WMAP year 7: We Know What We're Doing!

About two weeks ago, the WMAP (Wilkinson Microwave Anisotropy Probe) team released their seven-year results, and I'm finally ready to tell you all about it. WMAP, remember, is this guy.

By looking at two different points in the sky simultaneously, and looking at the proper frequencies of microwave light (it looks at five different frequencies every time it looks at the sky), it can measure the differences in the intensity of light left over from the big bangeverywhere in the sky. Why is this so important? Because the Universe is so uniform, and it was even moreso in the past. When we look back at the leftover glow from the Big Bang, this is what we see. (This is the entire sky shown in a Mollweide projection.)

That's right; we find that the Universe is 2.725 Kelvin in temperature everywhere. There's about a 0.003 Kelvin difference in the hottest part of the sky as compared with the coldest part of the sky, and that's it. But these differences can tell us something. So if we subtract out the 2.725 Kelvin average, we're left with temperature differences. What does that look like?

One part of the sky looks slightly hotter than average, and another part looks slightly colderthan average. This is really, really interesting, because the hot part is exactly 180 degrees in the opposite direction from the cold part! This would be exactly what we would see if we were in motion!

What if we subtracted that motion out? Well, for the first time in the high resolution, that's what WMAP allowed us to see. What do these tiny temperature fluctuations look like?

There are spots that are a few hundred-thousandths of a degree warmer (yellow and red), and there are spots that are a few hundred-thousandths cooler (green and blue). These correspond to regions where there's slight less matter and energy (red) and slightly more matter and energy (blue). Why are the denser spots colder? Because your light loses energy when it has to climb out of a gravitational field, making it cooler.

So we've got this incredibly detailed, intricate map of hot and cold spots in the Universe, which tells us how the matter and energy was distributed when the Universe was only 380,000 years old! (This is, by far, the earliest picture of the Universe we've ever taken.) There were no stars, no galaxies, and it's only at this time that we are forming neutral atoms for the first time. So what can we possibly learn from this picture after 7 years? Practically everything, including:

1. The composition of the Universe: about 4.5% normal matter, 22% dark matter, and 73.5% dark energy.
2. They strongly announce that there is no evidence for any deviation from this model.
3. The age of the Universe: about 13.7 billion years.
4. The curvature of the Universe: if there is any, it is less than 1% on the scale of our Universe. (This is like walking outside, looking at 100 miles of land around you, and concluding that the Earth is at least 10,000 miles in size if it's curved.)
5. Dark energy behaves like a cosmological constant. This new measurement tells us that if dark energy deviates from a cosmological constant, it does so by less than 14%, the most stringent constraint ever!
6. For the first time ever, they have directly detected helium atoms formed before the first stars, confirming Big Bang Nucleosynthesis in a brand new way!
7. And finally, simulations of the simplest cosmological models line up almost exactly with what WMAP observes!

There are other mission results that you can find here, but the big conclusion that you can draw from this is that all of the standard cosmology, including dark energy, dark matter, inflation, a flat Universe, and a hot big bang, are confirmed.

This could mean that there will be no new surprises, and that the only major challenges left for the largest endeavors in cosmology are to figure out what dark matter, dark energy, and inflation actually are! (Although, each of those are Nobel-worthy puzzles.) The one thing people were worried about? These big features that appear to be in the Cosmic Microwave Background?

(Affectionately referred to as "Fingers of God" by some, a name that is also used to refer tosomething else in cosmology.) They show up in simulations often enough that we shouldn't be worried that our Universe has them, according to the latest results. Just apply inflation to starts off a hot big bang, and what you should get lines up perfectly consistent with what we see. So get out there and enjoy your Universe!