PhD Imperial College London (2017), MPhys University of Manchester (2013)

Research Interests

Our current understanding of the universe rests on two great pillars of theoretical physics. The first is General Relativity, Einstein’s theory of gravity as the curvature of spacetime itself, which describes phenomena such as black holes and gravitational waves. The second is Quantum Field Theory, the theory of matter and its interactions, which can describe processes such as quantum tunnelling and particle-antiparticle pair production. These theories represent two of the most significant scientific achievements of the last century, and yet they are mutually incompatible. A coherent understanding of the most fundamental aspects of our universe requires that quantum physics and gravity be reconciled into a single, as of yet, unknown framework — Quantum Gravity.

The long-standing problem of Quantum Gravity is the central motivation behind my research, and I am currently investigating it from three main directions:

Measurements in Quantum Field Theory Quantum Field Theory has been experimentally verified to extremely high accuracy. Nevertheless, there are still outstanding issues within the theory, unaddressed by any experimental tests. For instance, there are many observables that the current theory says should be measurable, but, at the same time, we can also show that if we were to measure them we could send signals faster than light! If we are to reconcile quantum theory with relativity, and Einstein’s theory of gravity, then such superluminal signals should be avoided. The framework of Quantum Field Theory, therefore, needs to be modified in some way, either by excising these superluminal signalling observables, or by updating our description of measurement within the theory. Regardless of the particular resolution, a consistent description of measurement in the relativistic setting of Quantum Field Theory will likely have important implications for any complete theory of Quantum Gravity.

Spacetime Topology Change Predictions in quantum theory can be derived by summing over all the possible trajectories that the particles can follow. In direct analogy, physicists have tried to quantise gravity by attempting to sum over the different ways that spacetime can curve. One unanswered question regarding this sum is whether we should sum over spacetimes that “split” and/or “re-attach”, that is, spacetimes that undergo a topology change. A dramatic example of this would be the universe splitting in two. As radical as this sounds, similar processes may occur at the quantum level. There are multiple types of topology changes that can occur, and to properly address the question of whether a particular change can happen at the quantum level we must include the effects of matter via Quantum Field Theory. The only topology change that has been properly studied in this way is the 2D trousers spacetime, in which a single circle splits into two circles. In this case, the matter appears to prevent the trousers topology change from occurring. There are hints that all the different topology changes in 3D and 4D are also prohibited in the same way, except one. Remarkably, this single (possibly) viable topology change occurs in black hole pair-production — a process that intimately ties together quantum theory and gravity. Evidence for or against the viability of this topology change, and other spacetime topology changes, will undoubtedly be beneficial in the search for Quantum Gravity.

Causal Set Theory Causal Set Theory is an approach to Quantum Gravity in which the continuous spacetime of General Relativity is substituted for a discrete network — a causal set — in which the vertices are the ‘atoms’ of spacetime, and the links between vertices are causal relations. This approach is motivated by the fact that almost all of spacetime geometry, and hence gravity, can be encoded in causal relations. Additionally, the discrete nature of the theory provides a physical reason as to why black hole entropy should be finite. The manifestly causal nature of Causal Set Theory has also inspired the development of novel methods in Quantum Field Theory, e.g. the Sorkin-Johnston formalism. Further study of Quantum Field Theory and black holes within Causal Set Theory will undoubtedly improve our understanding of how to embed quantum theory within a relativistic framework.

STP, DIAS - Upcoming Seminars:
Tuesday 9 June 2020, 6pm
Sean A. Hartnoll (Stanford University)
‘Bootstrapping Matrix Quantum Mechanics’
Tuesday 16 June 2020 2:30pm
David Tong (University of Cambridge)
'Chiral Boundary States for Fermions'
dias.ie/stp/#DIASDiscovers

STP, DIAS Seminar Videolink:
Date: 19 May 2020
Sudeshna Sen (University College Dublin)
'Interplay of Molecular Symmetry & Strong Correlations in Molecular Junctions'
youtube.com/watch?v=u6CU4S…

CANCELLED -
STP, DIAS Statutory Public Lecture –
Monday 30 March 2020
'Dream & Realization of Quantum Communication'
Prof Pan Jianwei
(University of Science & Technology of China)
Monday, 30th March 2020, 6.30pm
Thomas Prior Hall, Ballsbridge, Dublin 4

STP, DIAS Statutory Public Lecture –
Monday 30 March 2020
'Dream & Realization of Quantum Communication'
Prof Pan Jianwei
(University of Science & Technology of China)
Monday, 30th March 2020, 6.30pm
Thomas Prior Hall, Ballsbridge, Dublin 4
Tickets: eventbrite.ie/e/dias-stp-sta…

STP, DIAS Statutory Public Lecture –
Monday 30 March 2020
'Dream & Realization of Quantum Communication'
Prof Pan Jianwei (University of Science & Technology of China)
Monday, 30th March 2020, 6.30pm
Thomas Prior Hall, Ballsbridge, Dublin 4
Tickets: eventbrite.ie/e/dias-stp-sta…

