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BEGIN:VEVENT
SUMMARY:Introduction
DTSTART;VALUE=DATE-TIME:20190924T153000Z
DTEND;VALUE=DATE-TIME:20190924T154000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5819@indico.ict.inaf.it
DESCRIPTION:Speakers: Mariateresa Crosta (Istituto Nazionale di Astrofisic
a (INAF))\nhttps://indico.ict.inaf.it/event/751/contributions/5819/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5819/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Screening of "Time Bandits"\, original version
DTSTART;VALUE=DATE-TIME:20190923T190000Z
DTEND;VALUE=DATE-TIME:20190923T210000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5927@indico.ict.inaf.it
DESCRIPTION:https://indico.ict.inaf.it/event/751/contributions/5927/
LOCATION:Sala Soldati\, Cinema Massimo
URL:https://indico.ict.inaf.it/event/751/contributions/5927/
END:VEVENT
BEGIN:VEVENT
SUMMARY:introductory round table
DTSTART;VALUE=DATE-TIME:20190923T183000Z
DTEND;VALUE=DATE-TIME:20190923T190000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5880@indico.ict.inaf.it
DESCRIPTION:Speakers: Stefano Liberati (SISSA)\, Lorenzo Maccone (Univ. de
gli Studi di Pavia)\, Mariateresa Crosta (Istituto Nazionale di Astrofisic
a (INAF))\nProf. Stefano Liberati (SISSA) and Prof. Lorenzo Maccone (Univ
. Pavia)\; \n\nModerators: Mariateresa Crosta (INAF-OATo)\n\nhttps://indic
o.ict.inaf.it/event/751/contributions/5880/
LOCATION:Sala Soldati\, Cinema Massimo
URL:https://indico.ict.inaf.it/event/751/contributions/5880/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Interrelations between local correlations\, nonlocal correlations
and causality
DTSTART;VALUE=DATE-TIME:20190923T142500Z
DTEND;VALUE=DATE-TIME:20190923T150500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5221@indico.ict.inaf.it
DESCRIPTION:Speakers: Eliahu Cohen (Faculty of Engineering\, Bar Ilan Uni
versity)\nThe set of quantum mechanical nonlocal correlations is unique an
d intriguing in many ways. Characterizing this set is expected to cast lig
ht on the fundamental physical principles governing quantum theory\, those
from which the mathematical structure of the theory arises. Recently\, we
have shown ([A. Carmi and E. Cohen\, Sci. Adv. eaav8370 (2019)] and follo
wup works) that this set may largely be derived from the requirement that
uncertainty relations\, broadly understood\, are local in the sense of bei
ng independent of the choices made by other parties. Relativistic independ
ence\, as we have named this condition\, treats nonlocal correlations and
uncertainty relations on an equal footing. Furthermore\, it implies that q
uantum mechanics can be as nonlocal as it is without violating relativisti
c causality thanks to the existence of intrinsic uncertainty.\nThe notion
of relativistic independence can be also encoded in a new kind of nonlocal
hidden variables we term "pseudolocal". We have shown that different kind
s of quantum hidden variables lead to backwards in time signaling if known
[A. Carmi\, E. Cohen\, L. Maccone\, and H. Nikolic\, arXiv:1903.01349].\n
In this talk we shall briefly present these previous works and then build
upon them to show how this view gives rise to causal structures. We will d
emonstrate how such a causal structure tightens the bounds on the set of n
onlocal correlations in any physical theory as the number of experimenters
\, measuring devices and incorporated statistical moments increases. Final
ly\, we will connect the failure of counterfactual definiteness with time-
irreversibility and discuss a sense in which entanglement gives rise to th
e arrow of time.\n\nhttps://indico.ict.inaf.it/event/751/contributions/522
1/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5221/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Entangled histories\, the two-state-vector and the pseudo-de
nsity formalisms: Towards a better understanding of quantum temporal corre
lations.
DTSTART;VALUE=DATE-TIME:20190923T134000Z
DTEND;VALUE=DATE-TIME:20190923T140000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5049@indico.ict.inaf.it
DESCRIPTION:Speakers: Marcin Nowakowski (Department of Theoretical Physics
and Quantum Information\, Gdansk University of Technology )\nThe two-stat
e-vector formalism\, the entangled histories and the pseudo-density formal
isms are attempts to better understand quantum correlations in time. These
formalisms share some similarities\, but they are not identical\, having
subtle differences in their interpretation and manipulation of quantum tem
poral structures [1\, 2]. I will show\, for instance\, that they treat ope
rators and states on equal footing\, leading to the same statistics for al
l measurements. I will discuss the topic of quantum correlations in time a
nd show how they can be generated and analysed in a consistent way using t
hese formalisms. I will also elaborate on an unconventional behaviour of t
emporal monogamic structures and quantum histories of evolving multipartit
e systems which do not exhibit global nonlocal correlations in time but ne
vertheless can lead to entangled reduced histories characterizing evolutio
n of an arbitrarily chosen subsystem.\n\n\n[1] M. Nowakowski\, E. Cohen\,
P. Horodecki\, Entangled Histories vs. the Two-State-Vector Formalism -Tow
ards a Better Understanding of Quantum Temporal Correlations\, Phys. Rev.
A 98\, 032312 (2018).\n[2] M. Nowakowski\, Quantum Entanglement in Time\,
AIP Conference Proceedings 1841\, 020007 (2017).\n\nhttps://indico.ict.ina
f.it/event/751/contributions/5049/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5049/
END:VEVENT
BEGIN:VEVENT
SUMMARY:On the unique evolution of solutions to wave equations
DTSTART;VALUE=DATE-TIME:20190924T074500Z
DTEND;VALUE=DATE-TIME:20190924T082000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5042@indico.ict.inaf.it
DESCRIPTION:Speakers: Jan Sbierski ()\nThe well-known theorem of Choquet-B
ruhat and Geroch states that for given smooth initial data for the Einstei
n equations there exists a unique maximal globally hyperbolic development.
In particular\, the time-evolution of globally hyperbolic solutions is un
ique. This talk investigates whether the same results hold for quasilinear
wave equations defined on a fixed background. We first present an example
of a quasilinear wave equation for which unique evolution of smooth globa
lly hyperbolic solutions in fact fails and contrast this case with the Ein
stein equations. We then proceed by presenting conditions which guarantee
unique evolution. This talk is based on joint work with Felicity Eperon an
d Harvey Reall.\n\nhttps://indico.ict.inaf.it/event/751/contributions/5042
/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5042/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum Measurements of time
DTSTART;VALUE=DATE-TIME:20190923T125500Z
DTEND;VALUE=DATE-TIME:20190923T134000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5218@indico.ict.inaf.it
DESCRIPTION:Speakers: Lorenzo Maccone (Univ. degli Studi di Pavia)\nWe pro
pose a time-of-arrival operator in quantum mechanics by conditioning on a
quantum clock. This allows us to bypass some of the problems of previous p
roposals\, and to obtain a Hermitian time of arrival operator whose probab
ility distribution arises from the Born rule and which has a clear physica
l interpretation. The same procedure can be employed to measure the "time
at which some event happens" for arbitrary events (and not just specifical
ly for the arrival time of a particle).\n\nhttps://indico.ict.inaf.it/even
t/751/contributions/5218/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5218/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Traversable Casimir Wormholes
DTSTART;VALUE=DATE-TIME:20190925T070000Z
DTEND;VALUE=DATE-TIME:20190925T074500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5039@indico.ict.inaf.it
DESCRIPTION:Speakers: Remo Garattini (Università degli Studi di Bergamo)\
nTraversable Wormholes are a prediction of General Relativity. After the d
iscovery of the Gravitational Wave signals detected in 2015\, Traversable
Wormholes have had another renaissance\, because they can be considered as
Black Hole Mimickers.\nIn this talk we give a pedagogical introduction an
d we present some theoretical aspects at classical and semiclassical level
\, namely when the source has quantum mechanical origin. A brief descripti
on of a Self-Sustained Traversable Wormhole\, namely a Traversable Wormhol
e ehich is sustained by its own quantum fluctuations is also presented.\n\
nhttps://indico.ict.inaf.it/event/751/contributions/5039/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5039/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Conjectures on SpaceTime
DTSTART;VALUE=DATE-TIME:20190925T105500Z
DTEND;VALUE=DATE-TIME:20190925T110000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5182@indico.ict.inaf.it
DESCRIPTION:Speakers: Alessandro Capurso ()\nIntroduction\n------------\n\
nThe current description of SpaceTime follows Quantum Mechanics principles
at the smallest scales\, while it is commonly associated to General Relat
ivity in cosmological terms. The opposite perspectives eventually differ i
n terms of discrete *versus* continuum analysis.\nTime seems *vanishing* i
n the latest formulations of Quantum theories (Loop Quantum Gravity)\, as
a static spin-foam that describes spatially entangled loops and *forgets*
