Current Quantum Gravity Theories, Experimental Evidence ... fileCurrent Quantum Gravity Theories, Experimental Evidence, Philosophical Implications carlo rovelli IHES 2017

Current Quantum Gravity Theories, Experimental Evidence,

Philosophical Implications

carlo rovelliIHES 2017

1. We have quantum gravity theories

2. We have have empirical evidence

3. There is some understanding on some issues of major philosophical relevance

i: nature of physical spaceii: nature of physical timeiii: relation between physical and experiential timeiv: connection between relational aspects of GR and QM

1. We do have quantum gravity theories

Many directions of investigation

loop quantum gravity, string theory, asymptotic safety, Hořava–Lifshitz theory, supergravity, AdS-CFT-like dualities twistor theory, causal set theory, entropic gravity, emergent gravity, non-commutative geometry, group field theory, Penrose nonlinear quantum dynamics causal dynamical triangulations, shape dynamics, ’t Hooft theory non-quantization of geometry …




Vastly different numbers of researchers involved



Most are highly incomplete






Several are only vaguely connected to the actual problem of quantum gravity



Several are related, boundaries are fluid








Many offer useful insights







A few offer rather completetentative theories of quantum gravity

Many offer useful insights



loop quantum gravity

string theory

Hořava–Lifshitz asymptotic safety

causal set theory

entropic gravity emergent

gravity

non-commutative geometry

twistor theory

supergravity

causal dynamical triangulations

shape dynamics

group field theoryAdS-CFT

dualities

’t Hooft theory

Penrose nonlinear quantum dynamics

Violation of QM non-quantized geometry

Several are related

Herman Verlinde at LOOP17 in Warsaw


string theory


causal set theory


gravity


twistor theory

supergravity


shape dynamics


dualities

’t Hooft theory


non-quantized geometry

No infinity in the small


string theory


causal set theory


gravity


twistor theory

supergravity


shape dynamics


dualities

’t Hooft theory



Infinity in the small



string theory


causal set theory


gravity


twistor theory

supergravity


shape dynamics


dualities

’t Hooft theory



Mostly still

classical




string theory


causal set theory


gravity


twistor theory

supergravity


shape dynamics


dualities

’t Hooft theory



Mostly still

classical



No major physical assumptions over GR&QM


string theory


causal set theory


gravity


twistor theory

supergravity


shape dynamics


dualities

’t Hooft theory



Mostly still

classical





string theory


causal set theory


gravity


twistor theory

supergravity


shape dynamics


dualities

’t Hooft theory


Supersymmetry High dimensions

Strings


Mostly still

classical





string theory


causal set theory


gravity


twistor theory

supergravity


shape dynamics


dualities

’t Hooft theory



Strings Lorentz Violation


Mostly still

classical





string theory


causal set theory


gravity


twistor theory

supergravity


shape dynamics


dualities

’t Hooft theory



Strings Lorentz Violation

Violation of QM non-quantized geometry

Discriminatory questions:

Is Lorentz symmetry violated at the Planck scale or not?

Are there physical degrees of freedom at any arbitrary small scale or not?Is Quantum Mechanics violated in the presence of gravity or not? Are there supersymmetric particles or not?

Lorentz violations at Planck scale

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

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 dynamics

No Yes No Yes No

Your favorite … … … … …

Is geometry discrete i the small?

2. We do have empirical evidence

Empirical evidence: 1: Lorentz invariance

Empirical evidence: 1: Lorentz invariance

Observation has already ruled out theories

Violation of Lorentz invariance → Renormalizability

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)

L L(β)

Lorentz invariance and quantum discreteness are compatible

L L(β)

Lorentz invariance and quantum discreteness are compatible

=> Geometry is quantum geometry

Empirical evidence: 2: Supersymmetry


Once again, no sign of supersymmetry


Once again, no sign of supersymmetry

Solution of QG using supersymmetry are under empirical stress


- Popper’s falsification: theories are either “OK” or “proved wrong”.

Karl Popper

A point about philosophy of science:


Karl Popper Bruno De Finetti

- Bayesian “confirmation”: we have “degrees of confidence” in theories; these are are lowered, of enhanced, by empirical (dis-)confirmation.


Not seeing a giraffe in the French Alps during a hike, does not prove that there are no giraffes in French Alps











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….







And we have now heard that supersymmetry is “going to be seen soon” for more than thirty years….





Solution of QG using supersymmetry are under empirical stress

Empirical evidence: 3: Lab experiments (future)

Analog systems

Planck scale effects in the lab

Quantum property of the metric

Empirical evidence: 3: Lab experiments

Violations of QM suggested by QG

Analog systems





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






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












Can falsify the hypothesis that the gravitational field is classical.



Is the metric a quantum entity?

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

Is the metric a quantum entity?

Can falsify the hypothesis that the 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 Spin 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 (future)

Empirical evidence: 4: The Sky

a) Early Universe:

b) Black holes:

“Quantum cosmology”

Disruption of the photon ring

Planck Stars

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!

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

- Wide quantum fluctuations of the metric

- Fluctuations of the causal structure allowing black hole to decay

- Boson condensate of low energy gravitons

Giddings

Haggard, Barrau, Vidotto, CR

Dvali

Small effects pile up over time




Giddings


Dvali





Giddings


Dvali



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

Exploding holes


Exploding holes

At MG2 and in a paper ’79-’81

Valeri Frolov

Grigori A. Vilkovisky (left)

Frolov, Vilkovinski ‘79Exploding holes


Valeri Frolov


In ’93

Cristopher R. Stephens

Gerard ’t Hooft

Bernard F. Whiting

Frolov, Vilkovinski ‘79

Stephen, t’Hooft, Whithing ‘93

Exploding holes

In ’05

Abhay Ashtekar

Martin Bojowald


Valeri Frolov


In ’93


Gerard ’t Hooft

Bernard F. Whiting



Ashtekar, Bojowald ’05

Exploding holes

In ’05

Abhay Ashtekar

Martin Bojowald


Valeri Frolov


In ’93


Gerard ’t Hooft

Bernard F. Whiting




Modesto ‘06

region 3

2

1

Figure 2: Penrose diagram for the gravitational collapse inside the event horizon (Region 1 and region2) 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].

