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BEGIN:VEVENT
SUMMARY:Quantum reference frames for space and space-time
DTSTART:20210614T164000Z
DTEND:20210614T172000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-91@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Časlav Brukner (University of Vienna)\n\nIn physics
\, a reference frame is an abstract coordinate system that specifies obser
vations within that frame. While quantum states depend on the choice of re
ference frame\, the form of physical laws is assumed to be covariant. Rece
ntly\, it has been proposed to consider reference frames as physical syste
ms and as such assume that they obey quantum mechanics. In my talk\, I wil
l present recent results in the field of "quantum reference frames" (QRF).
In particular\, I will formulate the covariance of dynamical physical law
s with respect to non-relativistic QRF transformations and show how relati
vistic QRFs can be used to solve a long-standing problem in relativistic q
uantum information or to address typical quantum gravity scenarios.\n\nhtt
ps://events.perimeterinstitute.ca/event/6/contributions/91/
URL:https://events.perimeterinstitute.ca/event/6/contributions/91/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Non-causal Page-Wootters circuits
DTSTART:20210614T152000Z
DTEND:20210614T160000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-90@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Veronika Baumann (IQOQI Vienna)\n\n"The process m
atrix framework was invented to capture a phenomenon known as indefinite o
r quantum causal structure. Due to the generality of that framework\, howe
ver\, for many process matrices there is no clear physical interpretation.
A popular approach towards a quantum theory of gravity is the Page-Wootte
rs formalism\, which associates to time a Hilbert space structure similar
to spatial position. By explicitly introducing a quantum clock\, it allows
to describe time-evolution of systems via correlations between this clock
and said systems encoded in history states. We combine the process matrix
framework with a generalization of the Page-Wootters formalism in which o
ne considers several observers\, each with their own discrete quantum cloc
k. \nThis allows for implementing processes with indefinite casual order.
The description via a history state with multiple clocks imposes constrain
ts on the implementability of process matrices intros framework and on the
perspectives of the observers. We describe how to to implement processes
were the different definite causal orders are coherently controlled and ex
plain why certain non-causal processes might not be implementable within t
his setting."\n\nhttps://events.perimeterinstitute.ca/event/6/contribution
s/90/
URL:https://events.perimeterinstitute.ca/event/6/contributions/90/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Composite quantum particles as ideal quantum clocks — operationa
l approach to quantum aspects of time
DTSTART:20210614T130000Z
DTEND:20210614T134000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-87@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Magdalena Zych (University of Queensland)\n\nIn gene
ral relativity time requires an operational description\, for example\, as
sociated with the reading of an idealised clock following some world line.
I will show that in quantum physics idealised clocks can be modelled as c
omposite quantum particles and discuss what foundational insights into the
notion of time is enabled by this approach. Moreover\, since quantum part
icles do do not follow classical trajectories a question arises to which e
xtent idealised quantum clocks can be associated with semi-classical paths
— in analogy with quantum particles in Gaussian states being associated
with semi-classical trajectories? I will show that for quantum clocks sem
i-classical propagation is not described by Gaussian but by a new class of
quantum states derived from a new uncertainty inequality for configuratio
n space rather than for phase space variables of the quantum clock.\n\nhtt
ps://events.perimeterinstitute.ca/event/6/contributions/87/
URL:https://events.perimeterinstitute.ca/event/6/contributions/87/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kappa-Minkowski: physics with noncommutative time
DTSTART:20210614T134000Z
DTEND:20210614T142000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-88@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Flavio Mercati (University of Burgos)\n\nThe kapp
a-Minkowski noncommutative spacetime has been studied for a long time as a
n example of quantum spacetime with nontrivial commutation relations betwe
en spatial and temporal coordinates which\, at first sight\, seem to break
Poincaré invariance. However kappa-Minkowski is invariant under a Hopf-a
lgebra deformation of the Poincaré group\, which involves some noncommuta
tive structures that prevent the sharp localization of reference frames. I
will describe recent progress towards the consistent construction of quan
tum field theories on this spacetime\, and the identification of physical
predictions that genuinely distinguish kappa-Minkowski from ordinary\, com
mutative Minkowski spacetime.\n\nhttps://events.perimeterinstitute.ca/even
t/6/contributions/88/
URL:https://events.perimeterinstitute.ca/event/6/contributions/88/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantizing causation
DTSTART:20210614T144000Z
DTEND:20210614T152000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-89@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Robert Spekkens (Perimeter Institute)\n\n"Spatio-tem
poral relations are often taken to be more primitive than causal relations
. Such a relationship is assumed whenever it is suggested that it is part
of the definition of a causal relation that the cause must precede the ef
fect in time. There are good reasons\, however\, to take causation to be t
he more primitive notion\, with spatio-temporal relations merely describin
g aspects of causal relations. In such an approach\, to understand what p
ossibilities there are for an intrinsically quantum notion of time\, it is
helpful to understand what possibilities there are for an intrinsically q
uantum notion of causation. In short\, how time is quantized is informed
by how causation is quantized. The latter question will be the focus of t
his talk. I will describe a research program wherein the transition from c
lassical to quantum is understood as an innovation to the notions of causa
tion and inference. This is done by introducing the notion of a causal-in
