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

huh?

[dirvish]

Anyone care to let us non-space nerds know what baryons, dark matter and dark energy are? TIA.

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.

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:huh?

[adminispheroid]

You missed the part where he said "in astronomy." In astronomy, a lot of wrong things are true. In this case, when astronomers say "baryons" they mean "baryonic matter" i.e. atoms, molecules, ions, etc. which includes the electrons. Of course, in baryonic matter the electrons make up something like 0.02% of the mass, so it's hardly worth quibbling about.

Re:huh?

[Captain Nitpick]

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

Nope. Baryons are the heavy particles made up of three quarks. Leptons are light particles that are themselves fundamental particles. In between are mesons, made of a quark and antiquark.

You've got to remember that the terminology astronomers use is a bit...different. This is much like how they call anything heavier than helium a "metal".

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".

Why do they call it "Dark Energy"?

[lingqi]

Really, now. That just makes the universe sounds sinister. I can just imagine Vader argue with Yoda in Ep.III (cutting out the huffing) "Ahh you see master yoda, the universe is mostly the dark side." Can't they go for a policitally correct / socially sensitive / thoughtful of the children phrase like "cannot-see energy" or "we have no fscking clue where it is energy"?

otoh, iirc the original background radiation measurements were done using a U2 (not the band, though it would be interesting) flying at some 70k ft, something about only a U2 can fly that steady (without resorting to satelites, anyway).

Re:Why do they call it "Dark Energy"?

[theCat]

[darkhumor style=kurtvonnegut]
It turns out some researchers called it God at first but that doesn't look as well in print outside of sacred texts. You know, "God is everywhere, but unevenly distributed and is repulsive, not that anyone would notice or at least they have not. Only we did notice so we're L337 and we're forming our own religion. We hereby declare all other religions apostate and anathema on the strength of our observations."

We pagans know all about Dark Energy. Heck, we're obsessed with it. Only I'm a little surprised that it's not more than 75% of the known universe. I bet a lot of the Cold dark Matter will turn out to be wanna-be Dark Energy too, just tettering on the edge of going over for the last few billion years.

The idea that only 4% of the Universe is "normal" really lines up with the notion many witches and Zen masters subscribe to, where 96% of Everything is utter nonsense. But you can still have loads of fun with the other 4% if you lay your hands on a good spell book. Just don't forget to close your sacred circle, and properly call the gates, and sanctify your athame first. Bless us but you don't want to upset the balance of entropy and cause any of that loitering Cold Dark Matter to get any fancy ideas.
[/darkhumor]

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.

Re:courtesy of Wikipedia

[WatertonMan]

What is funny is that "dark energy" is also termed "quintessence" or the fifth element. Quintessence was an other term for aether which, as you might recall, was the nebulous stuff in the cosmos prior to modern physics. Funny how things we thought we disproved pop back unexpectedly.

Of course aether was primarily brought up by Maxwell to explain certain phenomena. It was disproved by the "fact" that the speed of light was a constant in all inertial frames.

What's interesting is that there is a movement to suggest that perhaps, just perhaps, the speed of light wasn't a constant after all. While I rather doubt that, New Scientist has an interesting interview with the main proponent of that theory, Joao Magueijo. Interview with Joao Magueijo

He has a book partially about this coming out this month called Faster than the Speed of Light

I rather doubt Einstein is wrong on this matter, although some of Magueijo's criticisms of superstring theory are often made. Still quite a few people are discussing the issue. Landau, for instance, has a recent paper on the topic. "Charge Conservation and Time-Varying Speed of Light.

To tie all this together, here's an interesting paper that ties some of this all together, including "dark energy." "Perfect Fluid Cosmology with Varying Light Speed."

correction

[zaqattack911]

13.7 billion years old, flat, 4.4% baryons,
95% We don't know.

Re:correction

[Greedo]

13.7 billion years old, flat, 4.4% baryons ...

... and may contain traces of peanuts.

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.

In this universe...

[MrByte420]

You only get 73% of you daily dose of dark matter. That would leave eating bowl after bowl after bowl. Try my new "Extra Dark Total Universe" and get 100% of your Dark Matter in just one bowl!

Isn't this

[Timesprout]

4.4% baryons, 22% dark matter and 73% dark energy.

The recipe for coke ?

Sounds Familiar

[The_Rippa]

13.7 billion years old, flat, 4.4% baryons, 22% dark matter and 73% dark energy

Except for the age part, that sounds a lot like my ex-girlfriend.

Happy Valentines Day everybody!

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)

Cheap Science vs. Expensive Pork

[Tackhead]

From the launch press release

"MAP, an Explorer mission, cost about $145 million."

If I understand correctly...

Measuring the age of universe, calculating initial proportions of baryonic matter vs. energy, and deriving shape of universe: $145M.

Shuttle flight to install ISS module: $500M.