2 Gravitational collapse in Ashtekar variables

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

2.1 Ashtekar variables

In LQG the fundamental variables are the Ashtekar variables: they consist of an SU(2) connectionAi

a and the electric field Eai , where a, b, c, · · · = 1, 2, 3 are tensorial indices on the spatial section and

i, j, k, · · · = 1, 2, 3 are indices in the su(2) algebra. The density weighted triad Eai is related to the

triad eia by the relation Ea

i = 12ϵ

abc ϵijk ejb ek

c . The metric is related to the triad by qab = eia ej

b δij .Equivalently,

!

det(q) qab = Eai Eb

j δij . (10)

The rest of the relation between the variables (Aia, Ea

i ) and the ADM variables (qab, Kab) is given by

Aia = Γi

a + γKabEbjδ

ij (11)

where γ is the Immirzi parameter and Γia is the spin connection of the triad, namely the solution of

Cartan’s equation: ∂[aeib] + ϵijk Γj

[aekb] = 0.

The action is

S =1

κ γ

"

dt

"

Σd3x

#

−2Tr(EaAa) − NH− NaHa − N iGi

$

, (12)

where Na is the shift vector, N is the lapse function and N i is the Lagrange multiplier for the Gaussconstraint Gi. We have introduced also the notation E[1] = Ea∂a = Ea

i τi∂a and A[1] = Aadxa =

Aiaτ

idxa. The functions H, Ha and Gi are respectively the Hamiltonian, diffeomorphism and Gauss

4

Exploding holes

In ’05

Abhay Ashtekar

Martin Bojowald


Valeri Frolov


In ’93


Gerard ’t Hooft

Bernard F. Whiting




Hayward ’06

Modesto ‘06

region 3

2

1










i = 12ϵ

abc ϵijk ejb ek



!

det(q) qab = Eai Eb

j δij . (10)



Aia = Γi

a + γKabEbjδ

ij (11)



[aekb] = 0.

The action is

S =1

κ γ

"

dt

"

Σd3x

#


$

, (12)



Aiaτ


4

Sean A. Hayward in ’06

[see M. Smerlak’s talk]

Exploding holes

In ’05

Abhay Ashtekar

Martin Bojowald


Valeri Frolov


In ’93


Gerard ’t Hooft

Bernard F. Whiting




Hayward ’06

Hajicek Kieffer ’01

Modesto ‘06

region 3

2

1










i = 12ϵ

abc ϵijk ejb ek



!

det(q) qab = Eai Eb

j δij . (10)



Aia = Γi

a + γKabEbjδ

ij (11)



[aekb] = 0.

The action is

S =1

κ γ

"

dt

"

Σd3x

#


$

, (12)



Aiaτ


4



Exploding holes

In ’05

Abhay Ashtekar

Martin Bojowald


Valeri Frolov


In ’93


Gerard ’t Hooft

Bernard F. Whiting




Hayward ’06

Hajicek Kieffer ’01

Haggard, Rovelli ’15

Modesto ‘06

region 3

2

1










i = 12ϵ

abc ϵijk ejb ek



!

det(q) qab = Eai Eb

j δij . (10)



Aia = Γi

a + γKabEbjδ

ij (11)



[aekb] = 0.

The action is

S =1

κ γ

"

dt

"

Σd3x

#


$

, (12)



Aiaτ


4



Exploding holes

�

hf =Y

v

hvfTransition amplitudes

Vertex amplitude

State space

Operators: where

l

n

n0

Kinematics

Dynam

ics

�

8⇡�~G = 1

H� = L2[SU(2)L/SU(2)N ]�

WC(hl) = NC

Z

SU(2)dhvf

Y

f

�(hf )Y

v

A(hvf )

spinfoam(vertices, edges, faces)

Cf

ev

hl3 (hl)

A(hvf ) =

Z

SL(2,C)dg0e

Y

f

X

j

(2j + 1) Djmn(hvf )D

�(j+1) jjmjn (geg

�1e0 )

spin network(nodes, links)

Bou

ndar

yB

ulk

H = lim�!1

H�

W = limC!1

WC

Covariant loop quantum gravity. Full definition.

Satisfies all “requirements” listed by Steve Carlip in the last talk

• Quantum theory (Hilbert space, operators, transition amplitudes)

• Classical limit: GR (Barrett’s theorems)

• UV qft divergences (Han and Fairbairn’s theorems)

• Minimum length (Spectral properties of operators)

• Black hole thermodynamics

“Spacetime region”

Boundary

A = W ( )

Boundary state

Amplitude

= in

⌦ out

A process and its amplitude �

hl Boundary state

Quantum system=

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


Boundary

A = W ( )

Boundary state

Amplitude

= in

⌦ out


hl Boundary state

Quantum system=

Spacetime region



Spacetime region

Particle detectors = field measurements

Distance and time measurements= gravitational field measurements


Boundary

A = W ( )

Boundary state

Amplitude

= in

⌦ out


hl Boundary state

Quantum system=

Spacetime region


Full expression for the transition amplitude:

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 , and V are represented in black, red, green, and blue, respectively. FRB 140514 has 21 ± 7% (3-�) circular polarisationaveraged over the pulse, and a 1-� upper limit on linear polarisation of L < 10%. On the leading edge of the pulse the circular polarisationis 42 ± 9% (5-�) of the total intensity. The data have been smoothed from an initial sampling of 64 µs using a Gaussian filter of full-widthhalf-maximum 90 µs.

source given the temporal proximity of the GMRT observa-tion and the FRB detection. The other two sources, GMRT2and GMRT3, correlated well with positions for known ra-dio sources in the NVSS catalog with consistent flux densi-ties. Subsequent observations were taken through the GMRTToO queue on 20 May, 3 June, and 8 June in the 325 MHz,1390 MHz, and 610 MHz bands, respectively. The secondepoch was largely unusable due to technical di�culties. Thesearch for variablility focused on monitoring each source forflux variations across observing epochs. All sources from thefirst epoch appeared in the third and fourth epochs with nomeasureable change in flux densities.