ferential theory: a triple consisting of a theory of causal influences\, a
theory of inferences (of both the Boolean and Bayesian varieties)\, and a
specification of how these interact. The possibility of defining causal-
inferential theories by the axioms they satisfy provides a means of provid
ing abstract and structural characterizations of the notions of causation
and inference. In other words\, within this approach\, the new notions of
causation and inference will stand to the traditional notions in much the
same way that the notions of points and lines in nonEuclidean geometry st
and to their traditional counterparts in Euclidean geometry. \nBased on:
D. Schmid\, J. Selby\, and R. Spekkens\, Unscrambling the omelette of caus
ation and inference: The framework of causal-inferential theories\, arXiv:
2009.03297 (quant-ph)."\n\nhttps://events.perimeterinstitute.ca/event/6/co
ntributions/89/
URL:https://events.perimeterinstitute.ca/event/6/contributions/89/
END:VEVENT
BEGIN:VEVENT
SUMMARY:A New Perspective on Time Reversal Motivated by Quantum Gravity
DTSTART:20210615T130000Z
DTEND:20210615T134000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-92@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Abhay Ashtekar (Pennsylvania State University)\n\nTi
me Reversal T is usually discussed in the traditional framework of quantum
mechanics in which T is represented by an anti-unitary operator. But quan
tum gravity may well need generalization of standard quantum mechanics whi
ch may not preserve even its linear structure\, let alone the unitarity of
dynamics and anti-unitarity of T. Then the currently used arguments to co
nclude that T violation is a fundamental aspect of Nature will break down.
Fortunately\, it turns out that one can analyze the T-violation experimen
ts in a much more general setting\, of which classical and quantum mechani
cs are special cases. The setting does not require a Hilbert space\, or li
nearity of either dynamics or symmetry operations such as T. Nonetheless\,
somewhat surprisingly\, one would still be to use the current experiments
to conclude that there is T violation at a fundamental level under rather
minimal assumptions on the structure of the final quantum gravity theory.
\n\nhttps://events.perimeterinstitute.ca/event/6/contributions/92/
URL:https://events.perimeterinstitute.ca/event/6/contributions/92/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Space and Time in a Lorentzian path integral
DTSTART:20210615T134000Z
DTEND:20210615T142000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-93@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Bianca Dittrich (Perimeter Institute)\n\nI will p
resent a quantum gravity approach based on a Lorentzian path integral for
quantum geometries. The properties of quantum space time can be measured
using geometric operators. This allows also to discuss fluctuations of cau
sal structure as well as violations of (micro-) causality. I will explain
how the Lorentzian path integral comes with various options regarding whic
h quantum space times to sum over: e.g. whether to include causality viola
tions or not\, or whether to allow also for space times with Euclidean sig
natures in Lorentzian path integrals. I will sketch some consequences for
the resulting theories.\n\nhttps://events.perimeterinstitute.ca/event/6/co
ntributions/93/
URL:https://events.perimeterinstitute.ca/event/6/contributions/93/
END:VEVENT
BEGIN:VEVENT
SUMMARY:"TIME IN QUANTUM GRAVITY - From the fundamental level to the class
ical limit"
DTSTART:20210615T144000Z
DTEND:20210615T152000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-94@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Claus Kiefer (University of Cologne)\n\nTime cannot
be both absolute (as in quantum mechanics) and dynamical (as in general r
elativity). I present general arguments for the absence of time at the mos
t fundamental level of quantum gravity. I discuss possible concepts that c
ould replace it and present the recovery of standard time as an approximat
e concept. My discussion is restricted to quantum geometrodynamics\, but I
argue for the validity of my conclusions beyond that scheme.\n\nhttps://e
vents.perimeterinstitute.ca/event/6/contributions/94/
URL:https://events.perimeterinstitute.ca/event/6/contributions/94/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The emergence of quantum mechanics and space\, from a fundamental\
, active time
DTSTART:20210615T152000Z
DTEND:20210615T160000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-96@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Lee Smolin (Perimeter Institute)\n\n"We propose a re
alist completion of quantum mechanics\, in the sense of a complete descrip
tion of individual events. The proposed fundamental theory assumes that t
ime\, events\, causal structure\, momentum and energy are fundamental. But
space and the wave function are emergent.\n\nThe beables of the theory ar
e the views of the events\, which are a subset of their causal pasts. Thus
\, this theory asserts that the universe is a causal network of events\, w
hich consists of partial views of itself as seen by looking backwards from
each event.\n\nThe theory is based on a simple action principle\, which \
nextremizes the variety of the universe\, which is a measure of the divers
ity of its partial views. The Schroedinger equation is derived\, while t
o higher order\, there are computable corrections\, non-linear in the wave
function\, from which new physical effects may be predicted.\n\nFinally\,
a relativistic version is sketched\, in wqhich the views are built on the
celestial sphere. "\n\nhttps://events.perimeterinstitute.ca/event/6/contr
ibutions/96/
URL:https://events.perimeterinstitute.ca/event/6/contributions/96/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum measurements of time
DTSTART:20210616T134000Z
DTEND:20210616T142000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-98@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Lorenzo Maccone (University of Pavia)\n\n"We prop
ose a time-of-arrival operator in quantum mechanics by conditioning on a q
uantum clock. This allows us to bypass some of the problems of previous pr
oposals\, and to obtain a Hermitian time of arrival operator whose probabi
lity distribution arises from the Born rule and which has a clear physical
interpretation. The same procedure can be employed to measure the ""time
at which some event happens"" for arbitrary events (and not just specifica
lly for the arrival time of a particle).\n\nThis talk is based on the pape
r: L. Maccone\, K. Sacha\, Quantum measurements of time\, Phys. Rev. Lett.