the importance of *Memory*. On the other hand\, Time is described in relat
ivity terms as a *continuum existing block*\, of which we perceive instant
s that are part of an always existing word-line\, like *worms* in a 4D-pan
cake with the tail on the birth and the head on the last instant of existe
nce. \nIt seems that our latest descriptions of Time point at *everything*
(in relativity) or *nothing* (in quantum) but still strive to understand
entanglement\, coherence and eventually evolution in Time.\n\nRecently\, s
everal efforts have been done to reestablish a more *natural perspective*
on Science\, able to better face not only SpaceTime fabric description\, b
ut also debate on deeper *philosophical questions* concerning Time and its
role in the Universe. \nAn extended review of the importance of Time in e
lementary physics\, as well as in many other disciplines\, is given by Lee
Smolin in [1]. \nThe coming ideas follow a similar path\, trying to conti
nue the effort towards a physical description of SpaceTime that seems to *
frame better* quantum and cosmological scales with natural evolution.\n\n\
n\n\nAbstract and Summary\n--------------------\n\nThe aim of this contrib
ution is to propose new conjectures on SpaceTime variables and their descr
iption\, through the concepts of *network*\, *entropy* and *coherent decod
ing* (borrowed from Information Theory and quantum computation) and to off
er a possible wider perspective on SpaceTime fabric and evolution.\nGiven
the *unnatural physical existence* of a *Real continuum* and consequent *i
nfinities*\, in the context of a discrete universe on space and even time
on a Planck scale (as discussed in [2])\, starting from the definition of
a *new reference frame* based on an Absolute Time T[k]\, an imaginary time
*ict* and on the relative *momenta*\, a possible interpretation of AdS/CF
T correspondence\, SpaceTime fabric and elementary particles behavior is p
roposed.\n\nThe Absolute Time is described in the *AdS bulk* of the Maldac
ena correspondence. It is represented as *entangled memory links* (between
imaginary points on the surface) that develop highlighting *surface corre
lation* in a wavelet decomposition of the local pulse (phase shift info in
respect to the Absolute Time reference pulse). \nThe memory links are des
cribed as well as a *deep neural network* (growing in T[k]) that *stores a
nd project* the evolving surface information\, as discussed in [3]. The in
formation stored and projected through the Absolute Time is interpreted in
the context of SpaceTime fabric as the *most efficient quantum computatio
n network*\, as proposed also in [4]\, [5] and [6].\n\nImaginary time\, fo
llowing Hawking intuition\, maps the *surface* of the AdS/CFT corresponden
ce to a *diffusive space distance* in a relativistic and flat space\, in c
oherence *c* with the pulse of T[k]. It defines\, at any given k (*Now*)\,
the full *current 3D space*\, from -∞@T[k-1] to +∞@T[k+1]. \nIn an ev
olving 4D-SpaceTime\, the perceived 3D Space is interpreted as *emerging*\
, in each *current Now*\, as the current configuration of *SpaceTime infor
mation*. It is distributed on the Universe *Surface of Existence* along *i
ct* at a given k\, giving 2 probabilistic Real degrees of freedom in each
surface bit and the correlation derived on the memory-links\, entangled al
ong the past instants in the Absolute Time.\n\nThe *momenta* involved repr
esent the *phase variations* (along both times in respect to the relative
*reference of coherence*) and develop as in a logarithmic spiral\, followi
ng a relativistic description of the *information space* and *coherent tim
e* on the surface of the bulk. \nA mathematical description of the mention
ed momenta in relativistic terms is proposed.\n\nBosons are described as *
single qubits of information* and *elementary vibrating strings*\, flowing
with no *inertia* on the surface defined by the imaginary time.\nMatter e
lementary particles\, as *Entities* in SpaceTime\, are described as *Netwo
rks* of imaginary points sharing a *common beat* (decoding as a *coherent-
Self* in T[k]). They emerge from the entanglement in the Absolute Time of
surface strings\, that reduce their local degrees of freedom to become *in
terconnected in the bulk*\, pulsing as a single\, persisting Self (debated
in [7]\, [8]).\n\nFollowing the conjectures proposed and the parallel wit
h *information encoded* in the entanglement of surface strings in T[k]\, t
he Dirac equation is mapped to Shannon *Entropy*\, as a *summary* of the i
nformation content *shown on the surface*\, mathematically expressed as th
e sum of the information derived over the variations along the *past loopy
ticks* of the Absolute Time.\nThe geometry proposed is then applied to Da
rk Matter\, interpreted as diffusive *wrinkles* in the local fabric\, and
to Black Holes\, as coherent Self and quantum networks showing maximum sur
face entropy at current T[k]. \nBlack holes are described\, on the horizon
\, as *1 tick away* from the *coherent Now* (as a result of the *SpaceTime
decoding algorithm* local computation on both *momenta*). \nThe horizon r
esults *too out of phase* in the local *current T[k] coherence* to be *dec
oded* in the surrounding 3D local space (consequently with very little cha
nce of receiving\, on the outside\, any information).\nFurther reasoning o
n SpaceTime *info compression algorithm* and relative computational effici
ency as a quantum computer are presented in the context of fabric entangle
ment (as *living memory-roots* through past events) and maximum entropy on
the surface (as equivalent to Shannon max *info compression*).\n\nTo illu
strate possible wider similarities and consequences of the proposed conjec
tures\, the *Evolution* of Network-Entities and of information is describe
d as cycles of transformation in *ict* and new gained persistence in T[k]\
, in a growing of global surface entropy and local complexities\, levels o
f abstraction\, efficiency in equilibrium and Self-gained emerging propert
ies.\nFinally\, a possible interpretation of the *Origin* is proposed\, re
winding back both times\, in the context of Absolute Time and imaginary ti
me emerging from a *no-boundary* alike model (Hartle and Hawking).\n\nFurt
her developments on the proposed conjectures are still required. \nA wider
mathematical and physical analysis is suggested to extend the comprehensi
on of information in SpaceTime and to evaluate the implications on telecom
munication and energy production. \nA deeper philosophical understanding i
s expected.\n\nThe full paper is available at [9].\n\n \n\n\n\n\n\nReferen
ces\n----------\n\n[1] L. Smolin\, Time Reborn: From the Crisis in Physic
s to the Future of the Universe\, 2013. \n[2] C. Rovelli and M. Christodo
ulou\, “On the possibility of experimental detection of the discreteness
of time” arXiv:1812.01542v2\, 2018. \n[3] X.-L. Qi\, “Exact holograp
hic mapping and emergent space-time geometry” arXiv:1309.6282v1\, 2013.
\n[4] L. Zhou and X. Dong\, “Geometrization of deep networks for the in
terpretability of deep learning systems” arXiv:1901.02354v2\, 2019. \n[5
] L. Zhou and X. Dong\, “Spacetime as the optimal generative network of
quantum states: a roadmap to QM=GR?”arXiv:1804.07908v1\, 2018. \n[6] P
. Caputa and J. M. Magan\, “Quantum Computation as Gravity” PHYSICAL R
EVIEW LETTERS\, pp. 122\, 231302\, 2019. \n[7] G. Jaroszkiewicz and J. Ea
kins\, “Particle decay processes\, the quantum Zeno effect and the conti
nuity of time” arXiv:quant-ph/0608248\, 2006. \n[8] T. Ullrich\, D. Kha
rzeev and Z. Tu\, “The EPR paradox and quantum entanglement at sub-nucle
onic scales” arXiv:1904.11974\, 17 May 2019. \n[9] A. Capurso\, “Conj
ectures on SpaceTime” \nAvailable: http://www.tempiodicrono.net/download
/Capurso-Conjectures_paper.pdf.\n\nhttps://indico.ict.inaf.it/event/751/co
ntributions/5182/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5182/
END:VEVENT
BEGIN:VEVENT
SUMMARY:On Closed Timelike Curves\, Cosmic Strings and Conformal Invaria
nce
DTSTART;VALUE=DATE-TIME:20190923T100000Z
DTEND;VALUE=DATE-TIME:20190923T102000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5034@indico.ict.inaf.it
DESCRIPTION:Speakers: Reinoud Slagter (Univ of Amsterdam and ASFYON\, The
Netherlands)\nAbstract \nIn general relativity theory (GRT) one can constr
uct solutions which are related to real physical objects. The most famous
one is the black hole solution. One now believes that in the center of man
y galaxies there is a rotating super-massive black hole\, the Kerr black h
ole. Because there is an axis of rotation\, the Kerr solution is a member
of the family of the axially symmetric solutions of the Einstein equations
. A legitimate question could be: are there other axially or cylindrically
symmetric asymptotically flat solutions of the equations of Einstein with
a classical or non-classical matter distribution and with correct asympto
tical behavior\, just as the Kerr solution? Many attempts are made\, such
as the Weyl-\, Papapetrou- and Van Stockum solution. None of these attempt
s result is physically acceptable solution. Often\, these solutions posses
s closed timelike curves (CTC's). The possibility of the formation of CTC
's in GRT seems to be an obstinate problem to solve in GRT. At first glanc
e\, it seems possible to construct in GRT causality violating solutions. C
TC's suggest the possibility of time-travel with its well-known paradoxes.