4.4 Swift X-Ray Telescope

The first observation of the FRB 140514 field was taken us-ing Swift XRT (Gehrels et al. 2004) only 8.5 hours after theFRB was discovered at Parkes. This was the fastest Swiftfollow-up ever undertaken for an FRB. 4 ks of XRT datawere taken in the first epoch, and a further 2 ks of datawere taken in a second epoch later that day, 23 hours af-ter FRB 140514, to search for short term variability. A finalepoch, 18 days later, was taken to search for long term vari-ability. Two X-ray sources were identified in the first epochof data within the 150 diameter of the Parkes beam. Bothsources were consistent with sources in the USNO catalog(Monet et al. 2003). The first source (XRT1) is located atRA = 22:34:41.49, Dec = -12:21:39.8 with RUSNO = 17.5and the second (XRT2) is located at RA = 22:34:02.33 Dec= -12:08:48.2 with RUSNO = 19.7. Both XRT1 and XRT2appeared in all subsequent epochs with no observable vari-ability on the level of 10% and 20% for XRT1 and XRT2,respectively, both calculated from photon counts from theXRT. Both sources were later found to be active galacticnuclei (AGN).

4.5 Gamma-Ray Burst Optical/Near-InfraredDetector

After 13 hours, a trigger was sent to the Gamma-Ray BurstOptical/Near-Infrared Detector (GROND) operating on the2.2-m MPI/ESO telescope on La Silla in Chile (Greiner et al.2008). GROND is able to observe simultaneously in J , H,and K near-infrared (NIR) bands with a 100 ⇥ 100 field ofview (FOV) and the optical g0, r0, i0, and z0 bands with a60 ⇥ 60 FOV. A 2⇥2 tiling observation was done, providing61% (JHK) and 22% (g0r0i0z0) coverage of the inner partof the FRB error circle. The first epoch began 16 hours af-ter FRB 140514 with 460 second exposures, and a secondepoch was taken 2.5 days after the FRB with an identicalobserving setup and 690 s (g0r0i0z0) and 720 s (JHK) ex-posures, respectively. Limiting magnitudes for J , H, and Kbands were 21.1, 20.4, and 18.4 in the first epoch and 21.1,20.5, and 18.6 in the second epoch, respectively (all in theAB system). Of all the objects in the field, analysis iden-tified three variable objects, all very close to the limitingmagnitude and varying on scales of 0.2 - 0.8 mag in the NIRbands identified with di↵erence imaging. Of the three ob-jects one is a galaxy, another is likely to be an AGN, andthe last is a main sequence star. Both XRT1 and GMRT1sources were also detected in the GROND infrared imagingbut were not observed to vary in the infrared bands on thetimescales probed.

4.6 Swope Telescope

An optical image of the FRB field was taken 16h51m afterthe burst event with the 1-m Swope Telescope at Las Cam-panas. The field was re-imaged with the Swope Telescope on17 May, 2 days after the FRB. No variable optical sources

c� 0000 RAS, MNRAS 000, 000–000

Primordial black holes!

Signature: distance/energy relation

�obs

⇠ 2Gm

c2(1 + z)

vuut H�10

6 k⌦ 1/2⇤

sinh�1

"✓⌦⇤

⌦M

◆1/2

(z + 1)�3/2

#

A real-time FRB 5







4.6 Swope Telescope


c� 0000 RAS, MNRAS 000, 000–000

A real-time FRB 5







4.6 Swope Telescope


c� 0000 RAS, MNRAS 000, 000–000

2 4 6 8 10z

l

2 4 6 8 10z

l

Fast Radio Bursts and White Hole Signals Aurélien Barrau, Carlo Rovelli, Francesca Vidotto.

http://inspirehep.net/author/profile/Rovelli%2C%20Carlo?recid=1316456&ln=en

Publications of the Astronomical Society of Australia (PASA)doi: 10.1017/pas.2017.xxx.

