Super-Sensors To Sense Big Bang Output 50
New super-sensitive microwave detectors from the National Institute of Standards and Technology may soon tackle the question of what happened immediately following the big bang. "The new experiment will begin approximately a year from now on the Chilean desert and will consist of placing a large array of powerful NIST sensors on a telescope mounted in a converted shipping container. The detectors will look for subtle fingerprints in the CMB [cosmic microwave background] from primordial gravitational waves — ripples in the fabric of space-time from the violent birth of the universe more than 13 billion years ago. Such waves are believed to have left a faint but unique imprint on the direction of the CMB's electric field, called the 'B-mode polarization.' These waves — never before confirmed through measurements — are potentially detectable today, if sensitive enough equipment is used."
Exactly how sensitve are these sensors? (Score:4, Informative)
FTA:
By contrast, the new NIST detectors are designed to measure not only temperature but also the polarization. The B-mode polarization signals may be more than a million times fainter than the temperature signals.
...the colors represent the tiny temperature fluctuations, as in a weather map. Red regions are warmer and blue regions are colder by about 0.0002 degrees.
I might be missing something, but that sounds pretty impressive.
Re:Exactly how sensitve are these sensors? (Score:2, Informative)
Maybe I'm thinking of gravity wave experiments, but didn't the researchers have issues with unforeseen field effects the last time they tried this measurement?
Re:Exactly how sensitve are these sensors? (Score:2, Informative)
For what they're doing, it may well be very sensitive. Unless I'm doing my calculations wrong, though, it's not amazingly sensitive in the absolute sense -- 0.0002 degK is 2.32 eV. It's certainly reasonable to measure energies in the meV range. Alternately, the temperature of the CMB is a few Kelvin, so this is measuring fluctuations of roughly one part in ten thousand.
Re:Exactly how sensitve are these sensors? (Score:3, Informative)
Re:The Point... (Score:5, Informative)
Re:It would be a lot more interesting to know... (Score:1, Informative)
This is not the only such experiment (Score:4, Informative)
It's worth noting that more than one such telescope hopes to probe CMB polarization on a similar timescale. Caltech and JPL are leading the BICEP2 and SPIDER collaborations (also with NIST), which will also be deploying in a few months (the former at the South Pole, the latter on a high-flying balloon) to probe E-mode and B-mode CMB polarization. The Princeton experiment mentioned in this article isn't that different - it just apparently has better press!
E- and B-modes (Score:5, Informative)
The "E-modes" and "B-modes" referred to in the article aren't quite the same as electric and magnetic fields. Here's the basic story.
Suppose you try to map the polarization of the microwave background across the sky. Each direction on the sky has some polarization magnitude and direction, which we can represent by a little headless arrows on the sky (headless because flipping the polarization 180 degrees doesn't change it). A map of the CMB polarization thus looks like a bunch of little line segments of varying sizes and orientations all across the sky.
Now imagine looking at the pattern of polarization directions near some point on the sky. This arrangement of lines can be "curl-free" if the lines are oriented radially or circumferentially around the central point; this is called an "E-mode" pattern. The polarization pattern might instead have a curl component, which is called a "B-mode" pattern. another way of looking at it: an E-mode pattern looks locally the same when mirror-reversed, while a B-mode pattern does not. Any field on the sky can be written as the sum of an E-mode pattern and a B-mode pattern.
This technicality is important because of how polarization is generated in the microwave background. It turns out that all kinds of relatively mundane processes can generate E-modes - they're still very interesting and informative, but we know they're there (and have even detected them). B-mode patterns are much more unusual - it turns out that normal CMB physics cannot generate large-scale B-modes. Inflation, however, generates a background of gravity waves in the early universe that produce a B-mode contribution to the CMB. This is incredibly tiny and difficult to detect, but it's a smoking gun for inflation.