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 Weekly Seminar: 'The Complex Elliptic Genera of Simple Surface Singularities' with Katrin Wendland (Universität Freiburg) can be viewed here
👇
youtube.com/watch?v=HEpoNj…

John T. Lewis was born on this day in 1932. From January 1975 Professor Lewis took over the Directorship of STP, DIAS - a position he would hold for 25 years.
He's pictured 👇 with Lochlainn O'Raifeartaigh & Reverend Patrick Browne (Monsignor Pádraig de Brún)

Mainz Institute for Theoretical Physics, Johannes Gutenberg University - 12-23 April 2021
Gravity and Emergent Gauge Fields in Condensed and Synthetic Matter
indico.mitp.uni-mainz.de/event/228/

Happy World Quantum Day!
From DIAS’ own Erwin Schrodinger – one of the founding figures of quantum physics – to current research into quantum theory and its applications, DIAS is proud to celebrate over 80 years of quantum research.

DIAS STP Weekly Seminar: 'The Swampland and String Universality' with Miguel Montero (Harvard University) can be viewed here 👇
youtube.com/watch?v=kZv8Nl…

STP, DIAS Paper -
Can gravity be thought of as two gauge fields?
Check out ``Gauge × Gauge = Gravity on Homogeneous Spaces using Tensor Convolutions'' - By I. Jubb (DIAS) L. Borsten, V. Makwana, & S. Nagy (Heriot-Watt, Edinburgh & Queen Mary's, London). arxiv.org/abs/2104.01135

DIAS STP Weekly Seminar: Mithat Ünsal from North Carolina State University discusses non-invertible symmetries and string tensions beyond N-ality in semi-Abelian gauge theories. Catch it here:
youtube.com/watch?v=qI4Ekk…

As part of the DIAS Summer Studentships programme the School of Theoretical Physics of the Dublin Institute for Advanced Studies is delighted to be in a position to offer at least 4 Summer Studentships.
dias.ie/positions/inde…

STP, DIAS : Celebrating Synge Week - 23-30 March
Day 6: Synge was appointed Professor Emeritus in 1972. After his retirement he remained active for a long time and maintained very strong links with the Institute, coming in regularly for discussions, in particular with J.T. Lewis.

STP, DIAS : Celebrating Synge Week - 23-30 March 2021.
Day Five - Synge’s main lines of work were in general relativity and classical physics, but he also worked on various other topics including the hypercircle method in function space.

STP, DIAS : Celebrating Synge Week - 23-30 March 2021.
Day Four - Synge presented Eamon de Valera with signed first editions of Relativity: The Special Theory (1956) & Relativity: The General Theory (1960). Both are housed in the de Valera Collection in the STP Library Retweeted by
STP, DIAS

STP, DIAS : Celebrating Synge Week - 23-30 March 2021.
Day Four - Synge presented Eamon de Valera with signed first editions of Relativity: The Special Theory (1956) & Relativity: The General Theory (1960). Both are housed in the de Valera Collection in the STP Library

DIAS STP Weekly Seminar: Andrea Cappelli from INFN Florence discusses the conformal invariance and electric-magnetic self-duality of the surface of a topological insulator. Catch it here:
youtube.com/watch?v=X7nfBA…Retweeted by
STP, DIAS

STP, DIAS : Celebrating Synge Week - 23-30 March 2021.
Day Three - Synge's many contributions to spacetime geometry, including his pivotal work on black holes and the Synge world function, have been instrumental to our current understanding of gravity. Retweeted by
STP, DIAS

DIAS STP Weekly Seminar: Andrea Cappelli from INFN Florence discusses the conformal invariance and electric-magnetic self-duality of the surface of a topological insulator. Catch it here:
youtube.com/watch?v=X7nfBA…

STP, DIAS : Celebrating Synge Week - 23-30 March 2021.
Day Three - Synge's many contributions to spacetime geometry, including his pivotal work on black holes and the Synge world function, have been instrumental to our current understanding of gravity.

STP, DIAS : Celebrating Synge Week - 23-30 March 2021.
Day Two: Synge spent a short time as ballistic mathematician in the US Air Force during 1944-45 Retweeted by
STP, DIAS

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## 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, DIAS3 days agoSTP, DIAS Weekly Seminar: 'The Complex Elliptic Genera of Simple Surface Singularities' with Katrin Wendland (Universität Freiburg) can be viewed here 👇 youtube.com/watch?v=HEpoNj…

STP, DIAS3 days agoJohn T. Lewis was born on this day in 1932. From January 1975 Professor Lewis took over the Directorship of STP, DIAS - a position he would hold for 25 years. He's pictured 👇 with Lochlainn O'Raifeartaigh & Reverend Patrick Browne (Monsignor Pádraig de Brún)

STP, DIAS4 days agoMainz Institute for Theoretical Physics, Johannes Gutenberg University - 12-23 April 2021 Gravity and Emergent Gauge Fields in Condensed and Synthetic Matter indico.mitp.uni-mainz.de/event/228/

STP, DIAS4 days agoHappy World Quantum Day! From DIAS’ own Erwin Schrodinger – one of the founding figures of quantum physics – to current research into quantum theory and its applications, DIAS is proud to celebrate over 80 years of quantum research.