Fundamental Physics with the SKA: Dark Matter and

Astroparticles

K. Kelley1, S. Riemer-Sørensen2, E. Athanassoula3, C. Bœhm4,5, G. Bertone6, A. Bosma7, M.Brüggen8, C. Burigana9,10,11, F. Calore6,12, S. Camera13,14,15, J.A.R. Cembranos16, R.M.T.Connors17, Á. de la Cruz-Dombriz18,19, P.K.S Dunsby2, N. Fornengo13,14,15, D. Gaggero6, M.Méndez-Isla18,19, Y. Ma21,22,23, H. Padmanabhan24, A. Pourtsidou25, P.J. Quinn1, M. Regis13,14,M. Sahlén26, M. Sakellariadou27, L. Shao28, J. Silk29,30,31,32, T. Trombetti10,33,9, F. Vazza34,35, F.Vidotto36, F. Villaescusa-Navarro37, C. Weniger6 and L. Wolz381 International Centre for Radio Astronomy Research (ICRAR), University of Western Australia, Ken and Julie Michael Building, 7Fairway, Crawley, Western Australia 60092 Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo, Norway3 Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France4 Institute for Particle Physics Phenomenology, Durham University, South Road, Durham, DH1 3LE, United Kingdom5 LAPTH, U. de Savoie, CNRS, BP 110, 74941 Annecy-Le-Vieux, France6 GRAPPA, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands7 Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France8 University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany9 INAF, Istituto di Radioastronomia, Via Piero Gobetti 101, I-40129 Bologna, Italy10 Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via Giuseppe Saragat 1, I-44122 Ferrara, Italy11 Istituto Nazionale di Fisica Nucleare, Sezione di Bologna,Via Irnerio 46, I-40126 Bologna, Italy12 LAPTh, CNRS, 9 Chemin de Bellevue, BP-110, Annecy-le-Vieux, 74941, Annecy Cedex, France13 Dipartimento di Fisica, Università degli Studi di Torino, Via P. Giuria 1, 10125 Torino, Italy14 INFN, Istituto Nazionale di Fisica Nucleare, Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy15 INAF, Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Torino, Strada Osservatorio 20, 10025 Pino Torinese, Italy16 Departamento de FÃ�sica TeÃ�rica I, Universidad Complutense de Madrid, E20840 Spain17 API, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands18 Cosmology and Gravity Group, University of Cape Town, 7701 Rondebosch, Cape Town, South Africa19 Department of Mathematics and Applied Mathematics, University of Cape Town, 7701 Rondebosch, Cape Town, South Africa20 South African Astronomical Observatory, Observatory 7925, Cape Town, South Africa21 School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Private Bag X54001, Durban, 4000, South Africa22 NAOC-UKZN Computational Astrophysics Centre (NUCAC), University of KwaZulu-Natal, Durban, 4000 South Africa23 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China24 ETH Zurich, Wolfgana-Pauli-Strasse 27, CH8093 Zurich, Switzerland25 Institute of Cosmology & Gravitation, University of Portsmouth, Burnaby Road, Portsmouth, PO1 3FX, United Kingdom26 Department of Physics and Astronomy, Uppsala University, SE-751 20 Uppsala, Sweden27 Theoretical Particle Physics and Cosmology group, Physics Department, King’s College London, University of London, Strand,London WC2R 2LS, UK28 Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Mühlenberg 1, Potsdam 14476, Germany29 Institut d’Astrophysique, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis Blvd Arago, 75014 Paris, France30 AIM-Paris-Saclay, CEA/DSM/IRFU, CNRS, Univ Paris 7, F-91191, Gif-sur-Yvette, France31 Department of Physics and Astronomy, The John Hopkins University, Homewood Campus, Baltimore MD 21218, USA32 Beecroft Institute of Particle Astrophysics and Cosmology, Department of Physics, University of Oxford, Oxford OX1 3RH, UK33 Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara, Via Giuseppe Saragat 1, I-44122 Ferrara, Italy34 University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany35 Istituto di Radio Astronomia, INAF, Via Gobetti 101, 40122, Italy36 Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, P.O. Box 9010, 6500 GL Nijmegen, TheNetherlands37 Center for Computational Astrophysics, Flatiron Institute, 162 5th Avenue, New York, NY, 10010, USA38 Department of Physics, University of Melbourne, Parkville, 3010, Victoria, Australia

AbstractWhile not purpose built for dark matter (DM) observations, the Square Kilometer Array (SKA) canprovide crucial observations that might reveal the nature and identify of DM. Even if it does notdetect the DM directly, the observations can provide significant insight into DM properties as well asbackground sources, helping to constrain DM parameter space and disentangle it from astrophysicalsignals. This technological improvement o�ers the opportunity for astrophysical observations to make asignificant contribution in other areas of physics, most notably particle or high-energy physics.

There are several areas where the SKA observations are expected to contribute to the identificationor exclusion of DM particle candidates. The interaction of baryons with magnetic fields can potentiallylead to direct observations of filaments, where a significant portion of the baryons are thought to beâ��hiding". This will also allow for unique studies of the origin of magnetic fields in cosmologicalstructures such as galaxy clusters and filaments, and the production of high-energy cosmic rays providinga leap in our understanding of plasma physics and magneto hydrodynamics. If the astrophysical scenariocan be well enough understood, free-free emission can be used to test DM properties via their e�ect onthe HI power spectrum at small scales, or via synchrotron emission from annihilation products.

Whether the DM is a WIMP, any other particle type, or can be explained by primordial black holesor modifications of gravity, the SKA has the capability to provide groundbreaking new insights into itsnature.

Keywords: keyword1 – keyword2 – keyword3 – keyword4 – keyword5

1

24

Figure 20. Radio sources above the SKA1-MID point sourcesensitivity, for 1000h of data taking, if PBHs are ≥ 1% of the DM.

detectors currently in upgrade of development phase),an exciting set of complementary observations will helpto characterize the presence of compact objects both inour Galaxy and in the early Universe, and eventuallyshed light on the nature of the DM in the universe.

3.9.2 PBHs and Quantum GravityTo date the search for PBHs and for constraints on PBHshas mostly considered an almost monochromatic massspectrum, and the presence of Hawking evaporation forPBHs of small mass. Monochromatic mass spectrum hasbeen challenged by di�erent authors as unrealistic (forexample Carr et al. (2017a)). An extended mass functionis compatible with di�erent PBHs formation mechanics,from critical collapse to cosmic strings. Hawking evapo-ration is a phenomenon that becomes relevant on a timescale that depends on the mass of the BH. Its time scaleis M3

BH in Planck units. This implies that within theage of the universe only PBHs with mass smaller than1012 kg could have evaporated, and possibly producedvery high-energy cosmic rays (Barrau, 2000). As cosmicrays of such energies are rare, constraints are derived onthe very-small-mass end of the PBH mass spectrum.

Hawking evaporation, however, is a phenomenon pre-dicted in the context of quantum field theory on a fixedcurved background. This is a theory with a regime ofvalidity that may likely break down when approximatelyhalf of the mass of the hole has evaporated, as indicatedfor instance by the ‘firewall’ no-go theorem (Almheiriet al., 2013). The geometry around a BH can indeedundergo quantum fluctuations on a time scale shorterthan M3

BH , when the e�ects of the Hawking evaporationhave not not yet significantly modified the size of thehole. As any classical system, the hole has a charac-teristic timescale after which the the departure from

the classical evolution becomes important as quantume�ects manifest. This time can be much shorter than theHawking evaporation time M3

BH, as short as M2BH. this

is the minimal time after which quantum fluctuationsof the metric can appear in the region outside the BHhorizon. In fact, the presence of a small curvature pro-portional to M≠2

BH near the horizon allows us to definethe ‘quantum break-time’ as the inverse of this quan-tity, that is M2

BH (Haggard & Rovelli, 2014, 2016). Assoon as these quantum fluctuations of the geometry takeplace, the dynamics of the horizon can undergo dramaticbehaviours, to the point of the very disappearance ofthe horizon, possibly by an explosion.