Shuttle flight to watch ants float in zero-G: 7 deaths, $500M for launch, $2.0B for new shuttle.

Your Congressional District's seat at the trough of Shuttle/ISS pork: "Priceless."

Now that I've bashed, some constructive criticism - cut NASA in half.

One half - NAA - I'll call the National Aeronautics Administration. Its job will be pure Aeronautics. Launch vehicles. Rockets. Engines. From pricy Shuttles to half-decent Shuttle-C heavy-lift modifications, to cheap expendables, to funky crewed vehicles like X-33, VentureStar, or DC-X.

The other half - N(whoops!) let's call it the NSSA - National Space Science Administration - will do science. Build probes. Stick 'em on rockets built by the NAA, or LockMart, Boeing, or Armadillo, and do some frickin' science.

Under such a scenario, we could have avoided the Shuttle/ISS debacle completely; NAA might have had concerns about losing funding once the last Shuttle was built, and probably would have had a significant incentive to keep asking Congress for funding to build newer, better, cheaper-per-pound launch vehicles.

Why? Because they'd be under competitive pressure from every other contractor under the sun building launch vehicles to launch NSSA's space probes. Perhaps NSSA would have come to the same mistake NASA did - and decided that we Really Needed a Space Station - but even if that were the case, the design requirements of ISS would have immediately mandated a heavy lift vehicle, wholly unlike the Shuttle.

In such a scenario, NSSA would have had the choice between building ISS with three FooCorp Big Dumb Booster flights, or 30-40 NAA Shuttle flights.

Unlike the current NASA monolith, in which both halves exist to feed each other, a separate NSSA would have been loathe to spend its hard-begged budgetbucks to use another government department's (i.e. "NAA's") Shuttle, particularly in the face of cheaper alternatives. (And likewise, NAA, seeing that it had no Shuttle customers, would have been forced to spend its hard-begged budgetbucks building the Shuttle's successor, or find itself on the Congressional chopping block.)

Re: What's the remaining 0.6%

[Black Parrot]

> Subject says it all.

Apparently the universe is 0.6% rounding error.

Yeah, and their satellite is better too...

[TWX_the_Linux_Zealot]

"MAP ... to study variations in the cosmic microwave background, to much greater accuracy than the COBE satellite"

And their web page is better too. My satellite can beat up your satellite!

So...

[CrazyDuke]

I would interpret this to mean the following:
(no profit recycling please)

1. 4.4 of the energy is stored in atomic nucleuses and some exotic particles.
2. 22% is stored in matter we can't directly observe, but can observe its effects on surrounding objects.
3. 0.6% is electrons and other small mass particles, measurable energy, etc.

Guess: Up to 73% of the original mechanical energy of the big bang is still in the form of mechanical energy (kenetic energy + potential energy).
Guess#2: Or 73% of the original ME of the big bang has been lost to entropy.

Aside Question: Given 2 objects of the same mass and potential energy at rest. Raise one of the objects to a higher potential. Does that not raise its mass relative to the first since the mass is its total energy/c^2? I remember NASA was puzzled by the Voyager probes not making it as far out as they expected them to be by now. Perhaps because they gained mass relative to us? Also, if 2 objects accelarate relative to each other and thier KE increases (relitively), does that not increase the mass, and their for the attraction between the two objects?

Bah, time to RTFA.

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.

Why is the probe at the L2 point?

[Ponderoid]

Can anyone tell me what's so special about the Sun-Earth L2 point that made it attractive to put the probe there? I couldn't find any reference on that site about why that spot was chosen.

At first I thought that it might need permanent shade from the sun, but I checked and found that the Earth's umbra doesn't extend that far out.

Unlike L4 or L5, the L2 position is a meta-stable point, requiring frequent correction to remain in place. There had to be a very good reason to choose it. The site has quite a bit of info about what exactly that spot is (nothing I didn't know already) and how the probe got there, but not a word why.

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:This "science" is FILTH

[theCat]

In Other News:

God, having recently been photographed in the microwave part of the spectrum, has held a press conference. Her spokesangel says "The Almighty resents this intrusion on Her privacy and just wishes some respite from the snapping of paparazzi hounding Her all day and night, never a moment's peace. She will now retire to a private part of the universe for some escape from the tabloids, thank you. But really, She is most upset about those faked pictures of Her wearing a beard. Have you no decency at all?"

God was last seen as a filmy blotch, one millionth of a degree warmer than the next blotch, in the general vicinity of the constellation Sagittarius. She was wearing a floral kimono and sandals from Gucci.

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

Good agreement with COBE

[Dr. Mu]

When I first saw the COBE map awhile back, a little part of me said, "Well, that's nice, but such subtle data from a single platform isn't much to go on." But now, the new image certainly does seem to correlate well with it. The similarities are graphically obvious, and the fact that those data were obtained independently from COBE's is what makes this announcement most significant.