Although most physicists believe that Hawking's chronology protection con
jecture holds in our world\, it can be alluring to investigate the mathem
atical underlying arguments of the formation of CTC's. There are several s
pacetimes that can produce CTC's. Famous is the Tipler-cylinder. Most of t
hese spacetimes can easily characterized as un-physical. \nThe problems ar
e\, however\, more deep-seated in the vicinity of a (spinning) cosmic stri
ng or in the so-called Gott-spacetime. These cosmic string models gained m
uch attention the last decades. Two cosmic strings\, approaching each othe
r with high velocity\, could produce CTC's. If an advanced civilization co
uld manage to make a closed loop around this Gott pair\, they will be retu
rned to their own past. However\, the CTC's will never arise spontaneously
from regular initial conditions through the motion of spinless “cosmons
” ( “Gott’s pair”): there are boundary conditions that has CTC's
also at infinity or at an initial configuration. If it would be possibl
e to fulfil the CTC condition at t0\, then at sufficiently large times t
he cosmons will have evolved so far apart that the CTC's would disappear.
The chronology protection conjecture seems to be saved for the Gott spacet
ime. There are still some unsatisfied aspects around spinning cosmic stri
ngs. If the cosmic string has a finite dimension\, one needs to consider t
he coupled field equations\, i.e.\, besides the Einstein equations\, also
the scalar and gauge field equations. It came as a big surprise that there
exists a vortex-like solution in GRT comparable with the magnetic flux li
nes in type II superconductivity. Many of the features of the Nielsen-Oles
en vortex solution and superconductivity will survive in the self-gravitat
ing situation. These vortex lines occur as topological defects in an abeli
an U(1) gauge model\, where the gauge field is coupled to a charged scalar
field. It can easily be established that the solution must be cylindrica
lly symmetric\, so independent of the z-coordinate and the energy per unit
length along the z-axis is finite. There are two types\, local (gauged) a
nd global cosmic strings. We are mainly interested in local cosmic strings
\, because in a gauge model\, strings were formed during a local symmetry
breaking and so have a sharp cutoff in energy\, implying no long range in
teractions. It turns out that spinning cosmic string solutions can cause
serious problems when CTC's are formed which are not hidden behind a horiz
on\, as is the case for the Kerr metric. One can "hide" the presence of th
e spinning string by suitable coordinate transformation in order to get th
e right asymptotic behaviour and without a residue of the angle deficit.
One obtains then a helical structure of time\, not desirable. Further\, it
is not easy to match the interior on the vacuum exterior and to avoid the
violation of the weak energy condition (WEC). Many attempts are made to f
ind a physically acceptable solutions\, but all failed. It is clear that
an additional field must be added to compensate for the energy failure clo
se to the core of the string. That part of the mass density of a rotating
string due to its angular deficit is insufficient. In general one can conc
lude that there is an urgent need for a satisfying physical interpretation
of CTC’s in this spacetime.\nIn my talk I will consider the spinning st
ring in conformal gravity\, where the interior consists of a gauged scalar
field. Conformal invariance in GRT considered as exact at the level of t
he Lagrangian but spontaneously broken\, is an approved alternative for d
isclosing the small-distance structure when one tries to describe quantum-
gravity problems. Moreover\, the conformal invariant cosmological models c
ould solve the dark energy/matter problem.\nWe will write the metric as g
_μν=ω^2 g ̃_μν \, with ω a dilaton field\, handled on equal foo
ting with the Higgs field and g ̃_μν the “unphysical” metric. By de
manding regularity of the action\, no problems emerge when ω→0. For the
vacuum exterior\, exact (Ricci-flat) solutions are found with the correc
t asymptotic features which can be matched on the numerical interior solut
ion. For global cosmic strings\, the existence of CTC's can be avoided or
pushed to infinity by suitable values of the integration constants. These
constants can be used to fix the parameters of the cosmic string by the sm
ooth matching of the solutions at the boundary. There seems to be no probl
ems in order to fulfil the weak energy condition.\nOur result could be a
new possible indication that local conformal invariance and spontaneously
broken in the vacuum\, can be a promising method for studying quantum effe
cts in GR\, as was found in many other studies.\nR. J. Slagter and S. Pan\
, 2016\, Found of Phys\, 46\, 1075\nR. J. Slagter\, 2019\, Phys of the Da
rk Universe\, 24\, 100282\nR. J. Slagter and C. L. Duston\, 2019\, ArXiv:
gr-qc/190206088 [subm to Ann of Phys\n\nhttps://indico.ict.inaf.it/event/7
51/contributions/5034/
LOCATION:
URL:https://indico.ict.inaf.it/event/751/contributions/5034/
END:VEVENT
BEGIN:VEVENT
SUMMARY:New Classes of Warp Drive Solutions in General Relativity
DTSTART;VALUE=DATE-TIME:20190924T151000Z
DTEND;VALUE=DATE-TIME:20190924T153000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5483@indico.ict.inaf.it
DESCRIPTION:Speakers: Alexey Bobrick ()\nWe report on the results of our o
ngoing work on reducing the energy requirements of classical warp drives.
The existing warp drive solutions by van den Broek and Alcubierre assume s
pherical symmetry. We show that by considering their counterparts of arbit
rary shape\, one can reduce the energy requirements by orders of magnitude
. Further\, I will outline a method of constructing more general classes o
f warp drives. As a demonstration\, we have constructed\, for the first ti
me\, a warp drive solution with a region resembling the ergosphere region
of Kerr black holes. I will present on the properties of such drives and d
iscuss the possibility of applying the Penrose process to them.\n\nhttps:/
/indico.ict.inaf.it/event/751/contributions/5483/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5483/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Reversible time travel with freedom of choice
DTSTART;VALUE=DATE-TIME:20190924T094500Z
DTEND;VALUE=DATE-TIME:20190924T101500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5215@indico.ict.inaf.it
DESCRIPTION:Speakers: Ämin Baumeler (Institute for Quantum Optics and Q
uantum Information)\nGeneral relativity allows for the existence of closed
time-like curves\, along which a material object could travel back in tim
e and interact with its past self. Previous studies by Thorne and others s
howed that for any choice of initial conditions\, consistent dynamics —
even in the presence of closed time-like curves — exist. Moreover and co
unterintuitively\, they showed that the examples with self-interaction lea
d to an infinite number of consistent dynamics. While in these previous st
udies initial conditions only where subject to the experimenter’s choice
\, we allow for arbitrary operations to be performed in local space-time r
egions. We find that any such dynamics can be realised through reversible
interactions. We further find that consistency with local operations is co
mpatible with non-trivial time travel: Three parties can interact in such
a way to be all both in the future and in the past of each other\, while b
eing free to perform arbitrary local operations. Finally\, the states desc
ribed in our framework are uniquely determined.\n\nhttps://indico.ict.inaf
.it/event/751/contributions/5215/
LOCATION:
URL:https://indico.ict.inaf.it/event/751/contributions/5215/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Probing regular black hole spacetimes with scalar fields
DTSTART;VALUE=DATE-TIME:20190923T094000Z
DTEND;VALUE=DATE-TIME:20190923T100000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5208@indico.ict.inaf.it
DESCRIPTION:Speakers: Tayebeh Tahamtan ()\nWe study the properties of re
gular black holes using both test and gravitating scalar fields. The main
motivation being to discover features that distinguish them from real blac
k holes. One such characteristic is regularity of horizon which is spoilt
by scalar field in spherically symmetric static cases.\n\nhttps://indico.i
ct.inaf.it/event/751/contributions/5208/
LOCATION:
URL:https://indico.ict.inaf.it/event/751/contributions/5208/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum field theories with quantum causal structure
DTSTART;VALUE=DATE-TIME:20190925T151000Z
DTEND;VALUE=DATE-TIME:20190925T153000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5037@indico.ict.inaf.it
DESCRIPTION:Speakers: Ding Jia (Perimeter Institute: University of Waterlo
o)\nWe study quantum gravity induced quantum causal structure in the conte
xt of quantum field theories. We argue both conceptually and numerically t
hat when spacetime is treated quantumly\, (1) exact microcausality conditi
on\, (2) exact causal boundaries\, and (3) the distinction between particl
es and antiparticles cannot be maintained. These suggest possibilities of
"time travel" and "tunneling out of black holes"\, but to examine whether
such possibilities can be realized\, concrete calculations are needed. We
present a method to conduct calculations for quantum field theories on qua
ntum spacetime based on the expansion of Feynman diagrams into worldline d
iagrams. As a first application\, we show that quantum causal structure re
gularizes matter field UV singularities. This result reinforces previous s
uggestions from analyzing entanglement in the presence of quantum causalit
y.\n\nhttps://indico.ict.inaf.it/event/751/contributions/5037/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5037/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Matrix Product State Simulations of Quantum Fields in Curved 1+1 S
pacetime
DTSTART;VALUE=DATE-TIME:20190924T101500Z
DTEND;VALUE=DATE-TIME:20190924T103500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5231@indico.ict.inaf.it
DESCRIPTION:Speakers: Adam Lewis (Perimeter Institute\, Waterloo Ontario
)\nWhile the dynamics of black hole evaporation and closed-timelike-curve
physics in the presence of quantum fields are to some extent understood in
principle\, the computations necessary to produce concrete predictions fr
om them are often intractable in practice. Here we show how tensor-network
based numerics\, which assign a manageably sparse representation to certa
in quantum states\, can be used to perform them. As a first step wecompute
the Hadamard-regularized stress-energy tensor of a 1+1-D massive Dirac fi
eld in various quantum states\, demonstrating the Unruh effect in flat and