Di�erent approaches to quantum gravity converge inpointing out the possibility of instabilities of quantum-gravitational origin that can manifest in an explo-sive event in a timescale shorter than the evapora-tion time [(Gregory & Laflamme, 1993; Casadio &Harms, 2001, 2000; Kol & Sorkin, 2004; Emparan et al.,2003)]. In particular, Loop Quantum Gravity has re-cently provided a framework to compute explicitly thistime (Christodoulou et al., 2016). Loop Quantum Grav-ity removes the classical curvature singularities (Rovelli& Vidotto, 2013; Ashtekar & Bojowald, 2006; Corichi &Singh, 2016), such as the one at the BH center, becauseof quantum spacetime discreteness. The consequencesof this discreteness on the dynamics can be modeledat the e�ective level by an e�ective potential that pre-vents the gravitational collapse from forming the sin-gularity and triggers a bounce. The bounce connectsa collapsing solution of the Einstein equation, that isthe classical black hole, to an explosive expanding one,a white hole (Haggard & Rovelli, 2014), through anintermediate quantum region. This process is a typicalquantum tunnelling event, and the characteristic timeat which it takes place, the hole lifetime, can be as adecaying time, similar to the lifetime of conventionalnuclear radioactivity. The resulting picture is conserva-tive in comparison to other models of non-singular BHs.The collapse still produces a horizon, but it is now adynamical horizon with a finite lifetime, rather then aperpetual event horizon. The collapsing matter contin-ues its fall after entering the trapping region, forming avery dense object whose further collapse is prevented byquantum pressure (referred to with the suggesting nameof Planck Star Rovelli & Vidotto (2014)).

The collapsing matter that forms PBHs in the radia-tion dominated epoch is mainly constituted by photons.Seen from the center of the hole, those photons col-lapse through the trapping region, then expands passingthrough an anti-trapping region and eventually exitsthe white-hole horizon, always at the speed of light, theprocess is thus extremely fast. On the other hand, for anobserver sitting outside the horizon, a huge but finite red-shift stretches this time to cosmological times. This time,properly called the hole lifetime, as discussed before has

26

value of the lifetime. Using Equation 19 we canindeed compute the mass of BHs whose lifetimeis the Hubble time, yielding an explosion today.For a lifetime in the lower end of the viable win-dow, the Schwarzschild radius is of the order ofRBH ≥ 0.2mm and the observational depth allowsus to detect events in all the visible Universe.

For the highest values of Ÿ, the signal is emitted withenergy in the GeV, but a study of the photon emissionwith the code PHYTIA indicates that the photons withhigher density, therefore more likely to be detected,are those in the MeV (?). Some Short Gamma RayBursts (Nakar, 2007), whose source is still unclear, arepossible candidates in this range.

For the lowest values of Ÿ, the peak of the signal isin the millimetres. The corresponding frequencies arebeyond the sensitivity of SKA-mid. On the other hand,in a decay we expect a probability distribution of theevent to happen, and therefore there could be some eventhappening within SKA-mid frequency range. Further-more, the details of the decay mechanism are not fullyestablished, leaving open the possibility of the presenceof some factors that could shift the wavelength possiblyby 1-2 orders of magnitude. This makes it worthwhile toexplore for transients at the highest frequencies acces-sible to SKA-mid. In particular, it has been suggestedthat the quantum-gravitational BH explosion may belinked to FRBs (?). A number of hints seems to supportthis conjecture, such as the rapid impulse, of mostlyextra-Galactic origin, the enormous energy flux as theBH converts e�ciently its mass into radiation.

PBHs exploding in a quantum decay present a uniquefeature that makes them distinguishable from other as-trophysical sources. The time at which the decay hap-pens is a function of the BH mass. Therefore, smallerPBHs explode earlier, that is at a distance from us.The signal they produce also depends on their mass,the smaller the BH, the shorter the wavelength in boththe high and low energy channels. Signals from distantsources get redshifted, partially compensating for theshorter wavelength due to a smaller mass.

Generic astrophysical objects have an observed wave-length that scale linearly with the distance. On the otherhand, Hawking evaporation ends in the standard theorywhen BHs, of any initial mass, reach the Planck sizeand produce a signal with such wavelength. The phe-nomenon described above gives a completely di�erente�ect, the modified relation between wavelength and red-shift (Barrau et al., 2014) represented by the flattenedcurve (Figure 21). Observation of a burst whose sourcehas a known distance will allow us to see whether datafits such a curve. If so, it would represent a signature ofthe quantum-gravitational nature of BHs.

An exact localisation of burst sources could provedi�cult. This involves the dispersion measure of the

2 4 6 8 10z

l

Figure 21. The expected wavelength (unspecified units) of thesignal from black hole explosions as a function of the redshiftz. The curve flattens at large distance: the shorter wavelengthfrom smaller black holes exploding earlier get compensated by theredshift.

received signal, and possibly the source being hostedin a known astronomical object, for instance a galaxy.A further technique is available, and it is peculiar ofdecaying PBHs. BHs exploding far away are less massive,with a lower flux of energy (Kavic, 2017), the flux ofenergy of the measured burst lessens with distance.

