philosophies Article Changing, Annulling and Otherwising the Past G. C. Goddu Department of Philosophy, University of Richmond, Richmond, VA 23173, USA; [email protected] Abstract: Despite a growing number of models argument for the logical possibility of changing the past there continues to be resistance to and confusion surrounding the possibility of changing the past. In this paper I shall attempt to mitigate the resistance and alleviate at least some of the confusion by distinguishing changing the past from what Richard Hanley calls ‘annulling’ the past and distinguishing both from what I shall call ‘otherwising’ the past. Keywords: time travel; logical possibility; changing; fixing; annulling; otherwising 1. Introduction Almost a hundred years ago, science fiction editor, Hugo Gernsback wrote: “The question in brief is as follows: Can a time traveler, going back in time— whether ten years or ten million years—partake in the life of that time and mingle in with its people; or must he remain suspended in his own time-dimension, a spectator who merely looks on but is powerless to do more?” [1] (p. 610) His query was in response to several letters challenging earlier stories Gernsback had published in Amazing Stories. The letters insisted, that for the time travel stories to be consistent, the time travelers needed to be invisible. (See [2] (pp. 171–173) for discussion of these early ‘fan’ comments on time travel.) Citation: Goddu, G.C. Changing, The underlying concern perhaps, a concern made explicit in later philosophical ar- Annulling and Otherwising the Past. guments about time travel (see for example [3] (p. 177)) is that actually travelling to the Philosophies 2021, 6, 71. https:// past would entail changing the past and changing the past is logically impossible, so the doi.org/10.3390/philosophies6030071 best we can do is experience the past via early science fiction’s abundant chrono-scopes, chrono-cameras, time-radios, etc. The concern isn’t merely that time travelers might step Academic Editor: Alasdair Richmond off the safe path and accidentally crush the proverbial butterfly, [4] but that even building the ‘safe path’ in the first place would ‘damage’ or ‘change’ the time line. Received: 3 August 2021 Many philosophers resisted these arguments on the grounds that while changing the Accepted: 25 August 2021 Published: 30 August 2021 past is indeed logically impossible, time travel into the past does not entail changing the past—it merely entails affecting the past. [5] So given unrestricted time travel to the past Publisher’s Note: MDPI stays neutral you can visit the building of the pyramids or the Great Wall, you can help the Union or the with regard to jurisdictional claims in Confederacy, you can peruse the library at Alexandria, you can do almost anything in the published maps and institutional affil- past you might want—you can even try to change the past in some way, say by trying to iations. prevent Booth from killing Lincoln or by trying to prevent the Holocaust. If changing the past is impossible, you will fail, but if you want to try, time travel will certainly allow the trying. (See, for example, [6] for a self-defeating attempt to prevent the Holocaust.) Even more recently however several arguments have appeared that changing the past is, contra the prevailing view, logically possible. If you want to kill Hitler before Copyright: © 2021 by the author. Licensee MDPI, Basel, Switzerland. 1933 or put Aristotle on a ‘better’ path, you can, but you will also have to live with the This article is an open access article consequences of your changes. (See, for example, [7] for another twist on killing (or not distributed under the terms and killing) Hitler or [8] for the potential consequences of trying to influence Aristotle.) Despite conditions of the Creative Commons these arguments resistance and confusion surrounding the possibility of changing the past Attribution (CC BY) license (https:// persists. In this paper I shall attempt to mitigate the resistance and alleviate at least some creativecommons.org/licenses/by/ of the confusion. In Section2, I first articulate a common way to model the possibility 4.0/). of changing the past and then in Section 2.1 present and reject Nicholas J.J. Smith’s [9] Philosophies 2021, 6, 71. https://doi.org/10.3390/philosophies6030071 https://www.mdpi.com/journal/philosophies Philosophies 2021, 6, x FOR PEER REVIEW 2 of 12 the confusion. In Section 2, I first articulate a common way to model the possibility of Philosophies 2021, 6, 71 2 of 12 changing the past and then in Section 2.1 present and reject Nicholas J.J. Smith’s [9] most recent arguments that these sorts of models model avoiding the past rather than changing the past. In Section 2.2, I shall consider the possibility of fixing the past and argue that we mustmost distinguish recent arguments two types that of these fixes—one sorts ofis just models a kind model of change avoiding and theis possible, past