text:
\section{Introduction}
There have been extensive discussions in the philosophical and physical literature of the last couple of decades about the possibilities of time travel: the existence of solutions of the Einstein equations in which closed time-like curves (CTCs) occur has endowed the science-fictional character of the subject with a certain amount of scientific respectability. That the Einstein equations of general relativity do not exclude the existence of CTCs is easy to see. The Einstein equations impose \emph{local} conditions on spacetime: the local curvature properties must stand in a definite relation to the local energy and momentum of the matter fields. As long as these local conditions remain satisfied, the global topology of the spacetime may vary. Now, one particular solution of the Einstein equations is Minkowski spacetime, in which the curvature vanishes everywhere (Minkowski spacetime is flat) and in which there is no matter (all components of the energy-momentum tensor are zero). From this Minkowski spacetime we can build a new solution of the Einstein equations, with a different topology, by the simple operation of identifying two spacelike hypersurfaces (one ``in the future'', and one ``in the past''). Concretely, we cut a strip out of Minkowski spacetime and glue the upper and lower ends together. The cylindrical spacetime that results (a strip of Minkowski spacetime rolled up in the time direction) features CTCs: timelike worldlines going straight up in the time direction return to their exact starting points.

It is helpful to keep this simple example of CTCs provided by rolled-up Minkowski spacetime in mind during the discussion of strange features of CTCs below. However, it should not be thought that CTCs only arise by (arguably artificial) cut-and-paste constructions: there are quite a number of solutions of the Einstein equations known in which apparently plausible matter distributions give rise to CTCs.  The most famous solution with CTCs was found by Kurt G\"odel (G\"odel, 1949, \cite{Godel}). The G\"odel solution describes a non-expanding, rotating universe with a large cosmological constant. This G\"odel world is conceptually important, even though it has properties that conflict with what we empirically find in our universe. A solution of the Einstein equations that may be more relevant for our own world is that of a part of spacetime with a spinning black hole (described by the Kerr metric), in which a region with CTCs exists, the \textit{ergosphere} (see, for example, Carroll, 2014, \cite{Carroll}, p.\ 261.). There are also other, less drastic mass-energy distributions that feature CTCs, such as the first metric with CTC-properties to be discovered: van Stockum's rotating cylinder of dust particles (van Stockum, 1937, \cite{Stockum}).

It should be added that it is unclear whether the existence of these and similar solutions has the implication that there are possibilities for building a ``time machine''. The construction of a manageable time machine would require the creation of a singularity-free compact spacetime region in which CTCs occur, and results by Hawking and others indicate that this cannot be realized within classical general relativity because of energy-conditions that have to be satisfied by the matter fields (Hawking, 1992, \cite{Hawking}). In a quantum theory of general relativity there might be more room for time machines, but this remains speculative in view of the absence of a full quantum gravity theory. However, we are not concerned with the question whether it is possible to construct a useful time machine, but rather with the conceptual status \emph{per se} of CTCs, in relativistic worlds in general.

It is immediately clear that CTCs give rise to causal oddities. If someone could go back into his own past, even if not in our universe but in another physically possible world, it seems that he could change things there in such a way that logical inconsistencies result. The notorious example is the grandfather paradox: if a time traveler arrives at a point in his past at which his grandfather is still an infant, he could decide to kill the child. But if this were to be successful, it would obviously conflict with the very fact of the time traveler's own existence. So in order to have a consistent history on a CTC, certain consistency conditions have to be fulfilled. These conditions take the form of restrictions on what can happen. Although in the case of the grandfather paradox it is plausible at first sight that the time traveler can do whatever is within his capabilities when meeting his grandfather, he nevertheless must be constrained in his actions. This points into the direction of a \emph{determinism} that is stricter than what we are used to in physics; this is one of the points to be further discussed below.

In contrast, there are also cases in which the presence of CTCs appears to lead to a weakening of usual notions of determinism. Think of a spacetime that is globally Minkowski-like, but in which there is a finite region containing CTCs that are causally closed within themselves, so that nothing happens on them which has a cause external to the CTC. Closed worldlines of inertially moving particles would be an example. Since there is no causal relation to anything outside such worldlines, the processes that take place in the CTC region cannot be predicted from outside that region. This lack of predictability points into the direction of \emph{indeterminism}, the other issue to be discussed in more detail below.

The threats posed by logical inconsistency, causal anomalies and other strange features have sometimes been adduced to declare the possibility of CTCs ``unphysical''. CTCs should perhaps be ruled out by a ``cosmic censorship principle'' (Penrose, 1968, \cite{Penrose}) or a ``chronology protection principle'' (Hawking, 1992, \cite{Hawking}). The motivation behind conjecturing that such a principle is at work is that the alternative, with its CTC extravagances, goes against the very nature of physics: such features occur nowhere else in existing physical theory or practice. This then is taken to justify the inductive conclusion that they cannot happen at all.

In this paper we shall critically analyze this argument for the impossibility of cases of ``unphysical determinism and indeterminism.'' As we shall argue, it is not accurate to say that the ``causal anomalies'' associated with CTCs form a category of their own. Indeed, there exist similar cases in standard physics, and these cases are not considered to be exotic or even strange. Therefore, we shall conclude, such \textit{a priori} objections are not insuperable and hence at least part of the motivation for the dismissal of CTCs falls away.

\section{Closed Timelike Curves and Logical Consistency}
\subsection{A Toy Model: Deutsch-Politzer Spacetime}\label{DP}
A spacetime that is a bit more complicated than the rolled-up version of Minkowski spacetime that we considered in the Introduction, and which is suitable for  illustrating our arguments, is the so-called Deutsch-Politzer spacetime (Deutsch, 1991, \cite{Deutsch}; Politzer, 1992, \cite{Politzer}). It can be realized by making two cuts in flat Minkowski spacetime, as indicated in Figure \ref{fig:DPST}---the points in these cuts are removed from the manifold. The two inner edges of the cuts are subsequently identified (glued together); the same happens with the two outer edges. When a particle hits $L^-$ from below it will travel onward from the upper side of $L^+$. The other way around, a particle hitting the lower side of $L^+$ will reappear at the upper side of $L^-$. This creates a region where CTCs can occur: vertical lines, which represent particles at rest (in the depicted frame of reference) that would loop back onto themselves, as depicted by the particle worldline in the figure.

This cut-and-paste operation results in Minkowski spacetime with a kind of ``handle'', the latter having the internal topological properties of a rolled-up strip of Minkowski spacetime. The spacetime region of the handle can be entered from the rest of spacetime, namely from the two sides, on the left and on the right, where the handle merges with the surrounding spacetime. One can think of this spacetime as global Minkowski spacetime, which at two singular points makes contact with a rolled-up strip of Minkowski spacetime.\footnote{It has been shown that for the Deutsch-Politzer spacetime it is not possible to smooth out the metric such that we would obtain a global nonsingular asympotically flat Lorentzian metric (Chamblin et al., 1994, \cite{Chamblin}). This is because the end points of the ``cuts'' are singularities: as judged from the surrounding Minkowski spacetime, there is a finite spacetime interval between the lower and upper end points on both sides, but seen from the inside these points are identical. These two singularities raise questions about the empirical plausibility of Deutsch-Politzer spacetime. Nevertheless, consideration of this spacetime is helpful as it makes visualization of finite CTC-regions possible;  our conclusions will not depend on a commitment to this or another specific spacetime.}

\begin{figure}
\centering
\includegraphics[scale=0.7]{DeuPol.png}
\caption{Deutsch-Politzer spacetime, picture is based on (Arntzenius $\&$ Maudlin, 2013). $L^+$ and $L^-$ represent the `cuts' in Minkowski spacetime; the lower side of $L^+$ is identified with the upper side of $L^-$, while the lower side of $L^-$ is identified with the upper side of $L^+$. This can be visualized as a ``handle" on Minkowski spacetime, which particles may enter and leave again (in contrast with the rolled-up cylinder). $\Sigma$ is a spacelike hypersurface outside of the CTC-region; it is not a Cauchy surface. The green line represents a particle at rest, with a closed timelike worldline.} \label{fig:DPST}
\end{figure}

\begin{figure}
\centering
\includegraphics[scale=0.7]{DeuPol2.png}
\caption{ A particle traveling through Deutsch-Politzer spacetime. The particle enters the CTC-region with a certain velocity, and after hitting $L^+$ five times, it continues its path in the outer Minkowskian region. Picture is based on (Arntzenius and Maudlin, 2013).} \label{fig:DPST2}
\end{figure}

Because worldlines inside the handle do not cross the spacelike hypersurface $\Sigma$ (see Figure \ref{fig:DPST}), $\Sigma$ is not a Cauchy surface: specification of the physical state on $\Sigma$ does not fix the physical state on the whole manifold. In particular, there is no information available on $\Sigma$ about what happens inside the handle. There is consequently a ``Cauchy horizon'', which limits the part of spacetime that can be predicted from $\Sigma$. The unpredictable part comprises the handle, and also the two future lightcones with their apexes in the two singular endpoints of the handle. In Figure \ref{fig:DPST} these two singularities are represented by the two ends (on the left and right, respectively) of the lower cut. Since the singularities are not part of the manifold, they cannot contain initial conditions for worldlines that ``come out of them'' (this is a figurative way of speaking, since the singular points are not in the manifold and therefore not on any curve in the manifold---the past parts of the worldlines in question asymptotically approach one of the singularities). These worldlines do not have a starting point, and can in this respect be compared to worldlines coming in from infinity. There is no origin of such worldlines whose properties determine their nature or number. Clearly therefore, data available on $\Sigma$ cannot fix what is beyond the Cauchy horizon.

