A challenge to the standard cosmological model

by Prof. Subir Sarkar (University of Oxford)

Friday 20 Nov 2026, 10:00 → 11:00 Asia/Shanghai

Tsung-Dao Lee Institute/N6F-N600 - Lecture Room (Tsung-Dao Lee Institute)

Abstract:

In the standard ΛCDM model, the Universe is assumed to be isotropic and homogeneous when averaged on large scales, so described by the FLRW metric. That the cosmic microwave background has a dipole anisotropy is interpreted as due to our peculiar (non-Hubble) motion because of local inhomogeneity. A similar dipole is then expected in the sky distribution of distant sources. Using catalogues of radio galaxies and quasars, we find however that the amplitude of the matter dipole is a factor of 2-3 bigger than expected, i.e. the distribution of distant matter is not isotropic in the `CMB frame’. This calls into question all analyses of cosmological data, in particular of Type Ia supernovae, which assume the FLRW metric to infer that the Hubble expansion rate is accelerating, as if driven by a Cosmological Constant Λ or more general dark energy. In fact the inferred acceleration is anisotropic and local - so likely an artefact of the local peculiar bulk flow rather than due to the quantum vacuum. [Nature Rev. Phys. 7:68, 2025; Rev. Mod. Phys. 97:041001, 2025; Mon. Not. Roy. Astron. Soc. 549:stag844, 2026]

Speaker Bio:

Subir Sarkar was born & educated in India - at the Indian Institute of Technology, Kharagpur and the University of Bombay (PhD 1982). He was a Staff Associate of the Tata Institute of Fundamental Research, Bombay and has held visiting positions at SISSA, Trieste; CERN, Geneva; Astrophysics, University of Oxford, and Rutherford Appleton Laboratory, Chilton. Since 1990 he has been at the Rudolf Peierls Centre for Theoretical Physics, University of Oxford, where he was head of the Particle Theory Group and since 2021 is Professor Emeritus. He has also been visiting Niels Bohr Professor at Copenhagen University.

His research interests are at the interface between astrophysics & cosmology and fundamental physics — including cosmic rays, dark matter, inflation, neutrino cosmology etc. He also participates in astroparticle experiments such as the IceCube Neutrino Observatory and Cherenkov Telescope Array – as well as laser plasma experiments and the Dark Energy Science Collaboration of the Rubin Observatory. He was awarded the IUPAP-TIFR Homi Bhabha Medal & Prize in 2017 and shared in the 2021 Bruno Rossi Prize of the American Astronomical Society to the IceCube Collaboration.

Alternative online link: https://meeting.tencent.com/dm/6XK4hRdc2ILd
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