sylas
March 7th 2008, 09:26 PM
13.73 billion years, give or take 0.12 billion.
This is the result recently published by the Wilkinson Microwave Anisotropy Probe (WMAP (http://wmap.gsfc.nasa.gov/)) research team. Here is the press release: WMAP Reveals Neutrinos, End of Dark Ages, First Second of Universe (http://www.nasa.gov/topics/universe/features/wmap_five.html).
The WMAP probe has been one of the most exciting in recent cosmological research, and so here is a post to go over the new release, broken into a few sections.
The age is not that important
I used the age of the universe as a kind of hook to get you all in. It will also help keep the thread live, by provoking all kinds of responses focused on age, since this is something that matters to lots of folks. And that's fine, and welcome. Keep it polite please...
But for cosmologists, the age is not really all that significant. Well, it is; but the major issues over age got pretty much resolved a decade or so ago. We've known (as far as one knows anything in science) for some time that the age is around 14 billion years. Getting this more precise is not really interesting in its own right.
If you look at the press release, you'll see that the number I give is not mentioned; though you will find 13.7 mentioned in passing. You have to drill into the papers a bit to find a focus on age with associated error bars.
What is more interesting is:
Evidence for the cosmic neutrino background. This has always been predicted from cosmological models, in much the same way as the microwave background; except that the neutrino background will reflect an epoch from much much earlier in the universe's history. Cosmic neutrinos have very low energy, and will be almost impossible to detect directly. Unfortunately. Being able to measure them would be a fabulous way to look at the very early universe. But at least there has been some indirect evidence of cosmic neutrinos gleaned from effects they had on the microwave background back when the universe was younger and the neutrinos more energetic.
Details about the first stars, and how they in turn produced a thin fog of electrons. This data is able to falsify some of the competing ideas for how the first generation of stars was formed.
Tight constraints on rates of expansion in the very first trillionth of a second or so of the universe. This is really cool for hard core cosmology theoreticians... it puts hard constraints on the models for inflation in particular. Some ideas for inflation are falsified, and others find support. I'm a bit lost myself at this point, I won't attempt to contrast the various alternatives for inflation... there are a lot of them. But inflation does remain an important part of cosmological models, and WMAP data tends to support the idea of inflation in the very early universe.
How can they find an age?
An age like this is model dependent. That is, a particular model of the universe is applied, and observation constraints give you parameters for that model, one of which is age.
The other side of the story, of course, is that the model (the "concordance" model in cosmology) has been exceptionally successful at matching observational data. Nothing else comes close at the moment. However, it is as well to keep in mind that this age would change, possibly quite drastically, if anyone ever managed to match the data with a new model.
The current model is basically one of cold dark matter, and dark energy. The expansion rates of the universe fall out from general relativity, given an energy density. The expansion of the universe over time depends on how energy density develops over time. The concordance model has most of the energy density being associated with empty space (dark energy) and most of the rest being associated with matter. More matter than we can actually see: hence a substantial amount of invisible "dark matter" is required; about four times as much invisible dark matter as there is ordinary visible matter. There is considerable independent evidence for this dark matter as well; indeed it was predicted on the basis of gravitational interactions long before cosmology got around to giving relevant information on the subject.
It may be useful to compare with the measurement of the age of the earth. There are some interesting similarities. I refer those interested to a terrific essay by Richard Harter: Changing views of the history of the Earth (http://home.tiac.net/~cri/1998/geohist.html).
Basically, around the late nineteenth century scientists began to propose crude estimates for the Age of the Earth, based on geological observations and models for how they could have resulted. Note the model dependence here: you have a model for how geological structures arise, models which give a good fit to observations, and then apply the model to get numbers for how long the process took to give the result.
The models were very crude, and unable to give reliable estimates; although some got in the ball park.