curved spacetime.\n\nhttps://indico.ict.inaf.it/event/751/contributions/5
231/
LOCATION:
URL:https://indico.ict.inaf.it/event/751/contributions/5231/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Updates from the future
DTSTART;VALUE=DATE-TIME:20190923T121000Z
DTEND;VALUE=DATE-TIME:20190923T125500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5836@indico.ict.inaf.it
DESCRIPTION:Speakers: Seth Lloyd (MIT)\nThe possibility of closed timelike
curves in general relativity opens up the physical possibility of\ntime t
ravel. This talk reviews the different quantum mechanical theories of clos
ed timelike curves\, and\ndiscusses their various advantages and drawbacks
. We will discuss whether it is possible to use closed \ntimelike curves
to build a time machine.\n\nhttps://indico.ict.inaf.it/event/751/contribu
tions/5836/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5836/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Testing Gravitational Redshifts with Galileo 5 and 6
DTSTART;VALUE=DATE-TIME:20190925T085500Z
DTEND;VALUE=DATE-TIME:20190925T092500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5825@indico.ict.inaf.it
DESCRIPTION:Speakers: Christophe Le Poncin-Lafitte (SYRTE’ Deputy-Direc
tor\, Observatoire de Paris\, PSL Research University\, CNRS\, Sorbonne Un
iversités\, UPMC Univ. Paris 06\, LNE)\nhttps://indico.ict.inaf.it/event/
751/contributions/5825/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5825/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum enhanced correlated interferometry for Planck scale phys
ics
DTSTART;VALUE=DATE-TIME:20190925T133000Z
DTEND;VALUE=DATE-TIME:20190925T140000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5228@indico.ict.inaf.it
DESCRIPTION:Speakers: Elena Losero ()\nRecently\, hypothetical faint effec
ts in interferometers connected to non-commutativity of position variables
in different directions originating at the Planck scale have been consi
dered\, as a possible signature of quantum gravity. In particular\, this i
dea led to the realization of a double 40 m interferometer at Fermilab wit
h state of the art sensitivity in the MHz domain. Although instruments su
ch as optical interferometers represent probably the most sensitive device
s currently available\, their performance are still limited by shot noise\
, if operated with classical light. Quantum metrology\, allows to overcam
e these limits\, by exploiting quantum properties of light\, therefore rep
resenting a promising avenue for enabling new discoveries. \n\nHere we pre
sent an experiment of quantum-enhanced correlated interferometry\, showing
an improved sensitivity with respect to a single interferometer in revea
ling faint stochastic noise\, such as the ones predicted by some Planck sc
ale model. Using quantum-enhanced correlation techniques between two Miche
lson interferometers\, we reach a sensitivity of 10-17 m/(Hz)1/2 at 13.5
MHz in a few seconds of integration time\, which is 20 times better than t
he one of a single device. Moreover\, by injecting bipartite quantum corr
elated states\, we also demonstrated a sub shot noise sensitivity in the
comparison of different interferometers' signals. In perspective\, the pro
posed technique could allow either to reduce the size to a table top scale
or to further improve the sensitivity of large setup such as the Fermila
b facility.\n\nhttps://indico.ict.inaf.it/event/751/contributions/5228/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5228/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Pseudodensity Matrix of a quatum optical system as a tool for visu
alizing open timelike curves.
DTSTART;VALUE=DATE-TIME:20190925T130000Z
DTEND;VALUE=DATE-TIME:20190925T133000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5827@indico.ict.inaf.it
DESCRIPTION:Speakers: Marco Genovese (INRiM)\nQuantum optical systems pres
ent several interesting properties that allow using them as a tool for vis
ualizing physical phenomena otherwise subject of theoretical speculation o
nly\, as Bose Einstein condensation for Hawking radiation [1] or Page Woot
ters model [2-5].\n\nClosed Time-like Curves (CTC)\, one of the most strik
ing predictions of general relativity\, are notorious for generating parad
oxes\, such as the grandfather's paradox\, but these paradoxes can be solv
ed in a quantum network model [6]\, where a qubit travels back in time and
interacts with its past copy. However\, there is a price to pay. The reso
lution of the causality paradoxes requires to break quantum theory's linea
rity. This leads to the possibility of quantum cloning\, violation of the
uncertainty principle and solving NP-complete problems in polynomial time.
Interestingly\, violations of linearity occur even in an open time-like
curve (OTC)\, when the qubit does not interact with its past copy\, but it
is initially entangled with another\, chronology-respecting\, qubit. The
non-linearity is needed here to avoid violation of the monogamy of entangl
ement. To preserve linearity and avoid all other drastic consequences\, we
discuss how the state of the qubit in the OTC is not a density operator\,
but a pseudo-density operator (PDO) - a recently proposed generalisation
of density operators\, unifying the description of temporal and spatial qu
antum correlations. Here I present an experimental simulation of the OTC u
sing polarization-entangled photons\, also providing the first full quantu
m state tomography of the PDO describing the OTC\, verifying the violation
of the monogamy of entanglement induced by the chronology-violating qubit
. At the same time the linearity is preserved since the PDO already contai
ns both the spatial degrees of freedom and the linear temporal quantum evo
lution. These arguments also offer a possible solution to black hole entro
py problem.\n\n[1] J.Steinahauer et al.\, Nature Physics volume12\, 959
–965 (2016)\n\n[2] D.N. Page and W.K. Wootters\, Phys. Rev. D 27\, 2885
(1983)\; W.K. Wootters\, Int. J. Theor. Phys. 23\, 701 (1984).\n\n[3] E.Mo
reva\,M.Gramegna\,G.Brida\,L.Maccone\,M.Genovese\, Phys. Rev. A 89\, 05212
2 (2014).\n\n[4] V.Giovannetti\, S.Lloyd\, L.Maccone\, Phys. Rev. D\, 92
\, 045033 (2015).\n\n[5] E.Moreva\,M.Gramegna\,G.Brida\,L.Maccone\,M.Genov
ese\, Phys. Rev.D in press. arXiv:1710.00707\n\n[6] D. Deutsch\, Phys. Rev
. D 44\, 10\, 1991.\n\n[7] C. Marletto\, V. Vedral\, S. Virzì\, E.Rebufel
lo\,A.Avella\,M.Gramegna\, I.P. Degiovanni\,M.Genovese\, in press.\n\nhttp
s://indico.ict.inaf.it/event/751/contributions/5827/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5827/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Locality and causality in the Aharonov-Bohm effect
DTSTART;VALUE=DATE-TIME:20190925T122000Z
DTEND;VALUE=DATE-TIME:20190925T130000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5227@indico.ict.inaf.it
DESCRIPTION:Speakers: Chiara Marletto (University of Oxford\, ISI\, Nation
al University of Singapore)\nI will expose a local\, fully quantum-field-t
heory compliant model of the Aharonov-Bohm effect\, where the Aharonov-Boh
m phase is gradually and locally acquired. I will explore the theoretical
and experimental implications of this model\, especially in regard to loca
lity and causality in quantum theory.\n\nhttps://indico.ict.inaf.it/event/
751/contributions/5227/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5227/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Superpositions of Mesoscopic Objects for Sensing Quantum Gravity a
nd Gravitational Waves
DTSTART;VALUE=DATE-TIME:20190925T092500Z
DTEND;VALUE=DATE-TIME:20190925T101000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5826@indico.ict.inaf.it
DESCRIPTION:Speakers: Sougato Bose (Department of Physics and Astronomy\,
University College London)\nWe will show two fundamental applications of q
uantum superpositions of spatially separated states of mesoscopic objects
(nano- and micro-spheres). Firstly we are going to show how convenient it
may be to prepare and probe such superpositions through a pure ancillary s
ystem such as a spin. Next\, we are going to show how an entanglement betw
een two such interferometers can be generated purely through the Newtonian
interaction between the masses and that this can be probed\, at the end o
f the interferometry\, purely by measuring the correlations between spins.
We are going to justify why\, under the assumption of locality of physica
l interactions and under a reasonable definition of classicality\, the abo
ve entanglement signifies the qualitatively quantum nature of gravity. We
are also going to discuss how the same spin-induced and probed superposit
ions will open up the ability to detect low frequency gravitational waves\
, immune to initial thermal noise\, with a meter-scale apparatus.\n\nhttps
://indico.ict.inaf.it/event/751/contributions/5826/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5826/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Causal nature and dynamics of trapping horizons in black hole coll
apse
DTSTART;VALUE=DATE-TIME:20190923T102000Z
DTEND;VALUE=DATE-TIME:20190923T104000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5440@indico.ict.inaf.it
DESCRIPTION:Speakers: Ilia Musco (Institut de Ciències del Cosmos\, Univ
ersitat de Barcelona\, Facultat de Física)\nIn calculations of gravitatio
nal collapse to form black holes\, trapping horizons (foliated by marginal
ly trapped surfaces) make their first appearance either within the collaps
ing matter or where it joins on to a vacuum exterior. Those which then mov
e outwards with respect to the matter have been proposed for use in defini
ng black holes\, replacing the global concept of an event horizon\, which
has some serious drawbacks for practical applications. I here present resu
lts from a study of the properties of both outgoing and ingoing trapping h
orizons\, assuming strict spherical symmetry throughout. Their causal natu
re (i.e. whether they are spacelike\, timelike or null) is investigated\,
following two different approaches\, one using a geometrical quantity rela
ted to expansions of null geodesic congruences\, and the other using the h
orizon velocity measured with respect to the collapsing matter. The models
treated are simplified\, but do include pressure effects in a meaningful
way and we analyze how the horizon evolution depends on the initial condit
ions of energy density and pressure of the collapse. (NOTE: This work has
been published in Classical and Quantum Gravity 34 (2017) no.13\, 135012 )
\n\nhttps://indico.ict.inaf.it/event/751/contributions/5440/
LOCATION:
URL:https://indico.ict.inaf.it/event/751/contributions/5440/
END:VEVENT
BEGIN:VEVENT
SUMMARY:“Time” replaced by quantum correlations: experimental visualiz
ation.
