= I I . Region I I I I I I 2 vI < 0.

3 32m r r r F (u, v)= e 2m 1 e 2m = uv. Region II r 2m I ⇣ ⌘ 1 uI uI Matching rI (uI ,vI )=r(u, v) u(uI )= 1+ e 4m . vo 4m 3 ⇣ ⌘ 32m rq Region III F (uq,vq)= e 2m ,rq = vq uq. rq

Black hole fireworks: quantum-gravity effects outside the horizon spark black to white hole tunneling Hal Haggard, CR I

I

➜ Choose a “Boundary” surface around the quantum region.

/KPMQYUMK

3WCPVWOTGIKQP 5EJYCT\UEJKNF

/KPMQYUMK

Spin network Spinfoam Primordial black holes!

A real-time FRB 5

Figure 2. The full-Stokes parameters of FRB 140514 recorded in the centre beam of the multibeam receiver with BPSR. Total intensity, and Stokes Q, U,andV are represented in black, red, green, and blue, respectively. FRB 140514 has 21 7% (3-)circularpolarisation ± averaged over the pulse, and a 1- upper limit on linear polarisation of L<10%. On the leading edge of the pulse the circular polarisation is 42 9% (5-)ofthetotalintensity.Thedatahavebeensmoothedfromaninitialsamplingof64µsusingaGaussianfilteroffull-width ± half-maximum 90 µs.

source given the temporal proximity of the GMRT observa- 4.5 Gamma-Ray Burst Optical/Near-Infrared tion and the FRB detection. The other two sources, GMRT2 Detector and GMRT3, correlated well with positions for known ra- After 13 hours, a trigger was sent to the Gamma-Ray Burst dio sources in the NVSS catalog with consistent flux densi- Optical/Near-Infrared Detector (GROND) operating on the ties. Subsequent observations were taken through the GMRT 2.2-m MPI/ESO telescope on La Silla in Chile (Greiner et al. ToO queue on 20 May, 3 June, and 8 June in the 325 MHz, 2008). GROND is able to observe simultaneously in J, H, 1390 MHz, and 610 MHz bands, respectively. The second and K near-infrared (NIR) bands with a 100 100 field of epoch was largely unusable due to technical diculties. The ⇥ view (FOV) and the optical g0, r0, i0,andz0 bands with a search for variablility focused on monitoring each source for 60 60 FOV. A 2 2 tiling observation was done, providing flux variations across observing epochs. All sources from the ⇥ ⇥ 61% (JHK)and22%(g0r0i0z0) coverage of the inner part first epoch appeared in the third and fourth epochs with no of the FRB error circle. The first epoch began 16 hours af- measureable change in flux densities. ter FRB 140514 with 460 second exposures, and a second epoch was taken 2.5 days after the FRB with an identical 4.4 Swift X-Ray Telescope observing setup and 690 s (g0r0i0z0)and720s(JHK)ex- posures, respectively. Limiting magnitudes for J, H,andK The first observation of the FRB 140514 field was taken us- bands were 21.1, 20.4, and 18.4 in the first epoch and 21.1, ing Swift XRT (Gehrels et al. 2004) only 8.5 hours after the 20.5, and 18.6 in the second epoch, respectively (all in the FRB was discovered at Parkes. This was the fastest Swift AB system). Of all the objects in the field, analysis iden- follow-up ever undertaken for an FRB. 4 ks of XRT data tified three variable objects, all very close to the limiting were taken in the first epoch, and a further 2 ks of data magnitude and varying on scales of 0.2 - 0.8 mag in the NIR were taken in a second epoch later that day, 23 hours af- bands identified with di↵erence imaging. Of the three ob- ter FRB 140514, to search for short term variability. A final jects one is a galaxy, another is likely to be an AGN, and epoch, 18 days later, was taken to search for long term vari- the last is a main sequence star. Both XRT1 and GMRT1 ability. Two X-ray sources were identified in the first epoch sources were also detected in the GROND infrared imaging of data within the 150 diameter of the Parkes beam. Both but were not observed to vary in the infrared bands on the sources were consistent with sources in the USNO catalog timescales probed. (Monet et al. 2003). The first source (XRT1) is located at RA = 22:34:41.49, Dec = -12:21:39.8 with RUSNO =17.5 and the second (XRT2) is located at RA = 22:34:02.33 Dec =-12:08:48.2withR =19.7.BothXRT1andXRT2 USNO 4.6 Swope Telescope appeared in all subsequent epochs with no observable vari- ability on the level of 10% and 20% for XRT1 and XRT2, An optical image of the FRB field was taken 16h51m after respectively, both calculated from photon counts from the the burst event with the 1-m Swope Telescope at Las Cam- XRT. Both sources were later found to be active galactic panas. The field was re-imaged with the Swope Telescope on nuclei (AGN). 17 May, 2 days after the FRB. No variable optical sources

