Rethinking Cosmology | 8 -12 December, 2025 | Raman Research Institute, Bengaluru, India

Day 1 | Session 3
About the conference.
The standard Λ-Cold Dark Matter (ΛCDM) cosmological model has been very successful. For three decades, it has provided an excellent fit to the vast majority of cosmological data, and in the absence of any reasonably developed alternative, will continue to serve as the benchmark cosmology. The dominant components of the energy density of the Universe according to this model, dark matter and dark energy, have served to motivate a wide spectrum of lines of inquiry across the frontiers of theoretical and experimental high energy physics

Nevertheless, if history offers us any lessons, the phenomenological ΛCDM model must gradually give way to a deeper theory. It seems clear that this working model of cosmology is already experiencing a turbulent period driven by anomalies and tensions as new and more informative observations pour in. Notably, a disagreement between the value of the Hubble expansion rate determined from early and late Universe probes now exceeds 5σ in statistical significance, there are similarly significant indications of violations of the underlying statistical isotropy and homogeneity predicated by the ‘Cosmological Principle’, and there is increasing stress on the galaxy formation scenario within ΛCDM. The next decade will witness various observatories delivering data with an unprecedented level of statistics. For example, while the global cosmology community has observed ~2000 Type Ia supernovae (SNeIa) over the past two decades, The Vera Rubin Observatory (hereafter Rubin-LSST), starting in mid-2025, is expected to observe tens of thousands of SNe Ia every year. Other new and upcoming observatories such as the Dark Energy Spectroscopic Instrument (DESI), the Euclid and SPHEREx satellite missions, the James Webb Space Telescope (JWST), and Square Kilometer Array (SKA) will deliver a significantly deeper view of larger parts of the sky. There are prospects of detection of the signal of cosmic dawn in radio astronomy. Meanwhile we also expect advances in high energy neutrino/gamma ray astronomy and cosmic ray physics to start delivering results which have implications for cosmology.

The conference is intended to continue on a line of recent meetings that focus on a critical assessment of the current working model of cosmology. The conference will aim to iron out bones of contention within the community and build consensus on new lines of inquiry necessary at both observational and theoretical frontiers, while also highlighting the interface of cosmology with other areas of inquiry (in particular fundamental physics).

For the Indian community, this programme will be of particular relevance. We have active involvement in major ongoing international efforts like the analysis of Cosmic Microwave Background data, large scale structure surveys as well as upcoming observatories such as the Square Kilometre Array, the Thirty Metre Telescope, Rubin-LSST and LIGO-India. Over 90% of the information in CMB polarization data and nearly all the cosmological information in the CMB spectrum remain untapped, and CMB-Bhārat, a 4th generation space mission proposal to ISRO to be carried out with international cooperation, target these final frontiers of CMB science. India has also become a full member of the SKA Observatory. This will provide a boost to the ongoing efforts of the Indian cosmology community in testing the fundamental framework of the standard cosmology. Our programme will aim to explore synergies and common platforms with the established science goals of the communities involved in these efforts, while also charting new paths forward.

The winter of 2025-26 is an opportune moment for this programme, as new data will have just started coming in, providing an atmosphere of excitement for the whole programme. We have already secured the participation of leading cosmologists from around the world who will participate in the Conference.

14:30 - Richard Watkin
15:20 Sebastian von Hausegger
16:00 - Glenn Starkman