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BEGIN:VEVENT
SUMMARY:Quantum reference frames for space and space-time
DTSTART;VALUE=DATE-TIME:20210614T164000Z
DTEND;VALUE=DATE-TIME:20210614T172000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-91@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Časlav Brukner (University of Vienna)\nIn physics\,
a reference frame is an abstract coordinate system that specifies observa
tions within that frame. While quantum states depend on the choice of refe
rence frame\, the form of physical laws is assumed to be covariant. Recent
ly\, it has been proposed to consider reference frames as physical systems
and as such assume that they obey quantum mechanics. In my talk\, I will
present recent results in the field of "quantum reference frames" (QRF). I
n particular\, I will formulate the covariance of dynamical physical laws
with respect to non-relativistic QRF transformations and show how relativi
stic QRFs can be used to solve a long-standing problem in relativistic qua
ntum information or to address typical quantum gravity scenarios.\n\nhttps
://events.perimeterinstitute.ca/event/6/contributions/91/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/91/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Non-causal Page-Wootters circuits
DTSTART;VALUE=DATE-TIME:20210614T152000Z
DTEND;VALUE=DATE-TIME:20210614T160000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-90@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Veronika Baumann (IQOQI Vienna)\n"The process mat
rix framework was invented to capture a phenomenon known as indefinite or
quantum causal structure. Due to the generality of that framework\, howeve
r\, for many process matrices there is no clear physical interpretation. A
popular approach towards a quantum theory of gravity is the Page-Wootters
formalism\, which associates to time a Hilbert space structure similar to
spatial position. By explicitly introducing a quantum clock\, it allows t
o describe time-evolution of systems via correlations between this clock a
nd said systems encoded in history states. We combine the process matrix f
ramework with a generalization of the Page-Wootters formalism in which one
considers several observers\, each with their own discrete quantum clock.
\nThis allows for implementing processes with indefinite casual order. Th
e description via a history state with multiple clocks imposes constraints
on the implementability of process matrices intros framework and on the p
erspectives of the observers. We describe how to to implement processes we
re the different definite causal orders are coherently controlled and expl
ain why certain non-causal processes might not be implementable within thi
s setting."\n\nhttps://events.perimeterinstitute.ca/event/6/contributions/
90/
LOCATION:
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;VALUE=DATE-TIME:20210614T130000Z
DTEND;VALUE=DATE-TIME:20210614T134000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-87@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Magdalena Zych (University of Queensland)\nIn genera
l relativity time requires an operational description\, for example\, asso
ciated with the reading of an idealised clock following some world line. I
will show that in quantum physics idealised clocks can be modelled as com
posite quantum particles and discuss what foundational insights into the n
otion of time is enabled by this approach. Moreover\, since quantum partic
les do do not follow classical trajectories a question arises to which ext
ent 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 semi
-classical propagation is not described by Gaussian but by a new class of
quantum states derived from a new uncertainty inequality for configuration
space rather than for phase space variables of the quantum clock.\n\nhttp
s://events.perimeterinstitute.ca/event/6/contributions/87/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/87/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kappa-Minkowski: physics with noncommutative time
DTSTART;VALUE=DATE-TIME:20210614T134000Z
DTEND;VALUE=DATE-TIME:20210614T142000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-88@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Flavio Mercati (University of Burgos)\nThe kappa-
Minkowski noncommutative spacetime has been studied for a long time as an
example of quantum spacetime with nontrivial commutation relations between
spatial and temporal coordinates which\, at first sight\, seem to break P
oincaré invariance. However kappa-Minkowski is invariant under a Hopf-alg
ebra deformation of the Poincaré group\, which involves some noncommutati
ve structures that prevent the sharp localization of reference frames. I w
ill describe recent progress towards the consistent construction of quantu
m field theories on this spacetime\, and the identification of physical pr
edictions that genuinely distinguish kappa-Minkowski from ordinary\, commu
tative Minkowski spacetime.\n\nhttps://events.perimeterinstitute.ca/event/
6/contributions/88/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/88/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantizing causation
DTSTART;VALUE=DATE-TIME:20210614T144000Z
DTEND;VALUE=DATE-TIME:20210614T152000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-89@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Robert Spekkens (Perimeter Institute)\n"Spatio-tempo
ral relations are often taken to be more primitive than causal relations.
