Cosmology – James (Jim) Rohlf
Cosmology pages and tools from Jim Rohlf, Professor of Physics at Boston University and a member of the DESI collaboration — the model, what DESI measures, and where the model is under strain.
Start here
- Cosmology calculator — distances, ages and the BAO scale at any redshift, with a cosmic timeline you can jump through
- Evolving dark energy calculator — set w0 and wa and see what the DESI BAO distances allow
- How DESI works — the light path from galaxy to CCD, and the focal plane built at BU
The standard model of cosmology
- ΛCDM — dark energy and cold dark matter in six parameters, and the cosmic timeline from the Planck era to today
- Cosmological parameter estimation — how the six numbers are actually fitted
- Full shape — what the whole galaxy power spectrum adds beyond the BAO peak
What DESI measures
- Baryon acoustic oscillations — where the 147 Mpc standard ruler comes from
- Tracers — the galaxies, quasars and Lyman-α forest that map the volume
- Lyman-α — using absorption in quasar spectra to reach the highest redshifts
- Results — what DESI adds to the expansion history
- Data Release 1 — the first thirteen months of observations
Open questions
- The Hubble tension — why the early- and late-time measurements of H₀ disagree by about five standard deviations
- Evolving dark energy — DESI’s BAO, with the CMB and supernovae, prefers a dark energy density that changes with time
Groups and collaborations
- Boston University DESI group — the group, its people and its publications
- DESI collaboration — the survey and its data releases