Talks: 22 June 2015

We will be hosting two visitors to our group, Michel Buck and Ian Jubb, who will give seminars on Monday afternoon (June 22).  The talk will both be held in AP&M room 7421, at 1 pm (Michel Buck) and 2:30 pm (Ian Jubb).

Dr. Michel Buck
Northeastern University, Department of Physics

Title:  An overview of causal sets

Abstract:  Causal set theory is an approach to quantum gravity based on the idea that spacetime is fundamentally discrete and Lorentz invariant. Structurally, a causal set is a locally finite partial order, or a transitive DAG (directed acyclic graph). After a brief introduction to the idea, I will give an overview of some of the recent research activity in causal sets. Some topics I hope to touch on are: measures of discrete geometry (e.g. distance, curvature,…), dynamics on causal sets (e.g. classical and quantum fields), and phenomenology from causal sets (e.g. dark energy).

Ian Jubb
Imperial College London, Department of Physics

Title:  Boundary Terms for Causal Sets

Abstract:  In Causal Set theory the ordering of the spacetime “atoms” and their number are meant to give us all of the geometrical information. Thus, we should be able to construct causal set expressions that give us back particular geometrical quantities.  In this talk I will describe a recent result that allows one to determine the Gibbons-Hawking-York (GHY) boundary term for a causal set. The GHY term appears in the action for a spacetime with a boundary, and is simply the integral over the extrinsic curvature of that boundary. A side effect of the work behind this result was the emergence of a new way to calculate the dimension of a causal set. Finally, I would like to discuss the boundary contributions that are “hidden” in the bulk action for a causal set.

Meeting: 2 June 2015

Our second to last meeting of the year will take place on Tuesday, 2 June, from 11:30 to 1pm. The location is likely AP&M 7218 (unless one of the Davids tells us otherwise).

Here is the agenda:

(1) John Dougherty on counting indistinguishable elements and causal sets
(2) David Rideout and Orest Bucicovschi on ‘non-haecceity’ growth dynamics

This will be a fun meeting, make sure not to miss it!

Meeting: 21 April 2015

We will be meeting on Tuesday, 21 April 2015, from 11:30am to 1pm in AP&M 7218. In the unlikely case that the room is occupied, we will use the backup room AP&M 2402A. Our agenda will be as follows:

(1) Discussion of whether the group wants to apply for continued funding.
(2) Continuation of our discussion of the metaphysics of events and its implications for the dynamics.

Conference: Time in Quantum Gravity, UCSD, 13-14 March 2015

Our group is organizing the second installment of the ‘Beyond Spacetime’ conference series, to take place at UCSD on 13-14 March. This time, in accordance to our group’s main focus, the conference will focus on time in quantum gravity. Several of our group members will be presenting: David Rideout, John Dougherty, and Craig Callender. In fact, Craig will give a talk that is partially based on on earlier joint work that originated in our group (and is now forthcoming in the British Journal for Philosophy of Science). This is the link to the main conference website.

Meeting: 24 February 2015

We will be meeting on Tuesday, 24 February 2015, 12-2pm in APM 7218 (in the mathematics department). Here is the agenda, with the discussion leader for each topic:

– David Rideout about various things that came up on his recent trip to India.
– David Meyer about a Hawking-Malament type theorem for Euclidean space, and we might toss around some ideas for extending it.
– Chris Wüthrich on the metaphysics of basal causet events.

These topics will be addressed and discussed by all members.

Meeting: 16 June 2014

We will be meeting for our final meeting this academic year on Monday, 16 June, from 10 to 11:30am. We will meet in the seminar room of the Department of Philosophy on the 7th floor of the HSS building.

Our goal for this meeting is to articulate concrete research questions for the near future.

Meeting: 22 May 2014

We will be meeting again as a group on Thursday, 22 May, 11:00-12:20 in AP&M 7218. Luca Bombelli, our speaker on Tuesday, will be present as well. So we may start with taking up the discussion from Tuesday and talk about the central question of how smooth spacetimes can emerge from discrete causal sets. Either in this meeting or on an occasion in the near future, we will then continue with our exploration of follow up research based on the paper by Callender and Wüthrich.

20 May 2014: Luca Bombelli

Prof. Luca Bombelli, University of Mississippi, will be giving a seminar to our group. We will meet in 5402 AP&M, at 1pm on Tuesday, 20 May.

“Causal set kinematics: Partially ordered measure spaces as the context for the relationship with Lorentzian manifolds”

In this talk I will describe an approach to questions about the relationship between causal sets and smooth Lorentzian geometries based on considering both types of structures as examples of partially ordered measure spaces. There is a natural definition of closeness between any two objects of this type. I will introduce this definition, describe some of its properties, and comment on its application to manifoldlike causal sets.