Slashdot Mirror
BOSS: The Universe's Most Precise Measurement
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."'"
Isn't Slashdot supposed to be News For Nerds? Oh wait, it probably doesn't get any more nerdy than this. Good stuff.
It says the universe is precisely 13.75 billion years old, not 13.5 billion years old.
Shoes for Industry. Shoes for the Dead.
The title meant to say "BOSS: The Most Precise Measurement of the Universe". The other way round can mean these measurements are the most precise ever, which isn't even remotely true. For instance, the article says, "BOSS gives that distance to within 1.7 percent", whereas (to pick something out of a hat) the fine-structure constant has been measured to a precision of less than one part in a billion or within less than 0.0000001%.
Maybe a physicist can chime in here--how is the red shift actually measured in an experiment like this? You could of course measure the wavelength of incoming light, but how do you know what the wavelength "should" be? Are there some common spectral lines one can look for?
Also, is there any practical use to this experiment? I'm fine with pure research, but I was curious if maybe some of the techniques find application elsewhere. The article didn't mention any.
Obviously it's saying that no-one in the entire universe has ever measured anything to more than three significant figures.
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.
I'm sure that people who have studied cosmology, both theoretical and observational, in extreme depth, for a period of upwards of 20 years, are going to be devestated that "Proudrooster" and "decora" on Slashdot have shattered their entire field with a few brief sentences. Such a waste of man-hours! I'm sure the two of you will be quick to provide us with alternative models of cosmology and interpret them properly for the layman, causing no ambiguities in those who don't fully comprehend the fruits of your genius.
Seriously, "a headline grab"? This is the ninth data release of a massive project that's been going for more than twenty years since it was first planned in detail, it's been studied by hundreds of extremely well qualified physicists, astronomers and engineers, and is providing data for all of us in the field to use to test models which we construct, from which we extract observable parameters, and test against observation... and you think it's a fucking headline grab? You think it's arrogant? The mind fucking boggles.
Thought this was going to be about a Stones concert tour.
Never mind.
Have gnu, will travel.
Why do we use years as time measurement for events that happen in the universe? Years are an Earth measurement that have no bearing on anything else in the universe.
Personally, I like to view the expansion of the universe as simply a reduction in the Planck length/time relative to C. This would create the perception of a force pushing everything apart (light taking increasingly long, in terms of Planck units, to travel from one point to another). Ultimately, it's just a different perspective on the same thing, but I like it because it doesn't require the conception of some sort of mysterious "dark energy" -- just an explanation of why the Planck length would slowly shift.
And I find that, too, rather simple to envision, in a number of ways. For example, one that I've been thinking about recently is that if you view the universe in terms of information processing, the distance-limited interactions like the strong force decline in frequency as the universe ages. So if there's a fixed "processing power" of the whole universe but a decreasing number of "calculations" per "unit" time, then the number of steps per "unit" time increases, which could be expressed in any number of ways toward the universe's physical constants.
Virgin birth, water into wine; it's like Harry Potter, but it causes genocide and bad folk music.
If the Planck length were changing with respect to c, such that Planck's constant was changing with respect to c, you would be seeing the effects of changes to things like the fine structure constant and Rydberg constant, which would easily be visible spectroscopically over great distances.
If a mod point falls in the forrest, does anyone get karma?
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.
A year with him is like a day... :)