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Background this, background that: Planck, C-BASS, and the history of the universe

by Sarah Scoles

This is where you live (Credit: ESA/Planck).On March 21, the Planck space telescope team released their first round of data, which reveals (or, rather, clarifies and gives more precision to previously researched) secrets of the early, early universe. The European Space Agency-run mission looks at the cosmic microwave background (CMB) radiation--the earliest light we can possibly see from the timeline of the universe. Telescopes like Planck look for tiny fluctuations in the CMB. These peaks and valleys in the cosmos' baby picture eventually grew into clusters, galaxies, stars.


From the state of the universe in this old portrait, scientists can figure out how old it is now and what it's made of.

I won't go into detail about the process or meaning of the results, as many have already (Discover, JPL, Nature, Cosmic Log NBC, NYT Science), but the summary is that the universe

  • is 13.8 and not 13.77 billion years old.It's so dark in here (Credit: ESA/Planck).
  • is 26.8 percent and not 24 percent dark matter.
  • is 68.3 percent and not 71.4 percent dark energy.
  • is 4.9 percent and not 4.6 percent regular matter.
  • has a Hubble constant (which descibes its expansion) of 67.15 and not 69.32 km/s/Mpc

In short, it's still expanding really fast, it's still really old, and it's still really dark and handsome and mysterious.

But are these numbers final?

(Are any numbers final? Does your life have any stability?)

The calculations are based on the first 15.5 months of Planck data, or 10% of the amount scientists plan to gather before 2014. 

This is where all the stuff we can see is. Lighter = more regular matter. The line in the middle is the plane of our Galaxy, removed (Credit: ESA/NASA/JPL-Caltech).Right now, the Planck results mostly deal with how bright the CMB is and not its more subtle characteristics. Later, the team will tell us all about the ancient light's polarization--the orientations of the light waves. Do they look up-and-down perpendicular to the way the light is moving? Are they all arranged that way? Or are they randomly jumbled in all directions?

The conditions of the universe in its earliest state determine the directions the light waves are oscillating, so from observing the CMB's polarization, scientists can learn about what our home-verse was like right after the Big Bang. Specifically, they are interested in seeing how well the waves have lined up into the same polarizations and what/where deviations are. Deviations, in this case, come from gravitational waves travling through and variations in the density of the early universe.

But our home galaxy gets in the way of our exploration of the larger world outside the nest.

The Milky Way's radiation obscures the polarized CMB signal. UH OH. In order to figure out what's from the old universe and what's from annoying gasduststarsprocesses nearby, all of the annoying nearby stuff must be subtracted out, leaving behind a pristine CMB signal. To do that subtraction, though, scientists will have to know exactly what our galaxy's polarized signals look like.

And the team in charge of a new telescope called C-Bass says, "We'll halp."

C-Bass stands for "C-band all-sky survey," where C-band means the longer end of the microwave spectrum.

Dr Angela Taylor of Oxford University said in a press release: "C-BASS acts like an extra frequency channel for Planck, hugely extending the range of radio wavelengths we have available. C-BASS will measure the polarization signal from our galaxy with great accuracy, and will hugely improve our ability to remove the galactic signal from Planck data, revealing the true CMB signal."

C-BASS is made of two telescopes--one in the Northern hemisphere (California) and one in the Southern (Johannesburg)--originally meant to talk to satellites. They have now been repurposed to do science instead of communicate. They will take pictures of the whole sky's longer microwave emission, which will provide a map of Milky contamination.

After that, and after, you know, many more years of Planck data, we'll take a look at all those revised numbers again. Though we won't find that--gasp--the universe is only 5% dark energy or anything crazy like that, some 1s and 1/10ths digits may change.

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