124\, 110402 (2020)."\n\nhttps://events.perimeterinstitute.ca/event/6/con
tributions/98/
URL:https://events.perimeterinstitute.ca/event/6/contributions/98/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Measuring time with stationary quantum clocks
DTSTART:20210617T152000Z
DTEND:20210617T160000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-106@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Mischa Woods (ETH Zurich)\n\nTime plays a fundamenta
l role in our ability to make sense of the physical laws in the world arou
nd us. The nature of time has puzzled people –- from the ancient Greeks
to the present day -– resulting in a long running debate between philos
ophers and physicists alike to whether time needs change to exist (the so-
called relatival theory)\, or whether time flows regardless of change (the
so-called substantival theory). One way to decide between the two is to a
ttempt to measure the flow of time with a stationary clock\, since if time
were substantival\, the flow of time would manifest itself in the experim
ent. Alas\, conventional wisdom suggests that in order for a clock to func
tion\, it cannot be a static object\, thus rendering this experiment seemi
ngly impossible. We show that counter-intuitively\, a quantum clock can me
asure the passage of time\, even while being switched off\, lending suppor
t for the substantival theory of time.\n\nhttps://events.perimeterinstitut
e.ca/event/6/contributions/106/
URL:https://events.perimeterinstitute.ca/event/6/contributions/106/
END:VEVENT
BEGIN:VEVENT
SUMMARY:(Quantum) frame covariance: from foundations via gauge theories to
gravity
DTSTART:20210616T130000Z
DTEND:20210616T134000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-97@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Philipp Hoehn (University College London)\n\nI wil
l sketch how the perspective-neutral approach to (quantum) frame covarianc
e brings together some recent developments on dynamical reference frames i
n quantum foundations\, gauge theories and gravity. The survey will touch
on spatial frames\, quantum clocks and the problem of time\, edge modes\,
and the relativity of subsystems.\n\nhttps://events.perimeterinstitute.ca/
event/6/contributions/97/
URL:https://events.perimeterinstitute.ca/event/6/contributions/97/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Relative subsystems and quantum reference frame transformations.
DTSTART:20210616T144000Z
DTEND:20210616T152000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-99@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Esteban Castro Ruiz (ETH Zurich)\n\nTransformations
between reference frames play a crucial role in our understanding of physi
cal processes. In practice\, reference frames are realised by physical sys
tems\, which are standardly treated as classical. However\, assuming that
every physical system is ultimately quantum\, it is interesting to ask how
a theory of transformations wrt quantum reference frames would look like\
, and what implications it would have for our description of spacetime. Re
cently\, there has been a lot of effort towards developing a quantum gener
alisation of reference frame transformations\, unveiling novel phenomena t
hat are absent in the classical treatment of reference frames. Here\, we d
evelop a first-principles framework for quantum reference frame transforma
tions which clarifies important conceptual issues of previous treatments.