Such a relationship is assumed whenever it is suggested that it is part o
f the definition of a causal relation that the cause must precede the effe
ct in time. There are good reasons\, however\, to take causation to be the
more primitive notion\, with spatio-temporal relations merely describing
aspects of causal relations. In such an approach\, to understand what pos
sibilities there are for an intrinsically quantum notion of time\, it is h
elpful to understand what possibilities there are for an intrinsically qua
ntum notion of causation. In short\, how time is quantized is informed by
how causation is quantized. The latter question will be the focus of thi
s talk. I will describe a research program wherein the transition from cla
ssical to quantum is understood as an innovation to the notions of causati
on and inference. This is done by introducing the notion of a causal-infe
rential theory: a triple consisting of a theory of causal influences\, a t
heory of inferences (of both the Boolean and Bayesian varieties)\, and a s
pecification of how these interact. The possibility of defining causal-in
ferential theories by the axioms they satisfy provides a means of providin
g abstract and structural characterizations of the notions of causation an
d inference. In other words\, within this approach\, the new notions of c
ausation and inference will stand to the traditional notions in much the s
ame way that the notions of points and lines in nonEuclidean geometry stan
d to their traditional counterparts in Euclidean geometry. \nBased on: D.
Schmid\, J. Selby\, and R. Spekkens\, Unscrambling the omelette of causat
ion and inference: The framework of causal-inferential theories\, arXiv:20
09.03297 (quant-ph)."\n\nhttps://events.perimeterinstitute.ca/event/6/cont
ributions/89/
LOCATION:
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;VALUE=DATE-TIME:20210615T130000Z
DTEND;VALUE=DATE-TIME:20210615T134000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-92@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Abhay Ashtekar (Pennsylvania State University)\nTime
Reversal T is usually discussed in the traditional framework of quantum m
echanics in which T is represented by an anti-unitary operator. But quantu
m gravity may well need generalization of standard quantum mechanics which
may not preserve even its linear structure\, let alone the unitarity of d
ynamics and anti-unitarity of T. Then the currently used arguments to conc
lude that T violation is a fundamental aspect of Nature will break down. F
ortunately\, it turns out that one can analyze the T-violation experiments
in a much more general setting\, of which classical and quantum mechanics
are special cases. The setting does not require a Hilbert space\, or line
arity of either dynamics or symmetry operations such as T. Nonetheless\, s
omewhat surprisingly\, one would still be to use the current experiments t
o conclude that there is T violation at a fundamental level under rather m
inimal assumptions on the structure of the final quantum gravity theory.\n
\nhttps://events.perimeterinstitute.ca/event/6/contributions/92/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/92/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Space and Time in a Lorentzian path integral
DTSTART;VALUE=DATE-TIME:20210615T134000Z
DTEND;VALUE=DATE-TIME:20210615T142000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-93@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Bianca Dittrich (Perimeter Institute)\nI will pre
sent a quantum gravity approach based on a Lorentzian path integral for q
uantum geometries. The properties of quantum space time can be measured us
ing geometric operators. This allows also to discuss fluctuations of causa
l structure as well as violations of (micro-) causality. I will explain ho
w the Lorentzian path integral comes with various options regarding which
quantum space times to sum over: e.g. whether to include causality violati
ons or not\, or whether to allow also for space times with Euclidean signa
tures in Lorentzian path integrals. I will sketch some consequences for th
e resulting theories.\n\nhttps://events.perimeterinstitute.ca/event/6/cont
ributions/93/
LOCATION:
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;VALUE=DATE-TIME:20210615T144000Z
DTEND;VALUE=DATE-TIME:20210615T152000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-94@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Claus Kiefer (University of Cologne)\nTime cannot b
e both absolute (as in quantum mechanics) and dynamical (as in general rel
ativity). I present general arguments for the absence of time at the most
fundamental level of quantum gravity. I discuss possible concepts that cou
ld replace it and present the recovery of standard time as an approximate
concept. My discussion is restricted to quantum geometrodynamics\, but I a
rgue for the validity of my conclusions beyond that scheme.\n\nhttps://eve
nts.perimeterinstitute.ca/event/6/contributions/94/
LOCATION:
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;VALUE=DATE-TIME:20210615T152000Z
DTEND;VALUE=DATE-TIME:20210615T160000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-96@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Lee Smolin (Perimeter Institute)\n"We propose a real
ist completion of quantum mechanics\, in the sense of a complete descripti
on of individual events. The proposed fundamental theory assumes that tim
e\, events\, causal structure\, momentum and energy are fundamental. But s
pace and the wave function are emergent.\n\nThe beables of the theory are
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\, whi
ch consists of partial views of itself as seen by looking backwards from e
ach event.\n\nThe theory is based on a simple action principle\, which \ne
xtremizes the variety of the universe\, which is a measure of the diversit
y of its partial views. The Schroedinger equation is derived\, while to
