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This article is about scientific estimates of the age of the universe.
The age of the universe is defined inphysical cosmology as the time elapsed since the Big Bang. The best estimate of the age of the universe, as of 22 March 2013, is 13.798 ± 0.037 billion years (4.351 ± 0.017 × 1017 seconds) within the Lambda-CDM concordance model. The uncertainty of 37 million years has been obtained by the agreement of a number of scientific research projects, such as microwave background radiation measurements by the Planck satellite, the Wilkinson Microwave Anisotropy Probe and other probes. Measurements of the cosmic background radiation give the cooling timeof the universe since the Big Bang, and measurements of the expansion rate of the universe can be used to calculate its approximate age by extrapolating backwards in time.
The inverse of the Hubble constant H has the units of time because the Hubble law is
v = H d
where v is the velocity of recession, H is the Hubble constant, and d is the distance. Thus, from this equation, we have that 1/H = d/v. but d/v is distance divided by velocity, which is time (e.g., if I travel 180 miles at 60 miles/hour, the time required is t = d/v = 180/60 = 3 hours).
Thus, the Hubble time T is just the inverse of the Hubble Constant:
T = 1 / H
Taking a value of H = 20 km/s/Mly (where Mly means mega-light years),
where all the factors are necessary to convert the time units to years and I've rounded some numbers to simplify the display.
The physical interpretation of the Hubble time is that it gives the time for the Universe to run backwards to the Big Bang if the expansion rate (the Hubble "constant") were constant. Thus, it is a measure of the age of the Universe. The Hubble "constant" actually isn't constant, so the Hubble time is really only a rough estimate of the age of the Universe.
Reasonable assumptions for the value of the Hubble constant and the geometry of the Universe typically yield ages of 10-20 billion years for the age of the Universe. For example, H near 50 km/s/Mpc gives a larger value for the age of the Universe (around 16 thousand million years), while a larger value of 80 km/s/Mpc gives a lower value for the age (around 10 thousand million years). Therefore, we shall take this information, and additional information from other methods to estimate the age of the Universe that we have not discussed, to indicate an age of approximately 15 billion years for the Universe.
April 24, 2002 — The Hubble Space Telescope has read the embers of burnt-out stars to come up with a new way of estimating the universe’s age, scientists said Wednesday. The latest age estimate — 13 billion to 14 billion years — is consistent with the conclusions reached using other methods.
Past observations of faraway celestial objects known as Cepheid variable stars have yielded estimates of 12 billion to 15 billion years for the universe’s age. But those observations depended on assumptions related to how the universe has expanded over those billions of years.
Another method, used by the European Southern Observatory, depended on estimating the rate of radioactive decay within old stars. The European researchers came up with a figure of more than 12.5 billion years.
University of Chicago astrophysicist Michael Turner, commenting on the latest research, said that further studies were essential because the question of the universe’s age is so fundamental to our understanding of the cosmos.
“What’s exciting is, we’re now making enough measurements that we can do these critical tests for age consistency,” he toldMSNBC.com ."