Based on the algebra of relative observables between a system and a refer
ence frame\, our operational perspective leads naturally to a mixed-state
approach (incoherent twirling)\, in contrast to current pure-state approac
hes (coherent twirling). Within our framework\, the full invariant quantum
subsystem contains not only the algebra of relative observables between t
he system and the reference frame but also an “extra particle\,” relat
ed to the invariant degrees of freedom of the reference frame itself. Impo
rtantly\, this extra particle contains information about the “quantumnes
s” of the reference frame and is essential to the unitarity of quantum r
eference frame transformations. Our approach is general\, in the sense tha
t it can be applied to a vast set of symmetry groups and to any type of sy
stem. We illustrate the physical meaning of the concepts developed by anal
ysing quantum reference frame transformations with respect to the (central
ly extended) Galilei group.\n\nhttps://events.perimeterinstitute.ca/event/
6/contributions/99/
URL:https://events.perimeterinstitute.ca/event/6/contributions/99/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Relational dynamics: interacting clocks and systems and quantum ti
me dilation
DTSTART:20210616T152000Z
DTEND:20210616T160000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-100@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Mehdi Ahmadi (Santa Clara University)\n\nTime is abs
olute in quantum mechanics\, whereas it is dynamical in general relativity
. This is considered as one of the main obstacles towards unifying quantum
theory and gravity. Relational quantum dynamics offers a possible solutio
n by treating clocks as internal quantum systems\, which promotes time to
a dynamical quantity. This talk begins with a quick overview of time in re
lational quantum dynamics. We then explain that the inclusion of an intera
ction term coupling the clock and system causes the system dynamics to be
governed by a time-nonlocal Schrödinger equation. Moreover\, we demonstra
te a quantum time dilation phenomena wherein we analyze the effect of non-
classical states of quantum clocks on relativistic time dilation.\n\nhttps
://events.perimeterinstitute.ca/event/6/contributions/100/
URL:https://events.perimeterinstitute.ca/event/6/contributions/100/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The Issue of Time in Generally Covariant Theories
DTSTART:20210616T164000Z
DTEND:20210616T172000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-101@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Rodolfo Gambini (Universidad de Montevideo)\n\nA pos
sible solution of the problem of time in quantum gravitational systems is
presented based on a relational description between the parameterized Dira
c observables of the system under consideration and the clocks. The use of
physical clocks required by a quantum gravitational description of time i
s shown to induce a loss of unitarity. The evolution is described by a Lin
dblad-type master equation unless it is possible to construct a perfect cl
ock. I show that fundamental uncertainties in time measurements could aris
e due to quantum and gravitational effects\, leading to the conclusion tha
t there is always a loss of unitarity induced by the use of physical clock
s. The extension of the analysis to physical reference frames in totally c
onstrained systems is sketched.\n\nhttps://events.perimeterinstitute.ca/ev
ent/6/contributions/101/
URL:https://events.perimeterinstitute.ca/event/6/contributions/101/
END:VEVENT
BEGIN:VEVENT
SUMMARY:What can information theory tell us about time?
DTSTART:20210616T180000Z
DTEND:20210616T190000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-102@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Renato Renner (ETH Zurich)\n\nInformation theory i
s an invaluable tool for studying questions around the foundations of phys
ics. In thermodynamics\, for example\, it provides the key to resolving ap
parent contradictions\, such as the famous Maxwell's demon paradox. Conver
sely\, information theory lends itself to the conception of novel paradoxe
s\, such as the black hole information paradox\, which helps us sharpening
our physical intuition. One may therefore ask whether an information-theo
retic perspective can also yield insights on the nature of time. In this t
alk\, I will explain some of the conceptual problems that arise when one t
ries to capture time with information-theoretic methods\, and discuss poss
ible routes to move forward.\n\nhttps://events.perimeterinstitute.ca/event
/6/contributions/102/
URL:https://events.perimeterinstitute.ca/event/6/contributions/102/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Time and Noether's (first) theorem
DTSTART:20210617T130000Z
DTEND:20210617T134000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-103@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Harvey Brown (University of Oxford)\n\n"It is widel
y believed that the homogeneity of time is the symmetry related by Noether
's (first) theorem to the conservation of energy\, and indeed that it expl
ains energy conservation. Both claims are questionable\, and in particular
seemingly hard to reconcile with the modern version of Noether's first th
eorem due independently to Martínes Alonso (1979) and Olver (1986). \nThe
talk is based on: 'Do symmetries ""explain"" conservation laws? ...' \nar
Xiv:2010.10909v1"\n\nhttps://events.perimeterinstitute.ca/event/6/contribu
tions/103/
URL:https://events.perimeterinstitute.ca/event/6/contributions/103/
END:VEVENT
BEGIN:VEVENT
SUMMARY:God does not play dice (He plays sudoku)
DTSTART:20210617T134000Z
DTEND:20210617T142000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-104@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Emily Adlam (Basic Research Community for Physics)\
n\nI argue that modern physics gives us good reason to take seriously the
possibility of laws which are non-local\, global\, or in some other way no
n-dynamical. I set out a general framework for lawhood which does not pres
uppose the standard kinematical/dynamical split\, and I apply it to the pr
oblem of giving a generalized definition of determinism for the non-dynami
cal context. Finally I make some suggestions about how to draw conclusions
about the global structure of the laws of nature from the local observati
ons we are able to make.\n\nhttps://events.perimeterinstitute.ca/event/6/c
ontributions/104/
URL:https://events.perimeterinstitute.ca/event/6/contributions/104/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Time in Physics and Intuitionistic Mathematics
DTSTART:20210617T144000Z
DTEND:20210617T152000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-105@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Nicolas Gisin (University of Geneva & Schaffhausen I
nstitute of Technology-Geneva)\n\n"Physics is formulated in terms of timel
ess axiomatic mathematics. However\, time is essential in all our stories\
, in particular in physics. For example\, to think of an event is to think
of something in time. A formulation of physics based of intuitionism\, a
constructive form of mathematics built on time-evolving processes\, would
offer a perspective that is closer to our experience of physical reality a
nd may help bridging the gap between static relativity and quantum indeter
minacy.\nHistorically\, intuitionistic mathematics was introduced by L.E.J
. Brouwer with a very subjectivist view where an idealized mathematician c
ontinually produces new information by solving conjectures. Here\, in cont
rast\, I’ll introduce intuitionism as an objective mathematics that inco
rporates a dynamical/creative time and an open future. Standard (classical
) mathematics appears as the view from the “end of time” and the usual
real numbers appear as the hidden variables of classical physics. Similar
ly\, determinism appears as indeterminism seen from the “end of time”.