higher order\, there are computable corrections\, non-linear in the wave f
unction\, from which new physical effects may be predicted.\n\nFinally\, a
relativistic version is sketched\, in wqhich the views are built on the c
elestial sphere. "\n\nhttps://events.perimeterinstitute.ca/event/6/contrib
utions/96/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/96/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum measurements of time
DTSTART;VALUE=DATE-TIME:20210616T134000Z
DTEND;VALUE=DATE-TIME:20210616T142000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-98@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Lorenzo Maccone (University of Pavia)\n"We propos
e a time-of-arrival operator in quantum mechanics by conditioning on a qua
ntum clock. This allows us to bypass some of the problems of previous prop
osals\, and to obtain a Hermitian time of arrival operator whose probabili
ty distribution arises from the Born rule and which has a clear physical i
nterpretation. The same procedure can be employed to measure the ""time at
which some event happens"" for arbitrary events (and not just specificall
y for the arrival time of a particle).\n\nThis talk is based on the paper:
L. Maccone\, K. Sacha\, Quantum measurements of time\, Phys. Rev. Lett. 1
24\, 110402 (2020)."\n\nhttps://events.perimeterinstitute.ca/event/6/contr
ibutions/98/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/98/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Measuring time with stationary quantum clocks
DTSTART;VALUE=DATE-TIME:20210617T152000Z
DTEND;VALUE=DATE-TIME:20210617T160000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-106@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Mischa Woods (ETH Zurich)\nTime plays a fundamental
role in our ability to make sense of the physical laws in the world around
us. The nature of time has puzzled people –- from the ancient Greeks t
o the present day -– resulting in a long running debate between philosop
hers and physicists alike to whether time needs change to exist (the so-ca
lled relatival theory)\, or whether time flows regardless of change (the s
o-called substantival theory). One way to decide between the two is to att
empt to measure the flow of time with a stationary clock\, since if time w
ere substantival\, the flow of time would manifest itself in the experimen
t. Alas\, conventional wisdom suggests that in order for a clock to functi
on\, it cannot be a static object\, thus rendering this experiment seeming
ly impossible. We show that counter-intuitively\, a quantum clock can meas
ure the passage of time\, even while being switched off\, lending support
for the substantival theory of time.\n\nhttps://events.perimeterinstitute.
ca/event/6/contributions/106/
LOCATION:
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;VALUE=DATE-TIME:20210616T130000Z
DTEND;VALUE=DATE-TIME:20210616T134000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-97@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Philipp Hoehn (University College London)\nI will
sketch how the perspective-neutral approach to (quantum) frame covariance
brings together some recent developments on dynamical reference frames in
quantum foundations\, gauge theories and gravity. The survey will touch on
spatial frames\, quantum clocks and the problem of time\, edge modes\, an
d the relativity of subsystems.\n\nhttps://events.perimeterinstitute.ca/ev
ent/6/contributions/97/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/97/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Relative subsystems and quantum reference frame transformations.
DTSTART;VALUE=DATE-TIME:20210616T144000Z
DTEND;VALUE=DATE-TIME:20210616T152000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-99@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Esteban Castro Ruiz (ETH Zurich)\nTransformations be
tween reference frames play a crucial role in our understanding of physica
l processes. In practice\, reference frames are realised by physical syste
ms\, which are standardly treated as classical. However\, assuming that ev
ery 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. Rece
ntly\, there has been a lot of effort towards developing a quantum general
isation of reference frame transformations\, unveiling novel phenomena tha
t are absent in the classical treatment of reference frames. Here\, we dev
elop a first-principles framework for quantum reference frame transformati
ons which clarifies important conceptual issues of previous treatments. B
ased on the algebra of relative observables between a system and a referen
ce frame\, our operational perspective leads naturally to a mixed-state ap
proach (incoherent twirling)\, in contrast to current pure-state approache
s (coherent twirling). Within our framework\, the full invariant quantum s
ubsystem contains not only the algebra of relative observables between the
system and the reference frame but also an “extra particle\,” related
to the invariant degrees of freedom of the reference frame itself. Import
antly\, this extra particle contains information about the “quantumness
” of the reference frame and is essential to the unitarity of quantum re
ference frame transformations. Our approach is general\, in the sense that
it can be applied to a vast set of symmetry groups and to any type of sys
tem. We illustrate the physical meaning of the concepts developed by analy
sing quantum reference frame transformations with respect to the (centrall
y extended) Galilei group.\n\nhttps://events.perimeterinstitute.ca/event/6
/contributions/99/
LOCATION:
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;VALUE=DATE-TIME:20210616T152000Z
DTEND;VALUE=DATE-TIME:20210616T160000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-100@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Mehdi Ahmadi (Santa Clara University)\nTime is absol
ute in quantum mechanics\, whereas it is dynamical in general relativity.
