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First Cosmological Results From MAP
riptalon writes "The Wilkinson Microwave Anisotropy Probe, a NASA Explorer mission has announced the first results based on a year of observations from the L2 Lagrangian point. MAP carries two
back-to-back microwave telescopes to study variations in the cosmic microwave background, to
much greater accuracy than the COBE satellite. The excruciating details of the results
on the age, geometry and composition of the universe can be found in this paper. Executive summary: 13.7 billion years old, flat, 4.4% baryons, 22% dark matter and 73% dark energy."
Baryons
:)
Dark Energy
Dark Matter
Hope this helps you out a little.
~D:
More information can be found at (including a cosmology tutorial):
w s
http://www.astro.ucla.edu/~wright/cosmolog.htm#Ne
This press release was mentioned in a post in the previous slashdot story yesterday.
Mass media coverage can be found at CNN and the BBC. A list of all the MAP papers can be found here.
A baryon is a particle such as a neutron or proton. It's one of the two main classes of ordinary matter particles, the other is the lepton (e.g. an electron or neutrino). Baryons "feel" the strong nuclear force, leptons do not.
Dark matter refers to exotic forms of matter that are "ordinary" from a gravitational point of view, that isn't made up of baryons or leptons. This stuff either interacts weakly with ordinary matter, or doesn't interact at all (other than via gravity).
Dark energy has positive energy but negative pressure, so it causes a gravitational repulsion. Einstein's "cosmological constant" one possible example of dark energy. It can be thought of as a property of space.
The 4.4% baryons are the "normal" matter.
Confused by "Dark Energy," "Vacuum Energy," "Dark Matter," and "Exotic Matter?" Here's a great collection of papers. (Mostly from the SNAP project)
[-- Trust the Monkey --]
I suspect that all of the percentages given have been rounded to two significant figures, and that you folks shouldn't be concluding that 0.4% has been unspecified.
There are contributions to Omega from electrons and neutrinos, for example, but this is a tiny amount compared even to the 4.4% from baryons.
In astronomy, "baryons" can also include "leptons", simply because leptons are included in the mass that one measures using a galaxy rotation curve.
Mpc = Mega parsecs, i.e. millions of parsecs, where parsec stands for parallax arcsecond and equals about 3.26 light years.
Does Dark Energy suck or blow?
e nergy.html
Blow... sort of. It acts the opposite of gravity, pushing everything apart.
http://www.lbl.gov/Science-Articles/Archive/dark-
Remember "Bring 'em on"? *sigh
What does the Mpc stand for?
Megaparsec (a parsec is 3.26 light years, or 3.08*10^16 meters).
Basically, it means that an object 1 megaparsec away from you is moving away by 71km/second (since the whole universe is expanding like a 4-dimensional balloon, all points are moving away from all other points, and this speed increases with their relative distances)
Vacuum cleaners suck. Kings rule.
Time has not been proven to continue into infinity. Go read 'A Brief History of Time' for a good laymens introduction to cosmology.
Space and time are concepts deeply intertwined with energy and matter; they is not distinct from them. Thus, there is no 'before' the universe began, there is no time there, there is no there there either.
But, given this, let me add a little nota bene...
I found this by opening up a window to Google and typing the words +"L2" +"orbit" +"space". For me, it was the first entry returned.
"Give a man a fish and you have fed him for a day, but *teach* a man to fish and you have fed him forever". That is what makes sharing the 'tricks of the trade' so special.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
L2 is nice for several reasons. The instrument on MAP needs to be kept cold. Sitting at L2, the spacecraft can keep the instrument pointing away from the Sun, and still measuring data, without ever needing to worry about interference from the Earth or Moon, and there is this nice big dish (the solar array) shielding the instrumentation from direct sunlight. In addition, NASA has lots of experience with spacecraft at the collinear Lagrange points (L1 and L2), so the orbits and communications are very well understood there. And L2 is far enough away from the Earth-Moon system to avoid complicated orbit perturbations, but close enough for relatively easy communications (that is, the radio doesn't have to be too big).
Hope that helps!
A signature always reveals a man's character - and sometimes even his name. -- Evan Esar
This FAQ may help.
Do you have any idea about how NASA really operates?
NASA's budget and operations are firmly divided into unmanned and manned areas. Almost none of the unmanned science missions are launched by the Shuttle fleet... most are launched on corporate expendable launch vehicles.
Science in NASA is almost totally disengaged from launch vehicle & station planning & operations. This is a problem, not a cure.
