# CANCELLED 27 November, Tomasz Placek, "A No-Go Result for a Relativity-Proof Dynamic Concept of

**UPDATE 27 NOVEMBER: THIS EVENT HAS BEEN CANCELLED DUE TO SEVERE WEATHER CONDITIONS IN POLAND **

On 27 November, Tomasz Placek (Jagiellonian University) will deliver a talk entitled “A No-Go Result for a Relativity-Proof Dynamic Concept of Time” at the HPP/Ian Ramsey Centre's 2019-2020 seminar series.

Venue: Theology Lecture Room, Floor 2, Gibson Building, Radcliffe Observatory Quarter, Woodstock Rd, Oxford OX2 6GG Time: 17:00-18:15, refreshments served

**Abstract: **Combining relativity with the intuitive notions of past, present, and future is a challenging task. It is natural to define the present by a simultaneity relation, which is standardly postulated to be transitive, reflexive, and symmetric, i.e., an equivalence relation. Yet van Benthem’s theorem (in his *The Logic of Time*, 1983) shows that the only equivalence relations definable on a Minkowski space-time and invariant under that space-time’s automorphisms, is the identity and the universal relation. In contrast to explicating time in terms of simultaneity, there is a different tradition (James, Eddington, Whitrow, Ellis) that links time to real change (becoming), the radical consequence being: no real change, then no time. On this dynamic view, an event’s present is defined in terms of a co-presence relation rather than simultaneity, with co-presence being explicated by a pattern of real changes. Recently the dynamic time was explored independently by Müller (Founda- tions of Physics 2019) and Placek (Synthese 2019). Müller defines co-present events as events sharing the same causally relevant factors, whereas Placek starts with giving the modal truth conditions of sentences like “*e'* belongs to the future of *e*”. The results of these authors are relativity-friendly, yet each result has a (different) defect. These defects, we claim, are the consequences of a general no-go result, the proof of which we will give. We will prove that no concept of dynamic time can satisfy all desiderata from this list: For any event e, (1) no two of Past(*e*),Present(*e*), and Future(*e*) overlap; (2) any history *h* with event *e* is partitioned by Past*(e*),Present(*e*), and Future(*e*); (3) Past*(e*) is settled; (4) Past(*e*) and Future(*e*) are symmetric in the sense that *e*' ∈ Past(*e*) iff *e* ∈ Future(*e'*), and (5) a co-presence relation *CP*, defined by *CP*(*e', e*) ⇔df *e'* ∈ Present(*e*), is transitive.

**Tomasz Placek** majored in physics and philosophy at the Jagiellonian University in Kraków, Poland. He received a PhD in philosophy from the Jagiellonian University in 1991 followed by a habilitation in 2001. He was appointed a visiting scholar at the Universities of Princeton and New York as well as the London School of Economics. His current area of research is metaphysics and philosophy of physics with a particular interest in branching space-time theories and their applications in areas such as determinism and causality, theories of probability, interpretations of quantum mechanics, and questions concerning human agency. Professor Placek is the author of *Intersubjectivity and Mathematical Intuitionism*, Kluwer AP 1999, and *Is Nature Deterministic?* Jagiellonian UP, 2001.

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