STP DIAS has released a new issue of its journal Communications of DIAS - Series A (Theoretical Physics) No. 31 (2019). ISSN 0070-7414
Grassmann Variable Analysis for 1D and 2D Ising Models by V. N. Plechko - Edited by T. C. Dorlas
dias.ie/wp-content/upl…

STP, DIAS Events - Dublin Festival of History 2019 -
On Now!
'The thoughts of Hamilton and Schrödinger that stood the test of time'
Luuk Coopmans (DIAS)

STP, DIAS Events - Dublin Festival of History 2019 - THURSDAY 6.30PM
'The thoughts of Hamilton and Schrödinger that stood the test of time'
Luuk Coopmans (DIAS)
eventbrite.ie/e/the-thoughts…

A proud day for DIAS, celebrating our past and present female scientists: news that Dr Rebeca Garcia Lopez (DIAS) has received funding via @scienceirel Starting Investigator Research Grant & unveiling of the portrait of renowned scientist & 1st female Fellow of DIAS,Sheila Tinney Retweeted by
STP, DIAS

We were sad to hear of the passing of Sir Michael Atiyah last week, aged 89. Atiyah was a great former chair of the board of our School of Theoretical Physics here at DIAS from 2000-2005. Ar dheis Dé go raibh a anam dílis. (Below, pictured in DIAS's Conference Room) @StpDiasRetweeted by
STP, DIAS

## Dr. Ian Jubb

## Contact

email: ijubb@stp.dias.iephone: +353-1-6140128address: Rm. 208, DIAS, 10 Burlington Rd, D04 C932.## Education

PhD Imperial College London (2017),

MPhys University of Manchester (2013)

## Research Interests

Our current understanding of the universe rests on two great pillars of theoretical physics. The first is General Relativity, Einstein’s theory of gravity as the curvature of spacetime itself, which describes phenomena such as black holes and gravitational waves. The second is Quantum Field Theory, the theory of matter and its interactions, which can describe processes such as quantum tunnelling and particle-antiparticle pair production. These theories represent two of the most significant scientific achievements of the last century, and yet they are mutually incompatible. A coherent understanding of the most fundamental aspects of our universe requires that quantum physics and gravity be reconciled into a single, as of yet, unknown framework — Quantum Gravity.

The long-standing problem of Quantum Gravity is the central motivation behind my research, and I am currently investigating it from three main directions:

Measurements in Quantum Field TheoryQuantum Field Theory has been experimentally verified to extremely high accuracy. Nevertheless, there are still outstanding issues within the theory, unaddressed by any experimental tests. For instance, there are many observables that the current theory says should be measurable, but, at the same time, we can also show that if we were to measure them we could send signals faster than light! If we are to reconcile quantum theory with relativity, and Einstein’s theory of gravity, then such superluminal signals should be avoided. The framework of Quantum Field Theory, therefore, needs to be modified in some way, either by excising these superluminal signalling observables, or by updating our description of measurement within the theory. Regardless of the particular resolution, a consistent description of measurement in the relativistic setting of Quantum Field Theory will likely have important implications for any complete theory of Quantum Gravity.

Spacetime Topology ChangePredictions in quantum theory can be derived by summing over all the possible trajectories that the particles can follow. In direct analogy, physicists have tried to quantise gravity by attempting to sum over the different ways that spacetime can curve. One unanswered question regarding this sum is whether we should sum over spacetimes that “split” and/or “re-attach”, that is, spacetimes that undergo a topology change. A dramatic example of this would be the universe splitting in two. As radical as this sounds, similar processes may occur at the quantum level. There are multiple types of topology changes that can occur, and to properly address the question of whether a particular change can happen at the quantum level we must include the

effects of matter via Quantum Field Theory. The only topology change that has been properly studied in this way is the 2D trousers spacetime, in which a single circle splits into two circles. In this case, the matter appears to prevent the trousers topology change from occurring. There are hints that all the different topology changes in 3D and 4D are also prohibited in the same way, except one. Remarkably, this single (possibly) viable topology change occurs in black hole pair-production — a process that intimately ties together quantum theory and gravity. Evidence for or against the viability of this topology change, and other spacetime topology changes, will undoubtedly be beneficial in the search for Quantum Gravity.

Causal Set TheoryCausal Set Theory is an approach to Quantum Gravity in which the continuous spacetime of General Relativity is substituted for a discrete network — a causal set — in which the vertices are the ‘atoms’ of spacetime, and the links between vertices are

causal relations. This approach is motivated by the fact that almost all of spacetime geometry, and hence gravity, can be encoded in causal relations. Additionally, the discrete nature of the theory provides a physical reason as to why black hole entropy should be finite. The manifestly causal nature of Causal Set Theory has also inspired the development of novel methods in Quantum Field Theory, e.g. the Sorkin-Johnston formalism. Further study of Quantum Field Theory and black holes within Causal Set Theory will undoubtedly improve our understanding of how to embed quantum theory within a relativistic framework.

