Lower limit on the age of the universe
m (→See also) |
(→Globular Clusters) |
||
| Line 11: | Line 11: | ||
The oldest observable globular clusters contain stars of 0.7 solar masses or less, which places them between 11 and 18 billion years old. Uncertainties in distances prevent more precision.<ref name=WMAP>[http://map.gsfc.nasa.gov/m_uni/uni_101age.html WMAP Cosmology]</ref> Taking the lower estimate of 11 billion years for the age of these clusters, the universe must be even older than that, since it took time for the cluster to form in the first place. Taking the cluster formation time into account pushes the lower limit for the age of the universe based on the age of globular clusters to 12 or 13 billion years. Even if we hedge on that estimate, we can be confident that according to scientific evidence, the universe has existed for more than 10 billion years. | The oldest observable globular clusters contain stars of 0.7 solar masses or less, which places them between 11 and 18 billion years old. Uncertainties in distances prevent more precision.<ref name=WMAP>[http://map.gsfc.nasa.gov/m_uni/uni_101age.html WMAP Cosmology]</ref> Taking the lower estimate of 11 billion years for the age of these clusters, the universe must be even older than that, since it took time for the cluster to form in the first place. Taking the cluster formation time into account pushes the lower limit for the age of the universe based on the age of globular clusters to 12 or 13 billion years. Even if we hedge on that estimate, we can be confident that according to scientific evidence, the universe has existed for more than 10 billion years. | ||
| + | |||
| + | This is roughly 100,000 times older than the young earth creationist assertion, which is a rather large magnitude of error. | ||
==References== | ==References== | ||
Revision as of 23:42, 22 October 2007
A lower limit on the age of the universe is a value representing the minimum age for the universe. Lower bounds usually take the form of "Because we observe X, the universe must be at least Y years old". Astronomers, astrophysicists, and cosmologists have several tools to estimate the age of the universe.
Young earth creationists assert that the universe is 6,000 to 10,000 years old.
Globular Clusters
Logically, stars can't be any older than the universe that they occupy. Finding the age of the oldest stars or groupings of stars is thus one way to determine a minimum age for the universe. Old stars can be found in globular clusters--groupings of a few hundred thousand to one million stars or so.
Fortunately, the lifetime of a star is related to its mass. Massive stars burn out quickly; those that are 10 times more massive than the sun burn out in 20 million years. Stars half as massive as the sun can last 20 billion years.
If we assume that the stars in a given globular cluster formed at roughly the same time, and that there was a reasonable distribution of massive and non-massive stars in the cluster initially (reasonable assumptions, based on what is known about star formation), then we can get an estimate of its age by examining the stars it contains. We can estimate star masses by evaluating their luminosities and distances from Earth. If we observe no stars more massive than ten solar masses, indicating that all of those big stars burned all of their fuel and became something else, then the cluster must be at least 20 million years old. If we saw clusters containing only stars half as massive as the sun or less, then the cluster would have to be at least 20 billion years old.[1]
The oldest observable globular clusters contain stars of 0.7 solar masses or less, which places them between 11 and 18 billion years old. Uncertainties in distances prevent more precision.[1] Taking the lower estimate of 11 billion years for the age of these clusters, the universe must be even older than that, since it took time for the cluster to form in the first place. Taking the cluster formation time into account pushes the lower limit for the age of the universe based on the age of globular clusters to 12 or 13 billion years. Even if we hedge on that estimate, we can be confident that according to scientific evidence, the universe has existed for more than 10 billion years.
This is roughly 100,000 times older than the young earth creationist assertion, which is a rather large magnitude of error.
References