This is considered as one of the main obstacles towards unifying quantum t
heory and gravity. Relational quantum dynamics offers a possible solution
by treating clocks as internal quantum systems\, which promotes time to a
dynamical quantity. This talk begins with a quick overview of time in rela
tional quantum dynamics. We then explain that the inclusion of an interact
ion term coupling the clock and system causes the system dynamics to be go
verned by a time-nonlocal Schrödinger equation. Moreover\, we demonstrate
a quantum time dilation phenomena wherein we analyze the effect of non-cl
assical states of quantum clocks on relativistic time dilation.\n\nhttps:/
/events.perimeterinstitute.ca/event/6/contributions/100/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/100/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The Issue of Time in Generally Covariant Theories
DTSTART;VALUE=DATE-TIME:20210616T164000Z
DTEND;VALUE=DATE-TIME:20210616T172000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-101@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Rodolfo Gambini (Universidad de Montevideo)\nA possi
ble solution of the problem of time in quantum gravitational systems is pr
esented based on a relational description between the parameterized Dirac
observables of the system under consideration and the clocks. The use of p
hysical clocks required by a quantum gravitational description of time is
shown to induce a loss of unitarity. The evolution is described by a Lindb
lad-type master equation unless it is possible to construct a perfect cloc
k. I show that fundamental uncertainties in time measurements could arise
due to quantum and gravitational effects\, leading to the conclusion that
there is always a loss of unitarity induced by the use of physical clocks.
The extension of the analysis to physical reference frames in totally con
strained systems is sketched.\n\nhttps://events.perimeterinstitute.ca/even
t/6/contributions/101/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/101/
END:VEVENT
BEGIN:VEVENT
SUMMARY:What can information theory tell us about time?
DTSTART;VALUE=DATE-TIME:20210616T180000Z
DTEND;VALUE=DATE-TIME:20210616T190000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-102@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Renato Renner (ETH Zurich)\nInformation theory is
an invaluable tool for studying questions around the foundations of physic
s. In thermodynamics\, for example\, it provides the key to resolving appa
rent contradictions\, such as the famous Maxwell's demon paradox. Converse
ly\, information theory lends itself to the conception of novel paradoxes\
, such as the black hole information paradox\, which helps us sharpening o
ur physical intuition. One may therefore ask whether an information-theore
tic perspective can also yield insights on the nature of time. In this tal
k\, I will explain some of the conceptual problems that arise when one tri
es to capture time with information-theoretic methods\, and discuss possib
le routes to move forward.\n\nhttps://events.perimeterinstitute.ca/event/6
/contributions/102/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/102/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Time and Noether's (first) theorem
DTSTART;VALUE=DATE-TIME:20210617T130000Z
DTEND;VALUE=DATE-TIME:20210617T134000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-103@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Harvey Brown (University of Oxford)\n"It is widely
believed that the homogeneity of time is the symmetry related by Noether's
(first) theorem to the conservation of energy\, and indeed that it explai
ns energy conservation. Both claims are questionable\, and in particular s
eemingly hard to reconcile with the modern version of Noether's first theo
rem due independently to Martínes Alonso (1979) and Olver (1986). \nThe t
alk is based on: 'Do symmetries ""explain"" conservation laws? ...' \narXi
v:2010.10909v1"\n\nhttps://events.perimeterinstitute.ca/event/6/contributi
ons/103/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/103/
END:VEVENT
BEGIN:VEVENT
SUMMARY:God does not play dice (He plays sudoku)
DTSTART;VALUE=DATE-TIME:20210617T134000Z
DTEND;VALUE=DATE-TIME:20210617T142000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-104@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Emily Adlam (Basic Research Community for Physics)\
nI argue that modern physics gives us good reason to take seriously the po
ssibility of laws which are non-local\, global\, or in some other way non-
dynamical. I set out a general framework for lawhood which does not presup
pose the standard kinematical/dynamical split\, and I apply it to the prob
lem of giving a generalized definition of determinism for the non-dynamica
l context. Finally I make some suggestions about how to draw conclusions a
bout the global structure of the laws of nature from the local observation
s we are able to make.\n\nhttps://events.perimeterinstitute.ca/event/6/con
tributions/104/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/104/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Time in Physics and Intuitionistic Mathematics
DTSTART;VALUE=DATE-TIME:20210617T144000Z
DTEND;VALUE=DATE-TIME:20210617T152000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-105@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Nicolas Gisin (University of Geneva & Schaffhausen I
nstitute of Technology-Geneva)\n"Physics is formulated in terms of timeles
s axiomatic mathematics. However\, time is essential in all our stories\,
in particular in physics. For example\, to think of an event is to think o
f something in time. A formulation of physics based of intuitionism\, a co
nstructive form of mathematics built on time-evolving processes\, would of
fer a perspective that is closer to our experience of physical reality and
may help bridging the gap between static relativity and quantum indetermi
nacy.\nHistorically\, intuitionistic mathematics was introduced by L.E.J.