\subsection{Consistency Constraints: The Grandfather `Paradox'}\label{CC}
In the region of the handle in Deutsch-Politzer spacetime CTCs occur. These CTCs raise questions about the consistency of histories and the determination of events, as already mentioned in the Introduction.

For example, a person whose worldline is one of these CTCs will return into his own past, where he must find himself in exactly the same state as on earlier occasions. This uniqueness is simply a logical consequence of the demand that histories on the CTC must be unambiguous: there has to be exactly one physical state of affairs at each point of the CTC. This uniqueness gives rise to a consistency constraint: We can only have solutions that are consistent in the sense that they consist of well-defined unambiguous events along the CTC. This is a logical truism and as such a harmless requirement. Nevertheless, in the present context these consistency constraints introduce a restriction on possible histories that seems counter-intuitive and leads to what Smeenk and W\"utrich (2011, \cite{Smeenk}, p.\ 7) call \textit{modal paradoxes}, of which the grandfather paradox is a concrete instance.

In the grandfather paradox our time traveler, living on a CTC, goes back in time and meets his grandfather. Obviously, everything will have to happen in exactly the same way as recorded in history. In particular, it cannot happen, on pain of logical inconsistency, that the grandson undertakes actions that make his own birth impossible. The paradox, as usually formulated, is that this seems to take away some of the powers of the grandson: surely, one is apt to argue, he is \emph{able} to kill his grandfather. So how could it be that he cannot in fact do so? Stephen Hawking has argued that such paradoxes threaten time travel with ``great logical problems" and that we should hope for ``a Chronology Protection Law, to prevent people going back, and killing our parents" (Hawking, 1999, \cite{Hawking2}). Such a novel Law is not needed, though: as we shall argue the trivial constraint that everything is well defined and consistent will do the job.

Before discussing this further, we should mention that a more complicated solution of the paradox was suggested by David Deutsch in his quantum model of time travel. Here, physical systems can traverse so-called Deutsch-CTCs that go from one world to another in Everettian many-worlds quantum mechanics (Deutsch and Lockwood, 1994, \cite{Deutsch2}). This model connects events in different worlds, and the model therefore basically invokes multiple time dimensions---as noted, e.g., in (Dunlap, 2016, \cite{Dunlap}). It is true that multidimensional time offers a way out of  the grandfather paradox, since the fact that a grandson killed his grandfather in a world with time $t_2$ does not contradict that his grandfather stays alive in a world with time $t_1$, in which the grandson was born (cf.\ Dainton, 2010, \cite{Dainton}, p.\ 123). However, this response of invoking multiple time dimensions seems artificial in solving issues with time travel and, moreover, fails to address the original paradox, in which the time traveler goes back to his own past in his own time in his own world. It is only this original paradox that we shall consider here.

An important remark concerning the original paradox, which takes away some of the puzzlement, was made by David Lewis. As Lewis points out, in the formulation of the paradox there is an ambiguity in the use of `can' and `being able' (Lewis, 1976, \cite{Lewis}). Of course, the time traveling grandson \emph{is able} to kill his grandfather in the sense that he knows how to use a firearm, has the required muscular strength, training, and so on. But not everything that `can' be done in this sense will \textit{actually} be done---we do not at all need to consider time travel to recognize this and to realize that there is no contradiction here. In fact, it is a general truth, also in universes without CTCs, that only one act among all the acts that one is able to do will actually be done. In the case of a CTC, the grandson can accordingly be assumed to be able to kill his grandfather, in the sense of possessing the required means and capacities: he `can' shoot. But at the same time it is impossible that he will actually do so: if he did, he would contradict the historical record. Accordingly, no immediate contradiction between `can' and `cannot' arises. According to Lewis the paradox is therefore only apparent; there is an ambiguity in the word `can', which is not always visible, but which is highlighted in some cases---and it is highlighted very prominently in time travel situations. That the time travel story does not sit well with common sense is simply because we are not used to CTC-like situations.

Lewis' analysis is correct in our opinion, but its emphasis on human acts and capabilities invites questions, e.g.\ about the nature of volition and human powers, that distract from the physical aspects of the problem. We shall therefore discuss variations on the paradox that only involve physics. In section \ref{DtoI} we shall consider particles that obey \emph{deterministic} dynamical laws; in section \ref{ItoD} we shall consider an \emph{indeterministic} physical process (like radio-active decay, governed by quantum mechanics). As it will turn out, application of a deterministic theory to a spacetime in which there is a CTC-region leads to a particular kind of indeterminism. In section \ref{com}, we shall compare this CTC-indeterminism to other forms of indeterminism we know from physics. By contrast, in the case of an indeterministic quantum process, grandfather-paradox-like reasoning on a CTC will lead us to determinism---at first sight in conflict with what the standard interpretation of quantum mechanics tells us about the essentially indeterministic nature of the theory.

The latter result, the appearance of determinism in an initially indeterministic context, may perhaps be expected since we have already seen that consistency on CTCs reduces possibilities. That there is also a counterpart to this, namely the appearance of \emph{indeterminism}, has also already been indicated, in the previous subsection: beyond the Cauchy horizon there are worldlines that cannot be fully determined from $\Sigma$. This can be used to construct examples of indeterminism, even if the local physical laws are deterministic.

\section{From Determinism to Indeterminism} \label{DtoI}
In our construction we shall use the Deutsch-Politzer spacetime explained in section \ref{DP}. In Figure \ref{fig:DPST}, the chronology violating region (i.e., the region where CTCs occur) is located to the future of a spacelike hyperplane $\Sigma$. No worldlines from this region cross $\Sigma$, and in general no wordlines cross $\Sigma$ more than once. Everything looks  therefore ``normal'' on $\Sigma$, just as on an arbitrary hyperplane in Minkowski spacetime. However, the initial value problem on $\Sigma$ is not well-posed because $\Sigma$ does not qualify as a Cauchy surface. Indeed, the standard definition of a (global) Cauchy surface $\Sigma$ in a spacetime manifold $\mathcal{M}$ is a surface that is intersected exactly once by \emph{every} non-spacelike curve in $\mathcal{M}$. It is understandable that initial conditions on such a surface $\Sigma$ determine all events in $\mathcal{M}$ if the applicable laws of physics are locally deterministic, since the physical state on $\Sigma$ is propagated by these laws along the non-spacelike curves of $\mathcal{M}$. In the case of a Cauchy surface these curves fill the entire spacetime. But in the case of Figure \ref{fig:DPST} there clearly are worldlines that do not intersect $\Sigma$ and about whose behavior no information is available on $\Sigma$. Consequently, the state on $\Sigma$ does not contain enough information to fix the entire global state of $\mathcal{M}$.

One could say that the CTC-region to some extent forms a world in itself. It is true that particles can enter the CTC-region from outside, such as in Figure \ref{fig:DPST2}, and it is true that this can be predicted from the initial conditions on $\Sigma$. However, one may add an arbitrary number of undetermined worldlines with a particle on it, beyond the Cauchy horizon. This will of course lead to different global states of $\mathcal{M}$, with a different total mass and energy. Therefore, associated with any initial state on $\Sigma$ is an infinitude of global states of $\mathcal{M}$. This seems a clear case of indeterminism, which will typically occur in spacetimes in which isolated chronology violating regions occur. We shall christen this kind of indeterminism ``CTC-indeterminism.''

\section{CTC-Indeterminism Among Other Varieties of Indeterminism} \label{com}

In this section we shall compare the indeterminism that we have seen to arise when CTCs are present with other cases of indeterminism in physics. If the argument that CTCs can be dismissed because of their exotic and unphysical features is to work, the indeterminism that arises here should be in a category of its own, different from cases we encounter elsewhere in physics. In order to see whether this is in fact so, we shall successively review the indeterminism of Norton's Dome, the indeterminism of quantum mechanics, that of the hole argument, and finally the indeterminism of statistical physics.

