Friar Bellows

We are in the era of high-precision cosmology! Yesterday (Feb 11), the first year's worth of data from WMAP, the Wilkinson Microwave Anisotropy Probe, were released. WMAP was designed to determine the shape, content and evolution of the universe by measuring the anisotropy of the cosmic microwave background radiation (CMBR). WMAP was launched on June 30, 2001, and sent to the L2 Lagrange point, about 1.5 million km away from the Earth, in the anti-Sun direction. Read about it here in this press release:

New Image of Infant Universe Reveals Era of First Stars, Age of Cosmos, and More

Just a brief summary of results:

* Age of universe is 13.7 billion years (only 1% margin of error, or 200 million years)
* Universe is flat, no curvature
* First stars started forming just 200 million years after Big Bang.
* Universe made up of 73% dark energy, 23% unknown dark matter, 4% ordinary matter.
* Inflation theory well supported
* Hubble's constant further refined to 71+/-4 km/s/Mpc

Here's a small image showing two maps of the CMBR, firstly from COBE data (top map) and secondly from WMAP data (bottom map):



COBE was an earlier instrument, I think it was the first space-based instrument to probe the CMBR. WMAP has 45 times the sensitivity and 33 times the angular resolution of COBE.

Here's a link to a technical paper summarising the recent results:

First Year WMAP Observations: Preliminary Maps and Basic Results

Paul2

I breifly skimmed the report, and well, i wish i had half a clue as to what all that stuff means. No wonder some people still doubt "science" as i'm basically taking their word for it when i read their conclusion/summary. Only cause im ignorant though.

Shadowy Man

There are 14 papers that have recently been submitted to The Astrophysical Journal based on the first year of MAP. You can download PDF versions of each of those papers at the following website:

http://lambda.gsfc.nasa.gov/product/...liography.html

Jayjay

I'm also quite clueless when it comes to science, so perhaps someone could enlighten me in layman terms what the results actually mean...
Does this mean that the "4d balloon" metaphor of the expansion of the universe is inaccurate, and we're instead living on a "disc"?

What exactly does the inflation theory predict, that is evident in the new measurements?

muon

"Flat" here means that two parallel lines will never meet. So it's sort of like the difference between a plane and a sphere. (If you draw two parallel lines on the surface of the Earth, perpendicular to the equator, they meet at the poles.)

Inflation predicts that the universe should be almost perfectly flat, and that the fluctuations in the temperature of the microwave background should have a "Gaussian" distribution. See the paper on the NASA website for more discussion.

Other than inflation, there's no really good explanation for why the universe should be so flat. A flat universe has a matter/energy density of 1.0, relative to the critical density needed to close the universe. The WMAP result is 1.02 +- 0.02.

Shadowy Man

Well, further, "flat" means not saddle-shaped either - in the saddle shaped geometry, two parallel lines never meet either.

Feather

How about this, then: "flat" means two lines parallel at a given point neither converge toward nor diverge from any point?

Shake

So how does this discovery, Universe being flat, affect GR-predicted lensing effects of massive bodies? Does this mean that gravitationally large objects actually are bending lightwaves? I ask this because I remember that earlier postulations were that light always follows a 'straight line' and so if it appears to 'bend' that's because spacetime is curved. I like to think of the model of the sheet with metal balls representing things like planets or stars (even galaxies). The sheet has a grid, and so lines near large objects appear to curve around them. So, basically what I'm asking is, do we simply need to think of light as being able to be deflected and that there is no curvature to the Universe?

Shadowy Man

Yes, large clusters of galaxies do bend light. Check out this picture from Hubble's Advanced Camera for Surveys .

However, that bending is local, not global. What the MAP results say about the "flat" universe is the global curvature of spacetime.

Think of your sheet analogy, with the lines curved near massive objects, but a large grid going off to infinity. Curvature of the universe refers to what that grid looks like on a universal scale. For example, if the universe were "closed" the grid would look like longitude and latitude lines on the Earth. If the universe were "hyperbolic" or "saddle-shaped" then there would be negative curvature and the grid lines would actually move away from each other at large distances. With a flat universe, the grid is uniformly spaced over all space (with the caveat that near concentrations of matter like galaxy clusters, etc. it can be curved).

Does this make sense?

Demosthenes

The reason that the discovery that that the universe is indeed flat supports the inflatation theory is because the theory predicts that the universe underwent a period of rapid expansion, even exceeding the speed of light early in the cosmic history. Originally the universe had a significant curvature but the extremely rapid inflation "diluted" the curvature to the point of near flatness. A flatness of the universe is rather highly unlikely in terms of all the possibilites so the inflation theory gives a good explanation to why the universe is flat. From what I understand, the universe isn't flat in the sense that it's like a disco or something but in the sense that the sphere is so large that even from the distances of 13 billion years, the spacetime looks flat to us. I suppose if we were to generalize to even larger distances, possibly on the scale of trillions of light years we'd start to see some curvature in the spacetime but as it is now, it's not significant enough to influence the overall future evolution of the spacetime.

Though I'm also curious about the latest reports on the apparent acceleration of the spacetime expansion.