\nRelativity is often presented as incompatible with indeterminism. Hence
\, at the end of this presentation I’ll argue that these incompatibility
arguments are based on unjustified assumptions and present the “relativ
ity of indeterminacy”.\n\nReferences:\nC. Posy\, Mathematical Intuitioni
sm\, Cambridge Univ. Press\, 2020.\nN. Gisin\, Indeterminism in Physics\,
Classical Chaos and Bohmian Mechanics. Are Real Numbers Really Real?\, Erk
enntnis (2019)\, https://doi.org/10.1007/s10670-019-00165-8 \nN. Gisin\, R
eal Numbers are the Hidden Variables of Classical Mechanics\, Quantum Stud
ies: Mathematics and Foundations 7\, 197-201 (2020).\nFlavio Del Santo and
N. Gisin\, Physics without determinism: Alternative interpretations of cl
assical physics\, Physical Review A 100.6 (2019).\nN. Gisin\, Mathematical
languages shape our understanding of time in physics\, Nature Physics 16\
, 114-119 (2020).\nN. Gisin Indeterminism in Physics and Intuitionistic Ma
thematics\, arXiv:2011.02348\nFlavio Del Santo and N. Gisin\, The Relativi
ty of Indeterminacy\, arXiv:2101.04134"\n\nhttps://events.perimeterinstitu
te.ca/event/6/contributions/105/
URL:https://events.perimeterinstitute.ca/event/6/contributions/105/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Measuring Quantum Discreteness of Time in the Lab with Gravity Ent
anglement Interference
DTSTART:20210617T164000Z
DTEND:20210617T172000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-107@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Carlo Rovelli (Centre de Physique Theorique)\n\nT
he concrete perspective of using interference to measure Gravity Induced E
ntanglement in the lab is a very exciting development for quantum gravity.
While the measurements considered so far only test the nonrelativistic re
gime\, the same technique might allow access to genuine relativistic quant
um effects. Among these\, there might be the possibility of direct detecti
on of time quantum discreteness.\n\nhttps://events.perimeterinstitute.ca/e
vent/6/contributions/107/
URL:https://events.perimeterinstitute.ca/event/6/contributions/107/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Relational observables and quantum diffeomorphisms on the worldlin
e
DTSTART:20210618T130000Z
DTEND:20210618T132000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-108@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Leonardo Chataignier (University of Cologne)\n\n"Can
didate theories of quantum gravity must answer the questions: how can the
dynamics of quantum states of matter and geometry be defined in a diffeomo
rphism-invariant way? How are the quantum states related to probabilities
in the absence of a preferred time? To address these issues\, we discuss
the construction and interpretation of relational observables in quantum t
heories with worldline diffeomorphism invariance\, which serve as toy mode
ls of quantum gravity. In this context\, we present a method of constructi
on of quantum relational observables which is analogous to the constructio
n of gauge-invariant extensions of noninvariant quantities in usual gauge
(Yang-Mills) theories. Furthermore\, we discuss how the notion of a physic
al propagator may be used to define a unitary evolution in the quantum the
ory\, which is to be understood in terms of a generalized clock\, as is th
e classical theory. We also discuss under which circumstances this forma
lism can be related to the use of conditional probabilities in a generaliz
ation of the Page-Wootters approach. Finally\, we also examine how our for
malism can be adapted to calculations of quantum-gravitational effects in
the early Universe.\nRefs.: L. Chataignier\, Phys. Rev. D 101\, 086001 (
2020)\; 103\, 026013 (2021)\; 103\, 066005 (2021)"\n\nhttps://events.per
imeterinstitute.ca/event/6/contributions/108/
URL:https://events.perimeterinstitute.ca/event/6/contributions/108/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Relational dynamics in an emergent spacetime context
DTSTART:20210618T132000Z
DTEND:20210618T134000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-109@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Luca Marchetti (University of Pisa\, LMU Munich)\n\n
I discuss the new dimension that the relational approach to the problem of
time takes in quantum gravity contexts in which spacetime and geometry ar
e understood as emergent. I argue that\, in this case\, the relational str
ategy is best realized at an approximate and effective level\, after suita
ble coarse graining and only in terms of special quantum states. I then sh
ow a concrete realization of such effective relational dynamics in the con
text of a cosmological application of the tensorial group field theory for