\subsection{Norton's Dome}
Norton's Dome is an example in which Newton's second law of motion fails to have one unique solution (Norton, 2008, \cite{Norton1}). In this case the mathematical condition for the relevant differential equation to have a unique solution, the so-called Lipshitz continuity condition, is not satisfied.\footnote{The Lipshitz condition is the demand that the slope of the force function does not become too large. Specifically, a function $F$ satisfies the condition within a certain domain $D$ iff there is a constant $K>0$ such that $|F(x)-F(y)|\leq K|x-y|$. For a detailed discussion, see (Fletcher, 2012, \cite{Fletcher}).}

The set-up is as follows. Consider a dome-like surface, as shown in Figure \ref{fig:dome}, in a uniform gravitational field and with a particle of mass $m$ that can move on it. The height $h(r)$ of the surface of the dome as a function of the radial coordinate $r$, is given by
\begin{equation}
h(r)=\frac{2\alpha}{3g}r^{3/2},
\end{equation}
where $g$ is the gravitational acceleration, $\alpha$ a proportionality constant.  \\

\begin{figure}[h!]
\centering
\includegraphics[scale=1]{dome.jpg}
\caption{Norton's Dome from (Norton, 2008, \cite{Norton1}). The marble at the top of this dome is initially resting, but will spontaneously---that is, unpredictably---roll down the surface, as shown by the solution \ref{solution}. } \label{fig:dome}
\end{figure}

The net force on a particle at the surface will be tangentially directed and is hence given by
\begin{equation}
F=mg\sin\phi=mg\frac{dh}{dr}= \alpha \, m  r^{1/2},
\end{equation}
with $\phi$ the angle between the tangent and the horizontal direction. Newton's second law takes the form of the differential equation
\begin{equation} \label{2L}
\frac{d^2r(t)}{dt^2}=\alpha \,  r^{1/2}.
\end{equation}
 If the initial situation is a particle at rest at the top of the dome an obvious solution of Eq. \ref{2L} is $r=0$, $\forall t$. However, there are also other solutions with the same initial condition, namely\footnote{This is a solution since
\begin{equation}
\frac{d^2}{dt^2}\frac{\alpha^2}{144}(t-T)^4=\frac{\alpha^2}{12}(t-T)^2=\alpha\sqrt{\frac{\alpha^2}{144}[(t-T)^4}=\alpha r^{1/2}, \nonumber
\end{equation} satisfying Eq.\ \ref{2L}.}
\begin{equation} \label{solution}
r(t) =
\left\{
	\begin{array}{ll}
		0  & \mbox{if } t<T, \\
		\frac{\alpha^2}{144}[(t-T)]^4	  & \mbox{if } t>T, \\
	\end{array}
	\right.
\end{equation}
for an arbitrary value of $T$. Because of the arbitrariness of $T$, there is an infinity of possible solutions to this differential equation. Eq.\ \ref{solution} describes a particle initially at the origin, which starts rolling off the surface after the time $T$ has elapsed. Because the initial conditions do not fix one unique motion, determinism fails.

When comparing this indeterminism to our case of CTC-indeterminism, we see that there are various differences. In the dome case, all possibly relevant initial data have been specified, but the differential equation is not able to produce one unique solution from them because the Lipshitz condition is violated. In the CTC case the initial conditions and forces on $\Sigma$ do produce unique worldlines---Lipshitz conditions are everywhere assumed to be satisfied. But these uniquely determined worldlines departing from $\Sigma$ do not determine what goes on in the chronology violating region. To know how many particles find themselves in the handle of Figure \ref{fig:DPST} we need \emph{more initial data}, and these data are not available on $\Sigma$. We can conclude that CTC-indeterminism is not connected to the violation of a Lipshitz condition. CTC-indeterminism is therefore essentially different from the indeterminism in the dome case.

\subsection{Quantum Indeterminism}
The indeterminism of quantum mechanics is given a precise form by the Born rule, which states that the square of the amplitude of a particular term in the quantum state (written down as a superposition in some basis) yields the \emph{probability} for finding a measurement outcome corresponding to that term. According to the standard interpretation of quantum mechanics this probability is fundamental: it is not possible to refine the description by adding parameters to the wave function, in such a way that the predictions become more precise than allowed by the Born rule. In other words, even if the state of a physical system is completely specified, the theory only provides us with \emph{probabilities} for a \emph{range} of possible measurement outcome---the theory is thus indeterministic.

CTC-indeterminism and the indeterminism resulting from the Born rule have in common that in both cases a unique prediction of measurable quantities cannot be fixed by specifying all initial conditions at a given time (that is, say, on some spatial hypersurface). However, in the case of CTC-indeterminism the applicable equations do not tell us anything at all about probabilities for the different possibilities. One may draw an arbitrary amount of additional causally closed particle worldlines inside the CTC-region, which corresponds to an infinitude of possibilities, but the equations do not assign any chances to them---the equations do not speak about probabilities at all. This is an essential difference with quantum theory, in which the laws possess a probabilistic interpretation from the outset. Put differently, CTC-indeterminism does not come from the probabilistic character of the applicable theory, whereas quantum indeterminism does.

In section \ref{ItoD} we will come back to the status of probabilistic theories when applied to CTC-regions. For now, it suffices to observe that CTC-indeterminism is not similar to quantum indeterminism. In the latter the specification of probability values is essential, whereas in the former probabilities never enter the discussion.

\subsection{The Hole Argument}
The hole argument, basically devised by Einstein in 1913, makes use of the background independence of general relativity, which ensures that all different coordinate systems perform \emph{a priori} equally well when used to express the laws of the theory---there is no \emph{a priori} given spacetime geometry which could define a privileged frame of reference and coordinates adapted to it (Dieks, 2006, \cite{Dieks1}). The modern form of the argument was developed by (Stachel, 2014, \cite{Stachel}) and (Norton and Earman, 1987, \cite{EarmanNorton}), and extensively used in discussions about substantivalism versus relationism with respect to spacetime.

We are concerned with only one possible implication of the hole argument, namely that it proves general relativity to be indeterministic. The argument is as follows. The spacetime of general relativity in a concrete situation contains a labeled set of events placed in a manifold, plus a metric field specifying temporal and spatial relations between the events. Not all the degrees of freedom in the theory are physical, some of them are concerned with how the events are placed in the manifold. Because of the background independence this manifold does not possess a pre-given geometry, so that one can perform a gauge transformation (an active coordinate transformation) on this distribution of events---see Figure \ref{fig:hole}. All observable properties can be reduced to combinations of relativistic invariants and are left intact by such a transformation. If the transformation constitutes a real change in the world (as the spacetime substantivalist would maintain) then this real change---a different distribution of matter and energy over the manifold---cannot be dealt with by the theory: the initial and boundary conditions do not fix which one of the different possible distributions will be realized. This is because any two distributions of metric and matter agree on all observational properties, which are the only properties predicted by the dynamical laws of the theory. This amounts to indeterminism.

\begin{figure}
\centering
\includegraphics[scale=0.6]{hole.png}
\caption{The hole argument as presented by Norton (Norton, 2015, \cite{Norton2}). The invariant aspects of metric and matter fields of particles (here, even entire galaxies) and their distribution in spacetime are the same, although the events are differently placed in the manifold. The transformation from one situation to the other is accomplished by a `hole transformation' (a diffeomorphism) in the area indicated by the dotted line. The question then is: does the galaxy pass through spacetime point $E$ or not? }
\label{fig:hole}
\end{figure}

Compared to CTC-indeterminism, this type of indeterminism shares the characteristic that it leaves open an infinite range of possibilities, and does not assign any probabilities to these different options. Moreover, like CTC-indeterminism, hole indeterminism does not depend on violations of Lipshitz conditions: all differential equations are perfectly well behaved and have unique solutions in terms of invariant quantities. It is only because of general covariance, relating to the absence of a fixed spacetime background, that equally valid spacetime \emph{representations} of the physical situation (characterized by invariant quantities) arise---these representations relate to each other via diffeomorphisms.

The latter observation marks an essential difference between CTC-indeterminism and hole indeterminism. In the case of hole indeterminism all diffeomorphically related possibilities feature exactly the same values of all physical quantities like energy, mass, etc. For this reason, it may be argued that these different solutions are actually physically identical---as relationists do.  This is completely unlike the situation in CTC-indeterminism: here the possibilities are uncontroversially physically different, distinguishable as they are on the basis of the numbers of particles inside the CTC-region, the amounts of mass and energy, and so on. So CTC-indeterminism and hole indeterminism belong to very different categories.

\subsection{Lack of Knowledge}
When the state of a physical system is incompletely specified, it is to be expected that its future behavior cannot be fully predicted, even if the applicable laws are deterministic and if the Lipshitz conditions are satisfied. For example, if we only know the initial positions and velocities of a restricted number of particles, or only possess estimates for these quantities, Newton's equations will not enable us to accurately predict the future state of a many-particle system. More than one final state will be compatible with the initial data.

An example of such a situation in physical practice is the micro-description of systems characterized by macro-quantities, as in statistical physics. Statistical physics applies when the number of degrees of freedom of a system becomes too large to be practically tractable, as in the case of a macroscopic amount of a gas or the modeling of noise-effects in electronic devices. Although the laws of classical mechanics fix a unique evolution given the initial state, it is practically impossible to ascertain all individual initial momentum and position values. Statistical physics deals with this by considering ensembles of \textit{possible} microstates.

The crucial point is that the macrostate underdetermines the microstate: there are many microstates that would give rise to the same macrostate. Hence, statistical physics can be seen as quantifying our ignorance about the microphysical state. This leads us to a ``pragmatic'' type of indeterminism: in the absence of a full set of initial conditions, the future lies open---in the epistemic sense.

Clearly, this underdetermination is only to be expected when information is missing. The associated indeterminism is consequently harmless from a fundamental point of view: determinism can be restored by making the description more complete. In the ontological sense, only one microstate is actually realized, and this state has a fully deterministic evolution.  In the next section, we argue that this non-fundamental indeterminism is very similar to CTC-indeterminism.

\subsection{CTC-Indeterminism as Epistemic and Harmless}
CTC-indeterminism comes about as the result of the existence of Cauchy horizons, which restricts the amount of information available on  spacelike hypersurfaces---what is beyond the horizon is hidden from view. This indicates that CTC-indeterminism is of the same kind as the epistemically founded indeterminism just discussed, and hence of the harmless kind. This suggestion is supported by our earlier observation that CTC-indeterminism is fundamentally different from more problematic kinds of indeterminism in physics (Norton's Dome, quantum indeterminism and diffeomorphism-indeterminism).