Brouwer with a very subjectivist view where an idealized mathematician con
tinually produces new information by solving conjectures. Here\, in contra
st\, I’ll introduce intuitionism as an objective mathematics that incorp
orates a dynamical/creative time and an open future. Standard (classical)
mathematics appears as the view from the “end of time” and the usual r
eal numbers appear as the hidden variables of classical physics. Similarly
\, 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 a
rguments are based on unjustified assumptions and present the “relativit
y of indeterminacy”.\n\nReferences:\nC. Posy\, Mathematical Intuitionism
\, Cambridge Univ. Press\, 2020.\nN. Gisin\, Indeterminism in Physics\, Cl
assical Chaos and Bohmian Mechanics. Are Real Numbers Really Real?\, Erken
ntnis (2019)\, https://doi.org/10.1007/s10670-019-00165-8 \nN. Gisin\, Rea
l Numbers are the Hidden Variables of Classical Mechanics\, Quantum Studie
s: Mathematics and Foundations 7\, 197-201 (2020).\nFlavio Del Santo and N
. Gisin\, Physics without determinism: Alternative interpretations of clas
sical physics\, Physical Review A 100.6 (2019).\nN. Gisin\, Mathematical l
anguages shape our understanding of time in physics\, Nature Physics 16\,
114-119 (2020).\nN. Gisin Indeterminism in Physics and Intuitionistic Math
ematics\, arXiv:2011.02348\nFlavio Del Santo and N. Gisin\, The Relativity
of Indeterminacy\, arXiv:2101.04134"\n\nhttps://events.perimeterinstitute
.ca/event/6/contributions/105/
LOCATION:
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;VALUE=DATE-TIME:20210617T164000Z
DTEND;VALUE=DATE-TIME:20210617T172000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-107@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Carlo Rovelli (Centre de Physique Theorique)\nThe
concrete perspective of using interference to measure Gravity Induced Ent
anglement in the lab is a very exciting development for quantum gravity. W
hile the measurements considered so far only test the nonrelativistic regi
me\, the same technique might allow access to genuine relativistic quantum
effects. Among these\, there might be the possibility of direct detection
of time quantum discreteness.\n\nhttps://events.perimeterinstitute.ca/eve
nt/6/contributions/107/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/107/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Relational observables and quantum diffeomorphisms on the worldlin
e
DTSTART;VALUE=DATE-TIME:20210618T130000Z
DTEND;VALUE=DATE-TIME:20210618T132000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-108@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Leonardo Chataignier (University of Cologne)\n"Candi
date theories of quantum gravity must answer the questions: how can the dy
namics of quantum states of matter and geometry be defined in a diffeomorp
hism-invariant way? How are the quantum states related to probabilities in
the absence of a preferred time? To address these issues\, we discuss th
e construction and interpretation of relational observables in quantum the
ories with worldline diffeomorphism invariance\, which serve as toy models
of quantum gravity. In this context\, we present a method of construction
of quantum relational observables which is analogous to the construction
of gauge-invariant extensions of noninvariant quantities in usual gauge (Y
ang-Mills) theories. Furthermore\, we discuss how the notion of a physical
propagator may be used to define a unitary evolution in the quantum theor
y\, which is to be understood in terms of a generalized clock\, as is the
classical theory. We also discuss under which circumstances this formali
sm can be related to the use of conditional probabilities in a generalizat
ion of the Page-Wootters approach. Finally\, we also examine how our forma
lism can be adapted to calculations of quantum-gravitational effects in th
e early Universe.\nRefs.: L. Chataignier\, Phys. Rev. D 101\, 086001 (20
20)\; 103\, 026013 (2021)\; 103\, 066005 (2021)"\n\nhttps://events.perim
eterinstitute.ca/event/6/contributions/108/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/108/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Relational dynamics in an emergent spacetime context
DTSTART;VALUE=DATE-TIME:20210618T132000Z
DTEND;VALUE=DATE-TIME:20210618T134000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-109@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Luca Marchetti (University of Pisa\, LMU Munich)\nI
discuss the new dimension that the relational approach to the problem of t
ime takes in quantum gravity contexts in which spacetime and geometry are
understood as emergent. I argue that\, in this case\, the relational strat
egy is best realized at an approximate and effective level\, after suitabl
e coarse graining and only in terms of special quantum states. I then show