DTSTART;VALUE=DATE-TIME:20190923T154500Z
DTEND;VALUE=DATE-TIME:20190923T161000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5220@indico.ict.inaf.it
DESCRIPTION:Speakers: Ekaterina MOREVA (INRiM)\nThe description of time
in quantum mechanics and in particular in connection with quantum gravity
and cosmology has always presented significant difficulties. One of descri
ptions based on Page and Wootters (PaW) mechanism which considers “time
” as a quantum degree of freedom[1]. Here we give a complete review of t
he Page and Wootters' quantum time mechanism and provide experimental illu
strations that are able to describe time as an emergent property of quantu
m correlations and giving us access to the possibility of a test of the Le
ggett-Garg inequalities.\n
\n[1] D.N. Page and W.K. Wootters\, Phys. Rev
. D 27\, 2885 (1983). \n[2] E. Moreva\, M. Gramegna\, G. Brida\, L. Maccon
e\, M. Genovese\, “Quantum time: Experimental multitime correlations”\
, Physical Review D 96 (10)\, 102005 (2017)\n\nhttps://indico.ict.inaf.it/
event/751/contributions/5220/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5220/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Discussion - Closing remarks
DTSTART;VALUE=DATE-TIME:20190924T162000Z
DTEND;VALUE=DATE-TIME:20190924T163000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5824@indico.ict.inaf.it
DESCRIPTION:https://indico.ict.inaf.it/event/751/contributions/5824/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5824/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBD
DTSTART;VALUE=DATE-TIME:20190924T154000Z
DTEND;VALUE=DATE-TIME:20190924T160000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5823@indico.ict.inaf.it
DESCRIPTION:Speakers: Susanna TERRACINI (Dip. of Mathematics)\nhttps://ind
ico.ict.inaf.it/event/751/contributions/5823/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5823/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBD
DTSTART;VALUE=DATE-TIME:20190924T160000Z
DTEND;VALUE=DATE-TIME:20190924T162000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5820@indico.ict.inaf.it
DESCRIPTION:Speakers: Sumati SURYA (Raman Research Institute)\nhttps://ind
ico.ict.inaf.it/event/751/contributions/5820/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5820/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gravitational lensing hundred years after the Eddington expedition
DTSTART;VALUE=DATE-TIME:20190923T070000Z
DTEND;VALUE=DATE-TIME:20190923T074500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5480@indico.ict.inaf.it
DESCRIPTION:Speakers: Volker Perlick (ZARM\, University of Bremen\, German
y)\nExactly hundred years ago\, in May 1919\, Arthur Eddington and three c
olleagues observed the gravitational light deflection\, as predicted by Al
bert Einstein\, during a total Sun eclipse. After a historical introductio
n\, I'll discuss the relevance of gravitational lensing as an important to
ol for present-day astrophysics. In the last part of the talk I will inves
tigate in some detail the pictures of the shadow of the black-hole candida
te at the centre of M87\, which were released to the public on 10 April 20
19\, just hundred years after the Eddington expedition.\n\nhttps://indico.
ict.inaf.it/event/751/contributions/5480/
LOCATION:
URL:https://indico.ict.inaf.it/event/751/contributions/5480/
END:VEVENT
BEGIN:VEVENT
SUMMARY:What is the surface of a (dynamical) black hole?
DTSTART;VALUE=DATE-TIME:20190923T074500Z
DTEND;VALUE=DATE-TIME:20190923T083000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5481@indico.ict.inaf.it
DESCRIPTION:Speakers: José M.M. Senovilla (UPV/EHU)\nBlack holes in equil
ibrium are fundamental objects predicted by General Relativity. However\,
real black holes form\, evolve and eventually evaporate\, thus they are dy
namical. Do they have a well-defined boundary? Where? The usual Event Hori
zon is global and teleological\, thus not well defined for dynamical black
holes. The concepts of dynamical and trapping horizons\, based on closed
trapped surfaces\, are promising alternatives. I will show\, however\, the
fundamental problems inherent to dynamical or trapping horizons. I will t
hen introduce the concept of Core of a black hole\, and discuss the possib
ility that they can select a unique horizon.\n\nhttps://indico.ict.inaf.it
/event/751/contributions/5481/
LOCATION:
URL:https://indico.ict.inaf.it/event/751/contributions/5481/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Locally Covariant Quantum Field Theory on Causally Compatible Sets
DTSTART;VALUE=DATE-TIME:20190925T153000Z
DTEND;VALUE=DATE-TIME:20190925T161000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5755@indico.ict.inaf.it
DESCRIPTION:Speakers: James Vickers (Mathematical Sciences\, University of
Southampton\, UK)\nIn this talk I describe the mathematics required in or
der to provide a description of the observables for quantum fields on low-
regularity spacetimes. The first step involves constructing low-regularity
advanced and retarded Green operators as maps between suitable function s
paces. In specifying these we need to use graph norms on Sobolev spaces t
o ensure that the Green operators are well-defined inverses. The causal pr
opagator is then used to define a symplectic form on a topological vector
space $V(M)$. A key point is the way in which the causal propagator on a (
non-smooth) globally hyperbolic spacetime restricts to the causal propagat
or on a smaller causally compatible submanifold and therefore induces a sy
mplectic map between the vector spaces. This property enables one to provi
de a locally covariant description of the quantum fields in terms of the e
lements of quasi-local $C^*$-algebras on which one may define canonical co
mmutation relations. I end with a brief discussion on the choice of Sobole
v micro-local spectrum condition used to single out the physical states in
the low-regularity setting.\n\nhttps://indico.ict.inaf.it/event/751/contr
ibutions/5755/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5755/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Superpositions of causal orders in a timeless universe
DTSTART;VALUE=DATE-TIME:20190925T101000Z
DTEND;VALUE=DATE-TIME:20190925T105500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5226@indico.ict.inaf.it
DESCRIPTION:Speakers: Vlatko Vedral (University of Oxford\, ISI\, National
University of Singapore)\nI will first review the timeless Page-Wootters
picture of the quantum universe in which there is no overall dynamics\, bu
t where the states of quantum fields evolve relative to the quantum states
of the underlying space. I will then introduce the concept of superposing
different causal orders – a notion that could be naturally motivated wi
thin some approaches to quantum gravity – and ask if and how this phenom
enon could be incorporated within the Page-Wootters formalism. I hope to f
inish by speculating about some possible experimental implications.\n\nhtt
ps://indico.ict.inaf.it/event/751/contributions/5226/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5226/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Changing the interpretation of time
DTSTART;VALUE=DATE-TIME:20190924T103500Z
DTEND;VALUE=DATE-TIME:20190924T104000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5035@indico.ict.inaf.it
DESCRIPTION:Speakers: Luigi Foschini (Istituto Nazionale di Astrofisica (I
NAF))\nI would like to explore a change in the interpretation of time. By
thinking time as a cut\, and no more like a lapse\, there could be interes
ting opportunities. Particularly\, with such interpretation\, quantum grav
ity theories based on 3+1 spacetime (e.g. Kuchar or Ellis' evolving block
universe) may open unexpected and fruitful views. Among the many consequen
ces\, there will be no possibility for time machines.\n\nhttps://indico.ic
t.inaf.it/event/751/contributions/5035/
LOCATION:
URL:https://indico.ict.inaf.it/event/751/contributions/5035/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Conditional probabilities\, relativistic quantum clocks\, and the
trinity of relational quantum dynamics
DTSTART;VALUE=DATE-TIME:20190925T145000Z
DTEND;VALUE=DATE-TIME:20190925T151000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5206@indico.ict.inaf.it
DESCRIPTION:Speakers: Alexander R. H. Smith (Department of Physics and Ast
ronomy\, Dartmouth College)\nWhat allowed Einstein to transcend Newton’s
conception of absolute time was his insistence on an operational definiti
on of time in terms of the measure- ment of a clock. Quantum theory has ye
t to be liberated from this absolute time as evidenced by the Schr ̈oding
er equation in which time appears as an external classical parameter.\nIn
this talk I will introduce an operational formulation of quantum theory kn
own as the conditional probability interpretation of time (CPI) in which t
ime is defined in terms of an observable on a quantum system functioning a
s a clock\; in some contexts\, the CPI is known as the Page and Wootters m
echanism. This clock and the system whose dynamics it is tracking\, do not
evolve with respect to any external time. Instead\, they are entangled an
d as a consequence a relational dynamics emerges between them.\nI will pre
sent a generalization of the CPI to the case when the clock and system int
eract [1]\, which should be expected at some scale when the gravita- tiona
l interaction between them is taken into account. I will demonstrate how s
uch clock-system interactions result in a time-nonlocal modification to th
e Schro ̈dinger equation. I will then examine relativistic particles with
internal degrees of freedom that constitute a clock which tracks their pr
oper time [2]. By examining the conditional probability associated with tw
o such clocks reading different proper times\, I will show that these cloc
ks exhibit both classical and quantum time dilation effects. Moreover\, in
connection with quantum metrol- ogy\, it will be seen that the Helstrom-H
olevo lower bound requires that these clocks satisfy a time-energy uncerta
inty relation between the proper time they measure and their rest mass. Fi
nally\, I will show how the CPI constitutes one out of a trinity of distin
ct but equivalent formulations of the same relational quantum dynamics [3]
.\n\nReferences:\n[1] Quantizing time: Interacting clocks and systems\nA.