Indeed, there is a direct analogy between CTC-indeterminism and the indeterminism arising from lack of knowledge as in statistical physics. In statistical physics data about the macrophysics do not fix the initial conditions of microscopic particles; in the CTC case, initial conditions are hidden from view by Cauchy horizons. Although in statistical physics the microstate is underdetermined, this does not mean that there is no unique future of the system ontologically speaking: according to classical mechanics there is one unique set of initial conditions, one evolution and hence no indeterminism. In the case of CTC-indeterminism, there is also a fact of the matter concerning initial conditions and the precise shapes of the worldlines behind the horizon. Just as we can take away the lack of knowledge and the associated indeterminism in statistical physics by more fully specifying initial conditions, CTC-indeterminism can be taken away by specifying conditions beyond the horizon, namely at the upper side of $L^-$ of Figure \ref{fig:DPST} and at arbitrarily small spheres surrounding the two singular points (points on the lightcones emerging from these points in Figure \ref{fig:DPST}). These conditions added to the initial conditions on $\Sigma$ fully complement the initial-value problem and hence restore global determinism.

Our intuition might suggest that the specification of additional initial conditions on a hypersurface outside $\Sigma$ is unnatural. However, there is nothing in classical mechanics or relativity theory that implies that Cauchy surfaces should have the form of global spatial hypersurfaces. Even in classical theory one can easily define situations in which conditions on a plane cannot fix everything that is going to happen in the future. Think, for example, of a box with a region in it that is shielded from electromagnetic fields. This is a topological structure that in relevant aspects is analogous to that of Figure \ref{fig:DPST}: initial data inside the shielded region will be necessary to achieve a globally deterministic description. Similarly, taking away indeterminism by specifying initial conditions in the region behind the Cauchy horizon is the natural thing to do in time travel situations.

That there may be a need to explicitly look at the perhaps unusual nature of the global situation in order to determine initial conditions may seem counter-intuitive. However, this feeling is likely due to our impression that we directly experience the world at large, and have access to infinite spacelike hypersurfaces---from which we can make predictions. In reality, however, already special relativity teaches us that we can only have knowledge about limited spacetime regions so that our actual predictions have a local character. In other words, we do not know from experience that there are global Cauchy hypersurfaces and should be open to the possibility that our world is different. From this perspective, CTC-indeterminism is not stranger and more worrisome than the indeterminism arising from lack of knowledge in other areas of physics.

\section{From Indeterminism to Determinism} \label{ItoD}
There is an interesting counterpart to the indeterminism that arises in the presence of CTCs. As we already noted, consistency of histories on CTCs requires that constraints are satisfied that guarantee the uniqueness of events along each CTC. In the case of, e.g., the grandfather paradox these constraints lead to restrictions on what a human agent can do when returning to his own past---this suggests a kind of ``superdeterminism'' that imposes stronger conditions than what we are inclined to expect. The ``lack of freedom'' that results from this is a well-known reason not to take CTCs seriously.

As noted in section \ref{CC}, appeals to human agency and free will can easily obscure the physical points that are at stake. Fot this reason we shall analyze a variation on the grandfather paradox in which a quantum process is considered instead of the actions of a human time traveler. Think of an electron in a quantum state that is a superposition of two different eigenstates of energy, both with equal weights, and with energies $E_1$ and $E_2$, respectively. After some time the electron arrives at a measuring device designed to measure energy and interacts with it. Quantum theory predicts that there is a $50\%$ probability that $E_1$ will be found and recorded, and an equal probability that $E_2$ will be recorded.\footnote{The frequently discussed case of a superposition of \emph{spin} states, e.g.\ the singlet state, is basically identical. It is important to note that the predictions for the outcomes of measurements made by quantum mechanics do not depend on the presence of human observers; quantum predictions are statements about what is recorded by macroscopic measuring devices, regardless of whether a conscious agent becomes aware of the outcomes.}

According to the standard interpretation of quantum mechanics there are no underlying deterministic factors that determine the outcome of this experiment. The quantum state is taken to contain a full specification of everything that is relevant to the prediction, and this state only yields probabilities. In fact, one can derive technical results (Bell's inequalities and their violation) showing that the addition of ``hidden variables'' to the quantum state necessarily leads to theoretical schemes in which the added electron properties behave in unusual and undesirable ways: the hidden properties cannot be purely local (i.e., they must exert an instantaneous influence on each other, even when belonging to physical systems that are far apart). So the indeterminism of quantum mechanics is different from a simple consequence of a lack of knowledge of causal factors. If a proof could be given that quantum indeterminism nevertheless cannot be fundamental, this would be a far-reaching result.

Yet, the consistency conditions that are in force on CTCs seem to imply precisely such a non-fundamentality of quantum mechanical probabilities. Indeed, when we imagine the above-described experiment on a CTC, exactly \emph{one} of the two possible outcomes will be realized---let us assume it is $E_1$. Now, in the future of this outcome we return to the same quantum state of the electron that existed at the beginning of our experiment. Everything will ``repeat itself'', so that the outcome of the experiment will necessarily be $E_1$, the same as before. So there is no question of any probability or uncertainty: the outcome is completely fixed; this is logically forced due to the consistency constraints. Since there is only one unique outcome event on the CTC, with unambiguous properties, we have to conclude that this outcome is determined \emph{tout court}: what is recorded at the end of the experiment is an intrinsically fixed and determined event and there is no place for indeterminism.

If this argument is correct, the feeling that CTCs should be banned from physics by the introduction of a ``chronology protection principle'' may well be justified. Indeterminism as a possible fundamental feature of physical reality would be disproved by a simple CTC thought experiment. This seems to fly in the face of an enormous amount of foundational work in quantum theory. So this version of the grandfather paradox, even though not threatening inconsistency, seems worrisome---at least at first sight.

\section{Determinism versus Determination} \label{detdet}

The argument that CTCs are ``unphysical'' because of CTC-determinism, like the earlier argument from indeterminism, relies on the supposition that we are facing a consequence that only arises in the presence of CTCs. We have argued that this strategy does not work in the case of CTC-\emph{indeterminism}, because this indeterminism also occurs in other situations and is considered harmless there. We will argue now that the case of CTC-\emph{determinism} does not fare better. As a first step we shall show that in many cases CTC-determinism merely exemplifies a kind of logical \emph{determination} that trivially characterizes physical processes in general and does not conflict with \textit{physical} indeterminism.

To see the difference between physical \emph{determinism} and \emph{determination}, think of Minkowski spacetime (Newtonian spacetime will do as well) with a fundamentally indeterministic physical theory defined on it. Physical indeterminism implies that the complete physical state at a certain instant does not completely fix, via the laws of the theory, the physical state at later instants: more than one later states are compatible with the initial state according to the theory in question. Nevertheless, the later states are \emph{determined} in a trivial, logical sense: they are exactly what they are and nothing else. This is just the requirement of unambiguity of events that is needed to make sense of the idea of four-dimensional spacetime at all. If there were no unique physical state of affairs at each spacetime point, we could not have a well-defined history of the universe.

The indispensability of this kind of unambiguous \emph{determination} is especially clear within the conceptual framework of the so-called block universe, associated with the ``B-theory'' of time. According to this B-theory there are no absolute ontological distinctions between Past, Present and Future, and the whole of history can be thought of as laid out in one four-dimensional ``block''. Evidently, all events in this block must be \emph{determined} in the sense just mentioned. It is true that in the literature this has sometimes been taken to entail that the block universe necessarily is subject to determinism. However, this is now generally recognized as a fallacy, at least if \emph{physical determinism} is meant (cf.\ Dieks, 2014, \cite{Dieks2}). Indeed, the block universe exists, according to the B-theory of time, independently of whether the events in it are generated by deterministic laws, of a theory like classical mechanics, or by indeterministic laws like those of quantum mechanics. The crux is that the distinction between physical determinism and physical indeterminism is a distinction between two different kinds of \emph{relations} between physical states: in the deterministic case the laws of the theory make exactly \emph{one} later state compatible with the earlier one, in the indeterministic case there are more later states compatible with the earlier one, according to the theory. By contrast, in the case of logical determination the question of what physical theory applies is not relevant: for an event to be determined in this logical sense it is sufficient that the event is well defined, regardless of its relations to other events. Any \emph{bona fide} unambiguous event is \emph{determined} in this sense.

This argument may seem to rely on the B-theory of time and the associated ontology of the block universe, but on closer inspection it does not. Even if one subscribes to the ``A-theory of time'', and accordingly believes that there are ontological differences between Past, Present and Future, it remains tautological that each future event \emph{will be} exactly and uniquely what it \emph{will be}, and that past events \emph{were} exactly what they \emph{were}.  This tautology merely requires that there is exactly \emph{one} history of the world. So even here, all events are determined in the logical sense, regardless of whether a deterministic or an indeterministic physical theory applies.

Now think back of our thought experiment involving an electron on a CTC. We assumed that indeterministic quantum theory governed what happened in the experiment. This means that the physical state of our electron before its interaction with the measuring device is compatible with different measurement outcomes. This is an assumption about the \emph{relation} between two different states, defined at two different temporal stages of the experiment: the laws of quantum mechanics do not completely fix the measurement outcome when given the  initial electron state as their input.
This relation between the initial and final physical states is objective and unambiguously defined, even on a CTC: when in thought we follow the electron in its history, we return to exactly the same states as before when we arrive at the same points in the electron's existence. So the relation between any two states is uniquely defined. This relation can certainly be the indeterministic one specified by quantum mechanics. Nevertheless, the final outcome of the experiment is unambiguously determined since it corresponds to the single and unique measurement event (that we encounter again and again when we let our mind's eye traverse the CTC various times).

