Archive for 2020 Decadal Survey

No More CMB-S4…

Posted in The Universe and Stuff with tags , , , , , , on July 15, 2025 by telescoper

There was some sad news for cosmologists last week in that the Government of the United States of America – specifically the National Science Foundation (NSF) and the Department of Energy (DOE) – has cancelled the next generation of ground-based cosmic microwave background experiments, called CMB-S4. This would have been the fourth generation This would have consisted of several dedicated telescopes equipped with highly sensitive superconducting cameras.

The plan was that these telescopes would spend about seven years listening to the microwave sky at two locations already recognized for their suitability: the South Pole, which was to host several telescopes of varying sizes to observe across a wide range of microwave frequencies; and the Atacama Plateau in Chile, a high-desert site which would have hosted two large telescopes that can also observe several different frequencies. The South Pole telescopes were to conduct an ultra-deep survey of 3% of the sky, while the Atacama telescopes would conduct a complementary ultra-wide and deep survey of 70% of the sky. Together, the two sites promised to provide a dramatic leap forward in our understanding of the fundamental nature of space and time and the evolution of the Universe.

Longstanding readers of this blog will remember that in 2014 the BICEP2 experiment at the South Pole was claimed to have detected the B-mode polarization signal that would be a diagnostic of primordial gravitational waves generated during a burst of cosmic inflation. That result was later shown to be dominated by Galactic dust emission which could not be identified from its spectral properties, as BICEP2 operated at only one frequency. With an order of magnitude more detectors than previous ground-based CMB experiments, wider frequency coverage, and better control of systematic errors, CMB-S4 would have reduced the limits on earlier observations by a factor of five, enabling either the direct detection of primordial gravitational waves or ruling out large classes of inflationary models and dramatically impacting current thought on cosmic inflation.

For more technical information about CMB-S4 see the 2021 White Paper here.

Despite its very strong science case, and the fact that it was ranked as second-highest priority in the 2020 Decadal Survey, it seems that CMB-S4 is no more. Sad.

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The 2020 Decadal Survey

Posted in Science Politics, The Universe and Stuff with tags , , on November 4, 2021 by telescoper

Delayed by a year, the 2020 US Decadal Survey of Astronomy -full title Pathways to Discovery in Astronomy and Astrophysics for the 2020s – is now out.

It’s a hefty document of more than 600 pages so I haven’t had time to do anything but skim it. The top priority for NASA for the next decade seems to be a 6-m class space telescope capable of imaging Earth-like worlds orbiting sun-like stars, something that can’t be done with much larger telescopes from the ground though the plan does involve bringing very large ground-based telescopes (the Giant Magellan Telescope in Chile and the Thirty Metre Telescope in Hawaii) into service more quickly than currently scheduled. Any new space telescope won’t be built and launched on the timescale of course: it probably won’t fly until the 2040s by which time I’ll probably be retired,

I also noticed in the section on the Cosmic Microwave Background we have

Recommendation: The National Science Foundation and the Department of Energy should jointly pursue the design and implementation of the next generation ground-based cosmic microwave background experiment (CMB-S4).The panel suggests that third-generation CMB experiments aligned with CMB-S4―specifically, the SPO (South Pole Observatory) and the “nominal” version of the SO (Simons Observatory)―be high priorities for federal support.

The clarifications in parentheses are my additions.

The shopping list is a lot longer than these items however. There is plenty of discussion in the media already. See, for example, here. I may comment further if time allows.

UPDATE: there is a very user-friendly interactive overview of the survey here.

This is of course an American survey but Astronomy is a truly international enterprise so astronomers all round the globe will be studying it and trying to work out its implications for their own research environment.

And of course there’s a box below for comments from you!

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