Online research in philosophy

Recent attempts to fix the direction of causal priority without reference to the direction of temporal priority have begun with an analysis of the causal relation itself. I offer a method, based on causal modelling theory, designed to determine the direction of causal priority while remaining as agnostic as possible about the nature of the causal relation.

This paper aims to establish that time travel into the past is, at best, highly improbable. It does this by first establishing the causal dependency of identity relations for a person or object travelling into the past. The paper then goes on to show how hard it is to avoid a closed causal loop in time travel experiments, and the inherently contradictory nature of said loops. It then raises the question of how such loops could be avoided without affecting the identity requirements of the traveller, thus drawing the conclusion that while, strictly speaking, time travel has not been proved impossible, the combination of circumstance required to avoid contradiction is so unlikely as to render such activity highly improbable.

I argue that time travel can occur without causal loops.

In this essay, I challenge David P. Hunt's defence of the utility of simple foreknowledge for divine providence against the ‘Metaphysical Principle’. This principle asserts that circular causal loops are impossible. Hunt agrees with this principle but maintains that so long as the deity does not use simple foreknowledge in such a way that causal loops unfold, the Metaphysical Principle in not violated. I argue that Hunt's position still allows for the possibility of such causal loops and this itself is a breach of the Metaphysical Principle.

The most potentially powerful objection to the possibility oftime travel stems from the fact that it can, under the right conditions, give rise to closedcausal loops, and closed causal loops can be turned into self-defeating causal chains;folks killing their infant selves, setting out to destroy the world before they were born,and the like. It used to be thought that such chains present paradoxes; the receivedwisdom nowadays is that they give rise to physical anomalies in the form of inexplicably correlated events. I argue against the received wisdom. I can find nothing in them that argues against the possibility (even, the probability) of time travel.

There have been many objections to the possibility oftime travel. But all the truly interesting ones concern the possibility of reversecausation. What is objectionable about reverse causation? I diagnose that the trulyinteresting objections are to a further possibility: that of causal loops. I raisedoubts about whether there must be causal loops if reverse causation obtains; but devote themajority of the paper to describing, and dispelling concerns about, various kinds ofcausal loop. In short, I argue that they are neither logically nor physically impossible.The only possibly objectionable feature that all causal loops share is that coincidenceis required to explain them. Just how coincidental a loop will be varies: some arereally quite ordinary, and some are incredibly unlikely. I end by speculating thatthe tendency amongst physicists to avoid discussion of causal loops involving intentionalaction may have been unfortunate, since intentional action is an excellent way tonon-mysteriously bring about what otherwise would have been an unlikely coincidence. Hencecausal loops may be more likely in a world with beings like us, than in one without.

According to Hugh Mellor in Real Time II (1998, Ch. 12), assuming the logical independence of causal facts and the 'law of large numbers', causal loops are impossible because if they were possible they would produce inconsistent sets of frequencies. I clarify the argument, and argue that it would be preferable to abandon the relevant independence assumption in the case of causal loops.

It is frequently argued that there is a tension between quantum theory and the special theory of relativity, but there are no conclusive arguments for their incompatibility. In this paper I consider two recent arguments for the impossibility of certain types of relativistic quantum theory on the grounds of causal paradoxes, due to Frank Arntzenius and Tim Maudlin. The structure of both arguments is (in effect) similar: if these alleged relativistic theories were true, closed causal loops could easily be constructed, but such loops would exclude the very possibility of these theories. I argue that Arntzenius’s and Maudlin’s lines of reasoning fail because they are based on untenable assumptions about probabilities in causal loops. I also argue that the consistency of the quantum theories under consideration depends on the interpretation of the probabilities they prescribe, and the question of their empirical adequacy requires a metaphysical and empirical investigation into the nature of chances and frequencies in causal loops.