This is fully analogous to what takes place in situations \emph{without} CTCs. It is perhaps easiest to recognize this by again thinking of the block universe: according to quantum theory there are probabilistic relations between the physical properties instantiated at different spacelike hypersurfaces in this universe, but nevertheless these physical properties are unambiguously and uniquely determined in themselves. As we have already mentioned, the same argument can be used even if the notion of a block universe is rejected and some version of the A-theory of time is adopted. Accordingly, if we accepted the principle to brand as \emph{unphysical} processes that are governed by indeterministic physical theories but are nevertheless fully \emph{determined} in the logical sense, we would have to throw out all of physics.

However, this is not the whole story. The plausibility of the argument that CTCs lead to (super)determinism also derives from the fact that \emph{information} about the final outcome may already be present when the experiment starts. For example, we might imagine that the outcome is recorded in a book, which survives along the CTC and can be consulted at the beginning of the experiment. In this case it seems natural to assume that the physical state at the moment that the experiment starts contains this information, so that it becomes possible to derive the experiment's outcome from this initial state. This then appears to lead to physical determinism after all.

In order to discuss this argument and its relevance for the acceptability of CTCs we have to delve a bit deeper into the question of what the physical \emph{laws} on the CTCs look like, and whether these laws enable us to predict the outcome of experiments from their  initial states as just indicated.

\section{Prediction and Retrodiction on CTCs}\label{lawhood}

Suppose that the quantum experiment that we described in the previous section, with possible outcomes $E_1$ and $E_2$, is performed on a CTC and has the actual outcome $E_1$. Suppose further that a record of this is preserved along the CTC, up to the point at which the experiment is about to start. The total physical state at this point on the CTC does not only comprise the state of the electron, but also the record that reveals the outcome of the experiment. Therefore, in spite of the fact that the quantum state of the electron can only provide us with probabilities, the total state makes it possible to predict with certainty what the outcome of the experiment will be.

It should be noted that for this ``deterministic'' prediction the quantum state is not needed at all: the record does not supply a piece of missing information that is needed to supplement what is given by the quantum state, but does all the predictive work on its own. Logically speaking, this is not different from the laboratory situation (without any CTCs) in which a quantum experiment is done, its outcome noted down, after which the record is put in an archive from which we can retrodict the outcome even many years later. This retrodiction does not rely on a quantum mechanical calculation using the later state of the electron (if it still exists), but is based on the classical behavior of records. Books and similar records are designed to be more or less permanent and to follow the deterministic laws of classical physics to a very high degree of approximation. If we only had the later quantum state of the electron to guide us, we would not be able to retrodict unequivocally what the experiment's outcome was; what makes the retrodiction reliable is the approximately classical behavior of the record.
The situation in our thought experiment on the CTC is very similar. It is not the case that quantum theory has ceased to be applicable, but an additional factor has come into play, namely the presence of a classical deterministic record. When the experimenter consults the book, at the beginning of the experiment, and notes the recorded outcome, she is engaged in exactly the same activity as an observer who consults his  notebook in our Minkowski-like world to see what has happened. So just as we are not entitled to conclude that reliable retrodiction falsifies the fundamentally probabilistic nature of quantum mechanics in our world, can we draw that conclusion in the case of the CTC thought experiment.

One might object that the CTC experiment is essentially different from the familiar retrodiction case: what is at stake is not retrodiction at all but rather \emph{prediction} of the outcome of an experiment, on the basis of the initial physical state. But this counterargument does not succeed: the reliability of the statement that the outcome of the experiment will be as the book indicates, derives solely from the book's reliability as a retrodictor, in the same way as in the case without CTCs. The future-directed aspect only comes in because of the uniqueness (and determination) of events along the CTC: as it happens, the retrodicted event is the very same event as the future result of the experiment. So it is the combination of retrodiction and determination that is at work here, and not some new physical principle of prediction.

This becomes more transparent when we ask whether there are reasons to assume the existence of new lawlike physical principles on the CTC. For example, will there be a law telling us about the future? This should not be expected. It is not a general feature of CTCs that there are notebooks or similar records of the eventual outcome available at the beginning of each experiment---these may well have been erased or eroded long ago, if they ever existed at all. There is no reason to assume new regularities on CTCs that ensure that records will be more stable than usual; quite the opposite, if the outcome is to be recorded at the end of an experiment, any already existing record will have to be erased before. It is perfectly consistent to assume the usual laws of physics on CTCs plus the boundary condition of periodicity, i.e. the consistency constaints, without worrying about any new laws.

The consistency conditions that apply in worlds with CTCs thus need not be regarded as symptoms of the existence of novel physical principles, as has sometimes been suggested in the literature.\footnote{For example, Earman (Earman, 1995, \cite{Earman}, p. 194) writes: ``Indeed, the existence of consistency constraints is a strong hint---but nevertheless a hint that most of the literature on time travel has managed to ignore---that it is naive to expect that the laws of a time travel world which is nomologically accessible from our would will be identical with the laws of our world. In some time travel worlds it is plausible that the MRL laws [Mill, Ramsey and Lewis, or the ``best systems account"] include the consistency constraints; in these cases the grandfather paradox has a satisfying resolution. In other cases the status of the consistency constraints remains obscure; in these cases the grandfather paradox leaves a residual itch. Those who wish to scratch the itch further may want to explore other analyses of laws. Indeed, time travel would seem to provide a good testing ground for competing analyses of laws.'' In our view, the consistency constraints merely reflect consistency, which of course has to be satisfied as a trivial logical principle anyway, and do not introduce new laws of physics.} They just reflect uniqueness of events and, indeed, consistency; they have a logical rather than a physical character. There are no fixed patterns of events connected to them. The most one can say is that these consistency conditions enforce a violation of a principle that one is inclined to employ in calculations in which no CTCs are involved, namely that arbitrary initial conditions can be imposed locally---one only needs to think of rolled-up Minkowski spacetime to see that not all such specifications will lead to the periodical solutions that we need to be consistent.

The idea (which we argue is violated in the CTC-case) that arbitrary initial conditions can be imposed locally has been formulated by Deutsch and Lockwood (Deutsch $\&$ Lockwood, 1994, \cite{Deutsch2}, p.\ 71), which they have called the Autonomy Principle:
\begin{quotation}
\noindent it is possible to create in our immediate environment any configuration of matter that the laws of physics permit locally, without reference to what the rest of the universe may be doing.
\end{quotation}
It is true that \textit{we are not used to constraints on local initial conditions}---but then again, we are not used to taking into account global considerations at all. But, in principle, this is mistaken even in worlds without any CTCs, as we shall note in the Conclusion. At the end of the day, the constraints in question are nothing but the expression of ordinary physical laws in combination with the principles of logic and do not require new principles of physics.

\clearpage
\section{Conclusion}
\textit{Common sense may rule out such excursions---but the laws of physics do not.}

\hfill ---David Deutsch $\&$ Michael Lockwood (1994, p. 69). \\

The potential existence of closed timelike curves poses a challenge to our intuitions concerning determinism and indeterminism. Physical processes inside a time travel region must satisfy consistency conditions, which constrain the dynamics, and on the other hand the existence of Cauchy horizons implies a lack of predictability. However, when judging the seriousness of this conflict with intuition we should not forget that our common-sense notions about (in)determinism and predictability derive from untutored interpretations of everyday experience.

One such untutored common-sense idea is that we have immediate access to a global now, a plane, from which the world develops to its future states. Relativity theory has taught us that this notion is mistaken: we do not have epistemic access to a global now at all because of the existence of a finite maximum speed of signal propagation, and ontologically the theory does not single out preferred now-planes. In keeping with this, we should adapt our ideas about causality from  global to local notions. It is a basic message of relativity theory that criteria for determinism should first of all depend on local considerations, and not on considerations about the possible existence of global nows in the universe.

CTC-indeterminism hence turns out to be similar to a familiar and harmless type of indeterminism that occurs in many other places in physics. It is very different from the varieties of philosophically interesting indeterminism that have been focused on in the recent literature, and rather represents another instance of epistemically grounded lack of predictability that is pervasive in physics. From a local point of view, everything is completely deterministic and the lack of global predictability can be rectified by adding extra, not yet considered initial conditions. CTC-indeterminism is therefore not the extraordinary new phenomenon that it sometimes has been suggested to be.

Something similar can be said about the determinism in the sense of ``lack of freedom'' that results from consistency constraints on CTCs. What we are facing here is basically determination of events at the level of logic, instead of physical determinism. Also in this case there is no reason to think that new physical principles, too strange to be true, have to be invoked.

Summing up, both CTC-indeterminism and CTC-determinism do not involve new principles or new laws of physics; although intuitively strange at first sight, analysis shows that they are of the same kind as cases already familiar from well-known and accepted applications of physical theory. As a consequence, there is no justification for the argument that we are here facing phenomena that are so exotic that their potential presence suffices to rule out CTCs. What the \emph{prima facie} implausibility of CTC-determinism and CTC-indeterminism shows is that we have not yet succeeded in adapting our intuitions to the world of general relativity---and that we are unexperienced with traveling through time.