STP, DIAS1 week agoDIAS STP Weekly Seminar: 'The Swampland and String Universality' with Miguel Montero (Harvard University) can be viewed here 👇 youtube.com/watch?v=kZv8Nl…

DIAS1 week agoThe DIAS School of Theoretical Physics are pleased to announce the publication of "Gauge × Gauge = Gravity on Homogeneous Spaces using Tensor Convolutions" #DIASdiscovers #theoretical #physics #gravity #gauge #highenergy twitter.com/StpDias/status… Retweeted by STP, DIAS

David Malone1 week agoI guess you noticed who signed this one? @CardColm @StpDias @DIAS_Dublin twitter.com/aliiicv/status… Retweeted by STP, DIAS

STP, DIAS1 week agoSTP, DIAS Paper - Can gravity be thought of as two gauge fields? Check out ``Gauge × Gauge = Gravity on Homogeneous Spaces using Tensor Convolutions'' - By I. Jubb (DIAS) L. Borsten, V. Makwana, & S. Nagy (Heriot-Watt, Edinburgh & Queen Mary's, London). arxiv.org/abs/2104.01135

STP, DIAS2 weeks agoDIAS STP Weekly Seminar: Mithat Ünsal from North Carolina State University discusses non-invertible symmetries and string tensions beyond N-ality in semi-Abelian gauge theories. Catch it here: youtube.com/watch?v=qI4Ekk…

STP, DIAS2 weeks agoAs part of the DIAS Summer Studentships programme the School of Theoretical Physics of the Dublin Institute for Advanced Studies is delighted to be in a position to offer at least 4 Summer Studentships. dias.ie/positions/inde…

STP, DIAS3 weeks agoSTP, DIAS : Celebrating Synge Week - 23-30 March Day 6: Synge was appointed Professor Emeritus in 1972. After his retirement he remained active for a long time and maintained very strong links with the Institute, coming in regularly for discussions, in particular with J.T. Lewis.

STP, DIAS3 weeks agoSTP, DIAS : Celebrating Synge Week - 23-30 March 2021. Day Five - Synge’s main lines of work were in general relativity and classical physics, but he also worked on various other topics including the hypercircle method in function space.

STP, DIAS3 weeks agoSTP, DIAS : Celebrating Synge Week - 23-30 March 2021. Day Four - Synge presented Eamon de Valera with signed first editions of Relativity: The Special Theory (1956) & Relativity: The General Theory (1960). Both are housed in the de Valera Collection in the STP Library Retweeted by STP, DIAS

STP, DIAS3 weeks agoSTP, DIAS : Celebrating Synge Week - 23-30 March 2021. Day Four - Synge presented Eamon de Valera with signed first editions of Relativity: The Special Theory (1956) & Relativity: The General Theory (1960). Both are housed in the de Valera Collection in the STP Library

STP, DIAS3 weeks agoDIAS STP Weekly Seminar: Andrea Cappelli from INFN Florence discusses the conformal invariance and electric-magnetic self-duality of the surface of a topological insulator. Catch it here: youtube.com/watch?v=X7nfBA… Retweeted by STP, DIAS

STP, DIAS3 weeks agoSTP, DIAS : Celebrating Synge Week - 23-30 March 2021. Day Three - Synge's many contributions to spacetime geometry, including his pivotal work on black holes and the Synge world function, have been instrumental to our current understanding of gravity. Retweeted by STP, DIAS

STP, DIAS3 weeks agoDIAS STP Weekly Seminar: Andrea Cappelli from INFN Florence discusses the conformal invariance and electric-magnetic self-duality of the surface of a topological insulator. Catch it here: youtube.com/watch?v=X7nfBA…

STP, DIAS3 weeks agoSTP, DIAS : Celebrating Synge Week - 23-30 March 2021. Day Three - Synge's many contributions to spacetime geometry, including his pivotal work on black holes and the Synge world function, have been instrumental to our current understanding of gravity.

STP, DIAS4 weeks agoSTP, DIAS : Celebrating Synge Week - 23-30 March 2021. Day Two: Synge spent a short time as ballistic mathematician in the US Air Force during 1944-45 Retweeted by STP, DIAS

STP, DIAS4 weeks agoSTP, DIAS : Celebrating Synge Week - 23-30 March 2021. Day Two: Synge spent a short time as ballistic mathematician in the US Air Force during 1944-45