{"work":{"id":"4eb788a9-3263-49fe-af5c-2ee9a1a17416","openalex_id":null,"doi":null,"arxiv_id":"1607.05617","raw_key":null,"title":"The trouble with $H_0$","authors":null,"authors_text":"J","year":2016,"venue":"astro-ph.CO","abstract":"We perform a comprehensive cosmological study of the $H_0$ tension between the direct local measurement and the model-dependent value inferred from the Cosmic Microwave Background. With the recent measurement of $H_0$ this tension has raised to more than $3\\sigma$. We consider changes in the early time physics without modifying the late time cosmology. We also reconstruct the late time expansion history in a model independent way with minimal assumptions using distances measures from Baryon Acoustic Oscillations and Type Ia Supernovae, finding that at $z<0.6$ the recovered shape of the expansion history is less than 5 % different than that of a standard LCDM model. These probes also provide a model insensitive constraint on the low-redshift standard ruler, measuring directly the combination $r_s h$ where $H_0=h \\times 100$ km/s/Mpc and $r_s$ is the sound horizon at radiation drag (the standard ruler), traditionally constrained by CMB observations. Thus $r_s$ and $H_0$ provide absolute scales for distance measurements (anchors) at opposite ends of the observable Universe. We calibrate the cosmic distance ladder and obtain a model-independent determination of the standard ruler for acoustic scale, $r_s$. The tension in $H_0$ reflects a mismatch between our determination of $r_s$ and its standard, CMB-inferred value. Without including high-l Planck CMB polarization data (i.e., only considering the \"recommended baseline\" low-l polarisation and temperature and the high l temperature data), a modification of the early-time physics to include a component of dark radiation with an effective number of species around 0.4 would reconcile the CMB-inferred constraints, and the local $H_0$ and standard ruler determinations. The inclusion of the \"preliminary\" high-l Planck CMB polarisation data disfavours this solution.","external_url":"https://arxiv.org/abs/1607.05617","cited_by_count":null,"metadata_source":"pith","metadata_fetched_at":"2026-07-04T05:19:36.106251+00:00","pith_arxiv_id":"1607.05617","created_at":"2026-05-10T14:40:32.931081+00:00","updated_at":"2026-07-04T05:19:36.106251+00:00","title_quality_ok":false,"display_title":"The trouble with $H_0$","render_title":"The trouble with $H_0$"},"hub":{"state":{"work_id":"4eb788a9-3263-49fe-af5c-2ee9a1a17416","tier":"hub","tier_reason":"10+ Pith inbound or 1,000+ external citations","pith_inbound_count":17,"external_cited_by_count":null,"distinct_field_count":3,"first_pith_cited_at":"2018-07-17T04:05:07+00:00","last_pith_cited_at":"2026-06-30T08:57:18+00:00","author_build_status":"not_needed","summary_status":"needed","contexts_status":"needed","graph_status":"needed","ask_index_status":"not_needed","reader_status":"not_needed","recognition_status":"not_needed","updated_at":"2026-08-23T23:39:56.606056+00:00","tier_text":"hub"},"tier":"hub","role_counts":[{"context_role":"background","n":10},{"context_role":"dataset","n":1}],"polarity_counts":[{"context_polarity":"background","n":10},{"context_polarity":"use_dataset","n":1}],"runs":{},"summary":{},"graph":{},"authors":[]}}