c 0000 RAS, MNRAS 000,000–000 Signature: distance/energy relation

1 1/2 2Gm H0 1 ⌦⇤ 3/2 obs 2 (1 + z) 1/2 sinh (z + 1) ⇠ c v ⌦M u6 k⌦⇤ " # u ✓ ◆ t

l

A real-time FRB 5

l

Figure 2. The full-Stokes parameters of FRB 140514 recorded in the centre beam of the multibeam receiver with BPSR. Total intensity, and Stokes Q, U,andV are represented in black, red, green, and blue, respectively. FRB 140514 has 21 7% (3-)circularpolarisation ± averaged over the pulse, and a 1- upper limit on linear polarisation of L<10%. On the leading edge of the pulse the circular polarisation is 42 9% (5-)ofthetotalintensity.Thedatahavebeensmoothedfromaninitialsamplingof64µsusingaGaussianfilteroffull-width ± half-maximum 90 µs.

source given the temporal proximity of the GMRT observa- 4.5 Gamma-Ray Burst Optical/Near-Infrared tion and the FRB detection. The other two sources, GMRT2 Detector and GMRT3, correlated well with positions for known ra- After 13 hours, a trigger was sent to the Gamma-Ray Burst dio sources in the NVSS catalog with consistent flux densi- Optical/Near-Infrared Detector (GROND) operating on the ties. Subsequent observations were taken through the GMRT 2.2-m MPI/ESO telescope on La Silla in Chile (Greiner et al. ToO queue on 20 May, 3 June, and 8 June in the 325 MHz, 2008). GROND is able to observe simultaneously in J, H, 1390 MHz, and 610 MHz bands, respectively. The second and K near-infrared (NIR) bands with a 100 100 field of epoch was largely unusable due to technical diculties. The ⇥ view (FOV) and the optical g0, r0, i0,andz0 bands with a search for variablility focused on monitoring each source for 60 60 FOV. A 2 2 tiling observation was done, providing flux variations across observing epochs. All sources from the ⇥ ⇥ 61% (JHK)and22%(g0r0i0z0) coverage of the inner part first epoch appeared in the third and fourth epochs with no of the FRB error circle. The first epoch began 16 hours af- measureable change in flux densities. ter FRB 140514 with 460 second exposures, and a second epoch was taken 2.5 days after the FRB with an identical 4.4 Swift X-Ray Telescope observing setup and 690 s (g0r0i0z0)and720s(JHK)ex- posures, respectively. Limiting magnitudes for J, H,andK The first observation of the FRB 140514 field was taken us- bands were 21.1, 20.4, and 18.4 in the first epoch and 21.1, ing Swift XRT (Gehrels et al. 2004) only 8.5 hours after the 20.5, and 18.6 in the second epoch, respectively (all in the FRB was discovered at Parkes. This was the fastest Swift AB system). Of all the objects in the field, analysis iden- follow-up ever undertaken for an FRB. 4 ks of XRT data tified three variable objects, all very close to the limiting were taken in the first epoch, and a further 2 ks of data magnitude and varying on scales of 0.2 - 0.8 mag in the NIR were taken in a second epoch later that day, 23 hours af- bands identified with di↵erence imaging. Of the three ob- ter FRB 140514, to search for short term variability. A final jects one is a galaxy, another is likely to be an AGN, and epoch, 18 days later, was taken to search for long term vari- the last is a main sequence star. Both XRT1 and GMRT1 ability. Two X-ray sources were identified in the first epoch sources were also detected in the GROND infrared imaging of data within the 150 diameter of the Parkes beam. Both but were not observed to vary in the infrared bands on the sources were consistent with sources in the USNO catalog timescales probed. (Monet et al. 2003). The first source (XRT1) is located at RA = 22:34:41.49, Dec = -12:21:39.8 with RUSNO =17.5 and the second (XRT2) is located at RA = 22:34:02.33 Dec =-12:08:48.2withR =19.7.BothXRT1andXRT2 USNO 4.6 Swope Telescope appeared in all subsequent epochs with no observable vari- ability on the level of 10% and 20% for XRT1 and XRT2, An optical image of the FRB field was taken 16h51m after respectively, both calculated from photon counts from the the burst event with the 1-m Swope Telescope at Las Cam- XRT. Both sources were later found to be active galactic panas. The field was re-imaged with the Swope Telescope on nuclei (AGN). 17 May, 2 days after the FRB. No variable optical sources

c 0000 RAS, MNRAS 000,000–000

z 2 4 6 8 10 A real-time FRB 5

Figure 2. The full-Stokes parameters of FRB 140514 recorded in the centre beam of the multibeam receiver with BPSR. Total intensity, and Stokes Q, U,andV are represented in black, red, green, and blue, respectively. FRB 140514 has 21 7% (3-)circularpolarisation ± averaged over the pulse, and a 1- upper limit on linear polarisation of L<10%. On the leading edge of the pulse the circular polarisation is 42 9% (5-)ofthetotalintensity.Thedatahavebeensmoothedfromaninitialsamplingof64µsusingaGaussianfilteroffull-width ± half-maximum 90 µs.