a concrete realization of such effective relational dynamics in the conte
xt of a cosmological application of the tensorial group field theory forma
lism for quantum gravity.\n\nhttps://events.perimeterinstitute.ca/event/6/
contributions/109/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/109/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Times of arrival and gauge invariance
DTSTART;VALUE=DATE-TIME:20210618T140000Z
DTEND;VALUE=DATE-TIME:20210618T142000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-112@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Siddhant Das (Ludwig Maximilian University of Munich
)\n"We revisit the arguments underlying two well-known arrival-time distri
butions in quantum mechanics\, viz.\,\nthe Aharonov-Bohm and Kijowski (ABK
) distribution\, applicable for freely moving particles\, and the quantum\
nflux (QF) distribution. An inconsistency in the original axiomatic deriva
tion of Kijowski’s result is pointed out\,\nalong with an inescapable co
nsequence of the “negative arrival times” inherent to this proposal (a
nd generalizations thereof). The ABK free-particle restriction is lifted i
n a discussion of an explicit arrival-time setup\nfeaturing a charged part
icle moving in a constant magnetic field. A natural generalization of the
ABK distribution is in this case shown to be critically gauge-dependent. A
direct comparison to the QF distribution\,\nwhich does not exhibit this f
law\, is drawn (its acknowledged drawback concerning the quantum backflow
effect\nnotwithstanding).\n\nBased on a recent paper (https://arxiv.org/ab
s/2102.02661)\, to be published in Proceedings of the Royal Society A."\n
\nhttps://events.perimeterinstitute.ca/event/6/contributions/112/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/112/
END:VEVENT
BEGIN:VEVENT
SUMMARY:What does the Path Integral imply for Quantizing Time?
DTSTART;VALUE=DATE-TIME:20210618T144000Z
DTEND;VALUE=DATE-TIME:20210618T150000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-113@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Ken Wharton (San Jose State University)\n"Even thou
gh path-integral formulations of quantum theory are thought to be equivale
nt to state-based approaches\, path-integrals are rarely used to motivate
answers to foundational questions. This talk will summarize a number of i
mplications concerning time and time-symmetry which result from the path-i
ntegral viewpoint. Such a perspective sheds serious doubt on dynamical co
llapse theories\, and also pushes against efforts to extend configuration
space to include multiple time dimensions. A recently-developed map betwe
en all possible two-qubit entangled states and spacetime-based path-integr
als sheds further doubt on any need to extend spacetime to a large ontolog
ical configuration space. \n (References include arXiv:2103.02425\, 151
2.00740\, 1103.2492 .)"\n\nhttps://events.perimeterinstitute.ca/event/6/co
ntributions/113/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/113/
END:VEVENT
BEGIN:VEVENT
SUMMARY:An experiment to detect the Discreteness of time
DTSTART;VALUE=DATE-TIME:20210618T150000Z
DTEND;VALUE=DATE-TIME:20210618T152000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-114@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Marios Christodoulou (The University of Hong Kong)\n
To this date no empirical evidence contradicts general relativity. In part
icular\, there is no experimental proof a quantum theory of gravity is nee
ded. Surprisingly\, it appears likely that the first such evidence would
come from experiments that involve non relativistic matter and extremely w
eak gravitational fields. The conceptual key for this is the Planck mass\
, a mesoscopic mass scale\, and how it relates with what remains of genera
l relativity in the Newtonian limit: time dilation. Indeed\, current tech
nological capabilities can amplify differences in time dilation superposit
ion that are much smaller than the smallest time interval that can be meas
ured by an atomic clock. Inspired from recent proposals to detect non--cla
ssicality of the gravitational field\, we devise and examine the feasibil
ity of an experiment that could detect a granularity of time at the Planc
k scale.\n\nhttps://events.perimeterinstitute.ca/event/6/contributions/114
/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/114/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Representing time and time's arrow
DTSTART;VALUE=DATE-TIME:20210618T152000Z
DTEND;VALUE=DATE-TIME:20210618T154000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-115@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Bryan Roberts (London School of Economics & Politica
l Science)\nWhat does it mean to say that a curve in state space describes
change with respect to time\, as opposed to space or any other parameter?
