Gourt Home::Gourt :: Age of the universe
The age of the Universe (currently accepted to be 13.7 billion years), according to the Big Bang theory, is defined as the largest possible value of proper time integrated along a timelike curve from the Earth at the present epoch back to the "Big Bang". The time that has elapsed on a hypothetical clock which has existed since the Big Bang and is now here on Earth will depend on the motion of the clock. According to the preceding definition, the age of the universe is just the largest possible value of time having elapsed on such a clock.
Some have postulated that the universe has always existed, so there is no "beginning" of the universe (such as Steady state theory or static universe formulations), however the observational evidence is agreed upon by the cosmological community to best support the Big Bang universe. Below is a discussion of the age of the universe according to this theory.
Age based on WMAP
NASA's Wilkinson Microwave Anisotropy Probe (WMAP) project estimates the age of the universe to be:
- (13.7 ± 0.2) × 109 years.
That is, the universe is about 13.7 billion years old, with an uncertainty of 200 million years. However, this age is based on the assumption that the project's underlying model is correct; other methods of estimating the age of the universe could give different ages.
This measurement is made by using the location of the first acoustic peak in the microwave background power spectrum to determine the size of the decoupling surface (size of universe at the time of recombination). The light travel time to this surface (depending on the geometry used) yields a pretty good age for the universe. Assuming the validity of the models used to determine this age, the residual accuracy yields a margin of error near one percent.
This is the value currently most quoted by astronomers.
Age based on CNO cycle
Some recent studies found the carbon-nitrogen-oxygen cycle to be two times slower than previously believed, leading to the conclusion that the Universe could be billions of years older than previous estimates (via the CNO cycle). Bottleneck of CNO burning and the age of Globular Clusters [http://www.springerlink.com/(bwhdw255vct2bwqv1rmyjs2d)/app/home/contribution.asp?referrer=parent&backto=issue,2,3;journal,14,40;linkingpublicationresults,1:100506,1 Evolution of Population II Stars
Age of the Universe in terms of Planck units
In physics, the process of dimensional analysis serves to qualify physical problems on a conceptual level without a strict emphasis on mathematical formalism. This is an especially helpful tool for analyzing the age of the Universe when using Planck units, whereby the age of the universe can be related to the temperature. In a Planck unit analysis, the age is related to the inverse square of the temperature of the Universe. Dividing the current temperature of the Universe by the Planck temperature yields the ratio: 6 × 10-31. Its inverse square yields 2.72 × 1060, which is the age of the Universe expressed in Planck units. Multiplying by the Planck time converts from Planck units to real time and yields the approximate age of the Universe: 11.667 Gyr (the actual age of the Universe as measured by WMAP is 13.7 Gyr (+/- 2%)). Such a result is often called an order of magnitude calculation, or rather a "back-of-the-envelope" calculation. There are many other unit relations like this one, including the relationship between the critical density and the Planck temperature.
Assumption of strong priors
Calculating the age of the universe is only accurate if the assumptions built into the models being used are also accurate. This is referred to as strong priors and essentially involves stripping the potential errors in other parts of the model to render the accuracy of actual observational data directly into the concluded result. Although this is not a totally invalid procedure in certain contexts, it should be noted that the caveat, "based on the fact we have assumed the underlying model we used is correct", then the age given is thus accurate to the specified error (since this error represents the error in the instrument used to gather the raw data input into the model).
The age of the universe based on the "best fit" to WMAP data "only" is 13.4±0.3 Gyr (the slightly higher number of 13.7 includes some other data mixed in). This number represents the first accurate "direct" measurement of the age of the universe (other methods typically involve Hubble's law and age of the oldest stars in globular clusters, etc). It is possible to use different methods for determining the same parameter (in this case – the age of the universe) and arrive at different answers with no overlap in the "errors". To best avoid the problem, it is common to show two sets of uncertainties; one related to the actual measurement and the other related to the systematic errors of the model being used.
An important component to the analysis of data used to determine the age of the universe (e.g. from WMAP) therefore is to use a Bayesian Statistical analysis, which normalizes the results based upon the priors (i.e. the model).WMAP Year-One Results (including Bayesian Analysis) This quantifies any uncertainty in the accuracy of a measurement due to a particular model used.Bayesian Statistics in Astrophysics Bayesian Constraints On Cosmological Parameters
Related Links
Ancient estimates of the age of the Universe - Hindu cosmology, Abrahamic Religious view
References
- Peer-reviewed Astrophysical Journal article on WMAP Mission, Data, Sensitivity, and Drawbacks
- Peer-reviewed Nature Journal Article on model- and measurement-based age conflicts
- Peer-reviewed Astrophysical Journal article on metallicity-age relation for the Universe
- Ned Wright's Cosmology Tutorial Accessed 12/13/2005
- Edward L. Wright, Age of the Universe 2 Jul 2005 Accessed 12/13/2005
"Age of the universe"