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Measuring cosmological parameters

W L Freedman1

  • 1Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101, USA.

Proceedings of the National Academy of Sciences of the United States of America
|January 14, 1998
PubMed
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Cosmological measurements reveal a low matter density (Omegam) around 0.2-0.3 and a Hubble constant (H0) of 60-80 km/sec/Mpc. Future research will focus on cosmic microwave background anisotropies and systematic errors.

Area of Science:

  • Cosmology
  • Astrophysics

Background:

  • Current cosmological models rely on precise measurements of key parameters.
  • Understanding the universe's composition and expansion rate is crucial for theoretical physics.

Purpose of the Study:

  • To review the current status of measurements for matter density (Omegam), vacuum energy density (OmegaLambda), Hubble constant (H0), and ages of oldest objects (t0).
  • To identify areas for future improvements in cosmological measurements, particularly focusing on systematic errors.

Main Methods:

  • Review of three independent methods for measuring the Hubble constant: lensed quasar time delays, Sunyaev-Zel'dovich effect, and Cepheid-based distances.
  • Analysis of recent dynamical measurements for matter density.
  • Consideration of systematic errors and underlying assumptions in measurement techniques.

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Main Results:

  • Recent dynamical measurements suggest a low matter density (Omegam ≈ 0.2-0.3).
  • Independent Hubble constant measurements are converging to a range of 60-80 km/sec per megaparsec.
  • Cosmic microwave background anisotropies are highlighted as a key area for future advancements.

Conclusions:

  • The universe's matter density appears to be lower than previously thought.
  • A consensus is emerging for the Hubble constant value, aiding cosmological model refinement.
  • Addressing systematic errors and improving CMB measurements are critical for future cosmological research.