At the start of the twentieth century, understanding of radioactivity allowed for models that deal with observations relating to radioactive isotopes, and which had implications for age. From this point, increasing accurate estimates are obtained. Around the 1950s, the measurement of lead isotopes was able to be related to the origin of the Earth and solar system, and ages obtained that were correct, and had a precision of around 7%.
Since then, the precision of results continued to improve, and the underlying models for those results thoroughly tested and confirmed, to the point where the age of the Earth is established with a precision of less than a percent.
This age is model dependent, of course, with the model being the physics of radioactive decay. So there are two aspects to such measurements.
Accuracy. Is the model a good model for processes involved? That is, is the result obtained meaningful as an age. An accurate estimate is one which is correct to within its associated measurement errors.
Precision. How precisely can the model constrain ages? That is, how many significant figures are in the result? A precise estimate is one which has small range of allowed values.
What WMAP has done here is to increase the precision for estimates of the age of the universe; as well as give additional confidence in the accuracy of the result by virtue of the close fit of the model to observations.
It's not that long ago (a couple of decades) when there was a serious conflict over accuracy for ages of the universe. Models for star formation seemed to suggest that some stars were older that the universe, which was impossible and indicated that the models were wrong.
SInce then, the models both for star formation and for development of the universe have been tested and constrained and refined, and this conflict resolved. There is no longer a mismatch between results, and there is good reason to think the models are pretty solid. The implications are as given at the top of this post... the universe is 13.73 billion years old, to an accuracy of about 1%.
More reading.
The scientific papers. (http://lambda.gsfc.nasa.gov/product/map/dr3/map_bibliography.cfm) (Way over my head.)
Ned Wright's News of the Universe (http://www.astro.ucla.edu/~wright/cosmolog.htm#News). Ned is an author on the research papers, and also good at explaining cosmology at level for interested amateurs like myself.
Comment from first rate astronomy blogs: at Cosmic Variance (http://cosmicvariance.com/2008/03/05/wmap-5-year-results-released/), and Bad Astronomy (http://www.badastronomy.com/bablog/2008/03/05/the-universe-is-1373-12-billion-years-old/)
This is the result recently published by the Wilkinson Microwave Anisotropy Probe (WMAP (http://wmap.gsfc.nasa.gov/)) research team. Here is the press release: WMAP Reveals Neutrinos, End of Dark Ages, First Second of Universe (http://www.nasa.gov/topics/universe/features/wmap_five.html).
The WMAP probe has been one of the most exciting in recent cosmological research, and so here is a post to go over the new release, broken into a few sections.
The age is not that important
I used the age of the universe as a kind of hook to get you all in. It will also help keep the thread live, by provoking all kinds of responses focused on age, since this is something that matters to lots of folks. And that's fine, and welcome. Keep it polite please...
But for cosmologists, the age is not really all that significant. Well, it is; but the major issues over age got pretty much resolved a decade or so ago. We've known (as far as one knows anything in science) for some time that the age is around 14 billion years. Getting this more precise is not really interesting in its own right.
If you look at the press release, you'll see that the number I give is not mentioned; though you will find 13.7 mentioned in passing. You have to drill into the papers a bit to find a focus on age with associated error bars.
What is more interesting is:
Evidence for the cosmic neutrino background. This has always been predicted from cosmological models, in much the same way as the microwave background; except that the neutrino background will reflect an epoch from much much earlier in the universe's history. Cosmic neutrinos have very low energy, and will be almost impossible to detect directly. Unfortunately. Being able to measure them would be a fabulous way to look at the very early universe. But at least there has been some indirect evidence of cosmic neutrinos gleaned from effects they had on the microwave background back when the universe was younger and the neutrinos more energetic.
Details about the first stars, and how they in turn produced a thin fog of electrons. This data is able to falsify some of the competing ideas for how the first generation of stars was formed.