source given the temporal proximity of the GMRT observa- 4.5 Gamma-Ray Burst Optical/Near-Infrared tion and the FRB detection. The other two sources, GMRT2 Detector and GMRT3, correlated well with positions for known ra- After 13 hours, a trigger was sent to the Gamma-Ray Burst dio sources in the NVSS catalog with consistent flux densi- Optical/Near-Infrared Detector (GROND) operating on the ties. Subsequent observations were taken through the GMRT 2.2-m MPI/ESO telescope on La Silla in Chile (Greiner et al. ToO queue on 20 May, 3 June, and 8 June in the 325 MHz, 2008). GROND is able to observe simultaneously in J, H, 1390 MHz, and 610 MHz bands, respectively. The second and K near-infrared (NIR) bands with a 100 100 field of epoch was largely unusable due to technical diculties. The ⇥ view (FOV) and the optical g0, r0, i0,andz0 bands with a search for variablility focused on monitoring each source for 60 60 FOV. A 2 2 tiling observation was done, providing flux variations across observing epochs. All sources from the ⇥ ⇥ 61% (JHK)and22%(g0r0i0z0) coverage of the inner part first epoch appeared in the third and fourth epochs with no of the FRB error circle. The first epoch began 16 hours af- z measureable change in flux densities. ter FRB 140514 with 460 second exposures, and a second epoch was taken 2.5 days after the FRB with an identical 4.4 Swift X-Ray Telescope observing setup and 690 s (g0r0i0z0)and720s(JHK)ex- posures, respectively. Limiting magnitudes for J, H,andK 2 4 6 8 10 The first observation of the FRB 140514 field was taken us- bands were 21.1, 20.4, and 18.4 in the first epoch and 21.1, ing Swift XRT (Gehrels et al. 2004) only 8.5 hours after the 20.5, and 18.6 in the second epoch, respectively (all in the FRB was discovered at Parkes. This was the fastest Swift AB system). Of all the objects in the field, analysis iden- follow-up ever undertaken for an FRB. 4 ks of XRT data tified three variable objects, all very close to the limiting were taken in the first epoch, and a further 2 ks of data magnitude and varying on scales of 0.2 - 0.8 mag in the NIR were taken in a second epoch later that day, 23 hours af- bands identified with di↵erence imaging. Of the three ob- ter FRB 140514, to search for short term variability. A final jects one is a galaxy, another is likely to be an AGN, and epoch, 18 days later, was taken to search for long term vari- the last is a main sequence star. Both XRT1 and GMRT1 ability. Two X-ray sources were identified in the first epoch sources were also detected in the GROND infrared imaging of data within the 150 diameter of the Parkes beam. Both but were not observed to vary in the infrared bands on the sources were consistent with sources in the USNO catalog timescales probed. (Monet et al. 2003). The first source (XRT1) is located at RA = 22:34:41.49, Dec = -12:21:39.8 with RUSNO =17.5 and the second (XRT2) is located at RA = 22:34:02.33 Dec =-12:08:48.2withR =19.7.BothXRT1andXRT2 USNO 4.6 Swope Telescope appeared in all subsequent epochs with no observable vari- ability on the level of 10% and 20% for XRT1 and XRT2, An optical image of the FRB field was taken 16h51m after respectively, both calculated from photon counts from the the burst event with the 1-m Swope Telescope at Las Cam- XRT. Both sources were later found to be active galactic panas. The field was re-imaged with the Swope Telescope on nuclei (AGN). 17 May, 2 days after the FRB. No variable optical sources

c 0000 RAS, MNRAS 000,000–000

Fast Radio Bursts and White Hole Signals Aurélien Barrau, Carlo Rovelli, . Publications of the Astronomical Society of Australia (PASA) doi: 10.1017/pas.2017.xxx. 24

