Saturday, December 29, 2012

Echos of the Big Bang

I mentioned previously that Antarctica is a great place for us to do our science.  But is it really worth being away from family for more than a month over the holidays?  Maybe not, but the science we're up to is pretty cool.  Here's a cartoon of the early universe to give you a sense of what inspires us:
Early universe cartoon, by Wayne Hu
 Kinda looks like a lava-lamp, right?  If you don't find that mesmerizing, then feel free to skip this post.  For anyone else, the cartoon has three steps, labeled in the corner:
  1.  "Oscillations": The Big Bang triggered echos, and those sound waves are the flashing vertical red and blue stripes.  The red stripes are hot and the blue ones a cold.  Those yellow dots are electrons and protons- the universe was too hot then for atoms to exist.
  2. "Recombination": About 300,000 years after the Big Bang, the universe did cool enough for atoms to form.  Before that, the yellow dots scattered light rapidly, as depicted in the zig-zag yellow lines, making the universe look like a glowing thick fog.  This was going on since the Big Bang, but for simplicity, this cartoon only shows that scattering around the time that the atoms were forming.
  3. "Streaming": After the atoms formed, light stopped scattering and essentially traveled in a strait line.  Each of those points emit light in all directions, but again, for simplicity, the cartoon only shows the rays that head towards an observer at the center of the figure.  That expanding doghnut shows what the sky looks like to that observer.  As time goes on, they can see more of the universe and it has hot and cool spots across they visible edge.

One final simplification: the cartoon only shows one sound wave from the Big Bang.  In actuality, there many different waves traveling in different directions (not just left to right) and with different spacings between stripes (or wavelengths, as we say).  All those waves create a series of spots that ultimately look like this to our telescope (1 week of data in Keck Array):
Map from Keck Array

This is a baby photo of the universe, with temperature shown in false color,  If the universe were your 80 year old grandfather, then this photo would have been from within 24 hours of birth.  Those random spots eventually pulled more and more matter into them and formed galaxies, stars, planets, and us.

You may be wondering now: "You skipped Christmas to look at random spots in the sky?…  at radio frequencies???"  Here's the catch: they're not quite random.  Some sizes of spots are brighter than others.  Here's a plot from South Pole Telescope showing the average brightness of a spot vs the spot size from their map:
Extracted from South Pole Telescope's map

You can see those regular bumps, which are essentially echos of the Big Bang.  The positions and relative heights of those bumps, as well as the curve leading down to the right have let scientists learn that:
  1. Space between galaxies obeys standard high school geometry (it does't around black holes)
  2. Our universe is just barely light enough that it won't re-collapse into a "Big Crunch"
  3. There's five times as much "dark" matter than the stuff we're made of
  4. The universe is mostly made of "Dark Energy," an anti-gravity force pushing the galaxies apart faster and faster.

It's hard for me to see how any other experiment will substantially improve that plot over what the South Pole Telescope has done… unless you're interested in polarization.  That's where our project comes in… but that's enough nerdiness for one post.

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