The peculiar wavelength-redshift relation can beproven also without the knowledge of the distance of thesource, by studying the radiation integrated over thedetectable past explosions. SKA HI intensity mappingcan therefore provide the desired data in this respect.Studies of the integrated emission from PBH decay hasbeen started in (Barrau et al., 2016) for a large rangeof the Ÿ parameter in the PBH lifetime. The signal hasbeen obtained using the PYTHIA code (Sjöstrand et al.,2015), which for a given initial energy computes the par-ticle production for the process. The resulting radiationis not thermal, but it carries a distortion due to the char-acteristic redshift-wavelength relation of Figure 21. Thisappears for both the high energy and the low energychannel, as can be seen in Figure 22 for the case of theshortest lifetime. In principle the result depends on thePBH mass spectrum, but di�erent hypothesis for themass spectrum have been tested showing that the resulthas only a very weak dependence [(Barrau et al., 2016)].

Finally, in the presence of the ionized ISM, decay-ing PBHs can produce a radio pulse of the order of≥ 1GHz (Rees, 1977; Blandford, 1977). This frequencyis fully within the sensitivity of SKA-mid. Furthermore,it is interestingly close to that of an FRB. The emissionmechanism, in this case, relies on the presence of a shellof relativistic charged particles produced in the explo-sion. The shell behaves as a superconductor that expelsthe interstellar magnetic field from a spherical volumecentered in the original BH sites. The resulting signal iseasier to detect than the direct emission from the explo-sion, and can be used to constrain PBH (Cutchin et al.,

DM and Astroparticles 27

k=0.05 direct decayed

direct+decayed enlarged

Figure 22. The di�use emission of the low energy channel, andbelow the di�use emission of the high energy channel. We show herethe ones for the shortest BH lifetime, i.e. the lowest Ÿ parameter.The units in the ordinate axis are not specified: the normalisationof the spectrum depends on the percentage of PBHs as DM.

2016). More details about the mechanism for decayingBHs will appear in a forthcoming paper (?).

4 ASTROPARTICLES

In this section we discuss how SKA can provide tests onthe fundamental assumptions behind the very success-ful standard model of particle physics (Section 4.3) butalso well-motivated extensions such as neutrino masses(Section 4.1-4.2) and string theory 4.4. We also con-sider the problem of cosmic ray acceleration in magneticfields, and how the SKA can improve the relatively littleknowledge we have about magnetic fields (Section 4.5).

4.1 Constraining the Neutrino Mass

Determining the sum of the neutrino masses and theirhierarchy is one of the most important tasks of modernphysics. Unfortunately, setting upper bounds from lab-oratory experiments is very challenging. It is expectedthat in the near future katrin

17 will set an upper limitof M‹ =

qi m‹i < 0.6 eV. A di�erent way to determine

the sum of the neutrino masses is through cosmologicalobservables. The origin of this is the fact that neutrinoshave very large thermal velocities, in contrast with theassumed negligible ones for CDM. This produces a clear

17https://www.katrin.kit.edu

neutrino signature in many cosmological observables,and in particular, a suppression of power on small scalesin the matter power spectrum. Understanding and mea-suring this e�ect is also important for dark energy andgeneral relativity tests, as models of modified gravityor interacting DM/energy also lead to modifications ofsmall scales power (see e.g. Wright et al., 2017).

Current constraints on the sum of the neutrino masses,arising by combining data from the CMB, galaxy clus-tering and/or the Lyman-– forest, are M‹ . 0.12 eV(Riemer-Sørensen et al., 2014; Palanque-Delabrouilleet al., 2015; Cuesta et al., 2016; Vagnozzi et al., 2017).One would naively expect that those constraints wouldimprove by using galaxy clustering at higher redshifts,since the available volume is much larger and the non-linear clustering e�ects are weaker. Also the e�ects ofdark energy will be smaller at higher redshift.

The possibility of using high-redshift optical galaxysurveys (combined with CMB data, in order to lift param-eter degeneracies) to provide precision measurements ofthe neutrino masses is not new (see for example (Takadaet al., 2006)). High-z advantages include accessing alarger comoving volume for a given survey area, and awider range of scales in the linear or quasi-linear regime.However, the detection of galaxies at high redshifts be-comes more di�cult and expensive, and shot noise e�ectsmay dominate. In (Takada et al., 2006), a space-basedgalaxy survey with a 300 deg2 sky coverage at redshifts3.5 < z < 6.5 (assuming a very large number densityand bias of the galaxy tracers) was found to be able tomeasure the neutrino mass with ‡(m‹, tot) = 0.025eVcombined with CMB data.

Another possibility is to map the large scale structureof the Universe through 21cm intensity mapping (seeSection 2.1.1). Given the fact that neutrinos modify theabundance of halos (Castorina et al., 2014; Costanziet al., 2013), their clustering (Villaescusa-Navarro et al.,2014; Castorina et al., 2014) and also the internal haloproperties such as concentration (Villaescusa-Navarroet al., 2013), it is expected that they will also leave asignature on the abundance and spatial distribution ofcosmic HI in the post-reionization era. This has been ex-plicitly checked by means of hydrodynamical simulationsby Villaescusa-Navarro et al. (2015). The authors claimthat the key point to understand the impact of neutrinomasses on the abundance and clustering properties ofHI is the fact that halos of the same mass have verysimilar HI content, independently of the sum of the neu-trino masses. The results show that in cosmologies withmassive neutrinos the abundance of cosmic HI will besuppressed with respect to the equivalent massless neu-trino model. At the same time, the presence of massiveneutrinos will make the HI more clustered.

Villaescusa-Navarro et al. (2015) investigated the con-straints that intensity mapping observations using SKA1can place on the sum of the neutrino masses. They con-

Publications of the Astronomical Society of Australia (PASA)doi: 10.1017/pas.2017.xxx.

