astronomical constant Comparison Table

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astronomical constant comparison table

Subject has location has material has desintegration energy has volume has frequency has temperature has quantum behavior has velocity has wavelength has number of quark is an instance of has spin has momentum obey has unit has extent has mass has decay product has definition has charge has value has rate of change has lifetime has symbol has angular momentum

cosmological constant astronomical constant A parameter that determines the strength of the cosmological term in the equations of general relativity. This term was added by Einstein because he thought the universe was static, and the term provided a repulsive gravitational force that was needed to prevent the universe from collapsing under the force of ordinary gravity. The false vacuum of inflationary models creates a similar repulsive gravitational force, except that it prevails for only a brief period in the early universe. The cosmological constant is often assumed to be zero, but it might make a significant contribution to the evolution equations of our universe.

deceleration parameter astronomical constant A parameter (that denotes the rate of change with time of the Hubble constant. q₀

Hubble constant astronomical constant km/s/Mpc The rate of expansion of the universe. The Hubble constant is equal to the recessional speed of a distant galaxy, divided by its distance from us. Assuming a homogeneous and isotropic universe, the recessional speed of a distant galaxy is proportional to its distance; thus the Hubble constant as determined by any receding galaxy should be the same, yielding a universal rate of expansion of the universe. According to estimates, the current value of the Hubble constant is approximately 100 km/s/Mpc, meaning that the distance between any two distant galaxies will double in about 10 billion years at the current rate of expansion. 75 km/s/Mpc non-zero because gravity is slowing down the rate of expansion of the universe H₀

Hubble radius radius length unit The radius of the observable universe (). > 10²⁷ cm c/H

Hubble time time time unit The inverse of the Hubble constant and a crude measure of the universe's age. For a Hubble constant of 50, one can calculate that the Hubble time is 19.6 billion years; for a Hubble constant of 80, the Hubble time is 12.2 billion years. If there is no cosmological constant, the universe is younger than the Hubble time. In particular, if the mass density of the universe (designated Ω) is 0.1, the universe's age is 90 percent of the Hubble time; if Ω is 1.0, the universe's age is 67 percent of the Hubble time. 10 to 20 billion years H₀^-1

omega or center of gravity the total energy produced when the particle decays inversely proportional to the wavelength Fermi-Dirac statistics inversely proportional to its momentum 3 astronomical constant 1/2 or 3/2 uncertainty principle the products produced immediately after decay The ratio of the average density of mass in the universe to the critical mass density, the latter being the density of mass needed to eventually halt the outward expansion of the universe. In an open universe, omega is always less than 1; in a closed universe, it is always greater than 1; in a flat universe it is always exactly equal to 1. Unless omega is exactly equal to 1, it changes in time, constantly decreasing in an open universe and constantly increasing in a closed universe. Omega has been measured to be about 0.1, although such measurements are difficult and uncertain. (See critical mass density; closed universe; flat universe; open universe.) 10^-8 to 10^-10 seconds

Next constant: fundamental physical constant Up: constant Previous constant: unit prefix

Subject	has location	has material	has desintegration energy	has volume	has frequency	has temperature	has quantum behavior	has velocity	has wavelength	has number of quark	is an instance of	has spin	has momentum	obey	has unit	has extent	has mass	has decay product	has definition	has charge	has value	has rate of change	has lifetime	has symbol	has angular momentum
cosmological constant											astronomical constant								A parameter that determines the strength of the cosmological term in the equations of general relativity. This term was added by Einstein because he thought the universe was static, and the term provided a repulsive gravitational force that was needed to prevent the universe from collapsing under the force of ordinary gravity. The false vacuum of inflationary models creates a similar repulsive gravitational force, except that it prevails for only a brief period in the early universe. The cosmological constant is often assumed to be zero, but it might make a significant contribution to the evolution equations of our universe.
deceleration parameter											astronomical constant								A parameter (that denotes the rate of change with time of the Hubble constant.					q₀
Hubble constant											astronomical constant				km/s/Mpc				The rate of expansion of the universe. The Hubble constant is equal to the recessional speed of a distant galaxy, divided by its distance from us. Assuming a homogeneous and isotropic universe, the recessional speed of a distant galaxy is proportional to its distance; thus the Hubble constant as determined by any receding galaxy should be the same, yielding a universal rate of expansion of the universe. According to estimates, the current value of the Hubble constant is approximately 100 km/s/Mpc, meaning that the distance between any two distant galaxies will double in about 10 billion years at the current rate of expansion.		75 km/s/Mpc	non-zero because gravity is slowing down the rate of expansion of the universe		H₀
Hubble radius											radius				length unit				The radius of the observable universe ().		> 10²⁷ cm			c/H
Hubble time											time				time unit				The inverse of the Hubble constant and a crude measure of the universe's age. For a Hubble constant of 50, one can calculate that the Hubble time is 19.6 billion years; for a Hubble constant of 80, the Hubble time is 12.2 billion years. If there is no cosmological constant, the universe is younger than the Hubble time. In particular, if the mass density of the universe (designated Ω) is 0.1, the universe's age is 90 percent of the Hubble time; if Ω is 1.0, the universe's age is 67 percent of the Hubble time.		10 to 20 billion years			H₀^-1
omega	or center of gravity		the total energy produced when the particle decays		inversely proportional to the wavelength		Fermi-Dirac statistics		inversely proportional to its momentum	3	astronomical constant	1/2 or 3/2		uncertainty principle				the products produced immediately after decay	The ratio of the average density of mass in the universe to the critical mass density, the latter being the density of mass needed to eventually halt the outward expansion of the universe. In an open universe, omega is always less than 1; in a closed universe, it is always greater than 1; in a flat universe it is always exactly equal to 1. Unless omega is exactly equal to 1, it changes in time, constantly decreasing in an open universe and constantly increasing in a closed universe. Omega has been measured to be about 0.1, although such measurements are difficult and uncertain. (See critical mass density; closed universe; flat universe; open universe.)				10^-8 to 10^-10 seconds