QUIET

Key takeaways

QUIET belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect QUIET to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of QUIET from memory before moving on to harder problems.

Reference excerpt

QUIET was an astronomy experiment to study the polarization of the cosmic microwave background radiation. QUIET stands for Q/U Imaging ExperimenT. The Q/U in the name refers to the ability of the telescope to measure the Q and U Stokes parameters simultaneously. QUIET was located at an elevation of 5,080 metres (16,700 feet) at Llano de Chajnantor Observatory in the Chilean Andes. It began observing in late 2008 and finished observing in December 2010. QUIET was the result of an international collaboration that had its origins in the CAPMAP, Cosmic Background Imager (CBI) and QUaD collaborations. The collaboration consisted of 7 groups in the United States (the California Institute of Technology, the University of Chicago, Columbia University, the Jet Propulsion Laboratory, the University of Miami, Princeton University and Stanford University), 4 groups in Europe (the University of Manchester, the Max-Planck-Institut für Radioastronomie Bonn, the University of Oslo and the University of Oxford) and one group in Japan (KEK; the first time a Japan group has been involved in CMB studies). Other members of the collaboration are from the University of California, Berkeley, the Goddard Space Flight Center and the Center for Astrophysics | Harvard & Smithsonian.

Instrument QUIET had arrays of detectors at two frequencies: 43 GHz (Q band) and 95 GHz (W band). It used four telescopes, three of which were purpose-built 2 m types with the other being the 7 m Crawford Hill telescope used for CAPMAP. As a result, it had angular resolutions between a few arcminutes and several degrees. The detectors were mass-produced coherent correlation polarimeters. The instrument was constructed in three phases. The first phase consisted of a 7-element 95 GHz array to demonstrate the technology. The second phase mounted a 91-element 95 GHz array (with 18 GHz bandwidth) and a 19-element 43 GHz array (with 8 GHz bandwidth) on 1.4 m cassegrain telescopes, mounted on what was the CBI platform. It started observing in 2008. The third phase planned four further arrays by 2010. Two of these were at 43 GHz, with 91 elements each, and the other two were at 95 GHz, with 397 elements each. These were mounted on three 2 m dishes on the CBI platform and the 7 m telescope. The instrument was located at a height of 5,080 m at Llano de Chajnantor Observatory in the Chilean Andes. The site is owned by the Chilean government, and is leased to the Atacama Large Millimeter Array. The site was selected due to the altitude, infrastructure and accessibility, as well as the low humidity of the site, which reduces the contamination of the detected signals by the atmosphere.

Science QUIET measured the polarization of the cosmic microwave background radiation (CMB). This polarization is commonly split into two components: E-modes, which represent the gradient component, and B-modes, which give the curl component. It is thought that B-modes are formed both from primordial fluctuations due to cosmic inflation, and from gravitational lensing of the CMB. As of 2008, only E-modes have been detected. QUIET aims to detect and characterize the B-modes polarization for the first time, and to provide more accurate measurements of the E-mode polarization. B-modes are thought to be much fainter than E-modes, as they are formed by higher order effects. The ratio of the E-mode to B-mode polarization is currently unknown, and the minimum detectable value of this can be used as a measure of the sensitivity of a CMB instrument. For QUIET this value is r=0.009, which corresponds to the energy scale of cosmic inflation being around 10 16 {\displaystyle 10^{16}} GeV. QUIET's measurements of the CMB's power spectrum were designed to be between the multipoles of about 40 and 2,500, and will be made in a section of the sky known to have low foreground contamination.

Results The first season reported on power spectra from over 10000 hours of observation at 43 GHz in the multipole range ℓ = 25–475. The E-mode result was consistent with the standard cosmological model. A B-mode spectrum was not detected. The second season paper included 95 GHz data. Power spectra from ℓ = 25 to 975 were used to constrain the tensor-to-scalar ratio.

Status As of March 2011, the QUIET team described the status Observations were made from October 2008 through May 2009 using a 19-element 40 GHz instrument coupled to a 1.4 meter telescope located at the Llano de Chajnantor Observatory in Chile. Observations with a 91-element 90 GHz instrument on the same telescope finished in December 2010. The QUIET instrument has been dismantled from the old CBI mount.

Illustrations

Worked examples

Example 1 — a first encounter with QUIET

Start with the simplest possible case. Write down what QUIET claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to QUIET before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about QUIET ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of QUIET

In research: QUIET appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses QUIET in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: QUIET is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical observatories in Chile, Buildings and structures in Antofagasta Region, Cosmic microwave background experiments, so understanding it makes those chapters shorter.
In everyday life: Look for QUIET outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study QUIET in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what QUIET means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain QUIET out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is QUIET in simple terms?

QUIET was an astronomy experiment to study the polarization of the cosmic microwave background radiation. QUIET stands for Q/U Imaging ExperimenT.

Why does QUIET matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study QUIET?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on QUIET.