R. H. Smith and M. Ahmadi\, Quantum 3 160 (2019)\n[2] Relativistic quantum
clocks observe classical and quantum time dilation A. R. H. Smith and M.
Ahmadi\, arXiv:1904.12390 (2019)\n[3] The trinity of relational quantum dy
namics\nA. R. H. Smith\, M. P. E. Lock\, and P. A. Ho ̈hn\, Forthcoming (
2019)\n\nhttps://indico.ict.inaf.it/event/751/contributions/5206/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5206/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Contrary Inferences for Classical Histories in the Consistent Hist
ories Approach
DTSTART;VALUE=DATE-TIME:20190925T143000Z
DTEND;VALUE=DATE-TIME:20190925T145000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5066@indico.ict.inaf.it
DESCRIPTION:Speakers: Adamantia Zampeli (Charles University)\nTitle: Contr
ary Inferences for Classical Histories in the Consistent Histories Approac
h\n\n\nThe non-relativistic quantum theory is one of the most successful t
heories in the history of science\, since it has been verified experimenta
lly in several different situations and with extremely high precision. Des
pite the fact that its mathematical formalism is universally accepted\, it
s conceptual foundations have always been a subject of scientific dispute.
The standard interpretation is that of the Copenhagen school which has ma
ny conceptual and practical problems. One of the most prominent is the dis
tinction between the classical and quantum world\, as well as the issue of
the quantum-to-classical transition. Closely related to these is also the
famous measurement problem. \n\nAn alternative interpretation of quantum
theory based on the histories approach is the consistent histories theory
[1-5]. The space of states consists of all the possible histories of a qua
ntum system and the aim is to derive probabilities for the realization of
a (coarse-grained) history of this system. The probability of a history\,
which is defined in relation to the other histories belonging to the corre
sponding partition of the histories space\, are assigned only when a condi
tion defined on this coarse-grained-histories set holds. When such a set s
atisfies the consistency condition\, it is called consistent histories set
(CHS). Unfortunately\, there are many CHS which are not mutually compatib
le. This leads to the existence of contrary inferences\, which are defined
as two contradictory arguments both implied with probability one [6]. Of
course\, this issue does not arise in the classical world. The existence o
f contrary inferences comes from the existence of zero covers [7]\; specif
ically\, by covering the full histories space with two (overlapping) zero
quantum measure sets. It is known that\, in quantum theory\, many interpre
tational problems arise because of the existence of zero quantum measure c
overs\, e.g. the Kochen-Specker theorem and the contextuality [8]. The str
angeness of contrary inferences is typically justified by proponents of th
e consistent histories\, by arguing that these appear in the small scale (
far from the classical domain)\, where counterintuitive properties are exp
ected to appear. Then the technical way to avoid such issues is to focus o
n and compare propositions belonging to a single CHS\, an assumption justi
fied in the microscopic world\, but much less in classical scales. \n\nIn
this talk\, we give an example of two contrary classical propositions in t
he context of consistent histories approach. We analyze the arrival time o
f a (semi-) classical free particle in an infinite square well. By selecti
ng two different partitions of the histories space\, we find a quantum mea
sure of zero cover\, which consists of two coarse-grained sets. Thus\, we
end up with contrary inferences for a classical particle. The consequences
of this example for histories formulations of quantum theory will be shor
tly discussed. \n\n\nReferences\n\n[1] M. Gell-Mann and J. B. Hartle. Clas
sical equations for quantum systems. Phys. Rev.\, D 47:3345–3382\, 1993.
\n[2] R. B. Griffiths. Consistent histories and the interpretation of quan
tum mechanics. J. Statist. Phys.\, 36:219–272\, 1984.\n[3] R. Omnes. Log
ical Reformulation of Quantum Mechanics. 1. Foundations. J. Statist. Phys.
\, 53:893–932\, 1988.\n[4] R. Omnes. Logical Reformulation of Quantum Me
chanics. 2. Interferences and the Einstein-Podolsky- Rosen Experiment. J.
Statist. Phys.\, 53:933–955\, 1988.\n[5] R. Omnes. Logical Reformulation
of Quantum Mechanics. 3. Classical Limit and Irreversibility. J. Statist.
Phys.\, 53:957–975\, 1988.\n[6] A. Kent. Consistent sets and contrary i
nferences: Reply to Griffiths and Hartle. Phys. Rev. Lett.\, 81:1982\, 199
8.\n[7] P. Wallden. Contrary Inferences in Consistent Histories and a Set
Selection Criterion. Found.Phys.\, 44(11):1195–1215\, 2014.\n[8] S. Sury
a and P. Wallden. Quantum covers in quantum measure theory\,arxiv: 0809.19
51 [quant-ph]\, 2008.\n\nhttps://indico.ict.inaf.it/event/751/contribution
s/5066/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5066/
END:VEVENT
BEGIN:VEVENT
SUMMARY:A time machine allowing travel to the past by free fall
DTSTART;VALUE=DATE-TIME:20190924T092500Z
DTEND;VALUE=DATE-TIME:20190924T094500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5484@indico.ict.inaf.it
DESCRIPTION:Speakers: Livio Pizzocchero (Dipartimento di Matematica\, Un
iversit`a degli Studi di Milano and INFN\, Sezione di Milano )\nThis talk
illustrates a model of spacetime with closed timelike curves proposed in a
recent paper (D. Fermi and L. Pizzocchero\, Class. Quantum Grav. 35 (2018
)\, 165003\, 42pp). This spacetime is diﬀeomorphic to R4 and carries an
ad hoc metric\; it consists of a ﬂat outer region and of a “time machi
ne”\, formed by a toroidal interface and by an inner ﬂat region. The t
imelike geodesics of this model\, representing motions in free fall\, can
be analyzed qualitatively and computed analytically by quadratures\; in th
is way\, it is shown that a freely falling observer can start from the out
er Minkowskian region\, travel across the time machine and then return to
its initial position at an earlier time\, as evaluated by an inertial fram
e for the outer region with a clock ﬁxed in the initial position. With a
suitable choice of the initial conditions\, the amount of time travelled
in the past according to this ﬁxed clock can be made arbitrarily large\,
while keeping non large the duration of the trip according to the travell
er’s clock\; quantitative examples are given.\nThe price for the above f
eatures of the model is the violation of the standard energy conditions in
the interface of the time machine. Another problem are the tidal forces e
xperienced by the traveller within this interface: as shown by a quantitat
ive analysis\, these are non destructive for a human being only if the siz
e of the machine (and of the interface) is astronomical. A time machine of
this size also has a non large interfacial mass-energy density\, much sma
ller (in absolute value) than the density of water\; the energy density is
much below the Planck scale even for a machine of size comparable with th
e human scale\, which ensures that the treatment of these objects via clas
sical physics is correct.\n\nhttps://indico.ict.inaf.it/event/751/contribu
tions/5484/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5484/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dynamical wormholes in Robinson-Trautman class
DTSTART;VALUE=DATE-TIME:20190925T074500Z
DTEND;VALUE=DATE-TIME:20190925T080500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5207@indico.ict.inaf.it
DESCRIPTION:Speakers: Otakar Svitek ()\nWe present wormholes based on the
Robinson–Trautman class of spacetimes generally containing geometries w
ithout symmetries. We focus on a model sourced by a ghost scalar field inv
estigating its asymptotics\, stability and other issues. Within the same f
amily of geometries one can construct a thin-shell model which approaches
simple spherically symmetric wormhole in the distant future. The generaliz
ation of the second model to higher dimensions provides a possibility of a
voiding the energy condition violation.\n\nhttps://indico.ict.inaf.it/even
t/751/contributions/5207/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5207/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Causal set theory and quantum fields
DTSTART;VALUE=DATE-TIME:20190924T134000Z
DTEND;VALUE=DATE-TIME:20190924T140000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5067@indico.ict.inaf.it
DESCRIPTION:Speakers: Marco Letizia (University of Waterloo and Perimeter
Institute)\nIn this talk I will discuss the properties of quantum fields i
n causal set theory\, a theory of quantum gravity in which nonlocality eme
rges as a consequence of discreteness and local Lorentz invariance. In par
ticular I will present some recent results regarding the computation of en
tanglement entropy in this context and consider some comparisons with othe
r models of quantum spacetime with particular attention to the fate of Lor
entz symmetries.\n\nhttps://indico.ict.inaf.it/event/751/contributions/506
7/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5067/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Remote time manipulation
DTSTART;VALUE=DATE-TIME:20190924T143000Z
DTEND;VALUE=DATE-TIME:20190924T145000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5041@indico.ict.inaf.it
DESCRIPTION:Speakers: David Trillo (IQOQI-Vienna)\nHarnessing the flow of
proper time of arbitrary external systems over which we exert little or no
control has been a recurring theme in both science and science-fiction. U
nfortunately\, all relativistic schemes to achieve this effect beyond mere
time dilation are utterly unrealistic. In this work\, we find that there
exist non-relativistic scattering experiments which\, if successful\, free
ze out\, speed up or even reverse the free dynamics of any ensemble of qua
ntum systems present in the scattering region. This "time warping" effect
is universal\, i.e.\, it is independent of the particular interaction betw
een the scattering particles and the target systems\, or the (possibly non
-Hermitian) Hamiltonian governing the evolution of the latter. The protoco
ls require careful preparation of the probes which are scattered\, and suc
cess is heralded by projective measurements of these probes at the conclus
ion of the experiment. We fully characterize the possible time translation
s which we can effect on n target systems through a scattering protocol of
fixed duration\; the core result is that time can be freely distributed b
etween the systems\, and reversed at a small cost. For high n\, our protoc
ols allow one to quickly send a single system to its far future or past. I
n this sense\, we have devised a time machine for very small stuff.\n\nhtt
ps://indico.ict.inaf.it/event/751/contributions/5041/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5041/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum field measurements without superluminal signalling
DTSTART;VALUE=DATE-TIME:20190924T145000Z
DTEND;VALUE=DATE-TIME:20190924T151000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5183@indico.ict.inaf.it
DESCRIPTION:Speakers: Jason Pye (University of Waterloo)\nAlthough quantum
field theory inherits much of the basic structure laid out by the postula
tes of ordinary quantum mechanics\, it is known that the measurement theor
y cannot go through unscathed. There are examples of idealised measurement
s in quantum field theory which produce superluminal signalling. These exa
mples indicate that endowing quantum theory with a relativistic spacetime
structure restricts the set of admissible quantum operations. There is\, a
s of yet\, no characterisation of these operations. To this end\, here we
proceed to clarify the causality issues which arise in measurements of qua
ntum fields\, as well as characterise a class of permissible measurements.