the classical evolution becomes important as quantum eects manifest. This time can be much shorter than the Publications of the Astronomical Society of Australia (PASA) Hawking evaporation time M 3 , as short as M 2 .this doi:Fundamental 10.1017/pas.2017.xxx. Physics with the SKA:BH DarkBH Matter and is the minimal time after which quantum fluctuations of the metric can appear in the region outside the BH Astroparticles horizon. In fact, the presence of a small curvature pro- 2 portional to MBH≠ near the horizon allows us to define the ‘quantum break-time’ as the inverse of this quan- 2 Fundamental Physics withtity, that istheMBH (Haggard SKA: & Rovelli, Dark 2014, 2016). Matter As and soon as these quantum fluctuations of the geometry take Astroparticles place, the dynamics of the horizon can undergo dramatic behaviours, to the point of the very disappearance of K. Kelley1, S. Riemer-Sørensen2, E. Athanassoulathe horizon,3,C.Bœhm possibly by4,5 an, G. explosion. Bertone6, A. Bosma7,M. 8 9,10,11 6,12 Dierent approaches13,14,15 to quantum gravity converge16 in Brüggen , C. Burigana , F. Calore ,pointing S. Camera out the possibility, J.A.R. of instabilities Cembranos of quantum-,R.M.T. 17 18,19 2 13,14,15 6 Connors , Á. de la Cruz-Dombriz ,P.K.SDunsbygravitational, origin N. Fornengo that can manifest, in D. an Gaggero explo- ,M. Méndez-Isla18,19, Y. Ma21,22,23, H. Padmanabhansive24 event, A. in Pourtsidou a timescale25 shorter,P.J.Quinn than the1, evapora-M. Regis13,14, Figure 20. Radio sources above the SKA1-MID point source 26 27 28 29,30,31,32 10,33,9 34,35 sensitivity,M. Sahlén for 1000h, of M. data Sakellariadou taking, if PBHs are ,1% L.of Shao the DM. ,J.Silktion time [(Gregory, T.& Trombetti Laflamme, 1993;, F.Casadio Vazza & ,F. K. Kelley1, S. Riemer-Sørensen≥2, E. Athanassoula3,C.Bœhm4,5, G. Bertone6, A. Bosma7,M. Vidotto36, F. Villaescusa-Navarro37, C. WenigerHarms,6 and 2001, L. Wolz 2000;38 Kol & Sorkin, 2004; Emparan et al., 8 9,10,11 6,12 2003)]. In particular,13,14,15 has16 re- 1BrüggenInternational, C. Centre Burigana for Radio Astronomy, F. Calore Research, (ICRAR), S. Camera University of, Western J.A.R. Australia, Cembranos Ken and,R.M.T. Julie Michael Building, 7 17 18,19 2 13,14,15 6 Fairway,Connors Crawley,, Á. Westernde la Cruz-Dombriz Australia 6009 ,P.K.SDunsbycently provided, a N. framework Fornengo to compute, explicitly D. Gaggero this ,M. detectors currently in upgrade of development phase), 2Méndez-IslaInstitute of Theoretical18,19, Y. Ma Astrophysics,21,22,23, H. University Padmanabhan of Oslo,time24 P.O. (Christodoulou, A. Box Pourtsidou 1029 Blindern, et al.,25 2016).,P.J.Quinn N-0315 Loop Oslo, Quantum1 Norway, M. Grav- Regis13,14, an3 exciting set of complementary observations will help ity removes the classical curvature singularities (Rovelli M.Aix Sahlén Marseille26, Univ,M. Sakellariadou CNRS, LAM,27 Laboratoire, L. Shao d’Astrophysique28,J.Silk29,30, de31, Marseille,32, T. Trombetti Marseille,10 France,33,9, F.26 Vazza34,35,F. to4 characterizeInstitute for the Particle presence Physics of compact Phenomenology, objects both Durham in & University,Vidotto, 2013; South Ashtekar Road, & Durham, Bojowald, DH1 2006; 3LE, Corichi United & Kingdom 36 37 6 38 l ourVidotto5 Galaxy and, F. in Villaescusa-Navarro the early Universe, and eventually, C. WenigerSingh,and 2016), L. Wolz such as the one at the BH center, becausevalue of the lifetime. Using Equation 19 we can 1 LAPTH, U. de Savoie, CNRS, BP 110, 74941 Annecy-Le-Vieux, France indeed compute the mass of BHs whose lifetime shed6 InternationalGRAPPA, light on the Institute nature Centre of of for the Physics, Radio DM in Astronomy University the universe. Researchof Amsterdam, (ICRAR),of quantum Science University spacetime Park 904, of discreteness. Western1098 XH Australia, Amsterdam, The consequences Ken Netherlandsis and the Hubble Julie time, Michael yielding an Building, explosion today. 7 7Fairway, Crawley, Western Australia 6009 of this discreteness on the dynamics can be modeledFor a lifetime in the lower end of the viable win- 2 Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France dow, the Schwarzschild radius is of the order of 3.9.28 InstitutePBHs and of Theoretical Quantum Gravity Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo, NorwayR 0.2mm and the observational depth allows University of Hamburg, Gojenbergsweg 112, 21029 Hamburg,at the e Germanyective level by an eective potential thatBH pre-≥ 3 us to detect events in all the visible Universe. To9 dateAix the Marseille search for Univ, PBHs CNRS, and for LAM, constraints Laboratoire on PBHs d’Astrophysiquevents the gravitational de Marseille, collapse Marseille, from France forming the sin- 4 INAF, Istituto di Radioastronomia, Via Piero Gobetti 101, I-40129 Bologna, Italy has10Institute mostlyDipartimento considered for Particle di