\setstretch{1.0}

redpajama_set_name: RedPajamaArXiv


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ClassicReload » X-COM: Terror from the Deep
X-COM: Terror from the Deep
Zampabolas
Winter Olympics - Lillehammer 94
Flicky
Treasure MathStorm!
EF 2000 (testing)
Daleks (Dr. Who)
Murder on Violet Island
Select ratingGive X-COM: Terror from the Deep 1/5Give X-COM: Terror from the Deep 2/5Give X-COM: Terror from the Deep 3/5Give X-COM: Terror from the Deep 4/5Give X-COM: Terror from the Deep 5/5
How to play X-COM: Terror from the Deep
X-COM: Terror from the Deep Description
Terror from the Deep takes place mostly underwater, with base-building and combat all being submerged beneath the waves. This is also used as a plot device; all of the alien technology from the first game is unusable in salt water, forcing the player to capture and develop new technology.
Just like UFO: Enemy Unknown, the game consists of two parts. The first is the real time-based GeoScape, a global view of Earth where the player views alien and X-COM craft and bases, can hire and dismiss staff, buy and sell vehicles, weaponry, ammunition and items, and build and expand bases. The second part, the BattleScape, is used for combat between squads of aliens and humans, and takes the form of a turn-based battle from an isometric view.
Underwater battles use the same physics as the ground ones. The game features some mission types composing of multiple parts, such as alien shipping route terror attacks in which the first part is a battle of the upper floors of the ship while the second part takes places in the lower decks of the ship (all parts must be completed for these missions to be successful, and soldiers lost in previous parts do not appear in later parts).
Cheats/Hints/Walkthroughs for X-COM: Terror from the Deep
MB Bingo Construction Kit
Atari 2600 1984
Grand Prix Unlimited
Storm Across Europe
Interactive Math Journey
ColecoVision 1982
Best of the Best Championship Karate
Euro Soccer

redpajama_set_name: RedPajamaCommonCrawl


A boat trip to Fjäderholmarna was one of the more touristy activities from our Stockholm trip. It's a small archipelago island fifteen minutes away from the city centre by boat. Since neither of us could pronounce "Fjäderholmarna" (our attempts were hilarious), we handed a leaflet to the person working in the ticket booth and hoped for the best.
If you are reading this and plan to visit in the Summer, it's quicker to buy a ticket from the booth rather than buying one in line — the queue can be very long and the pre-paid tickets board first.
I would love to live in a painted wooden house. Maybe one day. This one would be nice.
I'm not sure what type of fish these heads are. Does anyone know? They might be cod but I'm not 100% sure. Fish heads were nailed to the outside of several buildings on the island, presumably fishing huts. I didn't find the sight of them that off-putting after visiting the stockfish frames in Norway — at least these didn't hold jellied eyeballs!!
We planned to sit on the rocks for a while but everyone else had the same idea so it was hard to find a decent spot. In the end, we just dawdled around the island and soaked in the scenery.
Birds nest freely on the island; you'll find them perched on rocks and under trees close to paths. Unfortunately, the majority of people ventured far too close to get photos which caused them quite a bit of stress — especially those with chicks. We actually had to run away from a hissing goose after a couple of people wound it up. Thankfully my lens had a decent zoom which mean't I didn't need to get too close.


The French "Challenge Hobie Cat 2018"…. Get on board!
In 2018, the French Hobie Class Association (AFHC) puts in place a National Challenge dedicated to Hobie Cat 14, Hobie Cat 16 and Wild Cat.
11 host clubs get involved in the Challenge, both on the Atlantic and Mediterranean seafronts.
12 competitions are proposed to teams. Among these championships, the Hobie Cat National Cup (organized in Hyères by the Coych) and the French Championship HC16 Classic (organized in Marseille by the club of La Pelle).
Teams can participate to all of competitions…. but only the three best results will be taking into account! This create a real great opportunity to take part in the adventure!


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Home › Research Centres▻Ryan Institute▻Research Themes▻Energy and Climate Change research theme
Energy and Climate Change research theme
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Energy & Climate Change Sustainability Challenges
Energy is an essential factor for future sustainable development and improving livelihoods of people in all countries. Nevertheless, it is estimated that in 2015 still about 2.8 billion people have no access to modern energy services and over 1.1 billion do not have electricity. Furthermore, around 4.3 million people are dying prematurely every year due to indoor pollution resulting from cooking and heating with unsustainable fuels. Transitioning all economies and societies to sustainable energy production and consumption patterns now stands at the centre of global efforts to induce a paradigm shift towards low-carbon energy systems, green economies, poverty eradication and ultimately sustainable development. The Ryan Institute is committed to transforming our economies from ones heavily reliant on fossil fuels to more sustainable low carbon economies.In this regard, the Ryan Institute's Energy Research Centre (ERC) and MaREI Galway are at the forefront of research efforts to transition to more sustainable energy systems.
Energy systems and climate change are intertwined. Due to global warming arising from use of non-sustainable energy sources, climate change will have a dramatic and largely negative effect on our economies, societies, environments and poses major challenges to future sustainable development in all countries. Both climate change mitigation and climate change adaptation measures need to be deployed at scale across all sectors and countries, if future human populations and livelihoods are to transition to a more sustainable trajectory than at present. The Ryan Institute's Centre for Climate & Air Pollution Studies (C-CAPS) conducts research in the area of atmospheric composition, climate change and natural feedbacks, air-sea exchange, and air quality impacts on health and ecosystems.