Fundamental Physics with the SKA: Dark Matter and

Astroparticles

K. Kelley1, S. Riemer-Sørensen2, E. Athanassoula3, C. Bœhm4,5, G. Bertone6, A. Bosma7, M.Brüggen8, C. Burigana9,10,11, F. Calore6,12, S. Camera13,14,15, J.A.R. Cembranos16, R.M.T.Connors17, Á. de la Cruz-Dombriz18,19, P.K.S Dunsby2, N. Fornengo13,14,15, D. Gaggero6, M.Méndez-Isla18,19, Y. Ma21,22,23, H. Padmanabhan24, A. Pourtsidou25, P.J. Quinn1, M. Regis13,14,M. Sahlén26, M. Sakellariadou27, L. Shao28, J. Silk29,30,31,32, T. Trombetti10,33,9, F. Vazza34,35, F.Vidotto36, F. Villaescusa-Navarro37, C. Weniger6 and L. Wolz381 International Centre for Radio Astronomy Research (ICRAR), University of Western Australia, Ken and Julie Michael Building, 7Fairway, Crawley, Western Australia 60092 Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo, Norway3 Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France4 Institute for Particle Physics Phenomenology, Durham University, South Road, Durham, DH1 3LE, United Kingdom5 LAPTH, U. de Savoie, CNRS, BP 110, 74941 Annecy-Le-Vieux, France6 GRAPPA, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands7 Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France8 University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany9 INAF, Istituto di Radioastronomia, Via Piero Gobetti 101, I-40129 Bologna, Italy10 Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via Giuseppe Saragat 1, I-44122 Ferrara, Italy11 Istituto Nazionale di Fisica Nucleare, Sezione di Bologna,Via Irnerio 46, I-40126 Bologna, Italy12 LAPTh, CNRS, 9 Chemin de Bellevue, BP-110, Annecy-le-Vieux, 74941, Annecy Cedex, France13 Dipartimento di Fisica, Università degli Studi di Torino, Via P. Giuria 1, 10125 Torino, Italy14 INFN, Istituto Nazionale di Fisica Nucleare, Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy15 INAF, Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Torino, Strada Osservatorio 20, 10025 Pino Torinese, Italy16 Departamento de FÃ�sica TeÃ�rica I, Universidad Complutense de Madrid, E20840 Spain17 API, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands18 Cosmology and Gravity Group, University of Cape Town, 7701 Rondebosch, Cape Town, South Africa19 Department of Mathematics and Applied Mathematics, University of Cape Town, 7701 Rondebosch, Cape Town, South Africa20 South African Astronomical Observatory, Observatory 7925, Cape Town, South Africa21 School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Private Bag X54001, Durban, 4000, South Africa22 NAOC-UKZN Computational Astrophysics Centre (NUCAC), University of KwaZulu-Natal, Durban, 4000 South Africa23 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China24 ETH Zurich, Wolfgana-Pauli-Strasse 27, CH8093 Zurich, Switzerland25 Institute of Cosmology & Gravitation, University of Portsmouth, Burnaby Road, Portsmouth, PO1 3FX, United Kingdom26 Department of Physics and Astronomy, Uppsala University, SE-751 20 Uppsala, Sweden27 Theoretical Particle Physics and Cosmology group, Physics Department, King’s College London, University of London, Strand,London WC2R 2LS, UK28 Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Mühlenberg 1, Potsdam 14476, Germany29 Institut d’Astrophysique, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis Blvd Arago, 75014 Paris, France30 AIM-Paris-Saclay, CEA/DSM/IRFU, CNRS, Univ Paris 7, F-91191, Gif-sur-Yvette, France31 Department of Physics and Astronomy, The John Hopkins University, Homewood Campus, Baltimore MD 21218, USA32 Beecroft Institute of Particle Astrophysics and Cosmology, Department of Physics, University of Oxford, Oxford OX1 3RH, UK33 Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara, Via Giuseppe Saragat 1, I-44122 Ferrara, Italy34 University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany35 Istituto di Radio Astronomia, INAF, Via Gobetti 101, 40122, Italy36 Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, P.O. Box 9010, 6500 GL Nijmegen, TheNetherlands37 Center for Computational Astrophysics, Flatiron Institute, 162 5th Avenue, New York, NY, 10010, USA38 Department of Physics, University of Melbourne, Parkville, 3010, Victoria, Australia

AbstractWhile not purpose built for dark matter (DM) observations, the Square Kilometer Array (SKA) canprovide crucial observations that might reveal the nature and identify of DM. Even if it does notdetect the DM directly, the observations can provide significant insight into DM properties as well asbackground sources, helping to constrain DM parameter space and disentangle it from astrophysicalsignals. This technological improvement o�ers the opportunity for astrophysical observations to make asignificant contribution in other areas of physics, most notably particle or high-energy physics.

There are several areas where the SKA observations are expected to contribute to the identificationor exclusion of DM particle candidates. The interaction of baryons with magnetic fields can potentiallylead to direct observations of filaments, where a significant portion of the baryons are thought to beâ��hiding". This will also allow for unique studies of the origin of magnetic fields in cosmologicalstructures such as galaxy clusters and filaments, and the production of high-energy cosmic rays providinga leap in our understanding of plasma physics and magneto hydrodynamics. If the astrophysical scenariocan be well enough understood, free-free emission can be used to test DM properties via their e�ect onthe HI power spectrum at small scales, or via synchrotron emission from annihilation products.

Whether the DM is a WIMP, any other particle type, or can be explained by primordial black holesor modifications of gravity, the SKA has the capability to provide groundbreaking new insights into itsnature.

Keywords: keyword1 – keyword2 – keyword3 – keyword4 – keyword5

1

Quantum Gravity observations are not absurd anymore.

- Decrease the Bayesian confidence of some current theories (absence of supersymmetry at energy where it was expected)

- Already rules out theories (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.)