malism for quantum gravity.\n\nhttps://events.perimeterinstitute.ca/event/
6/contributions/109/
URL:https://events.perimeterinstitute.ca/event/6/contributions/109/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Times of arrival and gauge invariance
DTSTART:20210618T140000Z
DTEND:20210618T142000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-112@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Siddhant Das (Ludwig Maximilian University of Munich
)\n\n"We revisit the arguments underlying two well-known arrival-time dist
ributions in quantum mechanics\, viz.\,\nthe Aharonov-Bohm and Kijowski (A
BK) distribution\, applicable for freely moving particles\, and the quantu
m\nflux (QF) distribution. An inconsistency in the original axiomatic deri
vation of Kijowski’s result is pointed out\,\nalong with an inescapable
consequence of the “negative arrival times” inherent to this proposal
(and generalizations thereof). The ABK free-particle restriction is lifted
in a discussion of an explicit arrival-time setup\nfeaturing a charged pa
rticle moving in a constant magnetic field. A natural generalization of th
e ABK distribution is in this case shown to be critically gauge-dependent.
A direct comparison to the QF distribution\,\nwhich does not exhibit this
flaw\, is drawn (its acknowledged drawback concerning the quantum backflo
w effect\nnotwithstanding).\n\nBased on a recent paper (https://arxiv.org/
abs/2102.02661)\, to be published in Proceedings of the Royal Society A."
\n\nhttps://events.perimeterinstitute.ca/event/6/contributions/112/
URL:https://events.perimeterinstitute.ca/event/6/contributions/112/
END:VEVENT
BEGIN:VEVENT
SUMMARY:What does the Path Integral imply for Quantizing Time?
DTSTART:20210618T144000Z
DTEND:20210618T150000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-113@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Ken Wharton (San Jose State University)\n\n"Even th
ough path-integral formulations of quantum theory are thought to be equiva
lent to state-based approaches\, path-integrals are rarely used to motivat
e answers to foundational questions. This talk will summarize a number of
implications concerning time and time-symmetry which result from the path
-integral viewpoint. Such a perspective sheds serious doubt on dynamical
collapse theories\, and also pushes against efforts to extend configuratio
n space to include multiple time dimensions. A recently-developed map bet
ween all possible two-qubit entangled states and spacetime-based path-inte
grals sheds further doubt on any need to extend spacetime to a large ontol
ogical configuration space. \n (References include arXiv:2103.02425\, 1
512.00740\, 1103.2492 .)"\n\nhttps://events.perimeterinstitute.ca/event/6/
contributions/113/
URL:https://events.perimeterinstitute.ca/event/6/contributions/113/
END:VEVENT
BEGIN:VEVENT
SUMMARY:An experiment to detect the Discreteness of time
DTSTART:20210618T150000Z
DTEND:20210618T152000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-114@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Marios Christodoulou (The University of Hong Kong)\n
\nTo this date no empirical evidence contradicts general relativity. In pa
rticular\, there is no experimental proof a quantum theory of gravity is n
eeded. Surprisingly\, it appears likely that the first such evidence woul
d come from experiments that involve non relativistic matter and extremely
weak gravitational fields. The conceptual key for this is the Planck mas
s\, a mesoscopic mass scale\, and how it relates with what remains of gene
ral relativity in the Newtonian limit: time dilation. Indeed\, current te
chnological capabilities can amplify differences in time dilation superpos
ition that are much smaller than the smallest time interval that can be me
asured by an atomic clock. Inspired from recent proposals to detect non--c
lassicality of the gravitational field\, we devise and examine the feasib
ility of an experiment that could detect a granularity of time at the Pla
nck scale.\n\nhttps://events.perimeterinstitute.ca/event/6/contributions/1
14/
URL:https://events.perimeterinstitute.ca/event/6/contributions/114/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Representing time and time's arrow
DTSTART:20210618T152000Z
DTEND:20210618T154000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-115@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Bryan Roberts (London School of Economics & Politica
l Science)\n\nWhat does it mean to say that a curve in state space describ
es change with respect to time\, as opposed to space or any other paramete
r? What does it mean to say it's time is asymmetric? Inspired by the Wigne
r-Bargmann analysis of the Poincaré group\, I discuss a general framework