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Articles tagged "san antonio"
Photo Of The Day: Tower Of The Americas
by Jake Thiewes on Sep 18, 2013
Nan Palmero, Flickr
He did it again. After last week's Riverwalk feature, Flickr member (and Gadling Flickr Pool contributor) Nan Palmero submitted yet another evocative, yet simple photo to the pool. Today's feature is the Tower Of The Americas in San Antonio, Texas. As the sun starts to set a bit earlier, does your commute home take on a sky like this? Or do you have to get out of town for such vibrant color?
We'd love to feature your photos and videos on Gadling, so please add them to our Flickr Pool (with Creative Commons licensing!), tag @GadlingTravel on Instagram or email us at OfTheDay@gadling.com.
Photo Of The Day: San Antonio Riverwalk
Entitled, "Skip The Puddles," today's featured photo was submitted by Flickr user Nan Palmero to the Gadling Flickr Pool. Palmero shows off the Johnson Street pedestrian bridge in San Antonio, Texas — the shallow depth-of-field and overcast skies highlight some of the turn in weather starting to affect the nation as fall sets in.
City of Angels To Become Cycling Destination?
by Rob Annis on Jul 25, 2013
Laurie Avocado via Flickr
Could the notoriously car-centric city of Los Angeles become America's next outdoor and cycling Mecca?
Plans are now underway to create a continuous greenway and bike path along all 51 miles of the Los Angeles River, stretching from San Fernando Valley all the way to Long Beach. With 26 miles of the current path already connected, officials hope to add an additional 25 miles by the end of the decade.
Greenway 2020 officials hope the revitalized riverfront will lead to a bike-commuting and outdoor recreation boom.
"The Greenway is a new way of living for Los Angeles, connecting our beautiful neighborhoods, connecting our natural landscapes, and connecting to one another," the group's website reads. "Instead of crowded streets and honking horns on your morning commute, imagine chirping birds, flowing water and numerous coffee shops along the way to work."
NBC Universal and Universal Studios Hollywood recently committed to donating $13 million for a 7-mile path extension from Griffith Park Zoo to Lankershim Boulevard by 2016.
Los Angeles' plan comes on the heels of Indianapolis' successful completion of its $62 million Cultural Trail earlier this year and could eventually become a larger version of San Antonio's famous Riverwalk path system.
Six Flags Texas Debuts Record-Breaking Hybrid Coaster (VIDEO)
by Libby Zay on May 15, 2013
Coaster enthusiasts, get ready to roll. Six Flags Fiesta Texas in San Antonio is introducing a new coaster with a first-of-its-kind looping zero-gravity barrel roll on a hybrid coaster. The new coaster, dubbed the Iron Rattler, will also feature the world's tallest and steepest drop, an 81-degree fall from a height of 180-feet. The coaster is fast, too; it tops out at 70 miles per hour as it snakes through four over banked turns and eventually flips riders upside down.
Here's a summary of the record-breaking stats, according to Six Flags Fiesta Texas:
A 180-foot lift hill makes it the tallest hybrid coaster in the world.
An 81-degree drop makes it the steepest hybrid coaster in the world.
A top speed of 70 mph makes it the fastest hybrid coaster in the world.
A zero-gravity barrel roll makes it the first hybrid coaster in the world to flip completely upside down.
Season pass holders will get a sneak peek at the Iron Rattler on Saturday, May 18 and Sunday, May 19, and then the coaster will be available for public rides on Saturday, May 25.
Events Worth Planning A Trip Around In 2013
by Libby Zay on Jan 21, 2013
Have you ever landed in a place to find out you arrived just after the town's can't-miss event of the year? Well, hopefully that won't happen again this year. Gadling bloggers racked their brains to make sure our readers don't overlook the best parties to be had throughout the world in 2013. Below are more than 60 music festivals, cultural events, pilgrimages and celebrations you should consider adding to your travel calendar this year – trust us, we've been there.
Above image: Throughout Asia, Lunar New Year is celebrated with lantern festivals, the most spectacular of which is possibly Pingxi. [Photo credit: Creative Commons]
Kumbh Mela, a 55-day festival in India, is expected to draw more than 100 million people in 2013. [Photo credit: Creative Commons]
January 7–27: Sundance Film Festival (Park City, Utah)
January 10–February 26: Kumbh Mela (Allahabad, India)
January 21: Presidential Inauguration (Washington, DC)
January 26–February 12: Carnival of Venice (Venice, Italy)
January 26–February 13: Battle of the Oranges (Ivrea, Italy)
During Busójárás in Hungary, visitors can expect folk music, masquerading, parades and dancing. [Photo credit: Creative Commons]
February 3: Super Bowl XLVII (New Orleans, Louisiana)
February 5–11: Sapporo Snow Festival (Sapporo, Japan)
February 7–12: Busójárás (Mohács, Hungary)
February 10: Chinese New Year/Tet (Worldwide)
February 9–12: Rio Carnival (Rio de Janeiro, Brazil)
February 12: Mardi Gras (Worldwide)
February 14: Pingxi Lantern Festival (Taipei, Taiwan)
February 24: Lunar New Year (Worldwide)
Several cities in India and Nepal increase tourist volume during Holi, when people enjoy spring's vibrant colors. [Photo credit: Creative Commons]
March 1-14: Omizutori (Nara, Japan)
March 8–17: South by Southwest (Austin, Texas)
March 20–April 14: Cherry Blossom Festival (Washington, DC)
March 27: Holi (Worldwide, especially India & Nepal)
Many Dutch people wear orange – the national color – and sell their secondhand items in a "free market" during Koninginnendag, a national holiday in the Netherlands. [Photo credit: Creative Commons]
April 12–14 & April 19–21: Coachella (Indio, California)
April 11-14: Masters Golf Tournament (Augusta, Georgia)
April 13–15: Songkran Water Festival (Thailand)
April 17–28: TriBeCa Film Festival (New York, New York)
April 25–28: 5Point Film Festival (Carbondale, Colorado)
April 30: Koninginnendag or Queen's Day (Netherlands)
Up to 50 men work together to carry their church's patron saint around the main square in Cusco, Peru during Corpus Christi. [Photo credit: Blogger Libby Zay]
May 4: Kentucky Derby (Louisville, Kentucky)
May 15–16: Festival de Cannes (Cannes, France)
May 20: Corpus Christi (Worldwide)
May 23–26: Art Basel (Hong Kong)
May 24–27: Mountainfilm Film Festival (Telluride, Colorado)
May 25-28: Sasquatch Festival (Quincy, Washington)
May 26: Indianapolis 500 (Speedway, Indiana)
2013 marks the 100th anniversary for the Tour de France. [Photo credit: Creative Commons]
June 13–16: Bonnaroo (Manchester, Tennessee)
June 13–16: Art Basel (Basel, Switzerland)
June 14–16: Food & Wine Classic (Aspen, Colorado)
June 21: St. John's Night (Poznan, Poland)
June 24: Inti Raymi (Cusco, Peru)
June 28–30: Comfest (Columbus, Ohio)
June 29–July 21: Tour de France (France)
The annual observance of Ramadan is regarded as one of the Five Pillars of Islam. Visit Istanbul, Turkey, at this time and see a festival-like atmosphere when pious Muslims break their fasts with lively iftar feasts at night. [Photo credit: Creative Commons]
July 6–14: San Fermin Festival (Pamplona, Spain)
July 9–August 2: Ramadan (Worldwide)
July 12–14: Pitchfork (Chicago, Illinois)
July 17: Gion Festival Parade (Kyoto, Japan)
July 18–21: International Comic Con (San Diego, California)
July 19–22: Artscape (Baltimore, Maryland)
July 24–28: Fete de Bayonne (Bayonne, France)
Festival-goers get their picture taken at a photo booth during Foo Fest, an arts and culture festival held annually in Providence, Rhode Island. [Photo credit: Flickr user AS220]
August 2–4: Lollapalooza (Chicago, Illinois)
August 10: Foo Fest (Providence, Rhode Island)
August 26–September 2: Burning Man (Black Rock Desert, Nevada)
August 31–September 2: Bumbershoot (Seattle, Washington)
More than six million people head to Munich, Germany, for beer-related festivities during the 16-day Oktoberfest. [Photo credit: Creative Commons]
September 5–15: Toronto International Film Festival (Toronto, Canada)
September 13–15: Telluride Blues & Brews Festival (Telluride, Colorado)
September 21–October 6: Oktoberfest (Munich, Germany)
Around 750 hot air balloons are launched during the nine-day Albuquerque International Balloon Fiesta. [Photo credit: Flickr user Randy Pertiet]
October 4–6 & 11–13: Austin City Limits (Austin, Texas)
October 5–13: Albuquerque International Balloon Fiesta (Albuquerque, New Mexico)
October 10–14: United States Sailboat Show (Annapolis, Maryland)
During Dia de los Muertos (Day of the Dead), family and friends get together to remember loved ones they have lost. Although practiced throughout Mexico, many festivals take place in the United States, such as this festival at La Villita in San Antonio, Texas. [Photo credit: Blogger Libby Zay]
November 1–2: Dia de los Muertos (Worldwide, especially Mexico)
November 3: Diwali (Worldwide)
November 8–10: Fun Fun Fun Fest (Austin, Texas)
November 11: Cologne Carnival (Cologne, Germany)
November 28: Macy's Thanksgiving Day Parade (New York, New York)
TBA: Punkin Chunkin (Long Neck, Delaware)
The colorful holiday of Junkanoo is the most elaborate festivals of the Bahamian islands. [Photo credit: Flickr user MissChatter]
December 2–3: Chichibu Yomatsuri (Chichibu City, Japan)
December 5–8: Art Basel (Miami, Florida)
December 26–January 1: Junkanoo (Bahamas)
So, what did we miss? Let us know what travel-worthy events you're thinking about journeying to in the coming year in the comments below.


* First column is Average Total Corners per Match for matches involving Gamba Osaka. 2nd column is for FC Tokyo.
* First column is Average Total Cards per Match for matches involving Gamba Osaka (Includes Opponent team cards). 2nd column is for FC Tokyo.
There is a Medium Chance that Gamba Osaka will score a goal based on our data.
There is a High Chance that Tokyo will score a goal based on our data.
Match offsides is calculated as the sum of Gamba Osaka's average Team Offsides and FC Tokyo's average Team Offsides throughout the J1 League 2019 season.
On 4th May 2019, Gamba Osaka and Tokyo go head to head in the J1 League. The last meeting ended with the following result : Gamba Osaka 3 - 0 Tokyo.
Out of 12 previous meetings, Gamba Osaka have won 3 matches while Tokyo won 5. 4 matches between them have ended in a draw.
Gamba Osaka is in very poor home form while Tokyo are performing good at away.
Previous matches between Gamba Osaka and Tokyo have averaged 3.33 goals while BTTS has happened 67% of the time.
So far this season in the J1 League, Gamba Osaka have averaged 0 Points Per Game at home matches and Tokyo 1.67 Points Per Game at away matches.