Fisica an Physicsalmost e Scienze monochromatic Phenomenology, della Terra, mass UniversitàDurhamgularity University, di Ferrara, and triggers South Via Giuseppe Road, a bounce. Durham, Saragat The DH1bounce 1, I-44122 3LE, connectsFor United the Ferrara, highest Kingdom values Italy of Ÿ, the signal is emitted with 5 energy in the GeV, but a study of the photon emission 11LAPTH, U. de Savoie, CNRS, BP 110, 74941 Annecy-Le-Vieux, France spectrum,Istituto and Nazionale the presence di Fisica of Hawking Nucleare, evaporation Sezione for di Bologna,Viaa collapsing Irnerio solution 46, I-40126 of the Einstein Bologna, equation, Italy with that the code is PHYTIA indicates that the photons with 6 z 12GRAPPA, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam,higher Netherlands density, therefore more likely to be detected, 2 4 6 8 10 PBHsLAPTh, of small CNRS, mass. Monochromatic 9 Chemin de Bellevue, mass spectrum BP-110, has Annecy-le-Vieux,the classical black 74941, hole, Annecy to an explosive Cedex, France expandingare those one, in the MeV (?). Some Short Gamma Ray 7 Figure 21. The expected wavelength (unspecified units) of the 13Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France Bursts (Nakar, 2007), whose source is still unclear, are been8 Dipartimento challenged by di di Fisica,erent authors Università as unrealistic degli Studi (for di Torino,a white Via hole P. Giuria (Haggard 1, 10125 & Rovelli, Torino, 2014), Italy through an signal from black hole explosions as a function of the redshift 14University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany possible candidates in this range. z.Thecurveflattensatlargedistance:theshorterwavelength exampleINFN, Carr Istituto et al. (2017a)). Nazionale An di extended Fisica Nucleare, mass function Sezioneintermediate di Torino, Via quantum P. Giuria region. 1, 10125 This process Torino, is Italy aFor typical the lowest values of Ÿ, the peak of the signal is from smaller black holes exploding earlier get compensated by the 9 redshift. 15INAF, Istituto di Radioastronomia, Via Piero Gobetti 101, I-40129 Bologna, Italy in the millimetres. The corresponding frequencies are is10 compatibleINAF, Istituto with di Nazionaleerent PBHs di formationAstrofisica, mechanics, Osservatorioquantum Astrofisico tunnelling di Torino, event, Strada and Osservatorio the characteristic 20, 10025 time Pino Torinese, Italy 16 Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via Giuseppe Saragat 1, I-44122beyond Ferrara, the sensitivity Italy of SKA-mid. On the other hand, Departamento de FÃsica TeÃrica I, Universidad Complutense de Madrid, E20840 Spain in a decay we expect a probability distribution of the from11 critical collapse to cosmic strings. Hawking evapo- at which it takes place, the hole lifetime, can be as a DM and Astroparticles 27 17 API,Istituto University Nazionale of di Amsterdam, Fisica Nucleare, Science Sezione Park 904, di Bologna,Via 1098 XH Amsterdam, Irnerio 46, I-40126Netherlands Bologna, Italy event to happen, and therefore there could be some event received signal, and possibly the source being hosted ration12 is a phenomenon that becomes relevant on a time decaying time, similar to the lifetime of conventionalhappening within SKA-mid frequency range. Further- in a known astronomical object, for instance a galaxy. 18 LAPTh, CNRS, 9 Chemin de Bellevue, BP-110, Annecy-le-Vieux, 74941, Annecy Cedex, France A further technique is available, and it is peculiar of scale13 Cosmology that depends and onGravity the mass Group, of the BH. University Its time of scale Cape Town,nuclear 7701 radioactivity. Rondebosch, The Cape resulting Town, picture South is conserva-Africamore, the details of the decay mechanism are not fully neutrino signature in many cosmological observables, 19 Dipartimento di Fisica, Università degli Studi di Torino, Via P. Giuria 1, 10125 Torino, Italy established, leaving open the possibility of the presence decaying PBHs. BHs exploding far away are less massive, 3Department of Mathematics and Applied Mathematics, University of Cape Town, 7701 Rondebosch, Cape Town, South Africa withk=0.05 a lower flux of energy (Kavic, 2017), the flux of and in particular, a suppression of power on small scales is 14MBH in Planck units. This implies that within the tive in comparison to other models of non-singularof some BHs. factors that could shift the wavelength possibly directin the matter power spectrum. decayed Understanding and mea- 20 INFN, Istituto Nazionale di Fisica Nucleare, Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italyby 1-2 orders of magnitude. This makes it worthwhile to energy of the measured burst lessens with distance. 