for understanding the meaning of time evolution and temporal symmetry in
terms of the representation of a semigroup that includes "time translation
s"\, amongst the automorphisms of a state space. I discuss the structurali
st and functionalist philosophical underpinnings of this view\, and show h
ow time reversal\, parity\, matter-antimatter exchange\, and CPT are best
viewed as extensions of a representation of continuous symmetries\, whose
existence is sensitive to the underlying structure of state space. I concl
ude with some comments on how an arrow of time can be defined in this fram
ework\, as well as prospects for such an arrow in the context of gravitati
on.\n\nhttps://events.perimeterinstitute.ca/event/6/contributions/115/
URL:https://events.perimeterinstitute.ca/event/6/contributions/115/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Arrows of time and locally mediated toy-models of entanglement
DTSTART:20210618T154000Z
DTEND:20210618T160000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-116@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Nathan Argaman (NRCN)\n\n"Making progress in quantu
m gravity requires resolving possible tensions between quantum mechanics a
nd relativity. One such tension is revealed by Bell's Theorem\, but this
relies on relativistic Local Causality\, not merely the time-reversal sym
metric aspects of relativity. Specifically\, it depends on an arrow-of-t
ime condition\, taken for granted by Bell\, which we call No Future-Input
Dependence. One may replace this condition by the weaker Signal Causalit
y arrow-of-time requirement -- only the latter is necessary\, both for emp
irical viability and in order to avoid paradoxical causal loops. There i
s then no longer any ground to require Local Causality\, and Bell's tensio
n disappears. The locality condition which is pertinent in this context
instead is called Continuous Action\, in analogy with Einstein's ""no act
ion at a distance\,"" and the corresponding ""local beables"" are ""spacet
ime-local"" rather than ""local in space and causal in time."" That s
uch locally mediated mathematical descriptions of quantum entanglement are
possible not only in principle but also in practice is demonstrated by a
simple toy-model -- a ""local"" description of Bell correlations. Descri
bing general physical phenomena in this manner\, including both quantum sy
stems and gravitation\, is a grand challenge for the future. \n[K.B. Wha
rton and N. Argaman\, ""Colloquium: Bell's Theorem and Locally-Mediated R
eformulations of Quantum Mechanics\,"" Rev. Mod. Phys. 92\, 21002 (2020).]
"\n\nhttps://events.perimeterinstitute.ca/event/6/contributions/116/
URL:https://events.perimeterinstitute.ca/event/6/contributions/116/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Time Symmetry in Decoherence and Stable Facts
DTSTART:20210618T162000Z
DTEND:20210618T164000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-117@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Anirban Ganguly (Aix-Marseille Université)\n\nIt h
as been previously discussed how events (interactions) in quantum mechanic
s are time-symmetric and an arrow of time is only due to the arrow of infe
rence in the paper “Quantum information and the arrow of time”\, arXiv
:2010.05734 by Andrea Di Biagio\, Pietro Dona\, and Carlo Rovelli. In the
relational interpretation of Quantum Mechanics\, these interactions are re
lative facts. Stable facts result from relative facts through the process
of decoherence as shown in the paper "Di Biagio\, A.\, Rovelli\, C.\, Foun
dations of Physics 51\, 30 (2021)". They are separate from observed facts
in laboratories due to the reason that they do not depend on a decision-ma
king agent for their creation. In my talk\, I will discuss my work with Ca
rlo Rovelli and Andrea Di Biagio where we show that the process of decoher
ence and the notion of stability of facts is indeed time-symmetric. This i
s in contrast to the observed facts of our everyday world where an arrow o
f time emerges due to the presence of agents and traces.\n\nhttps://events
.perimeterinstitute.ca/event/6/contributions/117/
URL:https://events.perimeterinstitute.ca/event/6/contributions/117/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Hierarchy of Theories with Indefinite Causal Structures: A Second
Look at the Causaloid Framework
DTSTART:20210618T164000Z
DTEND:20210618T170000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-118@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Nitica Sakharwade (Perimeter Institute)\n\n"The Caus
aloid framework [1] is useful to study Theories with Indefinite Causality\
; since Quantum Gravity is expected to marry the radical aspects of Genera
l Relativity (dynamic causality) and Quantum Theory (probabilistic-ness).