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This evening, LG announced a brand new flagship called the V10. As you know from the couple of leaks we have seen of the device, this phone sports a secondary display, dual front camera setup, and an interesting textured backside. That's not all, though. LG worked in all sorts of random things – seriously, this phone is full of stuff upon stuff upon stuff – to help try and differentiate this phone from the pack. Because this phone comes off on paper much like a G4, it needed all of these new things and stuff to do that.
First, let's talk specs. The LG V10 features a 5.7-inch QHD IPS LCD display with a secondary 2.1-inch IPS display (160×1040) above it. Inside, you will find a Qualcomm Snapdragon 808 processor, 4GB RAM, 64GB storage (with microSD slot), 16MP f/1.8 rear camera with OIS, 5MP dual lens front shooter(s), removable 3000mAh battery, LTE Cat.6, 802.11ac WiFi, and Android 5.1.1. See, it's kind of like a G4, only with an extra display and a secondary front camera.
As for the things I mentioned, this is what I'm talking about. It has that secondary display for showing notifications, weather, battery status, etc. when the phone's screen is off. But once you turn the phone on, it turns into an app shortcut area or a place for notifications when you are in an app and don't want to be bothered. We have seen others attempt this concept before and it didn't go well. Think Samsung Continuum and Note Edge.
The V10 has dual front cameras for this world's ridiculous selfie addiction. With the two, you can either take normal 5MP shots or wide-angle photos. With the rear camera, LG is introducing a manual video mode for the first time in a smartphone, with settings for shutter speed, frame rate, ISO, white balance, and focus. Within that new video mode, there are all sorts of steady/quick/share/etc. options.
The phone has a fingerprint sensor as well, along with 32 bit Hi-Fi audio, a Dura Guard steel frame, and Dura Skin on its back. LG says that they did a bunch of 3rd party drop tests with the phone and it performed quite well. Yay for drop tests.
See, it's all just stuff and things.
The LG V10 launches in Korea this month and will then reach the US, China, and other key countries later on down the road.
LG is doing some good things here, but it's still kind of the same old LG story. The problem with LG is their skin, pretty poor performing phones, cheap exteriors, and terrible update patterns. The cheap exterior may be gone here, thanks to the steel frame, but I just don't have any sort of high hopes for this phone in the performance, update, and software experience departments. While they added in a bunch of new headline grabbing dual this and that, it's all just masking the LG problem that has been there for years. None of us were asking LG to try and innovate by adding a second screen to a phone or to add in the highest end DAC they could or a second selfie camera or manual video controls. We just want them, sort of like Samsung did, to go back to the drawing board with their software approach and overall design. This just all feels like they needed another phone for 2015 because the G4 flopped so hard that they just tossed on a bunch of duct tape to leftover G4s and dual'd it up.
That's not a me hating LG thing, that's a me expecting LG to do better thing.
SEOUL, Oct. 1, 2015 ― LG Electronics (LG) today took the wraps off its newest smartphone featuring multimedia capabilities never before seen in a mobile device. The first of its V Series phones, the LG V10 was designed to provide a rich multimedia experience ― both consumption and creation ― for today's social network savvy consumers. Distinctive new features such as a Second Screen, Dual Front Cameras and Manual Video Mode differentiate the LG V10 from the competition. All this comes wrapped in a design that utilizes high-grade stainless steel and a durable silicone skin to make the V10 one of the rare smartphones to pass drop tests for shock conducted by an independent third party.
Wide angle images usually require a large, heavy lens which can distort the corners of photographs. The LG V10 features 5MP Dual Front Cameras with two separate lenses to capture standard 80 degree selfies or perfect wide angle selfies of 120 degrees, without the need to pan the smartphone which increases the likelihood of camera shake. For the wide angle shot, the V10 employs a sophisticated software algorithm to combine images from the two separate lenses which are just far enough apart to provide two different points of view. The ability to take group selfies without a selfie-stick has never been easier. Multi-view Recording can capture different angles utilizing all three cameras on the V10. Select and insert the version that looks best in your masterpiece.
As the LG G4 did with photography, the LG V10 offers users the ultimate in video capturing, editing and sharing. The V10 is the first smartphone to offer manual mode for video. First introduced for still photographs on the G4, the technology has been enhanced to handle video recordings as well. With Manual Video Mode, budding directors can easily create professional-quality videos by adjusting options such as shutter speed, frame rate, ISO, white balance and focus while recording. Videos can be recorded in three resolutions ― HD, FHD or UHD ― and two aspect ratios ― 16:9 standard or 21:9 cinematic.
The V10 carries on LG's tradition of providing alternative storage options with a microSD card slot. Compatible with cards of up to 2TB, V10 owners can shoot as much 4K video as they want. And with the 3,000mAh removable battery, you can always be ready with a second or third replacement battery to pop in if you ever run low on power while shooting. And with Qualcomm Quick Charge™ 2.0 technology built-in, it only takes 40 minutes to get a 50 percent charge.
The LG V10 was designed to be taken places other phones normally wouldn't feel at home. The resilient Dura Guard frame firmly secures the display to protect the phone from hard bumps and tumbles. The V10's frame is composed of SAE grade 316L stainless steel, the same tough, hypoallergenic material used to make surgical tools and high-end watches. Because the edges and corners are the most vulnerable areas of a phone, the extra protection provided by the Dura Guard frame ensures maximum durability.
On the back and bottom of the display, resilient but soft Dura Skin offers added protection from direct impacts to the device. Dura Skin is soft to the touch but also is highly resistant to nicks and scratches. What's more, the back grid pattern was designed specifically to offer a more secure grip, even when you're on the go. Independent testing and certification firm MET Laboratories tested the LG V10 by dropping it from height of 48 inches repeatedly at different angles and found it to be "MIL-STD-810G Transit Drop Compliant" for shock.
As an advanced multimedia smartphone, the sound in the V10 has been designed to be best-in-class. The V10 features 32 bit Hi-Fi DAC by ESS Technology, designers of high-performance audio products for professionals. The LG V10 automatically detects connected devices and provides sound control options which can be customized. And the LG V10 is the first commercial device to utilize Qualcomm Technologies TruSignal™ antenna boost technology designed to intelligently optimize signal strength at all times for fewer dropped calls, faster data and better call coverage, no matter how the phone is held.
The LG V10 will be available in Korea starting this month followed by markets such as the United States, China and key countries in Asia, Latin America and the Middle East. Information regarding additional markets and launch dates will be announced locally in the weeks to come.
Video: Google Now on Tap Tour!


After a disastrous World Cup, Die Mannschaft have continued their poor run of form with a rough start to their Nations League campaign It's official: 2018 is the German national team's worst year ever, at least in terms of defeats suffered.
With a 2-1 Nations League setback to France on Tuesday, Germany have now lost six matches in a calendar year for the first time in their history. Die Mannschaft have fallen to Brazil, Austria, Mexico, South Korea, the Netherlands and now Les Bleus in what has been a nightmare 2018.
On Tuesday, Toni Kroos scored from the spot in the first half at Stade de France, but a second-half Antoine Griezmann double consigned Joachim Low's side to the history-making defeat. Kroos at least managed to snap his country's scoreless drought in competitive matches, which had lasted three games.
But that was about the only good news to come out of Tuesday's match, with the 2014 World Cup champions continuing to establish a host of unwanted milestones. Germany are now winless in four successive competitive fixtures for the first time in nearly 20 years, with the last such run stretching from October 1999 to June 2000. Tuesday's defeat also marked the first time Germany have suffered defeats in two consecutive competitive matches since 2000.
In their 11 games in 2018, Germany have managed just one clean sheet – a 0-0 draw with France in September. The last year that Germany had a worse percentage of clean sheets was all the way back in 1964.
It could get better (or worse) for Germany next month, as Low's side have a friendly with Russia on November 15 followed by a Nations League encounter against the Netherlands four days later. Depending on how results go in November, Die Mannschaft could be relegated out of Nations League A.


Good morning. It's fourth week.
Two U of C Goldwater Scholars: Third-years Adel Rahman and Naomi Sweeting in the College were awarded the scholarships, becoming two of 211 selected this year. The prestigious Barry Goldwater Scholarship—which covers the cost of tuition, fees, books, and room and board up to $7,500 per year for one or two years—is annually awarded to academically exceptional students in the natural sciences, mathematics, computer science, and engineering.
UCPD shooting updates: Charles Thomas, the student who was shot by University police two weeks ago, appeared in court yesterday after being released from Northwestern Hospital on Wednesday.
A superseding indictment—which replaces the previous indictment—was filed Thursday, suggesting that new evidence may have allowed for new charges. Thomas was facing three felony charges and two misdemeanor charges relating to property damage and alleged assault of a peace officer.
At Riverside, California, UC Riverside student Shigufa Saleheen organized an event Monday titled "Overcoming: A Discussion on Mental Health and Social Justice" in support of his friend Thomas. The event focused in part on removing charges against Thomas for property damage.
Back on campus, Student Government (SG) has debated how to respond to Thomas's shooting. SG president Calvin Cottrell presented a resolution at College Council (CC) Tuesday calling for UCPD to release its use of force protocols and share any final reports on the shooting with the public in a timely manner. After some CC representatives vowed to oppose the resolution, as it did not sufficiently include "the voices and thoughts of community members," Cottrell and his slate decided to delay the vote till after the April 23 meeting of the SG Assembly.
Nicholas Twardak, the officer who shot Thomas, had no documented complaints on his record according to the University.
Members of the AAUP call for President Zimmer to discuss the purported "Chicago principles" of free speech and related issues in a public forum with UChicago faculty.
Columnist Alexa Perlmutter attended former Planned Parenthood president Cecile Richards' book tour. She argues that it excluded low-income women of color, reflecting a wider problem in their access to information about healthcare and reproductive rights.
Robert H. Malott, a trustee emeritus who served as vice chairman of the Board of Trustees from 1988 to 1993, passed away at the age of 91 on April 4. Malott, a World War II veteran who was known for his philanthropic work as a board member of a variety of cultural and academic institutions, served as former chairman and chief executive officer of FMC Corporation. He will be honored at a board meeting in May.
Fragile democracies: Former Secretary of State Madeleine Albright spoke at I-House during an IOP-sponsored event on Thursday. Before the Q&A portion, a range of topics were addressed to the crowd—from her new book, which focuses on fascism, to the "fragility" of democracy.
A look back at the career of football captain Andrew Beytagh. Baseballextended their win streak to seven games but softball is looking to returnto form after this week's games.
Nineteen University of Puerto Rico affiliates are on campus this quarter, as part of a series of relief programs created by the University in light of Hurricane Maria. Including a mix of undergraduates, graduate students, visiting scholars, and artists, the group will study at the University for around three months before returning home.
An anti-abortion group protested in front of Regenstein Library on Monday, distributing flyers and placing posters showing graphic images of purportedly aborted fetuses. Upon learning about the protest, the Young Democratic Socialists of America, the International Socialist Organization, and the Project for Reproductive Freedom organized a counterprotest.
TAPS and UChicago Arts presented a production of Heinrich von Kleist's dark comedy The Broken Jug, which uses a convoluted, destructive trial to invoke rot, suspicion, and guilt.
John Krasinski's third run as director has yielded an understated, unsettling film in A Quiet Place, which still finds time to ponder what it means to be a family.
MC'd by a prominent figure in Afrobeat radio broadcasts and catered by three of Chicago's best African and Caribbean restaurants, the Back to Basics Cultural Show was bound for success from the start.
Echosmith belted its choruses and threw roses to an crowd that enthusiastically welcomed the group's forays into modern, edgier music.
The University of Chicago Political Union (UCPU) and UChicago Common Cause debated Illinois's ban on rent control—which was instituted in 1997. Arguments on both sides addressed the welfare of low-income tenants and residents of color.
Opioid Crisis: Medical professional and law enforcement representatives discussed America's opioid crisis at the Quadrangle Club on Tuesday night. They focused on West Virginia, which they argued is heavily impacted by the crisis.Topics ranged from big data usage to medicine-assisted treatment methods.