15 South African Astronomical Observatory, ObservatoryThe 7925, collapse Cape still Town, produces South a Africa horizon, but it is now a suring this eect is also important for and age21 ofINAF, the universe Istituto only Nazionale PBHs with di Astrofisica, mass smaller Osservatorio than Astrofisico di Torino, Strada Osservatorio 20,explore 10025 for transients Pino at Torinese, the highest frequencies Italy acces- The peculiar wavelength-redshift relation can be 12 School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Private Bag X54001, Durban, 4000, South Africa tests, as models of modified gravity 1016 kg could have evaporated, and possibly produced dynamical horizon with a finite lifetime, rathersible then to SKA-mid. a In particular, it has been suggested proven also without the knowledge of the distance of the 22 DepartamentoNAOC-UKZN Computationalde FÃsica Teà Astrophysicsrica I, Universidad Centre Complutense (NUCAC), University de Madrid, of E20840KwaZulu-Natal, Spain Durban,that the quantum-gravitational4000 South Africa BH explosion may be source, by studying the radiation integrated over the or interacting DM/energy also lead to modifications of very17 high-energy cosmic rays (Barrau, 2000). As cosmic perpetual event horizon. The collapsing matterlinked contin- to FRBs ( ). A number of hints seems to support detectable past explosions. SKA HI intensity mapping small scales power (see e.g. Wright et al., 2017). 23 API,Purple University Mountain of Observatory, Amsterdam, Chinese Science Academy Park 904, of 1098 Sciences, XH Amsterdam, Nanjing 210008, Netherlands China ? rays18 of such energies are rare, constraints are derived on ues its fall after entering the trapping region, formingthis conjecture, a such as the rapid impulse, of mostly can therefore provide the desired data in this respect. Current constraints on the sum of the neutrino masses, 24 CosmologyETH Zurich, and Wolfgana-Pauli-Strasse Gravity Group, University 27, CH8093 of Cape Zurich, Town, Switzerland 7701 Rondebosch, Cape Town, South Africaextra-Galactic origin, the enormous energy flux as the Studies of the integrated emission from PBH decay has arising by combining data from the CMB, galaxy clus- 19 BH converts eciently its mass into radiation. been started in (Barrau et al., 2016) for a large range the25 very-small-massDepartment of end Mathematics of the PBH and mass Applied spectrum. Mathematics,very University dense object of whose Cape furtherTown, 7701collapse Rondebosch, is prevented Cape by Town, South Africa tering and/or the Lyman-– forest, are M‹ 0.12 eV Institute of Cosmology & Gravitation, University of Portsmouth, Burnaby Road, Portsmouth, PO1 3FX, United Kingdom of the Ÿ parameter in the PBH lifetime. The signal has . 20 quantum pressure (referred to with the suggestingPBHs name exploding in a quantum decay present a unique (Riemer-Sørensen et al., 2014; Palanque-Delabrouille 26HawkingDepartmentSouth evaporation,African of Astronomical Physics however, and Astronomy,is Observatory, a phenomenon Uppsala Observatory pre- University, 7925, SE-751 Cape Town, 20 Uppsala, South Africa Sweden feature that makes them distinguishable from other as- been obtained using the PYTHIA code (Sjöstrand et al., 21 trophysical sources. The time at which the decay hap- 2015), which for a given initial energy computes the par- et al., 2015; Cuesta et al., 2016; Vagnozzi et al., 2017). dicted27 School in the of context Chemistry of quantum and Physics, field theory University on a fixed of KwaZulu-Natal,of WestvilleRovelli Campus, & Vidotto Private (2014)). Bag X54001, Durban, 4000, South Africa pens is a function of the BH mass. Therefore, smaller ticle production for the process. Thedirect+decayed resulting radiation One would naively expect that enlarged those constraints would 22 Theoretical and Cosmology group, Physics Department, King’s College London, University of London, Strand, curvedNAOC-UKZN background. Computational This is a theory Astrophysics with a regime Centre of (NUCAC),The collapsing University matter of that KwaZulu-Natal, forms PBHs Durban,in thePBHs radia- explode 4000 earlier, South that isAfrica at a distance from us. is not thermal, but it carries a distortion due to the char- improve by using galaxy clustering at higher redshifts, 23London WC2R 2LS, UK The signal they produce also depends on their mass, acteristic redshift-wavelength relation of Figure 21. This since the available volume is much larger and the non- 28 validityPurple that Mountainmay likely breakObservatory, down when Chinese approximately Academy oftion Sciences, dominated Nanjing epoch 210008, is mainly China constituted bythe photons. smaller the BH, the shorter the wavelength in both appears for both the high energy and the low energy linear clustering eects are weaker. Also the eects of 24 Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Mühlenberg 1, Potsdam 14476, Germany half29 ofETH the massZurich, of the Wolfgana-Pauli-Strasse hole has evaporated, as 27, indicated CH8093 Zurich,Seen