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."

Comments

courtesy of Wikipedia

[goatasaur]

Baryons

Dark Energy

Dark Matter

Hope this helps you out a little. :)

Re:courtesy of Wikipedia

[jaoswald]

In this case "vacuum" is physicists' name for "empty space," meaning "as empty as possible." On earth, "empty" means "much less matter than in the atmosphere."

When that empty space is surrounded by the earth's atmosphere, the atmosphere presses on the container that encloses the empty space. Open a hole in the container, and the atmosphere rushes in---that's the sucking part. (Indirectly, it is Earth's gravity that creates the pressure, but you could also imagine the Earth is in a big closed box.)

Intergalactic space is presumably much emptier than any vacuum that we can achieve on earth. When the "empty space" in question is simply surrounded by more empty space, there isn't any sucking of matter. (Pressure is practically zero.)

It turns out that space itself can contain energy; that is, "empty" is not the same as "nothing." General relativity predicts that there is energy in the curvature of space, which is roughly equivalent to the energy in Newton's gravitational fields. (Not exactly equivalent for strong fields, however.) Also, quantum mechanically, there is always the possibility of a particle or field being present in the empty space. That possibility provides a "zero-point" energy, even when the matter or fields are not there. If we really knew all the possible particles and fields, we could calculate what this would be. There might be particles and fields that we haven't discovered yet, or other additions to quantum mechanics that we haven't discovered yet, which is why we have to look to astronomers to determine the properties of empty space.

The energy in otherwise empty space is the dark energy. That energy can cause dynamic behavior in the framework of space, causing it to expand and contract.

More information

[Anonymous Coward]

More information can be found at (including a cosmology tutorial):

http://www.astro.ucla.edu/~wright/cosmolog.htm#New s

This press release was mentioned in a post in the previous slashdot story yesterday.

Other links

[riptalon]

Mass media coverage can be found at CNN and the BBC. A list of all the MAP papers can be found here.

Re:huh?

[JoeBuck]

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.

Dark Energy/Dark Matter/Negative Energy

[monk]

Confused by "Dark Energy," "Vacuum Energy," "Dark Matter," and "Exotic Matter?" Here's a great collection of papers. (Mostly from the SNAP project)

Re:huh?

[(void*)]

In astronomy, "baryons" can also include "leptons", simply because leptons are included in the mass that one measures using a galaxy rotation curve.

Re:Expansion rate?

[riptalon]

Mpc = Mega parsecs, i.e. millions of parsecs, where parsec stands for parallax arcsecond and equals about 3.26 light years.

Answers here, dammit.

[Decimal]

Does Dark Energy suck or blow?

Blow... sort of. It acts the opposite of gravity, pushing everything apart.

http://www.lbl.gov/Science-Articles/Archive/dark-e nergy.html

Re:Why is the probe at the L2 point?

[djcinsb]

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!

Re:huh?

[Peter T Ermit]

First, he said baryons, not baryonic matter -- you will never hear any astronomer call a lepton a baryon.

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.

Re:huh?

[efuseekay]

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".