Tight constraints on rates of expansion in the very first trillionth of a second or so of the universe. This is really cool for hard core cosmology theoreticians... it puts hard constraints on the models for inflation in particular. Some ideas for inflation are falsified, and others find support. I'm a bit lost myself at this point, I won't attempt to contrast the various alternatives for inflation... there are a lot of them. But inflation does remain an important part of cosmological models, and WMAP data tends to support the idea of inflation in the very early universe.
How can they find an age?
An age like this is model dependent. That is, a particular model of the universe is applied, and observation constraints give you parameters for that model, one of which is age.
The other side of the story, of course, is that the model (the "concordance" model in cosmology) has been exceptionally successful at matching observational data. Nothing else comes close at the moment. However, it is as well to keep in mind that this age would change, possibly quite drastically, if anyone ever managed to match the data with a new model.
The current model is basically one of cold dark matter, and dark energy. The expansion rates of the universe fall out from general relativity, given an energy density. The expansion of the universe over time depends on how energy density develops over time. The concordance model has most of the energy density being associated with empty space (dark energy) and most of the rest being associated with matter. More matter than we can actually see: hence a substantial amount of invisible "dark matter" is required; about four times as much invisible dark matter as there is ordinary visible matter. There is considerable independent evidence for this dark matter as well; indeed it was predicted on the basis of gravitational interactions long before cosmology got around to giving relevant information on the subject.
It may be useful to compare with the measurement of the age of the earth. There are some interesting similarities. I refer those interested to a terrific essay by Richard Harter: Changing views of the history of the Earth (http://home.tiac.net/~cri/1998/geohist.html).
Basically, around the late nineteenth century scientists began to propose crude estimates for the Age of the Earth, based on geological observations and models for how they could have resulted. Note the model dependence here: you have a model for how geological structures arise, models which give a good fit to observations, and then apply the model to get numbers for how long the process took to give the result.
The models were very crude, and unable to give reliable estimates; although some got in the ball park.
At the start of the twentieth century, understanding of radioactivity allowed for models that deal with observations relating to radioactive isotopes, and which had implications for age. From this point, increasing accurate estimates are obtained. Around the 1950s, the measurement of lead isotopes was able to be related to the origin of the Earth and solar system, and ages obtained that were correct, and had a precision of around 7%.
Since then, the precision of results continued to improve, and the underlying models for those results thoroughly tested and confirmed, to the point where the age of the Earth is established with a precision of less than a percent.
This age is model dependent, of course, with the model being the physics of radioactive decay. So there are two aspects to such measurements.
Accuracy. Is the model a good model for processes involved? That is, is the result obtained meaningful as an age. An accurate estimate is one which is correct to within its associated measurement errors.
Precision. How precisely can the model constrain ages? That is, how many significant figures are in the result? A precise estimate is one which has small range of allowed values.
What WMAP has done here is to increase the precision for estimates of the age of the universe; as well as give additional confidence in the accuracy of the result by virtue of the close fit of the model to observations.
It's not that long ago (a couple of decades) when there was a serious conflict over accuracy for ages of the universe. Models for star formation seemed to suggest that some stars were older that the universe, which was impossible and indicated that the models were wrong.
SInce then, the models both for star formation and for development of the universe have been tested and constrained and refined, and this conflict resolved. There is no longer a mismatch between results, and there is good reason to think the models are pretty solid. The implications are as given at the top of this post... the universe is 13.73 billion years old, to an accuracy of about 1%.
More reading.
The scientific papers. (http://lambda.gsfc.nasa.gov/product/map/dr3/map_bibliography.cfm) (Way over my head.)
Ned Wright's News of the Universe (http://www.astro.ucla.edu/~wright/cosmolog.htm#News). Ned is an author on the research papers, and also good at explaining cosmology at level for interested amateurs like myself.
Comment from first rate astronomy blogs: at Cosmic Variance (http://cosmicvariance.com/2008/03/05/wmap-5-year-results-released/), and Bad Astronomy (http://www.badastronomy.com/bablog/2008/03/05/the-universe-is-1373-12-billion-years-old/)