What does it mean to say it's time is asymmetric? Inspired by the Wigner-
Bargmann analysis of the Poincaré group\, I discuss a general framework f
or understanding the meaning of time evolution and temporal symmetry in te
rms of the representation of a semigroup that includes "time translations"
\, amongst the automorphisms of a state space. I discuss the structuralist
and functionalist philosophical underpinnings of this view\, and show how
time reversal\, parity\, matter-antimatter exchange\, and CPT are best vi
ewed as extensions of a representation of continuous symmetries\, whose ex
istence is sensitive to the underlying structure of state space. I conclud
e with some comments on how an arrow of time can be defined in this framew
ork\, as well as prospects for such an arrow in the context of gravitation
.\n\nhttps://events.perimeterinstitute.ca/event/6/contributions/115/
LOCATION:
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;VALUE=DATE-TIME:20210618T154000Z
DTEND;VALUE=DATE-TIME:20210618T160000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-116@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Nathan Argaman (NRCN)\n"Making progress in quantum
gravity requires resolving possible tensions between quantum mechanics and
relativity. One such tension is revealed by Bell's Theorem\, but this r
elies on relativistic Local Causality\, not merely the time-reversal symme
tric aspects of relativity. Specifically\, it depends on an arrow-of-tim
e condition\, taken for granted by Bell\, which we call No Future-Input De
pendence. One may replace this condition by the weaker Signal Causality
arrow-of-time requirement -- only the latter is necessary\, both for empir
ical viability and in order to avoid paradoxical causal loops. There is
then no longer any ground to require Local Causality\, and Bell's tension
disappears. The locality condition which is pertinent in this context in
stead is called Continuous Action\, in analogy with Einstein's ""no actio
n at a distance\,"" and the corresponding ""local beables"" are ""spacetim
e-local"" rather than ""local in space and causal in time."" That suc
h locally mediated mathematical descriptions of quantum entanglement are p
ossible not only in principle but also in practice is demonstrated by a si
mple toy-model -- a ""local"" description of Bell correlations. Describi
ng general physical phenomena in this manner\, including both quantum syst
ems and gravitation\, is a grand challenge for the future. \n[K.B. Whart
on and N. Argaman\, ""Colloquium: Bell's Theorem and Locally-Mediated Ref
ormulations of Quantum Mechanics\,"" Rev. Mod. Phys. 92\, 21002 (2020).]"\
n\nhttps://events.perimeterinstitute.ca/event/6/contributions/116/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/116/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Time Symmetry in Decoherence and Stable Facts
DTSTART;VALUE=DATE-TIME:20210618T162000Z
DTEND;VALUE=DATE-TIME:20210618T164000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-117@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Anirban Ganguly (Aix-Marseille Université)\nIt has
been previously discussed how events (interactions) in quantum mechanics
are time-symmetric and an arrow of time is only due to the arrow of infere
nce in the paper “Quantum information and the arrow of time”\, arXiv:2
010.05734 by Andrea Di Biagio\, Pietro Dona\, and Carlo Rovelli. In the re
lational interpretation of Quantum Mechanics\, these interactions are rela
tive facts. Stable facts result from relative facts through the process of
decoherence as shown in the paper "Di Biagio\, A.\, Rovelli\, C.\, Founda
tions 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-maki
ng agent for their creation. In my talk\, I will discuss my work with Carl
o Rovelli and Andrea Di Biagio where we show that the process of decoheren
ce and the notion of stability of facts is indeed time-symmetric. This is
in contrast to the observed facts of our everyday world where an arrow of
time emerges due to the presence of agents and traces.\n\nhttps://events.p
erimeterinstitute.ca/event/6/contributions/117/
LOCATION:
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;VALUE=DATE-TIME:20210618T164000Z
DTEND;VALUE=DATE-TIME:20210618T170000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-118@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Nitica Sakharwade (Perimeter Institute)\n"The Causal
oid framework [1] is useful to study Theories with Indefinite Causality\;
since Quantum Gravity is expected to marry the radical aspects of General
Relativity (dynamic causality) and Quantum Theory (probabilistic-ness). To
operationally study physical theories one finds the minimum set of quanti
ties required to perform any calculation through physical compression. In
this framework\, there are three levels of compression: 1) Tomographic Com
pression\, 2) Compositional Compression and 3) Meta Compression.\n\nWe pre
sent a diagrammatic representation of the Causaloid framework to facilitat
e exposition and study Meta compression. We show that there is a hierarchy
of theories with respect to Meta compression and characterise its general
form. Next\, we populate the hierarchy. The theory of circuits forms the