To operationally study physical theories one finds the minimum set of quan
tities required to perform any calculation through physical compression. I
n this framework\, there are three levels of compression: 1) Tomographic C
ompression\, 2) Compositional Compression and 3) Meta Compression.\n\nWe p
resent a diagrammatic representation of the Causaloid framework to facilit
ate exposition and study Meta compression. We show that there is a hierarc
hy of theories with respect to Meta compression and characterise its gener
al form. Next\, we populate the hierarchy. The theory of circuits forms th
e simplest case\, which we express diagrammatically through Duotensors\, f
ollowing which we construct Triotensors using hyper3wires (hyperedges conn
ecting three operations) for the next rung in the hierarchy. Finally\, we
discuss the implications for the field of Indefinite Causality.\n\n[1] Jou
rnal of Physics A: Mathematical and Theoretical\, 40(12)\, 3081"\n\nhttps:
//events.perimeterinstitute.ca/event/6/contributions/118/
URL:https://events.perimeterinstitute.ca/event/6/contributions/118/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Interaction and Evolution in Classical and Quantum Physics\, and I
ndefinite Causal Structure
DTSTART:20210618T170000Z
DTEND:20210618T172000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-119@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Erik Curiel (Munich Center for Mathematical Philosop
hy )\n\nIn classical mechanics\, the representations of dynamical evolutio
ns of a system and those of interactions the system can have with its envi
ronment are different vector fields on the space of states: evolutions and
interactions are conceptually\, physically and mathematically different i
n classical physics\, and those differences arise from the generic structu
re of the very dynamics of classical systems ("Newton's Second Law"). Cor
relatively\, there is a clean separation of the system's degrees of freedo
m from those of its environment\, in a sense one can make precise. I pres
ent a theorem showing that these features allow one to reconstruct the ent
ire flat affine 4-dimensional geometry of Newtonian spacetime---the dynami
cs is inextricably tied to the underlying spacetime structure. In quantum
theory (QT)\, contrarily\, the representations of possible evolutions and
interactions with the environment are exactly the same vector fields on t
he space of states ("add another self-adjoint operator to the Hamiltonian
and exponentiate"): there is no difference between "evolution" and "intera
ction" in QT\, at least none imposed by the structure of the dynamics itse
lf. Correlatively\, in a sense one can make precise\, there is no clean s
eparation of the system's degrees of freedom from those of the environment
. Finally\, there is no intrinsic connection between the dynamics and the
underlying spacetime structure: one has to reach in and attach the dynami
cs to the spacetime geometry by hand\, a la Wigner (e.g.). How we disting
uish interaction from evolution in QT and how we attach the dynamics to a
fixed underlying spacetime structure come from imposing classical concepts
foreign to the theory. Trying to hold on to such a distinction is based
on classical preconceptions\, which we must jettison if we are to finally
come to a satisfying understanding of QT. These observatons offer a way t
o motivate and make sense of\, inter alia\, the idea of indefinite causal
structures.\n\nhttps://events.perimeterinstitute.ca/event/6/contributions/
119/
URL:https://events.perimeterinstitute.ca/event/6/contributions/119/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Goodbye & Closing Remarks
DTSTART:20210618T172000Z
DTEND:20210618T172500Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-120@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Flaminia Giacomini (Perimeter Institute)\, Alexander
Smith (Saint Anselm College & Dartmouth College)\n\nhttps://events.perime
terinstitute.ca/event/6/contributions/120/
URL:https://events.perimeterinstitute.ca/event/6/contributions/120/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Welcome and Opening Remarks
DTSTART:20210614T125500Z
DTEND:20210614T130000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-121@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Alexander Smith (Saint Anselm College & Dartmouth Co
llege)\, Flaminia Giacomini (Perimeter Institute)\n\nhttps://events.perime
terinstitute.ca/event/6/contributions/121/
URL:https://events.perimeterinstitute.ca/event/6/contributions/121/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Inequivalent clocks in quantum cosmology I
DTSTART:20210618T134000Z
DTEND:20210618T140000Z
DTSTAMP:20240224T092600Z
UID:indico-contribution-111@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Steffen Gielen (University of Sheffield)\n\nQuantum
cosmology faces the problem of time: the Universe has no background time\,
only interacting dynamical degrees of freedom within it. The relational v
iew is to use one degree of freedom (which can be matter or geometry) as a
clock for the others. In this talk we discuss a cosmological model of a f
lat FLRW universe filled with a massless scalar field and a perfect fluid.
We study three quantum theories based on three different choices of (rela
tional) clock and show that\, if we require the dynamics to be unitary\, a
ll three make drastically different predictions regarding resolution of th
e classical (Big Bang) singularity or a possible quantum recollapse at lar
ge volume. The talk is based on [arXiv:2005.05357] and a second paper to a
ppear on arXiv in May 2021. We plan to give two talks: one covering the fo
undations and general properties of the model\, and one showing detailed r
esults and physical interpretation. (We will merge these talks into one if
the organisers decide to accept only one talk.)\n\nhttps://events.perimet
erinstitute.ca/event/6/contributions/111/
URL:https://events.perimeterinstitute.ca/event/6/contributions/111/
END:VEVENT
END:VCALENDAR