Recent Publications## School of Theoretical Physics

STP, DIAS2 months agoIrish Times today - Article on former STP, DIAS Professor Cornelius Lanczos. irishtimes.com/news/science/c… #DIASdiscovers

STP, DIAS4 months agoSTP, DIAS - Upcoming Seminars: Tuesday 9 June 2020, 6pm Sean A. Hartnoll (Stanford University) ‘Bootstrapping Matrix Quantum Mechanics’ Tuesday 16 June 2020 2:30pm David Tong (University of Cambridge) 'Chiral Boundary States for Fermions' dias.ie/stp/ #DIASDiscovers

STP, DIAS4 months agoSTP, DIAS Seminar Videolink: Date: 19 May 2020 Sudeshna Sen (University College Dublin) 'Interplay of Molecular Symmetry & Strong Correlations in Molecular Junctions' youtube.com/watch?v=u6CU4S…

STP, DIAS4 months agoDIAS, STP Seminar: Tues. 19 May 2020, 2:30pm ‘Interplay of Molecular Symmetry & Strong Correlations in Molecular Junctions’ Speaker: Sudeshna Sen (UCD) dias.ie/stp/ #DIASDiscovers

STP, DIAS4 months agoDIAS STP Seminar: Tues. 12 May, 3pm Title: 'Euclidean Quantum Field Theory: Axioms and Automorphic Forms' Speaker: Werner Nahm (DIAS)

STP, DIAS7 months agoCANCELLED - STP, DIAS Statutory Public Lecture – Monday 30 March 2020 'Dream & Realization of Quantum Communication' Prof Pan Jianwei (University of Science & Technology of China) Monday, 30th March 2020, 6.30pm Thomas Prior Hall, Ballsbridge, Dublin 4

STP, DIAS7 months agoSTP, DIAS Statutory Public Lecture – Monday 30 March 2020 'Dream & Realization of Quantum Communication' Prof Pan Jianwei (University of Science & Technology of China) Monday, 30th March 2020, 6.30pm Thomas Prior Hall, Ballsbridge, Dublin 4 Tickets: eventbrite.ie/e/dias-stp-sta…

STP, DIAS7 months agoSTP, DIAS Statutory Public Lecture – Monday 30 March 2020 'Dream & Realization of Quantum Communication' Prof Pan Jianwei (University of Science & Technology of China) Monday, 30th March 2020, 6.30pm Thomas Prior Hall, Ballsbridge, Dublin 4 Tickets: eventbrite.ie/e/dias-stp-sta…

STP, DIAS9 months agoSTP, DIAS 2020 Matrix Membranes and Emergent Spacetime Summer School: June 13th – 19th Workshop: June 20th – 22nd Apply : dias.ie/stpsummerschoo…

STP, DIAS10 months agoSTP DIAS has released a new issue of its journal Communications of DIAS - Series A (Theoretical Physics) No. 31 (2019). ISSN 0070-7414 Grassmann Variable Analysis for 1D and 2D Ising Models by V. N. Plechko - Edited by T. C. Dorlas dias.ie/wp-content/upl…

STP, DIAS10 months agoPhysicists Can Finally Peek at Schrödinger's Cat Without Killing It Forever livescience.com/schrodingers-c…

STP, DIAS11 months agoDIAS Events : Weds. 30 October @ 6:00 - 7:00 pm Samhain agus Science – The Stars Look Very Different Today... #DIASdiscovers dias.ie/event/samhain-…

STP, DIAS11 months agoSTP, DIAS Events - Dublin Festival of History 2019 - On Now! 'The thoughts of Hamilton and Schrödinger that stood the test of time' Luuk Coopmans (DIAS)

STP, DIAS12 months agoSTP, DIAS Events - Dublin Festival of History 2019 - THURSDAY 6.30PM 'The thoughts of Hamilton and Schrödinger that stood the test of time' Luuk Coopmans (DIAS) eventbrite.ie/e/the-thoughts…

STP, DIAS1 year agoSTP, DIAS - Statutory Public Lecture 2019 - Prof. Don Zagier

STP, DIAS1 year agoSTP Statutory Public Lecture 2019 Speaker: Prof Don Zagier (Max Planck Institute, Bonn) Title: Numbers, Knots, & Quantum Theory Date: Thursday 23 May 2019, 6pm. Venue: Robert Emmet Theatre, Trinity College, Dublin. Tickets: eventbrite.ie/e/dublin-insti…

STP, DIAS1 year agoDIAS Research Forum 2019 – Friday10 May, 3-5pm

DIAS Dublin2 years agoA proud day for DIAS, celebrating our past and present female scientists: news that Dr Rebeca Garcia Lopez (DIAS) has received funding via @scienceirel Starting Investigator Research Grant & unveiling of the portrait of renowned scientist & 1st female Fellow of DIAS,Sheila Tinney Retweeted by STP, DIAS

DIAS Dublin2 years agoWe were sad to hear of the passing of Sir Michael Atiyah last week, aged 89. Atiyah was a great former chair of the board of our School of Theoretical Physics here at DIAS from 2000-2005. Ar dheis Dé go raibh a anam dílis. (Below, pictured in DIAS's Conference Room) @StpDias Retweeted by STP, DIAS

STP, DIAS2 years agoHi, can you mail me directly regarding the images of Schrodinger? grogers@stp.dias.ie