rather the other than ischanging stronger, the what past. I Incall, Section following 2.2, I Richard shall consider Hanley the [10] possibility ‘annulling’ of fixing and is the not. past In andSection argue 3, Ithat shall we further must distinguishclarify annulling two types the past of fixes—one by distinguishing is just a kindstrong of changeannulling and which is possible, is im- possiblethe other from is stronger, weak annulling what I call, which following is a kind Richard of change Hanley and is [10 possible.] ‘annulling’ In the and process, is not. I shallIn Section argue3 against, I shall Sam further Baron’s clarify [11]conflation annulling the of past strong by annulling distinguishing and change strong annullingand claim thatwhich Baron is impossible ultimately from concedes weak that annulling the sort which of changing is a kind the of past change that and recent is possible. theorists In have the beenprocess, interested I shall arguein is possible. against Sam Finally, Baron’s in Se [11ction] conflation 4, I shall of argue strong that annulling Peter Vranas’ and change [12] argumentsand claim thatthat Barona certain ultimately sort of change, concedes which that at the first sort blush of changingsounds like the strong past thatannulling, recent istheorists possible have in fact been support interested the possibility in is possible. of something Finally, in quite Section distinct4, I shall from argue strong that annul- Peter ment,Vranas’ which [12] arguments I shall call that ‘otherwising a certain sort the ofpast’. change, I shall which conclude at first that blush despite sounds the like high strong po- tentialannulling, for confusion is possible we in factshould support be careful the possibility to separate ofsomething the possibility quite of distinct changing from the strong past fromannulment, the impossibility which I shall of strongly call ‘otherwising annulling the the past’. past. I shall conclude that despite the high potential for confusion we should be careful to separate the possibility of changing the past 2.from Changing the impossibility the Past of strongly annulling the past. 2. ChangingThere are the two Past general strategies in the literature for arguing that changing the past is logically possible. Firstly, one can introduce another temporal dimension or another time- There are two general strategies in the literature for arguing that changing the past like structure in addition to normal time. (See, for example, [13–18]). Alternatively one can is logically possible. Firstly, one can introduce another temporal dimension or another keep just the single temporal dimension, but deny that earlier than/later than are always time-like structure in addition to normal time. (See, for example, [13–18]). Alternatively correlated. (See for example, [19,20], and especially [21]). I shall focus here on the first one can keep just the single temporal dimension, but deny that earlier than/later than are strategy,always correlated. though much (See of for what example, I say below [19,20], can and be especially adapted to [21 the]). Isecond. shall focus here on the first strategy,In some thoughworks, such much as of [13,15], what I sayand below[17], the can second be adapted temporal to the structure second. is a second orthogonalIn some time works, dimension. such as [In13 ,others15], and [14,22], [17], the what second we normally temporal structurethink of as is atime second is em- or- beddedthogonal in time another dimension. time-like In othersstructure, [14, 22not], nece whatssarily we normally orthogonal. think Either of as time way, is the embedded second temporalin another structure time-like is structure, generally not referred necessarily to as orthogonal. ‘hypertime’, Either and way,I shall the continue second temporalto do so. Onstructure either istreatment generally of referredhypertime, to asmomentary ‘hypertime’, time and slices I shall (or continuethe objects to or do events so. On of eitherthose slices)treatment can ofbe hypertime, hypertemporally momentary extended time slices or occur (or the again objects such or that events they of thosehave one slices) set can of properties,be hypertemporally say grandfather extended being or occur alive, again at one such hypertime, that they but have grandfather one set of properties,being dead say at another.grandfather being alive, at one hypertime, but grandfather being dead at another. Let ‘u’ be a complete universe state at a particularparticular time. Let ‘t’ be times and ‘H’ be hypertimes. Hence, aa universeuniverse without without time time travel travel could could be be partially partially represented represented as follows as fol- lowsin Figure in Figure1: 1: Figure 1. A hypertemporal universe with no time travel. Figure 1. A hypertemporal universe with no time travel. Given no time travel has happened, right now (t2021,H2021) Hitler survives past 1921— thatGiven is the wayno time the travel past ishas right happened, now.