deceleration parameter

A Dictionary of Astronomy | 1997 | 546 words | Copyright

deceleration parameter (symbol q) A figure that describes the slowing-down of the expansion of the Universe. In a Friedmann universe, the deceleration parameter is simply half the density parameter, Ω A value of q greater than 0.5 indicates that the expansion is decelerating quickly enough for the Universe eventually to collapse. A value less than 0.5 indicates that the expansion will continue for ever. In models with a cosmological constant, q can even be negative, indicating an accelerated expansion, as in the inflationary universe.

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