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Space Science

BOSS: The Universe's Most Precise Measurement 128

Cazekiel writes "Observing the primordial sound waves created 30,000 years after the Big Bang, physicists on the Baryon Oscillation Spectroscopic Survey have determined our universe's most precise measurements: 13.5 billion years old. The article detailing the study reports: '"We've made precision measurements of the large-scale structure of the universe five to seven billion years ago — the best measure yet of the size of anything outside the Milky Way," says David Schlegel of the Physics Division at the U.S. Department of Energy's Lawrence Berkeley National Laboratory, BOSS's principal investigator. "We're pushing out to the distances when dark energy turned on, where we can start to do experiments to find out what's causing accelerating expansion."'"
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BOSS: The Universe's Most Precise Measurement

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  • by Ralph Spoilsport ( 673134 ) on Monday April 09, 2012 @06:47PM (#39625189) Journal
    It says the universe is precisely 13.75 billion years old, not 13.5 billion years old.
  • by Anonymous Coward on Monday April 09, 2012 @07:16PM (#39625467)

    No it isn't, you're making a common mistake that people who pretend they know about physics make. Put it this way: leave the physics to the people who know anything about it and go back to masturbating over furry porn.

    Cosmology is based on the Robertson-Walker metric. The Robertson-Walker metric contains an unambiguous time coordinate. Put an observer in that metric and, yes, they will observe a different time -- but if they're not to violate the symmetries of the metric, the differences will be at a perturbative level, which is to say unimportant. When they say "the universe is 13.7bn years old" they don't mean to say "the time measured along every worldline would give 13.7bn years", because to say such would be nonsense. What they mean that "the time measured in a frame comoving with the metric is 13.7bn years and to an approximation good up to redshifts of approximately z=1 and quite possibly significantly less this is an estimate that holds for all observers who haven't gone dallying with black holes".

    Seriously, learn what the fuck you're talking about before you make yourself look stupid.

  • by Anonymous Coward on Tuesday April 10, 2012 @06:44AM (#39628999)

    No it doesn't because if you work with standard cosmology -- and if you've an alternative, please present it at a level of rigour that means people could actually work with it -- that's already ruled out. The universe is constrained to have 5% of the critical density in baryons, otherwise we get entirely the wrong abundances of heavier elements out of the models. So we've got 5% of the critical density in baryons. Excellent, that fazes no-one, we just have a very light, open universe, right? No, to get the clusters to form the way they do, we need another 25% of the critical density in *something*. We don't know what it is, just that it has to cluster, and has to act pressureless -- it's slow moving and doesn't interact with *anything* on a cosmologically appreciable level except through gravity, not with us ("baryons"), not with electromagnetism, nothing. If it's not there, we can't get clusters of galaxies to form right. This happens to tie very neatly in with a separate issue, that of the orbits of stars within galaxies, and of galaxies within clusters. Neither galaxies nor clusters can hold together (assuming standard gravity -- and if you've an alternative, please present it blah blah) without a lot of matter we don't see. Sure, some of that matter will be in "regular" matter that's hard to measure. Neutrinos are an immediate candidate, given that they're both numerous and have a small, but non-vanishing, mass. But neutrinos aren't enough. (Also they're extremely problematic; if you try and make neutrinos 25% of the critical density universe you wash out the clusters as they're forming. Neutrinos simply don't cluster enough to do what we need dark matter to do.)

    So we're lead at least to the conclusion that the universe is at least 30% of the critical density, 25% of which *cannot* be matter that we normally understand. It absolutely cannot be. If we then match up angular scales that we can measure -- such as the angular scale that BOSS measured -- we're lead to the conclusion that the universe is basically at the critical density, but only 30% is in clustering matter. The discrepency is "dark energy", a non-clustering quantity that has a strongly negative pressure. It's inescapable. If you use the standard model, these exist.

    This is based on assuming that general relativity is an accurate theory of gravity, and that we can base cosmology on a particular, highly-symmetric solution. Both of those assumptions can be, and intensively are, queried and tested. But the problem is that changing the model of gravity, for instance, introduces enormous problems. It's extremely hard to change gravity without breaking the solar system, and thus far almost every attempt is driven back to behaving like standard relativity in the presence of a cosmological constant -- and very often at least a certain amount of dark matter is necessary.

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