Switzerlandfrom the center of the hole, those photonsthe highcol- and low energy channels. Signals from distant channel, as can be seen in Figure 22 for the case of the dark energy will be smaller at higher redshift. Institut d’Astrophysique, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis Blvd Arago, 75014 Paris, France shortest lifetime. In principle the result depends on the 25 sources get redshifted, partially compensating for the The possibility of using high-redshift optical galaxy for30 instanceInstitute by of the Cosmology ‘firewall’& no-go Gravitation, theorem (Almheiri University oflapse Portsmouth, through the Burnaby trapping Road, region, Portsmouth, then expands PO1shorter passing 3FX, wavelength United due to a Kingdom smaller mass. PBH mass spectrum, but dierent hypothesis for the AIM-Paris-Saclay, CEA/DSM/IRFU, CNRS, Univ Paris 7, F-91191, Gif-sur-Yvette, France surveys (combined with CMB data, in order to lift param- 26 Generic astrophysical objects have an observed wave- mass spectrum have been tested showing that the result et31 al.,Department 2013). The of geometry Physics andaround Astronomy, a BH can Uppsala indeed University,through SE-751 an anti-trapping 20 Uppsala, region Sweden and eventually exits eter degeneracies) to provide precision measurements of 27 Department of Physics and Astronomy, The John Hopkins University, Homewood Campus, Baltimorelength that MD scale linearly 21218, with theUSA distance. On the other has only a very weak dependence [(Barrau et al., 2016)]. undergo32 BeecroftTheoretical quantum Institute Particle fluctuations of Physics Particle on anda Astrophysics time Cosmology scale shorter and group, Cosmology, Physicsthe white-hole Department Department, horizon, of King’s alwaysPhysics, College at University the speed London, of of light,hand, Oxford, University Hawking the Oxford evaporation of London, OX1ends in the 3RH,Strand, standard UK theory Finally, in the presence of the ionized ISM, decay- the neutrino masses is not new (see for example (Takada et al., 2006)). High-z advantages include accessing a 33London3 WC2R 2LS, UK when BHs, of any initial mass, reach the Planck size ing PBHs can produce a radio pulse of the order of than IstitutoMBH,whenthee Nazionaleects di Fisica of the Nucleare, Hawking evaporation Sezione di Ferrara,process Via is thusGiuseppe extremely Saragat fast. 1, On I-44122 the other Ferrara, hand,and Italyproducefor an a signal with such wavelength. The phe- 1GHz (Rees, 1977; Blandford, 1977). This frequency larger comoving volume for a given survey area, and a 28 Figure≥ 22. The diuse emission of the low energy channel, and 34 Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Mühlenberg 1, Potsdamnomenon described 14476, above Germany gives a completely dierent is fully within the sensitivity of SKA-mid. Furthermore, haveUniversity not not yet of significantly Hamburg, Gojenbergsweg modified the size 112, of 21029 the Hamburg,observer sitting Germany outside the horizon, a huge but finite red- below the diuse emission of the high energy channel. We show here wider range of scales in the linear or quasi-linear regime. 29 eect, the modified relation between wavelength and red- it is interestingly close to that of an FRB. The emission 35 Institut d’Astrophysique, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis Blvd Arago, 75014 Paris, France the ones for the shortest BH lifetime, i.e. the lowest Ÿ parameter. However, the detection of galaxies at high redshifts be- hole.Istituto As any di classical Radio Astronomia,system, the hole INAF, has Via a charac- Gobetti 101,shift 40122, stretches Italy this time to cosmological times. Thisshift (Barrau time, et al., 2014) represented by the flattenedThe unitsmechanism, in the ordinate in this case, axis are relies not on specified: the presence the normalisation of a shell comes more dicult and expensive, and shot noise eects 30 curve (Figure 21). Observation of a burst whose sourceof the spectrum depends on the percentage of PBHs as DM. teristic36 InstituteAIM-Paris-Saclay, timescale for Mathematics, after which CEA/DSM/IRFU, the Astrophysics the departure CNRS, and from Particle Univ Parisproperly Physics 7, F-91191, (IMAPP), called the Gif-sur-Yvette, hole Radboud lifetime, University, as France discussed P.O. before Box 9010, has 6500 GL Nijmegen, The of relativistic charged particles produced in the explo- may dominate. In (Takada et al., 2006), a space-based 31 has a known distance will allow us to see whether data sion. The shell behaves as a superconductor that expels 2 NetherlandsDepartment of Physics and Astronomy, The John Hopkins University, Homewood Campus, Baltimorefits such a MD curve. If 21218, so, it would USA represent a signature of the interstellar magnetic field from a spherical volume galaxy survey with a 300 deg sky coverage at redshifts 32 3.5

