Physikalisches Kolloquium

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This is an exciting and pivotal time for particle physics, where decisions that will be taken in the coming years will shape the long-term future of the field. In this colloquium, I will give a personal perspective on the status of particle physics and the prospects for the next ten years and beyond. I will discuss the importance of the Higgs boson and will give particular emphasis on the role of CERN in our exploration of the fundamental nature of the universe, both today and tomorrow. This colloquium will be largely at a non-technical level and is intended to be accessible to a broad audience.

In the ΛCDM cosmological model the Universe is assumed to be isotropic and homogeneous when averaged on large scales. That the Cosmic Microwave Background (CMB) has a dipole anisotropy is interpreted as due to our peculiar (non-Hubble) motion because of local inhomogeneity. There must then be a corresponding dipole in the sky distribution of sources at high redshift. Using catalogues of radio sources and quasars we find that this expectation is rejected at >5σ, i.e. the distribution of distant matter is not isotropic in the 'CMB frame’. This calls into question the standard practice of boosting to this frame to analyse cosmological data, in particular to infer acceleration of the Hubble expansion rate using Type Ia supernovae, which is then interpreted as due to a Cosmological Constant Λ. We find that the inferred acceleration is in fact anisotropic (in the direction of the CMB hotspot) and likely illusory because of our being embedded in a coherent bulk flow, rather than due to dark energy.