Second, technically, even in astronomy, baryonic matter is only the nuclei -- the leptons are counted separately, though they're unimportant masswise, as you mentioned. Here's why.
There are several ways of computing the amount of and types of matter in the universe. One of the most important is examining primordial gas clouds and looking at the relative abundances of hydrogen, helium, and lithium and their various isotopes. This tells us about the era of nucleosynthesis -- the time 3 seconds to 3 minutes after the big bang when the temperature and pressure of the universe was enough to induce nuclear fusion. After 3 minutes, this process ended and froze the ratios of primordial elements.
By looking at those ratios, scientists could figure out the abundance of those nuclei -- the nuclei, not the leptons, which don't affect the ratios at all. From this, they can figure out the density of nuclear matter in the universe, which is related to a quantity known as omega sub b. This number is thought to be about 4.5% from measurements of the elements in those gas clouds -- and MAP confirmed this by a different method. But this baryonic fraction does not have anything to do with the leptonic component of matter... including electrons and neutrinos.
So, when astronomers say that they have shown that 4.4% of the universe is made up of baryonic matter, they really mean baryons. It just so happens that there are pesky leptons hanging around the baryonic matter, too.
Flatness/curvedness refers to whether parallel lines meet and by extension what sum of angles there are in a polygon:
In a flat space (or plane as an example of a 2D space) angles in a triangle sum to 180 degree, always. Parallel lines never meet. This is a falt desk in 2D.
In positively curved space (or plane) internal angles of a triangle sum to >= 180 degrees (sum approaches 180 as size of triangle side lengths approach 0). Parallel lines cross twice. This is the surface of a globe.
In negatively curved space (or plane) internal angles of a triangle sum to <= 180 degrees (again sum approaches 180 as size approaches 0). Parallel lines diverge. This is a saddle.
It's easy to see the way this are if you think of the space as a 2D object since the curvature requires (to visualise) an extra dimension, but the principles are the same in higher dimensionalities
Don't believe the nonsense, unless you hear it from me directly.
nope.
Astronomy/astophysics pays my bills, and I can tell you that 4.4% of baryons from WMAP really means anything that is known in particle physics as quarks, leptons, blah blah blah.
A rule of thumb is that 'baryons' in astronomy/astrophysics is anything that is in the standard model (sans the higgs.)But that's not the whole story.
"baryons" (in the 4.4% of WMAP) is classified as matter that is not "dark". "Non-dark" means it interacts with other stuff and itself beyond just pure gravitation. That includes "radiation", which is stuff that behaves relativistically, and include things like photons, neutrinos,a nd perhaps other relics.
To summarize, there is no difference between "baryons" and "baryonic matter" in astronomy.
I will not call a lepton a baryon, but I will definetely lump leptons in when I say 4.4% of ther universe is made out of baryons. it's just a matter of context, and people in the field will udnerstand that.
Really, astrophysicists are sloppy when it comes to naming stuff. So you have to be careful not to read too much into nomenclature like this, even in the era of "precision cosmology".
Mode (3) smart-aleck mode. Press * to return to main menu.
The further away the object is from us, the greater the velocity it seems to be expanding away from us. So H=71km/s /Mpc means that for every Mpc the objet is away from us, it is flying away from us at the velocity of 71 km/s.
Mode (3) smart-aleck mode. Press * to return to main menu.
A way to visualize what flat (and open & closed) mean is to think of a plot of how two dimensions are shaped at very large distances. That is, if you had some ordinary (flat, straight lines are straight lines) reference and observed the path of a bunch of photons sent of at right angles (only two directions) to form a grid and plot that in 3D. Then if there is no curvature (=flat), you'll get a plot that looks like a sheet of paper or the surface of a desk. If the universe was curved (open or closed) then you'll get a hyperpolic saddle or sphere respectively.
In short, flat means space like we ordinary envision it; it has absolutely nothing to do with the whole universe only expanding in 2 dimensions (like flat earth vs. round) as some of the earlier posters seem to think.
Mathematically, flat is the most unlikely result since even the slightest deviation would translate into one of the other two states. Physically, it means that the universe's geometry is euclidean, that its volume is infinite, and that it expands FOREVER (yes sure, the expansion rate approaches zero, but you know how asymptotes are supposed to work).
Incidentally, it means that we won't be able to eat at Milliway's. Shit.
Imagine the Creator as a stand up commedian - and at once the world becomes explicable. -Mencken
You're correct. What's constant for all observers is the speed of light in a vacuum.
Tom Swiss | the infamous tms | my blog
You cannot wash away blood with blood