The discovery of gravitational waves (GWs) by the LIGO and Virgo Collaborations opened a new window on the Universe. They observed the mergers of stellar-mass black holes and neutron stars. The NANOGrav and other pulsar timing array (PTA) Collaborations have recently presented evidence for GWs with frequencies in the nanoHz range. I will discuss their possible origins and the prospects for other experiments to observe GWs in the range of frequencies between the PTAs and LIGO/Virgo/KAGRA, and detect the mergers of supermassive black holes, networks of cosmic strings or cosmological phase transitions, stressing the potential of atom interferometers to complement observations with laser interferometers.
Professor John Ellis earned his Ph.D. in theoretical particle physics in 1971 at Cambridge University. As the world-renowned particle physicist, he was awarded the Maxwell Medal and Prize (1982) and the Paul Dirac Medal and Prize (2005) by the Institute of Physics. He is an Elected Fellow of the Royal Society of London since 1985 and of the Institute of Physics since 1991. He won the First Award in the Gravity Research Foundation essay competition (1999 and 2005).Professor Ellis is currently the Clerk Maxwell Professor of Theoretical Physics at King's College London. He has been appointed Commander of the British Empire (CBE) since 2012. He was twice the Deputy Division Leader for the Theory Division of CERN, and served as Division Leader for 1988–1994. He was a founding member of the LEPC and the LHCC. He is the Chair of the committee to investigate Physics Opportunities for Future Proton Accelerators, and is a member of the extended CLIC (Compact Linear Collider) Steering Committee.
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