How Fast Is the Universe Actually Expanding Right Now

How fast is the universe expanding right now? The answer should be simple, but two of the most precise measurement methods in cosmology give different answers by about 8 percent. That gap, called the Hubble tension, is one of the most significant unsolved problems in modern physics. Tonight we follow the distance ladder from Cepheid variable stars through Type Ia supernovae, examine the cosmic microwave background and what it tells us about the early universe, explore what dark energy is actually doing to spacetime, and look at how gravitational wave standard sirens are beginning to offer a completely independent measurement. Subscribe for more deep-space documentaries every week. Sources: Riess, A. et al. (2022). A Comprehensive Measurement of the Local Value of the Hubble Constant. The Astrophysical Journal Letters. SHOES Team / Johns Hopkins. Planck Collaboration (2020). Planck 2018 results VI: Cosmological parameters. Astronomy and Astrophysics. ESA. Perlmutter, S. et al. (1999). Measurements of Omega and Lambda from 42 High-Redshift Supernovae. The Astrophysical Journal. Supernova Cosmology Project. Abbott, B. et al. (2017). A gravitational-wave standard siren measurement of the Hubble constant. Nature. LIGO/Virgo. DESI Collaboration (2024). DESI 2024 VI: Cosmological constraints from BAO measurements. arXiv. DESI. Leavitt, H. & Pickering, E. (1912). Periods of 25 variable stars in the Small Magellanic Cloud. Harvard College Observatory Circular. Wong, K. et al. (2020). H0LiCOW XIII: H0 from lensed quasars. MNRAS.