hubble parameter

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hubble parameter

The Hubble parameter helps astronomers measure the expansion of the universe.

Definition
  1. Noun:
    • (Cosmology): The Hubble parameter is the ratio of the speed at which a galaxy is receding from an observer (due to the expansion of the universe) to its distance from that observer. It is a measure of the current expansion rate of the universe. Although often called the Hubble constant, its value can change over cosmic time.
Usage Examples
  • Noun:
    • The precise measurement of the Hubble parameter is a major goal of modern cosmology.
    • Scientists use distant supernovae to calculate the Hubble parameter.
    • A discrepancy in measurements of the Hubble parameter is known as the "Hubble tension."
Advanced Usage
  • "Hubble parameter" vs. "Hubble constant": In strict usage, the Hubble parameter, denoted as H(t), describes the expansion rate as a function of time. The Hubble constant, H₀, specifically refers to the present-day value of the Hubble parameter.
    • While the Hubble parameter changes over the life of the universe, the Hubble constant gives its current value.
Variants and Related Words
  • Hubble constant (H₀) (n): The present-day value of the Hubble parameter.
    • The latest measurements of the Hubble constant suggest the universe is expanding faster than some models predict.
  • Hubble law (n): The observational correlation that a galaxy's recessional velocity is proportional to its distance, with the Hubble parameter as the constant of proportionality.
    • Edwin Hubble's discovery of the Hubble law provided evidence for an expanding universe.
Synonyms
  • Hubble constant (specifically for its present-day value)
  • Expansion rate (of the universe)
Related Terms and Concepts
  • Cosmological redshift (n): The increase in wavelength of light from distant galaxies due to the expansion of space, directly related to recessional velocity.
    • The cosmological redshift of a galaxy is used to determine its recessional velocity for the Hubble parameter calculation.
  • Scale factor (n): A function in cosmology describing how the size of the universe changes with time; the Hubble parameter is defined by the rate of change of the scale factor.
    • The Hubble parameter is mathematically related to the time derivative of the scale factor.
hubble parameter

The Hubble parameter helps astronomers measure the expansion of the universe.

Noun
  1. (cosmology) the ratio of the speed of recession of a galaxy (due to the expansion of the universe) to its distance from the observer; the Hubble constant is not actually a constant, but is regarded as measuring the expansion rate today

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