\n\nhttps://indico.ict.inaf.it/event/751/contributions/5183/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5183/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Preemptive chronology protection and superluminal travel.
DTSTART;VALUE=DATE-TIME:20190924T125500Z
DTEND;VALUE=DATE-TIME:20190924T134000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5229@indico.ict.inaf.it
DESCRIPTION:Speakers: Stefano Liberati (SISSA)\nIn this talk I shall revie
w the implications of superluminal travel and the means by which it can be
achieved in classical General Relativity. We shall then see in the specif
ic case of superluminal warp drives how it seems that a preemptive form of
chronological protection is at work once their dynamics it is analysed wi
thin quantum field theory in curved spacetime. Finally\, we shall discuss
the robustness of this chronological protection with respect the details o
f the spacetime structure.\n\nhttps://indico.ict.inaf.it/event/751/contrib
utions/5229/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5229/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dirac tunneling: superluminal velocities and closed time-like curv
es?
DTSTART;VALUE=DATE-TIME:20190924T121000Z
DTEND;VALUE=DATE-TIME:20190924T125500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5216@indico.ict.inaf.it
DESCRIPTION:Speakers: Randall Dumont (McMaster University\, Hamilton\, On
t.\, Canada)\nThe Hartman effect – first discovered by MacColl\, in 1932
– is the claimed observation that\, when a particle tunnels\, it arrive
s at the opposite side of the barrier the moment it encounters the barrier
. If this is so\, then sufficiently wide barriers and fast particles shoul
d produce superluminal effective velocities. However\, such superluminal e
ffective velocities have been dismissed as attributable solely to uncertai
nty in the initial position of the particle. We examine this position\, an
d further investigate this motif for superluminal velocities\, and associa
ted backward time travel – the latter expected in the particle frame of
reference\, when the particle travels superluminally in the barrier frame.
\n\nhttps://indico.ict.inaf.it/event/751/contributions/5216/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5216/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Black Holes are Time Machines
DTSTART;VALUE=DATE-TIME:20190923T090000Z
DTEND;VALUE=DATE-TIME:20190923T094000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5482@indico.ict.inaf.it
DESCRIPTION:Speakers: Francesca Vidotto (University of Western Ontario\, C
anada)\nWhat would happen if you could enter inside a black hole? You woul
d travel to the future\, coming out of a white hole! In fact\, the huge gr
avitational redshift distinguish two characteristic time for such a proces
s: the one of the infalling observer\, that is fast\, and the one of an ex
ternal observer\, that is extremely long. I discuss how such a process is
allowed by gluing classical metrics without violation of causality. On the
other hand\, the full process is a characteristic non-perturbative quantu
m phenomenon\, that involve the superposition of different geometries. I d
iscuss the condition for this to happen\, including an intriguing realisat
ion in the remnant phase of the black hole.\n\nhttps://indico.ict.inaf.it/
event/751/contributions/5482/
LOCATION:
URL:https://indico.ict.inaf.it/event/751/contributions/5482/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The quantum theory of time: from formalism to experimental test
DTSTART;VALUE=DATE-TIME:20190923T150500Z
DTEND;VALUE=DATE-TIME:20190923T154500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5219@indico.ict.inaf.it
DESCRIPTION:Speakers: Joan A. Vaccaro (Griffith University)\nThe violation
of the discrete symmetries of charge conjugation (C)\, parity inversion (
P)\, and time reversal (T) observed in high energy physics are clearly fun
damental aspects of nature. A new quantum theory [1\,2] has been introduc
ed to demonstrate the possibility that the violations have large-scale phy
sical effects. The new theory does not assume any conservation laws or equ
ations of motion. In particular\, if T violation is turned off\, matter i
s represented in terms of virtual particles that exist momentarily only. H
owever\, with T violation turned on\, what was the mathematical structure
of a virtual particle now traces out an unbounded world line that satisfie
s conservation laws and an equation of motion. The theory is then analogou
s to the 5 dimensional "proper time" formalism introduced by Feynman [3]\,
extended by Nambu [4] in the 1950's\, and developed as "parameterized rel
ativistic quantum theories" [5]. The important point here is that time evo
lution and conservation laws are not built into the new theory\, but rathe
r they emerge _phenomenologically_ from T violation. In other words\, the
new theory proposes that T violation is the _origin of dynamics and conser
vations laws_. It has experimentally testable predictions and offers new
insight into the quantum nature of time.\n\nThe talk will include an analy
sis of the nature of the T violation from known and expected sources such
as mesons\, neutrinos\, and a Higgs-like scalar field. In appropriate par
ameter regimes\, the commutator of the time-reversed versions of the assoc
iated T violating Hamiltonian\, $\\hat{H}_F$ and $\\hat{H}_B$\, is found t
o approach the canonical form $[\\hat{H}_F\,\\hat{H}_B]=i\\lambda \\hat{1}
$ where $\\hat{H}_B=\\hat{T}\\hat{H}_F\\hat{T}^{-1}$\, $\\hat{T}$ is Wigne
r's time reversal operator\, $\\hat{1}$ is the identity operator\, and $\\
lambda=\\langle i[\\hat{H}_F\,\\hat{H}_B]\\rangle$ represents the amount o
f T violation.\n\n[1] J.A. Vaccaro\, Quantum asymmetry between time and sp
ace\, _Proc. R. Soc. A_ __472__\, 20150670 (2016). \nhttps://dx.doi.org/1
0.1098/rspa.2015.0670\n\n[2] J.A. Vaccaro\, The quantum theory of time\, t
he block universe\, and human experience\, _Phil. Trans. R. Soc. Lond. A_
__376__\, 20170316 (2018). https://dx.doi.org/10.1098/rsta.2017.0316\n\n[3
] R.P. Feynman\, Mathematical Formulation of the Quantum Theory of Electro
magnetic Interaction\, _Phys. Rev._ __80__\, 440-457 (1950)\, Appendix A.