Keywords: keyword1 – keyword2 – keyword3 – keyword4 – keyword5 Quantum Gravity Observations are not absurd anymore.

There are:

- Already concerete results (Lorentz invariance)

- Suggested astrophysical observations motivating astronomers (Cosmology+Black holes)

- Interesting laboratory experiments (Entanglement via gravity)

(Result of a pool at a recent conference (3rd Karl Schwarzschild Meeting on Gravitational Physics and the Gauge/Gravity Correspondence, Frankfurt am Main, July 2017): 80% of the participants expect observational evidence for quantum gravity observations within the next decade.) General lesson and convergences between theories

Quantum effects can be “strong” and “soft”: strong quantum effects at large wavelength,

Local QFT can be strongly violated ( theorem) Quantum Gravity requires overcoming Local Field Operators.

On information loss in AdS/CFT A. Liam Fitzpatrick, Jared Kaplan, Daliang Li, Junpu Wang.

Boundaries: Strings: AdS-CFT Loops: boundary formalism (covariant version) A process and its amplitude

hl Boundary state = Boundary state in ⌦ out Amplitude A = W ( )

Boundary Quantum system = “Spacetime region” Spacetime region

➜ Hamilton function: S(q,t,q’,t’)

In GR, distance and time measurements are field measurements like any other one: they are part of the boundary data of the problem Boundary values of the gravitational field = geometry of box surface = distance and time separation of measurements

Particle detectors = field measurements Quantum relationalism Spacetime region = Spacetime relationalism Distance and time measurements = gravitational field measurements The search for a quantum theory of the

Prehistory

1920 The gravitational field needs to be quantized

1930 «Flat space quantization»

1950 «Phase space quantization»

1957 «Feynman Constraint theory quantization»

Classical period

1961 Tree-amplitudes ADM

1962 Background field method

1963 Wave function of the 3- geometry, spacetime foam

1967 Ghosts

Wheeler-DeWitt equation

1968 Minisuperspace Feynman rules The general landscape of the research completed directions has remained quite stable MiddleAges 1971 YM renormalization

1972 Twistors

1973 Nonrenormalizability

1974 Black Hole radiation

1976 Asymptotic savety

1976 Supergravity

1977 High derivative theories

1978 Euclidean QG

1981 But definite progress has happened 1983 Wave function of the Universe along some research directions Renaissance 1984 String renaissance

1986 Connection TQFT formulation of GR

1987

1988 2+1 Loop quantum gravity

1989 2d QG

1992 Weaves State sum models

1994

Nowdays

1995 Null Surface Eigenvalues of area and volume Formulation Nonperturbative strings

1996 BH radiation from loops Spin Foams BH radiation from strings

1997 « Quantum gravity Strings-noncommutative phenomenology » geometry Loops Strings open problems open problems in the late 80’ in the late 80’

Definition of the Finding a fundamental • • Hilbert space formulation of the theory Mathematical Deriving SU(3)xSU(2)xU(1) • • foundation from first principles • Coupling matter • Computing the parameters of the standard model • Recovering low energy GR • Supersymmetry breaking • • Compactification • Observables • Extend to the non- perturbative regime • Application to early universe • Produce tentative verifiable physical predictions • Produce verifiable physical predictions Progress has happened along some research directions

Theoretical Empirical success Empirical failure Theoretical success Key open issue failure

AdS-CFT Low-energy super Standard model Strings None Non-fundamental Lack of predictivity symmetry parameters appliacations Strings Loops None Low energy limit Infinite graph limit

Lorentz violation at Hojava-Lifshitz None Renormalizability Other scale? Planck scale

Increase evidence of Asymptotic savety None Computing amplitudes Loops fixed point

Your favorite … … … … … How do we best describe physical reality?

Descartes: Res extensa

Newton: Bodies (particles) Space Time

Faraday-Maxwell: Particles Fields Space Time

Special relativity: Particles Fields Spacetime

Quantum mechanics: Quantum-Fields Spacetime

General relativity: Covariant fields

Quantum gravity: Covariant Quantum fields

Matter, time and space: all aspects of a single entity