simplest case\, which we express diagrammatically through Duotensors\, fol
lowing which we construct Triotensors using hyper3wires (hyperedges connec
ting three operations) for the next rung in the hierarchy. Finally\, we di
scuss the implications for the field of Indefinite Causality.\n\n[1] Journ
al of Physics A: Mathematical and Theoretical\, 40(12)\, 3081"\n\nhttps://
events.perimeterinstitute.ca/event/6/contributions/118/
LOCATION:
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;VALUE=DATE-TIME:20210618T170000Z
DTEND;VALUE=DATE-TIME:20210618T172000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-119@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Erik Curiel (Munich Center for Mathematical Philosop
hy )\nIn classical mechanics\, the representations of dynamical evolutions
of a system and those of interactions the system can have with its enviro
nment are different vector fields on the space of states: evolutions and i
nteractions are conceptually\, physically and mathematically different in
classical physics\, and those differences arise from the generic structure
of the very dynamics of classical systems ("Newton's Second Law"). Corre
latively\, there is a clean separation of the system's degrees of freedom
from those of its environment\, in a sense one can make precise. I presen
t a theorem showing that these features allow one to reconstruct the entir
e flat affine 4-dimensional geometry of Newtonian spacetime---the dynamics
is inextricably tied to the underlying spacetime structure. In quantum t
heory (QT)\, contrarily\, the representations of possible evolutions and i
nteractions with the environment are exactly the same vector fields on the
space of states ("add another self-adjoint operator to the Hamiltonian an
d exponentiate"): there is no difference between "evolution" and "interact
ion" in QT\, at least none imposed by the structure of the dynamics itself
. Correlatively\, in a sense one can make precise\, there is no clean sep
aration of the system's degrees of freedom from those of the environment.
Finally\, there is no intrinsic connection between the dynamics and the u
nderlying spacetime structure: one has to reach in and attach the dynamics
to the spacetime geometry by hand\, a la Wigner (e.g.). How we distingui
sh interaction from evolution in QT and how we attach the dynamics to a fi
xed underlying spacetime structure come from imposing classical concepts f
oreign 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 co
me to a satisfying understanding of QT. These observatons offer a way to
motivate and make sense of\, inter alia\, the idea of indefinite causal st
ructures.\n\nhttps://events.perimeterinstitute.ca/event/6/contributions/11
9/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/119/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Goodbye & Closing Remarks
DTSTART;VALUE=DATE-TIME:20210618T172000Z
DTEND;VALUE=DATE-TIME:20210618T172500Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-120@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Alexander Smith (Saint Anselm College & Dartmouth Co
llege)\, Flaminia Giacomini (Perimeter Institute)\nhttps://events.perimete
rinstitute.ca/event/6/contributions/120/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/120/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Welcome and Opening Remarks
DTSTART;VALUE=DATE-TIME:20210614T125500Z
DTEND;VALUE=DATE-TIME:20210614T130000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-121@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Alexander Smith (Saint Anselm College & Dartmouth Co
llege)\, Flaminia Giacomini (Perimeter Institute)\nhttps://events.perimete
rinstitute.ca/event/6/contributions/121/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/121/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Inequivalent clocks in quantum cosmology I
DTSTART;VALUE=DATE-TIME:20210618T134000Z
DTEND;VALUE=DATE-TIME:20210618T140000Z
DTSTAMP;VALUE=DATE-TIME:20220518T225842Z
UID:indico-contribution-6-111@events.perimeterinstitute.ca
DESCRIPTION:Speakers: Steffen Gielen (University of Sheffield)\nQuantum co
smology faces the problem of time: the Universe has no background time\, o
nly interacting dynamical degrees of freedom within it. The relational vie
w is to use one degree of freedom (which can be matter or geometry) as a c
lock for the others. In this talk we discuss a cosmological model of a fla
t FLRW universe filled with a massless scalar field and a perfect fluid. W
e study three quantum theories based on three different choices of (relati
onal) clock and show that\, if we require the dynamics to be unitary\, all
three make drastically different predictions regarding resolution of the
classical (Big Bang) singularity or a possible quantum recollapse at large
volume. The talk is based on [arXiv:2005.05357] and a second paper to app
ear on arXiv in May 2021. We plan to give two talks: one covering the foun
dations and general properties of the model\, and one showing detailed res
ults and physical interpretation. (We will merge these talks into one if t
he organisers decide to accept only one talk.)\n\nhttps://events.perimeter
institute.ca/event/6/contributions/111/
LOCATION:
URL:https://events.perimeterinstitute.ca/event/6/contributions/111/
END:VEVENT
END:VCALENDAR