https://dx.doi.org/10.1103/PhysRev.80.440\n\n[4] Y. Nambu\, The Use of the
Proper Time in Quantum Electrodynamics I\, _Prog. Theor. Phys._ __5__\, 8
2 (1950). https://dx.doi.org/10.1143/ptp/5.1.82\n\n[5] J.R. Fanchi\, Revie
w of invariant time formulations of relativistic quantum theories\, _Found
. Phys._ __23__\, 487-548 (1993). https://dx.doi.org/10.1007/BF01883726\n\
nhttps://indico.ict.inaf.it/event/751/contributions/5219/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5219/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sound Propagation in the Ellis Wormhole
DTSTART;VALUE=DATE-TIME:20190925T080500Z
DTEND;VALUE=DATE-TIME:20190925T082500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5043@indico.ict.inaf.it
DESCRIPTION:Speakers: Zaza Osmanov (Free University of Tbilisi)\nFor the s
implest case of Ellis Wormhole (WH) the fluid moving through the mentioned
metrics is considered. For this purpose\, the set of linearized equations
composed of the Euler and continuity equations is examined. The propagati
on of sound waves has been considered and corresponding non-trivial analyt
ical and numerical results – obtained.\n\nhttps://indico.ict.inaf.it/eve
nt/751/contributions/5043/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5043/
END:VEVENT
BEGIN:VEVENT
SUMMARY:A gravitational collapse singularity theorem which does not requir
e chronology
DTSTART;VALUE=DATE-TIME:20190924T085000Z
DTEND;VALUE=DATE-TIME:20190924T092500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5181@indico.ict.inaf.it
DESCRIPTION:Speakers: Ettore Minguzzi ()\nI present a new gravitational co
llapse singularity theorem which improves Penrose's and which does not ass
ume predictability (global hyperbolicity) while it is compatible with chro
nology violation (closed timelike curves) and black hole evaporation.\n\nh
ttps://indico.ict.inaf.it/event/751/contributions/5181/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5181/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The role of causality in quantum gravity
DTSTART;VALUE=DATE-TIME:20190924T070000Z
DTEND;VALUE=DATE-TIME:20190924T074500Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5222@indico.ict.inaf.it
DESCRIPTION:Speakers: Sumati Surya (Raman Research Institute)\nThe notion
of causality\, both local or global\, is tied inextricably to the Lorentzi
an character of spacetime.\nThis is embodied by the causal structure poset
which\, given weak causality constriants\, determines the conformal\nspac
etime geometry. This is the starting point for the causal set approach to
quantum gravity\, where the\nunderlying continuum is replaced by a locally
finite partially ordered set. In this talk I will discuss the role played
by\ncausality both kinematically and dynamically in quantum gravity\, wit
h a focus on the causal set approach.\n\nhttps://indico.ict.inaf.it/event/
751/contributions/5222/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5222/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The temporally nonlocal character of the quantum computational spe
edup
DTSTART;VALUE=DATE-TIME:20190923T161000Z
DTEND;VALUE=DATE-TIME:20190923T163000Z
DTSTAMP;VALUE=DATE-TIME:20191017T185822Z
UID:indico-contribution-751-5038@indico.ict.inaf.it
DESCRIPTION:Speakers: Giuseppe Castagnoli (Elsag Bailey ICT Division and Q
uantum information Laboratory)\nOne says that there is a *quantum computat
ional speedup* when the computation of the solution of a problem is more e
fficient quantumly than classically. Let us consider\, as an example\, the
simplest case that Bob\, the problem setter\, hides a ball in a chest of
four drawers. Alice\, the problem solver\, is to locate in by opening draw
ers (by querying the oracle: is the ball in that drawer?). While in the cl
assical case Alice may need to open up to three drawers\, with the quantum
algorithm devised by Grover she only needs to open one.\nThe usual repres
entation of quantum algorithms is limited to the computation of the soluti
on of the problem. We extend it to the process of setting the problem. Bob
\, who operates on the quantum register B\, randomly selects the problem-s
etting (the number of the drawer with the ball) by an initial measurement
in a (possibly incoherent) superposition of all the possible problem-setti
ngs. He could then unitarily change it into a desired setting but for simp
licity we omit this operation. Alice\, who operates on the quantum regist
er A initially in an arbitrary sharp state (standing for a blank blackboar
d)\, unitarily computes the corresponding solution and reads it by the fin
al measurement. With probability one of reading the solution\, the process
between the initial and final measurement outcomes is reversible – no i
nformation is destroyed along it. \nWe physically represent the fact that
the problem-setting selected by Bob must be hidden from Alice (it would te
ll her the solution of the problem) by relativizing the extended represent
ation to her. In the representation with respect to Alice\, the projection
of the quantum state associated with the initial measurement is postponed
till the end of the unitary part of her problem-solving action. After the
initial measurement\, the quantum state of register B to Alice remains th
e quantum superposition of all the possible problem settings. It represent
s her complete ignorance of the problem setting selected by Bob. Alice uni
tarily changes the tensor product of this superposition and the sharp stat
e of register A into a superposition of tensor products\, each a problem s
etting in B multiplied by the corresponding solution in A. Then she select
s the problem setting already selected by Bob by the final measurement of
the solution. \nWe represent the reversibility of the process between the
initial and final measurement outcomes by time-symmetrizing it. In this ki
nd of process\, and in the usual way of seeing\, the information that spec
ifies the initial measurement outcome and consequently the final one (in t
he present example\, both the number of the drawer with the ball) is all s
elected by the initial measurement\; its outcome (encoding the problem set
ting selected by Bob in register B) undergoes the time forward unitary tra
nsformation until becoming the state before the final measurement (encodin
g the solution in register A). The latter measurement just reads the solut
ion encoded in A\, without selecting anything. However\, the thing could b
e seen in the time-symmetric way. The initial measurement does not select
anything\, the initial state superposition undergoes the unitary transform
ation that represents Alice’s problem solving action and the final measu
rement performs all the selection. The measurement outcome\, which encodes
the solution in register A\, by the Parisian Zigzag propagates backwards
in time by the inverse unitary transformation until becoming the outcome o
f the initial measurement\, encoding the problem setting in register B. \n
However\, either way of seeing\, introducing a preferred direction of time
\, is not symmetric in time. According to the tenet of the Two-State-Vecto
r Formalism\, we assume that the initial and final measurements evenly con
tribute to determining the process in between\, namely to selecting the in
formation that specifies either measurement outcome. The half information
selected by the initial measurement propagates forward in time\, that sele
cted by the final measurement backwards in time according to the Parisian
Zigzag. Since there are many ways of halving the information\, we should t
ake all the corresponding time-symmetrization instances in quantum superpo
sition. \nThis time-symmetrization procedure leaves the extended represent
ation of the quantum algorithm\, which is ordinary in character since no o
bserver is shielded from any measurement outcome\, unaltered.\nIt shows th
at the representation of the quantum algorithm relativized to Alice is a s
uperposition of (partly overlapping) superpositions\, the time-symmetrizat
ion instances\, each a quantum algorithm by itself. In each instance\, Ali
ce remains shielded from the information coming to her from the initial me
asurement\, not from that coming to her from the final measurement. The co
mputational complexity of the problem to be solved by her is corresponding
ly reduced. All is as if she knew in advance\, before performing the unita
ry part of her problem-solving action\, half of the information that speci
fies the problem-setting and thus the solution of the problem and could us
e this information to reach the solution with fewer oracle queries. This a
ccounts for the quantum computational speedup. The fact that the final mea
surement non-locally changes the state of register B to Alice at the begin
ning of the unitary part of the quantum algorithm\, from a superposition o
f all the problem setting to that of a reduced part thereof\, is of course
a form of temporal nonlocality. It cannot be seen in the usual representa
tion of quantum algorithm\, which\, by an application of the principle of
locality\, replaces the initial measurement by its measurement outcome.\nT
he above accounts for the computational speedup of all the quantum algorit
hms examined. These comprise the major quantum algorithms and cover both t
he quadratic and exponential speedups. More generally\, given an oracle pr
oblem\, the number of oracle queries required to solve it in an optimal qu
antum way is that of a classical algorithm (a Turing machine) endowed with
the advanced knowledge of half of the information that specifies the sett
ing and the corresponding solution of the problem.\nThe fact that\, in eac
h time-symmetrization instance\, Alice knows in advance half of the soluti
on she will read in the future and uses this information to reach the solu
tion with fewer oracle queries is a half causal loop. Its physical viabili
ty is discussed. The fact that there is apparently information going back
in time from the final to the initial measurement is compensated for by th
e fact that one has to take the superposition of all the instances (appare
nt backward causality is compensated for by the indeterminacy inherent in
the very notion of quantum superposition). This superposition – the quan
tum algorithm to Alice back again – is an ordinary quantum mechanical su
perposition\, where apparently no information is sent back in time.\n**Ref
erences**\nEkert\, A. K. and Jozsa\, R.: Quantum Algorithms: Entanglement
Enhanced Information Processing arXiv:quant-ph/9803072 (1998)\nDolev\, S.
and Elitzur\, A. C.: Non-sequential behavior of the wave function. arXiv:q
uant-ph/0102109 v1 (2001) \nCastagnoli\, G. and Finkelstein\, D. R.: Theor
y of the quantum speedup. Proc. Roy. Soc. A 1799\, 457\, 1799-1807 (2001)
\nCastagnoli\, G.: The quantum correlation between the selection of the pr
oblem and that of the solution sheds light on the mechanism of the quantum
speed up. Phys. Rev. A 82\, 052334-052342 (2010)\nAharonov\, Y.\, Cohen\,
E.\, and Elitzur\, A. C.: Can a future choice affect a past measurement o
utcome? Ann. Phys. 355\, 258-268 (2015)\nElitzur\, A.C.\, Cohen\, E.\, Oka
moto\, R. and Takeuchi\, S.: Nonlocal position changes of a photon reveale
d by quantum routers. Sci. Rep. 8\, 7730 (2018)\n\nhttps://indico.ict.inaf
.it/event/751/contributions/5038/
LOCATION:Turin
URL:https://indico.ict.inaf.it/event/751/contributions/5038/
END:VEVENT
END:VCALENDAR