Progress has happened along some research directions

Strings

Loops

Empirical success Empirical failure Theoretical success Theoretical failure Key open issue

Strings None Low-energy supersymmetry

AdS-CFTNon-fundamental

appliacationsStandard model

parameters Lack of predictivity

Loops None Low energy limit Infinite graph limit

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

Asymptotic savety None Increase evidence of fixed point Computing amplitudes

Your favorite … … … … …

Loops open problems in the late 80’


• Definition of the Hilbert space

• Mathematical foundation

• Coupling matter

• Recovering low energy GR

• Problem of time

• Observables

• Application to early universe

• Produce verifiable physical predictions




• Coupling matter


• Problem of time

• Observables






• Coupling matter


• Problem of time

• Observables






• Coupling matter


• Problem of time

• Observables






• Coupling matter


• Problem of time

• Observables






• Coupling matter


• Problem of time

• Observables






• Coupling matter


• Problem of time

• Observables






• Coupling matter


• Problem of time

• Observables






• Coupling matter


• Problem of time

• Observables



Strings open problems in the late 80’




• Coupling matter


• Problem of time

• Observables





• Finding a fundamental formulation of the theory

• Deriving SU(3)xSU(2)xU(1) from first principles

• Computing the parameters of the standard model

• Supersymmetry breaking

• Compactification

• Extend to the non-perturbative regime

• Produce tentative verifiable physical predictions



• Coupling matter


• Problem of time

• Observables














• Coupling matter


• Problem of time

• Observables














• Coupling matter


• Problem of time

• Observables














• Coupling matter


• Problem of time

• Observables














• Coupling matter


• Problem of time

• Observables














• Coupling matter


• Problem of time

• Observables














• Coupling matter


• Problem of time

• Observables














• Coupling matter


• Problem of time

• Observables














• Coupling matter


• Problem of time

• Observables



3. There is some convergence on some issues of major philosophical relevance

i: nature of physical spaceii: nature of physical timeiii: relation between physical and experiential timeiv: connection between relational aspects of GR and QM

i: nature of physical space

space

relation entity

AristotleDescartes Newton

Space is an entity independent from its content

Aristotle : Substance

Descartes: Res extensa




Newton: Time Space Particles



Faraday-Maxwell: Fields Particles




Einstein 05: Spacetime






Einstein 15: Covariant Fields








Quanta: Quantum fields







Quanta: Quantum fields


Quantum gravity: Covariant quantum fields

→

→

Quantum electromagnetic field: quanta of light

Quantum gravitational space: quanta of space

→“Emergence”

physical space is granular

→vn

jl

Space has a granular structure: spin networks

�

hf =Y

v


Vertex amplitude

State space

Operators: where

l

n

n0

Kinematics

Dynam

ics

�

8⇡�~G = 1

H� = L2[SU(2)L/SU(2)N ]�

WC(hl) = NC

Z

SU(2)dhvf

Y

f

�(hf )Y

v

A(hvf )


Cf

ev

hl3 (hl)

A(hvf ) =

Z

SL(2,C)dg0e

Y

f

X

j


�(j+1) jjmjn (geg

�1e0 )


Bou

ndar

yB

ulk

H = lim�!1

H�

W = limC!1

WC


ii: nature of physical time

�

hf =Y

v


Vertex amplitude

State space

Operators: where

l

n

n0

Kinematics

Dynam

ics

�

8⇡�~G = 1

H� = L2[SU(2)L/SU(2)N ]�

WC(hl) = NC

Z

SU(2)dhvf

Y

f

�(hf )Y

v

A(hvf )


Cf

ev

hl3 (hl)

A(hvf ) =

Z

SL(2,C)dg0e

Y

f

X

j


�(j+1) jjmjn (geg

�1e0 )


Bou

ndar

yB

ulk

H = lim�!1

H�

W = limC!1

WC


Doctors

Galileo

Time: t

What we observe: A, B, ...

Newton: A(t), B(t), ...

But we actually only see: A(B), B(A) ....

→ the world can be described without t

A

B

At the elementary level Nature is not organized in terms of evolution in time.

iii: relation between physical and experiential time

“Experiential Time” is a complex layer of structures and properties which appear (emerge) at different level of approximations and descriptions of the world:

Internal flow: Diff invariant qft

Flow and energy: Statistical mechanics:

(Perspectival?) low past entropy:

Replicating systems with memory:

Brain’s memory and anticipation “Sense of flowing time”, identity as narration

Connes’s flow of the vonN. algebra

Thermal time (Tomita flow)

Orientation -> traces

Biology and evolution

Unicity, present:

D. Buonomano, Your Brain is a Time Machine: The Neuroscience and Physics of Time, Norton, New York, 2017.

Connes, A. & Rovelli, C. Von Neumann algebra automorphisms and time thermodynamics relation in general covariant quantum theories. Class.Quant. Grav. 11, 2899–2918 (1994).

Price, H. Time’s Arrow. (Oxford University Press, 1996).Rovelli, C. Is Time’s Arrow Perspectival? 6 (2015).

Non-relativistic limit

Moral:

do not search in elementary physics what is not

in elementary physics

iv: connection between relational aspects of GR and QM


Boundary

A = W ( )

Boundary state

Amplitude

= in

⌦ out


hl Boundary state

Quantum system=

Spacetime region




Boundary

A = W ( )

Boundary state

Amplitude

= in

⌦ out


hl Boundary state

Quantum system=

Spacetime region



Spacetime region

Particle detectors = field measurements

Distance and time measurements= gravitational field measurements


Boundary

A = W ( )

Boundary state

Amplitude

= in

⌦ out


hl Boundary state

Quantum system=

Spacetime region


GR: localization of a system is relative to other systems

QM: events for system isare relative to other systems


Boundary

Understand the world as a net of system influencing one another

1. We do have quantum gravity theories

2. We do have have some empirical evidence

3. Results towards issues of philosophical relevance

i: nature of physical space

ii: nature of physical time

iii: relation between physical and experiential time

(We do not know which is right)

(Rule out and/or disfavour some theories, but no positive support yet)

(“material”, discrete)

(absent at the fundamental level)

(Time is a multilayer concept, Experiencial time is understood in terms of theormodynamics, biology, brain sciences.)

iv: connection between relational aspects of GR and QM (Understand the world as a net of system influencing one another.)

Documents

Current Quantum Gravity Theories, Experimental Evidence ... fileCurrent Quantum Gravity Theories, Experimental Evidence, Philosophical Implications carlo rovelli IHES 2017